Simulation of non-catalytic gas–solid reactions: application of grain model for the reduction of cobalt oxide with methane

Abstract

A mathematical model based on grain model, is presented. The model considers dynamic changes of gas and solid concentrations and temperature in the pellet of the solid reactant. In addition, structural changes of solid reactant (porosity and grain size changes) and diffusion of gaseous reactants through the product layer are considered. Effective diffusion coefficient is assumed to change with porosity in the pellet as a quadratic function in the mass balance equation. Effective heat capacity and conductivity are also modelled as functions of porosity in the heat balance equation. The finite volume method has been selected for solving mass and heat balance equations in the pellet and the computations are done by a program developed in MATLAB. The results of the program show good agreement in comparison with analytical solutions for both isothermal and non-isothermal systems. The model was used to simulate the reduction of cobalt oxide with methane and also the carbon gasification reaction with carbon dioxide. The results show good agreement for experimental conditions where both chemical kinetics and product layer diffusion are significant in the first reaction and the reaction obeys a non-linear chemical kinetics in the second reaction.