Numerical Simulation And Experimental Study On Downhole Electric Heater With Continuous Helical Baffles

At present,oil shale exploitation technology can be divided into surface retorting and underground in-situ pyrolysis.Surface retorting requires the mining of underground oil shale resources.Due to this characteristic,not only a lot of effort and money are required,the waste also occupies a large area.While underground in-situ pyrolysis,which is equivalent to the "refinery" underground,directly heats the oil shale underground without mining onto the surface.The oil and gas produced via pyrolysis are then transported to the surface.This technology can effectively overcome the drawbacks of surface retorting.According to different injection modes,underground in-situ pyrolysis can be divided into two modes,including surface injection and downhole direct heating.The process of surface injection technology requires two steps.First,the gas to be injected to oil shale formation is heated on the ground before its injection.In the second step,the hot gas is injected to oil shale formation.This technology suffers from its low energy utilization due to the significant heat loss during transporting.So it can only be applied to shallow oil shale exploitation.On the other hand,downhole direct heating outstands for its high energy utilization,because it uses downhole heater to heat the injection gas.So it can be applied to both deep and shallow oil shale exploitation.This study mainly focused on the key component of downhole direct heating technology-the downhole,especially on the electric heater with continuous helical baffles.A systematic design of the downhole heater was carried out firstly in this study.According to the operating conditions,the control system of the heater was analyzed theoretically,the PID control scheme and control process were then established.Based on the theory of shell-tube heat transfer,two heat transfer structures,transverse baffle and continuous helical baffle,were analyzed.It is concluded that the continuous heat transfer structure of spiral baffle is suitable for gas heating in oil shale wells.A kind of horizontal baffle plate heater with baffle spacing of 110 mm and four kinds of continuous helical baffle heaters with pitch of 50,110,160 and 210 mm are used as the model machine to study and give detailed Design Parameters.In the third chapter,the numerical simulation of five kinds of heater model machines proposed in Chapter 2 is carried out.A simplified model was established for the heat model using Soild Works software.The grid was divided by ANSYS Meshing 14.0 software and then calculated by numerical simulation of Fluent 14.0.The flow field of the shell side of the heater,the heat transfer coefficient and the temperature of the heating tube,the pressure drop of the shell side are analyzed.The results show that compared with the transverse baffle heater,the continuous helical baffle heater Uniform flow,there is no flow dead zone,the heating tube surface heat transfer coefficient and temperature uniformity,there is no local high temperature zone,shell pressure drop smaller;continuous helical baffle heater heating tube surface heat transfer coefficient.The pitch decreases and the surface temperature increases gradually with the increase of the pitch,and the pressure drop decreases gradually with the increase of the pitch.In the fourth chapter,four experimental experiments were carried out on four kinds of continuous helical baffle heater model.In the experiment,the temperature of the inlet and outlet of the heater,the inlet and outlet pressure and the surface temperature of the heating tube were collected.According to the purpose of the study,the experiment is divided into constant power experimental scheme and adopt the constant outlet temperature experimental scheme.The Reynolds number,the heat transfer coefficient and the shell pressure drop are studied by constant power experiment.The surface temperature of the heating tube is studied by constant temperature scheme.The Reynolds number,the heat transfer coefficient,the surface temperature and the pressure drop of the heating tube are studied.The results show that the gas viscosity increases gradually and the Reynolds number decreases gradually,which tends to develop in the process of plunger flow.The Reynolds number increases gradually with the pitch decrease,and the pitch The smaller the trend,the more obvious the lower trend;the heater shell Reynolds number and heat transfer coefficient to establish a good correlation,you can see the heater shell Reynolds number and gas properties determine the heat transfer performance of the heater,appropriate to improve the heater The Reynolds number measures can improve the heat transfer coefficient of the heater.The nominal heat transfer coefficient increases linearly with the increase of the mass flow rate.The smaller the pitch is,the higher the growth rate is.The same mass flow rate decreases with the pitch The surface temperature of the heating tube increases with the direction of the gas flow in the shell side,and the higher the pitch is,the higher the temperature is.The simulation results of h / ?P and h · ?P-1/3 are used to evaluate the simulated and experimental values of the continuous spiral baffle heater model of the four schemes.The results show that the H160,the optimal performance of the continuous helical baffle heater is optimal for the design of the heater in the in situ transformation of oil shale gas injection.