Experimental Study on the Fluidized Combustion Performance and Emission Characteristics of Full-Range Particle-Size Coal Gasification Fine Slag

A fluidized combustion platform was established to investigate combustion performance and emission characteristics of full-range particle-size coal gasification fine slag (CGFS). The effects of CGFS residence time in main combustion zone, furnace temperature, excess air coefficient, and air distribution were examined. The physicochemical properties and ecological risks of the ash residues were also evaluated. The results show that fluidized combustion significantly improved CGFS burnout compared with combustion of a fixed sample layer in thermogravimetric tests. The residual carbon content was 2.6% at particles residence time of 5 min. Moving secondary air nozzle upward strengthened the reducing atmosphere in main combustion zone and reduced NOx emissions from 267 ppm to 206 ppm. However, the slag discharge measure would be optimized to ensure sufficient effective residence time of bottom ash and enhanced burnout. In fluidized combustion, CGFS showed clear particle fragmentation and particle-size classification. Fe and Ca were enriched in the solid phase, whereas S and Na tended to volatilize, resulting in lower contents in the ash. Ash fusion characteristics indicated a limited slagging tendency within the experimental temperature range. Heavy metal concentrations in the ash leachates were below standard limits, suggesting low leaching toxicity. Thus, the ash residues can be disposed of as general industrial solid waste. However, some elements exceeded their theoretical enrichment values, indicating possible particle-induced furnace wall erosion. The Er and PLI assessment showed a certain cumulative pollution risk. Therefore, heavy metal enrichment in ash residues should be carefully evaluated after CGFS fluidized combustion.