Diagrams for Understanding Chemical Processes
- 1.1. Block Flow Diagram (BFD)
- 1.2. Process Flow Diagram (PFD)
- 1.3. Piping and Instrumentation Diagram (P&ID)
- 1.4. Additional Diagrams
- 1.5. Three-Dimensional Representation of a Process
- 1.6. The 3-D Plant Model
- 1.7. Operator and 3-D Immersive Training Simulators
- 1.8. Summary
- Short Answer Questions
The chemical process industry (CPI) is involved in the production of a wide variety of products that improve the quality of our lives and generate income for companies and their stockholders. In general, chemical processes are complex, and chemical engineers in industry encounter a variety of chemical process flow diagrams. These processes often involve substances of high chemical reactivity, high toxicity, and high corrosivity operating at high pressures and temperatures. These characteristics can lead to a variety of potentially serious consequences, including explosions, environmental damage, and threats to people’s health. It is essential that errors or omissions resulting from missed communication between persons and/or groups involved in the design and operation do not occur when dealing with chemical processes. Visual information is the clearest way to present material and is least likely to be misinterpreted. For these reasons, it is essential that chemical engineers be able to formulate appropriate process diagrams and be skilled in analyzing and interpreting diagrams prepared by others.
This chapter presents and discusses the more common flow diagrams encountered in the chemical process industry. These diagrams evolve from the time a process is conceived in the laboratory through the design, construction, and the many years of plant operation. The most important of these diagrams are described and discussed in this chapter.
The following narrative is taken from Kauffman  and describes a representative case history related to the development of a new chemical process. It shows how teams of engineers work together to provide a plant design and introduces the types of diagrams that will be explored in this chapter.
- The research and development group at ABC Chemicals Company worked out a way to produce alpha-beta souptol (ABS). Process engineers assigned to work with the development group have pieced together a continuous process for making ABS in commercial quantities and have tested key parts of it. This work involved hundreds of block flow diagrams, some more complex than others. Based on information derived from these block flow diagrams, a decision was made to proceed with this process.
- A process engineering team from ABC’s central office carries out the detailed process calculations, material and energy balances, equipment sizing, etc. Working with their drafting department, they produced a series of PFDs (Process Flow Diagrams) for the process. As problems arise and are solved, the team may revise and redraw the PFDs. Often the work requires several rounds of drawing, checking, and revising.
- Specialists in distillation, process control, kinetics, and heat transfer are brought in to help the process team in key areas. Some are company employees and others are consultants.
- Since ABC is only a moderate-sized company, it does not have sufficient staff to prepare the 120 P&IDs (Piping and Instrumentation Diagrams) needed for the new ABS plant. ABC hires a well-known engineering and construction firm (E&C Company), DEFCo, to do this work for them. The company assigns two of the ABC process teams to work at DEFCo to coordinate the job. DEFCo’s process engineers, specialists, and drafting department prepare the P&IDs. They do much of the detailed engineering (pipe sizes, valve specifications, etc.) as well as the actual drawing. The job may take two to six months. Every drawing is reviewed by DEFCo’s project team and by ABC’s team. If there are disagreements, the engineers and specialists from the companies must resolve them.
- Finally, all the PFDs and the P&IDs are completed and approved. ABC can now go ahead with the construction. They may extend their contract with DEFCo to include this phase, or they may go out for construction bids from a number of sources.
This narrative describes a typical sequence of events taking a project from its initial stages through plant construction. If DEFCo had carried out the construction, ABC could go ahead and take over the plant or DEFCo could be contracted to carry out the start-up and to commission the plant. Once satisfactory performance specifications have been met, ABC would take over the operation of the plant and commercial production would begin.
From conception of the process to the time the plant starts up, two or more years will have elapsed and millions of dollars will have been spent with no revenue from the plant. The plant must operate successfully for many years to produce sufficient income to pay for all plant operations and to repay the costs associated with designing and building the plant. During this operating period, many unforeseen changes are likely to take place. The quality of the raw materials used by the plant may change, product specifications may be raised, production rates may need to be increased, the equipment performance will decrease because of wear, the development of new and better catalysts will occur, the costs of utilities will change, new environmental regulations may be introduced, or improved equipment may appear on the market.
As a result of these unplanned changes, plant operations must be modified. Although the operating information on the original process diagrams remains informative, the actual performance taken from the operating plant will be different. The current operating conditions will appear on updated versions of the various process diagrams, which will act as a primary basis for understanding the changes taking place in the plant. These process diagrams are essential to an engineer who has been asked to diagnose operating problems, solve problems in operations, debottleneck systems for increased capacity, and predict the effects of making changes in operating conditions. All these activities are essential in order to maintain profitable plant operation.
In this chapter, the focus is on three diagrams that are important to chemical engineers: block flow, process flow, and piping and instrumentation diagrams. Of these three diagrams, the most useful to chemical engineers is the PFD. The understanding of the PFD represents a central goal of this textbook.
1.1. Block Flow Diagram (BFD)
Block flow diagrams were introduced early in the chemical engineering curriculum. In the first course in material and energy balances, often an initial step was to convert a word problem into a simple block diagram. This diagram consisted of a series of blocks representing different equipment or unit operations that were connected by input and output streams. Important information such as operating temperatures, pressures, conversions, and yield was included on the diagram along with flowrates and some chemical compositions. However, the diagram did not include any details of equipment within any of the blocks.
The block flow diagram can take one of two forms. First, a block flow diagram may be drawn for a single process. Alternatively, a block flow diagram may be drawn for a complete chemical complex involving many different chemical processes. These two types of diagrams are differentiated by calling the first a block flow process diagram and the second a block flow plant diagram.
1.1.1. Block Flow Process Diagram
An example of a block flow process diagram is shown in Figure 1.1, and the process illustrated is described below.
Figure 1.1. Block Flow Process Diagram for the Production of Benzene
- Toluene and hydrogen are converted in a reactor to produce benzene and methane. The reaction does not go to completion, and excess toluene is required. The noncondensable gases are separated and discharged. The benzene product and the unreacted toluene are then separated by distillation. The toluene is then recycled back to the reactor and the benzene removed in the product stream.
This block flow diagram gives a clear overview of the production of benzene, unobstructed by the many details related to the process. Each block in the diagram represents a process function and may, in reality, consist of several pieces of equipment. The general format and conventions used in preparing block flow process diagrams are presented in Table 1.1.
Table 1.1. Conventions and Format Recommended for Laying Out a Block Flow Process Diagram
Operations shown by blocks.
Major flow lines shown with arrows giving direction of flow.
Flow goes from left to right whenever possible.
Light stream (gases) toward top with heavy stream (liquids and solids) toward bottom.
Critical information unique to process supplied.
If lines cross, then the horizontal line is continuous and the vertical line is broken (hierarchy for all drawings in this book).
Simplified material balance provided.
Although much information is missing from Figure 1.1, it is clear that such a diagram is very useful for “getting a feel” for the process. Block flow process diagrams often form the starting point for developing a PFD. They are also very helpful in conceptualizing new processes and explaining the main features of the process without getting bogged down in the details.
1.1.2. Block Flow Plant Diagram
An example of a block flow plant diagram for a complete chemical complex is illustrated in Figure 1.2. This block flow plant diagram is for a coal to higher alcohol fuels plant. Clearly, this is a complicated process in which there are a number of alcohol fuel products produced from a feedstock of coal. Each block in this diagram represents a complete chemical process (compressors and turbines are also shown as trapezoids), and a block flow process diagram could be drawn for each block in Figure 1.2. The advantage of a diagram such as Figure 1.2 is that it allows a complete picture of what this plant does and how all the different processes interact to be obtained. On the other hand, in order to keep the diagram relatively uncluttered, only limited information is available about each process unit. The conventions for drawing block flow plant diagrams are similar to Table 1.1.
Figure 1.2. Block Flow Plant Diagram of a Coal to Higher Alcohol Fuels Process
Both types of block flow diagrams are useful for explaining the overall operation of chemical plants. For example, consider that you have just joined a large chemical manufacturing company that produces a wide range of chemical products from the site to which you have been assigned. You would most likely be given a block flow plant diagram to orient you to the products and important areas of operation. Once assigned to one of these areas, you would again likely be provided with a block flow process diagram describing the operations in your particular area.
In addition to the orientation function described earlier, block flow diagrams are used to sketch out and screen potential process alternatives. Thus, they are used to convey information necessary to make early comparisons and eliminate competing alternatives without having to make detailed and costly comparisons.
Mchoro wa Kuelewa Utaratibu wa Kemikali - 1.1. Block Flow Diagram (BFD) - 1.2 Process Flow Diagram (PFD) - 1.3. Pipe na Instrumentation Diagram (P&ID) - 1.4. Picha za ziada - 1.5. Uwakilishi wa tatu wa mchakato - 1.6. Mfano wa Mimea ya 3D - 1.7. Opereta na 3-D Immersive Mafunzo Simulators - 1.8. Maelezo mafupi: Sekta ya kemikali inahusika katika uzalishaji wa bidhaa mbalimbali ambazo zinaongeza ubora wa maisha yetu na kuzalisha mapato kwa makampuni na wanahisa wao. Kwa ujumla, michakato ya kemikali ni ngumu, na wahandisi wa kemikali katika sekta ya kukutana na aina mbalimbali ya michakato ya kemikali mtiririko michoro. Mara nyingi michakato hiyo huhusisha vitu vyenye uwezo mkubwa wa kemikali, sumu nyingi, na uharibifu mkubwa vinavyofanya kazi kwa shinikizo na halijoto kubwa. Sifa hizi zinaweza kusababisha athari mbalimbali zenye uwezekano mkubwa, ikiwa ni pamoja na milipuko, uharibifu wa mazingira, na vitisho kwa afya ya watu. Ni muhimu kwamba makosa au kutokuwepo kutokana na kukosa mawasiliano kati ya watu na au makundi kushiriki katika kubuni na uendeshaji si kutokea wakati wa kushughulika na michakato ya kemikali. Habari ya kuona ndiyo njia iliyo wazi zaidi ya kueleza habari na ni rahisi zaidi kueleweka vibaya. Kwa sababu hizi, ni muhimu kwamba wahandisi wa kemikali waweze kuunda michoro sahihi ya mchakato na kuwa na ujuzi wa kuchambua na kutafsiri michoro iliyoandaliwa na wengine. Sura hii inatoa na kujadili chati za mtiririko za kawaida zinazopatikana katika sekta ya mchakato wa kemikali. Mchoro huu huanza wakati mchakato unapotengenezwa katika maabara hadi wakati wa kubuni, ujenzi, na miaka mingi ya uendeshaji wa kiwanda. Muhimu zaidi ya michoro hii ni ilivyoelezwa na kujadiliwa katika sura hii. Hadithi ifuatayo inachukuliwa kutoka kwa Kauffman na inaelezea historia ya kesi ya mwakilishi inayohusiana na maendeleo ya mchakato mpya wa kemikali. Inaonyesha jinsi timu ya wahandisi kufanya kazi pamoja kutoa kubuni kiwanda na kuanzisha aina ya michoro ambayo itakuwa kuchunguzwa katika sura hii. Kampuni ya ABC Chemicals imepata njia ya kutengeneza alpha-beta-suptol (ABS). Wahandisi wa mchakato waliopewa kazi ya kufanya kazi na kikundi cha maendeleo wamekusanya mchakato wa kuendelea wa kutengeneza ABS kwa wingi wa kibiashara na wamejaribu sehemu muhimu za mchakato huo. Kazi hiyo ilihusisha mamia ya michoro ya mtiririko wa vitalu, baadhi yao wakiwa tata kuliko nyingine. Kwa kuzingatia habari inayotokana na michoro hii ya mtiririko wa block, uamuzi ulifanywa kuendelea na mchakato huu. - timu ya uhandisi mchakato kutoka ofisi kuu ABC hufanya mahesabu ya mchakato wa kina, nyenzo na nishati mizani, vifaa ukubwa, nk. Kwa kushirikiana na idara ya uchoraji, waliunda safu ya PFD (Process Flow Diagrams) kwa mchakato. Kama matatizo kutokea na ni kutatuliwa, timu inaweza kurekebisha na redraw PFDs. Mara nyingi kazi hiyo huhitaji michoro kadhaa, ukaguzi, na marekebisho. - Wataalamu katika distillation, mchakato wa kudhibiti, kinetics, na uhamisho wa joto ni kuletwa katika kusaidia timu ya mchakato katika maeneo muhimu. Baadhi yao ni wafanyakazi wa kampuni na wengine ni washauri. Kwa kuwa kampuni ya ABC ni ndogo, haina wafanyakazi wa kutosha kuandaa P&I 120 zinazohitajika kwa kiwanda kipya cha ABS. Kampuni ya ujenzi ya E&C, ambayo ni kampuni ya uhandisi na ujenzi, imepewa jukumu la kuunda mfumo wa ujenzi. Kampuni hiyo inatoa timu mbili za mchakato wa ABC kufanya kazi katika DEFCo kuratibu kazi. DEFCo's mchakato wahandisi, wataalamu, na idara ya uchoraji kuandaa P&IDs. Wao hufanya mengi ya uhandisi wa kina (ukubwa wa bomba, vipimo vya valve, nk.) kama vile mchoro halisi. Kazi hiyo yaweza kuchukua miezi miwili hadi sita. Kila mchoro ni kukaguliwa na DEFCo ya mradi wa timu na na ABC ya timu. Ikiwa kuna kutoelewana, wahandisi na wataalamu kutoka makampuni lazima wavumilie. - Mwishowe, PFDs zote na P&IDs zimekamilika na kupitishwa. ABC sasa inaweza kuendelea na ujenzi. Wanachama wanaweza kupanua mkataba wao na DEFCO ili kujumuisha awamu hii, au wanaweza kwenda kwa zabuni za ujenzi kutoka vyanzo kadhaa. Hadithi hii inaelezea mfululizo wa kawaida wa matukio kuchukua mradi kutoka hatua zake za awali kupitia ujenzi wa mmea. Ikiwa DEFCO ingekuwa imefanya ujenzi, ABC ingeweza kuendelea na kuchukua kiwanda au DEFCO ingeweza kupewa mkataba wa kufanya kuanza na kuanzisha kiwanda. Baada ya kukamilika kwa vipimo vya utendaji, ABC itachukua operesheni ya kiwanda na uzalishaji wa kibiashara utaanza. Kuanzia wakati wa kuanzishwa kwa mradi huo hadi wakati wa kuanza kwa ujenzi, miaka miwili au zaidi itapita na mamilioni ya dola zitakuwa zimetumika bila mapato yoyote kutoka kwa mradi huo. Kiwanda lazima kifanye kazi kwa mafanikio kwa miaka mingi ili kuzalisha mapato ya kutosha kulipia shughuli zote za kiwanda na kulipia gharama zinazohusiana na kubuni na kujenga kiwanda. Wakati wa kipindi hiki cha uendeshaji, mabadiliko mengi yasiyotazamiwa yanaweza kutokea. Ubora wa malighafi zinazotumiwa na kiwanda inaweza kubadilika, vipimo vya bidhaa vinaweza kuongezeka, viwango vya uzalishaji vinaweza kuhitaji kuongezeka, utendaji wa vifaa utapungua kwa sababu ya kuvaa, maendeleo ya catalysts mpya na bora yatatokea, gharama za huduma zitabadilika, kanuni mpya za mazingira zinaweza kuanzishwa, au vifaa bora vinaweza kuonekana kwenye soko. Kwa sababu ya mabadiliko hayo yasiyotazamiwa, shughuli za kiwanda lazima zibadilishwe. Ingawa habari ya uendeshaji juu ya michoro ya mchakato wa awali bado ni ya habari, utendaji halisi uliochukuliwa kutoka kwa kiwanda cha uendeshaji utakuwa tofauti. Hali ya sasa ya uendeshaji itaonekana kwenye matoleo ya kisasa ya michoro mbalimbali ya mchakato, ambayo itafanya kazi kama msingi wa msingi wa kuelewa mabadiliko yanayotokea katika kiwanda. Mipango hii ni muhimu kwa mhandisi ambaye ameombwa kugundua matatizo ya uendeshaji, kutatua matatizo katika shughuli, debugging mifumo kwa ajili ya kuongeza uwezo, na kutabiri athari za kufanya mabadiliko katika hali ya uendeshaji. Shughuli hizi zote ni muhimu ili kudumisha shughuli ya kiwanda faida. Katika sura hii, lengo ni juu ya michoro tatu ambayo ni muhimu kwa wahandisi wa kemikali: block mtiririko, mchakato mtiririko, na mabomba na instrumentation michoro. Kati ya michoro hii mitatu, moja ya muhimu zaidi kwa wahandisi wa kemikali ni PFD. Uelewa wa PFD inawakilisha lengo kuu la kitabu hiki. 1.1. Block Flow Diagram (BFD) ni mfumo wa kuunda na kuunda michoro ya mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko. Katika kozi ya kwanza katika usawa wa vifaa na nishati, mara nyingi hatua ya kwanza ilikuwa kugeuza tatizo neno katika mchoro rahisi block. Mchoro huu ulijumuisha mfululizo wa vitalu vinavyowakilisha vifaa tofauti au shughuli za kitengo ambazo ziliunganishwa na mito ya pembejeo na pato. Habari muhimu kama vile joto la uendeshaji, shinikizo, kubadilisha, na mavuno ilijumuishwa kwenye mchoro pamoja na viwango vya mtiririko na baadhi ya muundo wa kemikali. Hata hivyo, mchoro huo haukutia ndani maelezo yoyote ya vifaa ndani ya yoyote ya vitalu. block mtiririko mchoro inaweza kuchukua moja ya aina mbili. Kwanza, block mtiririko mchoro inaweza kuchorwa kwa ajili ya mchakato mmoja. Vinginevyo, block mtiririko mchoro inaweza kuchorwa kwa ajili ya kamili kemikali tata kuhusisha michakato mingi tofauti ya kemikali. Aina hizi mbili za michoro ni tofauti kwa wito wa kwanza block mtiririko mchakato mchoro na pili block mtiririko mmea mchoro. 1.1.1 Uwezo wa Mfano wa block mtiririko mchakato mchoro ni kuonyeshwa katika Picha 1.1, na mchakato kuonyeshwa ni ilivyoelezwa hapa chini. Picha ya 1. Block Mtiririko Process Chati kwa ajili ya Uzalishaji wa Benzene - Toluene na hidrojeni ni kubadilishwa katika reactor kuzalisha benzene na methane. Mmenyuko huo haufanyi kazi kikamili, na tolueni nyingi inahitajika. Gesi zisizoweza kuyeyushwa hutenganishwa na kutolewa. Bidhaa ya benzene na toluene unreacted ni kisha kutenganishwa kwa distillation. Toluene ni kisha recycled nyuma kwa reactor na benzene kuondolewa katika mkondo wa bidhaa. Mchoro huu wa mtiririko wa block hutoa muhtasari wazi wa uzalishaji wa benzene, unobstructed na maelezo mengi yanayohusiana na mchakato. Kila block katika mchoro inawakilisha mchakato kazi na inaweza, katika hali halisi, lina vipande kadhaa ya vifaa. Mfano wa kawaida na mikataba kutumika katika kuandaa block mtiririko mchakato michoro ni kuonyeshwa katika Jedwali 1.1. Tabla ya 1. Mikataba na Format ilipendekezwa kwa ajili ya Laying nje Block Mtiririko Process Diagram Operesheni iliyoonyeshwa na vitalu. Mistari mikubwa ya mtiririko iliyoonyeshwa na mishale inayoonyesha mwelekeo wa mtiririko. Mtiririko huenda kutoka kushoto kwenda kulia iwezekanavyo. Mtiririko mwepesi (gesi) kuelekea juu na mtiririko mzito (umajimaji na vitu vyenye nguvu) kuelekea chini. Taarifa muhimu ya kipekee kwa mchakato zinazotolewa. Kama mistari msalaba, basi mstari wa usawa ni kuendelea na mstari wima ni kuvunjwa (hierarchy kwa michoro yote katika kitabu hiki). Usawazishaji wa nyenzo uliotolewa. Ingawa habari nyingi zinakosa kutoka kwa Mchoro 1.1, ni wazi kwamba mchoro kama huo ni muhimu sana kwa <unk> kupata hisia <unk> kwa mchakato. Block mtiririko michoro mara nyingi fomu ya kuanzia kwa ajili ya kuendeleza PFD. Pia ni muhimu sana katika conceptualizing michakato mpya na kueleza sifa kuu ya mchakato bila kupata bogged chini katika maelezo. 1.1.2 Uwezo wa Mfano wa block-mtiririko mzunguko mzunguko mzunguko mzunguko kwa ajili ya kamili kemikali tata ni kuonyeshwa katika Picha 1.2. Hii block mtiririko mmea mchoro ni kwa ajili ya makaa ya mawe kwa juu ya pombe mafuta mmea. Ni wazi kwamba hii ni mchakato ngumu ambayo kuna idadi ya bidhaa za mafuta ya pombe zinazozalishwa kutoka kwa malighafi ya makaa ya mawe. Kila block katika mchoro huu inawakilisha mchakato kamili wa kemikali (compressors na turbines pia ni kuonyeshwa kama trapezoids), na block mtiririko mchakato mchoro inaweza kuchorwa kwa kila block katika Picha 1.2. Faida ya mchoro kama vile Picha 1.2 ni kwamba inaruhusu picha kamili ya nini kiwanda hiki hufanya na jinsi mchakato wote tofauti kuingiliana. Kwa upande mwingine, ili kuweka mchoro kiasi uncluttered, tu habari mdogo inapatikana kuhusu kila kitengo mchakato. Mifumo ya kuchora block mtiririko kiwanda ni sawa na Jedwali 1.1. Picha ya 1.2. Block Flow Plant Diagram ya Process ya Makaa ya Mawe ya Alcohol ya Juu Aina zote mbili za block flow diagrams ni muhimu kwa kuelezea utendaji wa jumla wa mimea ya kemikali. Kwa mfano, fikiria kwamba umejiunga na kampuni kubwa ya kutengeneza kemikali ambayo hutengeneza bidhaa mbalimbali za kemikali katika eneo ambalo umewekwa rasmi. Kwa kawaida, unaweza kupata mchoro wa mimea ya mtiririko wa block ili kukuelekeza kwenye bidhaa na maeneo muhimu ya operesheni. Mara baada ya kupewa moja ya maeneo haya, wewe ingekuwa tena uwezekano wa kuwa zinazotolewa na block mtiririko mchakato mchoro kuelezea shughuli katika eneo lako maalum. Mbali na orientation kazi ilivyoelezwa hapo awali, block mtiririko michoro ni kutumika kwa kuchora nje na skrini uwezekano mchakato mbadala. Kwa hivyo, zinatumiwa kutoa habari muhimu kufanya kulinganisha mapema na kuondoa mbadala zinazoshindana bila kufanya kulinganisha kwa kina na gharama kubwa.