Page 414 - Analysis, Synthesis and Design of Chemical Processes, Third Edition
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of stages in the extractor, case studies in which the number of stages are varied can be performed, and this
                    information used to determine the correct number of stages required to obtain the desired recovery of
                    98%. In other cases, such as a plug flow reactor module, the simulator can solve the design problem
                    directly—that is, calculate the amount of catalyst required to carry out the desired reaction. Therefore,
                    before  one  starts  a  process  simulation  it is  important  to  know  what  equipment  parameters  must  be
                    specified in order for the process to be simulated.


                    There are essentially two levels at which a process simulation can be carried out. The first level, Level 1,
                    is  one  in  which  the  minimum  data  are  supplied  in  order  for  the  material  and  energy  balances  to  be
                    obtained. The second level, Level 2, is one in which the simulator is used to do as many of the design
                    calculations  as  possible.  The  second  level  requires  more  input  data  than  the  first. An  example  of  the
                    differences between the two levels is illustrated in Figure 13.4, which shows a heat exchanger in which a
                    process stream is being cooled using cooling water. At the first level, Figure 13.4(a), the only information
                    that  is  specified  is  the  desired  outlet  condition  of  the  process  stream—for  example,  pressure  and

                    temperature or vapor fraction—if the stream is to leave the exchanger as a two-phase mixture. However,
                    this is enough information for the simulator to calculate the duty of the exchanger and the properties of the
                    process stream leaving the equipment. At the second level, Figure 13.4(b), additional data are provided:
                    the inlet and desired outlet temperature for the utility stream, the fact that the utility stream is water, the
                    overall heat transfer coefficient, and the heat-exchanger configuration or effectiveness factor, F.  Using
                    this information, the simulator calculates the heat-exchanger duty, the required cooling water flowrate,
                    and the required heat transfer area.


                    Figure 13.4 Information Required for Different Levels of Simulation
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