The Numerical Simulation Of Geothermal Power Generation Using Abandoned Oil Wells And Hot Cavity

Working fluid with low boling point can be injected into hot cavity underground taking advantage of the property of ORC (Organic Rankine Cycle) power system. The producted working fluid has high temperature and high pressure, and the heat energy in int can be converted into mechanical energy and electric energy through some certain thermodynamic cycle. The composition and working principle of geothermal power generation system using abandoned oil wells and hot cavity are studied in this article, and its difference and advantage from traditional ORC power system is discussed. Then the following contents are studied systematically on the basis of thatThe heat transfer system, that using abandoned oil wells as its injection and production well, and hot cavity as its geothermal reservoir, is studied. As for injection and production well, geothermal gradient is used as the vertical distribution of temperature, and the axial symmetry is considered. So one dimensional heat transfer model of vertical oil well and horizontal rocks adjacent are developed, their temperature fields are coupled with convection boundary. The energy partial differential equations are discreted by finite difference method and finite volume method, the temperature field is solved by MATLAB software calling physical property software REFPROP, and the idea of ADI (Alternative Direction Implicit) algorithm is refered at the same time. As for hot cavity, the three dimensionial finite element model is built in GAMBIT condering its symmetry and porous property. And the numerical solution is done in FLUENT using NIST real gas model.The one dimensionial model of injection and production well and the three dimensionial model of hot cavity are integrated in MATLAB. The parametric modeling in GAMBIT, the parametric analysis of oil wells’temperature field and the parametric analysis of cavity’s temperature field are achieved in MATLAB, the related M files are edited.The outlet temperature is studied, which is changing with running time, geothermal gradient, inlet pressure, inlet temperature, mass flow rate, rocks’thermal conductivity, different working fluid, and so on. Propertis of temperature and flow field in hot cavity and oil wells are also discussed as well as the optimal vapor temperature. The result indicates that the most important factors influcing outlet temperature are inlet temperature, geothermal gradient and mass flow rate. All these iactors should be the key consideration in the real exploration. On the other hand, the inlet pressure and inlet temperature has little influence, which should be determined by environmental temperature.Net power and efficiency of the whole geothermal power system under different working conditions are computed according to the result of analysis of heat transfer. The changing state of Net power and efficiency is compared for different conditions, and the optimal power parameters and power scheme are summarized. The result indicates that for a certain system, there is an optimal vapor temperature and mass flow rate; the inlet pressure should be lower but not too low to make the inlet fluid’s state liquid; the Net power is higher with bwer inlet temperature, so the system should better run in winter and shut down or run intermittently in summer; the organic working fluid should be chosen if the system is sealed well.