Question $1$

A stirred reactor is to neutralise an $HCl$ process stream by adding NaOH

solution $($Fig$.$ Q$1$ in the answer sheet$).$ Specifically, this reactor has $2$

inlet streams $($an $HCl$ and an NaOH aqueous solution stream$)$ and $1$

outlet stream, which is the neutralised process stream. Assume the $HCl$

process stream has only small variations in flow rate and composition

while the NaOH stream is subject to large fluctuations in flow rate due

to sudden variations in supply pressure. The flow rates of the NaOH

stream and the neutralised stream can be manipulated. Level and $pH$

sensors are available. You are required to achieve: $(1)$ keeping the

liquid level at $5m$; and $(2)$ keeping the $pH$ of the neutralised stream at

$7\mathrm{.}0,$ whilst never exceeding $7\mathrm{.}0.$

a$)$ Design control loops for the level and $pH$ control objectives by

completing the partial schematic of shown in Fig. Q$1.$ Identify the

controlled variables, measured variables and manipulated variables in

the system. The control loop schematic should contain controllers,

sensors$,$ and control elements. Explain how your proposed control

loops regulate the controlled variables.