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

Abstract

Co-firing coal and biomass under pressurized oxy-fuel combustion (POFC) mode in fluidized beds is a novel and promising technology to capture CO2 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 kWth 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 (Mb), 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 Mb significantly reduces NOx, N2O, SO2, and CO emissions and improves the SSR efficiency. Notably, the pressurized and co-firing conditions have a synergistic effect on SO2 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 CO2 capture.