CFD Numerical Simulation Study on Thermal Decomposition of Nickel Carbonate-Doped Calcium Carbonate Coupled with Hydrogen to Methane

Abstract Thermal decomposition of industrial CaCO3 is a major source of CO2 in cement and metallurgy. Coupled with H2, it yields methane, which enables carbon reduction and valorization. Ni doping lowers the reaction temperature and enhances CH4 selectivity, yet theoretical studies on heat transfer and process parameters remain insufficient. This work employs CFD to investigate the cothermal methanation of Ni-doped CaCO3 with H2 in a tubular fixed-bed reactor. A 2D axisymmetric local thermal equilibrium porous media model is developed via a UDF. Results show that Ni doping reduces the complete decomposition temperature by 150 K and accelerates decomposition at Tw = 850 K. Higher Tw promotes both CaCO3 conversion and CH4 production; smaller particle diameter favors decomposition; and in fine-particle systems, increased porosity more effectively improves conversion. This study elucidates Ni-doping effects from heat-transfer enhancement and reaction-coupling perspectives, providing theoretical guidance for low-temperature efficient conversion in CaCO3–H2 coheating systems toward industrial CO2 mitigation.