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

Ammonia cofiring in boilers has the potential to reduce CO<INF>2</INF> emissions but may increase the concentrations of NO<INF>x</INF> and H<INF>2</INF>O in the flue gas, which may impact the formation of particulate matter (PM). This study investigates the influence of different ammonia cofiring ratios (C<INF>NH<INF>3</INF></INF>) on biomass ash formation using a Hencken-type flat-flame burner. Increasing C<INF>NH<INF>3</INF></INF> resulted in a significant increase in the concentration of NO<INF>x</INF> and PM (especially PM<INF>1</INF>). As the C<INF>NH<INF>3</INF></INF> increased from 0 to 40% at 1500 K, the concentration of NO<INF>x</INF> increased from 1516 to 13,131 mg/Nm3, and the concentration of PM<INF>1</INF> increased from 3.47 to 5.58 mg/Nm3. Notably, a strong correlation between the PM<INF>1</INF> and NO<INF>x</INF> concentrations was observed. Then the elemental composition of PM<INF>1</INF> was analyzed, and it revealed no significant change in the mole fraction of the K element with varying C<INF>NH<INF>3</INF></INF> 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<INF>x</INF> and H<INF>2</INF>O in PM<INF>1</INF> formation and potential conversion of oxides into nitrates or other nitrogen-containing compounds. The results showed that NO<INF>x</INF> generated from NH<INF>3</INF> affects PM<INF>1</INF> formation, and the resulting issues (such as ash deposition, slagging, and corrosion) should also be given attention.