Experimental Study of SO2 Emission and Sulfur Conversion Characteristics of Pressurized Oxy-Fuel Co-combustion of Coal and Biomass

Pressurized oxy-fuel combustion is a solution to achieve low-cost CO2 capture and higher operating efficiency. The combination of pressurized oxy-fuel combustion technology and biomass combustion technology can achieve negative CO2 emissions. However, pressurized oxy-fuel co-combustion of coal and biomass lacks mechanism understanding and the studies on pollutant emissions are scarce. To investigate SO2 emission concentration, the conversion rate of fuel sulfur to SO2, sulfur mass balance, and sulfur content and forms in the fuel ash of pressurized oxy-fuel co-combustion of coal and biomass, a series of co-combustion experiments were carried out in a horizontal tube furnace. The experimental fuels were lignite and corn straw, and the experimental parameters were biomass blending ratio (M b = 0, 30, 50, 70, and 100%), combustion atmosphere (air, Oxy-21, Oxy-30, and Oxy-40), reaction pressure (0.1, 0.3, 0.5, and 0.7 MPa), and combustion temperature (800, 850, and 900 °C). The experimental results showed that SO2 actual emissions decreased as M b increased while the conversion rate of fuel sulfur to SO2 was lowest at 50% M b. Ash analysis indicated that more sulfur converted to CaSO4 at 50% M b. SO2 actual emissions was highest in the air atmosphere and lowest in the Oxy-21 atmosphere. Higher reaction pressure suppressed SO2 actual emissions and promoted the sulfur converted to other forms of sulfide, and reaction pressure had no obvious effect on CaSO4 and K2SO4 in the fuel ash. Higher combustion temperature slightly promoted SO2 actual emissions and conversion rate of fuel sulfur to SO2. Except for 100% M b, the three slagging indexes for all combustion experiments were in the criteria of low slagging trend. According to T-A, slagging caused by alkali metals may occur during 100% M b combustion.