Insights into the catalytic CO2 methanation of a boiling water cooled fixed-bed reactor: Simulation-based analysis

This article presents the simulation-based analysis of experimental results from a catalytic fixed-bed reactor for the methanation of CO2. During previously published experiments, temperature profiles inside bidisperse catalyst-silicon carbide fixed-beds were gathered and reactant conversions at the reactor outlet measured. On the basis of the temperature profiles along the fixed-bed length and outlet reactant conversions, a procedure for the numerical characterisation of these results was developed. Primary parameters like the inserted multipoint thermocouple and the heat transfer coefficient between reactor wall and surrounding boiling water cooling are systematically investigated. Concerning the binary bidisperse fixed-beds of porous catalyst cylinders and highly thermal conductive silicon carbide, a simple numerical method for the determination of the effective heat conductivity of the bed is presented. The modelling of effective reaction rates within an industrial sized catalyst and reactor is a non-trivial task, due to interlinking aspects like intrinsic reaction rate and internal and external transport limitations. Intrinsic reaction rate, internal and external transport limitations are linked, what makes a separate investigation challenging. Thus, a step by step analysis is presented and the single effects investigated in detail. From the results of the stepwise numerical characterisation, an excellent agreement between experiments and numerics was reached. Additionally, a novel partially resolved 3D fixed-bed reactor model is presented and selected results like particle overheating presented. Overall the present numerical investigations provided a deep insight into the methanation of CO2 in a cooled fixed-bed reactor.