Chemisorption and physisorption of fine particulate matters on the floating beads during Zhundong coal combustion

Abstract

Floating beads rich in silica-aluminum oxide are hollow glass microspheres that can be obtained from fly ash by flotation. Floating beads have the advantages of high yield, low cost and easy access in the power plants or industrial kilns and are used as the sorbent for reducing the fine particulate matter (PM) emissions during pulverized coal combustion in this work. The pulverized coals mixed with floating beads are burned in an electrically heated drop-tube furnace at 1573 K. The size distribution and yield of PM are analyzed by an electrical low pressure impactor (LPI). The results indicate that the internal mineral elements, especially Na/K, Ca, and S, form a large amount of PM during pulverized coal combustion and floating beads can efficiently reduce PM formation via chemisorption and physisorption. With floating beads addition, the yield of ultrafine mode particles (PM0.5), mainly consisted of Na/K and S, decreases by 55.76%, and the yield of central mode particles (PM0.5–7), mainly consisted of Ca, Fe and Si, decreases by 21.7%. The surface reaction (chemisorption) between mineral vapors and sorbent particles reduces the PM0.5 emissions, and PM0.5+ can be reduced by the particles colliding and coalescing (physisorption), resulting in aluminosilicates on the surface of the sorbents. The results gained from characterization tests show that floating beads have more active sites and free silicon dioxides due to the broken SiO and AlO bonds after high-temperature calcination, thereby promoting the capture of mineral vapors such as alkali metals.