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 NO x 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 (C NH3 ) on biomass ash formation using a Hencken-type flat-flame burner. Increasing C NH3 resulted in a significant increase in the concentration of NO x and PM (especially PM1). As the C NH3 increased from 0 to 40% at 1500 K, the concentration of NO x 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 NO x 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 C NH3 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 NO x and H2O in PM1 formation and potential conversion of oxides into nitrates or other nitrogen-containing compounds. The results showed that NO x generated from NH3 affects PM1 formation, and the resulting issues (such as ash deposition, slagging, and corrosion) should also be given attention.