Assessment of the effect of alkali chemistry on post-flame aerosol formation during oxy-combustion of biomass

The oxy-combustion of biomass enables negative CO2 emissions by combining subsequent CO2 capture technology. The potassium sulfation process significantly affects deposition and corrosion in heat transfer surfaces during biomass combustion. In the present work, a detailed aerosol dynamics model coupling with the detailed gas-reaction chemistry of K-S-Cl is proposed to investigate the effect of alkali chemistry on the evolution of postflame aerosol during oxy-combustion of biomass. According to the modelling results, the mass-based particle size distributions are generally unimodal. Changing the environment from the air (N-2 as a balance gas) to oxy (CO2 as balance gas) has a slight effect on the particle size distribution; yet, a slight left-shift particle size distribution was observed. The difference is mainly explained by the more substantial diffusion capacity of KCl(g) and K2SO4(g) in N-2 than that in CO2, indicating a bit higher heterogeneous condensation of KCl(g) and K2SO4(g) in a CO2-based atmosphere. Further, the modelling results revealed that oxy-combustion significantly affects the evolution of aerosol and sulfation of KCl regardless of flue gas recirculation strategy. The wet oxy-combustion case has the largest particle size of PM1.0, that is due to the higher concentration of water and SO2, which increased KCl sulfation with value of similar to 92%. The increased K2SO4 concentration in the flue gas causes earlier onset nucleation and prolonged the residence time for particle growth. Further ROP analysis results indicate that the reaction pathway for the sulfation of KCl via SO3 and K2SO4 condensation significantly influences the overall sulfation.