Dry additive desulfurization in oxyfuel bubbling fluidized bed combustor

This work presents research results of direct sorbent addition for SO2 capture from a lignite coal combustion in a bubbling fluidized bed (BFB). SO2 capture ratio in air and in full oxyfuel combustion conditions is compared in real environment, using a 30 kW BFB combustor. The first part studies the sulfur self-retention in the fuel ash. It shows significantly more efficient SO2 capture increase from 15% in air conditions to 45% in oxyfuel conditions. The next part concerns evaluation of optimal temperature for the SO2 capture and a sorbent performance is evaluated in the last part. Two varieties of sorbents based on CaCO3 were used, differing significantly in purity, geological age and BET surface area. The optimal fluidized bed temperature for SO2 capture was for air combustion about 840 degrees C and for oxyfuel combustion about 880 degrees C. The sorbent performance was studied at three different Ca/S molar ratios (1.5, 3 and 5). The results show the fundamental differences between air and oxyfuel conditions in real combustion environment, and also reveal the differences between the sorbents. In general, significantly higher SO2 capture ratio was reached in oxyfuel conditions. At Ca/S equal to 5, it is possible to reach the SO2 capture as high as 98% in oxyfuel mode. The BET surface of the sorbent is important mainly at lower Ca/S molar ratios. The difference in SO2 capture between the sorbents is below 10% relative at Ca/S molar ratio 3 and it further decreases with increasing Ca/S ratio.