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GATE 2021 CH – Question 41

Instrumentation and Process Control · Controller modes, control valves and tuning · 2 marks · Multiple choice

It is required to control the volume of the contents in the jacketed reactor shown in the figure. Which one of the following schemes can be used for feedback control?

V-1 controls reactant inflow, V-2 cooling-water inflow, and V-3 product outflow. L101 measures reactor level, T101/T102 temperatures, and F101 product flow.
  1. Measure L101 and manipulate valve V-2
  2. Measure T101 and manipulate valve V-1
  3. Measure L101 and manipulate valve V-3
  4. Measure F101 and manipulate valve V-1

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Show answer and explanation

Correct answer: (C) Measure L101 and manipulate valve V-3

Explanation

For a reactor with fixed cross section, volume is determined by liquid level. A feedback loop for volume must therefore measure **L101**, the level, and act on a flow that changes the inventory.

Valve **V-3** controls product outflow. Opening it when the level is high reduces the inventory; closing it when the level is low allows inventory to recover. Thus measuring L101 and manipulating V-3 provides volume feedback.

V-2 affects jacket cooling, while T101 and F101 measure temperature and flow rather than the controlled inventory. **Answer: C.**