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Temperature Controller Problem

 Suppose a chemical reactor is heated by steam. A temperature controller varies the amount of steam admitted to a “jacket” surrounding the reactor:

Temperature Controller Problem



Ever since this process was placed into service, operators have complained about poor temperature control. Several technicians have tried to tune the PID controller, but no combination of tuning constants seems to solve the problem of random reactor temperature fluctuations.

Then one day you notice that the “random” fluctuations of temperature are not really random at all: they directly follow fluctuations in steam supply pressure over time.

Explain the nature of the control problem (why do variations in steam supply pressure affect the reactor temperature?), and propose a solution for it.

Answer:
As the steam supply pressure rises and falls, a greater or lesser steam flow will result through the temperature valve (TV) for any given stem position.

The simplest and most direct solution to this problem is to stabilize the steam supply pressure: determine what is causing the pressure to fluctuate, and fix it!

Question for you:
Like so many real-life problems, there are usually multiple solutions. Try brainstorming more than one practical solution to this control problem! (assume possible cases).


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