Project ForgeA CSTR with a liquid phase endothermic reaction has two independent single control loops: a temperature controller (TC/TT) manipulating a steam valve V1, and a level controller (LC/LT) manipulating the product valve V2. Changes in physical properties are negligible. Which ONE of the following statements is TRUE?
- AChanging the level controller set point affects the opening of V2 ONLY
- BChanging the temperature controller set point affects the opening of V2 ONLY
- CChanging the temperature controller set point affects the opening of BOTH V1 and V2
- Changing the level controller set point affects the opening of BOTH V1 and V2
Explanation
Even though the loops are wired independently, changing the LEVEL set point changes the liquid volume (and hence residence time) in the CSTR, which changes the extent of the endothermic reaction and the heat duty required to hold temperature at its set point — the TC loop will respond by repositioning V1 to compensate. So a level set-point change affects BOTH V1 (indirectly, via the process interaction) and V2 (directly). Conversely, a temperature set-point change doesn't affect the mass/volume balance governing the level loop, so it affects V1 only.
Source: GATE CH 2011 (2011)
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