Performance Optimization And Experimental Study On Geothermal Power Generation System Based On Cycle Decoupling And Matching Reservoir Characteristics

In view of high energy utilization coefficient and little environmental influence of geothermal power generation system,which has an advantage for base load and variable load.To deal with the internal strong coupling issue of geothermal power generation system,single or multistage geothermal power generation system composed of flash system and ORC are taken as research object in this paper.Then,performance analysis and experimental study on geothermal power generation system are investigated in this paper,based on process decoupling and matching heat source characteristics,striving to improve the thermodynamic perfection of geothermal power generation system,meanwhile with excellent technique economics and the carrying capacity of the environment.The main contents and conclusions are as follows:Firstly,the thermodynamic process separating method is proposed for subscritical ORC written asη_ORC=f(η_TCη_CCη_BC).Research shows that,the thermal efficiency of subcritical saturated organic Rankine cycle is equal approximately,when the reduced evaporating temperature and condensing temperature of two working fluids are equal.When the reduced characteristic temperatures are equal,the cycle efficiency of dry working fluids decrease with the increase of degree of superheat,but wet working fluids are on the contrary,of which the variation of cycle efficiency is proportional to degree of superheat.The thermodynamic empirical correlation of the optimal cycle performance and its corresponding working conditions is established:W_net,opt=C*T_cti^m*ω_wfⁿ*T_AS^O.Then,the directed association between critical temperature,compression factor,heat source character and optimal cycle performance and operation condition is established.Secondly,thermodynamic optimization model of multistage cycle geothermal power generation matching geothermal character is proposed.When degree of dryness is 0.4 and geothermal fluid temperature is greater than 200℃,the efficiency is as follows:flash-binary（R245fa）combined system>single flash system>double flash system>flash-binary（R218）combined system.For flash-binary combined system,when geothermal fluid temperature is between 160℃and 200℃,the maximum power output is:R245fa>R227ea>R141b>R218.Thirdly,multi-objective optimization model of organic Rankine cycle based on noninferior solution is completed.Comprehensive thermal-economic comparison method for system construction and working fluids selection of organic Rankine cycle is proposed.The basic organic Rankine cycle（R245fa as working fluid）has the optimal comprehensive performance,which aims at the highest exergy efficiency and unit power investment.Without regard to security and environmental influence of working fluid,the best working fluid with comprehensive performance is R141b,R21 is the worst.At the same time,life cycle assessment of geothermal power generation system based on thermal optimization model is established.Four tipical heat reservoirs and their corresponding geothermal power plants are regarded as research objectives.The on-ground system is composed of power plant construction and unit production,operation,maintain process.The life cycle environmental impact of completion of underground drilling and on ground system on ground system is almost equal.Diesel,steel,copper and water are major factors affecting environmental impact potential of geothermal power generation.The bigger the temperature gradient of geothermal reservoir is,the more excellent geothermal generation potential is,meanwhile the smaller impact is.Finally,k W level of low and medium temperature geothermal combined Flash-Binary power generation test bench is built,and the working medium pump start-up and load change of the organic Rankine’s generating system reliability test is completed.While,relationships between working fluid flow and the performance of system and equipment are investigated.