Abstract:
In a combined cycle power generation plant in which a gas turbine is cooled by steam, pressure loss of the cooling steam is prevented from increasing and the cooling steam is recovered efficiently. The gas turbine&#39;s stationary blade or moving blade is provided with a plurality of mutually independent passages which are arranged in parallel, whereby pressure loss of the cooling steam can be reduced.

Description:
This application is a divisional application of Ser. No. 09/109,188, filed Jul. 2, 1998 (abandoned). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a combined cycle power generation plant including a gas turbine plant and a steam turbine plant. 
     2. Description of the Prior Art 
     A combined cycle power generation plant is a power generation system including a gas turbine plant and a steam turbine plant. A high temperature thermal energy is utilized by the gas turbine, and a low temperature thermal energy is utilized by the stream turbine. Thus, the thermal energy is recovered and effectively used. 
     In such a combined cycle power generation plant, research and development thereof has been done with emphasis on how much the high temperature thermal energy can be increased for enhancing the thermal efficiency of the combined cycle power generation plant. 
     However, there must be provided a cooling system for cooling the gas turbine after the high temperature thermal energy has been utilized. Air has been used as a cooling medium in this cooling system. 
     However, when air is used as the cooling medium, even if the high temperature thermal energy is attained, there are problems which prevent the thermal efficiency from being enhanced. These problems include a power loss at an air compressor used for elevating pressure of air which is used for cooling the gas turbine. These problems also include lowering of the mean temperature of a gas flowing in passages in the gas turbine, when the gas is mixed with the air which is used for cooling the gas turbine. This lowering of the mean temperature results in a lowering of energy contained in the gas. 
     In order to resolve these problems and to enhance the thermal efficiency, a cooling system using the stream s the cooling medium, in place of air, has been disclosed. 
     Japanese laid-open patent No. Hei 05(1993)-163960 discloses an idea to employ steam as the cooling medium of the gas turbine, but various problems exist therewith which must be resolved. 
     Japanese laid-open patent No. Hei 05(1993)-163960 discloses only a basic idea of using steam as the cooling medium. In this regard, steam is supplied into a hot gas turbine from a certain steam source and flows through portions to be cooled. Then, the steam is led into a recovery portion after it has cooled the gas turbine. However, no mention is made of particular consideration of problems such as pressure loss of the steam during cooling of the gas turbine. 
     That is, steam cooling is still in a stage of trial and error, wherein no satisfactory solution to the aforementioned problems has been realized. 
     The prior remains a basic idea, as mentioned above, wherein cooling steam passages are formed in series so as to communicate with one another along an entire portion of the gas turbine to be cooled, i.e. a stationary system or a rotating system. 
     That is, the stationary system to be cooled is constructed such that the cooling steam flows in series through a first stage stationary blade and then a second stage stationary blade. The steam becomes heated as it flows through these blades, and then it flows to a recovery portion. 
     In such a construction, there is caused a large pressure loss at the stationary system to be cooled, and accordingly, various restrictions are placed on the upstream side and the downstream side of the stationary system, which make designing and manufacturing more restrictive. Also, operation of the gas turbine is restricted, and plant efficiency is reduced. That is, if pressure of the steam is reduced when it is recovered, after cooling of the stationary system, output from the steam turbine is accordingly reduced, which results in lowering of plant efficiency. 
     On the other hand, if a predetermined pressure is to be obtained continuously at the steam turbine, with this pressure loss being considered in advance, a control valve having a capacity larger than is necessary must be provided. This means an increase of cost in designing and manufacturing, as well as employment of an impractically large control valve. 
     SUMMARY OF THE INVENTION 
     In view of the mentioned problems in the prior art it is an object of the present invention to provide a combined cycle power generation plant in which pressure loss is prevented from becoming large at the gas turbine to be cooled, and a cooling steam is recovered efficiently. 
     In order to attain this object, the present invention provides a combined cycle power generation plant including a gas turbine plant, a steam turbine plant, a waste heat recovery boiler using waste heat from a gas turbine of the gas turbine plant for generating steam for driving a steam turbine of the steam turbine plant, a steam system using steam for cooling the gas turbine, and a recovery system for recovering superheated steam from the gas turbine. There is provided at the gas turbine independent parallel cooling steam passages. Because the cooling steam passages are arranged in parallel, locations at which pressure loss of the cooling steam can occur are dispersed, whereby an aggregate of all the pressure losses can be reduced. 
     In one embodiment, the present invention provides a combined cycle power generation plant as mentioned above, wherein the parallel cooling steam passages consist of a cooling steam passage of a first stage stationary blade, and a cooling steam passage of a second stage stationary blade. Specifically, the stationary blades are provided with mutually independent cooling steam passages which are between the first stage stationary blade and the second stage stationary blade, whereby the pressure loss at the cooling steam passages is dispersed, and hence an aggregate of all the pressure losses can be reduced. 
     Also in this embodiment, the present invention provides a combined cycle power generation plant as mentioned above, wherein the parallel cooling steam passages consist of a cooling steam passage of a first stage moving blade, and a cooling steam passage of a second stage moving blade. Specifically, the moving blades are provided with mutually independent cooling steam passages which are between the first stage moving blade and the second stage moving blade, whereby the pressure loss at the cooling steam passages is dispersed, and hence an aggregate of all the pressure losses can be reduced. 
     In a second embodiment, the present invention provides a combined cycle power generation plant as mentioned above, wherein the parallel cooling steam passages consist of a plurality of mutually independent and parallel cooling steam passage systems, with each system comprising a plurality of stationary blades or moving blades sectioned with respect to one another in the same stage. Thus, the pressure loss at the cooling steam passages is dispersed, and hence an aggregate of all the pressure losses can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross sectional view showing a main part of a gas turbine cooled according to a first embodiment of the present invention. 
     FIG. 2 is a schematic radial cross sectional view showing a main part of a gas turbine cooled according to a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment according to the present invention will be described with reference to FIG.  1 . 
     Numeral  1  designates a first stage stationary blade, numeral  2  designates a second stage stationary blade, numeral  3  designates a first stage moving blade, and numeral  4  designates a second stage moving blade. Numeral  5  designates a cooling steam supply channel, which branches midway to communicate with a cooling steam passage  5   a  of the first stage stationary blade  1 , and a cooling steam passage  5   b  of the second stage stationary blade  2 . 
     The cooling steam passage  5   a  communicates with a steam recovery passage  6   a  of the first stage stationary blade  1  via a portion of the first stage stationary blade  1  to be cooled, and the cooling steam passage  5   b  communicates with a steam recovery passage  6   b  of the second stage stationary blade  2  via a portion of the second stage stationary blade to be cooled. Both the steam recovery passages  6   a  and  6   b  join together at a downstream location to communicate with a steam recovery passage  6 . 
     That is, the cooling steam passage  5   a  at a position of the first stage stationary blade  1 , an the cooling steam passage  5   b  at a position of the second stage stationary blade  2 , form mutually independent and parallel passages. The steam recovery passages  6   a  and  6   b  communicating therewith form likewise mutually independent and parallel passages. 
     Also, as seen on the moving blade side symmetrically with respect to the stationary blade side, numeral  7  designates a cooling steam supply channel, which branches midway to communicate with a cooling steam passage  7   a  of the first stage moving blade  3 , and a cooling steam passage  7   b  of the second stage moving blade  4 . 
     The cooling steam passage  7   a  communicates with a steam recovery passage  8   a  of the first stage moving blade  3  via a portion of the first stage moving blade  3  to be cooled, and the cooling steam passage  7   b  communicates with a steam recovery passage  8   b  of the second stage moving blade  4  via a portion of the second stage moving blade  4  to be cooled. Both the steam recovery passages  8   a  and  8   b  join together at a downstream location to communicate with a steam recovery passage  8 . 
     That is, like the stationary blade side, the cooling steam passage  7   a  at a position of the first stage moving blade  3 , and the cooling steam passage  7   b  at a position of the second stage moving blade  4  form mutually independent and parallel passages. The steam recovery passages  8   a  and  8   b  communicating therewith form likewise mutually independent and parallel passages. 
     In this embodiment, as seen on the stationary blade side first, the cooling steam supplied from an outside cooling steam supply source, which is not shown, is fed from the cooling steam supply channel  5  to branch to the cooling steam passages  5   a,    5   b  so as to be led into the first stage stationary blade  1  and the second stage stationary blade  2 . Then, the cooling steam is heating through cooling the portions of the first stage stationary blade  1 , and the second stage stationary blade  2 . This heated steam then flows into the steam recovery passage  6  via the mutual independent and parallel recovery passages  6   a,    6   b,  and is to be heat-recovered at a steam turbine, which is not shown. 
     In this case, the cooling steam flowing in the cooling steam passage  5   a  has nothing to do with a pressure loss due to the cooling steam passage  5   b,  and the cooling steam flowing in the cooling steam passage  5   b  has nothing to do with a pressure loss due to the cooling steam passage  5   a.  Hence, the pressure loss as a whole is reduced greatly. 
     Also, as seen on the moving blade side, the situation is quite the same as on the stationary blade side, and it will be easily understood without repeated explanation that the cooling steam flows with a reduced pressure loss and is heat-recovered at a steam turbine, which is not shown, via the steam recovery passage  8 . 
     Next, a second embodiment according to the present invention will be described with reference to FIG.  2 . 
     Numeral  10  designates a blade set of one stage, comprising a multitude of stationary blades or moving blades along the entire circumference. The blade set  10  is sectioned into six groups, each forming a group of independent cooling steam passages, so that the groups of passages are arranged mutually in parallel about the circumferential direction. 
     That is, a cooling steam passage  11  of a first blade group comprises a cooling steam supply channel  11   a  and a steam recovery passage  11   b,  a cooling steam passage  12  of a second blade group comprises a cooling steam supply channel  12   a  and a steam recovery passage  12   b,  and likewise cooling steam passages  13 ,  14 ,  15  and  16  of 3 rd , 4 th , 5 th  and 6 th  blade groups, respectively, comprise cooling steam supply channels  13   a,    14   a,    15   a  and  16   a  and steam recovery passages  13   b,    14   b,    15   b  and  16   b,  respectively, so that these six cooling steam passages are arranged mutually in parallel. 
     In this embodiment, because the cooling steam passages are in parallel about the circumferential direction as mentioned above, the pressure loss is dispersed and suppressed, and like the first embodiment, heat recovery is carried out at a steam turbine, which is not shown. 
     The present invention has been described with respect to the embodiments shown in figures, but the present invention is not limited thereto and may be modified with various modified within the scope of the claims as hereinbelow set forth. 
     According to the present invention, the following effect can be obtained. Namely, because the cooling steam flows separately in the mutually independent and parallel passages, as compared to the case in which the cooling steam flows in series through common passages, pressure loss is suppressed, and thus no unnecessary troubles in downstream equipment is realized 
     Also, by cooling the first and second stage stationary blades in parallel coupled with heat recovery of the steam, an effective apparatus having a suppressed pressure loss can be obtained. 
     Also, by cooling the first and second stage moving blades in parallel coupled with heat recovery of the steam, an effective apparatus having a suppressed pressure loss can be obtained. 
     Further, by parallel cooling blade groups in the same stage of stationary blades or moving blades, coupled with heat recovery of the steam, an effective apparatus having a suppressed pressure loss can be obtained.