Supercritical water oxidation of lurgi coal gasification wastewater and evaluation of the combined process with gasification

Degradation of Lurgi coal gasification wastewater in supercritical water was investigated in a batch reactor, and a combined process of supercritical water oxidation (SCWO) and gasification was put forward to utilize the material and energy in SCWO effluent. The technical feasibility and economy were evaluated. In the SCWO process, when operated at condition of 500 °C, 25 MPa, oxygen ratio of 3.5 and residence time of 15 min, the concentrations of COD, NH₃-N and volatile phenol in effluent reduced to 27, 11 and 0.4 mg/L, respectively, where the removal efficiencies were 99.81%, 99.85% and 99.99%, accordingly. The effluent could reach national discharge standard I (GB 8978-1996), and can be used as the gasification agents of gasifier via a pressure reducer. For a single Lurgi gasifier, the combied process could save 23 t/h of steam and 1550 kg/h of O₂, which is equal to 4996 yuan/h.