Process in supercritical water gasification of coal: A review of fundamentals, mechanisms, catalysts and element transformation

•Effects of key parameters on the complete gasification are conducted and summarized.•Molecular dynamics of coal gasification in supercritical water are summarized.•Transformation of sulfur and nitrogen in coal gasification in supercritical water is studied.•Future works and challenges for supercritical water gasification coal are summarized. Supercritical water gasification (SCWG) of coal is a new clean coal conversion technology. Due to the unique properties of supercritical water, SCWG has many advantages compared with other coal gasification technologies, such as higher gasification efficiency, higher H2 yield, and less NOX, CO2 and SOX emission. However, how to realize the complete gasification of coal in supercritical water at low temperature is a huge challenge. Through experimental and kinetic studies, it is found that temperature is a determining factor of SCWG of coal. There is no nitrogen-containing gas in gaseous products and H2S is the only sulfur-containing gas in gaseous products. The temperature for complete gasification can be reduced by using oxidant or catalyst. The molecular dynamics simulation shows that there is a virtuous cycle in the SCWG process of coal through the formation and extinction of H radical-rich water clusters. In addition to the challenges mentioned above, as a competitive and promising technology, there are still many other challenges to be solved for supercritical water gasification coal, such as corrosion problem of the SCWG reactor, high cost and system amplification method.