Process Design And Research On Operating Parameters Of Thermally Enhanced Sve Method To Repair Hydrocarbon Contaminated Soil

In recent years,the pollution problem of hydrocarbon-contaminated soil is becoming more and more serious.There are hidden dangers in ecological environment,food safety and human health.Because of its characteristics of volatility and diversity,it has increased the difficulty of restoration.Therefore,it is very important to develop a high efficient thermal enhanced SVE system for remediation of soil contaminated by hydrocarbons.In domestic,single factor experiments and shallow mechanism and dynamics models have been studied for most cases.However,the design parameters of optimal operation and process design have not been deeply studied yet.The current status of SVE,thermally enhanced SVE and HC outgas post-treatment system is systematically analyzed and summarized in this paper.First,through the self-made SVE reaction device and the steam heat strengthening SVE reaction device,and using the time of oil vapor concentration in outgas reaching specific concentration values as the evaluation indicator,the remediation process of hydrocarbon contaminated soil is studied.The effects of gas（flow,water vapor concentration and temperature）,soil（particle size,acidity or basicity）,organic pollutants（compound and concentration）on the treatment efficiency are discussed.The corresponding surface method is used to systematically optimize various parameters.Secondly,the physical and chemical properties of soil restoration before and after soil restoration are detected by infrared spectrometer（FT-IR）,specific surface area and pore volume tester and scanning electron microscope（SEM）.The mechanism of soil remediation by SVE method is analyzed,and the influence of soil structure on remediation efficiency is analyzed.In addition,through the experiment and COMSOL software simulation,the effect of the efficiency and the change of soil temperature in the process of ISTD enhanced SVE technology are studied,and the effects of the heating well layout on the treatment process are analyzed.Finally,according to the experimental results and the optimized parameters to improve the efficiency of treatment and realize the comprehensive utilization of internal energy heat of hydrocarbons,a new treatment system based on thermally enhanced SVE and adsorption system for HC gas and exhaust gas heat recovery is designed.The experimental results of soil remediation by SVE show that the outlet concentration decreases gradually with the prolongation of the ventilation time and many factors have an effect on the remediation efficiency.Comprehensive analyses indicate that temperature is the most important factor affecting the removal efficiency.Under the optimal condition,including the ventilation rate of 80ml/min,continuous ventilation method and the temperature of 80℃,the shortest ventilation time needed is 250min.The soil characterization experiments show that the organic groups vibrate strongly in the FT-IR diagram of polluted soil.The specific surface area of the uncontaminated soil is the largest.Due to partial hole structure collapse,the particle size of the remediation soil decreases to 18.968×10^-3mm.The surface is smoothed and the number of pores is reduced in contaminated soil.The contents of elements in three soils before and after remediation are different.The trend of the O element to increase first and then decrease is presented.Except for C and O elements,the overall content of the elements is decreasing,especially for the Si and Al elements.Experimental results of steam thermal enhanced SVE remediation of soil show that response surface methodology is adopted to optimize and the optimal parameters are determined ventilation rate with 81 mL·min^-1,the soil amount with 77 mL and the water vapor concentration with 14%,and the simulated desorption time is 213.58 min by heat enhanced SVE.The average desorption time of experimental results is 224 min,and the relative error between the model-predicted and the measured values is4.88%.For soil modification experiment,the removal efficiency of pollutants from high to low is unmodified soil,alkali modified soil,acid modified soil and salt modified soil.The remediation efficiency of soil with different pollutants from high to low is n-hexane,formaldehyde,gasoline,benzene,toluene.According to the soil FT-IR scheme before and after remediation,the direct correlation between peak intensity of organic matter and soil acid-base is not high,which is mainly determined by the composition of pollutants.The specific surface area of alkali modified soil is the smallest,with an average value of 1.137 m²/g,and the surface area of salt modified soil is large.When the soil was modified by acetic acid,the soil surface was changed,but the element was basically the same as the common soil,and the change trend of O element was the same.After repair,the content of Si is decreased and the metal elements are increased.The experimental results of ISTD remediation indicate that the optimal parameters are determined ventilation rate with 2L/min,temperature with 200℃and the soil pollution concentration with17280mg/kg.Comparison of temperature rise experiments and simulation results show that the heating rule is almost the same,but the rate of increase is different with the heating medium is different.The heating rate of heating medium for iron sand is larger than that of alumina.When the number of heating wells is homogeneous,the effect of uniform and symmetrical placement on the soil is good.The heating rate of soil increases and the influence range of heating well is bigger with the increase of heating well number.The four angle of four heating well is best arranged.According to the optimization parameters,a set of system is designed,which can realize the recycling of adsorption medium and internal energy in HC compounds.The economic analysis and the calculation of internal energy cycle are carried out.The results indicate that the heat generated from the desorption of pollutants in the soil is enough for the system.