Co-hydrothermal carbonization of sewage sludge and coal slime for clean solid fuel production: a comprehensive assessment of hydrochar fuel characteristics and combustion behavior

The fuel characteristics and combustion behavior of the hydrochar obtained from the co-hydrothermal carbonization (co-HTC) of sewage sludge (SS) and coal slime (CS) were investigated. The results showed that a synergistic effect existed during the co-HTC process of SS and CS, which could make the mass yield, high heating value, carbon retention rate, energy recovery efficiency, fuel ratio, and energy balance of the hydrochar increase by 1.87–6.52%, 4.04–17.54%, 7.52–16.80%, 4.20–19.59%, 7.58–25.45%, and 35.26–40.08%, respectively. Furthermore, thermogravimetric and derivative thermogravimetry analysis indicated that the weight loss of co-hydrochar was significantly increased with increasing of CS ratio, and it was 38.39%, 48.14%, and 58.08% when the CS ratio was 25%, 50%, and 75% respectively. Adding CS during HTC could significantly improve the combustion performance of the hydrochar. Moreover, SS and CS were efficiently converted into solid fuels with better combustion performance and reactivity. Graphical Abstract