Multistage Radial Turbine For Supercritical Compressed Air Energy Storage System

Electrical Energy Storage(EES) technologies are increasingly important in the power system. The Compressed Air Energy Storage(CAES) technology is one of two types of commercially available ESS technologies in large scale. However, the traditional CAES has the drawbacks of dependence on fossil fuels and low energy density. A supercritical CAES system is developed by researchers to conquer these problems. The multistage radial turbine is one of the key components of supercritical CAES, whose performance directly affects the efficiency of energy storage system. It is of imperative to make full and detailed investigate on developing the highly efficient and stable multistage radial turbine in order to improve the efficiency of whole energy storage system.In this thesis, the multistage radial turbine system of the supercritical CAES was thermodynamically analyzed. The four-stage radial turbine was designed and studied through an in-house coding and the turbine unit design results were obtained. Then it was studied through Computational Fluid Dynamics(CFD) to reveal its internal flow field and performance under various working conditions. The four-stage radial turbine rig of the supercritical CAES was built to conduct the experimental research.The main contents of the thesis were as follows:1. The performance and design criteria of air powered multistage turbine were studied thermodynamically. It was simulated the energy and exergy distributions. And the characteristics of multistage turbine with inter-heating were optimized in terms of maximum thermal efficiency, maximum exergy efficiency and maximum workoutput over different inlet temperatures. The systematic parameters of multistage radial turbine were developed for MW-level supercritical CAES system.2. The design method was investigated in detail, by which the four-stage radial turbine was designed. The impellers of the first and second stage radial turbines were closed impellers, and the third and fourth stage radial turbines were semi-open impellers. The design method consisted of one-dimensional design method, blade design method and three-dimensional optimization. The one-dimensional design method was based on the experimental data and simultaneously optimized such parameters as load factor, flow coefficient, specific speed and velocity ratio.3. The aerodynamic characteristics of radial turbine under design and off-design conditions were investigated in detail through the CFD technology. It was investigated the guide vane row and rotor row passages’Mach number, pressure and entropy distributions. The outlet parameters of the guide vane was agreed well with the designed results. The losses of the guide vane row mainly occurred in the throat and blade surface. The losses of the rotor row mainly occurred in the impeller tip and wake regions. The study of the radial turbine indicated that it could achieved a relatively high efficiency under a relatively large range of rotation speed and expansion ratio.4. The four-stage radial turbine experimental rig for MW-level supercritical CAES system was established including radial turbines, gear transmission system, load management system, pressure control system and temperature control system. This rig could fulfill experimental requirements of multistage radial turbine system with highspeed and high expansion ratio. The experiments were carried out to study its start-up characteristics and overall performance. It was concluded that:its start-up time was within5minutes; under7.0MPa inlet pressure the efficiencies from the first stage radial turbine to the fourth stage radial turbine were80.0%,87.9%,82.2%and89.1%, respectively; the total efficiency of the four-stage radial turbine system was84.4%.