Power plants – Combustion products used as motive fluid – Multiple fluid-operated motors
Reexamination Certificate
2000-11-13
2002-08-27
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Multiple fluid-operated motors
C060S775000
Reexamination Certificate
active
06438939
ABSTRACT:
BACKGROUND OF THE INVENTION:
1. Field of the Invention
The present invention relates to a combined cycle power plant in which a gas turbine plant and a steam turbine plant are combined, and to a cooling steam supply method for a gas turbine in operation thereof.
2. Description of the Prior Art
A combined cycle power plant is a power system in which a gas turbine plant and a steam turbine plant are combined, wherein a gas turbine takes charge of a high temperature section of thermal energy and a steam turbine takes charge of a low temperature section thereof. Therefore, the thermal energy is recovered for an effective use thereof and this power system is now being paid a high amount of attention.
In the combined cycle power plant research and development are being carried out aiming at a higher temperature gas turbine as one means for enhancing the efficiency.
On the other hand, in order to attain such a higher temperature, improvement of the cooling system which takes account of heat resisting ability of turbine structural elements must be pursued. As a result of various trials and errors, a steam cooled system which uses steam as the cooling medium, instead of a prior art use of compressed air, is now in progress.
One example thereof is the Japanese laid-open patent application No. Hei 05 (1993)-163960, wherein a cooling steam is obtained from intermediate pressure steam of a waste heat recovery boiler. However, a sufficient volume of steam is not obtainable which results in difficulty in achieving a stable and secure cooling.
Thus, as a further progress thereafter, in order to achieve a sufficient volume and a stable cooling, a cooling system using exhaust steam from a high pressure steam turbine as the cooling steam is now being developed.
In the prior art steam cooled system as mentioned above, progress has been made from the system using intermediate pressure steam as the cooling medium to that using high pressure exhaust steam, and thus the practicality has been enhanced further. However, the high pressure exhaust steam is of a high temperature at the same time, hence a gas turbine high temperature portion (which is a portion to be cooled) must be made of a selected material which can resist such a high temperature.
A high temperature resistible material, being required to be of properties necessary for that material, becomes very expensive. Furthermore, in case of a turbine disc among others for example, there is a large difficulty in obtaining an appropriate material therefor within limited conditions of price and the like, which leads to a serious problem in the design and manufacture of the plant.
SUMMARY OF THE INVENTION
In view of the problems in the prior art, it is an object of the present invention to provide a combined cycle power plant and a cooling steam supply method for a gas turbine thereof wherein the temperature of cooling steam used as a cooling medium is appropriately adjusted so that the functional stability of the steam cooled system is not damaged. Therefore, the gas turbine can be made of an easily obtainable material.
In order to attain the object, a first embodiment hereof provides a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant. The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from said air compressor. The waste heat recovery boiler generates steam by using exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pressure steam generating portion, an intermediate pressure steam generating portion and a low pressure steam generating portion. The high pressure steam generating portion comprises a high pressure economizer, a high pressure feed water pump, a high pressure evaporator and a high pressure superheater. The intermediate pressure steam generating portion comprises an intermediate pressure economizer, an intermediate pressure feed water pump, an intermediate pressure evaporator and an intermediate pressure reheater. The low pressure steam generating portion comprises a low pressure economizer, a low pressure feed water pump, a low pressure evaporator and a low pressure superheater.
The steam turbine plant is constructed of steam turbines, mutually connected by piping, including a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. The high pressure turbine is supplied with high pressure steam from the high pressure steam generating portion. The intermediate pressure turbine is supplied with intermediate pressure steam from the intermediate pressure steam generating portion, and the low pressure turbine is supplied with low pressure steam from the low pressure steam generating portion.
Steam supplied from the intermediate pressure evaporator is mixed into a cooling steam supply passage for supplying therethrough exhaust steam from the high pressure turbine as cooling steam into a high temperature portion of said gas turbine to be cooled.
That is, in the first embodiment, the exhaust steam from the high pressure turbine is first selected as the cooling medium of the gas turbine high temperature portion. Then, the intermediate pressure steam supplied from the intermediate pressure evaporator of the waste heat recovery boiler is mixed into the exhaust steam from the high pressure turbine. Thus, the cooling medium of a lowered temperature is made up and is supplied into the gas turbine high temperature portion for cooling thereof.
Thus, the high pressure exhaust steam, which is sufficient in volume, is mixed with the intermediate pressure steam, which is of a lower temperature but has a pressure nearly equal to that of the high pressure exhaust steam. Therefore, the high pressure exhaust steam is lowered in temperature and the high temperature portion to be cooled of the gas turbine can be made of a material of less heat resistant ability and a stable cooling can be effected without lowering of the entire efficiency.
Alternatively, the high pressure exhaust steam, which is sufficient in volume, may be mixed with a cooling water spray instead of the intermediate pressure steam. Therefore, the high pressure exhaust steam is appropriately lowered in temperature by the cooling water spray, so that the high temperature portion of the gas turbine is maintained at an appropriate temperature. As a result, the high temperature portion of the gas turbine which is to be cooled can be made of a material of less heat resistant ability, and a stable cooling can be effected without lowering of the entire efficiency of the power plant.
In other words, regardless of whether the intermediate pressure steam is mixed into the high pressure exhaust steam, the high pressure exhaust steam is mixed with the cooling water spray so as to be lowered in temperature anyway. Therefore, the intermediate pressure steam is stopped, and the cooling water spray is increased and mixed with the high pressure exhaust steam to be supplied into the high temperature portion of the gas turbine for cooling thereof. Thus, the steam from the intermediate pressure evaporator, which is available in less volume, is effectively supplied into the intermediate pressure turbine for work therein, and is effectively used for other necessary purposes. As a result, the steam is used more efficiently, and the efficiency of the combined plant is enhanced.
A second embodiment hereof includes a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant.
The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from the air compressor. The waste heat recovery boiler is for generating steam by using exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pre
Hirokawa Kazuharu
Mori Hidetaka
Sugishita Hideaki
Uematsu Kazuo
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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