In an exothermic chemical reactor under temperature control, which flow rate is most commonly selected as the manipulated variable to regulate reactor temperature while maintaining safe operation and stable conversion?

Introduction / Context:
Exothermic chemical reactors generate heat as reactions proceed. Without proper temperature control, runaway or poor selectivity can occur. In industrial practice, the temperature control loop must manipulate an accessible variable that swiftly influences heat removal or addition while keeping the reactor stable and safe.

Given Data / Assumptions:

• Reactor is exothermic and jacketed or coil-cooled.
• Goal is to control reactor temperature tightly around a set point.
• Manipulated variable should provide fast, direct effect on energy balance.

Concept / Approach:
For exothermic systems, removing excess heat is the primary need. Adjusting coolant flow rate (or coolant inlet temperature) directly changes the heat removal term in the energy balance: Q_removed = U * A * ΔT_effective. A higher coolant flow typically increases the heat transfer coefficient and reduces jacket outlet temperature, raising the driving force for heat removal. By contrast, manipulating reactant flow can affect both heat generation and residence time, coupling material and energy balances and often lagging in response. Product flow is even less direct for temperature control.

Step-by-Step Solution:

Verification / Alternative check:
Typical P&IDs show reactor temperature controllers (TIC) sending output to a valve on the coolant line (manipulating coolant flow) or to a mixing station that sets coolant temperature. This confirms industry convention.

Why Other Options Are Wrong:

Common Pitfalls:
Overlooking coolant inlet temperature as an alternative MV; both coolant flow and inlet temperature are valid, but flow is most common.

Final Answer:
Coolant