Numerical study on suspension co-combustion of pressurized coal gasification fine ash and bituminous coal: Effect of radial over-fire air ratio on combustion and slagging characteristics

Pressurized coal gasification fine ash (CGFA) is a byproduct of modern coal gasification processes. Current disposal methods, such as landfilling and stockpiling, have caused serious environmental pollution problems. Suspension combustion offers a viable route for its large-scale utilization. To further optimize the operating conditions of suspension combustion, this study employs the CFD method to simulate in-furnace flow, temperature, and gas distribution characteristics, investigating the effect of the radial over-fire air (ROFA) ratio (30%, 40%, 50%, 60%, 70%) on the co-combustion and slagging characteristics of pressurized CGFA and bituminous coal. The results show that at ROFA ratios of 30% and 70%, a stable flow field cannot be established in the furnace, and the combustion temperature is too low to meet the co-combustion conditions of pressurized CGFA and bituminous coal. At ROFA ratio of 50–60%, a favorable radial air-staged combustion is formed in the primary combustion zone, with an enlarged high-temperature region, creating a stable high-temperature environment for the burnout of pressurized CGFA. By adjusting the ROFA ratio, NO x emissions can be reduced to a minimum of 289.32 mg/m 3 @6%O 2 when ROFA ratio = 70%. When ROFA ratio = 50%–60%, low NO x emissions 322.46–332.90 mg/m 3 @6%O 2 are achieved while ensuring efficient char burnout and moderate particle adhesion rates on the walls of the pre-combustion chamber (PCC) and the furnace. Considering both the co-combustion and slagging characteristics, the recommended ROFA ratio for the co-combustion of pressurized CGFA with bituminous coal is 50–60%.