Performance Analysis of a Wind Powered Gas Storage System Available to Purchase

All over the world huge masses of gas are compressed in a number of storage stations to compensate seasonal fluctuations of the users’ demand versus the methane extraction from geological deposits. In the great majority of such plants, turbo-compressors are used, namely centrifugal machines. Since in this kind of machines compression is essentially adiabatic, gas temperature rises up even to dangerous values. Natural gas cannot be injected into the reservoirs too hot without risk of geological damage, so often an after-cooler has to be provided. Natural gas compressors are driven by gas turbines (GT), fuelled by part of the gas flowing through the station; otherwise electric motors connected to the general grid are used. In the paper the exploitation of the renewable energy of the wind to drive the compressors of the system is proposed. The matching with the driving wind turbine is different from the matching with a gas turbine or an electric motor. However whereas the stochastic character of the wind source affects power generation seriously, in the proposed use it is not a real problem: the only constraint consists of having enough wind energy to complete a charge all over a season. An in-house code, based on the lumped parameter approach and a quasi-steady dynamics, has been developed in order to simulate the system performance during a complete charge for a known wind distribution. The turbo-compressor is modeled through its characteristic maps. Similarly the wind turbines, that drive the storage station, and the fans, that counterbalance the friction losses of the after-cooler, are replaced with their characteristic curves. The after-cooler, which is a gas-air compact heat exchanger, is modeled by means of the overall heat transfer coefficient and the total pressure losses. Finally the reservoir is supposed omothermal and isothermal. In order to investigate the plant performance, different kinds of wind distributions have been considered and the corresponding operation paths as well as power and pressure evolutions are shown and discussed.