Numerical Simulation Study of Combustion Characteristics and Pollutant Emissions of a 350 MW Coal-Fired Boiler Under Low Load Conditions with Ammonia Co-Firing

With the advancement of low-carbon transition and deep load-following operation of coal-fired units, ammonia–coal co-firing is a retrofit-ready option for source decarbonization, but its coupled impacts on combustion and emissions remain to be quantified. A 350 MW corner-tangential pulverized-coal boiler at a 30% rated load was investigated using a three-dimensional ANSYS Fluent CFD model. Thirteen cases were designed by combining five ammonia shares (0–40%) with three injection locations (B, C, D). The temperature and key species fields were analyzed to track the reaction-zone shifts, and the outlet CO2, SO2, NO, and NH3 were evaluated. Increasing ammonia reduced and contracted the high-temperature core, dispersed the flame, extended the ignition distance of the ammonia-laden primary jet, and shifted heat release downstream. CO2 and SO2 decreased with an ammonia substitution; at 40% co-firing, CO2 fell by about 43% and SO2 declined markedly. NO showed a nonlinear, location-dependent response: B and C injection may raise NO at low ratios, but reduce it at higher ratios under lower temperatures and stronger reduction, whereas D injection tends to maintain higher NO in the upper furnace. The findings guide coordinated selection of the co-firing ratio and injection location for low-load retrofits.