Effect of wood-to-coal fuel percent and underfire air on sulfur emissions and percent fuel energy loss during cofiring of wood and coal
Wood and coal fines (2.7% sulfur) were mixed in various proportions (0%, 25%, 50%, 75%, and 100% wood) and burned at different underfire to overfire air percentages (20%, 40%, 60%, 80%) in a small, fixed-bed combustor to determine how SO2 emissions might be influenced by these variables. Results indicated that the addition of large amounts of wood increased the capture of SO2 in the bottom solids by 5 percentage points for the 50 percent wood/50 percent coal mixture and by 8 percentage point for the 75 percent wood/25 percent coal mixture. Within the constraints of our experiment, the 80 percent wood/20 percent coal mixture met the EPA SO2 emission standard for new combustion systems. An optimum fuel energy loss was obtained by limiting the underfire air to around 40 to 50 percent. Our results also indicated that cofiring of wood with coal slightly reduced SO2 emissions beyond simply what might have been expected from a dilution effect alone. These results may suggest that cofiring wood with high-sulfur coal, in selected proportions, may be a viable substitute for expensive scrubbing equipment in some cases.
Forest Products Journal
Helmer, W. A., Caraker, K., Workman, E. C., & Phelps, J. (1988). Effect of wood-to-coal fuel percent and underfire air on sulfur emissions and percent fuel energy loss during cofiring of wood and coal. Forest Products Journal 38(11-12): 49-54.