Investigation of reducing trace elements and PM emission from coal combustion by blending coal

Abstract

The fine particles and their associated trace elements derived from coal combustion had a severe adverse effect on the environment or human health. In this paper, HLH (lignite) and HS (bituminous) were blended under the predetermined ratio, and the blended coal was burned in a drop tube furnace (DTF). The particle size distribution (PSD) of particulate matter (PM) and trace elements (As, Se, Pb and Cd) were investigated during the blending coal combustion. The experimental results demonstrated that the mass concentration of PM from HLH coal combustion was higher than that of HS coal, which was attributed to the thermal instability of the minerals in HLH (lignite). In addition, it was found that PSD of PM was not consistent with that of trace elements. The blending coal combustion not only suppresses PM formation, but also reduces As, Se, Pb and Cd emission due to lowering ash fusion temperature of blending coal and liquidus capture of fine particles. Compared with the calculated values, the mass concentration of PM0.2–0.5, PM0.5–1.0, PM1.0–2.5 and PM2.5–10 from HS1HLH1 (the mass ratio of HS/HLH was 1.0) combustion was reduced by 6.06 %, 45.02 %, 50.17 % and 55.59 %, respectively. At the same time, the reduction efficiency of As, Se, Pb, and Cd emission concentration in PM0.2–0.5 by HS1HLH3 were the highest (about 91.7 %, 71.06 %, 83.45 % and 73.50 %), and their emission concentration was 0.16, 0.95, 0.97 and 0.02 μg/m3. While HS1HLH1 was the most effective for reducing As, Se, Pb, and Cd emission in PM0.5–10. Lastly, above 50 % As, Pb and Cd in PM10 was existed as the mobile phase during raw coal combustion, which had a harmfulness for the environment or human being. HS1HLH1 could stabilize Se, Pb, and Cd, and their residual fraction in PM10 were 59.4 %, 49.1 % and 29.2 %, respectively.