Bi-Directional Turbomachinery for Use in Pumped Thermal Energy Storage
Advisor: Dr. CS Tan, Professor E Greitzer
Grid-scale energy storage devices are a necessary component of a stable and environmentally friendly electric grid. When electricity supply exceeds demand, a pumped-thermal storage device uses a heat pump to transfer thermal energy from a cold body to a hot one, storing it. When demand rises, the process reverses, driving turbomachinery in a recuperated Brayton cycle. This withdraws the thermal energy from storage, passing it back into the grid as electric energy. Past research has explored the thermodynamic cycle in detail, determining appropriate storage media, designing heat exchangers, and estimating round-trip efficiency. A baseline system uses multiple turbomachines, for separate operation in each direction.
In this research, the MIT Gas Turbine Lab, in collaboration with Brayton Energy, is designing a bi-directional turbomachine to serve as both compressor and turbine. This bi-directional machine must be matched both geometrically and thermodynamically. Geometrically, the blade profiles must be designed for operation in either direction, with thin leading and trailing edges to reduce profile losses. Thermodynamically, the machine must achieve the desired pressure ratio in both directions, fulfilling the cycle requirements as both a heat pump and a Brayton cycle. Using one turbomachine instead of two separate single-direction turbomachines simplifies the storage device gas path, reducing parasitic losses in the system. Additionally, using a bi-directional turbomachine significantly reduces the cost of manufacturing the storage device as a whole.
