Control of Outlet Temperature in Adiabatic Tubular Reactors

Abstract

Adiabatic tubular reactors are used in many industrial processes. The conventional control scheme for these reactors is to maintain the inlet temperature to the reactor. However, the optimum operation of the entire process (reaction and separation sections) often requires that the reactor be run at the highest possible temperature, which occurs under steady-state conditions at the reactor exit if the reactions are exothermic. The process studied in this paper has the exothermic, irreversible, gas-phase reaction A + B → C occurring in an adiabatic tubular reactor. A gas recycle returns unconverted reactants from the separation section. Four alternative plantwide control structures for achieving reactor exit temperature control are explored. The reactor exit temperature controller changes different manipulated variables in three of the four control schemes: (1) CS1, the set point of the reactor inlet temperature controller is changed; (2) CS2, the recycle flow rate is changed; and (3) CS3, the flow rate of...