Numerical simulation of a reactor for heterogeneous pyrolysis of hydrocarbon gases over biochar granules

Abstract

A mathematical model of a high-temperature reactor for the pyrolysis of hydrocarbon gases during filtration through a porous carbon medium formed by carbonized wood granules is presented. A system of nonstationary differential equations describing reactor operation in cyclic mode was numerically solved. Methane and a mixture (methane, ethane, propane, butane, and nitrogen) resembling associated petroleum gas were used as feed hydrocarbon gases. The dependencies of pyrocarbon and hydrogen yields, the degree of hydrocarbon gas conversion, and gas mixture compositions at the reactor outlet on the specific mass flow rate of the feed gas were calculated. The influence of the reactor radius on the density inhomogeneity of the resulting carbon–carbon composite, pyrocarbon, and hydrogen productivities of the reactor was considered. It is shown that the dependence of the reactor productivity for both pyrocarbon and hydrogen on the methane mass flow rate has an optimum and, in the case of APG, grows in the whole considered range of the raw gas flow rate variation. The increase of the reactor radius leads to a decrease of its specific productivity (per unit cross section of the reactor) and a deterioration of the quality of the obtained composite, which is expressed in an increase of the variation of its density. For production of gas mixtures with high hydrogen content, it is necessary to use modes with low mass flow rate of raw gas. The obtained regularities allow to choose optimal technological parameters depending on the target product — carbon composite or hydrogen-enriched gas mixtures.

Graphical abstract