10.12.2004 - A customer in Germany ordered a HOFIM™ Sealed (tandem version) compressor for a gas storage application in 2002. The same customer compresses gas with a HOFIM™ compressor in standalone configuration since 1991. The most recent order comprises several new conceptual features. The technical improvements of the HOFIM™ Sealed make dry gas seals redundant, and even the motor cooling system is very simple since the motor is now cooled with process gas.

The above described machine was shipped after successful internal and contractually agreed tests in April 2003. After only 4 months of installation works and commissioning, the customer took over the machine for commercial operation.

Differences between gas supplies and demands in gas transport networks can be equalised by use of gas storage facilities. Gas storage is not only a viable solution technically to buffer energy, it is also commercially interesting since it allows the trading of gas and can satisfy short term demands.

Excess or cheap quantities of pipeline gas are pressed into underground gas caverns by compressors. When the pipeline system demands more gas, the operator of the gas storage facility sells gas from the stock to the grid. Gas naturally flows from high pressure sources to lower pressures. Should the cavern pressure fall below the pipeline pressure, the same compressor sucks gas from the cavern and pushes it into the pipeline grid. This is done with the same installation but in reverse direction. Gas parameters like pressure ratios and quantities continuously change during these processes, this requires a flexible compressor regime with high efficiencies over a large operating range to guarantee economics.

The HOFIM™ Sealed tandem compressor concept allows to operate two barrel type compressor in series or parallel mode. The equation of two modes, plus a speed control feature, give a larger compressor envelope with two optimum efficiency areas. Since the envelope of the series to the parallel mode are overlapping, one can switch between two significant basic operating modes. Either a map for low volume flows with a high polytropic head or a map with large volume flows and a low polytropic head. Thanks to the attribute of two envelopes in one machine, the energy costs to operate the plant can be considerably reduced.

HOFIM™ Sealed convinces through high flexibility for changing operating parameters. The other big advantage is the enhanced environmental compliance due to zero emissions of process or flue gases, a very low noise level, and much lower space requirements to install the machinery. The above highlighted advantages are based on the fully encapsulated design. The high frequency motor is cooled by process gas and is bolted with joint surfaces between the two barrel compressors. The rotor is one system without couplings and is centred in the machine with active magnetic bearings which makes the machine wear free.

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