Patent Publication Number: US-11655736-B2

Title: Combined cycle power plant with improved efficiency

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/523,085 entitled “Combined Cycle Power Plant With Improved Efficiency” and filed Oct. 24, 2014, which claims priority to European Application No. 13191037.4 filed Oct. 31, 2013. Each of the foregoing applications is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to combined cycle power plants, and, more particularly, to an improvement in cycle arrangement for optimizing the combined cycle power plant efficiency. 
     BACKGROUND 
     In a combined cycle power plant (CCPP), a gas turbine and a steam turbine combinedly produce electric power. The CCPP is arranged so that the gas turbine is thermally connected to the steam turbine via a heat recovery steam generator (HRSG). The HRSG is a heat exchanger which utilizes waste exhaust gas of the gas turbine to heat feedwater for the steam generation process for operating the steam turbine. The optimum utilization of heat captured in the HRSG is one the major criteria to increase CCPP efficiency. 
     Despite of various conventional techniques to capture the heat in HRSG, there may be chances that the heat, especially, at cold end of the HRSG may be left unused. It therefore exists a need to optimally utilize the heat at the cold end of the HRSG in order to improve CCPP efficiency and output. 
     SUMMARY 
     The present disclosure describes an improvement in cycle arrangement for optimizing the combined cycle power plant efficiency and output, that will be presented in the following simplified summary to provide a basic understanding of one or more aspects of the disclosure that are intended to overcome the discussed drawbacks, but to include all advantages thereof, along with providing some additional advantages. This summary is not an extensive overview of the disclosure. It is intended to neither identify key or critical elements of the disclosure, nor to delineate the scope of the present disclosure. Rather, the sole purpose of this summary is to present some concepts of the disclosure, its aspects and advantages in a simplified form as a prelude to the more detailed description that is presented hereinafter. 
     An object of the present disclosure is to describe an improved combined cycle power plant, which may be adaptable in terms of being improved in cycle arrangement for optimizing the combined cycle power plant efficiency. Further, object of the present disclosure is to describe a combined cycle power plant, which is convenient to use in an effective and economical way. Various other objects and features of the present disclosure will be apparent from the following detailed description and claims. 
     The above noted and other objects, in one aspect, may be achieved by an improved combined cycle power plant. The combined cycle power plant includes at least one gas turbine, at least one heat recovery steam generator, at least one steam turbine, at least one flash tank, and first and second supply lines. The at least one gas turbine is configured to produce gas to generate power and subsequently releasing the exhaust gas. The at least one gas turbine is configured to receive heated air from a gas turbine air preheating system for enabling efficient combustion of fuel to produce the gas. Further, the at least one heat recovery steam generator is thermally connected to the at least one gas turbine to use heat energy extracted from the exhaust gas of the at least one gas turbine to produce steam. Furthermore, the at least one steam turbine is thermally connected to the at least one heat recovery steam generator to utilize the steam produced by the at least one heat recovery steam generator to generate the power. The at least one flash tank fluidically connected at a cold end of the at least one heat recovery steam generator to extract hot water from the cold end. Connection to the cold end of a heat recovery steam generator means that the flash tank is connected to the exit of a heat exchanger pipe or pipe bundle which is arranged in the heat recovery steam generator closer to the downstream (cold) end than to the upstream (hot) end. For example the e.g. heat exchanger pipe or pipe bundle is arranged in the downstream half or downstream third of the heat recovery steam generator. Water is preheated in the cold end of the heat recovery steam generator relative to the extension of the heat recovery steam generator in flow direction of the flue gases passing through it. Moreover, the first supply line is configured to interconnect the at least one flash tank and the at least one steam turbine to enable supply of flash steam to the at least one steam turbine. The second supply line is configured to interconnect the at least one flash tank and the gas turbine air preheating system to enable supply of hot flash condensate to the gas turbine air preheating system. 
     In one embodiment of the present disclosure, the combined cycle power plant may include a feedwater preheating system thermally coupled to the cold end of the at least one heat recovery steam generator. This maintains the temperature requirement of feed water at the cold end of the heat recovery steam generator. In this embodiment, the hot water used for flashing purposes may be extracted from the feedwater preheating system. 
     In one further embodiment of the present disclosure, the combined cycle power plant may include a first bypass member to selectively bypass a part or all of the flash condensate from the second supply line for bypassing the gas turbine air preheating system. 
     In one further embodiment of the present disclosure, the combined cycle power plant may include a second bypass member to selectively bypass a part or all of the extracted hot water from the cold end of the heat recovery steam generator for bypassing the supply of the extracted hot water in to the at least one flash tank, and to serve as a recirculation system for heating the condensate at the at least one heat recovery steam generator to achieve a required minimum temperature. 
     In one further embodiment of the present disclosure, the combined cycle power plant may include at least one additional heat source fluidically connected the at least one flash tank to be utilized for additional hot water extraction to be supplied to the at least one flash tank. 
     In one further embodiment of the present disclosure, the combined cycle power plant may also include a provision for fuel gas preheating. In such embodiment, the combined cycle power plant may include a fuel gas preheating system configured to heat fuel to be supplied to the at least one gas turbine for effective combustion. In such configuration, the fuel gas preheating system is adapted to be configured in the second supply line to utilize the heat from the hot flash condensate to preheat the fuel to be supplied to the at least one gas turbine. 
     In one further embodiment, the combined cycle power plant a plurality of flash tanks, instead of one flash tank, is provided. The plurality of flash tanks is configured for hot water extraction and subsequently injecting the flash steam of varying pressure levels to a corresponding steam turbine stages. 
     In one further embodiment, the combined cycle power plant may also include at least one heat exchanger adapted to be configured to the second supply line. In such embodiment, the at least one heat exchanger is configured with the gas turbine air preheating system for preheating the air supplied in the gas turbine engine. 
     In yet further embodiment of the combined cycle power plant, the at least one gas turbine may preclude the gas turbine air preheating system, where heating is not required. Rather in this embodiment, the second supply line is configured to supply hot flash condensate from the at least one flash tank to a return line to the at least one heat recovery steam generator  120  or to the feedwater preheating system. 
     These together with the other aspects of the present disclosure, along with the various features of novelty that characterize the present disclosure, are pointed out with particularity in the present disclosure. For a better understanding of the present disclosure, its operating advantages, and its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features of the present disclosure will be better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawing, wherein like elements are identified with like symbols, and in which: 
         FIG.  1    illustrates an example line diagram of a Combined Cycle Power plant (CCPP) depicting a present invention incorporated therein, in accordance with an exemplary embodiment of the present disclosure; 
         FIG.  2    illustrates another example embodiment depicting a first variant of the CCPP of  FIG.  1   ; 
         FIG.  3    illustrates another example embodiment depicting a second variant of the CCPP of  FIG.  1   ; 
         FIG.  4    illustrates another example embodiment depicting a third variant of the CCPP of  FIG.  1   ; 
         FIG.  5    illustrates another example embodiment depicting a fourth variant of the CCPP of  FIG.  1   ; 
         FIG.  6    illustrates another example embodiment depicting a fifth variant of the CCPP of  FIG.  1   ; 
         FIG.  7    illustrates another example embodiment depicting a sixth variant of the CCPP of  FIG.  1   ; and 
         FIG.  8    illustrates yet another example embodiment depicting a seventh variant of the CCPP where a gas turbine precludes an air preheating system. 
     
    
    
     Like reference numerals refer to like parts throughout the description of several views of the drawings. 
     DETAILED DESCRIPTION 
     For a thorough understanding of the present disclosure, reference is to be made to the following detailed description, including the appended claims, in connection with the above described drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details. In other instances, structures and apparatuses are shown in block diagrams form only, in order to avoid obscuring the disclosure. Reference in this specification to “one embodiment,” “an embodiment,” “another embodiment,” “various embodiments,” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but may not be of other embodiment&#39;s requirement. 
     Although the following description contains many specifics for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to these details are within the scope of the present disclosure. Similarly, although many of the features of the present disclosure are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the present disclosure is set forth without any loss of generality to, and without imposing limitations upon, the present disclosure. Further, the relative terms, such as “first,” and “second” and the like, herein do not denote any order, elevation or importance, but rather are used to distinguish one element from another. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 
     Referring now to  FIGS.  1  to  7   , examples of a Combined Cycle Power Plant (CCPP)  100  depicting various exemplary embodiments of the present invention incorporated therein. In as much as the construction and arrangement of the CCPP  100 , various associated elements may be well-known to those skilled in the art, it is not deemed necessary for purposes of acquiring an understanding of the present disclosure that there be recited herein all of the constructional details and explanation thereof. Rather, it is deemed sufficient to simply note that as shown in  FIGS.  1  to  7   , the CCPP  100 , only those components are shown that are relevant for the description of various embodiments of the present disclosure. 
     Referring now to  FIG.  1   , the CCPP  100  for optimizing efficiency and output thereof includes at least one gas turbine  110 , at least one heat recovery steam generator (HRSG)  120 , at least one steam turbine  130 , at least one flash tank  140  and first and second supply lines  150 ,  160 . As conventionally, the at least one gas turbine  110  is thermally conjoined with the at least one steam turbine  130  via the HRSG  120  to generate the power output. Elaborately, as per present disclosure, the gas turbine  110  is configured to produce gas to generate power and subsequently releasing exhaust gas. The gas turbine  110  may include a gas turbine air preheating system  112  for preheating the air and supplying the heated air for enabling efficient combustion of the fuel to produce the gas in the gas turbine  110 . Further, the HRSG  120  is thermally connected to the at least one gas turbine  110  to use heat energy extracted from the exhaust gas of the at least one gas turbine  110  to produce steam. Furthermore, the at least one steam turbine  130  is thermally connected to the HRSG  120  to utilize the steam to generate the power output. 
     As described, the HRSG  120  is a heat exchanger which utilizes waste exhaust gas of the gas turbine  110  to produce steam for operating the steam turbine. The optimum utilization of heat captured in the HRSG  120  is one the major criteria to increase the CCPP  100  efficiency. However, despite of various conventional techniques to capture the heat in the HRSG  120 , there may be chances that the heat, especially, at a cold end  122  of the HRSG  120  may be left unused. the CCPP  100  of the present invention therefore includes the at least one flash tank  140  to optimally utilize the heat at the cold end  122  of the HRSG  120  in order to improve the CCPP  100  efficiency and power output. In as much as the construction and arrangement of the HRSG  120 , various associated elements may be well-known to those skilled in the art, and it is deemed sufficient to simply note that as shown in  FIGS.  1  to  7   , in the HRSG  120 , only those components are shown that are relevant for the description of various embodiments of the present disclosure. 
     As shown in  FIG.  1   , the flash tank  140  is fluidically connected, via a supply line  142 , at the cold end  122  of the HRSG  120  to extract unused hot water from the cold end  122 . A flash valve  141  may be incorporated to control extraction. In one embodiment of the present disclosure, the CCPP  100  may include a feedwater preheating system  170  thermally coupled to the cold end  122  of the HRSG  120  to maintain the temperature requirement of the feed water at the cold end  120 . Also in such embodiment, the flash tank  140  is fluidically connected at the cold end  122  of the HRSG  120  through the feedwater preheating system  170  in order to extract unused hot water of the cold end  122  via the feedwater preheating system  170 . A recirculation system  172  may be enabled to the feedwater preheating system  170  for cooperating thereto. Furthermore, a Low Pressure (LP) drum  126  may also be operative in conjunction to the feedwater preheating system  170 . 
     The flash tank  140  having the extracted hot water may direct therefrom for being utilized in the most optimized way in order to increase the efficiency of the CCPP  100 . For the said purpose, the CCPP  100  includes the first and second supply lines  150 ,  160 . 
     The first supply line  150  is configured to interconnect the flash tank  140  and the steam turbine  130  to enable supply of flash steam thereto. The flash steam from the first supply line  150  may be injected to the steam turbine  130 , more specifically, to a Low Pressure (LP) steam turbine, to generate an additional power, apart from the power generated in conventional CCPP cycle, in order to increase the efficiency and output of the CCPP  100  and thereafter is supplied back to the HRSG  120  via a return line  136  through a pump  137  via passing through a condenser  135 . 
     Further, the second supply line  160  is configured to interconnect the flash tank  140  and the gas turbine air preheating system  112  to enable supply of hot flash condensate in the flash tank  140  to the gas turbine air preheating system  112  to preheat the air to supply the preheated air to the gas turbine  110  for enabling expedite combustion. A pump  162  may be configured in the second supply line  160  to achieve the target. Further, the cold condensate therefrom may be returned to the return line  136  and resupplied to the HRSG  120  for reoperation. The second supply line  160  enables the provision of preheating the air supplied in the gas turbine  110 , thereby replacing the requirement of external source to preheat the fuel air in turn increasing the efficiency of the CCPP  100 . Further, the said provision of air preheating of the present invention precludes complex piping and heat exchanger arrangements as required in the conventional CCPP, making the present system simple and cost effective. 
     The CCPP  100  as depicted in  FIG.  1   , as per various embodiments, may be modified to different plant configurations.  FIGS.  2  to  7    depict various such variants of the CCPP  100 , and will be described herein in conjunction to  FIG.  1   . In  FIGS.  2  to  7    only those reference numerals with corresponding components are inserted where the variant are depicted, and the remaining components are left unnumbered in order to highlight the various variant, and that the all unnumbered components shall be read or referred from  FIG.  1   . 
     As per the first variant, as shown in  FIG.  2   , the CCPP  100  may include a first bypass member  180  to selectively bypass a part or all of the flash condensate from the second supply line  160  for bypassing the gas turbine air preheating system  112 . 
     As per the second variant, as shown in  FIG.  3   , the CCPP  100  may include a second bypass member  190  to selectively bypass a part or all of the extracted hot water from the cold end  122  for bypassing the supply of the extracted hot water in to the flash tank  140 . This serve as a recirculation system for heating the condensate to the HRSG  120  to achieve a required minimum HRSG inlet temperature. In such arrangement, the recirculation system  172  may be precluded, as shown in  FIG.  3   . 
     As per the third variant, as shown in  FIG.  4   , the CCPP  100  may include at least one additional heat source  200  fluidically connected the flash tank  140  to be utilized for additional hot water extraction to be supplied to the flash tank  140 . The additional heat source  200  may include condensate return from a carbon capture unit or a district heating unit. However, without departing from the scope of the present disclosure, the additional heating source may be any other as known in the art. 
     As per the fourth variant, as shown in  FIG.  5   , the CCPP  100  may include a fuel gas preheating system  300  configured to heat fuel to be supplied to the gas turbine  110  for effective combustion. The fuel gas preheating system  300  is adapted to be configured in the second supply line  160  to utilize the heat from the hot flash condensate to preheat the fuel to be supplied to the gas turbine  110 . For example, at least one heat exchanger, such as  310 , may be configured in series with a heat exchanger  320  of the second supply line  160  for enabling the heat to be supplied to preheat the fuel gas at the fuel gas preheating system  300  as and when required full temperature, normally 150-300° C., is not generated by the hot flash condensate of the second supply line  160 . 
     In one other variant, fifth, as shown in  FIG.  6   , the CCPP  100  may include a plurality of flash tanks  140  as against one flash tank  140 . The plurality of flash tanks  140  is adapted to work in cascading configuration, using as hot source the hot water from the cold end  122  of the HRSG  120 , flashing at different pressures and subsequently injecting the flash steam of varying pressure levels to corresponding steam turbine stages 
     In one further variant, sixth, as shown in  FIG.  7   , at least one heat exchanger  400  adapted to be configured to the second supply line  160 . As shown, the at least one heat exchanger  400  is configured in an intermediate heat transfer loop  420  with the gas turbine air preheating system  112  for preheating the air supplied in the gas turbine  110 . 
     In yet another variant, seventh, as shown in  FIG.  8   , of the CCPP  100 , the at least one gas turbine  110  may preclude the gas turbine air preheating system  112  as provided in the above embodiments. Rather in this embodiment, the second supply line  160  is configured to supply hot flash condensate from the at least one flash tank  140  to the return line  136  to the at least one heat recovery steam generator  120  or to the feedwater preheating system  170 . Valves  141  may be configured to control respective supply of the hot water and condensate. 
     The invention of the present disclosure is advantageous in various scopes. This provides an improved CCPP, which may capture the heat in the HRSG, especially, at the cold end of the HRSG that may be left unused in most optimal way in order to improve CCPP efficiency and output. Further, the CCPP with such variants is convenient to use and economical. Various other advantages and features of the present disclosure are apparent from the above detailed description and appendage claims. 
     The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present disclosure and its practical application, to thereby enable others skilled in the art to best utilize the present disclosure and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present disclosure.