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Problem Statement: How to read our Adobe Acrobat documentation? | Solution: User needs an Adobe Acrobat reader. This can be downloaded from a number of sources, including www.adobe.com.
Keywords: Version 10, Adobe Acrobat, reader, .pdf, documents
References: None |
Problem Statement: How Are Reaction Rate or Kinetics Affected by the Reaction Stoichiometry Written? | Solution: In Aspen Plus, the amount of reactants converted and products generated depends on how one enters the stochiometric coefficients. The kinetics expression in Aspen Plus is expressed as the rate of change in the Extent of Reaction. For a reaction:
aA + bB -> cC
(1)
If we use the symbol, E, to stand for the extent of
reaction, then the Extent of Reaction is defined as:
d E = - dA /a = - dB/b = dC/c
(2)
In the above equation dA, dB, and dC represents the change in moles for species A, B, and C, respectively. Note that the Extent of Reaction is independent of how the stochiometry is written.
In Aspen Plus, the kinetics the user enters on the kinetic form is based on the Extent of Reaction, i.e.,
r = (1/V)*dE/dt = k*C1*C2... (3)
where r is the reaction rate based on the Extend of Reaction, V the reaction volume, k the rate constant, and C1, C2, ... are concentrations, etc.
Thus, for a same reaction that is written in two different forms (i.e., two different but equivalent sets of stoichiometry coefficients) but with identical values of kinetic constants entered, the rate expressed by Eqn 3 will be the same but the simulation results will differ. This is because Aspen Plus interprets the the rate constants that users enter to be based on the Extent of Reaction (Eqn 3). Thus for the same rate constants (the pre-exponential factor and activation energy for the Power-Law kinetics), which would give the same k, the reaction rate based on the Extent of Reaction would be the same, independent of how the stochiometry is written. This can be easily understood from Eqn 3.
However, the reaction rate based on the conversion of a particular species, e.g., dA/dt,
dA/dt = - a * dE/dt (4)
would depend on the value of the stoichiometric coefficient (the value of a) entered. Obviously, depending on how the reaction is written, the value of a will certainly affect dA/dt. For two different expressions with two different values of a, the dA/dt will differ by a factor equal to the ratio of the two stochiometric coefficients.
For example, compare stoichiometry:
.5 O2 + 1 NO -> 1 NO2 (5)
with
1 O2 + 2 NO -> 2 NO2 (6)
From the chemistry point view, both expressions represent the exactly the same reaction, and how one writes it should not make any difference. However, in Aspen Plus, when user is entering the reaction rate kinetic constants, the user must make sure which stoichiometry the kinetic constants are derived for. While the reaction rate based on the extent of reaction remains the same for both expressions (when the same set of kinetic constants are used), the actual rate based on the conversion of O2 (or NO) will differ by a factor of 2, with the rate for the second reaction (Eqn 6) being twice as fast as the first one (Eqn 5).
In this case, if you are given, say, a set of experimental kinetic rate constants derived from the first expression (Eqn 5) but you want to use the second expression (Eqn 6)
in your Aspen Plus simulation, you must make sure to factor 0.5 into the preexponential factor. In other words, the preexponential factor for the first reaction (Eqn 5) must be twice the value for the second reaction (Eqn 6) to make the results identical.
Keywords: Reaction Kinetics
Stoichiometric coefficiencts
Stoichiometry
Reaction Rate
Extent of the reaction
rplug
rcstr
rbatch
References: None |
Problem Statement: Why do residue curves lines sometimes stop abruptly in the middle of a curve? | Solution: Every point on each of the residue curves represents a liquid composition. The curve end point is the initial composition of the liquid. Additional points are obtained by plotting liquid compositions as differential amounts of vapor are removed from the liquid.
If a line on a residue map stops abruptly, it is an indication that the line could be near a two liquid phase region.
The algorithm that calculates the curves is set up to stop when the temperature difference between successive points is less than a certain tolerance. One of the situations in which this can occur is when a second liquid phase is formed; however, this is not the only situation in which this criterion can occur. Hence, this phenomenon cannot be used to reliably show the two liquid regions on the residue map since this does not always happen in, or close to a two liquid phase region.
Keywords: analysis
liquid-liquid
LLE
two-phase
References: None |
Problem Statement: How do I read or write to the Control Panel and to Aspen Plus Files? | Solution: for Calculator Blocks:
In Fortran WRITE statements in a Fortran Calculator block, you can use the following predefined variables for the unit number:
Unit
Destination
NTERM
Control Panel (if running from the user interface)
Terminal (if running interactively outside of the user interface), or
Log file (if running batch)
NRPT
Aspen Plus report
NHSTRY
Simulation history
Interactive user input in a Calculator block can done with a READ statement from unit NTERM. Do not read from NTERM when running batch. An example file of an Interactive READ from a Calculator block is inSolution 102300: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=102300
Examples:
For writing to the Control Panel, enter:
WRITE(NTERM, *) A, B, C, X
For writing to the report file, enter:
WRITE(NRPT, *) A, B, C, X
For reading from the terminal, enter:
READ(NTERM,*) A
Read statements always require that a compiler is installed. Unformatted write statements as given in the examples above also require a compiler. Formatted write statements can be interpreted without a compiler. For more information about what statements need a compiler seeSolution 104149: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=104149.
For writing to the Control Panel using a formatted write statement, enter:
WRITE(NTERM, 100) A, B, C, X
100 FORMAT(4F10.2)
The diagnostic level for Calculator defined variables can be modified in the Diagnostics dialog box on the Calculator Sequence tabsheet. Setting the Calculator defined variables level to 5 will echo all variables to the Control Panel and/or history file. SeeSolution 103813 for more information: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=103813
Excel Calculator blocks do not have the ability to read or write to the Control Panel or Aspen Plus report or history files, but you may use VBA macros to display information in dialog boxes or to create a dialog box for interactive input.
For more information see the Aspen Plus User Guide, Chapter 19, Calculator Blocks and In-Line Fortran.
Solution for User Subroutines:
There is a utility (DMS_WRTALN) for writing to the History or Report file using any compiler. SeeSolution 119405 for details.
Use the DMS_WRTTRM utility (see User Models
Keywords: inline fortran
References: Manual, Chapter 4) to write to the Control Panel.
For example,
#include dms_maxwrt.cmn
.
.
.
1000 FORMAT ('FLASH OF STREAM', 2A4, 'FAILED')
WRITE (MAXWRT_MAXBUF, 1000) ID(1), ID(2)
CALL DMS_WRTTRM(1)
Notes
User subroutines cannot read from the Control Panel within the GUI.
When reading or writing using a user-defined file, use a Fortran unit number between 50 and 100. |
Problem Statement: In the Aspen Plus HEATX unit, how should a user enter the number of tubes in a U-Tube bundle? | Solution: Specify the number of holes in the tubesheet as the tube count and then specify two tube passes. In a U-tube bundle a long tube is bent into ''U'' shape. While it is physically one tube, for modelling purposes it is two separate tube segments. One segment has flow to the right, and the other segment has flow to the left.
Most exchanger vendors specify the number of U-tubes on the exchanger data sheet, not the number of holes in the tubesheet. When in doubt, review a drawing or fabrication specification of the bundle''s tubesheet.
Also, in HEATX, only the TEMA designation for the shell channel type is entered (i.e. E, F, G, H, J, or X). There are no entries for the front or rear head type.
Example:
A heat exchanger bundle contains 50 U-tubes.
there are 100 holes in the tubesheet, so the correct tube count would be 100.
the bundle has two tube passes
Keywords:
References: None |
Problem Statement: How does a user obtain access to the Phillips Petroleum proprietary Assay Library? | Solution: There is a utility (provided to Phillips Petroleum by AspenTech) that takes data from the Phillips Crude Library and generates Aspen Plus bkp files. These partial backup files can be stored into the asy directory of Aspen Plus GUI installation. The files can then be opened by or imported into Aspen Plus.
For information about purchasing access to the Phillips Crude Library, the customer should contact
Phillips Petroleum Co. (Licensing)
254 PLB
Bartlesville, OK 74004
Tel (908) 661-0620
Keywords: Phillips
petroleum
assay
crude
library
References: None |
Problem Statement: It is possible to to create a .dll for a Calculator block that
does not change to either save time or to give the model to someone without a compiler? | Solution: This is not currently possible in Aspen Plus.
Here are a couple of things that could be done to minimize the problem:
If the problem is that there is a lot of FORTRAN code in the calculator, the user may write a FORTRAN routine and call it from the CALCULATOR. Compile the FORTRAN and link a dll.
Keywords:
References: the dll from a dlopt file. The arguments to the subroutine would be the accessible variables from the CALCULATOR. The FORTRAN in the CALCULATOR would still have to be compiled, but at least it would be quick.
Another option would be to use a FORTRAN subroutine attached to a dummy USER or USER2 block. Sandwich the USER block between two CALCULATOR blocks. In the first CALCULATOR set elements in the USER block REAL array to the read vars for the CALCULATOR. In the USER FORTRAN, do the calculations and set the results elsewhere in the REAL array. When the second CALCULATOR is executed, set the actual write var defined variables to the values calculated in the REAL array. Using this approach the FORTRAN in the CALCULATOR block would not have to be compiled. The user could distribute the FORTRAN as source code, as a loose .obj file, or as a dll. |
Problem Statement: Why does version 11.1 give negative displacement warnings on positive displacement compressors (COMPR block), and earlier versions do not? | Solution: The calculated positive displacement compressor results in version 11.1 and version 10.2 are identical. The only difference is the new warning message for situations where a negative disiplacement has occured.
The typical cause of negative displacement is very large compression ratios (Pin/Pout). Large compression ratios cause the volume efficiency to go negative:
EV = 1.0 - (0.01 * Po/Pi) + ClearanceFraction * [1.0 - (VOLi/VOLo)]
where:
Po = Outlet Pressure
Pi = Inlet Pressure
VOLi = Inlet Volume
VOLo = Outlet Volume
The purpose of the message is to inform the user that a smaller clearance fraction needs to be specified. Higher volumetric compressions require a higher efficiency positive displacement compressor, with either a longer stroke or faster reciprocation speed, and hence, a smaller clearance fraction.
Keywords: clearance
References: : Aspen Plus Unit Operations Technical Documentation - COMPR
http://support.aspentech.com/Documents/Engineering/AES111SP1DOC/APLUS%20111%20Compr%20Unit%20Operations.pdf |
Problem Statement: For various reasons, Customer wants to run Aspen Plus 10.2 under Windows XP. During a silent install of several AES products (Aspen Plus, Aspen Dynamics, Aspen Custom Modeler, Aspen Split, Aspen OLI) an error message window appeared. A description of the error message is included below. What is aspCompress doing and what are the consequences of the missing entry point?
During installation of Component 7 of 29, an error window opened an OK had to be clicked to continue.
The title of the error window was:
Setup.exe - Entry Point Not Found.
The text of the message was
The Procedure entry point setupapi.CM_Disable_DevNode could not be located in the dynamic link library CFGMGR32.dll. Component number 7 is aspCompress.
After OK was clicked, the installation completed without any other apparent error. | Solution: Though AES 10.2 is not officially supported, it is often possible to install it on Windows XP. AspenTech does not guarantee that there will not be other problems since this configuration has not been tested. AES 11.1 SP1 is fully supported on Windows XP.
There is no consequences of the the missing entry point setupapi.CM_Disable_DevNode. What is happening is that the installation uses the setupapi.dll from the current core component directory. This is because the current directory comes before the system directory in the file search order. This file in the core directory is older than what is there in the system. And system is looking for some extra functions in the DLL, but could not find them, and hence displays a warning.
The fix is very simple. Copy the CD to your hard drive and delete SetupAPI.dll and cfgmgr32.dll from all sub-directories under the directory Core. This will force the installer to look for the file in the system and warning messages will not be displayed again. These two files were placed in those directories to take care of some models of Windows 95.
Keywords: setupapi.CM_Disable_DevNode.
CFGMGR32.dll
aspCompress
Windows XP
XP
Aspen 10.2
References: None |
Problem Statement: Which point in relief valve results gives the largest orifice size? | Solution: Aspen Plus''s pressure relief block is used to simulate a vessel undergoing pressure relief or for simple valve rating. Use pressure relief to either determine the steady-state flow rating of pressure relief systems or dynamically model vessels undergoing pressure relief due to a fire or heat input specified by the user. The modeling equations for nozzle flow, and for bubbly and churn-turbulent disengagement are based on technology developed by the Design Institute for Emergency Relief Systems (DIERS) Users Group of the AIChE. This technology is considered the best available for pressure relief system design. The Aspen Plus Pipeline model simulates flow through the inlet and outlet tail pipes in the relief system.
Pressure Relief always operates in rating mode. For dynamic scenarios, such as a fire, this means that given the initial conditions in a vessel, a description of the pressure relief system, and the heat flow into the vessel, Aspen Plus will calculate the flow rate through the pressure relief system and determine if the pressure relief system meets code requirements.
As part of theSolution algorithm, Aspen Plus solves the energy balance and flash equations along with the reaction equations for the vessel (if any) at the present time increment.Aspen Plus compares this to the maximum flow rate possible through the pressure relief system. This value is calculated by finding the smallest diameter of any pipe or valve in the system and calculating the sonic velocity through that diameter. Aspen then calculates the pressure at the end of the vessel neck, after each section of the inlet pipe, after the pressure relief device, and after each section of the tail pipe based on the current flow estimate. If the pressure at the end of the pressure relief system is within tolerance of the user-specified discharge pressure, Aspen increments to the next time step and repeats this procedure until one of the specified termination criteria (time, vessel contents, vessel pressure, or vessel conditions such as pressure, temperature, vapor fraction or total mass) has been reached or exceeded.
Therefore, Aspen does not clearly define a single point where one can say the Pressure Relief Device is rated or that gives the largest orifice size. The pressure relief rating is based on a complete set of flow, pressure, and composition calculations, all of which contribute to the rating.
On the Result Summary form the maximum vent flow rate in molar basis is reported, not mass or volumetric flow rates. For every output profile point, the vent flow rate and an status indicator is reported that shows if a choke point has been detected.
Keywords:
References: None |
Problem Statement: When installing Aspen Plus 10.2 on machine that has had Aspen Plus 10.1 previously installed, the following error message occurs when trying to run a simulation or when opening the file from the GUI:
Unable to load simulation engine. Probable cause: insufficient memory or disk space. and yet there is plenty of memory and disk space.
The problem does not usually occur when running the file from the Simulation Engine Prompt | Solution: This problem seems to relate to the long file names in the Path. To resolve the problem go to the registry as follows:
Click on Start>Run then type regedit then click on OK, this will open the Registry Editor.
Go to the following Key:
\HKEY_LOCAL_MACHINE\SOFTWARE\ASPENTECH\ASPEN PLUS\10.2\APLUS , Then edit the ASPTOP key and change the path to its DOS equivalent. Example: if the path was D:\Program Files\AspenTech\Aspen Plus 10.2\Engine, change it to: D:\Progra~1\AspenT~1\Aspenp~1.2\Engine
Keywords: ASPTOP
References: None |
Problem Statement: For RadFrac and MultiFrac, it is now possible to have a load stream for each stage or a cumulative load stream for a specified number of stages. The advantage of using a load stream is that it ensures feasible heat transfer and can be used in a MHEATX block. A cumulative load stream in RadFrac or MultiFrac is incomplete as it does not have a 0 duty point in the stream vector. To be able to use this cumulative heat load in a MHEATX block, or any other block which supports load streams, an additional temperature and duty point (equal to 0) must be added to the load stream with the use of a QTVEC block. | Solution: To specify a cumulative load stream in RadFrac, place a heat stream on the RadFrac block and redefine it as a load stream using the Data/Setup/Stream Class/Load Streams sheet. Then on the RadFrac/Heaters Coolers form, define the side heating (or cooling) for consecutive stages using the Side Duties sheet, and define the cumulative load stream on the Heat Streams sheet (Outlet Heat Streams). In that attached file, the heat duty for stages 22, 23 & 24 in the RadFrac column have been defined as a cumulative load stream.
The calculated cumulative load stream from the RadFrac block can be viewed on the Data/Blocks/RadFrac/Stream Results/Heat sheet. The load stream has an associated duty Q, and a corresponding start and end temperature, TBEGIN and TEND respectively. If TBEGIN is greater than TEND, then the duty is positive, else the duty is negative. The cumulative load stream captures the temperature and duty information of the material stream as it passes through the specified column stages. This information is presented in a vector format, which is viewed on the Data/Blocks/RadFrac/Stream Results/Load sheet. For example, the cumulative load stream for stages 22, 23 & 24 would be in the form:
QVEC TVEC
Q22 + Q23 + Q24 T22
Q23 + Q24 T23
Q24 T24
By definition, a load stream must contain a zero duty point and a TBEGIN. To add an additional temperature and duty point to the RadFrac cumulative load stream, (or any load stream), requires the use of a QTVEC block. QTVEC is a simple manipulator that effectively changes the load stream as follows:
QVEC TVEC
Q22 + Q23 + Q24 TBEGIN
Q23 + Q24 T22
Q24 T23
0 T24
If you do not specify TBEGIN on the Data/Blocks/QTVEC/Input form, it will be set to the first available temperature (T22 in this example). A warning will also appear in the control panel to this effect:
WARNING STARTING TEMPERATURE OF OUTLET LOAD STREAM NOT SPECIFIED. TEMPERATURE DIFFERENCE BETWEEN THE FIRST TWO POINTS WILL BE ASSUMED TO BE ZERO.
The load stream calculated from the QTVEC block can now be used in any block which supports load streams.
Keywords: load streams
QTVEC
QTvec
TBEGIN
QVEC
References: None |
Problem Statement: After setting up a Petrofrac model, it is possible to enter Murphree or Vapor tray efficiencies, but in some cases, the thermal efficiency forms are disabled. Why? | Solution: In some cases, the thermal efficiency entries would conflict with other entries. Specifically, thermal efficiencies are not allowed when: a) there is a pseudo stream with a phase of TL (total liquid) or TV (total vapor) b) when there is two liquid phase checking enabled below tray 1.
When the above two types of specs are removed, the thermal efficiency forms become enabled again.
Keywords:
References: None |
Problem Statement: Can I simulate tray columns without downcomers? | Solution: No. The algorithm was programmed with the assumption that a downcomer was always present. There is no workaround.
Keywords: radfrac
tower
References: None |
Problem Statement: When used in Aspen Plus, how does an ACM exported model set the output stream properties? | Solution: If the block energy balance option is checked (as it is by default), a PH (specified pressure, specified enthalpy) flash is done. Otherwise, a TP (specified temperature, specified pressure) is done. The flash is always a vapor-liquid flash, using the same property settings as the Component list assigned to the corresponding output port.
Note that the PH flash fills in missing stream variables which are not available in the Molefraction port (liquid and vapor fraction and entropy). However, it does not reset the temperature. This may lead to an inconsistency between the temperature and the enthalpy if the ACM model evaluates a non-equilibrium state for the output stream.
As there is no option to control how the output streams properties are set, you can add a dummy heater block to set the stream conditions as needed.
Keywords: None
References: None |
Problem Statement: I am getting incorrect results for the solubility of light gases in the liquid phase using Henry's Law with an activity coefficient model
or
I am getting the message:
SEVERE ERROR IN PHYSICAL PROPERTY SYSTEM
HENRY'S CONSTANT MODEL HENRY1 HAS MISSING PARAMETERS:
HENRY/1ST ELEMENT (DATA SET 1) MISSING FOR SUPERCRITICAL COMPONENT XXX WITH ALL SOLVENTS
which is followed by a Terminal error in the Physical Property system.
How can this be corrected? | Solution: Both of these problems may occur because Henry's Law is not correctly specified for components. If a light gas is not specified as a Henry Component, usually the amount of that gas in the liquid phase is overpredicted.
To use Henry's law for a given component, Henry's constants must be present between the component and at least one of the solvents. If the Henry's constant is available for only some of the solvent components, Aspen Plus will automatically normalize the Henry's constant of the mixture to that of the available components.
An error will occur if no solvents are present in all gas streams, or if Henry's parameters are not available for the Henry's components and any other components present.
Note that this error can occur midway through the execution of a simulation if the calculations result in a stream that has no solvents with parameters available.
If you have an all vapor feed stream, specify this in the form by entering Vapor-Only in the Valid phases field of the Streams / Input / Flash Options sheet.
Specify the following to use Henry's Law:
1. Create a Henry Component list on the Components / Henry Comps form that includes all gases that should be treated as Henry's components.
2. The Henry Components list name must appear on the Properties / Specifications / Global sheet in the Henry-Comps field, or where a Property Method is specified.
3. Choose an Property Method that uses Henry's Law. In Aspen Plus, this set includes IDEAL and other activity coefficient Property Methods.
4. The HENRY parameters must be available for each Henry Component value with at least one solvent. Parameters are available in the BINARY or HENRY databanks, or the parameters must be added on the Properties / Parameters / Binary Interaction / HENRY-1 form.
When using ElecNRTL for the enthalpy calculations, the infinite dilution enthalpy of the Henry's component is computed by calculating the Henry's constant of it in water. However, if water is not there, the last component in the feed flow is used instead. This means that it is necessary to supply Henry's constant for the Henry's component with the last component in the component list. The component list should be arranged so that a component with Henry parameters is at the end of the list.
Keywords: HENRY-COMPS
References: None |
Problem Statement: How is the required cooling duty calculated for the Plug Flow Reactor (RPlug) with a specified coolant? | Solution: Heating or cooling requirements for the RPLUG reactor is calculated with a log mean temperature difference (LMTD) calculation from node to node along the length of the reactor.
Keywords: RPLUG, coolant, LMTD, node, duty
References: None |
Problem Statement: The user receives the following message after clicking the Next button:
Water must be specified as a component when Use free-water calculations option is selected (Setup Specifications Global sheet) or Water-basis = Dry is specified for a Prop-Set property (Properties Prop-Sets Qualifiers sheet). | Solution: Free Water or Water basis = dry is specified somewhere in the flowsheet. If one of these options is desired somewhere, simply add Water to the Component list. If these options are not desired, they should be removed so that inadvertent incorrect calculations are not done.
Below are three places to check:
Check the flowsheet connectivity and make sure that no streams are connected to the Free-Water port. If you click on a block in the Process Flowsheet Window and then move the mouse over a port, the name of the port will pop-up.
In Setup / Specifications / Global, don''t select Use free water calculations.
In Properties / Prop-Sets, go through each property set''s Qualifiers tab and remove Water-basis = Dry.
Keywords:
References: None |
Problem Statement: What is Pad gas component in the Pressure Relief calculation block
and when should it be specified as a component in the Pressure Relief block? | Solution: A pad or padding gas is an inert (N2 or Air) component that is typically added to a storage or process vessel or tank to maintain its pressure at a constant value. It is mostly used in situations where the bubble point pressure of a liquid may be below atmospheric pressure or if it is desired to store a liquid above certain minimum pressure for safety reasons.
In the Aspen Plus pressure relief calculations it is used to set pressure in situations where the liquid level or fillage is also specified. Using the user specified composition or the stream composition referenced and temperatue, pressure or the molar vapor fraction and the total volume of the pressure vessel; Aspen Plus performs a flash equilibrium calculation to determine the amount vapor and liquid initially stored in the vessel.
However, if the flash calculation results in a single phase liquid with no vapor present, pressure relief block will assume that the vessel is full of liquid if no fillage is specified or if fillage is also specifed it will generate an error message similar to this:
*** SEVERE ERROR WHILE EXECUTING PRESSURE RELIEF BLOCK: PR-1
(PRSINV.6)
COULD NOT FIND INITIAL CONDITIONS FOR
SPECIFIED FILLAGE AND PAD GAS PRESSURE
TEMP= 3.109278D+02 PRES= 1.013529D+05 FILLAGE= 9.000000D-01
MOLES OF PAD GAS= 4.100000D+01 ITER= -7VOLUME OF LIQUID= 0.000000D+00
*** SEVERE ERROR WHILE EXECUTING PRESSURE RELIEF BLOCK: PR-1
(PRSCRB.2)
PRESSURE RELIEF ABORTING. COULD NOT CONVERGE INITIAL CONDITIONS.
In this situation a pad gas component should be added to generate enough vapor to fill the volume above the liquid in the vessel. The pad gas must be a vapor at the conditions of the vessel and must be specified in the Components Specification form. A single component can not be specified as both in the vessel composition form and the pad gas form; since single components vaporize at a constant temperature.
For more information of Aspen Plus Pressure relief calculations, please see the Aspen Plus User Guide.
Keywords: None
References: None |
Problem Statement: Since version 10.1, the Aspen Plus physical property system contains new temperature-dependent property correlations from IK-CAPE. These correlations are alternatives to existing models such as DIPPR. While the available DIPPR equations are documented (Physical Property Methods and Models Guide, page 3-5), there is no comprehensive list of available IK-CAPE equations. The present | Solution: aims to fill this information gap.
Solution
The following pure component properties can be calculated by IK-CAPE models:
Property Parameter Equation
Ideal gas heat capacity CPIGPO IK-CAPE polynomial (eq. 1/401)
Liquid heat capacity CPLPO IK-CAPE polynomial (eq. 1/401)
Enthalpy of vaporization DHVLPO IK-CAPE polynomial (eq. 1/401)
Liquid thermal conductivity KLPO IK-CAPE polynomial (eq. 1/401)
Vapor thermal conductivity KVPO IK-CAPE polynomial (eq. 1/401)
Liquid viscosity MULPO IK-CAPE polynomial (eq. 1/401)
Vapor viscosity MUVPO IK-CAPE polynomial (eq. 1/401)
Liquid vapor pressure PLPO IK-CAPE polynomial (eq. 1/401)
Surface tension SIGPO IK-CAPE polynomial (eq. 1/401)
Liquid molar volume VLPO IK-CAPE polynomial (eq. 1/401)
Solid molar volume VSPO IK-CAPE polynomial (eq. 1/401)
Liquid heat capacity CPLIKC IK-CAPE liquid heat cap. model (eq. 3/403)
Liquid viscosity MULIKC IK-CAPE liquid viscosity model (eq. 4/404)
Whether a given IK-CAPE property model is actually used depends on the availability of the corresponding parameter. The three different equations are:
Equation 1 or 401:
Y = A + BT + CT^2 + DT^3 + ET^4 + FT^5 + GT^6 + HT^7 + IT^8 + JT^9
Equation 3 or 403:
Y = A + BT + CT^2 + DT^3 + ET^4 + F/T^2
Equation 4 or 404:
Y = A * EXP(B/T) + C
where Y is the temperature-dependent property
T is the temperature
A, ...J are the coefficients of the correlation
For example, the IK-CAPE liquid heat capacity correlation uses equation no. 3/403. The mapping between the coefficients of the correlation and the elements of the parameter CPLIKC is such that element 1 (CPLIKC/1) corresponds to coefficient A, element 2 (CPLIKC/2) corresponds to coefficient B, and so on.
Keywords: IK-CAPE
correlation
equation
References: None |
Problem Statement: Is it possible to test for missing property parameters values in a user subroutine? | Solution: Aspen Plus uses the value RGLOB_RMISS to flag missing parameter values (i.e. values not entered by the user). The variable RGLOB_RMISS is defined in the common block DMS_RGLOB. Missing parameters are set to equal either -RGLOB_RMISS or RGLOB_RMISS. Therefore you need to write your code to test for the absolute value of the parameter instead of testing on the value.
Correct:
#include dms_rglob.cmn
DO J =1,9
PLXANT(J) = B(LPL+J)
C check for missing parameter
IF(DABS(PLXANT(J)).EQ.RGLOB_RMISS)THEN
C parameter is missing
....
ENDIF
END DO
Incorrect:
#include dms_rglob.cmn
DO J =1,9
PLXANT(J) = B(LPL+J)
C check for missing parameter
IF(PLXANT(J).EQ.RGLOB_RMISS)THEN
C parameter is missing
....
ENDIF
END DO
One example of the circumstances in which the missing parameter is -RGLOB_RMISS is for a T-dependent parameter, for which one element is left blank in the input file or on the parameter input form on the GUI. Example of input file:
USER-PROPS TDEP 1 1 3
PROP-DATA TDEP-1
IN-UNITS MET
PROP-LIST TDEP
PVAL H2O 1 2
Note the missing value for TDEP/3. It will become -RGLOB_RMISS.
Attached is an example of a gmu routine illustrating the symptoms.
Keywords:
References: None |
Problem Statement: When changing the petroleum characterization methods on the Petro Characterization / Property Methods forms, no change occurs in the calculated pseudo component properties. | Solution: The Petro Characterization / Property Method object manager allows the user to create new property methods for the calculation of pseudocomponent properties similar to the way one can create and modify simulation property methods in the Data/Properties/Property Methods folder. Changes on the Petro Characterization / Property Method form will not change the pseudo component properties unless a petro characterization generation form has been created and a specific property method chosen. If this is not not done, pseudo component properties will be calculated with the default property method (the ASPEN method) and the results will be the same even though different base methods are chosen on the Petro Characterization / Property Method folder.
Keywords: Property Methods, Petro Characterization, pseudo components
References: None |
Problem Statement: What type of Joules are used in Aspen Plus?
Please verify whether the Joules in Aspen Plus are International Joules or Thermochemical Joules. | Solution: Aspen Plus Joules are absolute (according to Perry's 6th Edition) or international joules. The Aspen Plus conversion factors are:
1 Joule * 1055.0559 = 1 BTU
1 Joule * 4.1868 = 1 calorie
The Ideal Gas constant (R) is 8314.33 J/kmol-K in the SI units used in Aspen Plus.
All internal Aspen Plus calculations are performed in SI units. Aspen Plus does NOT use 'thermo chemical' Joules.
When converting SI results to calories for reporting purposes, Aspen Plus converts Joules to thermochemical calories (as defined by Perry's 6th Edition, table 1-13, 1-9)
Keywords: joule
units of measure
000023628
gas constant
rgas
References: None |
Problem Statement: In addition to Pure, Binary, and Ternary Property Analyses, how do I use the interactive Analysis features to generate tables and plots for properties of flowsheet streams? | Solution: You do not have to complete the flowsheet definition or input specifications first. For example, to check your
Property Method, you can analyze a feed stream as soon as you define it.
To analyze streams that are not specified as feed streams to the flowsheet, the stream must have results that were
calculated in the current session.
There are nine types of interactive Stream Analyses:
Type
Description
Point
Stream properties for the total stream and each of the phases present
Component Flow
Component flow rates for the total stream and each of the phases present
Composition
Component fractions for the total stream and each of the phases present
Petroleum
Point properties, plus some common petroleum properties
Dist-Curve
Petroleum distillation curves (TBP, D86, D160, and vacuum)
Bubble/Dew
Bubble point temperature and dew point temperature versus pressure curves
PV Curve
Vapor fraction versus pressure curves at stream temperature
TV Curve
Vapor fraction versus temperature curves at stream pressure
PT-Envelope
Pressure-temperature envelope curves
To use interactive Stream Analysis:
1. First ensure that Setup, Components, and Physical Properties specifications are complete.
2. Ensure the Stream Specifications sheet for the stream is complete or the stream has results that were calculated in the current session.
3. Click the stream on the flowsheet diagram to select it.
4. From the Tools menu, select Analysis, then Stream, then the type of stream analysis you want to perform. (For Aspen Plus 10.1 only, you can also access Stream Analysis features by right-clicking on a selected stream, and choosing Analysis from the pop-up menu.)
5. Make any selections and specifications in the dialog box for selecting options, and click OK. Each stream analysis type has defaults for required input, except temperature range for TV curves.
Keywords: Stream, analysis, Property Analysis
References: None |
Problem Statement: What does it mean to deactivate a block? | Solution: Activate/Deactivate was introduced in Aspen Plus 10.2 so
that one could enable and disable different blocks and their connecting
streams in order to test different scenarios.
It is best to deactivate blocks and let the streams and other objects (design-spec, constraint, fortran, transfer, sensitivity, ...) be deactivated internally by Aspen Plus. It can also be useful to deactivate objects such as design-specs and sensitivities so that they can remain visible in the GUI, but not run.
Note that the input of any deactivated object has to be a VALID input, not just a COMPLETE input.
This feature is documented in the Aspen Plus User Guide, Chapter 11, Running Your Simulation and in the Help Topics under Using Aspen Plus \ Running Your Simulation \ Activating and Deactivating Blocks.
Summary of the documentation:
Various simulation objects can be activated and deactivated.
When deactivated, they still need to be completely specified to run
the problem, but they are ignored during simulation. Blocks and
Streams can be deactivated and activated by clicking the right
mouse button on the flowsheet object, and choosing
Deactivate/Activate. The following objects can be deactivated and
activated from the data browser tree view right mouse button
menu:
Blocks and Streams
Convergence blocks
Sequence
Most Flowsheeting Options: Design-Spec, Calculator, Transfer, Balance, and Pres-Relief blocks
Most Model Analysis Tools: Sensitivity, Optimization, Constraint, and Case-Study blocks
Regression
Properties Analysis (Prop-Table)
Explicitly deactivated items show up in the data browser with a
pair of green slashes through their icon.
In addition to items explicitly deactivated by the user, some objects
are deactivated by association. That is, they are deactivated
because they reference deactivated objects. The rules are:
Deactivating the inlet or outlet stream of a block does not cause a block to be deactivated, except as specified below.
Streams with both source and destination deactivated or not present are deactivated.
Referencing a deactivated block or stream causes an HxFlux block to be deactivated. The stream disabling logic is then repeated.
Referencing a deactivated block or stream causes a Cost block, Pres-Relief block, Calculator block, Transfer block, Design-Spec, Constraint, Optimization, Data-Fit block, Sensitivity block, or Balance block to be deactivated. Targets of a deactivated Calculator or Transfer block will not be deactivated.
Calculator, Transfer, and other blocks with Execute Before/After that reference a deactivated block will be deactivated.
Convergence blocks that reference a deactivated Tear Stream, Tear-Var, Design-Spec, Constraint, or Optimization are deactivated.
Sequences that reference deactivated blocks are ignored and revert back to automatic sequencing.
Deactivated Tear Streams or Tear-Vars are ignored.
Deactivated Convergence blocks in Conv-Order are ignored. Objects which are deactivated by association are listed in the history file.
Note: Deactivating items does not change flowsheet connectivity
(other than effectively removing the deactivated items) and does
not automatically cause any streams to be reinitialized. Some uses
of deactivation may require reinitializing streams which were
solved in a run with different activation.
A Selector block can also be used to model alternative simulation
trains. Copy the feed stream to the alternate trains with a Dupl
block, and connect the products of the alternate trains to a Selector
block. Deactivate all but one train, and choose the stream from the
active train in the Selector block.
Keywords:
References: None |
Problem Statement: How can you find a component in Aspen Plus if you know only a common name that is not in the databank?
Often, when only a common alias name is known for a component, it is difficult to find that component using the component search utility in Aspen Plus. Most component names in the Aspen Plus databank are related to the component''s molecular structure or IUPAC name. | Solution: There is a very helpful website, http://www.chemfinder.com , with a long list of alias names for most components. The user types an alias name and the search engine returns a list of all other known aliases and proper names for that component and most importantly, the Chemical Abstract Service (CAS) number.
The CAS number can then be used in the Aspen Plus component search utility''s to locate the component.
To locate a Component using the CAS number:
Go to the Component / Specification form.
Click on the Find button at the bottom of the form to open the Find dialog box that can be used to quickly find components in built-in databanks.
On the Find Form, click on the Advanced sheet.
At the bottom of the Advanced Sheet, type or paste the CAS number from the chemfinder website. Note: If you wish to paste the data to the Advanced form, you will have to use your right mouse button to complete the paste operation.
Propylene glycol is one example. In the Aspen Plus component databank, this component is know as PROPANEDIOL-1,2 or C3H8O2-2. If you did not know the name used by Aspen Plus, you could search the chemfinder website for PROPYLENE GLYCOL and retrieve the CAS number, 57-55-6. Using the Find utility, you could quickly locate Propylene Glycol in Aspen Plus by using its CAS number.
The chemfinder website is intended to help buyers find chemical suppliers. The product information they provide can be very useful not only for locating component names, but any time you might need to estimate missing property parameters for a chemical. Like the Aldrich Catalogue, the chemfinder website lists important pure component scalar properties such as: -molecular weight
-boiling point
-vapor pressure
-density
-water solubility
Property estimation is greatly improved when the boiling point is provided on the Property / Parameters / Pure Component / Scalar parameter form. The other properties can also be used to validate the quality of the estimations or can be used in data regression.
Keywords:
References: None |
Problem Statement: Which is better the DIPPR or NIST database for properties?
Is there any information available regarding a comparison of the data/results for the components in common between the two? | Solution: There are about 2000 compounds in common between NIST and DIPPR though the NIST database is much larger (>18,000 components). It is not feasible to make detailed comparison between the two databases - nor is it meaningful to do so. The parameters from these databases for the same compound will likely be different. The difference may be small for some properties and larger for others. This reflects the different sources of data that are collected by the two organizations and the different methodologies that are used by them. Many properties are also estimated. The estimation techniques used will have a large impact on the results. In general, parameters from both sources are good and valid and can be used in your similations.
The DIPPR database that we deliver does not contain any experimental data. The NIST database contains experimental data for a large number of compounds - thus providing you with traceability to the original sources of the parameters. The NIST ThermoData Engine is also a very powerful tool that can be used to provide critically evaluated properties parameters for any compounds for which you can provide molecular structure (with elements, C, H, N, O, S, F, Cl. Br, and I). We will continue to support both databases and see them as complementary to each other.
It is up to the user to decide which database they want to use. In general, compounds of interest in the similation that cannot be located in the DIPPR database can be found in the NIST database.
Keywords: None
References: None |
Problem Statement: Does the Aspen Plus mol dimensional unit imply g-mole or kg-mole?
On the Reactions | Reactions (Powerlaw) form, there is a list box of dimensional units adjacent to the activation entry text box. Does the mol dimensional unit imply g-mole or kg-Mole? Some of our dimensional units say Kmol such as J/kmol, but others only say Energy/mol. | Solution: The convention is that mol means g-mole. Any other mole has a prefix to indicate what type it is.
While it may seem like a simple change to convert all mol units to g-mole units, this would cause compatibility problems for models built in earlier versions of Aspen Plus.
Keywords: SI
References: None |
Problem Statement: When using the SR-Polar property method, the following error message occurs during the simulation:
*** SEVERE ERROR IN PHYSICAL PROPERTY SYSTEM
EQUATION OF STATE MODEL ESHOC HAS MISSING PARAMETERS: MUP (DATA SET 1) MISSING FOR COMPONENT 1,4 DABE
What does this message mean and how can it be avoided? This is perplexing to the user because MUP is not listed in the table of parameters needed for SR-POLAR in the help. | Solution: ESHOC refers to the Hayden-O'Connell (HOC) Equation of State and MUP is the dipole moment parameter used in it. The Hayden-O'Connell model uses the dipole moment (MUP). Other models such as NRTL-HOC would give a similar error message if MUP is not present for a component.
SR-Polar uses HOC to estimate parameters for the vapor phase and UNIFAC for the liquid phase. The parameters required for Hayden-O'Connell and UNIFAC in addition to the parameters required for SR-POLAR are necessary to use this method if estimation is needed. The additional required parameters are TC, PC, RGYR, MUP, and HOCETA.
The following parameters are used in SR-Polar, among others:
Parameter Name Symbol in equation
RKUKA0 k0(a,ij)
RKUKA2 k2(a,ij)
RKULA0 l0(a,ij)
RKULA2 l2(a,ij)
RKUKB0 k0(b,ij)
RKUKB2 k2(b,ij)
If you do not enter at least one of the parameters above the system estimates k0(a,ij), k2(a,ij), l0(a,ij) and l2(a,ij) from the UNIFAC/Hayden-O'Connell models using the dipole moment (MUP).
To solve the problem, there are a number of options:
Enter literature or regressed values for the SR-Polar parameters listed above.
Enter the first element of RKUKAO as 0 for all of the pairs with this component to stop the system from trying to estimate a value and use 0.
Enter a dipole moment (MUP) parameter for use in the estimation. If the component is nonpolar, enter a dipole moment of zero. If the particular component that is missing this parameter is not likely to ever exist in the vapor phase, then any dummy value can be entered for MUP.
Keywords: sysop18
References: None |
Problem Statement: VBA Example to take control (Open/Run/Close/Reinit) of an Aspen Plus simulation via ActiveX automation. | Solution: The attached Excel file contains a Visual Basic for Application (VBA) code that will:
Open any Aspen Plus simulation.
Run the simulation.
Reinitialize the simulation.
Close the simulation.
This example could be used as a starting point for building a VBA interface to retrieve specific Aspen Plus results.
To run this example, copy the included Excel file onto your hard-drive and open it. This Excel VBA code is setup to work with Aspen Plus 10.2. If you want to use it with other versions of Aspen Plus, proceed as follows:
Open the Excel file
Go to the Tools menu. Select Macro -> Macros -> Visual Basic Editor
Once in the VBA editor, go to the Tools menu and select reference
Select the library corresponding to the Aspen Plus version you have last installed on your PC (e.g. Aspen Plus GUI 1x.x Type Library, where 1x.x is the version number). If you can not find it, browse to the happ.tlb file (for Aspen Plus 10.x, it is by default located under \Program Files\AspenTech\Aspen Plus 10.2\GUI\xeq. For Aspen Plus 11.1, it is in \Program Files\AspenTech\APRSYSTEM 11.1\GUI\xeq).
Code Description
The VBA code contains a global variable that will hold the reference to the Aspen Plus ActiveX object: go_Simulation. This object is declared as an HappLS object.
To open the simulation:
Set go_Simulation = Getobject(lbFileName)
where lvFileName contains the full path to the simulation file to be opened.
The Graphical User Interface (GUI) is then made visible or not, depending on the value of the chk_IsVisble checkbox. The code to make the GUI visible/invisible, depending on the checkbox state, is:
go_Simulation.Visible = chk_IsVisible.Value
To run the simulation, the Run2 method of the Engine property of the HappLS object go_Simulation is called, as follows:
go_Simulation.Engine.Run2
The Run2 method has an optional argument (boolean type) that will make the run running synchronously or asynchronously (see Tech Tip # 102859 and # 104805 for more details).
To reinitialize the simulation, the Reinit method for the Engine property of the HappLS object is used in subroutine cmd_Init_Click:
go_Simulation.Engine.Reinit(IAP_REINIT_SIMULATION)
The argument passed to the Reinit method defines what part of the simulation should be reinitialized. Other valid arguments are:
IAP_REINIT_BLOCK
to reinitialize a block
IAP_REINIT_CONVERGENCE
to reinitialize a convergence block
IAP_REINIT_SIMULATION
to reinitialize the entire simulation
IAP_REINIT_STREAM
to reinitialize a stream
Technical tip 102365 provides more details about the Reinit method.
To close the simulation, the GUI must be made non-visible and the HappLS object should be set to nothing:
go_Simulation.Visible = False
Set go_Simulation = Nothing
See cmd_CloseSimulation_Click subroutine.
See Chapter 38 of the Aspen Plus User Guide for further details about the Aspen Plus ActiveX Automation Server.
Keywords: ActiveX,COM,Automation,Visual Basic for Applications (VBA), Reinit
References: None |
Problem Statement: My simulation in sequential modular mode (SM) runs fine; however, when I switch to equation oriented (EO), it fails immediately. | Solution: If theSolution fails in EO at the first step, the solver may be trying to solve too aggressively. To solve less aggressively, turn on Creep mode on the Convergence \ EO Conv Options \ DMO Basic \ Basic sheet. It is suggested that you turn it on for 10 iterations with a step size of 0.1 or 0.2. Another indication that using the Creep mode may be beneficial is when the Worst non-linearity ratios reported in the Control Panel and prob_id.atslv file is significantly different than 1.0 (negative or greater than 2).
If the EO problem fails to solve and gives an error message that the problem is infeasible or rank deficient, then it is possible that there is some additional calculations were used on the SM side to improve convergence or provide initial estimates that should not translate to EO. For example, if there was a Calculator block was used to calculate a makeup stream flow rate based on system losses, the problem would likely be rank deficient in EO. TheSolution is to simply remove the Calculator block since it is not needed in EO. One indication of a singular or near singular problem specifications is in the prob_id.atslv file, if the Shadow Prices listed are very large (O(1.D10) or larger). See the attached backup file singular_mkup.bkp for an example. While this file does not crash, it does not solve. Looking at atslv file, you will see the large Shadow Prices.
Other common causes of rank deficiency are related to closed loop systems. The two most common examples are a closed-loop refrigeration system and a recycle loop where all equipment pressure specifications are given as delta P. In the case of the refrigeration system, the easiestSolution is to break to closed loop - typically after the refrigeration compressor. The simplest example of the pressure loop is a flowsheet with two unit operations - a mixer which takes fresh feed and a flash vessel where the vapor (or liquid) from the flash recycles to the mixer. If both the mixer and flash have delta P = 0 specifications then any pressure less than the feed pressure is a validSolution to the problem. See the attached backup file singular_dp.bkp for an example.
Keywords:
References: None |
Problem Statement: In Aspen Plus 11.1, it is now possible to give pseudocomponents some properties such as sulfur content using the Components, Pseudocomponents, Petro Properties sheet. Can you explain what Aspen Plus does with this data? | Solution: The pseudocomponent properties do not have any effect on the Property Set property. The implementation of pseudo component properties has not been completed for Aspen Plus 11.1.
Attached is an example using user Property Sets to achieve the same calculations.
The methodology is to create a user parameter, i.e. SULF, which is the sulfur content of the component. The Property Set will then evaluate the mass fraction average. To make the Property Set subroutine more generic, the pure component parameter used for the calculation is the same as the name as the Property Set.
The parameter values for the pseudo components generated from the assay are copied from the assay results into the Flowsheeting Options, Add Input.
Keywords: prop-set
References: None |
Problem Statement: When trying to regress parameters, the case converges very quickly and the parameters remain at their initial values and have a standard deviation greater than 1e+10..
->Data Regression begins ...
BEGIN CASE CP TIME = 0.46
STARTING POINT TIME: 0.46
BL-ITER: 1 SSQ: 0.783739E+03 REL CHANGE: 0.000E+00 TIME: 0.63
BL-ITER: 2 SSQ: 0.783739E+03 REL CHANGE: 0.000E+00 TIME: 0.78
FINAL SSQ: 783.739
->Data regression completed
What is happening? | Solution: This generally occurs when the parameters have no effect on the data. For example, this can occur when the parameter CPLDIP is regressed to fit liquid heat capacity data and a liquid reference state or DHL09 is not used. For this case, either CPIG needs to be regressed or a liquid reference state needs to be used (seeSolution 3100 for more details about using a liquid reference state). The data regression system does not check if the data is affected by the parameters; therefore, it is possible to try to regress vapor pressure parameters using viscosity data. Since the two are not related, a similar result will occur.
Keywords: DRS Data Regression System
References: None |
Problem Statement: What is Free-water and how should it be used? | Solution: Free-water refers to the water layer in a system where two liquid phases are present and the water phase contains essentially no organic. In Aspen Plus, this is an option for three-phase separation. When Free-water = Yes, the second liquid phase (L2 phase) is treated as PURE water (no organic). In other words, the solubility of organic in the water phase is assumed to be zero. The solubility of water in the organic phase (L1 phase) is calculated by one of the four methods (water-solubility option = 0, 1, 2, 3), explained later.
The Free-water option is often used in refining applications to simulate crude/vacuum units. Liquid crude and water don't mix. They form two separate phases. Since the solubility of most crudes in water is very low, the water phase may be treated as pure. This simplification should not be used for chemical applications where rigorous two liquid phase flash calculations should be used.
When using free-water option, the flash calculations are done as follows:
1. When free-water=yes, L2 phase is treated as PURE water (no organic).
2. Water in the organic phase is calculated according to the solubility option code.
Water Solubility
Vapor Phase
L1 Phase
L2 Phase
0
Free-water property method
Ideal (gamma=1/xw)
pure water,
free-water property method
1
Primary property method
Ideal (gamma=1/xw)
pure water,
free-water property method
2
Primary property method
gamma = f(T, xw)
pure water,
free-water property method
3
Primary property method
Primary property method
pure water,
free-water property method
where xw is solubility of water in the organic phase, calculated using the water-solubility correlation (parameter=watsol).
3. Water Solubility option = 0 and 1 should not be used when there is only one liquid phase (not water saturated).
4. For refinery simulation, Water Solubility option = 2 is commonly used. Option 2 can handle the case when there is only one liquid phase present.
5. Water Solubility option = 3 should be used only if binary interaction parameters are available.
6. Rigorous 3-phase (vapor-liquid-liquid) should be used if organic in the water phase is significant.
7. If Rigorous 3-phase flash is specified, Water Solubility option is forced to be 3 (i.e., Water Solubility=0, 1, 2 are ignored). As a result, you must have good binary interaction parameters.
Keywords: None
References: None |
Problem Statement: How to the Access Dechema Data in Aspen Plus through the Internet and what are the commercial terms? | Solution: You can use the DETHERM Internet Client to access thermophysical property data in the DETHERM online database, maintained by DECHEMA e.V., Frankfurt am Main, Germany.
You can search for properties of given mixtures or pure components. The retrieved data are automatically placed on the Aspen Plus Properties Data forms, ready to be used in data regression. These data are also saved in the report and IK-CAPE neutral files.
The most cost effective way to access Dechema's DETHERM database is via the Internet. The DETHERM Internet Application comes with AspenPlus. (There is a DETHERM Internet button on the Main Toolbar). When you install Aspen Plus, all necessary software to access these data are installed by default.
The user can search for the data and down load the necessary data directly into Aspen Plus. The user pays for what he/she downloaded. A typical VLE data set (10-15 data points) cost $35. Customer will be billed quarterly.
When the user starts the search, he/she can find out whether or not data for the system of interest are available. This information is FREE. The user is charged only when the data are downloaded. The reference and the data points are accessible when the data set is downloaded.
The database can be queried without an account; however, users must register with DECHEMA before they can purchase data. Problems accessing the DETHERM internet site for searching are frequently due to a user's internal firewall.
Accessing DETHERM
Aspen Tech customers can access DETHERM data in two ways:
1. License DETHERM databases from DECHEMA
2. Access the DETHERM data via the Internet on a pay-as-you-use basis
Both methods feature seamless interface to Aspen Plus and Aspen Properties versions 10.2 and later.
Users pay for only the actual data tables downloaded. Data tables include:
Data and description
Complete substance identification
Literature reference
To sign up for DETHERM... on the Web, visit the DECHEMA at http://www.dechema.de/detherm.html
DECHEMA
DECHEMA e.V. is the German Society for Chemical Engineering & Biotechnology and the organizer of ACHEMA & ACHEMASIA. It is a non-profit scientific and technical society with its headquarters in Frankfurt on Main. It was founded in 1926 and at present has more than 5,000 private and institutional members.
DECHEMA's aim is to promote technical advances in the areas of chemical apparatus, chemical technology, environmental protection, and biotechnology.
DECHEMA is the producer of the DETHERM database which is the world's most comprehensive, single-source compilation of thermophysical properties of pure substances and mixtures. The partners are Professor J. Gmehling of the Oldenburg University (the Dortmund Databank), the University of Regensburg, and FIZ CHEMIE Berlin. The database features more than 4.9 million data sets for about 130,000 pure components and mixtures. The database includes:
Phase equilibrium data
PVT-Data
Thermodynamic Properties
Transport Properties
Interfacial Properties
Electrolyte data
More Information
For more information visit Dechema at http://www.dechema.de/detherm.html or contact Dr. Richard Sass, Dechema at +49 (0)69 7564 244 (or 245)
Keywords: Dechema
Dortmund
Internet
Commercial terms
References: None |
Problem Statement: Is it possible for an RStoic to determine the products of a combustion? | Solution: You can check the Generate combustion reactions on the Setup | Combustion sheet of an RStoic to have it automatically generate combustion reactions.
Full combustion is assumed when this option is specified: all carbon is converted to carbon dioxide and all hydrogen to water. The nitrogen combustion product may be specified as either NO or NO2.
Components containing atoms other than carbon, hydrogen, nitrogen, oxygen, and sulfur are ignored by this combustion option. N2 is treated as inert. Components specified as reactants on the Reactions sheet are not included in these combustion reactions.
Note that you must specify oxygen and the reaction products on the Components | Specifications sheet in order to use this option.
To see the reactions generated by Generate combustion reactions check Calculate Heat of Reaction on the Setup | Heat of Reaction tab. The reactions will be on the Results | Reactions sheet.
In the attached example file, there are two RStoic blocks. One lists all of the combustion reactions (BURNER) and the other automatically generates the reactions (BURNERC). The results are the same.
The heat of reaction results for the reactor where the combustion reactions are generated (BURNERC) are shown below:
Rxn No.
Reaction extent
Heat of reaction
Keywords: None
References: component
Stoichiometry
kmol/hr
cal/mol
C1
0
CH4
2 O2 + CH4 --> CO2 + 2 H2O
C2
0
C2H6
3.5 O2 + C2H6 --> 2 CO2 + 3 H2O
C3
0
C3H8
5 O2 + C3H8 --> 3 CO2 + 4 H2O
C4
0
C4H10
6.5 O2 + C4H10 --> 4 CO2 + 5 H2O
C5
1.14093815
-67629.999
CO
0.5 O2 + CO --> CO2
C6
0.11053756
-57800
H2
0.5 O2 + H2 --> H2O |
Problem Statement: How to read our Adobe Acrobat documentation? | Solution: User needs an Adobe Acrobat reader. This can be downloaded from a number of sources, including www.adobe.com.
Keywords: Version 10, Adobe Acrobat, reader, .pdf, documents
References: None |
Problem Statement: How Are Reaction Rate or Kinetics Affected by the Reaction Stoichiometry Written? | Solution: In Aspen Plus, the amount of reactants converted and products generated depends on how one enters the stochiometric coefficients. The kinetics expression in Aspen Plus is expressed as the rate of change in the Extent of Reaction. For a reaction:
aA + bB -> cC
(1)
If we use the symbol, E, to stand for the extent of
reaction, then the Extent of Reaction is defined as:
d E = - dA /a = - dB/b = dC/c
(2)
In the above equation dA, dB, and dC represents the change in moles for species A, B, and C, respectively. Note that the Extent of Reaction is independent of how the stochiometry is written.
In Aspen Plus, the kinetics the user enters on the kinetic form is based on the Extent of Reaction, i.e.,
r = (1/V)*dE/dt = k*C1*C2... (3)
where r is the reaction rate based on the Extend of Reaction, V the reaction volume, k the rate constant, and C1, C2, ... are concentrations, etc.
Thus, for a same reaction that is written in two different forms (i.e., two different but equivalent sets of stoichiometry coefficients) but with identical values of kinetic constants entered, the rate expressed by Eqn 3 will be the same but the simulation results will differ. This is because Aspen Plus interprets the the rate constants that users enter to be based on the Extent of Reaction (Eqn 3). Thus for the same rate constants (the pre-exponential factor and activation energy for the Power-Law kinetics), which would give the same k, the reaction rate based on the Extent of Reaction would be the same, independent of how the stochiometry is written. This can be easily understood from Eqn 3.
However, the reaction rate based on the conversion of a particular species, e.g., dA/dt,
dA/dt = - a * dE/dt (4)
would depend on the value of the stoichiometric coefficient (the value of a) entered. Obviously, depending on how the reaction is written, the value of a will certainly affect dA/dt. For two different expressions with two different values of a, the dA/dt will differ by a factor equal to the ratio of the two stochiometric coefficients.
For example, compare stoichiometry:
.5 O2 + 1 NO -> 1 NO2 (5)
with
1 O2 + 2 NO -> 2 NO2 (6)
From the chemistry point view, both expressions represent the exactly the same reaction, and how one writes it should not make any difference. However, in Aspen Plus, when user is entering the reaction rate kinetic constants, the user must make sure which stoichiometry the kinetic constants are derived for. While the reaction rate based on the extent of reaction remains the same for both expressions (when the same set of kinetic constants are used), the actual rate based on the conversion of O2 (or NO) will differ by a factor of 2, with the rate for the second reaction (Eqn 6) being twice as fast as the first one (Eqn 5).
In this case, if you are given, say, a set of experimental kinetic rate constants derived from the first expression (Eqn 5) but you want to use the second expression (Eqn 6)
in your Aspen Plus simulation, you must make sure to factor 0.5 into the preexponential factor. In other words, the preexponential factor for the first reaction (Eqn 5) must be twice the value for the second reaction (Eqn 6) to make the results identical.
Keywords: Reaction Kinetics
Stoichiometric coefficiencts
Stoichiometry
Reaction Rate
Extent of the reaction
rplug
rcstr
rbatch
References: None |
Problem Statement: Why do residue curves lines sometimes stop abruptly in the middle of a curve? | Solution: Every point on each of the residue curves represents a liquid composition. The curve end point is the initial composition of the liquid. Additional points are obtained by plotting liquid compositions as differential amounts of vapor are removed from the liquid.
If a line on a residue map stops abruptly, it is an indication that the line could be near a two liquid phase region.
The algorithm that calculates the curves is set up to stop when the temperature difference between successive points is less than a certain tolerance. One of the situations in which this can occur is when a second liquid phase is formed; however, this is not the only situation in which this criterion can occur. Hence, this phenomenon cannot be used to reliably show the two liquid regions on the residue map since this does not always happen in, or close to a two liquid phase region.
Keywords: analysis
liquid-liquid
LLE
two-phase
References: None |
Problem Statement: How do I read or write to the Control Panel and to Aspen Plus Files? | Solution: for Calculator Blocks:
In Fortran WRITE statements in a Fortran Calculator block, you can use the following predefined variables for the unit number:
Unit
Destination
NTERM
Control Panel (if running from the user interface)
Terminal (if running interactively outside of the user interface), or
Log file (if running batch)
NRPT
Aspen Plus report
NHSTRY
Simulation history
Interactive user input in a Calculator block can done with a READ statement from unit NTERM. Do not read from NTERM when running batch. An example file of an Interactive READ from a Calculator block is inSolution 102300: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=102300
Examples:
For writing to the Control Panel, enter:
WRITE(NTERM, *) A, B, C, X
For writing to the report file, enter:
WRITE(NRPT, *) A, B, C, X
For reading from the terminal, enter:
READ(NTERM,*) A
Read statements always require that a compiler is installed. Unformatted write statements as given in the examples above also require a compiler. Formatted write statements can be interpreted without a compiler. For more information about what statements need a compiler seeSolution 104149: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=104149.
For writing to the Control Panel using a formatted write statement, enter:
WRITE(NTERM, 100) A, B, C, X
100 FORMAT(4F10.2)
The diagnostic level for Calculator defined variables can be modified in the Diagnostics dialog box on the Calculator Sequence tabsheet. Setting the Calculator defined variables level to 5 will echo all variables to the Control Panel and/or history file. SeeSolution 103813 for more information: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=103813
Excel Calculator blocks do not have the ability to read or write to the Control Panel or Aspen Plus report or history files, but you may use VBA macros to display information in dialog boxes or to create a dialog box for interactive input.
For more information see the Aspen Plus User Guide, Chapter 19, Calculator Blocks and In-Line Fortran.
Solution for User Subroutines:
There is a utility (DMS_WRTALN) for writing to the History or Report file using any compiler. SeeSolution 119405 for details.
Use the DMS_WRTTRM utility (see User Models
Keywords: inline fortran
References: Manual, Chapter 4) to write to the Control Panel.
For example,
#include dms_maxwrt.cmn
.
.
.
1000 FORMAT ('FLASH OF STREAM', 2A4, 'FAILED')
WRITE (MAXWRT_MAXBUF, 1000) ID(1), ID(2)
CALL DMS_WRTTRM(1)
Notes
User subroutines cannot read from the Control Panel within the GUI.
When reading or writing using a user-defined file, use a Fortran unit number between 50 and 100. |
Problem Statement: Recommendations on the use of TABPOLY? | Solution: The use of TABPOLY in table or correlation form can sometimes lead to unexpected results for properties such as enthalpies, entropies, and heat capacities. TABPOLY has the
following characteristics:
The data used in TABPOLY is not regressed, instead a 3-point interpolation is executed every time that a property is requested. You should provide tabular data at small temperature intervals or enter data in the form of a polynomial coefficient
If a calculation is requested outside of the data (or polynomial) range, a linear extrapolation is performed for the Aspen Plus internal properties (enthalpy and entropy) using the estimated slope at the temperature limit of the data range. This results, for example, in a constant heat capacity above and below the temperature range of the data. Other heat capacity property models in Aspen Plus such as CPIG or CPLDIP are extrapolated linearly as a function of temperature. Also, the temperature range for most databank parameters is typically much greater than what users enter for TABPOLY.
TABPOLY is safest when used with self sufficient models such as vapor pressure (PL), density, and heats of vaporization. However, depending on the range of the data (and the models used) it may cause that the physical property calculations may not be consistent. For example, the predicted vapor pressure at the critical temperature may not be equal to the actual critical pressure PC.
A confusing part of TABPOLY is the use of different reference states for entropy and enthalpy. Aspen Plus uses the elements at 298.15K and 1 atm as the default reference state. The use of a different reference state in TABPOLY data will cause energy balance errors when reactions take place in the simulation. Aspen Plus can adjust the reference state of the enthalpy, entropy, and Gibbs free energy data that you entered. See Chapter 8 in the Aspen Plus User Guide for instructions.
Another area of problems lies in the fact that unless all components are specified in the TABPOLY data paragraph, the missing component property calculations will default to estimates using Ideal (IDEAL) routes for that property in spite of the property method declared on the Properties/Specifications form. For most properties, Aspen Plus calculates mixture properties using mole fraction average ideal mixing.
The individual property methods where TABPOLY is used can be specified on the TABPOLY forms. The default is to use TABPOLY in ALL property methods. If you are no longer using TABPOLY data in any Property method, you need to remove the object from the file.
Please refer to Chapter 8 in the Aspen Plus User Guide for
more information on the use of TABPOLY.
The TABPOLY input is entered on the
Properties / Advanced / Tabpoly form.
Attached is an example of using TABPOLY for liquid viscosity.
In conclusion, rather than use TABPOLY, it is preferable to do
a data regression of the correlation parameters for the chosen
Property Method employing the data presently
listed in the TABPOLY paragraphs. Many properties,
especially transport properties, can be regressed
directly using the appropriate model calls.
For thermodynamic properties, such as enthalpies, the sequence to follow
would be:
Regress parameters for the ideal gas heat capacity of the components not available in the the data bank.
Regress parameters for the heat of vaporization for those components unavailable in the data banks. One may be able to use the HL data available to help in the regression of the heat of vaporization.
SeeSolutions 3100 and 3168 for more information on how Aspen Plus
calculates enthalpy.
The Physical Properties Methods and Models reference manual covers the methods and routes used for the physical property estimations in great detail and will help you understand which models and routes are employed in each Property Method.
Keywords:
References: None |
Problem Statement: Where are the model switching parameters (thermo and transport switches) documented? | Solution: The Aspen Plus manuals for Releases 10.0 and earlier do not include documentation about the model switching parameters. Now they are documented in the Physical Properties Methods and Models reference manual.
Aspen Plus uses the model switching parameters (THRSWT and TRNSWT) to specify which equation format to use in the various temperature dependent property calculations for specific components.
Normally, these parameters do not need to be set by the user since the switches are set automatically when parameters are entered. The switches are needed when multiple sets of property parameters are entered for one property or the default equation is not desired for a set of DIPPR parameters.
Following is a table defining the different parameters and their definitions. The thermodynamic properties use the THRSWT submodel-selection parameter, and the transport properties use the TRNSWT submodel-selection parameter.
As the tables show, a property is associated with an element of the submodel-selection parameter. For example, THRSWT element 1 controls the submodel for solid volume. The following table shows the values for THRSWT or TRNSWT, and the corresponding submodels.
Thermodynamic Models:
Element Number
Property
Available Submodels
THRSWT/1
Solid Density
Aspen, DIPPR, PPDS, IK-CAPE
THRSWT/2
Liquid Density
Aspen, DIPPR, PPDS, IK-CAPE
THRSWT/3
Vapor Pressure
Aspen, Wagner, BARIN, PPDS, IK-CAPE
THRSWT/4
Heat of Vaporization
Aspen, DIPPR, PPDS, IK-CAPE
THRSWT/5
Solid Heat Capacity
Aspen, DIPPR, BARIN, PPDS, IK-CAPE
THRSWT/6
Liquid Heat Capacity
DIPPR, PPDS, BARIN, IK-CAPE
THRSWT/7
Ideal Gas Heat Capacity
Aspen, DIPPR, BARIN, PPDS, IK-CAPE
THRSWT/8
Second Virial Coefficient
DIPPR
Transport Models:
Element Number
Property
Available Submodels
TRNSWT/1
Liquid Viscosity (Route MUL01)
Aspen, DIPPR, PPDS, IK-CAPE
TRNSWT/2
Vapor Viscosity
Aspen, DIPPR, PPDS, IK-CAPE
TRNSWT/3
Liquid Thermal Conductivity
Aspen, DIPPR, PPDS, IK-CAPE
TRNSWT/4
Vapor Thermal Conductivity
Aspen, DIPPR, PPDS, IK-CAPE
TRNSWT/5
Liquid Surface Tension
Aspen, DIPPR, PPDS, IK-CAPE
The equation actually used to calculate the property for a given component depends on which parameters are available. If parameters are available for more than one equation, the Aspen Physical Property System uses the parameters that were entered or retrieved first from the databanks. The selection of submodels is driven by the data hierarchy, and controlled by the submodel-selection parameters.
The following table shows the values for THRSWT or TRNSWT, and the corresponding submodels.
Parameter Values
(Equation Number)
Submodel
0
Aspen
1 to 116
DIPPR
200
BARIN
301 to 302
PPDS or property-specific methods
401 to 404
IK-CAPE
501 to 515
NIST
For example, use the standard Aspen Plus equations, set the parameters to 0; to use the standard DIPPR equations set the value to 1 to use the default or use a specific code from the table at the end of this document.
All built-in databank components have model-selection parameters (THRSWT, TRNSWT) that are set to use the correct equations that are consistent with the available parameters. For example, suppose that parameters for the DIPPR equation 106 are available for liquid surface tension. For that component, TRNSWT element 5 is set to 106 in the databank. If you are retrieving data from an in-house or user databank, you should store the appropriate values for THRSWT and TRNSWT in the databank, using the appropriate equation number. Otherwise, the Aspen Physical Property System will search for the parameters needed for the Aspen form of the equations.
If a component is available in more than one databank, the Aspen Physical Property System uses the data and equations based on the databank list order on the Components | Specifications | Selection sheet. For example, suppose the databank search order is ASPENPCD, then PURE10, and that the Aspen Physical Property System cannot find the parameters for a particular submodel (equation) in the ASPENPCD databank. If the PURE10 databank contains parameters for another equation, the Aspen Physical Property System will use that equation (most likely the DIPPR equation) to calculate the property for that component.
If your calculation contains any temperature-dependent property parameters, (such as CPIGDP for DIPPR ideal gas heat capacity, entered on the Properties | Parameters | Pure Component form), the Aspen Physical Property System sets the corresponding THRSWT and TRNSWT elements for that component to the default values shown in the table above. This default setting might not always be correct. If you know the equation number, you should enter it directly on the Properties | Parameters | Pure-Component form. New THRSWT and TRNSWT parameter forms are found with the T-Dependent correlations in the Submodel selection option folder.
For example, suppose you want to use the:For example, suppose you want to use the:
DIPPR equation form of heat of vaporization (DHVLDP) for a component
Aspen equations for the remaining temperature dependent properties
Set the fourth element of the THRSWT parameter to 106, and the 1-3 and 5-8 elements to 0.
If you want to set the other temperature-dependent properties to use what is defined for that component in the databank, leave the element blank.
To see the values set by Aspen Plus, go to the Setup | Report Options | Property sheet and check All physical property parameters used (in SI units), run, and view the report file for the simulation. Search from THRSWT or TRNSWT to see the values of the parameter.
The Physical Properties Methods and Models reference manual chapter 3 describes the Aspen, DIPPR, BARIN, and IK-CAPE equations for each property. For descriptions of the the BARIN equations for heat capacity and enthalpy, see BARIN Equations for Gibbs Energy, Enthalpy, Entropy, and Heat Capacity.
Aspen Equations
Thermodynamic Models:
Element Number
Property
Aspen Model
Parameter Name
THRSWT/1
Solid Density
Aspen
VSPOLY
THRSWT/2
Liquid Density
Rackett
RKTZRA
THRSWT/3
Vapor Pressure
Extended Antoine
PLXANT
THRSWT/4
Heat of Vaporization
Watson
DHVLWT
THRSWT/5
Solid Heat Capacity
Aspen
CPSPO1
THRSWT/6
Liquid Heat Capacity
-
-
THRSWT/7
Ideal Gas Heat Capacity
Aspen
CPIG
THRSWT/8
Second Virial Coefficient
-
-
Transport Models:
Element Number
Property
Aspen Model
Parameter Name
TRNSWT/1
Liquid Viscosity
Andrade
MULAND
TRNSWT/2
Vapor Viscosity
Chapman-Enskog-Brokaw
See model
TRNSWT/3
Liquid Thermal Conductivity
Sato-Riedel
See model
TRNSWT/4
Vapor Thermal Conductivity
Stiel-Thodos
See model
TRNSWT/5
Liquid Surface Tension
Hakim-Steinberg-Stiel
See model
DIPPR Equations
The January 1993 version of DIPPR no longer uses a single equation for any individual property. There are ten different equations that DIPPR can use for any property of a component (although in general it is limited to two or three). The following table lists the equation forms used and the appropriate model number for each equation form.
In order to use a specific form of an equation, enter the model number as the parameter for THRSWT. The default equation form depends on the property being calculated. These default DIPPR equations are used automatically when the model-switching parameters are set to 1.
Thermodynamic Models:
Element Number
Property
DIPPR Eqn. #
Parameter Name
THRSWT/1
Solid Density
100
DNSDIP
THRSWT/2
Liquid Density
105/116*
DNLDIP
THRSWT/3
Vapor Pressure
101/115*
THRSWT/4
Heat of Vaporization
106
DHVLDP
THRSWT/5
Solid Heat Capacity
100
CPSDIP
THRSWT/6
Liquid Heat Capacity
100/114*
CPLDIP
THRSWT/7
Ideal Gas Heat Capacity
100/107(default)
CPIGDP
THRSWT/8
Second Virial Coefficient
104
Transport Models:
Element Number
Property
DIPPR Eqn. #
Parameter Name
TRNSWT/1
Liquid Viscosity
101
MULDIP
TRNSWT/2
Vapor Viscosity
102
MUVDIP
TRNSWT/3
Liquid Thermal Conductivity
100
KLDIP
TRNSWT/4
Vapor Thermal Conductivity
102
KVDIP
TRNSWT/5
Liquid Surface Tensio
100/106(default)
SIGDIP
? Equations 114 through 116 are used as the default only for water.
Key to DIPPR Equation Forms
Number Equation
------ --------
100 Y = A + BT + CT**2 + DT**3 + ET**4
101 Y = exp[A + B/T + ClnT + DT**E ]
102 Y = (AT**B)/(1 + C/T + D/T**2)
103 Y = A + B exp [ -C/T**D ]
104 Y = A + B/T + C/T**3 + D /T**8 + E/T**9
105 Y = A/B**(1 + (1 - T/C)**D )
106 Y = A ( 1 - Tr )**( B + CTr + DTr**2 + ETr**3 )
107 Y = A + B[(C/T)/SINH(C/T)]**2 + D[(E/T)/COSH(E/T)]**2
114+ Y = (A**2)/t + B - 2ACt - ADt**2 - (C**2t**3)/3 - (CDt**4)/2 - (D**2t**5)/5
where t = (1 - Tr)
115++ Y = A + B/T + C lnT + DT**2 + E/T**2
116+++ Y = A + Bt**0.35 + Ct**(2/3) + Dt + Et**4/3 where t = (1 - Tr)
Y = property value
T = temperature in Kelvins
A, B, C, D, E = parameter elements
+ Equation 114 limited for use in liquid heat capacity regressions (January 1993).
++ Equation 115 limited fir use in vapor pressure regressions(January 1993).
+++ Equation 116 limited for use in liquid density regressions (January 1995).
Barin Equations
The following equations are used when parameters from the Aspen Physical Property System inorganic databank are retrieved first.
The phase can be solid, liquid, or ideal gas. For each phase, multiple sets of parameters from 1 to n are present to cover multiple temperature ranges. The value of the parameter n depends on the phase.
The four properties Cp, H, S, and G are interrelated as a result of the thermodynamic relationships and one set of parameters (CPxSPn) can be used to calculate all of them.
Gibbs Energy:
Gi = A + BT + C(TlnT) + DT**2 + ET**3 + FT**4 + G/T + H/T**2
Enthalpy:
Hi = A - CT - DT**2 - 2ET**3 - 3FT**4 + 2G/T + 2 H/T**2
Entropy:
Si = -B - C(1 + lnT) - 2DT - 3ET**2 - 4FT**3 + G/T**2 + 2H/T**3
*Heat Capacity:
Cpi = -C - 2DT - 6ET**2 - 12FT**3 - 2G/T**2 - 6H/T**3
where
T = temperature in Kelvins
A, B, C, D, E = CPxSPn parameter elements
Vapor Pressure:
The Barin equation for vapor pressure is
lnP = (GL - GV)/(R*T) + lnPref
where GL is the Gibbs Free energy for the liquid phase
GV is the Gibbs Free energy for the vapor phase Pref is the reference pressure (1 atm)
The equation for the solid vapor pressure is
lnP = (GS - GV)/(R*T) + lnPref
where Gs is the Gibbs Free energy for the solid phase.
Thermodynamic Models:
Element Number
Property
Barin Eqn. #
Parameter Name
THRSWT/1
Solid Density
-
-
THRSWT/2
Liquid Density
-
-
THRSWT/3
Vapor Pressure
200
THRSWT/4
Heat of Vaporization
-
-
THRSWT/5
Solid Heat Capacity
200
CPSXP1, CPSXP2, ..., CPSXP7
THRSWT/6
Liquid Heat Capacity
200
CPLXP1, CPLXP2
THRSWT/7
Ideal Gas Heat Capacity
200
CPIXP1, CPIXP2, CPIXP3
THRSWT/8
Second Virial Coefficient
-
-
PPDS Equations
The PPDS equations are available only to the customers who have licensed the PPDS databank from NEL.
IK-CAPE Equations
In order to use a specific form of an equation, enter the model number as the parameter for THRSWT or TRNSWT.
Thermodynamic Models:
Element Number
Property
IK-CAPE Eqn. #
Parameter Name
THRSWT/1
Solid Density
401
VSPO
THRSWT/2
Liquid Density
401
VLPO
THRSWT/3
Vapor Pressure
401
PLPO
THRSWT/4
Heat of Vaporization
401
DHVLPO
THRSWT/5
Solid Heat Capacity
401
CPSPO
THRSWT/6
Liquid Heat Capacity
401/403
CPLPO/CPLIKC
THRSWT/7
Ideal Gas Heat Capacity
401
CPIGPO
THRSWT/8
Second Virial Coefficient
-
-
Transport Models:
Element Number
Property
IK-CAPE Eqn. #
Parameter Name
TRNSWT/1
Liquid Viscosity
401/404
MULPO/MULIKC
TRNSWT/2
Vapor Viscosity
401/402
MUVPO/MUVSUT
TRNSWT/3
Liquid Thermal Conductivity
401
KLPO
TRNSWT/4
Vapor Thermal Conductivity
401
KVPO
TRNSWT/5
Liquid Surface Tension
401
SIGPO
Key to IK-CAPE Equation Forms
Number
Equation
401
Y = A + BT + CT**2 + DT**3 + ET**4 + FT**5 + GT**6 + HT**7 + IT**8 + JT**9
402
Y = AT**0.5 / ( 1 + B/T )
403
Y = A + BT + CT**2 + DT**3 + E/T**2
404
Y = A exp( B/T ) + C
Y = property value
T = temperature in Kelvins
A, B, C, D, E = parameter elements
NIST Equations
In order to use a specific form of an equation, enter the model number as the parameter for THRSWT or TRNSWT.
Thermodynamic Models:
Element Number
Property
NIST Eqn. #
Model
Parameter Name
THRSWT/1
Solid Density
503
NIST ThermoML polynomial
DNSTMLPO
THRSWT/2
Liquid Density
503
504
514
515
NIST ThermoML polynomial
NIST TDE expansion
NIST TDE Rackett
NIST COSTALD
DNLTMLPO
KNLEXSAT
KNLRACK
KNLCOSTD
THRSWT/3
Vapor Pressure
501
502
NIST TDE Polynomial
NIST Wagner 25
PLTDEPOL
WAGNER25
THRSWT/4
Heat of Vaporization
505
NIST TDE Watson equation
DHVLTDEW
THRSWT/5
Solid Heat Capacity
503
NIST ThermoML polynomial
CPSTMLPO
THRSWT/6
Liquid Heat Capacity
503
506
NIST ThermoML polynomial
NIST TDE equation
CPLTMLPO
COKTDECS
THRSWT/7
Ideal Gas Heat Capacity
503
513
NIST ThermoML polynomial
NIST Aly-Lee
CPITMLPO
CPIALEE
THRSWT/8
Second Virial Coefficient
-
-
-
Transport Models:
Element Number
Property
NIST Eqn. #
Model
Parameter Name
TRNSWT/1
Liquid Viscosity
508
509
NIST TDE equation
NIST PPDS9
MULNVE
MULPPDS9
TRNSWT/2
Vapor Viscosity
503
NIST ThermoML polynomial
MULTMLPO
TRNSWT/3
Liquid Thermal Conductivity
503
510
NIST ThermoML polynomial
NIST PPDS8 equation
KLTMLPO
KLPPDS8
TRNSWT/4
Vapor Thermal Conductivity
503
NIST ThermoML polynomial
KVTMLPO
TRNSWT/5
Liquid Surface Tension
505
511
512
NIST TDE Watson equation
NIST TDE expansion
NIST PPDS14 equation
SIGTDEW
SIGISTE
SIGPDS14
Keywords: thermoswitches
transport switches
References: None |
Problem Statement: What are the API 1997 Liquid Viscosity and Twu Liquid Viscosity methods? | Solution: API 1997 Liquid Viscosity and Twu Liquid Viscosity methods are new for 2004.
API 1997 Liquid Viscosity
The liquid mixture viscosity is calculated using a combination of the API and Andrade/DIPPR equations. This model is recommended over the earlier API viscosity model. This model is applicable to petroleum fractions with normal boiling points from 150 F to 1200 F and API gravities between 0 and 75. Testing by AspenTech indicates that this model is slightly more accurate than the Twu model for light and medium boiling petroleum components, while the Twu model is superior for heavy fractions.
For pseudocomponents, the API model is used:
mul = fcn(T, x, TB, API, Vl)
Where:
fcn = A correlation based on API Procedures and Figures 11A4.2, 11A4.3, and 11A4.4 (API Technical Data Book, Petroleum Refining, 1997 edition)
Vl is obtained from the API liquid volume model.
TB and API are scalar parameters that can be entered for each component.
For real components, the Andrade/DIPPR model is used.
Twu Liquid Viscosity
The Twu liquid viscosity model is based upon the work of C.H. Twu (1985). The correlation uses n-alkanes as a reference fluid and is capable of predicting liquid viscosity for petroleum fractions with normal boiling points up to 1340 F and API gravity up to -30.
Given the normal boiling point TB and the specific gravity SG of the system to be modeled, the Twu model estimates the viscosity of the n-alkane reference fluid of the same normal boiling point at 100 F and 210 F, and its specific gravity. These are used to estimates the viscosity of the system to be modeled at 100 F and at 210 F, and these viscosities are used to estimate the viscosity at the temperature of interest.
Keywords:
References: C.H. Twu, Internally Consistent Correlation for Predicting Liquid Viscosities of Petroleum Fractions, Ind. Eng. Chem. Process Des. Dev., Vol. 24 (1985), pp. 1287-1293 |
Problem Statement: When accessing the DUTY of a unit operation block in a Calculator or Design Specification, the value is always zero. | Solution: The variable DUTY is the user specified duty set in block.
The calculated heat duty variable is QCALC. QCALC is the difference of enthalpies of inlet and outlet material streams. QCALC is set to zero if duty is specified.
The net heat duty NET-DUTY is the sum of the inlet heat streams minus the actual (calculated) heat duty.
Keywords: enthalpy
References: None |
Problem Statement: When using License Manager licensing, user cannot receives licensing error in Point | Solution: Activator not attached, missing License Key file.
Solution
This problem could be caused by the License Management Selector program being configured for Activator licensing rather than using License Manager.
Open a License Manager Status window on the Client PC and enter the command asplmadm -s. This will list all available License Manager Servers on the network. Note the name of the desired server.
Open the License Management Selector Program and locate the desired product. Select the desired product.
Select License Manager, Connect to named License Server and enter the name shown in Step 1 in the line titled License Server Name.
Keywords:
References: None |
Problem Statement: How do you test binary vapor-liquid equilibrium data for thermodynamic consistency? | Solution: It is important to test binary vapor-liquid equilibrium (VLE) data for thermodynamic consistency since the use of inconsistent data in data regression results in poor parameter values and may cause convergence problems. When you request consistency test for a data group in a regression, you can specify whether or not the data group is to be included in the regression, if it is found to be thermodynamically inconsistent. The reasons for inconsistent phase equilibrium data are often systematic errors. For example, the experimentator did not wait with his measurement until the true equilibrium was reached.
There are two test methods available: the area test of Redlich-Kister, and the point test of Van Ness and Fredenslund, et al. Both methods use the Gibbs-Duhem equation. For a more detailed discussion of both tests, please refer to J. Gmehling and U. Onken, Vapor-Liquid Equilibrium Data Collection, DECHEMA Chemistry Data Series, Vol. I, Part 1, ed. Dieter Behrens and Reiner Eckermann (Frankfurt/Main: DECHEMA, Deutsche Gesellschaft für Chemisches Apparatewesen, 1977).
You can use the area test for both isothermal and isobaric data. Use the point test for isothermal data only. The area test is applicable to systems at subcritical temperatures and at low pressures. Do not use the area test for systems with temperatures higher than the critical temperature for any of the components. The point test is applicable to systems at subcritical, as well as supercritical, temperatures. You can use the point test for either low pressure or high pressure data. For either test, you must have composition data for both the liquid and the vapor phases (redundant information). Also, you must supply at least five data points.
Area Test
The area test employs the integral form of the Gibbs-Duhem equation. For the area test, the natural logarithm of the ratio for the activity coefficients is plotted versus the liquid mole fraction. This curve intersects the x-axis and thus creates two areas: one above and one below the x-axis. If the area above the x-axis is designated A, and the area below the x-axis is designated B, for isothermal data the data are consistent when the difference between A and B is close to zero. For practical purposes a parameter D is used and defined as follows:
D = |(A-B)/(A+B)| * 100 %
For isothermal data, the data are consistent if D is smaller than the area-test tolerance.
D less than or equal to tolerance (defaults to 10%)
For isobaric data-sets, the excess enthalpy term (-hE/(R*T^2)) in the Gibbs-Duhem equation must be taken into account. In Aspen Plus the method of Herington is used. Herington defines J as follows:
J = 150 * ( |DeltaTmax|/Tmin )
Where:
Tmin = The lowest boiling temperature within x=0 to x=1. This is normally the boiling point of the more volatile component. For low boiling azeotropes, it is the boiling temperature of the azeotrope.
DeltaTmax = The maximum difference of boiling points within x=0 to x=1. This is usually the difference between the boiling points of the pure components. For azeotropic systems, DeltaTmax is the difference between the boiling temperature of the azeotrope and the temperature of the component most distant from it.
In Aspen Plus, the isobaric data are consistent if the following statement is true:
D-J less than or equal to tolerance
The default value for tolerance in the area test is 10%.
Point Test
The point test is limited to isothermal data only. Unlike the area test, it can be used to test high-temperature, high-pressure data. The point test is more rigorous than the area test, because each data point is checked individually. The method involves calculating the vapor-phase mole fraction y from the experimental liquid-phase mole fraction x and the total pressure P, by making use of the differential form of the Gibbs-Duhem equation and the orthogonal collocation technique. The calculated y (y_calc) is compared with the experimental value of y (y_exp) as follows:
delta_y = y_exp - y_calc
The data set is consistent if the average difference (i.e., the average delta_y) is less than 0.01.
VLE Thermodynamic Consistency Tests Compared
Area Test
Pro''s
More accurate extrapolation to the infinite dilute limit due to the integral form.
Detects phase composition analysis problems.
Applicable to isothermal and isobaric data.
Con''s
Requires measurements over the complete composition range.
Fails to detect measurement errors in pressure or temperature.
Does not allow the identification of outliers.
Point Test
Pro''s
Tests each point individually, thus permitting the immediate elimination of outliers.
Identifies problems in phase composition analysis and pressure (or temperature) measurements.
Can be used to test high-temperature, high-pressure data.
Con''s
Applicable to isothermal data only.
Keywords: data regression
consistency test
consistent
inconsistent
area test
point test
Redlich-Kister
Gibbs-Duhem
Herington
References: None |
Problem Statement: The simulation terminates with the following error message:
****EXECUTION ERROR
UNABLE TO LOAD DYNAMIC LIBRARY PPPOLY
! Calculations terminated because of ASPEN PLUS internal errors | Solution: The cause of the problem is that at least one input specification requires the presence of Polymers Plus. This could be a property method such as POLYNRTL, or a component being declared as polymer, or segment. Note that the sheer presence of any polymer-related input specification requires Polymers Plus (including the dynamic library pppoly.dll) to be installed. However, from Aspen Plus 10.2 onwards, Polymers Plus is no longer part of a full installation of Aspen Plus.
The action depends on whether your simulation is a Polymers Plus application, or not.
If you are not planning to run a Polymers Plus application, you might have selected a polymer-related input specification by mistake. Remove the input specification(s) (e.g., POLYNRTL) from the file to eliminate the cause of the error message.
If your simulation is a Polymers Plus application, install Polymers Plus from the Aspen Engineering Suite 10.2 CD-ROM, making sure you have a valid license to run this layered product.
Keywords: Polymers Plus
PPPOLY
Execution error
POLYSRK
polyme
dynamic library
References: None |
Problem Statement: I am having problems converging a three phase, highly nonideal column. What are some recommendations to address problems like this? | Solution: Here are some general practical ideas that one can try when addressing convergence problems in RadFrac. The items mentioned below usually are sufficient to solve most problems when combined with patience, good analysis skills and process knowledge.
Physical properties
Pick the top five to ten most important components. Ensure that binary interaction parameters are available for at least these components and realize the effect of missing parameters on the predicted interactions between the most important components.
Generate TPXY curves from the Tools/Analyze/Binary menu and ensure that azeotropes and two-phase regions are predicted correctly (compared to whatever published data is available). Also, consider looking at the residue curves and evaluate the correct prediction of ternary azeotropes.
Confirm from the TPXY that two liquid phases will or will not form in the simulated tower.
It is unlikely that complex tower convergence will be easily obtained without good physical properties.
Design Specifications & General specifications
As a general rule of thumb, when one has the choice of several operating specifications, choose the specification that is numerically smaller, e.g. the smaller of the distillate to feed ratio (D:F ratio) or reboiler duty will be the D:F ratio. There is no specific mathematical reason for this rule but instead one typically finds that the numerical smaller specification is more flexible and does not give as many convergence problems.
Avoid design specifications initially unless it will help the convergence. Add the design specifications later once the tower had converged.
Decanter specifications
Sometimes specifying 0 or 1 for the fractions of the first liquid phase (L1) or the second liquid phase (L2) returned to the tower can yield convergence problems - instead use 0.00001 or 0.999999 as a workaround.
Second Liquid Phase Detection
Ensure that vapor-liquid-liquid (VLL) calculations are done where ever two liquids may exist. Flash results for a 3-phase (VLL) system using a 2-phase (VL) flash will yield errors. At the same time checking the whole tower for 2 liquids may slow down the simulation significantly. Consider doing a TPXY analysis first and based on the predictions from the TPXY analyzes, select certain tower sections e.g. from feed tray to top tray to check for 2 liquid phases.
Homotopy a.k.a. 'Simplify First'
Please note that although Aspen Plus contains a homotopy algorithm as part of the equation orientated (EO) solver, this discussion does not refer to said solver but merely to the general topic of homotopy. Homotopy loosely defined is a method which allows convergence in cases where it otherwise could not be converged by approaching theSolution in steps from another state where the solver is known to converge.
With regards to distillation towers, this means simply the tower first, converge the simplified problem and use the results from the simplified run to start the next run which is more complicated. This can be done with components, number of stages, tightness of separation specifications etc. For example, when applied to components, try to reduce the number of components as much as possible. Once the simulation is converged, go back and add the additional components that are absolutely required in a step-by-step fashion. Converge the tower each time new components are added and use the converged results to generate new composition, flow and temperature profile estimates for the tower. Potentially one can just keep adding components and generate column estimations from converged results to help with the next run with more components. Sometimes it might be required to eliminate unnecessary components by lumping e.g. combining all heavies greater than component X together with component X. This works in particular if there is no real interest in the individual concentrations of these lumped components.
Convergence approach
A highly nonideal tower will likely require the Broyden/Newton convergence method, as these will take into account the interactions between the different components and other variables when trying to converge the tower. However do note that both these methods have a serious weakness in the fact they need a good (and consistent) starting point (estimation). These methods may easily diverge or fail from bad initial estimates.
Take care so as not to specify infeasible initial estimates. Start with temperature estimates and, if needed, expand to component concentration estimates. Once again the principle of homotopy should be considered. When applied to convergence methods, one can perhaps try to converge a simplified tower with say the standard or another method. Then increase the complexity of the tower to the final level, switch the convergence method to Newton or Broyden (custom convergence method) and converge the tower starting somewhere close to the finalSolution.
Keywords: radfrac, convergence
References: None |
Problem Statement: Does the condenser heat stream include the duty for subcooling? | Solution: No, Aspen Plus reports the Condenser heat stream as the duty required for condensing the vapor. This is separate from the Subcooling duty which is the duty required to subcool the product coming off the condenser (i.e., distillate). Subcooling specifications are set on the Condenser sheet of the RadFrac Setup form.
Note: This specification changes the temperature of the distillate stream not the stage temperature. So, in this example, the distillate stream drawn off the condenser is 20 F less than the condenser stage (1) temperature.
The Column Results Summary form reports the Condenser Heat duty and the Subcooled duty separately:
Both values are displayed on the flowsheet as QC (Condenser Duty) and QS (Subcooled Duty).
Keywords: Condenser, duty, column, RadFrac, subcooled
References: None |
Problem Statement: Is it possible to model reactors, such as hydrotreaters, that use assays and pseudocomponents? | Solution: See the attached Aspen Plus 10.1 example file! This file can be opened in Aspen Plus 10.1 and higher.
The simplest and most direct way to model reactors such as FCCU's, hydrotreaters, and hydrocrackers is with an RYield reactor. The RYield reactor simply performs a mass balance and uses the user-specified yield to calculate the flowrate of each component in the product stream.
If detailed calculations are required, there two important issues in using the reactor models with pseudocomponents:
Heat of reaction is not likely to be correct since it depends on the difference of very large heat of formation values. The heat of formation for pseudocomponents is only a correlation based on the original assay data.
The atom balance, especially the important carbon/hydrogen ratio will not be preserved since this is a yield reactor and not a stoichiometric reactor. In addition, these are pseudocomponents and not conventional components with a specific molecular formula.
Reactors can be modeled in more detail using other products such as Aspen FCC.
Specifying the yield distribution (component by component) for an RYield reactor is an easy task, when all of the components are specified on the Component Specification form. For petroleum applications, the resulting pseudocomponents are not listed on the Components \ Specification form - therefore, you won't find them as possible choices on the RYield's yield form. The pseudocomponents can be found on the stream results form after a run completes, but they do not, by default, show up on any input forms.
There is a way to add them to the Yield list, with the assay generation feature.
Navigate down the Data Browser to Components \ Petro Characterization \ Generation.
In the Generation object manager, click the New button. You can accept the default name G-1 or modify the name.
On the Generation form, skip the specification sheet, and find the sheet called Cuts. On the Cuts sheet, specify the number of cuts to be used and the temperature increment. The defaults (found in Help) are:
TBP Range, F
Number of Cuts
Temp Increments, F
100 - 800
28
25
800 - 1200
8
50
1200 - 1600
4
100
Even if you like the above defaults, you must manually enter them on the Cuts sheet to enable the feature described in the next step. This form defines the boiling point range that will be covered by each system-generated pseudocomponent. The smaller increments you use, the more components you will have to name in the next step.
In the Naming Options sheet (still within Generation), select User Defined List. In the text box below, enter the name you want to use for each of the pseudocomponents or cuts that you defined in step 3. You should name all the cuts.
Finally, go back to the RYield / Setup form's Yield sheet. When you click on the drop down box, you will now see your user-named pseudocomponents.
You can skip steps 1 - 5 if you enter each pseudocomponent on the Component / Specification form. This is a little more work as you will have to specify enough phyical property data on each component to satisfy the API correlations (two or three of Gravity, MW, NBP)
In the attached example, for simplicity, 10 pseudocomponents are generated and named for the entire boiling range of the crude oil feed. On the RYield's Yield sheet, 2 of the pseudocomponents are specified in the product. N2 passes through unreacted (see the inert declaration).
Keywords: petroleum
ada
assay
pseudo
pseudocomponent
naming
generation
reactor
RYIELD
References: None |
Problem Statement: How many baffles are needed to model an H-shell heat exchanger? There is a severe error that bypasses the block saying that the number of baffles needs to be greater than 2, even though 8 baffles have been specified? | Solution: The H-shell in the Aspen Plus HEATX block is modeled as 8 E-shells. Each E-shell needs 2 baffles so the H-shell needs 16. F-shells need 2 baffles and G-shells need 8.
Keywords: heatx
References: None |
Problem Statement: When trying to use the interface to heat exchange design programs for an existing flowsheet simulation, is it possible to add the HXDESIGN property set when it is missing? | Solution: The HXDESIGN property set is included in many of the application template (.apt) files provided with the software. The General with English Units and General with Metric Units both include this property set.
Steps
Open a new simulation with either the General with English Units or General with Metric Units templates.
Go to the Properties \ Prop-Sets \ HXDESIGN object in the left hand frame of the Data Browser.
Click on the Right Mouse Button and select Export. Give this piece of a backup (.bkp) file a name.
Go to any existing simulation.
From the File menu, select import, and choose the file created in step 3.
The last two steps can be repeated for any number of simulations.
Keywords: prop-set
References: None |
Problem Statement: What equations are used in the GMMNRTL model? | Solution: The GMMNRTL is a modified NRTL model. It was modified by one of our large customers who asked us to integrate it with Aspen Plus so their engineers could use it. Unfortunately, it was never documented.
The equation for the tij and the alpha function for NRTL (GMRENON) are shown in our help and Physical Property Methods and Models manual. The equation for alpha is the same for both GMMNRTL and GMRENON:
alpha = c + d (T - 273.15K)
where c and d are the NRTL c and d parameters, elements 3 and 4 of the NRTL binary parameter array..
Three additional parameters are used for tau (tij) in addition to the NRTL a and b parameters (elements 1 and 2 of the NRTL binary parameter array):
where aij and bij are the NRTL a and b parameters
c1ij is GMREC0
c2ij is GMREC1
c3ij is GMREC2
Since the above function is much different than the GMRENON tij, our databank NRTL parameters cannot be used in GMMNRTL. To use this model, you should regress the NRTL and GMREC parameters. It is convenient to use the Generate Data option based on some other property method such as UNIQUAC. This causes Aspen Plus to generate the regression input data using our UNIQUAC parameters and then use this data to regress the parameters. This is reasonable since the UNIQUAC and NRTL parameters were generated from the same data source. GMRENON cannot be used to generate the data since you will be trying to determine new values for the NRTL a and b parameters.
Keywords: GMMNRTL, NRTL
References: None |
Problem Statement: The user has selected in THRSWT/2 the value of 0 and entered DNLDIP (DIPPR density parameters) for a component.
In Aspen Plus 10.1, Aspen Plus still uses the DIPPR correlation; however, in Aspen Plus 10.2, it uses the Rackett correlation.
In Aspen Plus 10.2 if you set THRSWT/2 to 0, and do a Retrieve Parameter Results from the tools menu, it does not show the DNLDIP parameters while Aspen Plus 10.1 shows them.
Note that if you set THRSWT/2 to 105, both Aspen Plus 10.1 and 10.2 give the same density using the DIPPR correlation. | Solution: A thermoswitch (THRSWT) is a parameter that controls which form of an equation is used to calculate a thermodynamic property when there are multiple equations available. Thermoswitches are entered in the Properties/Parameters/Pure Components folder as T-Dependent objects. For more information on For more information on Thermoswitches seeSolution 3026.
As per the documentation in the Aspen Plus 10.2
Keywords: density
DIPPR
Rackett
THRSWT
TRNSWT
References: Manual Physical Properties Models and Methods page 132 (section 3 page 4), if the THRSWT is set to 0 it uses Aspen. If it is set to 1, if uses the DIPPR correlation, guessing the formula to use. For density it should use 105. To prevent problems in this guessing we recommend to set the value of THRSWT to the appropriate code (but for density, setting to 1 is ok).
Aspen Plus 10.2 is behaving as documented. The behavior in Aspen Plus 10.1 is actually a bug that it would use DIPPR even if you had told it to use Aspen.
In Aspen Plus 10.1, if there are input for parameters and also THRSWT or TRNSWT settings, certain switch settings are assumed and THRSWT input may be ignored. This problem is fixed in Aspen Plus 10.2. So if you enter both THRSWT and prop-data of two types of parameters (e.g., CPIG and CPIGDP), the THRSWT setting is used.
It is important not to rely on the bug in Aspen Plus 10.1: i.e. don''t set THRSWT or TRNSWT to 0 to have the DIPPR correlation, rather set it to 1 or the appropriate formula code. |
Problem Statement: As the concentrations of components in the batch reactor RBatch are inherently dynamic, what value is used in the power law model calculations and how often are they updated? | Solution: The component concentrations used in the reaaction kinetic calculations are the actual values for a given iteration. The concentrations are updated for each iteration.
Keywords: batch reactor
References: None |
Problem Statement: With Aspen Plus 11.1, it is possible to export using an XML format. What is the use of this feature?
Do you provide a starting example? | Solution: The XML file format is used in Aspen Plus 11.1 to provide an alternative way of saving the results. Having the results in this format allows one to perform searches and filtering in a much more efficient way than using VBA or the Summary File Toolkit.
For the Summary File Toolkit approach, see:
http://support.aspentech.com/webteamasp/KB.asp?ID=102670
The applications that are likely to benefit from the XML format summary file are those where one has to repeatedly extract large amount of data of the same kind from large flowsheets.
The provided example shows how to get the duties of all HEATER blocks and all FLASH2 blocks plus the condenser and reboiler duties of all RADFRAC blocks.
The testprob.xml file was obtained running the testprob (cyclohexane hydrogenation) file and selecting File->Export->XML Summary.
The file that actually does the job is testprob.xsl.
To see the example at work, place all the files in the same folder and open the file testprob.htm with Internet Explorer 5.0. The file testprob.jpg shows how this page is displayed in the browser.
Note that this example has been tested with versions 3 and 4 of the Microsoft XML Core Services 4.0 RTM (formerly called MSXML parser). It will not work if you have Internet Explorer 5.x even on Windows 2000. You can download the latest update from Microsofts'' webiste: http://msdn.microsft.com/xml.
Keywords: extended markup language stile sheets XPATH XSL XML
References: None |
Problem Statement: Is it possible to model multiple immiscible phases of the same | Solution: using the FactSage Interface? Native calculations in FactSage support up to three immiscible phases of the sameSolution.
Solution
To deal with immiscibleSolution phases, it is necessary to modify the components andSolutions in the databanks.
Add theSolution phases to the FACTSOLN.TXT file in the APRSystem 11.1\Engine\xeq directory. For example to allow for up to three immiscible liquid phases for SLAG, one needs to make the following additions to FACTSOLN.TXT:
2
SLAG
Slag-liquid#1
2
SLG2
Slag-liquid#2
2
SLG3
Slag-liquid#3
SeeSolution 110663 for more details about addingSolution phases.
Create user databank with new components for CaO, Al2O3, and SiO2 in the second and third slag phases.
SeeSolution 110401 for more details about how to add components to the existing Fact pure component databanks Alternatively, it is probably best to create a user or inhouse databank with the new components. SeeSolution 110665 for more details.
Keywords: chemapp
fact
sage
interface
References: None |
Problem Statement: In my user databank some components have incorrect names. Is it possibile to rename these components with DFMS? | Solution: Besides using the COPY paragraph to copy information from one databank to another, you can also use it to copy records within a databank. If you combine a COPY [NEW-NAMES] paragraph with a DELETE paragraph (e.g., to delete any data for a given component from a databank), you can actually rename an existing component.
Example: Creating a User Databank
A user databank USRPP2A with some pure-component parameters is created. The components are named ETHANOL and ACETONE.
TITLE ''EXAMPLE FOR A USRPP2 DATABANK''
;
; create the databank
;
FILE USRPP2A NOSECRET NEW
;
; specify that the databank can be written to
;
WRFILE NOSECRET
;
; define the properties
;
NEW-PROP MW 1 / TC 1 / PC 1 / VC 1 / ZC 1 / DHFORM 1 / DGFORM 1 / OMEGA 1 /
CPIG 11 / PLXANT 9 / DHVLWT 5 / WILSON 6
;
; define the pure components and binary pairs
;
NEW-COMP
ETHANOL C2H6O /
ACETONE C3H6O
;
; enter the data; all data must be in SI units
;
; pure component scalar parameters
;
PROP-DATA
PROP-LIST MW 1 / TC 1 / PC 1 / VC 1
PVAL ACETONE 58.0798 / 511.732 / 0.480250E+07 / 0.209500
PROP-LIST ZC 1 / DHFORM 1 / DGFORM 1 / OMEGA 1
PVAL ACETONE 0.236473 / -0.216050E+09 / -0.154540E+09 / 0.283437
PROP-LIST MW 1 / TC 1 / PC 1 / VC 1
PVAL ETHANOL 46.0688 / 520.062 / 0.575664E+07 / 0.166500
PROP-LIST ZC 1 / DHFORM 1 / DGFORM 1 / OMEGA 1
PVAL ETHANOL 0.221667 / -0.234790E+09 / -0.170860E+09 / 0.557097
;
; pure component temperature-dependent correlation parameters
;
PROP-LIST CPIG 1
PVAL ACETONE 13717.6 227.328 -0.753951E-01 -0.177424E-05
0.000000E+00 0.000000E+00 280.000 1100.00
36029.2 7.55350 1.50000
PROP-LIST PLXANT 1
PVAL ACETONE 56.2699 -5324.86 0.000000E+00 0.000000E+00
-4.93262 0.160956E-16 6.00000 329.300
511.732
PROP-LIST DHVLWT 1
PVAL ACETONE 0.297146E+08 329.300 0.438274 -0.179791
329.300
PROP-LIST CPIG 1
PVAL ETHANOL 6638.87 224.991 -0.108875 0.183462E-04
0.000000E+00 0.000000E+00 280.000 1100.00
36029.2 0.755423 1.85027
PROP-LIST PLXANT 1
PVAL ETHANOL 81.6864 -7523.17 0.000000E+00 0.000000E+00
-8.32377 0.203101E-16 6.00000 351.500
520.062
PROP-LIST DHVLWT 1
PVAL ETHANOL 0.374890E+08 351.500 0.424613 -0.292566
351.500
;
; print the databank''s parameter values for verification
;
PRINT-DATA NOSECRET
;
; end of databank input file
;
END-INPUT
====================================================================
Example: Renaming ETHANOL
The component ETHANOL in USRPP2A is renamed to ALCOHOL.
TITLE ''EXAMPLE FOR RENAMING A COMPONENT IN A USRPP2 DATABANK''
;
; source / destination for copy command
;
FILE USRPP2A NOSECRET OLD / USRPP2A NOSECRET OLD
;
; specify that the databank can be written to
;
WRFILE NOSECRET
;
; rename component ethanol to alcohol
;
COPY NOSECRET COMPS=ETHANOL PROPS=ALL NEW-NAMES=ALCOHOL
DELETE COMPS=ETHANOL
;
; print the databank''s parameter values for verification
;
PRINT-DATA NOSECRET
;
; end of databank input file
;
END-INPUT
Example: Verify new name and contents
Use the following DFMS input file to verify the entire contents of the databank, including the new name of ETHANOL (= ALCOHOL).
FILE USRPP2A NOSECRET
PRINT-DATA NOSECRET
END-INPUT
====================================================================
Tip: Copy and paste the examples of thisSolution to DFMS input files (*.inp) in order to run them.
Keywords: DFMS
user databank
in-house databank
rename
copy
delete
References: None |
Problem Statement: How many segments should be chosen in RateFrac or RateSep for simulating packed column? | Solution: For a trayed tower, it is usually clear that each tray can be represented by a segment in RateFrac or RateSep.
However, for a packed tower, there is usually a little more involved in defining the number of segments. It is generally true that as the number of segments increases, the packing height per segment decreases and the accuracy of the results increases. One must specify the number of segments to achieve a certain accuracy level. The question is how many segments for a given section of packing would be sufficient? This document addresses this issue.
The major governing equations for RateFrac or RateSep are the mass and heat transfer equations, which require the value of concentration or temperature at any given point inside the column. For example, the mass transfer flux from the gas/liquid interface to the bulk flow is given by the following equation:
N = k*(Cs - C) (1)
where N is the flux (mass/area/time), k is the mass transfer coefficient, Cs is the concentratioin at the gas/liquid interface, and C is the concentration in the bulk fluid (vapor or liquid phase). The mass balance over a differential height of the packing (dh) is:
Q*dC = k*(Cs - C)*a*A*dh (2)
where Q is the volumetric flow, a is the packing surface area per unit volume of packing, and A is the column cross-sectional area.
The value of Cs can be determined by thermodynamic equilibrium calculations and varies with the local temperature at a particular location inside the packing. C is also a variable depending on the location in the column, and varies at different packing height. Ideally the mass transfer equation should be applied to a very thin slice of the packing (dh) where the Cs and C both have a finite value.
Like solving any differential equation, defining segments allows for using averages rather than the exact local values. Then the average C for a segment can be used while the Cs can be calculated based on the average temperature and pressure for the segment, allowing the governing equations to be solved by the finite difference. Therefore the height of a segment is actually the step size in solving the finite difference equations. Of course, the smaller each segment, the closer the averages are to the true value. In general, the accuracy would improve as the number of segments increases. However, more segments would take more computation resources and convergence might start to become a problem. Therefore, user must select a number that gives satisfactory accuracy without causing convergence problems.
In any event, the segment height chosen should always be smaller than the Height Equivalent to Theoretical Plate (HETP). This is obvious since if the segment height is equal to the HETP, each segment would be an equilibrium stage and you run the risk of C = Cs, which could cause convergence problems.
For random packings, the rule-of-thumb in selecting the number of segments is to make the packing height per segment equal to 10 to 12 times the size of the packing as a good starting point. Note that the segment height chosen should be less than HETP. For structured packings, the segment height equal to 1/2 of the HETP would be a good starting point. The number of segments can then be increased to obtain a satisfactory accuracy.
Note that the number of theorectical stages is not the number of segments. Rather it is calculated from the HETP (total height of packing divided by HETP). The Murphree Efficiencies are back calculated from the converged column results.
Although in theory the number of segments would have to approach infinity to truly match a continuous column profile since all the governing equations are continuous (disregarding the physical discontinuity in the packing structure), very often the calculated results reach an asymptote as the segments for a given height of packing are increased to a certain number (i.e., the change in results between any two increments should decrease). In other words, as the number of segments increases, the change in the results will become smaller and smaller.
For some applications that require greater accuracy, one could try to increase the segments to obtain the desired accuracy. However, sometimes it is difficult to reach that plateau where the change in results falls within the desired accuracy. So when should one stop, or how much confidence one should place on the results if the desired plateau is not reached? In other words, how believable can the calculated results be if the simulation results continue to show changes as one increases the segments and the changes are not negligible for the trace components? This is difficult to determine because of multiple factors. First one would have to determine how meaningful the calculated results are since there might be larger error involved in the built-in (or user provided) mass/heat transfer correlations used for the calculation. Second, at certain point, the numerical behavior and noise starts to interfere with the calculation. For example, the Fortran double precision can usually only go as low as 1E-15 in reSolution. Anything below that limit would be treated as zero. For flow that lower numerical limit would be 1E-15 kmol/second or 3.6E-9 mol/hr.
Keywords: RateFrac
Segment
Segment height
References: None |
Problem Statement: How do I model an orifice in Aspen Plus? | Solution: There are a few options for modeling orifices though there is no explicit model in Aspen Plus:
Use a valve with a small valve opening.
Use a pipe model (large pipe connected to short pipe) with a short pipe length e.g. 1 inch.
Use Fortran to change the pressure drop. You will need one Fortran block for each orifice. SeeSolution 102347 for more details: http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=102347
Write your own user model for a USER or USER2 block.
The Pipe model has been extented to handle sudden enlargement, contractions and orifices in Aspen Plus 12.2 and higher.
Keywords: orifice
pipe
References: None |
Problem Statement: Is there an easy way to model particle size increase? Most solids unit operations seem to be directed towards either separation, or reduction in particle size. | Solution: Attached is a report that presents a user model for the PSD increase in a granulator and demonstrates its use in a standalone granulator simulation and a simulation of a granulator circuit. Both simulations demonstrate how the Excel Calculator block in Aspen Plus enables useful visualization of the simulation results.
The Aspen Plus Granulator Particle-Size Distribution Model is a
semi-empirical granulator particle-size distribution (PSD) model developed using the
RYield unit-operation model in Aspen Plus. The granulator PSD model has been combined with
Aspen Plus models for a Screen and a Crusher to produce a simulation of the evolving particle-size distributions in a granulator circuit.
Keywords: None
References: None |
Problem Statement: What should I do if a tear stream will not converge with any convergence method
Wegstein, Broyden, or Newton? | Solution: If a tear stream will not converge, try the following steps:
Provide a reasonable estimate for the tear stream on the Stream.Main form.
Confirm that all components have a method of leaving the process. If not, the problem may not be feasible from an engineering point of view (there might not be a steady stateSolution).
Reinitialize the simulation. Try to converge the simulation using Wegstein with Qmin=Qmax=0. This is equivalent to direct substitution. Look for a continuing buildup of one or more components as the iterations proceed.
If the maximum error/tolerance initially improves but then levels off, consider tightening the tolerance of individual blocks within the convergence loop or loosening the tolerance of the convergence loop. Make the convergence loop tolerance greater than or equal to { 2 block tolerance number of blocks within the convergence loop}.
Confirm that the sequence for the simulation (either ASPEN PLUS defined or user defined) is reasonable. Note: If you supply a complete sequence (including all convergence blocks) that is incorrect, ASPEN PLUS will not recognize that it might need to tear additional streams.
Try to simplify the problem. It may be possible to do one or more of the following to reduce the complexity of the problem:
Add a Mixer block to reduce the number of tear streams
Replace a HEATX with an MHEATX to reduce the number of tear streams
Define and use a Component Group to reduce the number of variables
Choose a Tear stream that has fewer components
Choose a Tear stream from a block that sets an outlet temperature
Keywords: None
References: None |
Problem Statement: When using the option Estimate only the selected parameters for property estimation of a compound you are required to enter its molecular structure even when the compound is available in the Aspen Plus databanks.
How can you avoid the tedious step of entering in the Molecular Structure form information that is already stored in the databank?
Can you import .mol files? | Solution: Aspen Plus release 11.0 and higher has a very convenient feature that displays the molecular structure of components in the database. The structures can be viewed on the Properties\Molecular Structure\Structure sheet.
Many components have their structure in the database that is delivered with Aspen Plus. In addition, it is possible to import a structure as a MDL mole file (*.mol).
These MOL files can be exported from common chemical drawing or molecular modeling sofware packages such as Chemdraw. A free molecule drawing program is available at: http://www.acdlabs.com/download/
In addition, files are available from many third party sources such as chemical vendors and public web sites. For example, the structures of thousands of components are available as MOL files free of charge at the U.S. National Institute of Standards web site: http://webbook.nist.gov/chemistry/
To load a molecular structure from an MDL mole file (*.mol):
Click on the Import Structure button on the Properties/Molecular Structure/Structure sheet.
Renumber the atoms if desired. (This is for accounting purposes only.)
Click on the Calculate Bonds button to have the Aspen Physical Property System fill in the General tab on this form with the connectivity data from the molecular structure. This information can be used by the Aspen Plus Property Constant Estimation System (PCES) to determine functional groups for the group contribution methods used to estimate properties.
Keywords: MOL
draw
molecule
References: None |
Problem Statement: Is there a way to retrieve Sensitivity tabular results from Aspen Plus into Excel? | Solution: Navigate down the Variable Explorer (Under the Tools Pull down menu) to Data > Model Analysis Tools > Sensitivity and then to your sensitivity block. For example, to retreive the 3rd define variable from the tabulate form for the first case study:
Sample Path-To-Node Name for retrieving the Reboiler Duty (the 4th column) from the first sensitivity row on the Sensitivity Results form:
go_simulation.Tree.Data.elements(Model Analysis Tools).Sensitivity.Elements (S-1).Output.SENSVAR.elements(1).elements(4).value
Elements(1) in the above refers to the first child or row in the collection of sensitivity cases [9 rows of sensitivity cases - elements(1) is the first sensitivity row and elements(9) would be the last sensitivity row].
Elements(4) in the above refers to the 4th column on the results form. There are only 3 columns defined on the tabulated data input form, but on the results form, the first column is a reprint of the sensitivity's manipulated variable.
The entire tabular data can be retrieved by nesting two For/Next loops. The outer loop sets the row number in the sensitivity case, and the inner loop retrieves the columnar data for that row. You can repeat this process twice - once to obtain the column labels, and then a second set of nested for/next loops to retrieve the data.
Here is sample code from the attached example's GetOuputValues subroutine in Module1:
Dim Rowcount As Integer, ColumnCount As Integer, i As Integer, j As Integer
Rowcount = _
go_Simulation.Tree.Data.Elements(Model Analysis Tools).Sensitivity.Elements (S-1).Output.SENSVAR.Elements.Count
ColumnCount = _
go_Simulation.Tree.Data.Elements(Model Analysis Tools).Sensitivity.Elements (S-1).Output.SENSVAR.Elements(1).Elements.Count '
For i = 1 To 7 'print the 7 lines of header
For j = 0 To ColumnCount - 1
Range(str2Flow).Offset(i - 6, j) = _
go_Simulation.Tree.Data.Elements(Model Analysis Tools).Sensitivity.Elements(S-1). _
Output.Elements(LINE & CStr(i)).Elements.Item(j).Value
Next j
Next i
'print the tablular data
For i
= 0 To Rowcount - 1
For j = 0 To ColumnCount - 1
Range(str2flow).Offset(i, j) = _
go_Simulation.Tree.Data.Elements(Model Analysis Tools).Sensitivity.Elements (S-1).Output.SENSVAR.Elements(i).Elements(j).Value Next j
Next i
Keywords: ActiveX
Visual Basic
VBA
Automation
References: None |
Problem Statement: Out of Disk space Error during DAIS core component Installation.
After installing many of the Microsoft core components, the installation halts with a message that there is insufficient space available on the target drive to complete the installation, and that you should free up more space and then try to continue. There is plenty of Disk space in the system. | Solution: Look for a file called dais.ini in the windows directory and rename it to dais.bak and re-do the install. This will reset the original location of Dais so that it should not be pointing to a non-existing drive or at least it should point the installation to a drive with available space.
Keywords: Core component
Out of disk space
AES
Dais
References: None |
Problem Statement: Many components in the system databanks have values for elements 9, 10, and 11 of CPIG, the ideal gas heat capacity parameter. How are these values determined? | Solution: Elements 1 through 6 of CPIG contribute to the ideal gas heat capacity values at temperatures above CPIG/7. This is usually the temperature range used.
For temperatures below CPIG/7, elements 9, 10 and 11 are used.
CPIG/9 is a limiting value for CPIG at 0 K, which is determined as follows:
CPIG/9 = 5/2 R for a monatomic molecule (for example, He)
CPIG/9 = 7/2 R for a linear, polyatomic molecule (for example, N2)
CPIG/9 = 8/2 R for a nonlinear, polyatomic molecule (for example, H2O)
ASPEN PLUS determines CPIG/10 and CPIG/11 so that CPIG and its temperature derivative are continuous at a temperature equal to CPIG/7.
Keywords: None
References: None |
Problem Statement: The results in Aspen Hetran generated with the interface to Aspen Plus do not agree with the stream resuts shown in Aspen Plus. Outlet temperatures and vapor fractions are different. | Solution: The Aspen Plus interface to Aspen Hetran passes into the Hetran file a constant pressure heat release curve. Hetran designs the exchanger based upon this constant pressure VLE. Hetran then passes back into Aspen Plus the pressure conditions at the outlet of the exchanger based upon the calculated pressure drop. Aspen Plus then performs a reflash to determine the temperature and vapor fraction. For most applications, the difference between the temperature results due to the change in pressure is very small but for vacuum operations or very large exchanger pressure drops the difference could be significant.
The new AES 11.1 release will resolve this problem. If the temperature difference is greater that 0.5 F when the reflash is performed in version 11.1, Aspen Plus will pass a new reduced pressure VLE back into Aspen Hetran for a recalculation until the temperatures converge.
Keywords:
References: None |
Problem Statement: Where are the changes to databanks documented when a new ASPEN PLUS release is distributed? | Solution: A file called PURECOMP.DIF documents the changes made to the PURECOMP databank since ASPEN PLUS, Release 8.5-6. You can find this file in the ModelManager executable directory (such as, C:/MM91/XEQ).
For ASPEN PLUS, Release 9.3-1, there is a file AQUEOUS.DIF that documents the changes made to the AQUEOUS databank.
For each release of ASPEN PLUS , we publish a manual called, What's New in ASPEN PLUS Release X, where X is the version number such as 9.3. If individual
changes have been made to important binary parameters, component names, and pure component parameters in the new release, you can find these changes listed in the Physical Properties and Databanks section of the manual. In addition, you should check the New Capabilities and the Upward Compatibility sections for other databank changes.
Keywords: None
References: None |
Problem Statement: DECHEMA''s A_ij and A_ji parameters are converted into b_ij and b_ji respectively upon using the Dechema button on the Binary Parameters T-Dependent sheet. Is that correct? What is the conversion formula behind the Dechema button in Aspen Plus / Aspen Properties? | Solution: You can enter DECHEMA binary parameters for the Wilson, NRTL, and UNIQUAC activity coefficient property methods, and their variants in Aspen Plus and Aspen Properties, respectively. The most comprehensive source of those parameters is the DECHEMA Chemistry Data Series [e.g., Gmehling, J., U. Onken, W. Arlt, Vapor-Liquid Equilibrium Data Collection, DECHEMA Chemistry Data Series, Frankfurt/Germany]. DECHEMA publishes constant (i.e., scalar) parameter values which are similar to the original formulation in the activity coefficient models:
ln tau = A / RT
ij ij
where:
tau_ij : actual binary interaction parameter in the activity coefficient model equations A_ij : tabulated binary interaction parameter
AspenTech''s activity coefficient model temperature dependencies are of the form:
ln tau = a + b / T + e lnT + f T
ij ij ij ij ij
By comparing coefficients, you can see that DECHEMA''s A_ij corresponds to AspenTech''s b_ij. This (along with a division by the universal gas constant R) is what the conversion utility behind the Dechema button does. So the conversion formula is:
AspenTech''s b = DECHEMA''s A_ij / R
ij
where R is 1.98721 cal / mol * K
Keywords:
References: None |
Problem Statement: Is it possible to use Aspen Plus or HYSYS to combine assays with conventional components (like any hydrocarbon), and report the combined stream distillation curve? | Solution: Both Aspen Plus 11.1SP1 and HYSYS 3.01 are capable of computing the distillation curves in the presence of conventional components. Note that in Aspen Plus there is a limitation that the distillation curve cannot be computed if less than 4 components are present.
The following is based on the TBP (True Boiling Point) curve which has an immediate physical meaning; other more useful curves like the ASTM D86 can be computed based on the TBP using API (American Petroleum Institute) conversion algorithms (that are implemented in the simulators).
The TBP curve should be equivalent to the temperature curve you get distilling the mixture in a column with many stages and very high reflux. In practice this can be approximated closely enough using just three stages and a reasonable reflux (see plot aboozar-compare in the attached spreadsheet). Of course using a distillation column for each value of the StdVol D:F you get two temperatures, the top and bottom; the best fit with the TBP is obtained by taking as average of the two the following expression:
T = (TB*V + TD*L) / (V + L)
Comparing the TBP and the T/vol% curves obtained with the 3-stage separation for several assays shows a qualitative fit with errors in the range of 10-20 C (see plots arabhv and brent in the attached spreadsheet).
When conventional components (linear chain hydrocarbons between C5 and C15) are mixed with the assay or when the mixture is composed exclusively of conventional components the 3-stage separation provides a way of checking the TBP results.
The Brent-C10 plot shows what happens when the Brent assay from the Aspen Plus assay library is mixed 1:1 by weight with n-decane. The TBP curve will exhibit a plateau in correspondence with the actual boiling point of the pure component. The C5-C15 plot shows results for a mixture composed exclusively of conventional components.
The results can be reproduced with the attached BKP file and the attached HYSYS 3.01 case file.
Keywords: Assays, Distillation Curve, TBP Curve
References: None |
Problem Statement: The RadFrac block allows specification of subcooling even when condenser is toggled to None. | Solution: When a user specifies degrees of subcooling or a subcooled reflux temperature, the RadFrac block cools the liquid from stage 1 to the specified temperature. This allows the simulation of columns in which there is a separate cooler between stage 1 and stage 2. The duty for this cooler shows up as subcooled duty in the RadFrac Results Summary form.
A user who wishes to completely remove a condenser with subcooling from a RadFrac block should clear any subcooling information from the Condenser tab of the RadFrac Setup form (in addition to toggling Condenser to None on the Configuration sheet).
Keywords:
References: None |
Problem Statement: Can I get some more details about Reid vapor pressure is calculated and can be used in a simulations? The specific questions are as follows:
1. How is the Reid vapor pressure calculated in Aspen Plus?
2. Does it match the API method documented in the API databooks?
3. What is the difference between the Properties REIDVP, RVP-ASTM, and RVP that can be selected for a Property Set?
4. Can Reid vapor pressure be used as a column design specification? | Solution: The answers to the questions are given below:
1. The Reid vapor pressure is vapor pressure of liquid at 100 F, as measured according to ASTM D-323 procedures. Reid vapor pressure is often used to determine the appropriate type of storage tank (cone roof or floating roof) for petroleum stocks with undefined components.
The Reid vapor pressure as measured by the ASTM D-323 differs from the true vapor pressure of the sample due to some small sample vaporization and the presence of water vapor and air.
Aspen Plus simulates these procedures by a series of flashes as follows:
A. Check if N2 or O2 is present; if so, determine their index values.
B. Setup to the ideal gas property method.
C. Calculate volume for AIR at 32 and 100 Degree F, 1 atm.
D. Determine bubble point pressure of the liquid stream at 100 F.
E. Saturate the liquid with air at 32 degree F.
F. Mix liquid with 4 vol% equivalent of air and flash at 100 F under constant volume.
G. If the calculated Reid vapor pressure is greater than 26 psi repeat w/o air saturation.
2. API Technical Data Book Vol. 1 Figure 5B1.1 page 5-30, and Figure 5B1.2 page 5-33 are implemented in Aspen Plus as RVP-API.
3. The Prop-sets REIDVP and RVP-ASTM are identical. Both are kept for upward compatibility, and can be requested like any other Prop-set. RVP however, is available only if you define a Petroleum property curve for the Reid vapor pressure in the Components | Assay/Blend | Basic Data | Property Curves form, by providing a table of Mid-Percent distilled vs. Reid vapor pressure values.
4. If you are designing a column using PetroFrac, the Reid Vapor Pressure (REIDVP and RVP-ASTM) can be specified directly as design specification in the PetroFrac | Design Specs form.
In RadFrac, first define a Prop-Set containing REIDVP, RVP-ASTM, or RVP-API as the only property. Then create a design spec on the RadFrac | Design Spec form within RadFrac and specify Type of Property Value with the Target equal to the desired Reid vapor pressure, and Property Set is the name given to the Prop-Set defined in the Properties | Prop-Sets object manager.
Keywords: None
References: None |
Problem Statement: How can I merge two flowsheets? | Solution: Two flowsheets can be merged quite easily in Aspen Plus.
This feature is very useful for building large flowsheets
since each new piece can be tested separately and then
merged into the main flowsheet after you have it operating
to your satisfaction.
The flowsheet that is being merged into the current flowsheet
needs to have previously been saved as a backup file (*.bkp).
The steps are as follows:
Open the current flowsheet.
Go to Import... from the File menu.
Select the backup file that you want to merge into the current flowsheet.
If there are ID conflicts, an object manager screen will come up so that they can be resolved. A conflict usually occurs because two items have the same name. Components, streams, blocks, etc. can all have ID conflicts. There are a number of ways to resolve the conflicts:
a. Replace
- Replace the old object with the new object.
b. Merge
- Combine the old object with the new object.
If any information conflicts, the information for
the new object will be used.
c. Edit ID
- Change the ID of the new object to a new name so
it will now be a separate object.
d. Remove
- Don't merge the new object into the flowsheet.
Hierarchy blocks behave slightly differently.
If you expand the Process Flowsheet Window for a Hierarchy block and select a .bkp file in the File/Import dialog box, the simulation contained in the .bkp file is imported into the top-level Process Flowsheet Window (rather than the Hierarchy block Process Flowsheet Window) of your current simulation. To import a simulation/flowsheet into a Hierarchy block, in the Data Browser, right-click on the Hierarchy block and select Import, and the simulation from the selected .bkp file will be inserted in the Hierarchy level.
For more information seeSolution 103283.
Keywords:
References: None |
Problem Statement: Do you have an automated way to help select a Property Method? | Solution: See the attached spreadsheet provided by one of our customers Rémy Gressly of Syngenta.
Keywords:
References: None |
Problem Statement: In a HEATER block, the temperature of the inlet and outlet streams does not match the heat curve temperature results. How can this happen given that the delta H across the heat exchanger is consistent? | Solution: In a heat curve, if Heat Duty is specified as the Independent Variable, then the heat duty will be varied at intermediate points between the inlet and outlet conditions of the block, including phase transition points (bubble and dew points). For each one of these intermediate points, temperature, pressure, vapor fraction (and optional additional properties) will be calculated.
In such a heat curve, the Heat Duty will range from zero (inlet condition of the block) to the specified or calculated Heat Duty (outlet condition of the block). The calculated temperature profile, by definition, should then range between the stream inlet and outlet temperatures. If there is an inconsistency in the heat curve temperature results, then it is likely due to the valid phase specification, particularly if the system has the potential to form 2 liquid phases.
By default, most of the stream and block flash options will have a valid phase specification of Vapor-Liquid only. If a second liquid can be expected then the Vapor-Liquid flash will not always converge to the correctSolution, leading to this discrepancy between stream and heat curve results. This can be resolved by ensuring that you have the correct Valid Phase specification for the system.
The Valid Phase can either be set globally on the Data\Setup\Specifications\Global sheet, or on a stream and/or block basis as necessary.
Keywords: Heater
Heat Curve
Heat Duty
References: None |
Problem Statement: How can you tell if you have CH1 installed? | Solution: Selecting About Aspen Plus from the Help menu indicates Aspen Plus Version 11.1.4 for Aspen Plus 11.1 CH1.
The Version in the history file indicates VERSION: 11.1 Build 194 Patchlevel 1
The only difference in history and report files of SP1 and CH1 is the build number, i.e. 193 vs. 194. Aspen Version 11.1 was build 193 and then AES SP1 (11.1.1) changed to Build 193 Patchlevel 1.
Summary:
Version
Help About Version Number
History and Report File Build Number
Aspen Plus 11.1
11.1
Build 193
Aspen Plus 11.1 SP1
11.1.1
Build 193 Patchlevel 1
Aspen Plus 11.1 CH1
11.1.4
Build 194
Keywords:
References: None |
Problem Statement: The Aspen Plus files Kent-Eisenberg-1.bkp and ElecNRTL-1.bkp perform the same simulation of a distillation column that strips H2S from a loaded | Solution: of aqueous DEA. Kent-Eisenberg-1 uses the Kent-Eisenberg property method, called AMINES in Aspen Properties, while ElecNRTL-1 uses the ElecNRTL property method, called ELECNRTL in Aspen Properties, with parameters from the INSERT KEDEA. Both simulations have the same feed and use column specs to attain a temperature of 45?C in the condenser and a 93.5% recovery of H2S in the distillate. The product streams from the two columns are the same, but significant differences are predicted for condenser and reboiler duties and related column-design results, as shown in the Table 1.
Table 1 - Results for Regenerator Simulations with AMINES and ELECNRTL Property Methods
Property Method
AMINES
ELECNRTL
% Difference
Condenser Duty, MMkcal/hr
-18.20
-10.65
-41.5
Reboiler Duty, MMkcal/hr
28.07
19.99
-28.8
Reflux Rate, kg/hr
29,956
17,521
-41.5
Reflux Ratio
9.34
5.45
-41.6
Boilup Rate, kg/hr
53,365
37,655
-29.4
Reboiler Temperature, ?C
128.40
128.83
0.3
The differences due to the two physical-property methods are quite large. Which prediction is more reliable and what is the uncertainty of the results?
Solution
The insert KEDEA is as accurate as it can be given the available experimental data.
Analysis of Property Accuracy
The most important physical property is vapor-liquid equilibrium (VLE), i.e., the absorption of H2S in the aqueous DEASolution. Figure 1 compares predictions from the AMINES and ELECNRTL models with data from Lawson and Garst.
The comparison focuses on a 5.4 Mol% aqueousSolution of DEA, which is close to the amine concentration used in simulations. Analysis of the results indicates that both models provide a good fit of the data, but the ELECNRTL model is slightly better. The range of H2S mole fractions in the regenerator cover a range from 0.005 down to very low concentrations. At these low concentrations, the data are fewer and considerably scattered; the measurement uncertainty is probably a factor of 2 or even somewhat higher.
The ELECNRTL model predicts higher partial pressures for H2S at the low concentrations of interest. This explains why the separation is easier with the former model, and the condenser and reboiler duties are smaller in magnitude (Table 1).
The ELECNRTL model provides more accurate predictions for the absorption of H2S in aqueous amines, but the results have a high uncertainty of at a factor of 2 or more at low H2S loadings.
Other physical properties, like the heat of absorption of H2S, were separately evaluated. In general, the agreement between the two property methods is good and is unlikely to be the source of the big simulation discrepancies noted in Section 1. The reason why properties other than the absorption of the H2S are accurate is that the H2S loadings are small and hence the effect on properties like enthalpy and heat capacity is also small.
Analysis of Simulation Uncertainties
In order to better understand the effect of the two physical-property methods on the simulation results, the design-specs on the regenerator were modified. The spec of 45?C on the temperature of the condenser was retained, but the reflux ratio, rather than the H2S recovery, was used as the second spec. The variation of the condenser and reboiler duties with the H2S recovery have been studied through a Sensitivity analysis. The calculations have been done in simulation files Kent-Eisenberg-2.bkp and ElecNRTL-2.bkp, and key results are summarized in the Table 2.
Table 2 - Effect of Reflux Ratio on Regenerator Simulation
Reflux
AMINES
AMINES
AMINES
ELECNRTL
ELECNRTL
ELECNRTL
Ratio
Reb Duty
Con Duty
H2S Recovery
Reb Duty
Con Duty
H2S Recovery
MMkcal/hr
MMkcal/hr
MMkcal/hr
MMkcal/hr
4.0
17.26
-7.50
0.896
16.96
-7.68
0.918
4.5
18.29
-8.49
0.902
18.00
-8.70
0.925
5.0
19.29
-9.48
0.907
19.04
-9.72
0.931
5.5
20.30
-10.48
0.912
20.08
-10.74
0.935
6.0
21.30
-11.47
0.915
21.11
-11.77
0.940
6.5
22.31
-12.47
0.919
22.15
-12.79
0.943
7.0
23.32
-13.47
0.923
23.19
-13.82
0.946
7.5
24.34
-14.47
0.926
24.22
-14.84
0.949
8.0
25.35
-15.48
0.928
25.25
-15.87
0.952
8.5
26.37
-16.49
0.931
26.29
-16.90
0.954
9.0
27.38
-17.50
0.933
27.32
-17.93
0.956
If the reflux ratio is specified, the difference between the two property methods on the condenser and reboiler duties is very small, about 2% or less; it is now clear why Table 1 indicates that the percentage differences in the reflux ratio and the condenser duty are almost the same. The big effect of the reflux ratio is on the H2S recovery, as shown in the Figure 2. It is also now clear why, in Table 1, the predicted duties are strongly dependent on the specified H2S recovery, and so strongly dependent on the VLE model used in the simulation.
Another factor to consider is that amines distillation columns are usually mass-transfer limited. This introduces further uncertainty in the H2S recovery at a given reflux ratio.
Conclusions and Recommendations
This note has analyzed the effect of uncertainties in physical properties on the simulation of an amine regenerator. The conclusions and recommendations are as follows:
Amine regenerators have low concentrations of acid gases. Hence the chemical complexation effects on thermodynamic properties like enthalpy and heat capacity are small. These properties are expected to be accurate and similar from most applicable models.
The key property affecting regenerator performance is the absorption of the acid gas, H2S in this case, at low concentrations. This quantity is subject to large uncertainties, probably a factor of 2 or more. Hence, the largest uncertainty in the simulation is the recovery of the acid gas.
It's best to model the regenerator using the reflux-ratio spec and accept that the recovery of the acid gas is subject to a large uncertainty.
The recovery of the acid gas will be even more uncertain in practice since amine regenerators are mass-transfer limited and the present simulation assumes that physical equilibrium is reached.
Keywords: None
References: None |
Problem Statement: I have noticed that in Aspen Plus 11.1 in the EO Configuration folder there is a EO Sensitivity folder. What is it used for ? Any difference with the old Sensitivity Analysis in the Model Analysis Tools folder? And how does it compare with Case Studies?
Who can benefit from that? | Solution: In Sequential Modular (SM) mode a sensitivity analysis is carried on by repeatedly executing the blocks involved, at all possible combinations of different values of all the varied variables. A case study takes only selected combinations of values (cases) of the varied variables.
In Equation Oriented (EO) mode, on the other hand, the sensitivity is intended as the Jacobian matrix at the current steady state - a matrix containing for each varied variable all the partial derivatives of each dependent variable with respect to it.
To compute these derivatives, in SM mode you need to perturb numerically the model while in EO they are immediately available. The Jacobian matrix can then be used to build a linearized model of the process, for use in:
advanced control applications
production planning models
If the matrix of sensitivities of interest is small, there is no real advantage in using the EO sensitivity analysis feature. There is a potential for performance gains using EO if the sensitivities with respect to more than 10 variables are to be computed.
For more details, see attached document.
Keywords: jacobian matrix performance linerazation partial derivative perturbation
References: None |
Problem Statement: Why does the pressure relief fire scenario require specification of a fire duration as a time constraint? | Solution: Most companies have equipment to extinguish the fires so they more or less know the fire duration. Furthermore, this specification enables the user to model the effects of any external heat input, such as fire, on the rate of any chemical reactions that may be occurring in the vessel. In such a case, the fire can be suppressed in the specified time period, and any subsequent temperature rise would be indicative of an exothermic reaction, which may increase the pressure in the vessel.
Keywords: pressure relief
References: None |
Problem Statement: User cannot run Aspen Plus independently, it can only be run through Aspen Custom Modeler / Aspen Dynamics.
The following Error message is given:
*****TERMINAL ERROR
USE OF ASPEN SIMULATION CAPABILITIES NOT PERMITTED AT THIS INSTALLATION
CALL ASPEN TECHNOLOGY, INC. AT 888-996-7001 FOR ASSISTANCE. | Solution: License key is enabled for use of Aspen Plus with other products but not stand alone.
For Aspen Plus 10.x
Check Product License Key Certificate for line stating:
Properties Plus Only: Yes
For AES 11.1
Check Vendor line in Flexlm License Key file. Look for SIMOK Parameter. If SIMOK=0; This means you can not use Aspen Plus except within Aspen Dynamics
If you need an updated license, Call AspenTech Product Manager.
Keywords:
References: None |
Problem Statement: When simulating a Tungsten Hexafluoride (WF6) process, the normal boiling point is about 62 F which is reasonable. However, the vapor pressure (PL) range predicted by Aspen Plus between 0 and 150 F ranges from 2.05 E 16 to 1.5 E 16 psia. Not only are these numbers way off, but the trend produced is wrong too. The vapor pressure trend is to decrease with temperature!
Checking further shows that the databank is actually MISSING the Antoine Vapor Pressure coefficients (PLXANTs) for WF6. No warning/error is produced, and Aspen actually grabs some information and generates a curve. | Solution: There are some gaseous components such as WF6 in the databanks that only have limited data available for them.
The only data available are Gibbs Free Energy (G), Enthalpy (H), Entropy (S), and Heat Capacity (CP) for ideal gas. In Aspen Plus, we want to make sure that this component stays as vapor, so we make its liquid Gibbs free energy larger than its vapor Gibbs free energy by a very large amount (artificially). This is a common practice in metallurgy. As a result, Gibbs Free Energy of the liquid (GL) is greater than the Gibbs Free Energy of the vapor (GV); therefore, the vapor state is more stable. For data from the INORGANIC databank, vapor pressure can be calculated from (GL-GV)/RT; not from PLXANT. With an artificial value of GL, PL is artificially large. This is in a way good. We know that this component will always be a gas. As to the trend, we did not want to change the Temperature dependency because it may cause GL to cross with GV. PL is very very large anyway. Ignore the vapor pressure values and any liquid properties. Only gas properties for WF6 can be calculated by Aspen Plus with the parameters available in the databanks.
Keywords: PL
References: None |
Problem Statement: How do I make a plot update automatically when a new run is made? | Solution: When any plot is the active window, from the Edit menu choose Live plot. The plot will then be redrawn when new results are available.
For plots that are created with the Plot Wizard, you can turn this on at creation by going all the way through the Wizard to the last form and checking the Live plot option box.
Keywords: None
References: None |
Problem Statement: How can the Aspen Plus system administrator suppress the echoing of the physical property paramaters used in a simulation despite the PROPERY-REPORT PARAMS being invoked by the user? | Solution: PROPERY-REPORT PARAMS sentence is used at user level to report all physical property parameters used in a simulation. At times, the Aspen Plus administrators would like to disable this feature to prevent the end-users from accessing proprietary property parameters.
There is no SDF table to make this change system wide. The system wide change would have to be done at the source code level in the routine PRRSMP.F. This routine processes the PROPERTY-REPORT primary keyword (PKW).
Within the routine the 1st value of a given keyword (ITABLE) is the default.
For example,
DATA ITABLE /
1 4HNORE, 4HPORT, 4HREPO, 4HRT ,
2 4HNONE, 4H , 4HALL , 4H ,
3 4HNOCO, 4HMPS , 4HCOMP, 4HS ,
4 4HNOOP, 4H-SET, 4HOP-S, 4HETS ,
5 4HNORO, 4HUTES, 4HROUT, 4HES ,
6 4HNOSO, 4HURCE, 4HSOUR, 4HCES ,
7 4HNOPA, 4HRAMS, 4HPARA, 4HMS ,
8 4HNONC, 4H-PRO, 4HNC-P, 4HROPS,
9 4HNOPC, 4HES , 4HPCES, 4H ,
1 4HNOPR, 4HOP-D, 4HPROP, 4H-DAT,
2 4HNODF, 4HMS , 4HDFMS, 4H ,
3 4HNOPR, 4HOJEC, 4HPROJ, 4HECT ,
4 4HNOPA, 4HRAM-, 4HPARA, 4HM-PL,
5 4HNONE, 4HUTRA, 4HNEUT, 4HRAL /
In this DATA statement for ITABLE, the REPORT NOPARAMS is the default as shown by
7 4HNOPA, 4HRAMS, 4HPARA, 4HMS ,
To make PARAMS the default you will need to switch the order of the words as follows:
X 4HPARA,4HMS ,4HNOPA,4HRAMS,4H ,4H ,4H ,4H ,
To eliminate PARAMS as being an option, you will replace the word PARAMS with the word NOPARAMS as follows:
X 4HNOPA,4HRAMS,4HNOPA,4HRAMS,4H ,4H ,4H ,4H ,
In the event that the user does specify PROPERTY-REPORT PARAMS an IT error message will be generated stating:
INVALID PROPERTY-REPORT OPTION :PARAMS, OPTION IGNORED
Upon making these changes, the routine should be compiled and the Aspen Plus executable will need to be rebuilt.
For Aspen Plus 10.x the routine PPRSMP.F is located in the node ZESEM2.
Keywords: PROPERTY-REPORT
PARAMS
NOPARAMS
PRRSMP
ZESEM2
References: None |
Problem Statement: Is it possible to model a simple Chlor-Alkali cell using the RStoic block? | Solution: Here is a simple example showing how to use RStoic to represent a Cl/Alkli cell.
Each RStoic in this example represents a half cell. RStoic CL2-HALF represents the Anodic reaction and H2-HALF represents the Cathodic reaction.
ANODIC REACTION:
2CL- - 2e -> CL2
CATHODIC REACTION:
2H2O + 2e -> H2 + 2OH-
OVERALL:
2Cl- + 2H2O -> H2 + Cl2 + 2OH-
In an actual cell, the ionic transfer is taking place through the diaphragm (cell separator) continuously along the flow through the cell. Aspen Plus can only represent this process by a Sep block to allow Na+ to direct Na+ flow into the cathode compartment. As a result, two streams, the stream coming out of the anodic RStoic and the stream that transfer Na+ are not in charge balance. These two warnings can be ignored.
The Conversion at the Cathode has to be such that the overall charge balance is maintained at the exit of the Cathode. Design-Spec DS-1 is used to maintain the charge balance.
In addition, the charge balance must be maintained for the anode exit. The Split block is used to transfer Na+ to the Cathode compartment, which simulates the diaphragm. Design-Spec DS-2 is used to maintain the charge balance at the Anode.
Please see attached input and backup files.
Keywords: electrolyte
References: None |
Problem Statement: How do you enter binary temperature-dependent parameters for activity coefficient models in a User or Inhouse databank using the legacy DFMS method? What is the syntax for the DFMS input language for WILSON, NRTL, UNIQ and HENRY parameters? | Solution: The correct DFMS syntax for binary Temperature-dependent parameters is:
NEW-PROP NRTL 8
PROP-DATA
PROP-LIST NRTL 1
BPVAL C1 C2 -3.050599 1052.0 0.30 0.0 0.0 0.0 0.0 1000.000 -5.418060 2837.0 0.30 0.0 0.0 0.0 0.0 1000.000
or more generally:
NEW-PROP NRTL 8
PROP-DATA
PROP-LIST NRTL 1
BPVAL C1 C2 a12 b12 c12 d12 e12 f12 Tlower Tupper
a21 b21 c21 d21 e21 f21 Tlower Tupper
The DFMS input format for UNIQUAC parameters is
NEW-PROP UNIQ 6
PROP-DATA
PROP-LIST UNIQ 1
BPVAL C1 C2 a12 b12 c12 d12 Tlower Tupper
a21 b21 c21 d21 Tlower Tupper
This format is slightly different that the Aspen Plus input language format.
For more information about DFMS input language please go to the Help Contents tab and navigate to Aspen Plus
Keywords: None
References: | Physical Property Data Reference Manual | Using DFMS to Manage Databanks. The DFMS input files can be imported into the new Aspen Properties Enterprise Database (APED) system available in 2006 and higher.
In addition to the User or Inhouse databanks created using DFMS input language described, the user interface contains special databanks for binary and pair parameters. These parameters appear on the Properties | Parameters | BinaryInteraction and Parameters | ElectrolytePair forms. These databanks are available only when you use the user interface. See the Aspen Plus System Management Guide or the Aspen Properties System Management and Customization Guide for more information. |
Problem Statement: Opening the Data Browser causes the error Unable to load form control. None of the forms are able to be displayed. | Solution: For Aspen Plus versions 10.0 and 10.1:
Run regfix.bat and then run ApwnSetup.exe. They are found in the folder \program files\AspenTech\Aspen Plus 10.1-0\gui\xeq. Accept all the defaults. Then try Aspen again. If it doesn''t work, go to step 2.
Install the DAO from the Aspen Plus CD. This is under i386/Systems/DAO/Disk1. Run the setup.exe in that folder. Take all the defaults to make a complete install.
Run the file mdac_typ.exe. This is also found on the Aspen CD under i386/Systems. Take all the defaults to make a complete install.
Reboot
Try running Aspen. If you still get the same problems, then reinstall Aspen Plus, when prompted for Upgrade, say NO (You want to reinstall), select the same path and select CUSTOM install (instead of FULL), select all the components. Then try Aspen again.
Download and run Regclean.exe from Microsoft. This has been known to solve this problem in the past.
For Aspen Plus version 10.2, the process is a little different:
Run ApwnSetup.exe, found in the folder \program files\AspenTech\Aspen Plus 10.2\GUI\xeq. Accept all the defaults. Then try Aspen again. If it doesn''t work, go to step 2.
Install the DAO from the Aspen Plus CD, found under \core\DAO. Run the setup.exe in that folder and accept all the defaults.
Re-install MDAC from the CD, found in \core\Mdac. Again run the setup.exe and accept any defaults.
Reboot
Try running Aspen. If you still get the same problems, then reinstall Aspen Plus and select. Then try Aspen again.
Download and run Regclean.exe from Microsoft. This has been known to solve this problems.
Keywords: graphical user interface gui forms mmscrollarea from control
References: None |
Problem Statement: How does a user add the API Upper and Lower Heating values to the stream results? | Solution: These properties are available as the Property-Set parameters:
QVALGRS (Gross Heating Value) - API High Heating Value
QVALNET (Net Heating Value) - API Low Heating Value
To add these parameters to the stream report, use the Data Browser to visit the Prop-Set sub-folder under Properties. Add a new property set and then add QVALGRS and QVALNET to the property set. You may want to visit the QUALIFIERS sheet for the new Property-Set and in the very bottom text box, WATER BASIS, select either WET and/or DRY.
Note: If you select WET and DRY, both values will print in the stream results, but neither will have the WET OR DRY qualifier. They will print in the order requested. For example, if the user enter WET in the first column and DRY on the second column of the QUALIFIER sheet, and both the QVALGRS and QVALNET properties, the data would be printed in the following sequence:
QVALGRS (WET - although the wet qualifier will not be displayed)
QVALNET (WET - although the wet qualifier will not be displayed)
QVALGRS (DRY - althought the dry qualifier will not be displayed)
QVALNET (DRY - althought the dry qualifier will not be displayed)
QVALGRS and QVALNET will calculate the heating values for pure components or pseudo components (from petroleum fractions). In the case of pseudo components, the heating value is caluculated using API Procedure 14A1.3, 4th Edition (1983). The heating value is a function of API gravity corrected for impurity concentrations of H2O, S and other inert.
The calculation method for heating values of petroleum fractions (pseudo components) is documented inSolution Document 102280 (60 Commonly Asked Petroleum Application Questions About Aspen Plus):
Heating value is also called heat of combustion. The heat of combustion of a substance is the change in enthalpy when that substance is converted to its final oxidation products by means of molecular oxygen. The beginning and ending state :
standard heat of combustion: 77 F and 1 atm
gross heat of combustion: 60 F and 1 atm
The normal state for the water formed by the reaction is liquid in both cases. Since the sensible heat of water from 60 to 77 F is usually negligible in comparison with the heat of combustion, the gross and standard heats of combustion are approximately equal.
The net heat of combustion is the heat evolved in combustion beginning and ending at 60 F with product water in gaseous phase. Therefore, the net heat of combustion is less than the gross heat of combustion by the heat of vaporization of the water product.
Net/Gross heating value can be reported in Dry/Wet basis for a stream:
Dry basis - excludes water already present in the stream before combustion,
Wet basis - includes water already present in the stream before combustion.
The methods for calculating pure component and petroleum fractions heating value are different. (The method for calculating pure component heating values is documented in the attachedSolution document #3179)
Keywords: API, heating values, lower heating value, upper heating value.
References: None |
Problem Statement: How is the Heat of Reaction calculated in Aspen Plus? How can I see the value? | Solution: Enthalpy calculation is based on the Heat of Formation of the reaction components at reference state (DHFORM). Because Aspen Plus can calculate the enthalpy of a compound at the given conditions, the Heat of Reaction is implicitly included in the enthalpy calculations. The Heat of Reaction is the difference in enthalpies (which include heat of formation plus departure terms) between the components entering and the components leaving the reactor.
Heat of Reaction = Enthalpy Leaving block - Enthalpy Entering block - Heating or Cooling Duty
In Aspen Plus 10:
To report the calculated Heat of Reaction for a reaction at a given temperature and pressure, simply use the RStoic / Setup / Heats of Reaction sheet to calculate or specify the heats of reaction. The default is to not calculate or specify heat of reaction.
You must provide specifications for ALL reactions using the same reaction number as given on Setup / Reactions sheet and a reference component that must be a reactant for that reaction.
Heat of reaction are calculated at the specified reference conditions based on consumption of a unit mole of the reference reactant selected for each reaction.
Different reference states can be given; the default is 25 C and 1 atm.
For the same effect, you could adjust the heats of formation (DHFORM) of one or more components to make the heat of reaction match data.
If the specified heat of reaction differs from the heat of reaction that Aspen Plus computes from the differences of the enthalpies between products and reactants, RStoic adjusts the calculated reactor heat duty to reflect the differences. Outlet stream enthalpy will not be consistent with reactor duty except if the Heat duty set to zero where the outlet temperature will include the specified heat of reaction.
In Aspen Plus 9:
To report the calculated Heat of Reaction for a reaction at a given temperature and pressure, create an Aspen Plus Flowsheet run using a single RStoic block. Specify the reaction stoichiometry and a complete conversion of the reaction. Specify the reactor temperature and pressure to be the same as those of the inlet stream so that no additional duty is added to the system. The heat duty reported in the reactor Block Results form is the Heat of Reaction in units of enthalpy/time. Divide this value by the extent of a reactant or product. Molar extent is calculated by dividing the molar flowrate by the stoichiometric coefficient of that component.
The simplest case is a reaction of stoichiometric coefficients of 1. If you specify inlet flowrates of 1 g-mol/hr for each reactant, then the duty reported for the reactor would be the Heat of Reaction per g-mol.
Keywords:
References: None |
Problem Statement: What is the Campbell-Thodos model for liquid density and how is it used? | Solution: The Campbell-Thodos model is essentially the same as the Rackett equation for liquid mixture molar volumes except that it contains an additional term which permits varying the RKTZRA pararameter as a linear function of (1-Tr).
ZRA,mixture = sumi ( xi RKTZRA ( 1 + di (1 - Tr) )
The model uses T-dependent parameters RACKET/1..5.
RACKET/1 = R*TCI/PCI
RACKET/2 = RKTZRA
RACKET/3 = di = CAMPBELL-THODOS PARAMETER RACKET/4 = LOWER TEMPERATURE LIMIT
RACKET/5 = UPPER TEMPERATURE LIMIT
The third RACKET parameter is a flag which determines whether the Campbell-Thodos or Rackett model is used, i.e.:
If RACKET/3 < 0.11, Campbell-Thodos is used
If RACKET/3 = 2/7, Rackett is used
The Rackett model is documented in Chapter 3 of the Physical Property Methods and Models Manual. For the model to work correctly, the value should less than 0.11 to use Campbell-Thodos or equal to 2/7 for all components to use Rackett (default). Other values are not valid. If the user inadvertently specifies a different value for any of the components, a warning is issued, e.g.:
WARNING IN PHYSICAL PROPERTY SYSTEM
EXPONENT IN RACKETT EQN. FOR X IS NOT 2/7.
DENSITIES OF MIXTURE INCLUDING X MAY BE WRONG.
where X is the component ID.
Note that in the graphical user interface, it is not possible to only enter RACKET/3 in the parameter form, RACKET/1 and /2 must be entered explicitly to complete the form. If using an input file in the Simulation Engine, RACKET/3 can be entered alone and the default for RACKET/1 and /2 are used in the simulation.
Keywords: Campbell-Thodos
Rackett
RACKET
RKTZRA
References: None |
Problem Statement: How to the Access Dechema Data in Aspen Plus through the Internet and what are the commercial terms? | Solution: You can use the DETHERM Internet Client to access thermophysical property data in the DETHERM online database, maintained by DECHEMA e.V., Frankfurt am Main, Germany.
You can search for properties of given mixtures or pure components. The retrieved data are automatically placed on the Aspen Plus Properties Data forms, ready to be used in data regression. These data are also saved in the report and IK-CAPE neutral files.
The most cost effective way to access Dechema's DETHERM database is via the Internet. The DETHERM Internet Application comes with AspenPlus. (There is a DETHERM Internet button on the Main Toolbar). When you install Aspen Plus, all necessary software to access these data are installed by default.
The user can search for the data and down load the necessary data directly into Aspen Plus. The user pays for what he/she downloaded. A typical VLE data set (10-15 data points) cost $35. Customer will be billed quarterly.
When the user starts the search, he/she can find out whether or not data for the system of interest are available. This information is FREE. The user is charged only when the data are downloaded. The reference and the data points are accessible when the data set is downloaded.
The database can be queried without an account; however, users must register with DECHEMA before they can purchase data. Problems accessing the DETHERM internet site for searching are frequently due to a user's internal firewall.
Accessing DETHERM
Aspen Tech customers can access DETHERM data in two ways:
1. License DETHERM databases from DECHEMA
2. Access the DETHERM data via the Internet on a pay-as-you-use basis
Both methods feature seamless interface to Aspen Plus and Aspen Properties versions 10.2 and later.
Users pay for only the actual data tables downloaded. Data tables include:
Data and description
Complete substance identification
Literature reference
To sign up for DETHERM... on the Web, visit the DECHEMA at http://www.dechema.de/detherm.html
DECHEMA
DECHEMA e.V. is the German Society for Chemical Engineering & Biotechnology and the organizer of ACHEMA & ACHEMASIA. It is a non-profit scientific and technical society with its headquarters in Frankfurt on Main. It was founded in 1926 and at present has more than 5,000 private and institutional members.
DECHEMA's aim is to promote technical advances in the areas of chemical apparatus, chemical technology, environmental protection, and biotechnology.
DECHEMA is the producer of the DETHERM database which is the world's most comprehensive, single-source compilation of thermophysical properties of pure substances and mixtures. The partners are Professor J. Gmehling of the Oldenburg University (the Dortmund Databank), the University of Regensburg, and FIZ CHEMIE Berlin. The database features more than 4.9 million data sets for about 130,000 pure components and mixtures. The database includes:
Phase equilibrium data
PVT-Data
Thermodynamic Properties
Transport Properties
Interfacial Properties
Electrolyte data
More Information
For more information visit Dechema at http://www.dechema.de/detherm.html or contact Dr. Richard Sass, Dechema at +49 (0)69 7564 244 (or 245)
Keywords: Dechema
Dortmund
Internet
Commercial terms
References: None |
Problem Statement: How to accurately fit binary density data over a wide range of composition if consistent mixture effects are present? | Solution: In general Chemical Engineering practice the density of a mixture is not a critically important property. It becomes relevant for specific applications like:
Storage system design
Reactors (effect of density on residence time)
Most hydrocarbon systems can be modeled accurately using the default model for density computations, which is Rackett. But if temperature dependence and composition dependence have to be represented accurately, Rackett may not offer the necessary flexibility. What we normally advice then is to use a linear mixing rule plus a DIPPR-like correlation (see for example http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=104143).
For some systems the linear mixing rule is not really appropriate, because the non-idealities that yield complex Vapor-Liquid effects can also yield correspondently complex density behaviors.
For these cases, there is no option but to write a FORTRAN subroutine to implement a user-defined density correlation.
This is done using the following steps:
Changing the route for the VLMX computation
Writing a VL2U subroutine
In the Aspen Plus Simulation Engine Window, compile the user subroutine using aspcomp and package it for redistribution using asplink (see http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=4334 and http://support.aspentech.com/webteamcgi/SolutionDisplay_view.cgi?key=102367)
The VL2U subroutine is documented in the User Models
Keywords: molar volume
physical properties
non-ideal routes
VLMXUSR
vlmxusr
References: Manual at page 6-9.
The attached model is very basic, being based on the expression:
VL = Sum [(Ai + (T - 273.15) Bi) xi]
where:
T in K
VL in m3 / kmol
The user would need to fit experimental data in a separate tool, and copy the resulting equation in the FORTRAN subroutine.
An alternate approach would be to define a user parameter for the mixture effect, link the FORTRAN subroutine to this parameter and so fit the experimental values in Aspen Plus. |
Problem Statement: What parameters are needed to create a non-volatile component? | Solution: For an activity coefficient Property Method, the values of the Extended Antoine vapor pressure parameter (PLXANT) of -20 and 0 for the first and second elements respectively will make a component effectively non-volatile. This assumes that other parameters are available or will be entered for a component.
However, for completely non-volatile components that have limited data available such as electrolyte ions. It is possible to use a value for the first element of PLXANT less than or equal to -1 x 1015 (entered as -1e15 or -1d15). This value is a flag that will also provide nominal values for TC, PC, ZC, TB, CPIG, DHVLWT, OMEGA and others. A full list of the parameters and the values used is attached. Most of the ions in the Aspen databanks use -1e20 for PLXANT; however, it is possible to enter any value less than or equal to -1e15 to set these non-volatile parameters.
To enter PLXANT go to the Data Browser under Properties / Parameters / Pure Component and create a New T-Dependent Correlation type of parameter. Select PLXANT-1 from the list under Liquid Vapor Pressure and click OK. Then, enter the Component ID in the Components field and the values of the elements.
It is necessary to use a different approach for an equation of state Property Method. For an equation of state, TC needs to be large and PC needs to be small. Some equations of state have model specific TC and PC parameters (e.g. TCPR for Peng-Robinson); however, these generally default to TC or PC if they are not available. A large value of TC such as 2000 K and a small value of PC such as 1E-10 atm would generally have the desired effect.
To enter these scalar parameters go to the Data Browser under Properties / Parameters / Pure Component and create a new Scalar type of parameter and click OK. Then enter the Components, Parameters and values in the grid.
Keywords: solid
nonvolatile
References: None |
Problem Statement: What are the units of aromatic, olefin, sulfer or other petroleum assay content on the input form and also in the report file when a property set is used to report this property? Is it percent or fraction? | Solution: The units of the petroleum assay properties is mass percent or mass fraction depending on what is selected for the UNITS of measurement, e.g. When ENG is selected it is in percent, when SI is selected it is in fraction. To see this, you need to look at the Setup\Units sets\ENG\Concentration\Content which is under concentrated related quantities.
The assay properties in the Aspen Plus databanks are stored as weight fraction.
SeeSolution document 104198 for more information about how to specify petroleum property curves and bulk values in Aspen Plus.
Keywords: UNITS, Content, SULFUR, Petroleum content.
References: None |
Problem Statement: Is RATES Vector in User Kinetic Routine Packed or Unpacked? | Solution: The RATES is a vector and is one of the arguments being passed between the RPLUG model in Aspen Plug and the user kinetic subroutine. In the subroutine, RATES is used to calculate the reaction rates of each component that participate in the kinetic reaction.
A packed vector in Aspen Plus means that the vector does not include components that have zero flows going into the reactor block, whereas an unpacked vector is a vector that includes every component in the problem.
The RATES vector in the user kinetic subroutine is UNPACKED. That is, the order of the components in the RATES vector follows the order of the components as listed in the Components.Main Form (or Components paragraph if input language is used). For example, if the component list is:
COMPONENTS C1 H2O /
C2 CH4 /
C3 CO2 /
C4 SO2
then RATES(1) = rate of C1
RATES(2) = rate of C2
RATES(3) = rate of C3
RATES(4) = rate of C4
Keywords: user kinetic
fortran subroutine
References: None |
Problem Statement: What is a .apmbd file? What is it's function? | Solution: The .apmbd file is paired with the .bkp file. It contains the binary embedded component of the problem file when the simulation is saved as an ASCII bkp file. The .apmbd file only exists when something has been embedded into the process flowsheet (PFS) from another windows application or when a Calculator block that uses Excel is present in the simulation. The .bkp and .apmbd need to be transported in pairs, and the .apmbd file is not used separately. When a simulation is saved as an .apw file, there is no need for an .apmbd since the .apw includes the binary component.
Keywords: .apmbd, apmbd, binary file
References: None |
Problem Statement: When defining a property set, I saw two kinematic viscosity properties: KVISC and KINVISC. Are they the same? | Solution: No, KVISC and KINVISC are not the same. Though they both report the kinematic viscosity of a mixture, one is calculated from user entered curve data and the other from internal property correlation.
KVISC is calculated directly from interpolation/extrapolation of kinematic viscosity curve as entered in the ASSAY petroleum property. If the user does not enter the kinematic viscosity curve data in the assay input, KVISC will not be calculated and reported. The help message in the bottom of the window when KVISC is highlighted states:
Kinematic viscosity for a petroleum mixture. You can request for Prop-Set only if you specified data in Assay Data Analysis.
In Aspen Plus release 10.x, kinematic viscosity curve data is entered in assay input, Property Curves\Viscosity.
KINVISC is kinematic viscosity calculated from a correlation (API) at a given temperatures.
Keywords:
References: None |
Problem Statement: How can I access flow or composition information for electrolyte systems on a True or Apparent basis when the simulation is in the other basis? | Solution: There are a number of built in property sets (Prop-sets) for accessing just such information. The prop-set properties are:
FTRUE
FAPP
mole flow on a true basis
mole flow on an apparent basis
XTRUE
XAPP
mole fraction on a true basis
mole fraction on an apparent basis
MTRUE
MAPP
molality on a true basis
molality on an apparent basis
WTRUE
WAPP
mass flow on a true basis
mass flow on an apparent basis
WXTRUE
WXAPP
mass fraction on a true basis
mass fraction on an apparent basis
Property sets with these properties are included in the Electrolytes template files with English and Metric units, or they can be added to a user-defined Prop-set on the Properties / Prop-Sets form.
Prop-set properties can be included in the stream table by selecting them on the Setup/Report Options/Stream form.
Keywords:
References: None |
Problem Statement: In an DFMS input file PROP-LIST sentence such as
Prop-list MW 1 0 / TC 1 0 /
What are the 1 and 0 in these statements? Are they srcodes as documented
on page 1-12 of Release 9 | Solution: The documented syntax is:
PROP-LIST pnam1 srcode1 [ucode1]/...
where pnam is parameter name
srcode is the source code (our current documentation states use any
integer number for srcode)
ucode is the units code.
Presently, only SI units are allowed
(ucode=0). Default is 0
So, ucode does not need to be entered since it always defaults to 0.
Apparently since we only allow DFMS input in SI, ucode has been
dropped from the documentation for PROP-LIST (although it's still there
in the middle of the CVAL sentence).
Keywords: DFMS
srcode
PROP-LIST
References: Manula Vol. 3. 3, and if so, what is this. The Documentation gives only examples with one number. What is the 2nd number |
Problem Statement: How do you automatically select a different Default working folder for each user on a server installation so that the users do not need to enter a Default Working Directory on the Connect to Engine screen. | Solution: If working directory is not entered or the entered value does not exist, the system searches the following registry entry for a working directory:
HKEY_CURRENT_USER\Software\AspenTech\Aspen Plus\11.1\aplus\DefaultWorkingDir.
For a server installation, AspenTech recommends setting the above registry as follows:
Using regedt32 in the above registry entry, add the DefaultWorkingDir string value as a REG_EXPAND_SZ. After adding the string value DefaultWorkingDir, assign Drive:\%USERNAME% to it, where Drive is C, D, E or any other local drive .
After this change, make sure every Simulation Engine user has a directory with proper rights on that drive. The Simulation Engine user''s Directory name should be identical to the username entered on the Connect to Engine screen.
Using regedt32, If the string is entered into the registry as a REG_EXPAND_SZ then any environment variables will be expanded. So %USERNAME% becomes available as a variable.
Keywords: Default working folder
Engine
References: None |
Problem Statement: Why am I getting mass balance and strange phase problems when using the ChemApp FactSage interface? | Solution: One common cause of this problem is that one of the components for
a phase in FactSage is not defined for that phase in Aspen Plus.
For example, this problem could cause a solid gas phase.
If in one block, there was a minute amount of a solid component trying to form; however, if the component is only specified as a gas component (not a gas and solid component), there would be a solid gas phase formed in Aspen Plus since the component would have to go somewhere and the component was only defined as a gas. Once the solid phase is defined the problem will go away.
Keywords: chemapp
factsage
References: None |
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