Exothermic and endothermic reaction characteristics and operation methods of integrated combustion-reforming reactors

Abstract

Catalytic reactors for carrying out endothermic or exothermic reactions are of great importance in the particular examples being reactors for the endothermic steam reforming of methanol and reactors for the exothermic catalytic combustion reaction. The present study aims to provide a fundamental understanding of the exothermic and endothermic reaction characteristics and operation methods of integrated combustion-reforming reactors. Particular emphasis is placed upon the simultaneous implementation of the endothermic steam reforming and the heat-supplying exothermic catalytic combustion such that the thermal stability of the reaction system is increased. The effect of catalyst layer thickness on the reaction characteristics is investigated in order to understand how to design and operate such reactors with high efficiency. The results indicate that unique jet design features can be implemented in order to suppress homogeneous combustion and promote heterogeneous catalytic combustion on the channel wall. Diffusion within these small pores in the catalyst layers is typically Knudsen in nature for gas phase systems, whereby the molecules collide with the walls of the pores more frequently than with other gas phase molecules. The composition in the combustion chamber is reacted to produce sufficient heat to sustain the micro-combustion process without energy input. The combustion and reforming processes can be stably and efficiently operated at lower temperatures, without the need for energy input to sustain or even to start the combustion process. Since a palladium component is alloyed with the zinc, generation of carbon monoxide due to the methanol decomposition reaction is suppressed. Direct heating is of considerable advantage as it largely overcomes the problems encountered with reaction rates being limited by the rate of heat transfer through the tube wall especially near the reformer entrance. The conventional methods are suitable for large scale hydrogen gas production, but they are not adequate for middle to small scale hydrogen gas production. As the channel dimension nears the quench diameter or drops below, the contribution of the unwanted gas phase homogeneous combustion reaction is reduced. Keywords: Catalytic reactors; Reaction characteristics; Heat exchange; Carbon monoxide; Partial oxidation; Thermal stability