Large eddy simulation of coal-ammonia flames with varied ammonia injection locations using a flamelet-based approach

The co-combustion characteristics of ammonia with pulverized coal have been investigated by applying a three-mixture fraction flamelet/progress variable (3Z-FPV) approach to a highly resolved large eddy simulation. In this 3Z-FPV model, fuel streams from the ammonia, coal volatiles, and char-off gases are represented by their respective mixture fractions. Two different cases of co-combustion of pulverized coal and ammonia have been investigated in which ammonia has been injected into burner (case 1) and side measurement port located at 1.0 m downstream from the burner (case 2). Comparison of numerical results to experimental data showed reasonable agreement for temperature, oxygen mole fraction, and NO emissions. 3Z-FPV-LES approach has successfully described the flow field and combustion characteristics of the coal-NH₃ flame in both cases. In case 1, ammonia injected through the burner penetrates internal recirculation zone, causing flame front to shift slightly downstream than case 2. During the experiment, peak NO was 60% higher and closer to the burner for 1.0 m downstream ammonia injection case than the burner ammonia injection case. This trend was also observed in the FPV-LES model, which predicted a 45% higher peak NO concentration for case 2 than for case 1.