1. Field of the Invention
The present invention relates to a two-shaft gas turbine in which a high-pressure turbine for driving a compressor and a low-pressure turbine for power output are configured to have respective different shafts. The two-shaft gas turbine is applied to a gas turbine system having an increased amount of fluid flowing into a combustor compared with a simple cycle, such as, e.g., a humid air system, a steam injection system, a nitrogen injection system, or a low-calorific fuel firing system.
2. Description of the Related Art
For example, JP-A-2003-83081 (FIG. 5) and JP-A-5-18271 describe the technology of a two-shaft gas turbine in which a high-pressure turbine for driving a compressor and a low-pressure turbine for driving a generator or a pump are configured to have respective different shafts.
The two-shaft gas turbine can rotate the compressor and the high-pressure turbine at high speeds even if a driven device (load) such as a pump or a screw is low in rotation speed. Because of this, the two-shaft gas turbine can increase the torque of the low-pressure turbine in a low rotation speed zone. For this reason, the two-shaft gas turbine is mainly used to drive a machine such as a pump or a screw. However, the two-shaft gas turbine can also be used for electric power generation by use of the low-pressure turbine driving a generator. If the low-pressure turbine is used without reduction gears, the two-shaft gas turbine has an advantage that high-efficiency can be achieved by rotating the compressor at high speeds. Even if the reduction gears are used, a reduction ratio can be reduced to advantageously provide reduced cost and improved efficiency.
Incidentally, FIG. 5 of JP-A-2003-83081 describes the technology of a humidity gas turbine system in which moisture is added to gas turbine working fluid (e.g. air) for humidification and the thermal energy of the gas turbine exhaust gas is recovered by a recuperator, thereby improving output power and efficiency.
On the other hand, WO00/25009 discloses the technology of a humidity gas turbine system in which water is added for humidification to the working fluid (e.g., air) of a gas turbine, and the thermal energy of exhaust gas discharged from the gas turbine is recovered by such humidified air and supplied to the gas turbine for improving output power and efficiency.