You have been transferred to a $1,4-$butanediol $($C$4$H$10$O$2)$ production plant following your

recent appointment as process control engineer. One of your main responsibilities

involves process control improvement projects for a high quality of product production.

$1,4-$butanediol is a colorless and non$-$corrosive solution which is widely used as a

solvent in the industry to manufacture elastic fibers, technical plastics and

polyurethanes. Commonly, Reppe and Davy processes are the two widely used and

well$-$established alternative processes available to produce $1,4-$butanediol.

After a thorough study of the unit, you and your team feel certain that tighter control can

improve the yield of the product and reduce operating costs.

In your analysis, Reppe process as illustrated in FIGURE Q$1$ is studied. The raw

materials needed for Reppe process are formaldehyde $($CH$2$O$),$ acetylene $($C$2$H$2)$ and

hydrogen $($H$2).$ Formaldehyde and acetylene are fed into two batch reactors which

operate at $5$ bar, $80$o

C and are arranged in parallel. Formaldehyde is reacted with

acetylene in the presence of copper, bismuth and silicon dioxide supporting catalyst to

produce $1,4-$butynediol as an intermediate product with a conversion rate of $60\%.$

Aqueous sodium hydroxide and hydrochloric acid are used to maintain the pH of the

medium in the reactor within the range of pH $6$ to $8.$ The product from the batch reactors

is sent to a tank and is stored for approximately $130$ h before feeding to a distillation

column for further separation. After separation, the bottom product stream of the

distillation column is rich in $1,4-$butynediol and is fed to a trickling and hydrogenation

reactor for further reaction to produce $1,4-$butanediol as the main product with a

conversion rate of $90\%.$ The operating condition of this reactor is $160$o

C and $150$ bar.

Currently, standard feedback controllers are employed for controlling the key variables

in the distillation column. To convince the top$-$level management on the benefits of

advanced control, it is imperative for your team to prove that enhanced control can work

on this part.

You are required to perform the following:

a$.$ Identify the key control objectives and possible disturbances for the distillation

column.

Design enhanced control strategies for energy efficiency and product purity of

the distillation column. Your design must include the appropriate schematic

diagram of the proposed control strategies, detailed justification on the selection

of the proposed control strategies, and explanation on the effectiveness of the

proposed strategy in improving energy efficiency and product purity. Cite all

references.