Influence of thermal treatment condition on release behavior of selenium in coals

Release behaviors of selenium (Se) during pyrolysis of seven Chinese coals were studied at 200℃～1000℃ in a quartz tube fixed-bed reactor. Effects of heating rate, residence time and atmosphere on the release of Se in HDG and HLH coals were investigated. The results show that the release of Se mainly occurs below 700℃. The release ratio of Se is about 34%~63% at 700℃. The release of Se is peaked at 500℃ for bituminous coal and 400℃ for lignite, respectively. There is no significant effect of heating rate on the release ratio of Se when temperature is lower than 500℃. However, the lower heating rate leads to the higher release ratio of Se above 500℃. At 1000℃, the release ratio of Se increased with residence time within the first 15min, while there is no significant change with the further increase of the time. In comparison with N₂ atmosphere, both air and H₂ promote the release of Se, especially the air atmosphere. Under the experimental conditions, no Se enrichment in pyrolysis char is observed.