Present day water spray based dust removal technologies do not effectively remove respirable submicron coal and silica dust particles in the underground coal mines causing Coal worker’s pneumoconiosis (CWP). The objective of this research was to study the electrostatic charges present in the airborne coal dust in order to develop efficient water spraying based dust removal technology where water drops charged using ionic compounds and surfactants would be used to capture the oppositely charged coal particles. In an experimental scrubbing column, coal particles dispersed in an air stream by a Fluidized Bed Aerosol Generator were captured by water drops sprayed by an atomizer. Characterization studies performed using an Aerodynamic Particle Sizer and Aerosol Electrometer showed that airborne coal particles have a significant amount of positive charge with an average of 140 elementary units of charge. The capture efficiencies of the water drops evaluated were found to be higher than those predicted by previously determined mathematical models. It was predicted that apart from the effects of Brownian diffusion, interception and impaction, the effect of Coulombic attraction was present and the charge of the water drops was predicted to be between - 2 x 10-6 C and -2 x 10-4 C.

Beetle-killed trees and woody residues degenerate and may lead to wildfires and uncontrolled CO2 emission. Woody biomass is known as a neutral CO2 solid fuel since it generates the same amount of CO2 that takes from atmosphere during its growing up. Cofiring woody biomass with coal in existing coal power plants is a reasonable solution to reduce the net amount of CO2 emission and decrease the risk of wildfires. However, there are some challenges ranging from providing and handling the woody biomass to the operation of cofiring woody biomass with coal. Co-milling of the fuels and ash deposition on the heat exchanger surfaces during cofiring are among the most critical challenges. A CFD model simulated the behavior of the pulverized particles and evaluate the impact of geometry and operational changes on mill performance. In addition, we measured the ash deposit rate derived from cofiring woody biomass with coal in a pilot combustor (1500 kW) and full-scale furnace. Moreover, we developed a model to predict ash deposit rate during combustion of coal and its blend with a variety of biomass. The post-processing analysis of CFD modelling of co-milling woody biomass with coal shows that the entrained large woody biomass particles exit the pulverizer along with the fine coal particles due to their lower density than that of coal particles. Some simple geometry and operational changes can optimize mill performance by reducing the number of large biomass particles in the product stream. Therefore, it makes the particle size distribution (PSD) of the product stream of co-milling more like that of coal. The collected data set of fly ash particles and ash deposit samples shows that the ash formation and deposit rates were not impacted significantly by cofiring woody biomass with coal. The concentration of alkali metals in the ash aerosol during cofiring was slightly higher than that of coal. Cofiring in pilot scale combustor made a tri-modal PSD of ash aerosol particles; however, the distribution was bimodal in the full-scale boiler. The ash deposit rates during cofiring in 1500 kW combustor were higher (30 to 70%) at locations closer to the burner at short operation times. Our developed model of ash deposit rate investigated two types of stickiness models of fly ash particles to the surface of heat exchanger: melt fraction stickiness model (MFSM) and kinetic energy stickiness model (KESM). The developed model suggested that the MFSM, which is based on the melt fraction of ash and our novel approach to condensation of alkali vapor species, was more accurate in predicting ash deposit rate of a variety of fuel combustion of a 100-kW combustor. The model calculated four mechanisms: inertial impaction, thermophoresis, condensation, and eddy impaction.