Evolution of particulate matter in the post-combustion zone of Zhundong lignite

Understanding the conversion of particulate matter (PM) in the post-combustion zone is important for controlling the emissions and ash deposition from coal combustion. In this study, the evolution of PM in the post-combustion zone of coal was investigated experimentally and numerically. The air combustion of three Zhundong lignite was performed in a drop tube furnace. PM was sampled at different flue gas temperature from 473K to 1273K. Low pressure impactor, X-ray fluorescence, scanning electron microscope, and scanning mobility particle sizer were applied to analyze mass-based particle size distribution (MPSD), elemental compositions, morphology, and number-based particle size distribution (NPSD) of PM. The results show that when the flue gas temperature decreases from 1273K to 473K, the MPSD and compositions of PM_0.4-10 remain stable, while PM_0.4 moves towards larger particle size. The reduction of NaCl concentration in the flue gas between 1073K and 1273K may be due to the sulfation of NaCl. The critical condensation temperature of NaCl in flue gas is between 843K and 902K. When the flue gas was sampled beyond the critical condensation temperature, NaCl vapors is converted to PM_0.4 through nucleation and condensation during the cooling of the sampling system. The particle size distribution of submicron particles in the post-combustion zone is well described by an aerosol dynamics model with moment method. In the post-combustion zone of Zhundong lignite, coagulation is the dominate mechanism controlling the evolution of PM_0.4 from 1273K to 473K.