Co-combustion characteristics of coal gasification fly ash and coal gangue preheated by circulating fluidized bed

Abstract

The improper disposal of coal gasification fly ash (CGFA) and coal gangue (CG) is highly susceptible to environmental pollution. Preheating combustion is a proven technology for the efficient combustion of solid fuels. On the basis of this technology and combining the complementary physical properties of CGFA and CG, the synergistic combustion of these two typical solid wastes is expected to occur. In this study, the preheating modification and co-combustion characteristics of CGFA and CG with different blending ratios were investigated. The evolution of the physicochemical structure of the activated char was analyzed via a particle size analyzer, scanning electron microscope, N₂ adsorption–desorption and Raman spectroscopy. The results indicated that stable operation of the preheated combustion system could be achieved when the blending ratio of CG was 25 %-50 %. The apparent structure of the blended fuel can be improved by CGFA, while the specific surface area and chemical reactivity of the resulting char can be increased significantly. The highest activity of the preheated char was achieved at a blending ratio of 25 % (R = 25 %). In addition, there was a synergistic effect between the fixed carbon in CGFA and the volatiles in CG during co-combustion. The combustion efficiency of the blended fuel was improved at blending ratios of 25 % to 50 %. With the comprehensive evaluation of preheating modification and co-combustion characteristics, the optimal blending ratio of CG was R = 25 %. In this case, the NO and N₂O emissions were 121 mg/cm³ (@6% O₂) and 14 mg/cm³ (@6% O₂), respectively.