June 14, 2015
June 14, 2015
June 17, 2015
26.233.1 - 26.233.7
Process simulators allow students to perform in-depth analyses of chemical process designs, includingeconomic optimization, due to the ability to run multiple case studies rapidly. However, students oftenuse them carelessly and treat the results superficially. One example of careless use of a process simulator is when a zoned analysis is needed for a heatexchanger. Many chemical processes have a liquid feed that must be vaporized and superheated beforeentering a reactor, requiring a multi-zone heat exchanger. The typical simulator interface for a heatexchanger requires one input for a heat transfer coefficient, which does not correctly model a multi-zoneheat exchanger. Each zone must be treated as a separate heat exchanger. Another example occurs whenstudents are taught about heat integration and include it in a design. A heat exchanger that, for example,uses a reactor effluent stream to help preheat the reactor feed might have a close temperature approach. Itis very common to see a 1-2 exchanger used without regard for the low, or even impossible, log-mean-temperature-difference correction factor. Another commonly observed situation is a reactor with heat exchange that is way oversized, becausethe concentration profiles were not examined, and the product composition has either leveled out or begunto decrease due to side reactions. Experience shows that it is one thing for students to answer questionsabout selectivity in a reaction engineering class, but it is different when they have to recognize poorselectivity in the context of a simulation. Examples of these and other similar situations will be presented, along with suggested methods forteaching students to simulate their processes correctly. It is hoped that the audience will participate andsuggest other examples of the careless use of process simulators.
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