Numerical study of sorption-enhanced methane steam reforming over Ni/Al2O3 catalyst in a fixed-bed reactor

Abstract

The present work deals with the Sorption-Enhanced Methane Steam Reforming (SE-MSR), an interesting and energy-efficient hydrogen production route with in situ CO2 capture. A computational fluid dynamics (CFD) model for an industrial-scale fixed-bed reactor, with Ni/Al2O3 as catalyst and CaO as an adsorbent for CO2 capture, is developed taken into consideration also the coke deposition. Temperature is shown to be the key parameter of the SE-MSR chemical process at large scales. H2 production is constant and maximum until the saturation of CaO sorbent occurs, after which the concentrations of all the other compounds start to vary, and the efficiency of the process begins to drop. When the exothermic carbonation reaction stops, an alteration of the thermal regimes is observed. The absence of the contribution of the exothermic carbonation reaction results in a decrease of the temperature, which in turn determines a lower conversion of CH4 and H2O, according to the endothermic reforming reactions.The maximum H2 outlet mole fraction (dry basis) is 0.8, and it occurs in the presence of CO2 sorption; the value drops to 0.42 once the adsorbent reaches its maximum conversion degree. The molar selectivity in hydrogen relative to the quantity of CH4 fed to the reactor is of the order of 1.75 (with CO2-capture) and 0.8 (without CO2 capture).The molar fluxes obtained and the kinetics of the system model show the excellent choice of the operating conditions of the catalyst to produce a large quantity of hydrogen as well as of the adsorbent, which eliminates the CO2 responsible of coke deposition.