Novel designs for the reliability and safety of supercritical water oxidation process for sludge treatment

For strengthening the safety and reliability for supercritical water oxidation (SCWO) process, the essential causes and solutions of key challenges such as the high corrosion risk of the heat-exchanger and the entrance part of SCWO reactor, the blockage problems resulted from the solid deposition, and the safety and environmental issues caused by the emergency discharge of supercritical aqueous fluids, were investigated theoretically and experimentally. The thermodynamic state division between chemical- and electrochemical corrosion and the corrosion sensitive temperature range of 280−450 °C featuring the predominant electrochemical corrosion were proposed. A set of optimized parameters for the petrochemical sludge treatment such as a temperature of 520–580 ℃, a pressure of 23−25 MPa, and an oxidation coefficient of 1.1–1.3, which not only can ensure the high enough removal rate of organic pollutants but also prevent the corrosion of construction materials as much as possible; the critical velocity of conveying fluid for avoiding the deposition of solid particles were also obtained. On the bases of innovatively developing the “indirect heat transfer” unit, the mixing-preoxidation equipment, the oxygen removal process for SCWO effluents, and the emergency discharge protection device, a novel SCWO process and its corresponding control scheme were proposed and analyzed.