Abstract:
A fuel heating system for a power plant includes a fuel source for a gas turbine system, wherein the fuel source contains a fuel at a first temperature. Also included is a feedwater source for distributing a feedwater. Further included is a fuel heater configured to receive the fuel at the first temperature and distribute the fuel to the gas turbine system at a second temperature and capable of receiving the feedwater from the feedwater source. Yet further included is at least one boiler drum for containing a boiler substance. Also included is at least one heat exchanger for receiving the feedwater and the boiler substance and distributing the feedwater to the fuel heater and the boiler substance to the blowdown system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to power plants, and more particularly to a system and method of heating fuel within power plants. 
         [0002]    Typical gas turbine combined cycle systems often include one or more heating sources for multiple operations, including startup procedures. During the starting process, a fuel gas supply is heated to meet fuel gas minimum superheat temperature requirements by a heater, thereby allowing operation of the gas turbine at only low load conditions. While the fuel gas heater is at adequate temperature to provide the fuel when the plant is loaded and operating normally, it has been observed that during startup, the heat source is often at lower enthalpy conditions. Thus, during startup, the fuel gas performance heater is not adequate to provide fuel gas at a suitable temperature until the heater is supplemented with additional heating sources or the plant bottom cycle warms up. Such an arrangement results in delayed loading and wasted fuel due to the delay. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a fuel heating system for a power plant includes a fuel source for a gas turbine system, wherein the fuel source contains a fuel at a first temperature. Also included is a feedwater source for distributing a feedwater. Further included is a fuel heater configured to receive the fuel at the first temperature and distribute the fuel to the gas turbine system at a second temperature and capable of receiving the feedwater from the feedwater source. Yet further included is at least one boiler drum for containing a boiler substance. Also included is at least one heat exchanger for receiving the feedwater and the boiler substance and distributing the feedwater and the boiler substance to the fuel heater. 
         [0004]    According to another aspect of the invention, a fuel heating system for a power plant includes a fuel source for a gas turbine system, wherein the fuel source contains a fuel at a first temperature. Also included is an economizer for distributing a feedwater. Further included is a fuel heater configured to receive the fuel and the feedwater and capable of distributing the fuel to the gas turbine system. Yet further included is at least one boiler drum for containing a boiler substance. Also included is at least one heat exchanger for receiving the fuel and the boiler substance and distributing the fuel and the boiler substance to the fuel heater. 
         [0005]    According to yet another aspect of the invention, a method of heating fuel in a power plant includes supplying a fuel to a fuel heater for heating prior to distribution to a gas turbine system. Also included is extracting a boiler substance from at least one boiler drum and distributing the boiler substance to at least one heat exchanger. Further included is supplying feedwater from an economizer to the at least one heat exchanger for mixing with the boiler substance. Yet further included is heating the feedwater in the at least one heat exchanger. Also included is distributing the feedwater to the fuel heater. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a schematic illustration of a first embodiment of a fuel heating system for a power plant; 
           [0009]      FIG. 2  is a schematic illustration of a second embodiment of the fuel heating system for the power plant; 
           [0010]      FIG. 3  is a schematic illustration of a third embodiment of the fuel heating system for the power plant; and 
           [0011]      FIG. 4  is a schematic illustration of a fourth embodiment of the fuel heating system for the power plant. 
       
    
    
       [0012]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to  FIG. 1 , in one exemplary embodiment, a fuel heating system for a power plant is generally referred to as  10 . The power plant comprises a gas turbine system, which is not illustrated, but the direction of which is referenced by  12 . The fuel heating system  10  is configured to heat a fuel prior to distribution of the fuel to the gas turbine system  10  for combustion purposes within the gas turbine system  12 . Within the fuel heating system  10 , the fuel is initially delivered from a fuel source to a fuel heater  14  along a fuel line  16 . 
         [0014]    The fuel heating system  10  generally includes a boiler system  17  that comprises at least one boiler drum  18  that contains a boiler substance, such as steam or water. In a multiple boiler drum system, a common arrangement is to have a low pressure boiler drum, an intermediate pressure boiler drum and a high pressure boiler drum, where the respective pressures within each of the plurality of boiler drums  18  are relative to one another. The at least one boiler drum  18  is typically used in conjunction with a steam turbine, whereby superheated steam is distributed along path  20  to the steam turbine for operation therein. Each of the at least one boiler drums  18  employ “blowdowns” to maintain steam chemistry and typically consists of startup blowdown for startup chemistry purposes, intermittent blowdowns that are used intermittently during startup and normal operation depending on chemistry buildup, and continuous blowdowns that operate continuously to remove any solids buildup and to maintain other chemistry related parameters on a continuous basis. Intermittent blowdown is sent along an intermittent blowdown line  22 , while a continuous blowdown line  24  transports continuous blowdown. The intermittent blowdown line  22  and the continuous blowdown line  24  lead to and through at least one heat exchanger, and in the illustrated embodiment the intermittent blowdown line  22  leads to a first heat exchanger  26 , while the continuous blowdown line  24  leads to a second heat exchanger  28 . The intermittent blowdown line  22  and the continuous blowdown line  24  each lead to blowdown tank(s), with a first control valve  30  controlling flow and state characteristics of the intermittent blowdown line  22  and a second control valve  32  controlling flow and state characteristics of the continuous blowdown line  24 . Although the description above and the illustrated embodiment refer to multiple heat exchangers  26 ,  28 , it is contemplated that both the intermittent blowdown line  22  and the continuous blowdown line  24  lead to a single heat exchanger. 
         [0015]    The illustrated embodiment shown in  FIG. 1  relates to blowdown generated by a high pressure boiler drum, but it is to be appreciated that the blowdown employed in the fuel heating system  10  may be that of another boiler drum, specifically an intermediate pressure boiler drum, for example. The flow conditions associated with blowdown generated by the high pressure boiler drum and the low pressure boiler drum may vary based on the application of use. Illustrative flow condition ranges for the high pressure boiler drum include a temperature of approximately 500° F.-600° F., a pressure of approximately 700-1,500 psia, and a flow rate of approximately 15,000-70,000 lbm/hr. The flow condition ranges for the intermediate pressure boiler drum include a temperature of approximately 375° F.-450° F., a pressure of approximately 200-400 psia, and a flow rate of approximately 5,000-15,000 lbm/hr. The aforementioned ranges are merely presented for illustrative purposes and it is to be appreciated that temperatures, pressures and flow rates outside of the illustrative ranges may be generated by the at least one boiler drum  18  and may still be suitable for use in the fuel heating system  10 . Irrespective of the boiler drum  18  employed, the fuel heating system  10  utilizes feedwater discharged from a feedwater source, such as an intermediate pressure economizer  15 , to inject directly or indirectly into the fuel heater  14  to accelerate the heating process of the gas that is to be delivered to the gas turbine system  12 . It is to be appreciated that the economizer  15  is merely one example of the feedwater source and various alternatives may be employed to supply the feedwater. The feedwater is directed along a feedwater path  34  toward a junction  36  that selectively permits the feedwater to bypass the first heat exchanger  26  and the second heat exchanger  28 . The feedwater path  34  is controlled by a third control valve  38  that determines whether the feedwater flows through or bypasses the first heat exchanger  26  and the second heat exchanger  28 . Regardless of whether the feedwater flows through or bypasses the first heat exchanger  26  and the second heat exchanger  28 , the feedwater is routed along a heated feedwater line  40  to the fuel heater  14 . 
         [0016]    In operation, during startup the third control valve  38  is closed and the feedwater passes through the first heat exchanger  26  and the second heat exchanger  28 . The heat exchangers  26 ,  28  pre-heat the feedwater prior to feedwater distribution to the fuel heater  14 , thereby accelerating the fuel heating process prior to distribution to the gas turbine system  12 . Upon reaching a suitable temperature proximate the fuel heater  14 , the third control valve  38  is opened, thereby allowing the feedwater to bypass the first heat exchanger  26  and the second heat exchanger  28 . This process provides temperature control of the feedwater along heated feedwater line  40 . 
         [0017]    Referring now to  FIG. 2 , another exemplary embodiment of the fuel heating system  100  is illustrated. The fuel heating system  100  is similar to fuel heating system  10 , with the exception of the addition of a third heat exchanger  42  and a fourth heat exchanger  44 , which are operably connected to an intermediate pressure intermittent blowdown line  46  and an intermediate pressure continuous blowdown line  48 , respectively. Both the intermittent blowdown line  22  and the intermediate pressure intermittent blowdown line  46  are configured to selectively bypass the first heat exchanger  26  and the third heat exchanger  42 , respectively. A fourth control valve  50  and a fifth control valve  52  control whether throughflow or bypass is performed. Such control permits the bypass option when the flow rate is not required for fuel heating. 
         [0018]    The fuel heating system  100  employs multiple boiler drums  18 , such as the high pressure boiler drum and the intermediate pressure boiler drum, for example. Similar to fuel heating system  10 , intermittent blowdown and continuous blowdown from each of the boiler drums  18  is utilized to pass through the heat exchangers  26 ,  28 ,  42 ,  44 . 
         [0019]    Referring now to  FIG. 3 , another exemplary embodiment of a fuel heating system  200  is illustrated. Fuel heating system  200  is of a configuration similar to fuel heating system  10 , with the notable exception that the feedwater is directly fed into the fuel heater  14  via the feedwater path  34 , while the fuel line  16  is arranged to feed fuel through the first heat exchanger  26  and the second heat exchanger  28 . The fuel line  16  is configured to bypass the first heat exchanger  26  and the second heat exchanger  28  with the selective control of the third control valve  38 . The fuel heating system  200  provides selective pre-heating of the fuel prior to entry into the fuel heater  14 . 
         [0020]    Referring now to  FIG. 4 , yet another exemplary embodiment of a fuel heating system  300  is illustrated. The fuel heating system  300  is similar to fuel heating system  200 , with respect to the pre-heating of the fuel prior to entry to the fuel heater  14 , but combines aspects of fuel system  100 . As shown, fuel system  300  employs the third heat exchanger  42  and the fourth heat exchanger  44 , while also combining intermittent and continuous blowdown from multiple boiler drums  18 , such as the high pressure boiler drum and the intermediate pressure drum. 
         [0021]    Advantageously, the fuel heating systems  10 ,  100 ,  200 ,  300  reduce fuel heating time required during a startup sequence. The fuel heater  14  is provided with increased heat input, thereby providing a more rapid and efficient startup of the power plant. Furthermore, a reduction in fuel consumption and emissions is achieved during startup by reducing or eliminating high emissions hold time for the gas turbine system  12 . Additionally, otherwise wasted heat from the blowdown process is reclaimed, which improves efficiency, even during steady-state operation. Additionally, fuel temperature is increased achieving higher fuel gas temperature and associated higher thermodynamic efficiency. 
         [0022]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.