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Problem Statement: Are Knock Out Drum (KO Drum) sizing calculations possible in Aspen Flare System Analyzer (Aspen FLARENET)? | Solution: Prior to Aspen Flare System Analyzer V7.0, knock out drum sizing calculations were NOT possible. Aspen FLARENET could only do pressure drop calculations across a knock out drum. In Aspen Flare System Analyzer V7.0 and later, it is possible to size horizontal and vertical knock out drums according to the sizing procedure of API 521 RP.
Horizontal Knock out drum sizing procedure (Section 5.4.2.1 (API 521 RP)):
The final result of the sizing procedure is the length of the knockout drum. This is a function of the flow rate upstream of the drum, conditions in the drum (P, T and vapor fraction), physical properties of the fluid, average droplet size in the flashing fluid as well as the diameter and liquid level in the drum. Droplet size, diameter and liquid level are user inputs.
Vertical Knock out drum sizing procedure (Section 5.4.2.1( API 521 RP)):
The final result of the sizing procedure is the diameter of the knockout drum. This is a function of the flow rate upstream of the drum, conditions in the drum (P, T and vapor fraction) and physical properties of the fluid.
Note: The sizing calculation will not be done for vapor fraction = 1
Tip: Under File ll Preferences menu option check the box for Save Phase Properties and RUN the file once more before doing design calculation.
Keywords: knock out, KO, knock out drum, drum, size, API
References: None |
Problem Statement: In Aspen Flare System Analyzer exported files, there are some numerical values (0, 1, 2) to represent the configurations of the network and set up. Where can I find those meanings of numerical values? | Solution: You can find those information in Appendix B (File Format) of
Keywords: Export, Import, MS Excel, MS Access, XML
References: Manual. Only missing number is -32767, which represents EMPTY in Aspen Flare System Analyzer. |
Problem Statement: How is the acceleration pressure drop calculated using a homogeneous method? | Solution: The acceleration pressure drop is calculated using the equation below.
Acceleration pressure drop = Outlet (mass flux^2 / density) - Inlet (mass flux^2 / density)
Keywords: Acceleration pressure drop, mass flow, density
References: None |
Problem Statement: How to transfer Model Summary to Aspen Simulation Workbook (ASW)? | Solution: If you wish to export the model summary information to ASW then you need to select the Send to Excel/ASW option.
After you select this make sure you select the highlighted Export Option and then click Export tables to Excel as shown in the screenshot below.
Provide a file name and then once it is exported a message box will pop up giving the user options. Select the Open Excel File option.
By selecting the Open Excel File option, you can see that model summary tabs have been transferred. If you hover over any user specified value (Blue Values) in Excel, you can see that they are connected to an ASW variable path.
You can now enable the ASW and this will link it to the simulation case.
When the ASW is enabled, a window will pop with an option to automatically link information. Select Yes.
Then, it will ask you if the current running needs to be attached or not. Select Yes,
After the connection, please make sure the simulation case is not closed.
Now, you can see that the case is linked with Excel.
Keywords: Model Summary , ASW
References: None |
Problem Statement: Does Flarenet use the Fixed Roughness value on the Options settings for the pressure drop calculations of the pipe? | Solution: The fixed roughness value specified in the calculation options is used for the equivalent length calculation for the pipe fittings. The program always uses the roughness value specified on the dimensions tab for actual pipes.
Keywords: Fixed roughness, equivalent length, pipe fittings
References: None |
Problem Statement: Why doesn't the pipe sizeable feature show as a dotted line on the Process Flow Diagram? | Solution: It works in design mode only. Run the case file in design mode.
Keywords: Sizeable, PFD, Dotted
References: None |
Problem Statement: How does Aspen Flare System Analyzer size Relief Valves using the HEM method. | Solution: The HEM method is based on the Homogeneous Equilibrium Model and assumes no slip conditions and thermal equilibrium between each of the phases.
A detailed description of the method may be found in the following reference; Leung, J.C. , Easily Sized Relief Devices and Piping for Two-Phase Flow, Chemical Engineering Progress, p.28 (December 1996.
The HEM method requires finding the limit in the mass flow G.
G = where
(stagnation enthalpy)
(local enthalpy)
(local specific volume)
= inlet vapour mass fraction (quality)
= local vapour mass fraction (quality)
Note that the the evaluation of the local quantity is along an isentropic line.
Keywords:
References: None |
Problem Statement: Sometimes in Ver 7.3, when you want to enter pipe diameters manually, it gives messages to enter diameters not smaller than 1000mm. | Solution: This is a known issue, the reason is Aspen Flare System Analyzer does not appreciate , instead of . in some language setting as a decimal point. Right now there are 2 workarounds for this problem
First approach:
Go to Control Panel | Regional languages and options | set the language to English(United States)
Second approach:
1. Go to Control Panel | Regional languages and options
2. Click on customize button, customize regional options dialog will open up
2. Set the decimal symbol to .
Then please unzip the attached file and copy them to your folder: C:\ProgramData\AspenTech\Aspen Flare System Analyzer V7.3\Formats or C:\Documents and Settings\All Users\Application Data\AspenTech\Aspen Flare System Analyzer V7.3\Formats
If you can not find above folder, your companies installation patch is slightly different. Go to File | Preferences | General tab and copy the address on the Work Directory to windows explorer and navigate to \AspenTech\Aspen Flare System Analyzer V7.3\Formats. Then copy attached files to the Format folder.
Keywords: Pipe diemeter, 1000 mm
References: None |
Problem Statement: How are 'upstream static pressure', 'static source back pressure' and 'system back pressure' defined in Aspen FLARENET? | Solution: Upstream static pressure refers to the static pressure at the inlet of the pipe.
Static source back pressure refers to the static pressure at the outlet flange of the source.
System back pressure refers to the static pressure at the outlet of the flare tip. By default, this is set to atmospheric pressure.
Keywords: upstream, static, pressure, source, back pressure, system
References: None |
Problem Statement: How is Static pressure calculated? | Solution: The Static pressure is calculated based on Bernoulli's principle:
Static Pressure (P/rho) + Velocity head (V^2/2) + Elevation(z*g) = Constant (for no frictional loss).
where:
V is the fluid flow speed at a point on a streamline,
g is the acceleration due to gravity,
z is the elevation of the point above a reference plane, with the positive z-direction pointing upward – so in the direction opposite to the gravitational acceleration,
P is the pressure at the chosen point, and
rho is the density of the fluid at all points in the fluid.
Equation -A (Refer page 75 eqn 4.25 - Unit Operation in Chemical Engineering Fifth edition ISBN 0-07-112738-0)
Keywords: Static pressure, Bernoulli, velocity head
References: None |
Problem Statement: How does Aspen Flare System Analyzer model hot tap in relief system? | Solution: There is not a direct way to model the hot tap. You have to use the tee to connect to Header. Then you can add a zero length pipe (with proper diameter) between tee and tail pipe. Then you can add the fitting to this pipe. In order to do it, you can create your own fitting (Database->Pipe fittings).
Keywords: hot tap, fitting
References: None |
Problem Statement: How does one add components, pipe schedule and fittings to the FLARENET database? | Solution: There are two ways to edit the FLARENET database:
1. In Aspen FLARENET, select Database | Component / Pipe Schedule / Pipe Fittings from the main menu, then click on the Add button in the ensuing form. Refer to the image below:
2. Edit the FLARENET database using MS Access. The location for the FLARENET database can be found via the File | Preferences | Database menu option, as shown below:
Please note that the added information may be found in the middle of the table (i.e. the new information is not always added to the bottom of table). The user may therefore need to scroll up or down in the table to find the added information.
Keywords: database, pipe, component, fitting, edit
References: None |
Problem Statement: How is the Downstream Density calculated in Aspen Flare System Analyzer? | Solution: The vapor density calculations are based on Static Pressure (Ps) not Total Pressure (Pt). This pressure is always used for the physical properties. Hence vapor density is calculated as follows:
Attached is a sample file with an example of the density calculation. Note that KB #116954 explains how is the static pressure defined
Keywords: density, static pressure, physical properties
References: None |
Problem Statement: How are the phase fractions defined in Flarenet? | Solution: The Upstream Fraction and Downstream Fraction reported on the View\Results->Physical Properties page (note you must have the Save Phase Properties option selected on File\Preferences to see these results) and the Vapour Fraction results reported on the PFD are phase molar fractions.
Thus for the vapour phase the phase fraction is defined as the molar flow of vapour divided by the total molar flow in the pipe.
Keywords: fraction, fractions, phase, vapour
References: None |
Problem Statement: How can I make the pressure drop calculation across the flare tip dependent on flowrate? | Solution: Typically, the pressure drop across the flare tip is calculated with the standard fittings correlation, e.g. K = A + B*Ft, where Ft is the turbulent friction factor. Using this approach, the pressure drop variation will not be all that large given any change in the flow through the flare tip. Many flare tip manufacturers will supply their own characteristic curves for the flare tip, normally pressure drop versus flowrate.
Aspen FLARENET allows the user to input a characteristic pressure drop curve. The program will interpolate along the curve to calculate the pressure drop based on the flowrate. Aspen FLARENET also allows the user to supply multiple curves at different reference molecular weights to account for variations in the composition of the fluid being flared.
The following procedure illustrates what is needed to input a single curve:
1. Open the property view for the flare tip and select the Calculations page.
2. To enable the use of the curves, check the Use Curves box.
3. Select the Add button on the Curves tab to add a pressure drop vs. flow value. This will add another row to the table which can then be filled in with the appropriate data. Keep adding rows until the requisite data has been input.
If you wish to add multiple curves at varying molecular weights, do the following:
1. Select the Add Mol. Wt. Button to add an additional curve. (Note : a default molecular weight will be assigned. To change the default value, simply highlight the molecular weight and type in the new value).
2. Input a reference temperature for the newly created curve.
3. Select the desired curve using the Molecular Weight drop down menu.
4. Once the proper curve is selected, follow the same procedure as listed above to input the curve data.
As a final note, the program will not extrapolate past the endpoints of the supplied data unless the Mol. Wt. Extrapolation or Flow Extrapolation boxes are checked. For example, if the calculated flow through the flare tip is above the highest supplied value in the curve and the Flow Extrapolation box is not checked, Aspen FLARENET will use the boundary pressure drop value.
Keywords: flare tip, pressure drop, curves, Mol. Wt., molecular weight, vendor curves
References: None |
Problem Statement: How can I change VLE, enthalpy and pressure drop calculation methods for all objects? | Solution: You can change VLE, Enthalpy and pressure drop calculation methods for all objects. Go to Calculations || Options || Methods. The following picture shows the interface.
Keywords: Overall, VLE, Enthalpy, pressure drop, method, multiple objects, all objects
References: None |
Problem Statement: How to prevent the error, operation must use an updateable query when creating the user pipe schedule | Solution: This problem could arise from the pipe database in the file being read-only and can't be edited. Access files have different password security options that may have been activated.
OneSolution is to try and open the database file directly with Access to investigate if it can be modified from the following address:
C:\ProgramData\AspenTech\Aspen Flare System Analyzer V8.4\Data\pipe_schedule.mdb
To resolve this issue, the access data base installation needs to be investigated by the systems expert. The following technical tip document may be useful:Solution ID 104919: Could not delete from specified tables Local Security Error
Keywords: Pipe schedule data base
References: None |
Problem Statement: How to add View Point in Aspen Flare System Analyzer V8.2 | Solution: Adding different View Point in Aspen Flare System Analyzer will help you navigate large pipe network and quickly find the objects you are looking for. ThisSolution will introduce how to add How to add View Point in Aspen Flare System Analyzer 8.2.
1. Look at your whole network and divide different zones. So that they can help you read the values and look for the objects. Objects locations can be served as this purpose.
2. Open the PFD and use Zoom All to make sure Default as shown whole network
                      Â
3. Click Add a view port and change name: e.g. Flare tip.
4. Â Find the portion of the PFD, zoom and arrange that you would like to add to your view port.
5. After you finish the proper view, select default and then select Flare Tip to see whether it is working or not.
6. You can continue to add more view points by repeating steps 3-5.
Keywords:
References: None |
Problem Statement: Why is there no graphical profile displayed for my model? | Solution: No graphical profile will be shown in Aspen FLARENET if flow is splitting or merging together in a flow network (i.e. there is no single path for which a profile can be displayed).
Refer to the attached file 'Sample-C1.fnw', where a graphical profile is displayed.
In the file 'Sample-S1.fnw', no graphical profile is displayed as flow is splitting at 'Tee 4'. To view a graphical profile for this model, ignore the pipe 'Header 8' to have a single path for flow.
Keywords: profile, graphical, view, plot
References: None |
Problem Statement: How do I quickly find objects (pipes, relief valves etc) on the PFD? | Solution: To find objects on the PFD, click on the PFD. Hold down the <ctrl> key and press the F key. A list of all the operations in the PFD will appear. Scroll down the list and select the specific operation you are looking for. Once you have selected the desired operation, Aspen FLARENET centres the PFD at the object of choice.
Keywords: PFD, find, nodes, objects
References: None |
Problem Statement: What is happening to my temperatures and pressures in dead parts of the flare network? | Solution: Where no flow exists in part of the flare network, i.e. branches are connected to relief sources with no flow, Aspen FLARENET follows the following rules for pressure and temperature displayed on the PFD:
1. Aspen FLARENET propagates the source temperature forwards until it meets a pipe with a non-zero flow. The temperature of this zero flow has a negligible effect on the mixed flow. The pressure used to perform a flash calculation is taken at the first node where flow is encountered.
2. Aspen FLARENET takes the pressure from the first non-zero flow node downstream and applies this pressure back at the relief source with zero flow and does a flash as long as there is a temperature dependent EOS enthalpy method specified.
Keywords: dead, zero flow
References: None |
Problem Statement: What is the Relieving Pressure and how is it calculated in Aspen Flarenet? | Solution: The Relieving Pressure is the pressure increase over the Maximum Allowable Working Pressure (MAWP) allowed during discharge of the relief device. In API 520 this is termed the Accumulation or Accumulated Pressure.
According to API 520, the value of the Relieving Pressure is 110% of the MAWP for Operating contingencies and 121% of the MAWP for Fire contingencies.
In FlareNet, the Relieving Pressure for Relief Valve sources can be either user-specified or calculated automatically by checking the appropriate Auto checkbox or clicking the appropriate Set button on the Relief Valve Editor...Conditions tab.
The Relieving Pressure is a function of the user-specified Maximum Allowable Working Pressure (MAWP) and the Contingency (Operating or Fire). Therefore, from the general guidelines given above, when calculated automatically the Relieving Pressure is related to the MAWP by:
Relieving Pressure = K * MAWP equation (1)
where:
K is the relieving pressure calculation factor (110% for Operating and 121% for Fire) .
Note:
1. The equation (1) is based on gauge pressures, whereas the MAWP and Relieving Pressure values shown on the Relief Valve Editor...Conditions tab are absolute pressures.
2. Below 30 psig, the allowable overpressure is 3 psig, instead of 110%. 110% rule is followed above 30 psig.
Sample Calculation:
3 psi = 0.206842719 bar
Ambient Pressure = 1 atm = 1.01325 bar a
MAWP = 2.01325 bar abs = 1 bar g
Relieving Pressure = 1.206842719 barg = 1.206842719 + 1.01325 bar a = 2.220092719 bar a
3. Multiple valve: The relieving pressure is 110% of MAWP unless you have a multiple valve assembly in which case it is 116% of MAWP.
Keywords: Relieving pressure
References: None |
Problem Statement: What operating system (OS) requirements does FLARENET need? | Solution: Operating system requirements for FLARENET installation:
The Windows Installer being used by FLARENET requires Internet Explorer 4.02 or higher. We believe there may be some issues with the SLM installation on IE4 so we would suggest IE5 for safety if this is possible.
Under WinNT, FLARENET requires Service Pack 5 or higher.
Under Win95, FLARENET requires SR2 or higher with the OLE updates.
Under Win98, WinME, Win2000 and Win XP there are no additional requirements other than the Internet Explorer requirement.
Keywords: operating system, explorer, windows,service pack
References: None |
Problem Statement: What is the difference between solved on pressure and solved on flow in the Trace window? Is it possible to force the convergence to be solved on pressure? | Solution: The Solved On Flow indicates that FLARENET has been able to solve the mass balance of your looped flare system to within the mass balance tolerance but has been unable to achieve the pressure convergence tolerance. The tolerances for your FLARENET model are set on the General tab under the Calculation - Options menu. In the case of getting a Solved On Flow, the first thing that we would suggest is to tighten the tolerance to which the mass balance is solved within the case. If you rerun the case you should hopefully find that the case will be able to solve on pressure.
You need to be very careful, a case which solves on flow can still have significant errors on the pressure convergence.
Keywords: solved on flow, solved on pressure, convergence, tolerance
References: None |
Problem Statement: What does the Elements / Two Phase Elements input variable represent? | Solution: The Elements / Two Phase Elements in the Aspen FLARENET pipe model defines the number of cells into which the pipe is divided for pressure drop calculations when a two phase pipe pressure drop method is used (even if the flow is actually single phase).
For Aspen FLARENET 2004 and onwards, this option was renamed from Two Phase Elements to Elements.
The variable can be found on the Methods page of the pipe editor. If the value is blank in the pipe editor, this indicates that the model default value is being used, as defined on Calculations | Options | Methods.
The default value of 10 elements normally gives the best compromise between accuracy and speed, although this decision is somewhat subjective. Experience has shown that 25 to 30 elements is adequate for all but the longest pipes.
Note that this option is not used if a single phase pipe pressure drop method is used (either Isothermal Gas or Adiabatic Gas) since these methods used analytically derived pressure drop equations based on the assumption of isothermal or adiabatic flow respectively.
Keywords: element, elements, two phase elements, pipe
References: None |
Problem Statement: What are improvements in the Process Flow Diagram (PFD) for Aspen Flare System Analyzer V7.3? | Solution: ? Copy and paste in the Process Flowsheet is now allowed.
? New zoom capabilities in the Process Flowsheet.
? Connecting objects in the Process Flowsheet has been significantly improved.
? New Grid controls used in Results and Input Views let you sort and apply a custom filter on every field. Copy and paste, as well as quick export to Excel is also supported for data worksheets.
? Error List; Errors, Warnings and Notes are populated while a simulation is running. The view lets you filter warnings and errors according to categories.
? Significant digits and formats of every variable can be controlled through Preferences
Keywords: Improvements, Copy and Paste, PFD
References: None |
Problem Statement: What are the differences between the 2.56 and 3.x program calculations? | Solution: When importing a model from FLARENET version 2.56 into 3.0x, the user should be aware that there is a fundamental change in philosophy. The wide range of philosophy changes leads to different answers when importing directly a 2.56 case into 3.0x. This article deals with the changes necessary to compare the results of 2.56 cases with 3.0x cases.
With 2.56 you had to model the tip as a pipe with appropriate fittings losses which were in turn modeled as equivalent lengths. 3.0x models all nodes (a node is any unit operation that is not a pipe segment) as a series of expansions and contractions as appropriate with connectors. As a consequence of the wider range of unit operations and they way with which they map to 3.0x objects, the import of 2.56 cases makes a best guess about the user's real intent. During the import the user is warned about this. It would be quite rare to get an exact match with the user's requirements.
To compare the results of 2.56 and 3.0x users should make the following changes to the raw cases in each respective version of FLARENET. The cases should not be read into the same version and compared as this will again give a 3rd set of different answers.
Take the file in 2.56:
In FLARENET 2.56 make sure that there are no fittings to take into account the losses associated with tees / branches (whatever your preference is for naming) in the pipes upstream of the branch - in the original 2.56 this was already the case. Set the autocalc node fittings to none.
Take the same raw file in 3.0x:
In 3.0x the user should chop the flare system off after the separator (since the 2 versions handle flare tips differently) and set the pressure upstream of the separator as a boundary where the user should attempt to match the pressures in the 2 versions - look at the 2 pressures upstream of the separator in both cases. The user should do this by setting an inflow performance curve in the flare tip of the 3.0x and setting a single point with a massaged DP. Downstream of the separator the user should see that the pressures are the same as the inlet to the separator in 3.0x (this wouldn't be the case if the separator was the same diameter as the pipe of course normally. To do this the user should ignore the expansion loss as per the info below).
Calculation of pressure drops:
2.56 uses a simple approximation for interpolating the physical properties in 2.56. It does not calculate new physical properties for every segment in the pipe. 2.56 only refreshes the vapour density estimate in every cell. This interpolation can lead to over or underprediction of the pressure drop in the particular pipe. 3.0x rigorously calculates the physical properties for each phase in every segment of the specific pipe (default is 10 segments per pipe). FLARENET 3.0x is slower but provides more accurate pressure drops than 2.56 because of this. 2.56 also used an equivalent length addition to the pressure drop to account for fittings e.g. tees, expansions and contractions etc. Where there is a momentum change at an expansion (a rho v2 change) no account is taken in 2.56 except the fitting pressure loss. In 3.0x to compare the results against 2.56 you will have to turn all the tees to ignored and all the expanders. Also, version 2.56 displays the equivalent of static pressures so in 3.0x you will need to turn off the total pressure in file preferences to compare the cases.
To ignore all the node calculations not to account for expansion / contractions momentum changes:
Sort all nodes by type. This will group all the e.g. tees together.
Select all the tees via the Node Manager view list box then click edit. This allows the user to edit certain fields in more than one instance.
Leave all fields as * (which means leave as it is) except for the fittings loss method which should be modeled as ignored.
Keywords:
References: None |
Problem Statement: Is the fitting database network-based or computer-based? Do we need to add new fittings every time we open the model in different computers? | Solution: When you customize the fittings database the files are available on the computer you have modified. If you want to send the Flarenet file to someone else you have to send the fittings.mdb file as well. It is located under C:\Documents and Settings\All Users\Application Data\Aspen Tech\Aspen FLARE NET (version)\Database\fittings.mdb (for Pipe Fittings).
Keywords: Fittings database
References: None |
Problem Statement: How to create a Black Oil fluid package in Aspen HYSYS? | Solution: To create a Black Oil fluid package in HYSYS you will need the HYSYS Upstream installed. The Black Oil package is available under the COMThermo group.
It is recommended to add a list of light components first with the Peng Robinson property package to represent the light end gas composition
In the Simulation Basis Manager click Add button and then select COMThermo radio button. From the list of available property packages in the Property Package Selection group, select Neotec Black Oil.
Keywords: Property Package, Neotec Black Oil
References: None |
Problem Statement: Can I fix the outlet pressure / back pressure of a relief / control valve?
Can I control the outlet pressure / back pressure of a relief / control valve? | Solution: Aspen Flare System Analyser (formerly Flarenet) performs the hydraulic calculations backward (from flare tip to source). As a result the flare system will dictate the outlet pressure of the control/relief valve. You can not specify an outlet pressure of a valve. You can control it by controlling pressure drops downstream by manipulating pipe diameter etc) or by changing the flowrate.
TheSolution document 122225 explains how the back pressure of a valve is calculated.
Keywords: control valve, relief valve, pressure, fix, control
References: None |
Problem Statement: How do I change the value used for atmospheric pressure? | Solution: To change the atmospheric pressure value used in all calculations, go to the Calculations menu and select Options. The Atmospheric Pressure field is located at the top of the General page. Once you have made your change, click on the OK button.
Keywords: flare tip
References: None |
Problem Statement: Are the Expansion/Contraction losses in Separators accounted for? | Solution: The separators (Knock Out Drum) in Aspen Flare System Analyser includes expansion/contraction losses associated with the piping connections for the inlet and outlet respectively. Therefore if pipe exit losses are accounted for from Pipe fitting, losses will be accounted twice. This might lead to an over prediction of the source back pressures.
However, the two pressure loss methods are different hence might likely not give the same results. This is described briefly in Appendix A of the Aspen Flare System Analyser user guide.
Keywords: Inlet Outlet losses, Expansion, Contraction.
References: None |
Problem Statement: How can I zoom in on separate sections of the PFD without having to zoom in and out constantly? | Solution: In some Aspen FLARENET cases, the PFD can become quite large and it becomes difficult to locate and view sections or areas of a flare system comfortably and legibly. The PFD has the facility to create multiple viewports. A viewport is essentially a specific view focused on one particular section of the full PFD. To add a viewport to your existing case, follow these steps :
1. Open the PFD.
2. Find the portion of the PFD that you would like added to your viewport.
3. Right-click on the title bar of the PFD. An object inspection menu will appear with a) Print window and b) Add View Port. (Note: If the PFD is maximized, right-clicking on the blue title bar will not launch the aforementioned object inspection menu. To be able to add viewports, the PFD must not be maximized.)
4. Select Add Viewport.
The drop down menu in the upper right hand side of the PFD will now show User View 1. This is the newly created viewport. The name for the viewport may be changed by highlighting the name in the drop down menu and typing in the new name. Once a view port is selected, you may zoom in or out and focus the current viewport on the desired section of the network. The zoom percentage may be changed using the Select Zoom Percentage drop down menu. To switch between viewports, you can access the viewport drop down menu and choose the appropriate one.
Keywords: PFD, viewport, zoom
References: None |
Problem Statement: What are the methods used for relief valve sizing in Aspen FLARENET? | Solution: In Aspen FLARENET version 2004 and higher there are three different methods available for sizing a relief valve (calculating the rated flow) in Aspen FLARENET: HEM, API 1976 and API 2000. Versions of Aspen FLARENET prior to version 2004 have the HEM and API 1976 methods available. The sizing method can be chosen on the Methods tab of the Relief Valve Editor.
The HEM method is based on the Homogeneous Equilibrium Model and assumes no slip conditions and thermal equilibrium between each of the phases. A description of the method may be found in the following reference:
Leung, J.C. , Easily Sized Relief Devices and Piping for Two-Phase Flow, Chemical Engineering Progress, p.28 (December 1996).
The API 1976 method was proposed by the American Petroleum Institute (API RP 520, 4th edition, 1977) and has been in use for many years. This method may yield undersized relief valves in 2 phase flow situations.
The new API 2000 method (API RP 520 7th edition, 2000) includes the more rigorous two phase Leung Omega Method. This is very similar to the method recommended by DIERS (Design Institute for Emergency Relief Systems - AIChE) and gives similar results in most cases.
It should be noted that based on their specific valve designs the valve vendors should perform the final sizing of relief valves. Aspen FLARENET will give an indicative size of PSV required but should not be used as the final decision tool. Variations on valves, especially with two phase flow can lead to a range of applicable sizes.
Keywords: Relief valve, sizing, DIERS, Leung, two phase, API, 2 phase
References: None |
Problem Statement: Why is the friction factor different if calculated by Beggs & Brill and Adiabatic methods when we have some water in the vapour? | Solution: When you have a VF=1, there is no difference between the Adiabatic method and Beggs & Brill method as the friction factor ratio is 1, as per the Beggs and Brill model in this case.
However, when there is liquid present and we have two phases, the friction factor is correctly calculated for vapour fractions as high as 99.68%. At this point, we are in a distributed regime, as per the Beggs & Brill flow regime map and consequently we get a 2 phase friction factor ratio of ~ 2.0. This is why we are getting friction factor calculated with Beggs&Brill of almost twice as compared to adiabatic flow.
So even with a small amount of liquid, we can get completely different result from the Beggs &Brill model as it determines a completely different flow regime.
Keywords: Friction factor, Beggs & Brill, Adiabatic
References: None |
Problem Statement: Is it possible to specify a pipe elevation greater than its length? | Solution: No, the pipe length in Aspen FLARENET is its total length, so it cannot be less than the elevation. A total pipe length that is less than the elevation can result in flash errors when the model is run.
Keywords: pipe length, elevation
References: None |
Problem Statement: What options are there for modelling the nozzle losses at the inlet and outlet of the separator in Aspen Flare System Analyzer? | Solution: The available options are:
A? Equal Static Pressure - Pressure drop calculation is ignored and static pressure in the inlet and outlet is equal.
A? Calculated Ignore Vena Contracta - Pressure drop is calculated in accordance with the Swage method but ignores the loss due vena contracta
A? Calculated a?? Pressure drop is calculated in accordance with the Swage method including the loss due vena contracta.
In the attached example file, open the Vertical Separator 1, go to Calculations tab, and then change the selected fitting loss method for Horizontal Separator 13. Now change the swage method for connector 15 to compressible. Run the model and observe the pressure drop calculated and the effect of back pressure on RV 1 and 11. This could be critical since relief valves are designed in order to relief under a certain back pressure not greater than the MABP.
Keywords: Fitting loss, KO Drum, Back Pressure
References: None |
Problem Statement: What does the trace buffer size in Preferences / General do? | Solution: This options lets you to specify the size in bytes of the text buffer displayed by the Trace window. Larger values will allow more text to be stored. The default value of 32000 is adequate for most cases.
Keywords: Trace buffer size, preferences
References: None |
Problem Statement: When should the kinetic energy contribution option be used? | Solution: For a rigorous design, the kinetic energy option should always be checked (i.e. select Calculation | Options from the main menu and activate the Include Kinetic Energy checkbox on the General pagetab). Not taking into account the kinetic energy changes in a simulation could culminate in less accurate results.
In general, the option to include or ignore the kinetic energy in the energy balance in Aspen FLARENET becomes more important for high velocity flows. By considering the kinetic energy changes in your simulation, the variations in velocity could influence fluid temperature (and as a result, transport properties such as density, viscosity, etc.).
Keywords: kinetic, energy, contribution
References: None |
Problem Statement: Can Aspen Flare System Analyzer calculate the Sound Power Level (SPL) due to Acoustically Induced Vibrations (AIV) within the flare header piping? | Solution: Aspen Flare System Analyzer V9 can calculate the SPL due to AIVs. Noise generated by gas flowing through high pressure drops across mechanical equipment like control valves, orifices, or relief devices may cause high-frequency vibrations in the pipe wall. This high-frequency vibration (i.e. AIV)Â can cause fatigue failure of flare header piping.
The AIV calculations can be activated by accessing the Calculation Settings window on the Home Ribbon, selecting the AIV tab, and activating the Calculate Network Sound Power Levels checkbox.
Once the AIV calculations have been activated, the results can be reviewed on the Summary tabs of each equipment as SPL (dB) (Sound Power Level)
The results are also displayed on the Pressure/Flow Summary results from the Navigation Pane:
Keywords: Acoustic Induced Vibrations, AIV Sound Pressure Level, SPL, Noise.
References: None |
Problem Statement: What is recommended value of Mach number in Aspen Flare System Analyzer? | Solution: While rating the network you may define a Mach number constraint of 1.00, in order to highlight only choked flow conditions.
Mach number of 1.00 is NOT recommended for design calculations where a more reasonable value such as 0.5 or 0.7 will lead to a more rapidSolution towards the maximum allowable back pressure constraints.
Whenever having different source conditions, each scenario can have unique design limitations that will be used either to size the pipes or to highlight problems when an existing flare system is being rated.
For example, a Mach number limit of 0.30 might be applied for normal flaring compared to a Mach number limit of 0.50 or greater at the peak flows encountered during plant blowdown.
Keywords: Mach
References: None |
Problem Statement: How can I tell if one of my constraints has been violated for a particular scenario? | Solution: When a scenario's calculations have been completed, there is a variety of ways to find out if one of the constraints has been violated:
Look at the PFD. Anything that appears in red, i.e. the name of a pipe segment indicates that one of the constraints has been violated. Unfortunately, no indication of which constraint is given.
Go to the View menu, select Results and then Messages. Any violated constraints will be listed specifically on the Problems page of the Messages view.
Go to the View menu, select Results and then Pressure Flow Summary. Any constraint variable that is violated will appear in red, i.e. Mach number of .4 is greater than limit of 0.3.
Keywords: violations, messages, constraints
References: None |
Problem Statement: I get a message 'choked flow at flange for source', whenever I input a flange diameter for my sources. Once removed the flange diameter(s) the message(s) disappear. | Solution: 1) If you get a choked flow error message at the outlet of the source it indicates that the source outlet flange diameter is not sufficient to relieve the flow. Hence the choked flow message appears. You need to find out from the relief valve vendor what is the allowable diameter of the outlet flange to be specified.
2) If you delete the flange diameter of the Pressure Safety Valve(PSV) the messages disappear. This is because Aspen Flarenet assumes the PSV outlet flange diameter same as the downstream tailpipe diameter. Since the tailpipe diameter is much bigger than the PSV flange diameter, you experience no choked flow.
Keywords: Choked flow, flange diameter
References: None |
Problem Statement: How does Tee's pressure drop calculate in Flarenet? | Solution: The static pressure change across the TEE is given by:
DeltaP = Tee's Pressure drop
K = static pressure loss coefficient
V = Average Velocity of fluid across Tee
Tees pressure drop are modeled either by using a flow independent loss coefficient for each flow path or by using variable loss coefficients that are a function of the volumetric flow and area for each flow path as well as the branch angle. The following numbering scheme is used to reference the flow paths.
Constant Loss Coefficients
The following static pressure loss coefficients values are suggested by the API:
The selection of the coefficient value is dependant on the angle and the direction of flow through the tee.
For flow into the run, the loss coefficient for tee is:
For flow in branch
For flow in tail
Variable Loss Coefficients
The loss coefficients (K) are a function of the branch angle, branch area to total flow area ratio and branch volumetric flow to total volumetric flow ratio.These coefficients can be determined either from graphical representation by Miller or from the Gardel equations. For more information refer to the appendix A, page 293 of the Aspen Flarenet reference manual.
Keywords: Tee, Static Pressure Drop, API 251
References: None |
Problem Statement: How do I create a new scenario from my existing FLARENET case? | Solution: It is a relatively easy task to create a new scenario in an existing FLARENET case. It is good practice to build the Default Scenario or your base case to include all equipment which currently exists in or may be included in the flare network. Once you are satisfied that your default scenario is complete and you wish to evaluate a specific scenario, i.e. unit fire or cooling water failure in one area, you can do the following:
Select Scenarios from the Build menu.
Click on the Add button.
Select the scenario you would like to clone.
Input any of the scenario specific design/system constrains, i.e. backpressure, tailpipe velocity.
Keywords: scenario
References: None |
Problem Statement: What is the Maximum Allowable Back Pressure (MABP) and how is it calculated in FlareNet? | Solution: The Maximum Allowable Back Pressure (MABP) on a relief device is the maximum pressure that can exist at the outlet of the device without affecting the capacity of the device.
In general the MABP for a conventional pressure relief valve should not exceed 10% of the set pressure at 10% overpressure. For a balanced pressure relief valve the MABP in general should not exceed 40% of the set pressure at 10% overpressure (although some manufacturers quote different values, usually in the range 30-50%).
In FlareNet, the MABP for Relief Valve sources can be either user-specified or calculated automatically by checking the appropriate Auto checkbox or clicking the appropriate Set button on the Relief Valve Editor...Conditions tab.
The MABP is a function of the user-specified Maximum Allowable Working Pressure (MAWP) and the Valve Type (Conventional or Balanced). Therefore, from the general guidelines given above, when calculated automatically the MABP is related to the MAWP by:
MABP = KBP * MAWP
where:
KBP is the percentage back pressure correction factor (10% for Conventional valves and 40% for Balanced Valves) .
Note that this equation is based on gauge pressures, whereas the MAWP and MABP values shown on the Relief Valve Editor...Conditions tab are absolute pressures.
Keywords: Maximum allowable back pressure, MABP, backpressure
References: None |
Problem Statement: Can I choose which scenarios should be calculated when I run my FLARENET model? | Solution: Yes, it is possible to pick which scenarios are to be included in the calculations when you run your model. There are three options available on the Scenarios page of the Calculation Options Editor:
Current Scenario: only the current scenario is calculated.
All Scenarios: all scenarios are calculated sequentially.
Selected Scenarios: if you choose this option, you can check off which scenarios are to be calculated via the check boxes in the Calculate column.
Once you have made your selection, click the OK button and these options will be used the next time your model is run.
Keywords: scenario, calculation options
References: None |
Problem Statement: Why is the Source Back Pressure not equal to the Upstream Pressure in a tailpipe? | Solution: If there is a change in flow area between the source flange and the downstream tailpipe, Aspen FLARENET will perform a swage calculation across this diameter change (unless you have specified otherwise). This leads to a pressure difference between the Source Back Pressure (the pressure at the source flange) and the Upstream Pressure of the tailpipe immediately downstream.
The calculation parameters for this swage calculation are defined on the Methods tab of the source in question.
See alsoSolution ID 109496: Why is the downstream pressure at a node (connector or tee) higher than the upstream pressure?
Keywords: back pressure, upstream pressure, source, tailpipe
References: None |
Problem Statement: Is the swage option taken into account in the inlet piping? | Solution: No. Currently, there is no option to take into account contraction or swage in the inlet piping.
Hence, the Swage option that is shown under the Methods tab in the valve refers only to the outlet.
As a workaround, you can include an equivalent length in the inlet piping to take into account the pressure losses.
Keywords: swage, contraction
References: None |
Problem Statement: When I run a Flare System scenario I get multiple note messages stating Recycle Molar at 'segment name'. The scenario then fails to converge. | Solution: These error messages appear if during theSolution of the network topography discovers a separator unit operation within the body of a looped circuit. (This configuration is indicated by a separator whose fluid flow direction is unknown until after calculations are complete). This toporgraphy is not supported for multiphase flow. If the user considers that the separator on the loop will not encounter multiphase, then the procedure described inSolution 137769 (section D. point 3) is recommended.
Keywords: cycle recycle vapor liquid converge failure loop
References: None |
Problem Statement: How is the flare tip pressure drop calculated from the diameter and fittings loss coefficient specified in the Flare Tip Editor? | Solution: The static pressure drop of a flare tip in Aspen FLARENET is calculated from the following equation :
dP = 0.5 K Rho * v ^2
where :
dP = Pressure drop
K = Fittings loss coefficient
v = Velocity
Note : The diameter of the attached pipe has no impact upon the pressure drop calculation and Aspen FLARENET does not calculate the pressure drop from the tip diameter to the pipe diameter.
Keywords: Flare Tip, Pressure Drop
References: None |
Problem Statement: I have very big network for relief system. How do I find or locate the particular valve or pipe segment on PFD? | Solution: In Aspen Flare System Analyzer V7.2 or previous versions, you can use the shortcut key Ctrl + F. Aspen Flare System Analyzer will pop up the interface: Locate Object.
If you click the desired Object, Aspen Flare System Analyzer will bring you to the location and highlight the object.
If you use the Aspen Flare System Analyzer V7.3, you can click the right button of your mouse. You can use Locate Object function.
Keywords: locate, objects, PFD
References: None |
Problem Statement: Where does the K=8 fixed value come from when using the Miller Chart NO extrapolation method in a Tee? | Solution: As you can find in the
Keywords: Miller Chart, Gardel
References: Manual ( |
Problem Statement: Open Profile graphical view - does not show any profile | Solution: It is due to loop in the system. User would need to ignore some of the pipes so that flow path does not form a loop.
Keywords: profile, loop
References: None |
Problem Statement: How is the rated flow calculated for a relief valve ? | Solution: On the Conditions page of the relief valve view, there is a Set button located next to the Rated Flow cell, which when clicked will calculate the rated flow for that specific valve. Before calculating the rated flow, the user should first ensure that the valve dimensions have been input properly. On the Dimensions page of the relief valve view, you can input:
1. The flange diameter at the valve exit connecting the valve to the tailpipe.
2. The number of valves.
3. The orifice area for each valve.
4. The valve type, e.g. balanced or conventional.
Once this information has been provided, pressing the Set button will calculate the maximum possible throughput for that valve size as per the sizing method selected on the Methods tab of the relief valve. The currently available sizing methods are API 1976, API 2000 and HEM. For more information on these methods please refer toSolution 109481.
Note that this is not intended to be a rigorous sizing tool - whenever possible it is always recommended to use vendor data.
Keywords: relief valve, sizing, API, HEM, rated flow
References: None |
Problem Statement: Is it possible to change the source data for all scenarios? | Solution: In Aspen Flare System Analyzer, each scenario will hold its own data. It means that source data (composition, pressure, temperature, flowrate) are being shared among scenarios.
You will have to change one scenario a time.
One workaround is to export your data into the Excel file by Export Wizard. You can manipulate the source data in Excel and make changes for all scenarios and import back to your case by Import Wizard.
Keywords: Export wizard, import wizard, all scenarios, sources' data.
References: None |
Problem Statement: What is the difference between the fittings Tee-Standard and Tee-Swept? | Solution: The difference is the angle between the branch and the body. A Standard tee has an angle of 90 degrees. A Swept tee has an angle typically between 30 and 60 degrees.
Keywords: Tee, Standard, Swept, Fittings
References: None |
Problem Statement: In Aspen Flare System Analyzer, why the Flow Map is reporting Annular flow while the Pipe Summary is reporting Slug flow and also a slug flow warning message appears. | Solution: In Aspen Flare System Analyzer (AFSA), flow regime results are reported in Flow Map and also in the Summary page of each pipe unit (seeSolutions 131382 & 134868). Sometime user may received different results from the two reports, such as annular flow in Flow Map and slug flow in pipe Summary page.
The reason is that Flow Map in AFSA was developed from horizontal flow and the Summary page results are reported from pipe calculation method selected, such as Beggs & Brill which is applicable to horizontal, inclined and vertical pipes.
Therefore, for inclined and vertical pipes, the results from Summary page is more reliable compared to the results in the Flow Map. User should adjust the model, e.g. change pipe diameter, flow rate, orifice ratio, etc., in order to eliminate the slug warning message.
Keywords: Flow Regime, Flow Map, Slug Flow
References: None |
Problem Statement: Is it possible to fix a constant pressure drop in a flare knock out (KO) drum? | Solution: In Aspen Flare System Analyzer, it is not possible for the user to fix a constant pressure drop in the KO drum, since KO drum only considers inlet and outlet pressure changes. However, the user can model a bleed for a fixed (constant) pressure drop between two KO drums to represent the horizontal separator.
See attached example file.
Keywords: Fixed Pressure Drop, KO Drum
References: None |
Problem Statement: How do I change the units used to display the calculated values? | Solution: There are two ways to change the display units:
Go to the File menu and select Preferences. The units can be changed via the Display Units drop down box.
Directly below the menus at the top of the Flarenet window is a row of icons. There are two icons located directly to the right of the printer icon. Pressing the icon with m will display Metric units and clicking on the icon with the ft label will display Imperial/British units.
Unfortunately, the units for individual variables cannot be customized, e.g. the unit set cannot yet be modified to show pressure in kPa.
Keywords: units, preferences
References: None |
Problem Statement: What does the r/d ratio shown for elbow fittings on the pipe Fittings tab refer to? | Solution: The r/d ratio in an elbow fitting is the ratio of the curve radius to the diameter of the fitting. This is a standard term for bends in elbows that defines how sharp or shallow the bend is.
In Aspen FLARENET, the pressure loss coefficients are taken from the Crane Manual (Technical Paper 410) appendix A-29 which lists different values of the fittings loss coefficients for different r/d ratios. In general, the losses are higher for larger values of r/d, as seen in the attached excerpt from Crane.
Keywords: Angle, Pipe radius
References: None |
Problem Statement: How do I model a seal drum more accurately? | Solution: A typical flare stack seal drum can be represented by the following diagram. Those drums can be either horizontal or vertical.
The major pressure drop through seal drum comprises 3 components. In here, we can ignore frictional losses and losses due to drum internals and direction changes within the drum body if the drum has been correctly designed.
1) Pipe exit loss for sudden expansion into the vessel. Depending upon the piping confirmation, you may also wish to include the loss for a 90 degree bend here. This should either be part of the fitting losses for the pipe segment upstream of the seal drum or a separate zero length pipe segment with the appropriate fittings losses.
2) Static head loss due the height of water seal. This should be modeled as a fixed pressure drop segment, e.g. 1m of water is approximately a 0.1 bar head loss. This is can be implemented by Bleed.
3) Pipe entrance for the fluid leaving the vessel. This should either be part of the fittings losses for the pipe segment downstream of the seal drum, or a separate zero length pipe segment with the appropriate fittings losses.
Keywords: Seal drum, bleed, fitttings
References: None |
Problem Statement: How to get volumetric flow rate in the Aspen Flare System Analyzer results summary. | Solution: You cannot add volumetric flow rate in Aspen Flare System Analyzer Results| Pressure / Flow Summary. However, you can do the calculation outside Flarenet, e.g. using Excel. Starting from V7.3, you can export these summary results into excel. In the results table, you will see Mass Flowrate, velocity and Rhov2. From these data, you can calculate Volumetric Flowrate as below:
VF = Mass Flowrate / (Rhov2 / velocity^2)
An example is attached. The data is taken from C:\Program Files\AspenTech\Aspen Flare System Analyzer V7.3\Samples\Convergent\Sample-S1.fnwx.
Keywords: Volumetric flow rate
References: None |
Problem Statement: When I run a Flare System scenario I get multiple note messages stating Recycle Molar at 'segment name'. The scenario then fails to converge. | Solution: These error messages appear if during theSolution of the network topography discovers a separator unit operation within the body of a looped circuit. (This configuration is indicated by a separator whose fluid flow direction is unknown until after calculations are complete). This toporgraphy is not supported for multiphase flow. If the user considers that the separator on the loop will not encounter multiphase, then the procedure described inSolution 137769 (section D. point 3) is recommended.
Keywords: cycle recycle vapor liquid converge failure loop
References: None |
Problem Statement: Flarenet launch some times fail on Windows 2003 R2 with an error message popped up. | Solution: 1. Right-click My Computer, select Properties.
2. Select Advanced tab
3. In the Performance section, click Settings
4. Select Data Execution Prevention tab in Performance Options Window. select option Turned on DEP for all programs....those I select
5. Click Add... Locate the EXE file of Flarenet, and check the box.
6. Apply all the settings.
7. Launch Flarenet successfully.
Notice that you should be an administrator to execute the procedure above.
Keywords: Flarenet, Application, Launch, fail, Windows
References: None |
Problem Statement: What value of the multiphase discharge coefficient (Relief Valve Editor | Methods tab | Multiphase Cd) is used for rated flow calculations using the API 2000/HEM sizing method? | Solution: If either of the API 2000 or HEM methods are selected as the sizing method (Relief Valve Editor | Methods tab | Sizing Method), Aspen Flarenet uses the following discharge coefficient values for rated flow calculations:
1. If the flow is single phase vapour at the inlet and the outlet of the relief valve, Cd = 0.975.
2. If the flow is single phase liquid at the inlet and the outlet of the relief valve, Aspen Flarenet uses the Liquid Cd value specified on Relief Valve Editor | Methods tab.
3. If the flow is two phase at the inlet or the outlet of the relief valve, Aspen Flarenet uses the multiphase Cd value specified on Relief Valve Editor | Methods tab.
Keywords: multiphase Cd, rated flow, API 2000, HEM
References: None |
Problem Statement: How can one display stream properties in Aspen FLARENET? In the summary tab of a unit's edit view, I can find select process conditions but no physical properties? | Solution: Physical properties are reported at upstream and downstream conditions for every object in Aspen FLARENET. To view all physical properties, select View | Results | Physical Properties from the main menu.
Note that one cannot double click on a stream and view its physical properties, since a connection between two pipes is not considered a material stream (i.e. it is simply a connection between two objects).
For information on viewing phase properties, seeSolution 109495.
Keywords: physical, properties, stream, property, vapor, fraction, density, heat, capacity, surface, tension
References: None |
Problem Statement: What criteria does Aspen FLARENET use for its Possible Ice Formation warning? | Solution: Aspen FLARENET will display this warning if the stream contains water and the temperature of the stream is less than 0 oC (32 oF).
Keywords: Ice Formation
References: None |
Problem Statement: How do I convert a case from Aspen Flare System Analyzer V7.3 or newer to V7.2 or older versions? | Solution: In order to downgrade your case in Aspen Flare System Analyzer V7.3, you will have to use Export Case In pre-V7.3 XML format.
Set up the file name and path.
Then launch the older version such as Aspen Flare System Analyzer V7.2. Go to File->Import Wizard. Follow import procedure and use default definition file. You should be able to convert your case to older version.
Keywords: Compatibility, Import Wizard
References: None |
Problem Statement: I have an empty data base and need to create a new model. Can you give me some advice on how to begin? | Solution: Use the starter model of APS and send this model to SQL, these are the steps needed:
1. Create the model tables in an SQL database using the script to create tables found in the application folder:
2. Create a DSN file pointing to that database.
3. Copy the starter model using the DBCOPY utility. You can Find the utility in the next page:
http://support.aspentech.com/webteamcgi/Solutiondisplay_view.cgi?key=136643
The starter model can be found in:
C:\Users\Public\Documents\AspenTech\Aspen Petroleum Scheduler\Starter Model
The DBCOPY utility requires that the ORIONDBGEN to be in the same folder that the utility. So you will need to copy the ORIONDBGEN to the folder of the utility.
4. The utility will ask for the source database (APS_Starter.mdb) and the destination database (.dsn )
If you are using your windows credentials then User ID and Password is not required for the destination database.
5. When you open the model you will find empty screens:
6. In order to simulate the model successfully, please add a description to the VOL property in the properties dialog box:
I recommend you to build the model using this starter database and using the APS interface. Nevertheless, there will be cases that you need to enter entries directly in the database eg. USERS, TRANSMODES, MODEL_TABLES etc.
Keywords: New SQL model, starter database, empty
References: None |
Problem Statement: Aspen FLARENET seems to run very slowly - how can I speed up the calculations? | Solution: You can speed up calculations in Aspen FLARENET by doing one or all of the following:
1. Turn off the status bar at the bottom of the screen. This is done by unchecking the Show Status Bar checkbox under File | Preferences | General. Turning off the status bar can free up to 25% of the PC CPU resources during calculations.
2. Either close the PFD or switch the display variable on the PFD to an unchanging one, e.g. pipe name. Constantly refreshing the PFD uses up CPU resources.
3. Minimize the number of components in the case. Often when users import information from Aspen HYSYS into Aspen FLARENET, there are many heavy components present in very small amounts; these trace amount of heavy components rarely have much of an effect on the flare system, but can significantly increase the solving time. Removing these components from the component list can greatly speed up calculations.
4. For an initial rough Design case use the less rigorous Compressible Gas/Ideal Gas/Isothermal Gas VLE/ Enthalpy/Pressure Drop methods, respectively.
5. When in Design mode, provide reasonable initial pipe size estimates.
Keywords: speed, slow, faster
References: None |
Problem Statement: Where is the Sort Scenarios option in Aspen Flare System Analyzer V7.3? | Solution: Sorting scenarios has been replaced with a filter option. You can use the filter query to show / hide particular scenarios.
You can choose (Custom) to add customized filter query.
Keywords: Scenarios
References: None |
Problem Statement: Noise Calculation has been improved in Aspen Flare System Analyzer V7.3 | Solution: In previous version of Aspen Flare System Analyzer, pipes with a negative pressure drop will have a 0 noise value. Now, Aspen Flare System Analyzer V7.3 will give the correct calculated value.
Keywords: Noise, a negative pressure drop, pipe.
References: None |
Problem Statement: What does the message No FlowPath Data for Source mean when viewing the Profile results? | Solution: The Profile form (accessed via the View->Results->Profile menu) is used to display FlareNet results (pressure, temperature, flow etc.) along a flow path from the specified source to the flare tip.
In general such a profile can only be plotted if there is a single, unique flow path from the source to the flare tip. Therefore, for flare networks with loops or divergent paths, FlareNet will not attempt to display a Profile and instead will issue the message No FlowPath Data for Source on the Profile results form.
Keywords: FlowPath, Data, Source, Profile, Results, Flow, Path
References: None |
Problem Statement: How is the K term (the ideal gas ratio of specific heats) used in Aspen Flare System Analyzer? Is it Cp/Cv or Cp/Cp-R? | Solution: API 520, specifically recommends the K term should be ideal, not the rigorous one, hence Aspen Flare System Analyzer uses Cp/Cp-R.
Keywords: Ideal Gas Ratio, Specific Heats
References: None |
Problem Statement: How to generate a PDF report in Aspen Flare System Analyzer | Solution: In Aspen Flare System Analyzer (AFSA) you have an option to generate a PDF report under File menu, selecting the Print option.
The Print editor allows you to select the information you want to show in your PDF report. The available items are the same that AFSA shows in the Navigation Pane.
Before printing the report, please make sure that the simulation has been converged so that the results can be displayed. After this, just check the desired options to print in the report and click on the PDF button.
Finally, AFSA will ask you to save the PDF file in your preferred location and it will be generated.
Note: Please notice that you also have an option to generate a Text file. For further details regarding this option, please seeSolution ID 139507
Keywords: Report, PDF File, Results, Print.Â
References: None |
Problem Statement: Why do Inlet piping non recoverable pressure drop warnings appear even when the pressure drop is below the 3% of MAWP? | Solution: There is a minor bug in Aspen Flare System Analyzer V7.3, where even the calculated values are below 3% of MAWP, the warnings are still generated. The work around is to go to Options tab, and manually put in a barrier as 3%.
Keywords: warning, inlet piping, pressure drop 3%, MAWP
References: None |
Problem Statement: How to import composition to Aspen Flare System Analyzer V7.3? | Solution: Aspen Flare System Analyzer V7.3 currently does not allow user to copy/paste composition from Excel to sources directly. However, to avoid inputting composition one by one, user can use Aspen Hysys as a workaround:
1. Create one stream in Hysys. Copy the composition from excel to Hysys and make sure the stream is fully solved.
2. Find the AspenOne Icon at the left top corner of the interface, and then select Import Sources | Hysys Sources.
3. By clicking Import Sources | Browse and Open, you should be able to see the window like the one shown below:
4. Select the P/T location for the valve.
5. Change the Scenarios to the one that applies in step 3 and find the source such as relief valve and control valve.
6. Finally, click OK to finish importing the composition.
The compositions should be in Composition tab of the sources in the Flare System Analyzer. The operating condition, e.g. temperature, pressure, can be changed manually from the Condition tab of the sources if the imported values are not appropriate for the scenario.
Keywords: Import Sources, copy/paste composition, excel
References: None |
Problem Statement: Why won't my FLARENET version 2.53 or 2.52 case open in version 3.0 properly? | Solution: FLARENET version 3.0x is designed to be able to read in cases saved in versions 2.55 or 2.56. When cases saved in versions older than 2.55 are read into version 3.0x, the program will produce a blank PFD and none of the data will have been converted. These old cases will need to be opened and saved in either version 2.55 or 2.56 and subsequently loaded into version 3.0x. If you have old cases and do not have access to version 2.55 or 2.56, please contact [email protected].
Keywords: 2.53, 2.52, file conversion
References: None |
Problem Statement: Why are the specific heat ratio and compressibility empty in the relief valve editor? | Solution: Specific heat ratio (K(Cp/Cp-R)) and compressibility will be calculated when you will ask the solver to calculate the Rated flow i.e. when you will check the Auto box for rated flow as below:
If you input your own value of Rated flow or Auto box is not checked, then these fields will be blank.
Keywords:
References: None |
Problem Statement: I want to see the properties and composition of the liquid flow that is removed from the knock out drum. | Solution: Because Aspen Flare System Analyzer is meant to work mainly with gas flows, knock out drums automatically remove all the liquid flow from the inlet. If you want to see the properties and composition of the liquid leaving the drum two approaches exist. The one you choose will depend on the accuracy of the values you need. One approach uses the same software Flare System Analyzer to show the properties and the other one is using a flash calculation in Aspen HYSYS.
Approach 1: Using Aspen Flare System Analyzer
With this option the properties that can be retrieved correspond to the conditions at the inlet of the separator. These properties will have less accuracy because they are not calculated at the real pressure of the separator since no pressure drop has been considered at that point. However, if the pressure drop is very small or is not considered in your separator then the properties will be accurate. To use this option follow this step by step.
1. Go to File > Preferences and in the General tab check the Save phase properties option.
2. Run the simulation and once it is converged, go to the Physical Properties view. You will be able to display the different phases and properties of each pipe by clicking on the + sign.
NOTE- If your Flare Net is very big or complex, using this option might consume a lot of memory and delay your calculations. If this is the case and you need to know the properties of liquid outlet from the drum, the second approach is probably the best.
Approach 2: Simulating only the separator as a Flash tank in HYSYS
For this approach we will take the conditions of the inlet of the separator to define a new stream in Aspen HYSYS. We will adjust the pressure calculations of Aspen Flare System Analyzer (AFSA) in the HYSYS Separator and alow it to calculate the flash separation. From this simulation we will be able to take properties of the liquid stream.
Step by step guide:
1. Create a new simulation in Aspen HYSYS using as components the same you are using in the Aspen Flare System Analyzer.
2. For the property package you should use as follows:
*Peng Robinson in HYSYS for Peng Robinson method in AFSA
*SRK in HYSYS for SRK method in AFSA
*Antoine for Vapor Pressure in AFSA
3. Go to the simulation environment and create a stream with the same conditions and composition as the Downstream of the pipe connecting with the separator.
4. Connect to the stream a Flash separator and add a vapor and liquid stream.
5. In the Design > Parameters specify 0 for the Inlet Delta P and delete the Vapor outlet Delta P.
6. Then go to the Worksheet tab. Here you will specify the vapor pressure with the same value that AFSA calculated for the Outlet of the separator.
7. With this you should have your separator solved and if you compare the values with the ones in AFSA you will find them pretty similar. Properties can be checked in the streams or in the separator. In HYSYS you can request for additional properties to be calculated if you need so.
An example is attached for the three methods in HYSYS along with its corresponding AFSA simulation under same conditions.
NOTES:
· The Antoine method is the one with a highest difference compared to the results of Vapor Pressure in AFSA.
· The Enthalpy in HYSYS Peng Robinson cannot be compared since it has modifications that are not available in Flare System Analyzer.
Keywords: Flare System Analyzer, knock out drum, separator, liquid properties, Aspen HYSYS
References: None |
Problem Statement: How should I connect the different unit operations in my PFD? | Solution: When connecting the unit operations, we always need to remember to do so on the direction of the process flow (i.e. from left to right).
If we follow the color code on the PFD we will notice that the red dots at the border of any block represent an inlet, while the blue dot represents an outlet.
When we have two sets of pipes that we want to connect, or when we have two nodes or a source and a node, Aspen Flare System Analyzer will be adding either a connector (if we are connecting two pipes) or a pipe (if we are connecting other blocks).
If we connect the blocks from right to left, the blocks that the program will add will not be connected correctly to our simulation. Refer to the image below. In this case, the blue dots will be connected with blue dots and red dots with red dots. And although we could rotate the icons, whenever we have some flow going through the unit operations, the program will detect that the flow should go in the opposite direction and we will be having problems trying to converge our simulation.
Keywords: PFD
Best practices
References: None |
Problem Statement: How to model inlet pipe work to PSV's with pipe diameter changes? | Solution: There is no option to have multiple pipe diameters in the inlet pipe to PSV. The workaround is to consider inlet pipe as inlet pipe to the PSV and add pipe length for reduced/increased diameter by fifth order of pipe diameter ratio i.e.:
Equivalent length = (Length of inlet pipe @D1) + (Length of pipe @ D2) X (D1/D2) ^ 5.
Note that in the pressure drop calculation formula for pipes we have:
dP = f.L/D (V^2) / (2.g)
By having constant volumetric flow rate (negligible pressure drop), Velocity (V) changes in 2nd order of diameter ratio. So V^2 / D term in the formula changed by order of 5 in respect to (D1/D2). In turbulent flow the friction factor (f) is constant according to Moody Diagram. So by considering turbulent flow, the pressure drop varies in 5th order of diameter ratio.
Keywords: inlet pipe, pressure drop, multi diameter
References: None |
Problem Statement: What property models are available for use in an Aspen Hydraulics Sub-Flowsheet? | Solution: Aspen Hydraulics requires either a COMThermo or Aspen Properties fluid package in order to function properly. When a native HYSYS property package is assigned to an Aspen Hydraulics Sub-Flowsheet, HYSYS creates a COMThermo property package to use. Currently, the only property packages that HYSYS can convert to COMThermo in this manner are the PR and SRK. If you choose a property model that is neither of these, then HYSYS will create a PR property model by default to be used within the Aspen Hydraulics Sub-Flowsheet. To use another property model, the user should first create a COMThermo or Aspen Properties fluid package in the basis environment and then assign this package to the Aspen Hydraulics Sub-Flowsheet. The Aspen Hydraulics Sub-Flowsheet will then directly use this property package directly.
Keywords: hydraulics, Property package
References: None |
Problem Statement: What are the best options to have a good consistency of Calsep PVTSim files in Aspen HYSYS? | Solution: Calsep PVTSim information can be transferred to HYSYS using two different options:
· PSTSim Database Text File Import: This option is available for all AspenTech HYSYS users. Any problem detected while using this option should be reported to AspenTech for review and this is the recommended option to transfer consistently information from Calsep PVTSim into Aspen HYSYS.
· PVTSim link: This option is provided directly by Calsep and is only available for AspenTech users who have installed Calsep PVTSim software in their computer. Any problem while using this tool should be reported directly to Calsep.
In a recent effort to improve the consistency between Calsep PVTSim and Aspen HYSYS properties for the PVT data AspenTech has released in CP01 for Aspen HYSYS V8.8 a fix for volume correction parameters import. This provides the best consistency for flash and property results. If you have V8.8 we strongly encourage you to install the patch.
If you are observing differences in the properties results between the two products for previous versions while using the PVTSim Database Text File Import option we suggest you change the default import settings in the following way:
If the problem persists, please contact Aspen Technical Support to have the case evaluated.
Keywords: Calsep PVTSim, HYSYS, PVT laboratory, PVTSim link
References: None |
Problem Statement: What is the difference between property giveaway and an infeasibility breaker in Aspen Refinery Multi-Blend Optimizer? | Solution: An infeasibility breaker comes into play when the optimizer cannot find an optimalSolution in the feasible region because of some constraint defined in the model. So, the optimizer will try to find aSolution beyond the bounds and will put a penalty on objective function. This way a user will still get a feasibleSolution even if some of the constraints in the model are unsatisfied.
Property giveaway is when user has a situation where we are getting better property values than what is expected. This is where user is losing value because of giving away better quality product for the same product grade price. Putting a property giveaway penalty helps to adjust the property specs as desired. If we don’t have this penalty value, optimizer will still be able to find aSolution within feasible region with a value lost due to the better propertySolution.
Keywords: Property giveaway
Infeasibility breaker
References: None |
Problem Statement: What is the difference between molecular seal and water seal and how can I model them in Aspen Flare System Analyzer? | Solution: Molecular seal
Water seal
Refer to www.johnzink.com
Refer to www.nao.com
Molecular seal and water seal drums are the accessories of a flare system that protects the stack from flame front or flash back.
Molecular seals:
1. Molecular seals work based on the difference between the density of the air and hydrocarbon mixture. Actually, the hydrocarbon acts like a seal and prevents the air to ingress into the flare stack and makes a flammable air/HC mixture that potentially has high tendency to explode.
2. A molecular seal also could be very efficient in reducing the amount of purge gas required to maintain a positive pressure in the flare network piping system and the stack. The level of decreasing the purge gas flow rate is directly dependant to the molecular seal manufacturer. Using a suitable molecular seal can reduce the required flow velocity from 50 ft/sec down to .01 ft/sec and this would lead to a considerable savings in purge gas quantity.
3. Molecular seals require a continuous purge gas flow to prevent flame flash back into the flare system. if the purge gas flow cuts off, then the device would have no reliability to protect the system. For this reason engineers will employ a secondary gas (e.g. nitrogen) as a backup for purge gas.
Water seals:
1. A water seal drum functions the same way except that the sealing fluid is water and the drum is installed at the flare stack base after the knock-out drum vessel, whereas molecular seal is installed at the top of flare stack before the tip.
2. Utilizing water seal drum as a flame front protection device doesn't need to feed purge gas into the flare network piping system, but it should be fed into the large stack to protect it from flash back.
Aspen Flare System Analyzer does not directly handle seal drums. The workaround is to add a dummy vertical pipe and it will model the pressure drop for a multiple phase system. Or you can use the bleed to assign a fixed pressure drop to model it. The different flow regions will be seen in the flow map.
Keywords: Molecular seal, water seal
References: None |
Problem Statement: How is the pressure drop across a Flare Tip calculated using Pressure Drop Curves? | Solution: Many flare tip manufacturers will supply their own characteristic curves for the flare tip, normally given in terms of the pressure drop versus flowrate.
The main features of the Pressure Drop Curves in FlareNet are:
They allow the user to input characteristic pressure drop curve data and therefore to calculate the pressure drop based on the actual flowrate at the flare tip.
The user can supply multiple curves at different molecular weights to account for variations in the composition of the fluid being flared.
FlareNet automatically provides a correction for differences between the flowing temperature at the flare tip and the reference temperature at which the pressures drop curve(s) were supplied.
Pressure Drop Versus Flow Rate
Pressure Drop Curves allow the user to input characteristic pressure drop curve data and therefore to calculate the pressure drop based on the actual flowrate at the Flare Tip. The pressure drop is calculated by linear interpolation of the supplied pressure drop versus flow rate data. The calculated pressure drop is then corrected for molecular weight and temperature (see below).
Note that FlareNet will not extrapolate past the endpoints of the supplied data. For example, if the calculated flow through the flare tip is above the highest supplied value in the curve, FlareNet will simply use the boundary pressure drop value. Note also that FlareNet currently does not give any warning messages when you are operating outside the boundary flow limit.
Correction for Molecular Weight
FlareNet allows the user to enter multiple pressure drop curves to account for variations in the composition of the fluid being flared. When multiple curves are specified, FlareNet adjusts the calculated pressure drop according to the molecular weight of the fluid at the flare tip using linear interpolation between the specified curves.
Note that FlareNet will not extrapolate past the endpoints of the supplied data. For example, if the calculated molecular weight of the fluid flowing through the flare tip is above that of the highest specified molecular weight, FlareNet will use the pressure drop values from the highest molecular weight that has been supplied. Note also that FlareNet currently does not give any warning messages when you are operating outside the envelope of specified data.
Correction for Temperature
The temperature correction is based on the fact that the pressure drop across the flare tip is related to the velocity and density upstream of the flare tip, according to:
deltaP = K * (1/2) * Rho*V^2 [1]
where
deltaP pressure drop
K fittings loss coefficient
rho homogeneous fluid density
V homogeneous fluid velocity
Also noting that:
Pressure drop is proportional to the density times the square of the velocity (equation [1])
Density is inversely proportional to the absolute temperature
Velocity is proportional to absolute temperature
From 1, 2, and 3, it can be seen that the pressure drop across the flare tip is proportional to the absolute temperature.
Using this information, FlareNet will apply a temperature correction with respect to the reference temperature by multiplying the uncorrected pressure drop by the ratio of the actual temperature at the Flare Tip to the reference temperature. If no reference temperature is specified, then no temperature correction will be carried out.
See alsoSolution ID 109475 How is the tip pressure drop calculated from the diameter and fittings loss variable specified in the tip editor?Solution ID 109487 How can I make the pressure drop calculation across the flare tip dependent on flowrate?Solution ID 112835 How can I specify a fixed pressure drop across a Flare Tip?
Keywords: Flare Tip, pressure drop, pressure drop curves
References: None |
Problem Statement: Are there any examples of programmatically accessing and controlling Aspen FLARENET through OLE Automation?
In Aspen Flareent, the OLE example doesn't work. | Solution: There are several examples in the \Samples\Ole sub-directory of the Aspen FLARENET installation. Additionally other examples will be posted in this folder as they are created.
Information on automation with Aspen FLARENET can be found in Section 12 of the Aspen FLARENET
Keywords: OLE Automation
References: Manual.
The Flarenet2006.Application object is available in the Aspen Flarenet version 2006 (build 20.0.0.557) in the library. The user will get an error message if Flarenet.Application is referred as an object. This is done to control different version in Aspen Flarenet in the same machine.
The user need to open the code and change the the Flarenet.Application to Flarenet2006.Application. |
Problem Statement: Can I have multiple databases to use in different projects? | Solution: Yes, by editing the databases and storing them on your PC in different directories you can use them for different projects. This applies to the piping, fittings and component databases.
Keywords: databases , projects
References: None |
Problem Statement: To run silent installation for Aspen Flare System Analyzer EP patches (or any executable patches in general) | Solution: There is a command line for the patch, which in this case is from KB 132848.
In this example:
Emergency Patch (Aspen Flare System Analyzer V7.3): EP10: Summary
of all hot fixesSolution ID:
132848
Product(s):
Aspen Flare System Analyzer
Version(s):
V7.3
Primary subject:
Patch, Cumulative Patch
Last Modified:
19-Jun-2012
Attached files (filesize):
AFSAV7.3.EP10.exe (2729k):
AFSAV7.3.EP10.exe - New Installation file and need run it as an Administrator
AspenFlareSystemAnalyzerV7.3-EP10.exe (2802k):
AspenFlareSystemAnalyzerV73EP10.exe - the executable zip file and need run Regengine.bat after unzip
The command line to use is AFSAV7.3.EP10.exe /S -a //NoLogo UILevel=2
Note: this patch works for an executable based patch, as it does not run the vbscript. .vbs or .msi installer.
Keywords: Patches, silent installation, Flarenet, no user intervention
References: None |
Problem Statement: Is the Orifice area per valve field on the Relief Valve, a user specified value? | Solution: In the Relief Valve Editor, under Conditions tab, you will see the Orifice area per valve field.
Aspen Flare System Analyzer (AFSA) does not have the capability of calculate a valve orifice size. Hence, user must enter this value.
You have the option to select one of the API 526 standard orifice sizes from the drop down menu or select the Not Defined option in order to specify a custom orifice size.
If your objective is to calculate an orifice size, you should use PSV sizing feature in Aspen HYSYS or Aspen Plus. Further details can be found inSolution 138399. You could later use these PSV sizing calculations in AFSA.
An easy way to include your HYSYS or Aspen Plus results into AFSA, is using the Aspen Plus / HYSYS Relief Valve Sources feature. You could find the detailed steps inSolution ID 144923.
Keywords: Orifice Size, Relief Valve, API, PSV.
References: None |
Problem Statement: What is the velocity value shown on the summary tab of the pipe segment and how is it calculated? | Solution: The velocity on the Summary tab is the superficial velocity. It is calculated using simple formula:
V=Q/A, where Q is volumetric flow rate and A is pipe area
When it is a two phase stream, it represent the bulk superficial velocity which is the sum of superficial gas velocity and superficial liquid velocity. Attached is the excel file which explains in detail how the superficial velocity is calculated. Please note that in this example Sample-S1.fnw provided under Samples folder is used for demonstration.
Keywords: Superficial velocity, pipe segment, vapor phase, liquid phase, summary tab.
References: None |
Problem Statement: How is the valve outlet temperature calculated in Aspen FLARENET? | Solution: If you have selected Ideal Gas as the enthalpy method, Aspen FLARENET is not able to calculate the source outlet temperature, and hence you are required to specify a value in the Outlet Temperature field for the valve.
If you have the enthalpy method set to something other than Ideal Gas (e.g. Peng Robinson), then the user-specified value in the Outlet Temperature field is not used and instead the downstream temperature is obtained from an isenthalpic flash across the valve based on the specified inlet temperature and pressure, composition, and MABP.
Keywords: temperature calculations
References: None |
Problem Statement: How do I increase the display accuracy in Aspen Flare System Analyzer? | Solution: The user can increase or change the display accuracy (decimal points) of data in Aspen Flare System Analyzer. This can be done via File/Preferences. From the Preference Editor select Formatting tab and then click on Edit Variable Formats
This will display Variable Formats Dialog window where the user can select the object and the specific variable associated with that object. For example, Mass Flow format in the source can be changed from object SourceData as highlighted in the screenshot below.
Keywords: Decimal Point, Formatting
References: None |
Problem Statement: Whats the difference between the simple and the Miller Methods for calculating a tee piece? | Solution: The simple method takes into account the relative diameters of the run, branch and tail in calculating the k factors.
The Miller method uses the relative flowrates as well as the diameters in calculating the k factor. This gives a much better accuracy.
Keywords: Miller, Tee, Simple
References: None |
Problem Statement: What does the Use Pipe Class check box in the pipe segment refer to? How do you set up the Pipe Class editor? | Solution: The Use Pipe Class check box in conjunction with the Pipe Class editor allows the user to define which pipe schedules are available for specific pipe diameters. One advantage is that this allows the user to restrict a certain pipe diameter to a particular schedule or prevent that diameter from being available for use, e.g. only 3, 6, 12 and 24 schedule 40 pipe sizes are to be used for a project. This allows for standardization across a particular project.
If the user desires to use this feature, the first step is to define the pipe schedule/pipe diameter associations in the Pipe Class editor. The editor can be accessed via the Tools menu. Once the editor is visible the user can simply choose the correct pipe schedule for each diameter of pipe using the drop down menus. If the pipe schedule for a pipe diameter is set to Do not use that pipe diameter will not be made available for those pipe segments with the Use Pipe Class box checked.
Once the changes in the Pipe Class editor have been set up, the user can then check off the Use Pipe Class box in the appropriate pipe segments. If the Pipe Class feature is to be used within a case that has already been built, the check box must be enabled in each of the desired pipe segments. (Note: it is possible to edit multiple pipes simultaneously. To do so, select Pipes from the Build menu and multi-select the desired pipes by holding down the ctrl key and picking the different pipes from the list.) If the user is using the Pipe Class with a new case, enabling the check box on the Defaults page of the Preferences will ensure each newly created pipe has this option enabled.
Keywords: pipe class, pipe schedule
References: None |
Problem Statement: How do I import components from Aspen HYSYS to Aspen Flare System Analyzer? | Solution: 1. Select File | Import Sources| Aspen HYSYS Sources from the main Aspen Flare System Analyzer menu.
2. Click on the Browse button and choose the Aspen HYSYS simulation file you wish to use as a data source, then press the Open button near the bottom right corner of the dialog to confirm your selection.
3. Next, press the Open button on the Aspen HYSYS Import of Source Data window, ensuring that Use Aspen HYSYS Components is selected in the Component Data dropdown menu (for the purpose of importing the component information, P/T Location doesn't matter).
4. Click the OK button near the bottom right corner of the Aspen HYSYS Import of Source Data window.
The component information for the Aspen HYSYS simulation will be added to the existing component list.
Keywords: import, components, HYSYS components
References: None |
Problem Statement: According to Crane reference, the friction velocity factor for fittings is K = C*fT,
Where fT is the fully turbulent friction factor for clean carbon Steel. With that in mind, K is only dependant of diameter and not of the actual material and roughness of the fitting.
However if I change the material for a fitting in Aspen Flare System Analyzer (leaving the diameter the same), the pressure drop is different, when according to cane it should be the same. Why is that? | Solution: Aspen Flare System Analyzer includes to methods for calculating the K values, using the ft (as Crane reference) or using the actual friction factor f due to the specified material roughness. It uses the simulation-specified friction factor f by default. To use the ft as per Crane you have to go Calculation Options | Methods tab and select fixed roughness in pipe fittings groupbox:
Keywords: Crane API fitting friction velocity
References: None |
Problem Statement: The TAILPIPE / YES option has been selected for a pipe in FlareNet. Are results for this based on nominal flow, or rated flow? | Solution: If Rated Flow For Tailpipes check box (Calculations --> Options --> General tab) is checked, results shown are based on data from both the nominal flow case, and the rated flow case.
Pressure /pressure drops are based on calculations done using rated flow. Call presure at any point in the tailpipe Pr.
Reported mass flow is always nominal mass flow : Call this Mn
Density is calculated using Pr. Call this Dr.
Velocity / Mach number is calculated using Mn and Dr, ie a mix of data.
In the next release of FlareNet the user will have the choice of showing tailpipe data based on either nominal flow or rated flow.
Keywords: Tailpipe
Rated Flow
Nominal Flow
References: None |
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