Abstract:
A system for use in a combined cycle power plant including gas and steam turbines includes a single kettle boiler and a valve system. The valve system is operated such that feedwater from a first source passes into the kettle boiler during certain operating conditions, whereas feedwater from a second source passes into the kettle boiler during other operating conditions, wherein the first and second sources have feedwater under different pressures. Rotor cooling air extracted from a compressor section of the gas turbine is cooled with the feedwater in the kettle boiler, wherein at least a portion of the feedwater is evaporated in the kettle boiler by heat transferred to the feedwater from the rotor cooling air to create steam, wherein the valve system is operated to selectively deliver the steam to a first or second steam receiving unit depending on the operating conditions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a combined cycle power plant including a single kettle boiler in communication with both first pressure, e.g., low pressure, and second pressure, e.g., intermediate pressure, feedwater sources, which selectively provide feedwater to the kettle boiler during various modes of operation of the power plant. 
     BACKGROUND OF THE INVENTION 
     Combined cycle power plants (CCPP) are known in the art as an efficient means for converting fossil fuels to thermal, mechanical and/or electrical energy. Examples of such systems are described in U.S. Pat. Nos. 4,932,204, 5,255,505, 5,357,746, 5,431,007, 5,697,208, and 6,145,295, the entire disclosures of each of which are incorporated by reference herein. 
     Typical CCPPs include multiple feedwater sources under various pressure, e.g., low and intermediate pressures (LP and IP), wherein each feedwater source is associated with its own kettle boiler. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, a system is provided for use in a combined cycle power plant including a gas turbine and a steam turbine. The system comprises a single kettle boiler and a valve system. The kettle boiler selectively receives feedwater from both a first source and a second source, wherein a pressure of the feedwater in the first source is less than a pressure of the feedwater in the second source. The valve system comprises first and second inlet valves upstream from the kettle boiler that selectively deliver feedwater from the respective first and second sources to the kettle boiler, and first and second outlet valves downstream from the kettle boiler that selectively deliver steam from the kettle boiler to respective first and second steam receiving units. During a first mode of operation of the combined cycle power plant, the first inlet valve is open and the second inlet valve is closed such that feedwater from the first source is delivered into the kettle boiler but feedwater from the second source is not delivered into the kettle boiler; rotor cooling air extracted from a compressor section of the gas turbine is cooled with the feedwater in the kettle boiler from the first source and delivered back into a turbine section of the gas turbine, wherein at least a portion of the feedwater from the first source is evaporated in the kettle boiler by heat transferred to the feedwater from the rotor cooling air to create first steam; and the first outlet valve is open and the second outlet valve is closed such that the first steam is delivered from the kettle boiler into the first steam receiving unit but not to the second steam receiving unit. During a second mode of operation of the combined cycle power plant, the first inlet valve is closed and the second inlet valve is open such that feedwater from the second source is delivered into the kettle boiler but feedwater from the first source is not delivered into the kettle boiler; rotor cooling air extracted from the compressor section of the gas turbine is cooled with the feedwater in the kettle boiler from the second source and delivered back into the turbine section of the gas turbine, wherein at least a portion of the feedwater from the second source is evaporated in the kettle boiler by heat transferred to the feedwater from the rotor cooling air to create second steam; and the first outlet valve is closed and the second outlet valve is open such that the second steam is delivered from the kettle boiler into the second steam receiving unit but not to the first steam receiving unit. 
     The first and second steam receiving units may each comprise a drum that receives the respective first and second steams from the kettle boiler, and the first and second steam receiving units may each further comprise a superheater that provides additional heat to the first and second steam to create superheated steam, wherein the superheated steam is provided to drive the steam turbine to produce power. 
     The first mode of operation may be less than full load operation and the second mode of operation may be full load operation. 
     The system may further comprise a controller to operate the valve system to selectively open and close the inlet and outlet valves based on a rotor cooling air temperature setpoint. 
     The rotor cooling air temperature setpoint may be higher during full load operation than during less than full load operation. 
     The system may further comprise at least one injection port in communication with the kettle boiler for providing a fluid into the kettle boiler to effect a change in a pressure within the kettle boiler when the combined cycle power plant is transitioned between the first and second modes of operation. The at least one injection port may comprise at least one water injection port and at least one steam injection port, wherein water may be injected into the kettle boiler by the at least one water injection port to reduce the pressure within the kettle boiler when the combined cycle power plant is transitioned from the second mode of operation to the first mode of operation, and steam may be injected into the kettle boiler by the at least one steam injection port to increase the pressure within the kettle boiler when the combined cycle power plant is transitioned from the first mode of operation to the second mode of operation. 
     The single kettle boiler is preferably the sole kettle boiler provided in the combined cycle power plant, such that operation of the combined cycle power plant during the first and second modes of operation is performed without bypassing any additional kettle boilers. 
     In accordance with a second aspect of the present invention, a method is provided for operating a combined cycle power plant including a gas turbine and a steam turbine. During a first mode of operation of the combined cycle power plant, feedwater is delivered from a first source into a kettle boiler but feedwater is not delivered from a second source into the kettle boiler, the first and second sources being in communication with the kettle boiler via first and second inlet valves, wherein a pressure of the feedwater in the first source is less than a pressure of the feedwater in the second source. Rotor cooling air extracted from a compressor section of the gas turbine is cooled with the feedwater in the kettle boiler from the first source, wherein at least a portion of the feedwater from the first source is evaporated in the kettle boiler by heat transferred to the feedwater from the rotor cooling air to create first steam. The cooled rotor cooling air is delivered back into a turbine section of the gas turbine, and the first steam is delivered from the kettle boiler into a first steam receiving unit but not to a second steam receiving unit, wherein the first and second steam receiving units are in communication with the kettle boiler via first and second outlet valves. During a second mode of operation of the combined cycle power plant, feedwater from the second source is delivered into the kettle boiler but feedwater from the first source is not delivered into the kettle boiler. Rotor cooling air extracted from the compressor section of the gas turbine is cooled by the feedwater in the kettle boiler from the second source, wherein at least a portion of the feedwater from the second source is evaporated in the kettle boiler by heat transferred to the feedwater from the rotor cooling air to create second steam. The cooled rotor cooling air is delivered back into the turbine section of the gas turbine and the second steam is delivered from the kettle boiler into the second steam receiving unit but not to the first steam receiving unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a diagrammatic illustration of a combined cycle power plant in accordance with an embodiment of the invention; and 
         FIG. 2  is a diagrammatic illustration of a system included in a heat recovery steam generator of the combined cycle power plant of  FIG. 1 , the system including a selective pressure kettle boiler. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of a preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring now to  FIG. 1 , there is shown a combined cycle power plant (hereinafter “CCPP”)  10  having, generally, a gas turbine  12 , a steam turbine  14 , and a heat recovery steam generator (hereinafter “HRSG”)  16 . The gas turbine  12  includes a compressor section (hereinafter “GT compressor”)  18  that compresses air drawn into the gas turbine  12 , a combustion section  20  where compressed air from the GT compressor  18  and fuel are ignited to generate hot combustion products defining hot working gases, and a turbine section (hereinafter “GT turbine”)  22  where the hot working gases from the combustion section  20  are expanded to drive a gas turbine rotor  24 . The steam turbine  14  may include conventional components, including, for example, a high/intermediate pressure turbine and a low pressure turbine, as will be appreciated by those having ordinary skill in the art. 
     Referring now to  FIG. 2 , a system  30  of the HRSG  16  from  FIG. 1  is illustrated and will now be described. The system  30  shown in  FIG. 2  comprises a first source of feedwater  32 , also referred to herein as a low pressure (hereinafter “LP”) feedwater source  32 , having a first pressure, and a second source of feedwater  34 , also referred to herein as an intermediate pressure (hereinafter “IP”) feedwater source  34 , having a second pressure greater than the first pressure. The LP and IP feedwater sources  32 ,  34  may include conventional components, such as, for example, one or more condensate supplies, condensate preheaters, economizers, and pumps. The HRSG  16  may also include one or more additional sources of feedwater, such as a third source of feedwater comprising a high pressure feedwater source. Hence, the present invention is not intended to be limited to the HRSG  16  including only the two sources of feedwater  32 ,  34  shown in  FIG. 2 . 
     The system  30  also includes a single kettle boiler  40  that selectively receives feedwater from both the LP and IP feedwater sources  32 ,  34  as will be described herein. Since the single kettle boiler  40  services both the LP and IP feedwater sources  32 ,  34 , separate kettle boilers for the LP and IP feedwater sources  32 ,  34  are not required. 
     The kettle boiler  40  may include, for example, a tube and shell type heat exchanger having compressed air on the tube side and water/steam on the shell side, as will be appreciated by one having ordinary skill in the art. As shown in  FIG. 2 , the system  30  also includes water and steam injection ports  42 ,  44  in communication with the kettle boiler  40  for respectively providing fluids, i.e., water and steam, into the kettle boiler  40  to effect a change in a pressure and/or temperature within the kettle boiler  40  as will be described in greater detail herein. 
     Referring still to  FIG. 2 , the system  30  additionally includes a first steam receiving unit  46 , also referred to herein as an LP steam receiving unit  46  and a second steam receiving unit  48 , also referred to herein as an IP steam receiving unit  48 . The LP and IP steam receiving units  46 ,  48  illustrated in  FIG. 2  include respective drums  50 ,  52  for holding respective portions of LP and IP water/steam, and superheaters  54 ,  56  for heating respective portions of LP and IP steam to create LP and IP superheated steam, also referred to herein as first and second steam, which may then be conveyed on to the steam turbine  14  as will be described in greater detail herein. The LP and IP steam receiving units  46 ,  48  may additionally include other conventional components without departing from the scope and spirit of the invention. The HRSG  16  may also include one or more additional steam receiving units, such as a third steam receiving unit comprising a high pressure drum and a corresponding superheater. Hence, the present invention is not intended to be limited to the HRSG  16  including only two steam receiving units  46 ,  48 , although the HRSG  16  preferably includes the same number of steam receiving units as sources of feedwater. 
     The system  30  further includes a controller  58  that controls operation of a valve system  60  of the system  30 . The valve system  60  includes first and second inlet valves  62 ,  64  upstream from the kettle boiler  40  that selectively deliver feedwater from the LP and IP feedwater sources  32 ,  34  to the kettle boiler  40 . The valve system  60  also includes first and second outlet valves  66 ,  68  downstream from the kettle boiler  40  that selectively deliver steam from the kettle boiler  40  to the LP and IP steam receiving units  46 ,  48 . In this regard, it is noted that the steam delivered from the kettle boiler  40  into the LP and IP steam receiving units  46 ,  48  may pass directly into the corresponding drums  50 ,  52  and then on to the corresponding superheaters  54 ,  56 ; or the steam may pass directly into the corresponding superheaters  54 ,  56  and then on the corresponding drums  50 ,  52 ; or the steam may pass into the respective drums  50 ,  52  or superheaters  54 ,  56  and then optionally onto other components of the CCPP  10  without subsequently passing into the others of the drums  50 ,  52  or superheaters  54 ,  56 . The steam in the LP and IP steam receiving units  46 ,  48  may then be delivered to other components of the CCPP  10 , such as, for example, to appropriate sections of the steam turbine  14  as will be apparent to those having ordinary skill in the art. 
     The controller  58  may also control operation of the water and steam injection ports  42 ,  44 , and may further control operation of a kettle boiler bypass valve  70 , which will be described in further detail below. 
     Operation of the CCPP  10  will now be described. It is noted that operation of components of the CCPP  10  not related to the system  30  will not be specifically described herein, as operation of those components will be apparent to those having ordinary skill in the art. 
     During a first mode of operation, also referred to herein as less than full load operation or part load operation, the controller  58  controls the valve system  60  such that the first inlet valve  62  is open and the second inlet valve  64  is closed, wherein feedwater from the LP feedwater source  32  is delivered into the kettle boiler  40  but feedwater from the IP feedwater source  34  is not delivered into the kettle boiler  40 . Rotor cooling air extracted from the compressor section  18  of the gas turbine  12  (the GT compressor  18 ) is delivered into the kettle boiler  40  and is cooled with the feedwater in the kettle boiler  40  from the LP feedwater source  32 . The cooled rotor cooling air is then delivered back into the turbine section  22  of the gas turbine  12  (GT turbine  22 ) where it may be used to cool components within the turbine section  22 , such as, for example, stationary vanes, rotating blades (not shown), and/or the rotor  24 . As a result of the heat transferred from the rotor cooling air to the LP feedwater in the kettle boiler  40 , at least a portion of the LP feedwater is evaporated in the kettle boiler  40  to create first steam, also referred to herein as LP steam. 
     The LP steam then exits the kettle boiler  40 , wherein, during the first mode of operation, the controller  58  controls the valve system  60  such that the first outlet valve  66  is open and the second outlet valve  68  is closed, wherein the LP steam is delivered from the kettle boiler  40  into the LP steam receiving unit  46  but not into the IP steam receiving unit  48 . As noted above, the LP steam may be delivered into the corresponding drum  50  or superheater  54 , wherein it may then be conveyed into either the other of the corresponding drum  50  or superheater  54 , or it may be delivered to other components in the CCPP  10 . For example, if the LP steam is delivered into the superheater  54 , either after, before, or without being delivered into the drum  50 , the LP steam, which is further heated in the superheater  54  with additional heat to create superheated LP steam, may be delivered to the steam turbine  14  where it may be used to drive a component of the steam turbine  14 , e.g., the low pressure turbine, to produce power in a manner that will be apparent to those having ordinary skill in the art. 
     During a second mode of operation, also referred to herein as full load operation or base load operation, the controller  58  controls the valve system  60  such that the first inlet valve  62  is closed and the second inlet valve  64  is open, wherein feedwater from the IP feedwater source  34  is delivered into the kettle boiler  40  but feedwater from the LP feedwater source  32  is not delivered into the kettle boiler  40 . Rotor cooling air extracted from the compressor section  18  of the gas turbine  12  is delivered into the kettle boiler  40  and is cooled with the feedwater in the kettle boiler  40  from the IP feedwater source  34 . The cooled rotor cooling air is then delivered back into the turbine section  22  of the gas turbine  12  where it may be used to cool components within the turbine section  22 . As a result of the heat transferred from the rotor cooling air to the IP feedwater in the kettle boiler  40 , at least a portion of the IP feedwater is evaporated in the kettle boiler  40  to create second steam, also referred to herein as IP steam. 
     The IP steam then exits the kettle boiler  40 , wherein, during the second mode of operation, the controller  58  controls the valve system  60  such that the first outlet valve  66  is closed and the second outlet valve  68  is open, wherein the IP steam is delivered from the kettle boiler  40  into the IP steam receiving unit  48  but not into the LP steam receiving unit  46 . As noted above, the IP steam may be delivered into the corresponding drum  52  or superheater  56 , wherein it may then be conveyed into either the other of the corresponding drum  52  or superheater  56 , or it may be delivered to other components in the CCPP  10 . For example, if the IP steam is delivered into the superheater  56 , either after, before, or without being delivered into the drum  52 , the IP steam, which is further heated in the superheater  56  with additional heat to create superheated IP steam, may be delivered to the steam turbine  14  where it may be used to drive a component of the steam turbine  14 , e.g., the high/intermediate steam turbine, to produce power in a manner that will be apparent to those having ordinary skill in the art. 
     According to an aspect of the present invention, the controller  58  may control operation of the valve system  60  to selectively open and close the inlet and outlet valves  62 ,  64 ,  66 ,  68  based on a rotor cooling air temperature setpoint, which is typically selected as a function of the operating mode of the CCPP  10 . For example, during less than full load operation, i.e., the first mode of operation discussed above, the rotor cooling air temperature setpoint may be lower than during full load operation, i.e., the second more of operation discussed above. Hence, during less than full load operation where the rotor cooling air temperature setpoint is lower, LP feedwater may be delivered into the kettle boiler  40  to cool the rotor cooling air to a first temperature, which is lower than a second temperature to which IP feedwater delivered into the kettle boiler  40  may cool the rotor cooling air to during full load operation where the rotor cooling air temperature setpoint is higher. 
     The controller  58  may also control operation of the water and steam injection ports  42 ,  44  to adjust the pressure and/or temperature within the kettle boiler  40  as needed. For example, if it is desired to reduce the pressure and/or temperature within the kettle boiler  40 , the controller  58  may cause the water injection port  42  to inject water into the kettle boiler  40  to reduce the pressure and/or temperature within the kettle boiler  40 . This may be desirable when the CCPP  10  is transitioned from full load operation to less than full load operation. As another example, if it is desired to increase the pressure and/or temperature within the kettle boiler  40 , the controller  58  may cause the steam injection port  44  to inject steam into the kettle boiler  40  to increase the pressure and/or temperature within the kettle boiler  40 . This may be desirable when the CCPP  10  is transitioned from less than full load operation to full load operation. 
     Moreover, the controller  58  may further control operation of the kettle boiler bypass valve  70  such that some or all of the rotor cooling air from the CT compressor  18  bypasses the kettle boiler  40  and is then delivered back into the GT turbine  22  without being cooled in the kettle boiler  40 . This may be desirable to fine tune cooling of the components within the turbine section  22  and/or to fine tune performance of the gas turbine  12 . For example, by adjusting the temperature of the rotor cooling air, the temperature of the hot working gases passing through the turbine section  22  may be controlled, e.g., since at least some of the rotor cooling air introduced into the turbine section  22  ends up mixing with the hot working gases to cause cooling of the hot working gases after the rotor cooling air provides its cooling function, wherein the temperature of the hot working gases directly impacts the efficiency of the gas turbine  12 . 
     According to another aspect of the present invention, since the single kettle boiler  40  is the sole kettle boiler  40  provided in the exemplary CCPP  10  shown, and the single kettle boiler  40  services both the LP and IP feedwater sources  32 ,  34  and LP and IP steam receiving units  46 ,  48 , operation of the CCPP  10  during the full load operation and less than full load operation performed without bypassing any additional kettle boilers. Since switching between multiple kettle boilers can be complex and expensive, these difficulties that may be present with such kettle boiler bypassing are avoided by the present system  30 . 
     While a particular embodiment of the present invention has been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.