Numerical study of HCl and SO2 impact on potassium emissions in pulverized-biomass combustion

The potassium vapor released during the combustion of biomass are known to result in serious ash deposition, fouling and corrosion issues of biomass furnaces. To develop potassium control technologies to mitigate these issues and achieve clean utilization of biomass fuel, a better understanding of the fundamental formation and transformation mechanisms of potassium in biomass combustion is essentially required. In the present study, potassium emissions during pulverized-biomass combustion, for the first time, have been simulated in both one-dimensional (1D) premixed/diffusion flames of the biomass volatile and an early-stage two-dimensional (2D) pulverized-biomass flame. The properties of corn straw are used. The volatile-gas combustion is described by the DRM22 skeletal mechanism, while the homogeneous reaction of potassium species is modeled using a detailed mechanism encompassing the elements K, C, H, O, Cl and S. The initial species of K, Cl and S in the volatile gas is set to be KOH, HCl and SO2, respectively. The transformation characteristics of the potassium species are numerically investigated in both the 1D and 2D flames. Results show that KOH is the most significant potassium product under fuel-lean, stoichiometric and fuel-rich conditions, while the productions of sulfurous and chloric potassium species are secondary. Parametric studies with HCI, SO2 or both species replaced with N-2 in volatile gas are then performed to study their impacts on potassium emission characteristics in both the 1D and 2D flames. The results indicate that HCl has a stronger ability to react with potassium species than SO2.