Co-firing of coal and biomass under pressurized oxy-fuel combustion mode in a 10 kWth fluidized bed: Nitrogen and sulfur pollutants

• Oxy-fuel co-firing of coal and biomass in a PFB reduces NOx, N 2 O, SO 2 , CO emissions. • The pressurized and co-firing conditions have a synergistic effect on promoting sulfur self-retention (SSR). • SSR occurs through direct sulfation route at the typical temperature in an oxy-fuel PFB. • The increase in NOx and SO 2 with temperature under POFC mode is smaller than that under atmospheric condition. • The ash and bed material have a low potential for slagging, fouling, and agglomeration. Co-firing coal and biomass under pressurized oxy-fuel combustion (POFC) mode in fluidized beds is a novel and promising technology to capture CO 2 at a low cost and with eco-friendly waste disposal. However, large knowledge gaps exist in combustion characteristics and pollutant generation owing to the tremendous lack of practices. Following our successful testing of co-firing coal and biomass under POFC mode in a10 kW th pressurized fluidized bed (PFB) [Chem. Eng. J. 2022, 431,133457], this study conducted a special and in-depth investigation of nitrogen and sulfur pollutants. Based on a comprehensive analysis of flue gas and solid residues, the effects of key operating parameters, such as combustion pressure ( P ), biomass blending ratio ( M b ), and combustion temperature ( T ), on the emissions of gaseous and solid pollutants, transformation and distribution of nitrogen and sulfur, sulfur self-retention (SSR) process, and ash properties and potentials of deposition and agglomeration, were investigated. The results show that increase in P and M b significantly reduces NOx, N 2 O, SO 2 , and CO emissions and improves the SSR efficiency. Notably, the pressurized and co-firing conditions have a synergistic effect on SO 2 emission reduction. The T dependence of these products under POFC mode is clearly less than that under atmospheric oxy-fuel combustion mode. Within the typical operating temperature range of an oxy-fuel PFB, SSR occurs through the direct sulfation route. The ash and bed material have an overall low potential for slagging, fouling, and agglomeration, with no indication of ash-related problems during testing. This work will be helpful for the development of oxy-fuel co-firing in PFBs for CO 2 capture.