Effect of kinetic, design, and operating parameters on reactor gain

Many industrial reactions are carried out in adiabatic tubular reactors. The desired inlet feed temperature is usually achieved by using the hot reactor effluent to preheat the cold feed in a feed-effluent heat exchanger (FEHE). This positive feedback of energy introduces the potential for open loop instability. Previous papers have explored the control of this type of process. The key parameter in FEME/reactor systems is the reactor gain, i.e. the change in the reactor exit temperature T-out for a given change in the reactor inlet temperature T-in: K-R = Delta T-out/Delta T-in. The larger the reactor gain, the more likely open loop instability will occur and the more difficult the control problem will be. This paper explores the impact of various kinetic, design, and operating parameters on reactor gain. Three reaction systems are studied. The first is the hypothetical reaction A + B --> C, where kinetic parameters (activation energy and heat of reaction) can be varied. Then two real industrial reactions are studied: the hydrodealkylation of toluene (HDA process) and the chlorination of propylene (allyl chloride process), where design parameters (inlet reactant feed concentration and reactor length) are varied. Larger reactor gains occur for increases in reactant feed concentration, activation energy, and heat of reaction. Reactor gains can vary non-monotonically for some design parameters when interactions between concentration and temperature effects occur.