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In a compressor drive system for a natural gas liquefaction plant including a plurality of gas turbines each provided in an individual refrigeration cycle for pressurizing a different refrigerant, an electric motor is provided for each of the gas turbines so as to serve both as an auxiliary electric

In a compressor drive system for a natural gas liquefaction plant including a plurality of gas turbines each provided in an individual refrigeration cycle for pressurizing a different refrigerant, an electric motor is provided for each of the gas turbines so as to serve both as an auxiliary electric motor for generating a startup torque and as an AC generator, and the excess output power of the gas turbine is converted into electric power by this electric motor when the power requirement of the associated compressor is less than the power output of the gas turbine. Additionally, at least two of the gas turbines are of an identical make which is suitable for driving the compressor of one of the associated refrigeration cycles requiring a larger driving power. Therefore, the gas turbines can be operated at optimum conditions at all times without regard to seasonal changes of the operating conditions, and the efficient operation of the gas turbines will result in a significant reduction in the operation costs through a substantial saving of fuel consumption. Moreover, any excess power output of one of the gas turbines can be allocated so as to reduce the burden of the in-plant power station and/or to supplement the shortage of the power output of the other gas turbine, and the management of the stand-by units and spare parts can be simplified. These factors have a compounded effect in reducing the investment costs of the plant.

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A compressor drive system for a natural gas liquefaction plant including: a pair of gas turbines, each of said gas turbines being installed in a corresponding one of a pair of different refrigeration systems using a propane refrigerant and mixed refrigerant, respectively, each of said refrigerants c

A compressor drive system for a natural gas liquefaction plant including: a pair of gas turbines, each of said gas turbines being installed in a corresponding one of a pair of different refrigeration systems using a propane refrigerant and mixed refrigerant, respectively, each of said refrigerants circulating in a respective independent closed loop, and each of said gas turbines being adapted to drive an associated compressor for pressurizing the corresponding refrigerant, a pair of electric motors, each of said electric motors being associated with a respective one of said gas turbines so as to serve both as an AC generator and as an auxiliary motor for generating a startup torque for the associated gas turbine and the associated compressor, a single frequency converter, switching means for selectively connecting a main power line to either of said motors via said single frequency converter for starting up said gas turbines, at least one of said electric motors being operated as s generator for converting any excess power output of the corresponding gas turbine into electric power when power produced from said corresponding gas turbine is greater than power required by the associated compressor, synchronizing means for synchronizing said at least one electric motor to a prevailing phase and frequency carried by said main electric power line, and means for feeding said electric power converted from said excess power output by said at least one electric motor into said main electric power line.