PM10 formation during the combustion of N2-char and CO2-char of Chinese coals

Abstract

The formation of PM10 (particles less than or equal to 10 µm in aerodynamic diameter) during char combustion in both air-firing and oxy-firing was investigated. Three Chinese coals of different ranks (i.e., DT bituminous coal, CF lignite, and YQ anthracite) were devolatilized at 1300 °C in N2 and CO2 atmosphere, respectively, in a drop tube furnace (DTF). The resulting N2-chars and CO2-chars were burned at 1300 °C in both air-firing (O2/N2 = 21/79) and oxy-firing (O2/CO2 = 21/79). The effects of char properties and combustion conditions on PM10 formation during char combustion were studied. It was found that the formation modes and particle size distribution of PM10 from char combustion whether in air-firing or in oxy-firing were similar to those from pulverized coal combustion. The significant amounts of PM0.5 (particles less than or equal to 0.5 µm in aerodynamic diameter) generated from combustion of various chars suggested that the mineral matter left in the chars after coal devolatilization still had great contributions to the formation of ultrafine particles even during the char combustion stage. The concentration of PM10 from char combustion in oxy-firing was generally less than that in air-firing. The properties of the CO2-chars were different from those of the N2-chars, which was likely due to gasification reactions coal particles experienced during devolatilization in CO2 atmosphere. Regardless of the combustion modes, PM10 formation in combustion of N2-char and CO2-char from the same coal was found to be significantly dependent on char properties. The difference in the PM10 formation behavior between the N2-char and CO2-char was coal-type dependent.