Abstract
The paper presents the prototype of the first Romanian Compressed Air Energy Storage (CAES) installation. The relatively small scale facility consists of a twin-screw compressor, driven by a 110 kW threephase asynchronous motor, which supplies pressurized air into a 50m3 reservoir, of 20 bar maximum pressure. The air from the vessel is released into a twin-screw expander, whose shaft spins a 132 kW electric generator. The demonstrative model makes use of a 5m3 water tank acting as heat transfer unit, for minimising losses and increasing efficiency and the electric power generated. Air compression and decompression induce energy losses, resulting in a low efficiency, mainly caused by air heating during compression, waste heat being released into the atmosphere. A similar problem is air cooling during decompression, lowering the electric power generated. Thus, using a thermal storage unit plays an essential role in the proper functioning of the facility and in generating maximum electric power. Supervisory control and data acquisition is performed from the automation cabinets. During commissioning tests, a constant stable power of around 50 kW with an 80 kW peak was recorded.
Highlights
Electrical energy storage [1, 2] is a process in which electrical energy from a power network is converted into a form that can be stored, and converted back to electrical energy when needed
Compressed air energy storage (CAES) is a technique for supplying electric power to the grid for meeting peak load requirements, conventional compressed air energy storage being a practicable technology for electric load levelling
The heat of the cooling oil is partially recovered by the 5 m3 water tank, that stores the thermal energy of the oil tray, and transfers it to the oil heating the expander, since air expansion is accompanied by a severe temperature drop
Summary
Electrical energy storage [1, 2] is a process in which electrical energy from a power network is converted into a form that can be stored, and converted back to electrical energy when needed. A CAES power generation facility uses electric motor-driven compressors to inject air into a reservoir, later releasing the compressed air to turn turbines and generate electricity into the grid. The low efficiency is mainly caused by air heating during compression This waste heat, which holds a large share of the energy input, is released into the atmosphere. In the compression and expansion processes occurring in a CAES installation, the heat loss in the compression process, respectively the useful energy loss in the expansion process, are high, in a direct dependency with compressor and expander systems. Depending on the process heat recovery solution chosen, the efficiency of an energy storage station can vary between 41% and 75%, and a share of more than 65% of the heat resulted from compression can be recovered in the form of transferred energy [8]
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