| With the extensive use of renewable energy and the urgent need for power grid peak-cutting and valley-filling,large-scale energy storage technologies have been developed in recent years.Among many methods of energy storage,Compressed Air Energy Storage(CAES)is considered as the most promising large-scale energy storage system.Institute of Engineering Thermophysics,Chinese Academy of Sciences independently designed and developed advanced compressed air energy storage system,which effectively overcame the weaknesses of traditional compressed air energy storage systems,such as fossil fuel combustion,reliance on natural gas storage cave,and low system efficiency.Based on this,a world's first MW-class compressed air energy storage demonstration system has been built to promote the development of compressed air energy storage technology.As the main equipment that converts the internal energy of compressed air into mechanical energy and promotes the power generation of generators,the expander is the core component in the compressed air energy storage system,and its efficiency directly affects the working capacity of the compressed air energy storage system.On the one hand,compressed air energy storage systems,as energy storage equipment in power transmission,need to be operated under variable conditions.On the other hand,there is a long-term pressure difference between the gas storage device and the inlet of the expander.Therefore,it is necessary to perform a reasonable and effective air distribution adjustment on the expander to match the inlet pressure of the expander and achieve variable working condition adjustment.The current air distribution method used in the system is throttling governing.However,through this method,all the air flowing into the expander has been throttled,causing a lot of losses.To solve the above problems,this thesis initially applies the nozzle governing mode in a centripetal expander of a compressed air energy storage system to reduce the flow of throttled gas,thereby reducing the throttling losses.In this thesis,numerical calculation and analysis of the whole expander under variable working conditions are carried out through computational fluid dynamics(CFD)method.The main research contents are as follows:1.According to the existing structural characteristics,a three-dimensional mathematical model of the nozzle governing expander is established.Based on the results of grid-independent verification and numerical method verification,it is believed that the established model in this thesis can perform accurate numerical simulation on the research objects.2.By adjusting the air state at the inlet of each nozzle group,the effects of air distribution on the performance of the regulating was studied.The results show that under the condition of nozzle governing,the flow rate of the expander varies between 0.86 and 1.42 times of the rated flow rate,which meets the regulation needs;at specified flow rate,during the entire operation,the output of the regulating stage can be increased by 11.2% compared with the throttled governing,and the total efficiency can be maximumly increased by 9.4%.3.Based on the above numerical calculations,the three-dimensional structure and loss mechanism of the internal flow field of the expander during nozzle governing mode are further analyzed and revealed.The research results show that under the condition of nozzle governing,the design of the partition of the chamer basically does not affect the aerodynamic performance of the chamber;As the pressure at the inlet of the governing passage decreases,the total pressure loss coefficient of the governing passage-corresponding chamber will increase when there is no fully-closed passage in the system,otherwise it will basically remain unchanged;The change in the pressure at the inlet of the governing passage does not affect the total pressure at the outlet of the adjacent stator passage.As the total pressure at the inlet of the governing passage is reduced,the aerodynamic load of the rotor is translated downward,and at the outlet of the rotor,the total pressure reduces while the static entropy increases.The above research reveals the effects of air distribution on the performance of the radial expander,which provides a theoretical basis for the design,optimization and system operation control of the nozzle governing radial expander. |
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