Analysis of Gas-Assisted Pulverized Coal Combustion in Cambridge Coal Burner CCB1 Using FPV-LES

摘要

Gas-assisted pulverized coal combustion in the laboratory-scale Cambridge Coal Burner configuration CCB1 is studied using a large eddy simulation (LES) coupled with a multistream flamelet/progress variable (FPV) model in an Euler-Lagrange framework. The FPV-LES implementation is coupled with an enthalpy correction method for two-phase energy transfer. Both nonreacting and reacting (pure pilot and coal flame) cases are simulated, and the simulation results are compared with the experimental evidence. The agreement of the simulation results with the measurements is found to be reasonable. However, it is necessary to note that the experimental data mainly focus on the far upstream region where coal combustion effects are limited. The flame structures of the pure pilot flame and coal flame are carefully analyzed across the entire simulation domain. Different gas flame modes are identified for the coal flame as a function of the downstream coordinate, namely typical premixed flame (far upstream), double flame (middle), and typical nonpremixed flame (far downstream). The time histories of coal particles are traced to demonstrate the relation between gas flame modes and the devolatilization process. Moreover, the average distance between the particles is used to distinguish between the group combustion mode found near the center of the burner and the individual particle combustion mode located in the outer region of the flame, which is in agreement with experimental observations. This study provides new insights into the flame characteristics of swirling gas-assisted pulverized coal flames and adds to the knowledge database on FPV-LES modeling of pulverized coal combustion.