Experimental investigation on thermal modification and burnout of residual carbon in coal gasification fine slag

Disposal of coal gasification fine slag (CGFS) has caused environmental pollution and resource waste. Its decarbonization is the bottleneck of aluminum and silicon resource utilization. A fluidization-melting combustion system is proposed in this study to realize the decarbonization. The fluidized thermal modification and burnout characters of residual carbon in CGFS were investigated experimentally on a bench-scale test rig. A two-stage decarburization path of CGFS was concluded and verified. The fluidized modification of CGFS is first conducted to decrease the particle size and improve the specific surface area and combustion reactivity. So, the modified exposed carbon in CGFS rapidly burns in the melting furnace to generate the condition above the fluid temperature of minerals. Then the mineral shell of the amorphous mineral covered carbon in CGFS is molten and damaged, and the carbon appears and burns out. The decrease in the thermal modification temperature induced deceases in melting combustion temperature and decarbonization efficiency. Efficient decarbonization of CGFS produced by three different entrained bed gasifiers was realized by the fluidization-melting combustion, the decarburization efficiencies are all above 95% and the comprehensive carbon contents of ash and slag are all below 5%.