Effects of ammonia co-firing on the formation of fine particles during staged gasification-combustion of coal

This study investigated the impact of ammonia-coal co-firing on fine particulate matter (PM) formation on a staged gasification-combustion furnace. The roles of ammonia blending ratio (w_NH3), gasification chamber temperature (T_g), combustion chamber temperature (T_c), and air distribution strategy (α_g) were explored. The results showed that as w_NH3 increases from 0 % to 40 %, fine PM follows an “increase-decrease-increase” trend, with the lowest value occurring at around 30 %. The impact of w_NH3 on inorganic element volatilization is mainly influenced by ammonia's role in promoting coal ignition, oxygen consumption during ammonia combustion, the increase in flue gas specific heat, and the reduction and volatilization of refractory elements by H₂ and H₂O. Increasing T_g from 1000 °C to 1300 °C significantly raises fine PM, but fine PM is reduced by 14.4 %–39.9 % at various T_g with 30 % ammonia. This is due to ammonia lowering coal combustion temperature, reducing the vaporization of refractory minerals. Ammonia also weakens the effect of T_c on char combustion, decreasing mineral element volatilization at high temperatures, leading to a 26.6 %–41.4 % reduction in fine PM. When 30 % ammonia was blended in the primary air, an α_g value of 0.7 provided the best suppression of fine PM by inhibiting inorganic element volatilization. Deviations from this value significantly increased the volatilization of elements such as Mg, Ca, and Fe, as well as sulfur content in fine PM. Reducing the w_NH3 and increasing T_g and T_c both reduced ammonia escape. Escaped ammonia reacted with SO₃ in low-temperature zone to form ammonium sulfate salts, which were concentrated in particles smaller than 100 nm. The study shows that controlling ammonia ratio, temperature, and air distribution can significantly reduce fine PM during ammonia-coal co-firing.