Effect of SO₂ Addition on PM Formation from Biomass Combustion in an Entrained Flow Reactor

The sulfation process during biomass combustion and cofiring, by converting KCl into K₂SO₄, can affect particulate matter (PM) formation, ash deposition, and corrosion in a furnace. In this study, the effects of temperature, SO₂ concentration, O₂ concentration, and oxy-combustion atmosphere on the sulfation and PM formation were investigated in an entrained flow reactor. Results show that the particle size distribution (PSD) of PM₁₀ from biomass combustion is bimodal and that PM₁₀ is dominated by PM_1.0 consisting of KCl and K₂SO₄. Enhanced sulfation by SO₂ addition generally increases the particle size of PM_1.0 and the K₂SO₄ content in PM_1.0, but its effect on PM_1.0-10 is marginal. The effect of sulfation on PM_1.0 formation strongly depends on the temperature: at high temperature (e.g., 1300 °C), sulfation is not favorable, thereby having negligible influence on PM_1.0 formation; while at moderate temperature (e.g., 1100 °C), sulfation is significantly promoted, resulting in a larger size and higher yield of PM_1.0. With the increase of the SO₂ and O₂ concentration, the particle size and the sulfur content in PM_1.0 increase, indicating an enhanced sulfation process. When the combustion atmosphere switches from O₂/N₂ to O₂/CO₂, the PM_1.0 emission increases, while the sulfation process is inhibited. The comparison between the nucleation-growth modeling of KCl(g) and K₂SO₄(g) shows that the presence of K₂SO₄(g) advances homogeneous nucleation, resulting in a longer residence time for particle growth and therefore a larger PM_1.0 size.