| Oil shale is a kind of solid flammable sedimentary rock with high content of organic matter.After heating to 300-550 ~oC,kerogen in oil shale can mature to produce shale oil and flammable gas.Oil shale is widely distributed in China.The amount of shale oil resources is about 47.6 billion tons,which is 0.5 times the amount of traditional oil resources,ranking the second position in the world.Jilin Province is rich in oil shale resources.At present,the proven reserves are 86 billion tons,equivalent to 3.944 billion tons of shale oil,accounting for 81%of the country.Speeding up the development of oil shale development technology is of great significance to industrial upgrading and economic development of China and Jilin ProvinceConventional oil shale surface distillation technology will produce a large"three wastes",which will have a great negative impact on the environment and ecology,and restrict large-scale development.Oil shale in-situ pyrolysis technology is a method to obtain oil and gas from oil shale by underground in-situ heating treatment,which is an important direction of oil shale resources development and utilization.At present,the oil shale in-situ pyrolysis technology can be divided into four categories:electric heating conduction technology,radiation heating technology,gas heat convection technology and chemical reaction heat diffusion technology.However,no matter what kind of technology involves heating oil shale,the heating efficiency becomes an important indicator to measure the in-situ technological advancement.Electrical heating conduction technology uses the resistance heat of the buried electric heater as the heat source,and the heat is transmitted to oil shale to make kerogen pyrolysis.Because of the high content of organic matter,the thermal conductivity of oil shale is poor,which leads to the shortcomings of low heating efficiency and long heating time.Radiation heating technology transmits energy in the form of energy wave,while compact oil shale is not conducive to energy wave conduction,so radiation heating technology has high energy consumption and low heating efficiency.Gas Thermal Convection Technology based on convective heat transfer,heat transfer is direct and heating efficiency is high.Chemical reaction heat diffusion technology relies on the reaction heat of oil shale itself to heat oil shale formation,which has the highest efficiency and relatively low production cost.Gas thermal convection technology and chemical reaction heat technology all need to inject pre-heated gas or liquid medium into oil shale.The heating efficiency of fluid medium directly determines the practicability of these two technologis.Therefore,it is very important to study an efficient heat injection system suitable for oil shale gas thermal convection technology and chemical reaction heat technology.At present,China is building three pilot projects for in-situ cracking of oil shale,all located in Jilin Province.They are:Nong’an TS-A method of Jilin University,"Pilot of project for underground in-situ pyrolysis of oil shale","Fuyu SCW method of Jilin University of Pilot of project for underground in-situ pyrolysis of oil shale","Pilot of project of fracturing chemical retorting of Zhongcheng Group".In this paper,t Nong’an TS-A method of Jilin University,"Pilot of project for underground in-situ pyrolysis of oil shale",is taken as the research background to study the in-situ surface heat injecting system of oil shale.The heat injecting system mainly consists of three subsystems:combustion heat generation subsystem,high temperature and high pressure heat exchange subsystem and high temperature heat injection and insulation pipe string subsystem.Start the burner,the combustion gas supply module supplies combustible gas and air to the burner.After ignition,the combustion tail gas and the injected gas medium exchange heat in the high temperature and high pressure heat exchanger,and the heated gas medium injects oil shale layer through the high temperature heat injection pipe string to crack oil shale to generate oil and gas.Firstly,the subsystem of combustion heat generation is studied.Starting from classical theory,the combustion theory of semi-enclosed small chamber is studied to clarify the combustion mechanism;the combustion control theory is studied to optimize the combustion effect of combustible gas;the combustion control logic is designed,and the combustion control valve group is integrated to optimize the burner suitable for pyrolysis gas combustion.Form a complete design of combustion heat generation subsystem.Then,the sub-system of high temperature and high pressure heat transfer is studied.Select the form of heat exchanger,carry out thermal calculation,determine the basic parameters of heat exchanger,and then simulate the heat exchanger.Four kinds of bow baffle heat exchangers are selected.By simplifying geometric model and combining with theoretical calculation,the parameters of fluid flow field,temperature field on the surface of heating tube and comprehensive heat transfer performance on the shell side of bow baffle heat exchanger are analyzed,and the type and spacing of bow baffle in heat exchanger are determined.Form a complete high temperature and high pressure heat exchange subsystem design.Then,the subsystem of high temperature heat injection and insulation pipe string is studied.The subsystem of high temperature heat injection and insulation pipe string includes surface high temperature and pressure pipeline and in-well heat injection and insulation pipe string.The thermal stress design of surface high temperature and high pressure pipeline is carried out to improve the stress state of pipeline under extreme working conditions and ensure the safety of gas injection.The thermal conductivity and efficiency analysis of borehole heat injection and insulation pipe string is carried out to optimize the type and size of insulation material and enhance the heat injection effect.Form the subsystem design of high temperature heat injection and insulation pipe string.Finally,in-situ pyrolysis of oil shale surface heat injection system test and thermal efficiency analysis are carried out.The developed heat injection system is used in in-situ pyrolysis engineering.By collecting the key data of temperature,pressure and flow rate,the efficiency and adaptability of heat injection are analyzed,and then the heat injection system suitable for in-situ pyrolysis of oil shale is designed according to the needs of in-situ process optimization and upgrading.In the in-situ pyrolysis test project,the heat injection system studied operates normally,the combustion heat transfer efficiency is high,and the work is stable,which lays a solid foundation for the implementation of in-situ pyrolysis technology of oil shale.Finally,the first barrel of shale oil was produced by using this heat injection system in Nong’an Pilot of project for underground in-situ pyrolysis of oil shale of Jilin University. |
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