note_4_last_topc - Fall 2004 ICE Topics: Process Control by...

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Fall 2004 ICE Topics: Process Control by Design 10.492 Lecture Notes 5: What lies beyond revised 2004 Dec 17 Dr. Barry S. Johnston, Copyright 2004. 1 we should emphasize that our heat exchanger work has all been at steady state In approaching the heat exchanger network, we took the point of view that early in design, we did only steady state calculations. Thus we used steady-state energy balances to describe normal operation in the network. We calculated the RGA and DC from a linear system approximation to these equations, and used it to make statements about controllability. There is not a contradiction here, merely a simplification: RGA and DC tell us the results of disturbances that moved the operation from one steady-state to another. To say any more about the time required to reach the new steady state, or the path followed, or the effects of continuing disturbances, we must make a dynamic analysis. Seider et al (3) show how the RGA and DC may be extended to account for time-varying disturbances. In particular, they show that the severity of control loop interaction can vary with the frequency content (that is, the time-varying nature) of the input disturbance. These topics are beyond our scope, but you should return to them if you do this again for money. but here’s a transient problem that we wouldn’t have caught with the RGA: Kister (1) describes how trace components in a feed stream may accumulate to considerably higher concentrations in distillation towers. Imagine a chemical species with lower volatility
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This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

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note_4_last_topc - Fall 2004 ICE Topics: Process Control by...

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