| Renewable energy sources such as solar energy and geothermal energy have low temperatures,and research on efficient and stable power cycles can help improve the utilization of low-temperature heat sources.The organic Rankine cycle power generation technology adopts organic working medium.Compared with the traditional organic Rankine cycle,the working temperature and working pressure are lower,and the low temperature heat source can be effectively utilized.In this paper,a technical and economic study of a solar-geothermal combined organic Rankine cycle power generation system is carried out to determine the optimal design parameters of the system.This paper takes a 300 k W solar-geothermal combined-driven organic Rankine cycle power generation system as the research object,and establishes a system dynamic power generation model based on EBSILON.In this software,the simulation model including the collector,the heat storage tank,the condenser,the evaporator and the pump and the control strategy for the operation of the system are established.Firstly,the performances of six different organic working fluids in the system were compared and analyzed,and the influence of the evaporation temperature and the temperature change of the heat transfer oil outlet of the collector field on the power generation and efficiency of the system were studied.Secondly,the basic control strategy of the system is determined,and the dynamic simulation of the typical days of the four seasons in the whole year is carried out,and the dynamic characteristics of the system performance parameters with the changes of solar radiation and geothermal water parameters are studied.Finally,with DNI(direct solar radiation),SM(solar multiple)and heat storage hours as variables,and LCOE as the calculation index,the economic calculation of the system is carried out.The research results show that from the three aspects of system stability,power generation and system efficiency,the most suitable organic working fluids for the system are R123,R114 and R245 fa.Taking R245 fa as an example,with the increase of the evaporation temperature and the outlet temperature of the heat transfer oil in the collector field,the power generation of the system first increases and then decreases.The optimal evaporation temperature is 127.3 °C,and the corresponding evaporation pressure is 2.2MPa.The oil temperature was 230°C.Through the simulation of all-day working conditions on typical days,it is found that due to the similar solar radiation conditions in spring and autumn,the parameters of system operating conditions change similarly.In typical days in winter,due to insufficient solar radiation illuminance,the focusing coefficient of the collector field is greater than 0.9 during normal operation.On a typical day in summer,the focusing coefficient is about 0.4 due to the high solar radiation.By studying the change of the proportion of heat provided by geothermal,it is found that with the increase of geothermal temperature,the proportion of heat provided by geothermal basically increases linearly,and the power generation basically shows an upward trend.With the increase of geothermal flow,the proportion of heat provided by geothermal tends to be stable,and the power generation first increases and then decreases.This is because the pump power consumption exceeds the output work provided by the geothermal heat to the power generation system.With the decrease of the design DNI,the increase of the SM and the increase of the heat storage time,the area of the heat collecting field and the capacity of the heat storage tank increase,the power generation increases,and the cost increases accordingly.Under the environmental conditions of the local subtropical monsoon climate,there are optimal design conditions that make the LCOE the lowest.The calculation results show that when the design DNI=700k W/m2,SM=1.4,TES hours=2h,the LCOE=0.772 (?)/k Wh,the power generation E=1199100k Wh.The research in this paper helps to grasp the characteristics of the solar-geothermal organic Rankine cycle power generation system,and provides a useful reference for the optimal design of the system. |
