Characteristics of coal tar residue treated with microwave-assisted hydrothermal treatment

To achieve an efficient large-scale use of the coal tar residue (CTR), a microwave-assisted hydrothermal treatment was investigated to reduce its viscosity. The CTR was treated at various temperature with various liquid/solid (L/S) ratio by microwave-assisted hydrothermal. Then the thermogravimetry (TG) and the tube furnace combustion experiment were employed to study the combustion behavior and the NOx and SO2 emissions of the treated CTR. The results indicated that the microwave-assisted hydrothermal treatment with higher temperature and higher L/S ratio was beneficial to the viscosity reduction of the CTR. The TG results suggested that the treated CTR achieved a complete combustion only at a heating rate of 10 °C/min. Moreover, increasing the temperature and the L/S ratio reduced the comprehensive combustion characteristic index of the treated CTR. The results of combustion experiment indicated that the NOx emission of the treated CTR was less than 140 mg·m−3, while the SO2 emission was less than 100 mg·m−3. The microwave-assisted hydrothermal treatment is a promising method for the CTR, and the treated CTR can be applied as the fuel of circulating fluid beds (CFB) for industrial production.