Investigation of fragmentation and coalescence behavior of ash particles in simulated coal combustion

•Change of numbers of EM and IM particles were measured in a DTF reactor.•Rate constants of EM fragmentation were estimated from simulated EM heating experiment.•Thermal shock resulted in EM fragmentation.•Functions for numbers of EM and IM were derived as a kinetic model.•Rate constants of detachment and coalescence were affected by char structure.

In order to predict ash deposition in a pulverized coal combustion process, the fragmentation, detachment, and coalescence behavior of ash particles in coal were quantitatively evaluated to distinguish between excluded and included minerals. The experiments for simulated EM heating and simulated coal combustion were carried out in a drop tube furnace. Change in the numbers of EM and IM particles were measured at different residence times by scanning a sampling probe along the flow direction in the reactor tube. The rate constants of EM fragmentation were estimated from the simulated EM heating experiment. The solution to a system of differential equations that includes the effects of fragmentation, detachment, and coalescence as functions for the numbers of EM and IM was obtained as a kinetic model. These functions were fitted to the experimental results for simulated coal combustion experiment to obtain the rate constants for detachment and coalescence. This method was also applied to previous experimental results using three actual coal samples. The rate constants of detachment and coalescence were mainly affected by char structure during coal combustion.