The coal water slurry (CWS) prepared from low rank coals (LRC)

such as lignite or subbituminous coals always has a higher viscosity and poor fluidity while the solid concentration is smaller than high rank coal water slurry.The reason is there are larger inherent moisture and oxygen composition in LRC.Under high temperature and high pressure conditions

LRC was upgraded in hot water in a short time period of an hour.The heating value of LRC was also increased in such a process

and the physical and chemical characteristics of LRC changed meanwhile to improve its slurry ability which meant a higher solid concentration with a lower viscosity.The results showed that after hot water treatments

the maximum solid concentration of Xiaolongtan CWS increased from 44.6% to 64.55%

while that of MIP CWS increased from 39.71% to 64.61%.The improvement of LRC slurry ability depended much on the final temperature of hot water treatments.The mechanism was explained by the chemical analysis of oxygen-containing groups and the measurement of contact angle between coal surface and water.