Calcium transformation during the high-temperature pyrolysis process of high-alkali coal from Xinjiang

The existence forms of calcium contained in the high-alkali coal from Xinjiang,China and the calcium trans- formation during the high-temperature pyrolysis process were investigated using extraction method. The results show that the calcium contained in high-alkali coal mainly exists in the form of ammonium acetate soluble calcium and hy- drochloric soluble calcium,while there is some water soluble calcium contained in Tianchi Energy coal. The water sol- uble calcium in Tianchi Energy coke prepared at 1 500 ℃ is apparently high because CaS contains in Tianchi energy coal and CaS is still left in the coke. The ammonium acetate soluble calcium in Wucaiwan coke prepared at 1 500 ℃is apparently higher than that in the cokes from other coals because the content of silicon and aluminum in Wucaiwan coal is low and a part of CaO is still left in the coke. With the increase of pyrolysis temperature,the calcium content of the resulted coke increase. The calcium contained in the coke prepared at 1 200 ℃ mainly exists in the form of ammo- nium acetate soluble calcium species including anhydrite and quicklime and others. In the case of the coke prepared under the temperature range of 1 200-1 400 ℃ ,the contained anhydrite decomposition leads to a slightly increase of water soluble calcium,however,the calcium still mainly exists in the form of ammonium acetate soluble calcium as CaO. When the pyrolysis temperature increases from 1 400 ℃ to 1 500 ℃ ,the chemical reaction between CaO and sil- icon and aluminum makes ammonium acetate soluble calcium be transformed into hydrochloric soluble calcium.