Supercritical Hydrothermal Treatment And Heavy Metal Stabilization Of Oil Sludge Containing Auxiliary Fuel

With the increasing exploitation of petroleum,a large number of oily sludge will be produced,which contains a large number of organic pollutants and harmful heavy metals that are difficult to degrade,posing a great threat to the natural environment and human health.Because of its special physical and chemical properties,supercritical water can be used as an ideal medium for water-bearing waste disposal,thus realizing rapid and effective degradation of stubborn pollutants in high-temperature hydrothermal environment.In this paper,the supercritical water oxidation technology of auxiliary fuel is applied to the disposal of oily sludge to explore the mechanism of the enhanced degradation of pollutants by auxiliary fuel,and to clarify the migration and transformation law and stabilization mechanism of heavy metals in the hydrothermal process.The main research conclusions are as follows:The enhanced degradation mechanism of auxiliary fuel methanol on oily sludge under supercritical hydrothermal condition was studied.The preliminary test results showed that 800mmol/L methanol significantly promoted the degradation of TOC and NH₄-N in sludge.The improvement of the reaction parameters has a positive effect on the degradation of C and N elements in the sludge.When the oxidation coefficient is 1.7 and the reaction time is 20min,the TOC and TN removal rates of the effluent after the reaction reach 97.9%and 67.9%,respectively.The analysis of the organic components before and after the reaction showed that the long chain alkyl in the oil sludge gradually decomposed into short chain alkyl,and the nitrogen compounds in the liquid phase products decreased significantly in the presence of methanol.According to the mechanism and kinetics analysis of methanol supercritical water oxidation reaction,the kinetic and thermal effects of 800mmol/L auxiliary fuel promoted the oxidative degradation of the stubborn components.The enhanced degradation characteristics of auxiliary fuel were further studied.The results show that at 500℃ and 550℃,glycerol has the most significant promoting effect on the degradation of C and N elements in oil sludge due to its rapid free radical and heat release rate.At 550℃,oxidation coefficient 1.7 and reaction time 10min,when the COD concentration of 38.4wt%glycerin exists,the TOC removal rate,TN and NH₄-N concentration of the effluent after hydrothermal degradation are 98.7%,84.6mg/L and 69.4mg/L,respectively.Experimental verification shows that methanol two-stage feeding scheme has a positive effect on the supercritical hydrothermal degradation of C and N elements in oil sludge,because the graded feeding method can effectively prolong the free radical action time of auxiliary fuel,and then optimize its enhanced degradation effect.Finally,the stabilization mechanism of heavy metals in supercritical hydrothermal treatment of oily sludge was explored.The results show that almost all the heavy metals in the original solid-liquid mixture are stabilized in the residual solid phase after supercritical hydrothermal treatment,and the stabilization effect is most significant in the presence of ethylene glycol.Under the conditions of 500℃,oxidation coefficient 1.7,reaction time 5min,adding different auxiliary fuels,the metal elements Fe,Cu,Zn,Pb production rate reached the maximum.The analysis of weight loss characteristics of solid phase products shows that organic matter is almost completely degraded after supercritical hydrothermal treatment,indicating that solid phase components in oil sludge are effectively reduced.The content of heavy metals in the solid residue leaching solution is lower than the limit specified in GB 5085.3-2007,which proves that the supercritical hydrothermal treatment of oil sludge can realize the stabilization of heavy metals.