Multifluid modeling of coal pyrolysis in a coupled downer-hopper reactor

In the coal pyrolysis process, the diameter of particles normally changes with the process of reaction, which not only affects the hydrodynamic behavior but also influences the heat generation and yield of the products. However, most of the previous simulation work assumes a constant diameter in the model, which may disobey the law of mass conservation at the particle scale. In this work, a multifluid framework is developed to simulate the coal pyrolysis in a coupled downer-hopper reactor. The advanced kinetic theory for particulate phase stress and particle-particle drag force, the cluster behavior modified gas-particle drag force and gas-particle heat transfer have been considered in the present study. Based on the default constant particle diameter model, the expression of coal particle size and density changing with the reaction process is derived according to the mass conservation of a single particle. Results show that the flow and reaction characteristics, including the particle density and velocity distribution, temperature behavior, pyrolysis rate and yield are significantly affected by the variable particle diameter