Integrating multi-scale mass transfer model with discrete-DAEM to simulate the coal pyrolysis in a novel conical-type downer pyrolyzer

Abstract

The performance of a novel conical-type downer pyrolyzer is carefully evaluated via numerical simulation. The study explicitly accounts for mass transfer effects by using a multi-scale mass transfer model. To achieve simultaneous high precision and computational efficiency, an enhanced strategy for calculating the multi-scale mass transfer coefficient in heterogeneous phase reaction systems is proposed by treating mass transfer and reaction as independent processes. This strategy is coupled with a discrete distributed activation energy model formulated in the Arrhenius framework. A comprehensive analysis is performed to investigate the axial distributions of key parameters, including the average concentration of solid reactants (X_s), the volatile concentration on particle surfaces (X_sf), and the volatile concentration in the bulk gas phase (X_f) under varying pyrolysis temperatures, carrier gas velocities, and solid mass fluxes. The findings reveal that X_s and X_f exhibit intuitive, monotonic trends, while X_sf demonstrates a more complex behavior, increasing due to ongoing reactions yet decreasing with mass transfer proceeding. The simulation results verify the advantages of the conical-type downer pyrolyzer, which can achieve significantly higher volatile concentrations than conventional designs.