Extensions of the Simultaneous Design of Gas-Phase Adiabatic Tubular Reactor Systems with Gas Recycle

Abstract

Luyben studied the simultaneous design of a simple gas-phase tubular reactor system with a single feed stream and independent reactor preheating and cooling for a reversible reaction. Reyes and Luyben studied an irreversible reaction system with a reactor feed preheating system (feed-effluent heat exchanger and furnace) but assumed equimolal concentrations of reactants in the recycle gas. A simple separation was assumed in both of these studies. Reyes and Luyben recently explored systems with more realistic separation systems (a distillation column) for gas-phase tubular reactors with liquid recycle and with a dual recycle system. This paper extends this work for two cases: (1) the reversible reaction system is explored with a realistic feed preheating system and with two fresh feed streams, and (2) the irreversible reaction system is studied for nonequimolal reactant concentrations. The exothermic gas-phase reaction A + B ⇔ C occurs in an adiabatic tubular reactor. A gas recycle returns unconverted reactants from the separation section consisting of a simple separator in which product C is removed in the liquid phase and reactants A and B are recycled in the gas phase back to the reactor inlet. Optimum steady-state economic designs are shown to lead to poor dynamic responses. Slight modifications of the plant design lead to a much more easily controlled plant. In the reversible case, the additional furnace heat input leads to a better dynamic performance. In the irreversible case, a higher reactor inlet temperature improves dynamics.