(585d) Effects of Ammonia Injector Design on Co-Firing Characteristics of Pulverized Coal Burner with High Ammonia Co-Firing Ratio

Recently, the co-firing ammonia with coal in boiler has been paid more and more attention. A CFD simulation has been undertaken to investigate the co-firing characteristics of ammonia with coal in an experimental facility (1 MW_th), in which a pulverized coal burner was mounted. One case for coal combustion and three for ammonia co-firing were simulated. The three cases for ammonia co-firing had different ammonia injectors inserted into the center of burner, but the same co-firing ratio of 60 cal.%. The different ammonia injectors were designed corresponding to different flow distributions of ammonia into axial and radial directions. According to the simulation results, the following conclusions could be drawn. Firstly, basically, the cases of ammonia co-firing have higher NO concentration, higher unburnt carbon content in fly ash at exit, lower CO concentration at exit and less heat amount absorbed by walls, compared with that in the case of coal combustion. Additionally, as the increase of ammonia amount into radial direction, the NO concentration at exit is decreased. This could be mainly attributed to the de-NOx effect of ammonia inside the flame and inhabitation of ammonia after-burning. In the case with the most ammonia amount into radial direction, a lower NO concentration at exit than that in the case of coal combustion can be obtained. However, as the increase of ammonia amount into radial direction, the unburnt carbon content in fly ash and CO concentration at exit are increased. This could be mainly attributed to the competition of ammonia with char in O₂ consumption. These conclusions will be very helpful in the design of a high-performance burner for co-firing of ammonia with coal even under the conditions of quite high co-firing ratio.