Flame Morphology and Characteristic of Co-Firing Ammonia with Pulverized Coal on a Flat Flame Burner

Ammonia as a new green carbon free fuel co-combustion with coal can effectively reduce CO 2 emission, but the research of flame morphology and characteristics of ammonia-coal co-combustion are not enough. In this work, we studied the co-combustion flame of NH 3 and pulverized coal on flat flame burner under different oxygen mole fraction ( X i , O 2 ) and NH 3 co-firing energy ratios ( E N H 3 ). We initially observed that the introduction of ammonia resulted in stratification within the ammonia-coal co-combustion flame, featuring a transparent flame at the root identified as the ammonia combustion zone. Due to challenges in visually observing the ignition of coal particles in the ammonia-coal co-combustion flame, we utilized Matlab software to analyze flame images across varying E N H 3 and X i , O 2 . The analysis indicates that, compared to pure coal combustion, the addition of ammonia advances the ignition delay time by 4.21 ms to 5.94 ms. As E N H 3 increases, the ignition delay time initially decreases and then increases. Simultaneously, an increase in X i , O 2 results in an earlier ignition delay time. The burn-off time and the flame divergence angle of pulverized coal demonstrated linear decreases and increases, respectively, with the growing ammonia ratio. The addition of ammonia facilitates the release of volatile matter from coal particles. However, in high-ammonia environments, oxygen consumption also impedes the surface reaction of coal particles. Finally, measurements of gas composition in the ammonia-coal flame flow field unveiled that the generated water-rich atmosphere intensified coal particle gasification, resulting in an elevated concentration of CO. Simultaneously, nitrogen-containing substances and coke produced during coal particle gasification underwent reduction reactions with NO x , leading to reduced NO x emissions.