Exergy and energy analysis on coal/biomass co-gasification in supercritical water

Supercritical water gasification (SCWG) is a promising technology for clean and efficient utilization of carbonaceous organic materials at high temperature and pressure. Coal/biomass co-gasification in supercritical water (SCW) is a better choice for both coal and biomass to offset their disadvantages. Therefore, based on the experimental results of coal/carboxymethylcellulose (CMC, as a model compound of biomass) co-gasification in SCW by continuous flow thermal-catalytic reaction system at a reactor wall temperature of 650 �C, pressure of 25 MPa, a residence time 30 s and 0.1 wt% NaOH additive, the effects of heat transfer efficiency, heat supply methods, and CMC fraction on exergy and energy efficiency of reactor (the core device in reaction system) were investigated. The results show that energy and exergy efficiencies are in excess of 69% and 43%, respectively. The priority order of heat supply for the reactor is as follow: lower temperature heat source > higher temperature heat source > direct electricity heat supply method. The heat transfer efficiency has great influence on the energy and exergy efficiencies in terms of thermophysics. The higher CMC fraction is helpful to improve exergy efficiency.