| Energy storage technology is an effective way to solve the problem of renewable energy consumption,and has received more and more attention in recent years.Compressed Air Energy Storage(CAES)is one of the most suitable technology for large-scale energy storage.It has many advantages such as high reliability,low energy storage cost,flexible layout,and negligible environmental impact,and is regarded as one of the most promising energy storage technologies.In the application scenario combined with renewable energy generation,variable operating conditions are a key issue for CAES systems.A variety of variable working conditions,represented by changes in air storage pressure and fluctuations in load demand,often exist simultaneously in the operation of the system,and have an important impact on the efficiency and technical economy of CAES systems that are in a state of long-term operating under variable working conditions.It also put forward higher requirements and new challenges for its the design and operation.Regarding the issue above,this paper takes the Low-temperature Adiabatic Compressed Air Energy Storage(LTA-CAES)system as the research object to carry out the research on its off-design performance analysis and design optimization respect to its integration with renewable energy generation.Complex variable operating conditions including changes in air storage pressure and load fluctuations are considered.The main research contents of the paper are as follows:(1)Analysis of the LTA-CAES system characteristics under variable working conditions was carried out,revealing the variation of key parameters and the conversion and utilization characteristics of energy under different variable operating conditions including air storage pressure changes and load fluctuations.The off-design charging characteristics based on the multistage-intercooled reciprocating compressor was studied,and it was found that the energy storage efficiency will be significantly reduced only when the load deviates too much from the design value.Therefore,the effective energy conversion efficiency of the charging process is maintained at a high level of around 80%.The analysis of the off-design discharge characteristics for the multi-stage reheating expander based on valve throttling shows that the discharge efficiency is significantly affected by the load fluctuation and the air storage pressure changes,while excessive throttling loss is the main reason for the performance deterioration.(2)A mean-line model capable of the performance prediction of the radial turbine in the case of pressure ratio changes and nozzle opening changes was established.Based on it,the feasibility of using the load control method based on nozzle opening regulation was carried out.Moreover,a computationally efficient bi-directional nozzle control strategy was developed to optimize nozzle openings of multistage radial turbines during the discharge process.It was found that the combination regulation of the nozzle opening in multistage radial turbine can effectively improve the oif-design discharge efficiency under the condition that the output power is negatively adjusted and the adjustment amplitude is greater than about 40%.Compared to valve throttling control that is used commonly,despite the reduced turbine efficiency,the proposed bi-directional nozzle control strategy increased discharge efficiency significantly under part-load operation due to the absence of throttling losses.(3)The design optimization of the multistage reheating radial turbine based on nozzle control was carried out from two aspects:the overall parameter design and the preliminary design of the radial turbine stage.It was found that,for the specific operating conditions of the LTA-CAES system,the heat storage temperature has little effect on the expansion ratio distribution,but the optimized value of the turbine stage is closely related to the heat storage temperature.The preliminary design study of the radial turbine with the off-design performance as the optimization target shows that the different design values of the nozzle outlet flow angle will lead to significant differences in the efficient operating range of the radial turbine.The above findings can result in radial turbine designs with different ofF-design performance under the variable nozzle opening condition,which can provide a useful guide for the design of the multistage-reheating radial turbine based on the nozzle opening regulation.(4)Combined with the research results and engineering design requirements of LTA-CAES system performance analysis and design optimization,a special design software was developed for the scheme design and simulation analysis of LTA-CAES system.It can help researchers and engineers make more efficient work. |
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