Lnyben?s original proposal (1994) for the Alternative 2 control structure incorporated a reactor level controller using F₀ as the manipulated variable. However, the level controller prevents specifying the plant?s production rate by a flow controller on F₀, as can be done with Alternative 1. To deal with the problem that arises when F₀ is allocated for Level control, Luyben proposed that the steady- state relation given by Eq. 23-11 be rewritten to provide a type of feedforward control based on measurements of z_0?nd F_0.?F_sp, the set point of the reactor effluent flow controller, can be used to approximate F. The set point for the reactor level controller would then be:

In the following steps, you are to evaluate Luyben? proposed alternative. If necessary, detune any of the controllers to keep oscillations to a minimum.

(a) Determine how Luyben?s proposed alternative structure responds to a step change in z₀.

(b) Implement Luyben?s proposed feedforward controller, that is, the equation above, and implement a similar step change in z₀.

(c) What can you say about the speed of response of this controlled plant with and without the feed- forward controller?

(d) What are the advantages and disadvantages of Luyben?s proposal?

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