Thesis

Thermal Design and Analysis of a Solid-State Grid-Tied Thermal Energy Storage for High Temperature Hybrid Compressed Air Energy Storage System

With the ever-growing demand of energy to power homes, businesses and intuitions, power plants are placed in increasingly difficult situations of predicting energy consumption and balancing power output. Peak hour energy can cost up to twice as much as energy generated during non-peak hours. With alternative solutions needed, the High Temperature Hybrid Compressed Air Energy Storage (HTH-CAES) system can be used to counter costly energy generation during peak hours. The HTH-CAES system converts electrical energy during non-peak hours into a combination of storable form of intermediary energy (compressed air and thermal energy). Part of the electrical energy is converted to heat using resistive wires in a High Temperature Thermal Energy Storage (HTES). During the discharge cycle, the compressed air is released to be passed through the charged HTES. The thermal energy is transferred to the passing air and sent to a turbine to generate power back to the grid. The HTES is a solid state system that utilizes high temperature concrete as the storage medium. For system output optimization, the HTES is studied computationally through a transient Finite Volume Method by a commercial CFD package (ANSYS FLUENT). The computational model is validated by comparing theoretical calculations to energy output and grid-refinement study. The objectives of this study is to optimize the configuration of resistive heaters to prevent overheating, achieve temperature uniformity, ensure heated air is at desired temperature and ensure heat losses are manageable. In the next phase, computational fluid dynamics (CFD) was implemented to verify the heat transfer performance during discharge cycle. CFD results with all objectives achieved with 0.4 kg/s and 0.6 kg/s as successful mass flow rates for operation.

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