Entropy generation minimization of steam methane reforming reactor with linear phenomenological heat transfer law

Abstract

This paper investigates a class of tubular plug flow steam methane reforming reactor coupling among heat exchange, fluid flow and chemical reaction, in which the heat transfer between the heat reservoir outside the conversion tube and the reactants inside the tube is assumed to obey the linear phenomenological heat transfer law [ q ∝ Δ ( T − 1 ) ]. Under the condition that all of the hydrogen production rate, the inlet pressure, the total inlet molar flow rate, the inert gas (N2) molar flow rate are given, and the reservoir temperature is assumed to be controllable completely, both the minimum entropy generation rate of the process and the corresponding optimal reservoir temperature profile are obtained for minimizing the total entropy generation due to heat transfer, fluid flow and chemical reaction and by applying the theory and method of finite time thermodynamics with the help of nonlinear programming method. The obtained results are also compared with other two classes of reference reactors under the heat transfer strategies of constant and linear reservoir temperature operations and the optimization results for the minimum entropy generation of the case with Newtonian heat transfer law [ q ∝ Δ ( T ) ]. The results show that compared to the two classes of the reference reactors, optimizing the reservoir temperature profiles could reduce the entropy generation by more than 58%, which is mainly due to the decrease in the entropy generation caused by heat transfer; a shorter reactor may perform equally well, and the optimal path shows immediate regions of either a constant thermal force or a constant chemical force; heat transfer laws have significant effects on the optimal temperature configurations of both the heat reservoir and the reaction mixture for the minimum entropy generation of the chemical reactor.