Single Multi Shaft Turbines 6d642t

Single-Shaft Configurations GE pioneered the single-shaft STAG equipment configuration. A single-shaft STAG system consists of one gas turbine, one steam turbine, one generator and one HRSG. The gas and steam turbines are coupled to the generator in a tandem arrangement on a single shaft. Advantages of the single-shaft configuration include: 

Lower capital cost

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Single generator and electricals

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Simple unit control system

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Smaller footprint that is ideal for optimizing space limitations

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Single-shaft arrangements are particularly advantageous for modern reheat combined cycle plants. It simplifies the starting and steam by systems associated with multiple heat recovery steam generators and a single steam turbine Multi-Shaft Configurations Multi-shaft STAG systems have one or more gas turbine generators and HRSGs that supply steam through a common header to a separate single steam turbine generator. This configuration allows a combined cycle plant to be installed in two phases, if necessary, driven by factors such as financing availability, fuel costs and load demand. The gas turbine, for example, can be installed first and provide revenue-producing power generation while the steam system is being installed. In a multi-shaft configuration, the generators are smaller, making the arrangement well-suited to unique steam turbine designs such as cogeneration or district heating. In addition, when two gas turbines are employed, the multi-shaft arrangement can have favorable capital costs based on the use of a single steam turbine. Advantages of multi-shaft configurations include:

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Phased installation

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Simple cycle operation gas turbines can be operated without steam cycle

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Flexible arrangement; customized unit configurations

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The gas turbine can be run independently of the steam turbine

For power generation, the multi-shaft aeroderivative turbines have advantages of lesser starting power requirements for "black plant" starts, and they can usually be brought to full load quicker than single-shaft machines. For power generation, the multi-shaft machines tend to have better part-load efficiency than "otherwise comparable" single-shaft machines. Since all gas turbines tend to be more than a bit fuel hungry at less than full load conditions, it may be better to think of the multi-shaft machines as having less-poor part-load efficiency than single-shaft machines. Large single-shaft power generation gas turbines are usually optimized for maximum efficiency at their constant operating speed and maximum rated continuous loading condition, so they commonly achieve higher maximum efficiencies than multi-shaft machines. As long as the single shaft machines can be operated at or very near their maximum efficiency loading, the relative fuel savings will justify their selection over multi-shaft machines. When part-load operation can be expected for a non-trivial portion of the machine's service life, then multi-shaft machines may present a more attractive choice.