Thermodynamic and exergy assessments of supercritical water gasification of oily sludge assisted by hydrothermal flame

A novel supercritical water gasification (SCWG) system using hydrothermal flame as internal heat source (HSCWG) for oily sludge treatment was proposed to achieve rapid preheating and promote gasification rate. The proposed system was firstly simulated using Aspen Plus 11, and the simulation model was validated by comparison with experimental data. The exergy input, output, and destruction for the HSCWG are far smaller than those for the traditional SCWG system using hot water as heat source (TSCWG). The oxidation reactor and electric heater contribute to the maximum exergy destructions in the HSCWG and TSCWG, with the exergy distribution coefficients of 30.80 % and 37.16 %, respectively, indicating the preheating method is a key factor affecting the energy consumption and system efficiency. Lower exergy efficiencies are present at higher gasification temperatures, indicating more exergy destructions are present in the oxidation reactor and electric heater. Moreover, the net operating cost for the TSCWG increases significantly with increasing gasification temperature, which is far higher than that for the HSCWG. The HSCWG is more competitive for the treatment of oily sludge compared with the TSCWG. Fuel concentration adjustment is more efficient than fuel flow adjustment in the regulation of the gasification temperature.