Study On Supercritical Hydrothermal Combustion Characteristics And Kinetics Of Nitrogen Compounds

At present,the eutrophication of water bodies caused by improper treatment of nitrogencontaining pollutants in industrial wastewater and sludge or direct dischearge without reatment has caused increasingly serious surface pollution prpblems and seriously threatened the health and safety of our people.Supercritical hydrothermal combustion technology is a new combustion method.When the concentration of organic matter is high enough and the temperature is higher than its spontaneous combustion temperature,it is possible to form a hydrothermal flame.Aiming at the problem of harsh degradation conditions of nitrogencontaining pollutants,this paper takes typical nitrogen-containing compounds（Quinoline,ammonia）as the research object,and uses the method of adding auxiliary fuels to carry out supercritical water oxidation enhanced degradation and supercritical hydrothermal combustion experiments on intermittent and continuous experimental devices,respectively,to clarify the interaction mechanism between auxiliary fuels and organic pollutants.The main conclusions of this paper are as follows:The enhanced degradation of quinoline by supercritical water oxidation was carried out.The results showed that when the pressure was 25 MPa,the oxidation coefficient is 1.5,the reaction temperature is 450℃,and 800 mmol/L methanol was added,the X_TOC and X_TN of 1.125 wt%quinoline SCWO reaction can reach 95.9%and 62.7%,respectively,which is much higher than that of pure quinoline reaction.Increasing the reaction temperature and oxidation coefficient can improve the kinetic effect of methanol.In addition,the enhanced degradation effects of methanol,ethylene glycol and glycerol were compared.Due to the excellent kinetic and thermal effects of polyols,the order of the three promoting effects on quinoline oxidation is CH₃OH<（CH₂OH）₂<C₃H₈O₃.Finally,the SCWO reaction pathway of quinoline is analyzed.The presence of intermediate products phenol,aniline and indole-2,3-dione in the reaction pathway suggest that the ring-opening pathway of quinoline in the reaction pathway is mainly ring-opening by pyridine ring,and then benzene and phenol are cracked and opened to form carboxylic acids,which are further mineralized into CO₂ and H₂O.The key intermediate product phenol of quinoline reaction was studied by continuous supercritical hydrothermal combustion experiment.The experimental results show that the phenol solution with initial concentration[COD]₀ of 73g/L can be successfully ignited at the preheating temperature of 460℃,and the temperature T_I at the inlet of the reactor L=0.2m rises rapidly from 461.3℃ to 616.9℃.The experimental results of phenol/methanol reaction at three preheating temperatures in the range of 420℃-460℃ show that the reaction temperature decrease with the increase of methanol ratio at the preheating temperature of 460℃,and T_I decrease from 613.8℃ to 565.9℃.When the preheating temperature is 440℃,the reaction temperature show a parabolic trend with the change of methanol ratio.T_I first decrease from 506.9℃ to 482.60C and then increase to 576.7℃.At the preheating temperature of 420℃,methanol promoted the oxidation heat release of the mixture,and T_I increase from 446.5℃ to 567.7℃.Finally,the enhance degradation of phenol and methanol during the decomposition of the refractory component ammonia is compared.When the preheating temperature is 460℃ and the oxidation coefficient is 2.5,phenol can increase the reaction temperature by 63.8℃ and the NH₄-N removal rate reaches 59.37%.Compared with methanol with the same COD concentration,the NH₄-N removal rate can reach 97.33%at the preheating temperature of 420℃.Therefore,as an auxiliary fuel,the kinetic and thermal effects of phenol on the degradation of refractory components are weaker than those of methanol.Finally,a detailed chemical reaction dynamics model for supercritical hydrothermal combustion of phenol was revised and established.Using the Peng-Robinson state equations and deviation functions,real thermodynamic materiality of each reaction component was obtained;the reaction dynamic parameters of the key reactions were corrected;and the dynamic model was validated based on the experimental results of preheating temperatures ranging from 4000C to 500℃.The results showed that the established mechanical dynamic model could well simulate the supercritical water-thermal combustion reaction of phenol.