Design of a Multi-Tubular Catalytic Reactor Assisted by CFD Based on Free-Convection Heat-Management for Decentralised Synthetic Methane Production

Abstract

A simple reactor design for the conversion of CO2 methanation into synthetic methane based on free convection is an interesting option for small-scale, decentralised locations. In this work, we present a heat-management design of a multi-tubular reactor assisted by CFD (Ansys Fluent®) as an interesting tool for scaling-up laboratory reactor designs. The simulation results pointed out that the scale-up of an individual reactive channel (d = 1/4′, H = 300 mm) through a hexagonal-shaped distribution of 23 reactive channels separated by 40 mm allows to obtain a suitable decreasing temperature profile (T = 487-230 °C) for the reaction using natural convection cooling. The resulting heat-management configuration was composed of three zones: (i) preheating of the reactants up to 230 °C, followed by (ii) a free-convection zone (1 m/s air flow) in the first reactor section (0-25 mm) to limit overheating and, thus, catalyst deactivation, followed by (iii) an isolation zone in the main reactor section (25-300 mm) to guarantee a proper reactor temperature and favourable kinetics. The evaluation of the geometry, reactive channel separation, and a simple heat-management strategy by CFD indicated that the implementation of an intensive reactor cooling system could be omitted with natural air circulation.