Mineralogy and geochemistry of ash and slag from coal gasification in China: a review

China is the largest coal gasification market in the world. The gasifiers have been commercialized for producing syngas for coal-to-liquids, coal-to-olefin, and coal-to-substitute natural gas. During coal gasification at high temperature and pressure, the differences in reactivity of organic matter in coal are almost negligible; however, the transformation behaviour of minerals is important to the stability of the process. Detailed knowledge of the mineralogical properties of ash and slag is essential for optimizing the operational parameters. It is also significant for determining the influence of the solid wastes on the environment: for example, trace elements carried in bottom slag, fly ash, condensate water, and gaseous products migrate to natural water and soil and into the atmosphere. With this in mind, the mineralogy of ash and slag from typical coal gasification processes in China are reviewed, including the transformation of minerals typically found in coal, and the effects of operating conditions on mineral transformation and melting/slagging behaviour of minerals during gasification process. In addition, trace element migration behaviour in commercialized gasifiers is discussed.