Heat management of thermally coupled reactors for conducting
simultaneous endothermic and exothermic reactions
Computational fluid dynamics simulations are carried out to better understand how to manage thermally coupled reactors for conducting simultaneous endothermic and exothermic reactions. Particular emphasis is placed upon the mechanisms involved in the heat transfer processes in thermally coupled reactors for hydrogen production by steam reforming. The effects of catalyst layer thickness on the enthalpy of reaction, methanol conversion, and hydrogen yield are delineated. The oxidation and reforming reaction rates involved in the endothermic and exothermic processes are determined. Contour maps denoting temperature, enthalpy, and species mole fractions are constructed and design recommendations are made. The results indicate that the waste heat can efficiently be recovered in a low-temperature region, although the reactivity of a steam reforming reaction is low in such a region. The steam reforming device is configured as to be heated by part of the combustion heat to cause a steam reforming reaction in the device. The steam reforming reaction is endothermic and is therefore typically carried out in an externally heated steam reforming reactor. The incorporation of a simultaneous exothermic reaction to provide an improved heat source can provide a typical heat flux of roughly an order of magnitude above the convective heat flux. Structured catalysts offer heat transfer benefits and extra activity, which is more effective in the inlet zone of the steam reformer. The metallic support is formed substantially to have the same shape as the reactor wall and is arranged in a direct heat conduction relationship with the reactor wall. Desirably all of the tubes contain the same proportions of structured catalyst and particulate catalyst, which provides the benefits of the higher activity, higher heat transfer, and low pressure drop of the structured catalyst at the inlet end and the benefit of the stronger particulate catalyst at the outlet end. Heat transport is more efficient when catalyzed hardware is used in the steam reforming process.
Keywords: Heat transfer; Heat management; Heat fluxes; Heat losses; Heat resistances; Heat exchange