| Isothermal compressed air energy storage(I-CAES)system,as an efficient,environmentally friendly and flexible compressed air energy storage system,has great development significance and commercial value.At the same time,improving the efficiency of the compressed air energy storage system has always been a goal pursued by scholars.The current compressed air energy storage power station is mainly based on non-adiabatic compressed air energy storage,however,its thermodynamic performance is not as good as an isothermal compressed air energy storage system.If isothermal compressed air energy storage power station technology can be widely promoted in the future,this will be of great significance for energy utilization and environmental protection.The research goal of this thesis is to increase the efficiency of the energy storage system,so it is necessary to analyze its thermodynamic mechanism.First of all,the conservation of energy and the balance of exergy in the energy storage process of the isothermal compressed air energy storage system were analyzed.The results show that the input energy is equal to the output energy under ideal condition,and its cycle efficiency can reach 100%.At this condition,the mechanical exergy of the compressed air is the largest and the thermal exergy is zero.In practice,it is necessary to reduce the internal frictional losses and irreversible losses caused by small temperature differences,and to enhance the heat transfer efficiency in the compression process for increasing the efficiency of isothermal compressed air energy storage.Secondly,the system operation process was simplified,polytropic constant-pressure cycle and polytropic constant-capacity cycle were proposed to fit the isothermal cycle,and the system efficiencies under the single stage and multistage schemes were studied.It is concluded that the efficiency of the former is higher than the latter under the single stage scheme,and the appropriate pressure ratio plays an important role in the cycle efficiency.Under the multistage scheme,the cycle efficiency increases with the increase of the number of stages;When the total pressure ratio and the number of stages are fixed,the order of pressure ratio distribution has no effect on the cycle efficiency,and the system with the same partial pressure ratio has the highest efficiency.Polytropic constant-pressure cycle efficiency is closer to the isothermal cycle,and changing the initial temperature has no effect on the two cycle efficiency under single stage or multistage program.Finally,a near-isothermal compression model and an isothermal inflatable model with the polytropic exponent close to 1 were established,the water spraying flow rate under different parameters was analyzed with process heat.At the same time,the energy efficiency and exergy efficiency of system were obtained,it provided theoretical data and reference value for the actual test and application.The main research results are as follows:(1)Pressure ratio,heat transfer efficiency and final temperature have affects on the mass ratio of air to water respectively;(2)When other conditions are fixed,crankshaft speed has no effect on air-water mass ratio,but it increases the water spraying flow rate;(3)The smaller temperature differences lead to the smaller influence of the initial temperature on the water spraying flow rate,and the high pressure ratio weaken the effect of the initial temperature on the water spraying flow rate;(4)There is no difference in the methods of calculating the water spraying flow rate,and it leads to the similar calculation results with difference accuracy of 0.1;(5)The system exergy efficiency will be up to 96% under certain conditions,and the increasing of pressure ratio and the temperature difference will reduce the system efficiency. |
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