Simulation of the coal pyrolysis process in downer reactor with a mass transfer model based on the spatial superposition assumption

A mass transfer model based on the spatial superposition assumption is constructed to investigate the coal py-rolysis process in the downer. The simulated volatiles yield using this developed model are in better agreement with the experimental data than that based on the conventional Jung-La Nauze equation. It is found that the mass transfer coefficients (Kf) calculated by the Jung-La Nauze equation are approximately two orders of magnitude higher than that of this work, indicating that the mass transfer process predicted with the uniform structure is overestimated. Moreover, the concentration difference between the surface of dilute particles and gas bulk is small and close to zero, which means that the reaction is the rate controlling step, while the concentration difference between the surface of the clusters and gas bulk is relatively large, which implies that the mass transfer process also becomes the rate controlling step. All these results obtained in this work are expected to deepen the understanding of the mass transfer and reaction process by considering the influence of heterogeneous structures in gas-solid fluidized system.

Automated summary

A mass transfer model based on the spatial superposition assumption is developed to study the coal pyrolysis process. The simulated volatiles yield using this model shows better agreement with experimental data compared to the conventional Jung-La Nauze equation. It is found that the mass transfer coefficients calculated by the Jung-La Nauze equation are overestimated, indicating an overestimation of the mass transfer process predicted with a uniform structure. The results provide insights into the mass transfer and reaction process in gas-solid fluidized systems by considering the influence of heterogeneous structures.