Study On The Influencing Factors Of Soil Thermal Desorption Technology And Simulation System Development

In recent years,as economy developed and the industrial enterprises relocated,the environmental risks of industrial sites in city are increasing,and the soil pollution situation has become more and more serious.With demand of soil remediation on the rise,thermal desorption technology,especially the in-situ thermal desorption technology,has been one of the main technologies for the contaminated sites treatment.Under certain conditions,it will even be irreplaceable.However,at present,there are few researches on the mechanism of in-situ thermal desorption process in China,and the research methods are relatively lacking.The engineering case reports are also rare.Therefore,this dissertation has carried out corresponding researches and experiments to solve these problems.In this paper,nitrobenzene and naphthalene,two common organic pollutants,were selected as study objects.Firstly,to obtain the desorption law of nitrobenzene and naphthalene,several key factors during thermal desorption process in artificially contaminated soil were studied by using tubular furnace.On this basis,designing and developing a set of high-temperature multi-point heating pilot-plant simulation system and carrying out some researches on the temperature of thermal desorption process.The main conclusions are as follows:(1)With the prolongation of heating time,the removal efficiency of nitrobenzene and naphthalene in soil gradually increased,and finally tended to a certain limit value.The removal efficiency of nitrobenzene and naphthalene after heated for 120 min were 95.60% and 97.83%,respectively.The temperature in the soil where nitrobenzene and naphthalene began to vaporize had great influence to the removal efficiency,and their removal efficiency can both reach above 99.9% at 365?.The removal efficiency of nitrobenzene and naphthalene won't be satisfying when soil moisture content was too high or low.Nitrobenzene can reach a maximum removal efficiency of 95.68% at a moisture content of 6.9%,while a maximum removal efficiency of 95.54% for naphthalene at a moisture content of 16.2%.With the initial concentration of nitrobenzene and naphthalene increased,the removal efficiency of both showed a slight decrease.The removal efficiency of nitrobenzene decreased from 94.11% to 86.32%,and the removal efficiency of naphthalene decreased from 90.02% to 88.28%.When the heating time was short(5~10 min),nitrobenzene and naphthalene were desorbed relatively faster from the soil with less organic matter,but after a period of time(>20 min),their removal efficiency in both two kinds of soil samples would almost reach a same level.(2)In view of the existing problems of in-situ thermal desorption technology,such as heating,exhaust,integration and automation control,a set of high-temperature multi-point heating(3 heating wells)pilot-plant simulation system was designed and developed.Real-time on-line monitoring and automatic control of key simulation parameters such as temperature,pressure and flow in the system are realized.This simulation system can provide good basic conditions for the future researches on heating process control,tail gas treatment,sewage treatment and system integration of in-situ thermal desorption technology.(3)In the temperature study conducted by the in-situ thermal desorption simulation system,several experimental conclusions have been obtained.During the pre-heating phase,the moisture in the simulated system played a leading role in the vertical heat transfer.In the operation phase,the soil temperature in the simulation system was closely related to the distance from the heating well,and the highest temperature can reach above 530?.The soil temperature at each point won't rise rapidly until all the moisture has evaporated,and heat conduction would be at equilibrium when temperature reached to a certain limit.The extraction effect also had certain influence on heat conduction at the same time.Due to the influence of the extraction,the temperature field of heating rod in the simulation system will be deformed,and the cold spot in the system is not the farthest point from the heat source.