$2.$ Currently, standard feedback controllers $($PI or PID$)$ are employed for controlling the

variables, which have been found to be less effective in controlling the variations in some

of the control loops. It is suggested that model$-$based control can help to improve the

performance of certain critical loops. As an appointed control engineer, you have

identified that the available process control loops of the Reppe Process follow Tennessee

Eastman Process Flowsheet as in FIGURE Q$2.$

FIGURE Q$2$: Tennessee Eastman Process Flowsheet

a$.$ From the available information, select a minimum of TWO $(2)$ control loops that

would benefit the most from the model$-$based control strategies, and design

model$-$based controllers of your choice for those loops. With appropriate

justifications based on relevant process knowledge and proper references, you

may assume the process models for the associated control loops to be firstorder system.

$[15$ marks$]$

b$.$ Operability is important because of process conditions change. For the Reppe

process in FIGURE Q$1,$ identify a minimum of THREE $(3)$ possible sources of

variability that require operability analysis. Cite all references.

$[6$ marks$]$