Experimental Investigation on Fine Particle Formation in Ammonia/Biomass Co-combustion

Ammonia cofiring in boilers has the potential to reduce CO2 emissions but may increase the concentrations of NOx and H2O in the flue gas, which may impact the formation of particulate matter (PM). This study investigates the influence of different ammonia cofiring ratios (CNH3) on biomass ash formation using a Hencken-type flat-flame burner. Increasing CNH3 resulted in a significant increase in the concentration of NOx and PM (especially PM1). As the CNH3 increased from 0 to 40% at 1500 K, the concentration of NOx increased from 1516 to 13,131 mg/Nm3, and the concentration of PM1 increased from 3.47 to 5.58 mg/Nm3. Notably, a strong correlation between the PM1 and NOx concentrations was observed. Then the elemental composition of PM1 was analyzed, and it revealed no significant change in the mole fraction of the K element with varying CNH3 but increased the mole fraction of N elements indicating the conversion of gaseous N (N-gas) to ash N (N-ash) during co-combustion with ammonia. A parameter Q, representing the mole ratio of O elements to N, S, and P elements in PM, is introduced to assess the proportion of oxides and salts in PM. Q values were found to be greater than 1 without ammonia addition, suggesting higher oxide content in PM. However, Q values fluctuated around 1 after cofiring with ammonia, further supporting the participation of NOx and H2O in PM1 formation and potential conversion of oxides into nitrates or other nitrogen-containing compounds. The results showed that NOx generated from NH3 affects PM1 formation, and the resulting issues (such as ash deposition, slagging, and corrosion) should also be given attention.