CO2 conversion to synthetic natural gas: Reactor design over Ni–Ce/Al2O3 catalyst

Abstract

Within the Power-to-Gas concept, the catalytic conversion of renewable hydrogen and carbon dioxide to methane for injection to the gas grid has recently attracted much attention. In the present work, the implementation of a nickel–ceria–alumina catalyst on a multitubular reactor for CO2 methanation was studied. The reaction kinetics were experimentally obtained and considered for a CFD model by means of Ansys® Fluent software, to evaluate the behaviour of a multitubular heat-exchange reactor. The simulations showed that most reaction occurs at the beginning of the reactor tube and the temperature raises rapidly. At the kinetic regime zone, a proper control of the temperature is required to avoid excessive hot-spots. In contrast, the final reactor volume is mainly controlled by the reaction thermodynamics. In this zone, the reaction is shifted toward products by using a cooling medium at low temperature. The effect of several design variables on the final methane yield and on the temperature profile was carried out, and finally, a reactor able to convert the CO2 present in the biogas to synthetic natural gas is proposed. The modelling showed that the proposed reactor tube (di=9mm and L=250mm) should be able to obtain a high methane content (>95%), at high GHSV (14,400h−1), and keeping the hot-spots at minimum (Δ100K). Within this reactor design approach, almost 1000 of tubes are necessary for the methanation of a medium-size biogas plant.