In-Furnace Sulfur Capture by Cofiring Coal With Alkali-Based Sorbents

Abstract

This manuscript presents experimental results on the reduction of sulfur oxide emissions from combustion of a high-sulfur content pulverized bituminous coal (Illinois #6 Macoupin) using a dry sorbent injection method. The coal particles were in the size range of 90–125 μm and were blended with calcium-, sodium-, potassium-, and magnesium-containing powdered sorbents at different proportions. The alkali/sulfur molar ratios were chosen to correspond to stoichiometric proportions (Ca/S = 1, Mg/S = 1, Na2/S = 1, and K2/S = 1) and the effectiveness of each alkali or alkali earth based sorbent was evaluated separately. Combustion of coal took place in a drop-tube furnace, electrically heated to 1400 K under fuel-lean conditions. The evolution of combustion effluent gases, such as NOx, SO2, and CO2 was monitored and compared among the different sorbent cases. The use of these sorbents helps to resolve the potential of different alkali metals for effective in-furnace sulfur oxide capture and possible NOx reduction. It also assesses the effectiveness of various chemical compounds of the alkalis, such as oxides, carbonates, peroxides, and acetates. Reductions in SO2 emissions were in the range of 5–72%, with sodium being the most effective metal followed by potassium, calcium, and then magnesium. Acetates were effective as dual SO2 and NOx reduction agents.