Study On Application Of Wastewater Treatment By Supercritical Water Oxidation

The equipment corrosion, salt precipitation, and high operational cost are three serious bottlenecks in the application of supercritical water oxidation (SCWO). Solving these problems is the most pressing issue in the promotion of SCWO development. A 2D numerical and experimental study on the hydraulics characteristic of a transpirating wall reactor, which can anti corrosion and salts precipitation, is reported in this paper. The thermodynamics analysis of SCWO process is also conducted in order to find an available method of recovering the reaction heat of SCWO.First, the developed transpirating wall reactor model is established, and the effects of transpiration temperature and intensity, as well as the temperature and flux of the bulk flow are simulated and analyzed with the model. The simulation results show: the most obvious effect parameter to the transpiration effect is the transpiration intensity, the protection at the wall can be realized when it equals to 1%; The effects of other parameters to the transpiration effect are small; Big temperature difference of transpiration and bulk flow may lead to natural convection effects; The natural convection effects can be decreased by increasing the flux of bulk flow.On the base of numerical simulation, the experiments about the effects of transpiration intensity and flux of bulk flow to the temperature and residence time distribution have been run on the self designed cold state apparatus. The temperature results are corresponding with the numerical simulation with the developed model. The results of the residence time distribution indicate: the back mixing effects increase with the increase of transpiration intensity. However, the fluxion of the reactor is similar to the plug reactor. Numerical simulations are performed, which take the experiment conditions are boundary conditions. The comparison of the calculated with the experimentally measured values shows generally a good agreement.Then the numerical simulation method has been used to calculate and analyze the effects of transpiration intensity and temperature to SCWO. The calculation results show: the effects of transpiration intensity and temperature are not strong; the reactor wall is protected by the transpiration. And the residence time distribution tells us: there is short circuit or channeling in the reactor, and the fluxion of the reactor is similar to the plug reactor: the average residence time decreases with the increase of transpiration intensity while the dimensionless variance increases; the average residence time and dimensionless variance decreases with the increase of transpiration temperature.At last, the process of SCWO for phenol is simulated with the Aspen Plus processsimulator, and the results show that the influence of temperature on reaction heat is small at a constant pressure. It is reasonable to neglect the effect of temperature and to estimate the heat of reaction with average temperature when the temperature changes in a small range. The condition to realize an energetically self-sufficient SCWO process is analyzed and the thermodynamics analysis shows that energetically self-sufficient SCWO process with an Organic Rankine Cycle is a feasible technology for the recovery of SCWO reaction heat, and the energy balance point for phenol is 2wt%.The investigation of this paper reveals the hydraulics characteristic of transpirating wall reactor, and the reaction heat of SCWO process, which can not only provide meaningful ideas for the future work but also promote the development of SCWO technology.