4/8/2013 1 DEVELOPMENT OF CHEMICAL PROCESSES CHE-644 Simulation of Chemical Processes Abubakar Tafawa Balewa University Chemical Engineering Programme 1 El-Nafaty Definition of Simulation • Simulation : Process of designing an operational model of a system and conducting experiments with this model for the purpose of either understanding the behavior of the system or of evaluating alternative strategies for the development or operation of the system. It has to be able to reproduce selected aspects of the behavior of the system modeled to an accepted degree of accuracy.
Definition of Simulation • Simulation: Process of designing an
operational model of a system and conducting experiments with this model for the purpose of either understanding the behavior of the system or of evaluating alternative strategies for the development or operation of the system. It has to be able to reproduce selected aspects of the behavior of the system modeled to an accepted degree of accuracy.
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The Manufacturing Process(Saider, Seider and Lewin)
Figure: Interrelation between Design and simulation activities
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Typical steps in development of new chemical process
• R&D group of company ATIL worked out a way of producing a new chemical ABS.
• Process Engineers of ATIL are assigned to work with the development group to piece out a continuous process of producing ABS in commercial quantities. (This step involves hundreds of BFD’s, of varying complexity.
• Based on the BFD’s, a decision was made to proceed with the process.
• A process engineering team (PET) in CHEP_ATBU carries out detailed process calculations i.e. materials and energy balances, equipment sizing etc.
Typical Steps ……• PET in conjunction with the drafting department (DD)
produced a series of PFD’s (Process Flow Diagrams) for the process.; (this steps may involve several rounds of drawing, checking and revising as problems arise).
• PET consults with specialists in distillation, process control, kinetics and heat transfer to assist in key areas. The specialists may be in house or external consultants.
• ATIL may not have sufficient staff to prepare the 120 P&ID’s (Piping and Instrumentation Diagrams) needed for the new plant. ATIL hires a reputable engineering and construction firm DEFCo LTD to carry out this job for them.
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• ATIL assigns two of its PET members to work with DEFCoon the job. DEFCo’s process engineers, specialists and drafting department prepared the detailed P&ID’s (pipe sizes, valve specifications etc.). Every drawing is reviewed by DEFCo’s project team and ATIL;s team and all areas of disagreements are mutually resolved by the two teams. This step may take two to six months.
• Finally, all the PFD’s and P&ID’s are completed and approved. ATIL can now go ahead with construction. They may contract out construction to DEFCo, or they may engage another company.
• Commissioning and start-up
Typical Steps ……
• The period from conception of the process to the time the plant starts up, may take two or more years and hundreds of millions of Naira will have been spent with no revenue from the plant!!!.
Typical Steps ……
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• Possible challenges that may occur after a chemical plant is commissioned:
• The quality of the raw materials used by the plant may change,
• Product specifications may be raised, • Production rates may need to be increased, • Equipment performance will decrease because of
wear, • Development of new and better catalysts will occur,
Challenges
• Costs of utilities will change, • New environmental regulations may be
introduced, • Improved equipment may appear on the market. • Actual performance taken from the operating
plant may differ from the original diagrams.•• As a result of these unplanned changes, plant
operations must be modified leading to difference between actual performance taken from the operating plant and the information on the original process diagrams.
Challenges…..
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Stages in Chemical Process Design
1. Inception2. Preliminary evaluation of economics and market3. Development of data necessary for final design4. Final economic evaluation5. Detailed engineering design6. Procurement7. Construction8. Startup and trial runs9. Production
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• Block Flow Diagram (BFD):– A simple representation of a process as, operating conditions (T,P), block showing basic process information such as input and output streams, conversion and recovery. Process Flow Diagram (PFD):– Give more detailed information on streams, utilities, equipment and topology. Process units are shown using standard symbols. Piping and Instrumentation Diagram (PID):– Most detailed of the diagram including all mechanical aspects of the process. It is the final design needed by engineers to begin construction work.
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Table: Conventions for laying out typical BFD
1. Operations shown by blocks.2. Major flow lines shown with arrows giving
direction of flow.3. Flow goes from left to right whenever possible.4. Light stream (gases) toward top with heavy stream
(liquids and solids) toward bottom.5. Critical information unique to process supplied.6. If lines cross, then the horizontal line is continuous
and the vertical line is broken. 7. Simplified material balance provided.Note: There are two forms of BFD’s.
Block Flow Process Diagram and Block Flow Plant Diagram (see slides 12-13)
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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.
Example. Typical process description for production of Benzene via hydrodealkylation of Toluene
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Figure: Block Flow Diagram (BFD) for production of Benzene via Hydro-dealkylation of Toluene
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Figure: Block Flow Plant Diagram for Coal to Higher Alcohol fuels process 16El-Nafaty – OCT-2011
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Process Flow Diagram (PFD)
Ø Contain more information hence more detailed and complex than BFDs.
Ø Contains the bulk of the chemical engineering data necessary for the design of a chemical process.
Ø Typical contents of a PFD (may vary from one company to another).:1. All the major pieces of equipment in the process will be represented on the
diagram in standard symbols along with a description of the equipment. Each piece of equipment will have assigned a unique equipment number and a descriptive name.
2. All process flow streams will be shown and identified by a number. A description of the process conditions and chemical composition of each stream will be included. These data will be displayed either directly on the PFD or included in an accompanying flow summary table.
3. All utility streams supplied to major equipment that provides a process function will be shown.
4. Basic control loops, illustrating the control strategy used to operate the process during normal operations, will be shown.
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Figure: Symbols for Process Flow Diagrams (may vary slightly from one company to another) 18El-Nafaty – OCT-2011
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The basic information provided by a PFD can be categorized intoi-Process topology, ii-stream information and iii Equipment information.
1. Process topology: The location of and interaction between equipment and process streams. Each major piece of process equipment is identified by a number on the diagram. General format for identifying equipment is XX-YZZ A/B, whereXX refers to C - Compressor or Turbine; E - Heat Exchanger; H - Fired HeaterP – Pump; R – Reactor; T - TowerTK - Storage Tank; V – Vessel;
Y designates an area within the plantZZ is the number designation for each item in an equipment classA/B identifies parallel units or backup units not shown on a PFD
2. Stream information: Data regarding each stream3. Equipment information: Data regarding each equipment
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Topology: Example of equipment identification
Consider the unit operation P-101A/B and what each number or letter means.
• P-101A/B identifies the equipment as a pump• P-101A/B indicates that the pump is located in area 100
of the plant• P-101A/B indicates that this specific pump is number 01
in unit 100.• P-101A/B indicates that a back-up pump is installed.
Thus, there are two identical pumps P-101A and P-101B. One pump will be operating while the other is idle.
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Table: Conventions for identifying process and utility streams
Process StreamsAll conventions shown in Table 1.1 apply.Diamond symbol located in flow lines.Numerical identification (unique for that stream) inserted in diamond.Flow direction shown by arrows on flow lines.
Utility Streamslps Low-pressure Steammps Medium-pressure Steamhps High-pressure Steamhtm Heat Transfer Media cw Cooling Water: wr River Water: rw Refrigerated Waterrb Refrigerated Brine
cs Chemical Waste Water ss Sanitary Waste Water el Electric Heat ng Natural Gasfg Fuel Gasfo Fuel Oilfw Fire Water
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Table: Stream Information provided in a typical flow summary
* MOC – materials of construction26El-Nafaty – OCT-2011
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Table : Equipment summary for Benzene Process
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Table : Equipment summary for Benzene Process ..cont
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EXAMPLES1. From the given PFD and the stream information,
perform an overall material balance on the process and verify if the balance equation is satisfied.
2. From the given PFD and the stream information, perform an overall energy balance on the benzene distillation unit and verify if the balance equation is satisfied.
3. Determine the conversion per pass of toluene to benzene in Reactor R-101 if conversion is defined as:
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100% ×=IntroducedTolueneproducedBenzeneConversion
References:Alexandre C. Dimian (2003), “Integrated Design and Simulation
of Chemical Processes”, Elsevier, Vol 13 of Elsevier Series in Computer-Aided Chemical Engineering.
Turton, R., Bailie, R. C., Whiting, W. B., and Shaeiwitz (2003), “Analysis, Synthesis, and Design of Chemical Processes”, 2nd
Edition, Prentice Hall Int.
Seider, W. D., Seader, J. D., and Lewin, D. R., “Product and Process Design Principles: Synthesis, Analysis and Evaluation”, 2nd Edition, John Wiley & Sons Inc.
