Experimental study of combustion characteristics and ash-related issues of ammonia co-firing with high alkali pulverized coal in a 4 MW boiler

Co-firing ammonia with coal is a promising solution for reducing carbon emissions from coal power plants. In this study, we conducted experimental research in a 4 MW pilot boiler and successfully achieved stable operation of full ammonia combustion and co-firing. The effects of the ammonia co-firing ratio and combustion method on the combustion characteristics and alkali- and ash-related issues of co-firing ammonia with Zhundong (highalkali) coal were mainly discussed. The results showed a positive correlation between NOx emissions and the ammonia co-firing ratio. However, although a 20 % (thermal ratio) fuel-staged combustion can lower NOx emissions compared with pure coal burning, this may have an adverse impact on CO emissions. The distance at which ammonia was injected into the furnace positively affected both NOx and CO emissions. The spectral diagnosis results indicated that co-firing ammonia significantly reduced the particle radiation of the flame in the furnace. When the co-firing ratio was 60 %, the particle radiation in the boiler upper area was reduced by approximately 50 %. A 20 % ammonia co-firing ratio in the main combustion zone (including staged combustion with 40 % ammonia) effectively reduced the gas-phase sodium content leaving the furnace area. A co-firing ratio of 20 % was the best working condition in terms of the NOx emission ratio and alkali release. Compared to pure coal combustion, co-firing has no significant impact on the chemical properties of ash and slag and does not become a bottleneck in the utilization of ammonia for power plants. However, considering that the introduction of ammonia reduces the amount of ash entering the furnace, this may be beneficial for the promotion and utilization of Zhundong coal.