Question

3. (26pts) Consider the fol I I. * * * 2.6 nsider the following distillation column pressure control sch distillation column pressure, the pressures distillation Column Ad cause a serious safety a manipulating the unco rol chemsTot biective is to maintain a desired distillation inulating the uncondensable vapors vent flow. Note that the distillation lumn should not be too high, otherwise the process would cause a serious safe (a) (2pt) Discuss the objectives of this control (b) (2pt) What is the measured output? (C) (2pt) What is the manipulated input? (d) (2pt) What are possible disturbances? (e) (2pt) Is this a continuous or batch process? (1) (2pt) Is this a feedforward or feedback controller? (8) (2pt) Draw the control block schematic diagram. (h) (2pt) Is the process gain relating the manipulated flow rate to the measured temperature positive or negative? (i) (3pt) Should a A-C or A-O valve be selected? Why? 6) (3pt) should the temperature controller have direct or reverse action? Why? (k) (4pt) If process fluid inlet flowrate can be measurable and the cascade control will be applied. Draw the cascade control block schematic diagram.

Answer 1

Answer a - The objective of this control strategy is to maintain a desired distillation column pressure.

Answer b - Measured output in this problem is flow rate of vapour coming from the top plate(stage).

Answer c - Manipulated input in this problem is the uncondensable vapours vent flow.

Answer d - Possible disturbance can be feed flow rate, feed composition, Reflux ratio because by changing any three our vapour flow rate coming from top plate will change so our pressure will change and we have to maintain desired pressure.

Answer e - This is continuous process.

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