MODELLING AND EXPERIMENTAL VALIDATION OF A CO2 METHANATION ANNULAR COOLED FIXED-BED REACTOR EXCHANGER

A simulation model of a fixed-bed reactor-exchanger dedicated to CO2 methanation on an industrial Ni/gamma-Al2O3 catalyst has been built on the basis of experimental characterization of heat transfer and kinetic parameters. An effective thermal conductivity of the bed and a wall heat transfer coefficient are determined from cooling experiments of different Ar-H-2 mixtures (thermal conductivity 0.02-0.25 W . m(-1) . K-1) at different Reynolds numbers (particle Reynolds number 1-50). The flow dependent component of the Nusselt number correlates to the gas Prandtl number as Pr-0.72. These heat transfer parameters and a kinetic model adapted to the Ni/g-Al2O3 catalyst are integrated in mass, heat, and momentum balance equations in the bed and at the particle scale to build a 2D heterogeneous model of the fixed-bed reactor. CO2 methanation experiments in an annular fixed-bed reactor-exchanger filled with 400 g of Ni/gamma-Al2O3 catalyst at pressures from 0.4 to 0.8 MPa and coolant temperatures from 473 to 548 K (200 to 275 degrees C) are described in this paper and simulated by the model. CO2 conversion rate and CH4 selectivity at the reactor outlet and temperature elevations in the reactor are simulated by the model with a discrepancy lower than 10 %. For pressures above 0.4 MPa, a strong mass diffusion limitation inside the catalyst particles is shown and the efficiency decrease of the three reactions is explained.