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, turbocompressors
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.
