Extensions of the simultaneous design of gas-phase adiabatic tubular reactor systems with gas recycle

Luyben studied the simultaneous design of a simple gas-phase tubular reacto r system with a single feed stream and independent reactor preheating and c ooling for a reversible reaction. Reyes and Luyben studied an irreversible reaction system with a reactor feed preheating system (feed-effluent heat e xchanger 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 s ystems (a distillation column) for gasphase tubular reactors with liquid re cycle 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 irreversibl e reaction system is studied for nonequimolal reactant concentrations. The exothermic gas-phase reaction A + B <-> C occurs in an adiabatic tubular re actor. A gas recycle returns unconverted reactants from the separation sect ion consisting of a simple separator in which product C is removed in the l iquid 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 f urnace heat input leads to a better dynamic performance. In the irreversibl e case, a higher reactor inlet temperature improves dynamics.