Abstract:
A fuel heating system for a power plant includes an exhaust structure having an interior region for receiving an exhaust gas therein. Also included is a fluid injection arrangement comprising a first fluid duct for transferring a fluid, the first fluid duct extending at least partially throughout the interior region of the exhaust structure for heating the fluid. Further included is a heat exchanger for receiving the fluid and a liquid fuel, the fluid heating the liquid fuel during passage of the liquid fuel through the heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to power plants, and more particularly to a fuel heating system for such power plants, as well as a method of heating fuel within a power plant. 
         [0002]    Power plants may include a gas turbine system having at least one combustor and a turbine section, among other sections. Such a power plant also may include a water injection system employed for emission control by injecting the water into the at least one combustor. The water is typically injected into the at least one combustor at or near ambient temperature. Additionally, the power plant includes a fuel injection system, with one such arrangement configured to accommodate liquid fuel for injection into the at least one combustor. Prior to combustor injection, the liquid fuel is typically heated by one or more electric heaters to achieve and maintain a desired viscosity. Unfortunately, the one or more heaters are relatively costly and also require substantial power consumption to adequately operate. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a fuel heating system for a power plant includes an exhaust structure having an interior region for receiving an exhaust gas therein. Also included is a fluid injection arrangement comprising a first fluid duct for transferring a fluid, the first fluid duct extending at least partially throughout the interior region of the exhaust structure for heating the fluid. Further included is a heat exchanger for receiving the fluid and a liquid fuel, the fluid heating the liquid fuel during passage of the liquid fuel through the heat exchanger. 
         [0004]    According to another aspect of the invention, a fuel heating system for a power plant includes a turbine section having an exhaust outlet for expelling an exhaust gas. Also included is a first heat exchanger in operable connection with the exhaust outlet for receiving the exhaust gas, the first heat exchanger also receiving a fluid from a fluid injection arrangement, wherein the fluid is heated by the exhaust gas therein. Further included is a second heat exchanger configured to receive a liquid fuel, the second heat exchanger in operable connection with the first heat exchanger for receiving the fluid subsequent to heating by the exhaust gas in the first heat exchanger, the fluid heating the liquid fuel within the second heat exchanger. 
         [0005]    According to yet another aspect of the invention, a method of heating fuel for a power plant is provided. The method includes heating a fluid with an exhaust gas of a turbine section of the power plant. Also included is routing the fluid heated by the exhaust gas to a heat exchanger. Further included is routing a liquid fuel to the heat exchanger from a liquid fuel supply. Yet further included is heating the liquid fuel with the fluid within the heat exchanger. 
         [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 DRAWINGS 
         [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 power plant having a fuel heating system according to a first embodiment; 
           [0009]      FIG. 2  is a plot illustrating water injection temperatures within the fuel heating system as a function of power plant load at various ambient temperatures; 
           [0010]      FIG. 3  is a schematic illustration of the power plant having the fuel heating system according to a second embodiment; and 
           [0011]      FIG. 4  is a flow diagram illustrating a method of heating fuel within 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 , a power plant according to a first embodiment is schematically illustrated and generally referred to with numeral  10 . The power plant  10  includes a turbine system, such as a gas turbine system  12  having a compressor section  14 , a combustor section  16 , a turbine section  18  and a rotor  20 . It is to be appreciated that one embodiment of the gas turbine system  12  may include a plurality of compressors  14 , combustors  16 , turbines  18  and rotors  20 . The compressor section  14  and the turbine section  18  are coupled by the rotor  20 . The rotor  20  comprises a single shaft or a plurality of shaft segments coupled together to form the rotor  20 . 
         [0014]    The combustor section  16  uses a combustible fuel, such as a liquid fuel, to run the gas turbine system  12 . For example, fuel nozzles are in fluid communication with a main flow exiting the compressor  14  and a liquid fuel supply line  24 . The fuel nozzles create an air-fuel mixture, and discharge the air-fuel mixture into the combustor section  16 , thereby causing a combustion that creates a hot pressurized exhaust gas. The combustor section  16  directs the hot pressurized gas through a transition piece into a turbine nozzle (or “stage one nozzle”), and other stages of buckets and nozzles causing rotation of turbine blades within an outer casing of the turbine section  18 . A hot exhaust gas  26  is expelled from the turbine section  18  into an exhaust structure  28 , such as an exhaust bypass or exhaust stack. The exhaust structure  28  includes an interior region  30  configured to receive the hot exhaust gas  26 , the temperature of which may vary, and in an exemplary embodiment the temperature of the hot exhaust gas  26  exceeds about 800° F. (about 427° C.). 
         [0015]    The power plant  10  includes a fluid injection arrangement  32  configured to inject a fluid, such as a water  34 , into the combustor section  16  at a high pressure. Although an exemplary embodiment of the fluid comprises water, it is contemplated that other fluids may be employed. The water  34  is converted to steam in the combustor section  16  which provides desirable emission control, such as NOx reduction. The water  34  is provided by a fluid supply  36 , such as a demineralized water storage tank, to a fluid injection skid  38  having numerous components therein for manipulating the water  34 . The components may include pumps and filters, for example. The fluid injection arrangement  32  includes a first fluid duct  40  that transfers the water  34  from the water injection skid  38  into and through at least a portion of the interior region  30  of the exhaust structure  28 . During transfer through at least a portion of the interior region  30 , the first fluid duct  40 , and therefore the water  34 , is exposed to the hot exhaust gas  26 . The exposure to the hot exhaust gas  26  heats the water  34  from a first temperature to a second temperature. The first temperature of the water  34 , measured prior to entry of the water  34  to the interior region  30  of the exhaust structure  28 , is typically about ambient temperature, which may correspond to about 70° F. (about 21° C.) in many environments, but it is understood that the first temperature is dependent upon the ambient conditions. The second temperature of the water  34 , measured subsequent to exit of the water  34  from the interior region  30  of the exhaust structure  28 , is greater than the first temperature and is dependent upon load conditions of the gas turbine system  12 , as well as the ambient conditions which determine a saturation temperature of the water  34 . 
         [0016]    Subsequent to heating within the exhaust structure  28 , the water  34  is transferred to a heat exchanger  42 . The heat exchanger  42  is in communication with a liquid fuel injection arrangement  43  and is configured to receive a liquid fuel  44  from a liquid supply  46  via the liquid fuel supply line  24 . Prior to entry of the liquid fuel  44  into the heat exchanger  42 , the liquid fuel  44  is directed through a liquid fuel forwarding skid  47  having numerous components therein for manipulating the liquid fuel  44 . The components may include pumps and filters, for example. The liquid fuel  44  is heated within the heat exchanger  42  by the water  34  that has been heated by the hot exhaust gas  26  in the exhaust structure  28 , as described in detail above. Heating of the liquid fuel  44  is necessary to achieve a viscosity of the liquid fuel  44  suitable for injection to the combustor section  16 . The liquid fuel  44  may rise to and from various temperatures through the heat exchanger  42 , and in one exemplary embodiment the temperature rises from about 80° F. (about 27° C.) to about 180° F. (about 82° C.). Both the liquid fuel  44  and the water  34  are directed from the heat exchanger  42  to the combustor section  16 . The liquid fuel  44  may be directed along the liquid fuel supply line  24  through one or more components, such as a liquid fuel selection skid  50  and/or a liquid fuel atomizing air skid  52 . Ultimately, the liquid fuel  44  is directed to the combustor section  16 . 
         [0017]    In the case of the water  34 , a second fluid duct  48  may be employed to route the water  34  to the combustor section  16 , with the water  34  having cooled slightly as a result of losses attributed to heating of the liquid fuel  44 . It is to be appreciated that the second fluid duct  48  may simply be an extension of the first fluid duct  40 . The injection temperature of the water  34  to the combustor section  16  is dependent upon the ambient conditions, as noted above, with the saturation temperature providing an upper limit on the injection temperature. Two injection temperature profiles at different ambient temperatures are illustrated in  FIG. 2 . It is shown that as the gas turbine operating load increases, the fluid injection temperature increases due to a higher temperature of the hot exhaust gas  26  present for heating of the water  34 . The plot illustrates a first temperature profile  54  for about 32° F. (about 0° C.) and a second temperature profile  56  for about 122° F. (about 50° C.). 
         [0018]    Referring now to  FIG. 3 , a power plant according to a second embodiment is schematically illustrated and generally referred to with numeral  100 . The second embodiment of the power plant  100  is similar in many respects to that of the first embodiment, such that each component need not be discussed in further detail or repetitively. Where applicable, similar reference numerals used to describe the first embodiment may be employed. Rather than expelling all of the hot exhaust gas  26  to the exhaust structure  28 , the turbine section  18  directs at least a portion of the hot exhaust gas  26  through an exhaust outlet  102  to a first heat exchanger  104  disposed at an external location to that of the turbine section  18  and the exhaust structure  28 . The first heat exchanger  104  is also configured to receive the water  34  at about ambient temperature from the fluid supply  36  via the fluid injection skid  38 . The water  34  is heated by the hot exhaust gas  26  during passage through the first heat exchanger  104 . As discussed above with respect to the first embodiment, the exit temperature of the water  34  is limited by the saturation temperature which is dependent upon ambient conditions. The hot exhaust gas  26  is then expelled from the first heat exchanger  104  to the exhaust structure  28  or to the environment. 
         [0019]    Subsequent to heating within the first heat exchanger  104 , the water  34  is transferred to a second heat exchanger  106 . The second heat exchanger  106  is in communication with the liquid fuel injection arrangement  43  and is configured to receive the liquid fuel  44  from the liquid supply  46  via the liquid fuel supply line  24 , similar to the heat exchanger  42  of the first embodiment. The remaining components and operations are similar to that of the first embodiment. Specifically, the liquid fuel  44  is heated by the water  34  within the second heat exchanger  106  to achieve a viscosity suitable for injection to the combustor section  16 . As described in detail above, both the water  34  and the liquid fuel  44  are then routed to the combustor section  16 . 
         [0020]    Advantageously, both the first and second embodiments of the power plant  10 ,  100  provide an efficient system for heating the water  34  and the liquid fuel  44 . Additionally, heating of the water  34  to a temperature greater than ambient temperature provides greater efficiency of overall power plant performance, based on the reduced latent heat consumed in the combustor section  16  during heating of the water for emissions control. Overall, equipment and operation costs are decreased, while efficiency of the power plant  10 ,  100  is increased. 
         [0021]    As illustrated in the flow diagram of  FIG. 4 , and with reference to  FIGS. 1-3 , a method of heating fuel for a power plant  200  is also provided. Both the first and second embodiments of the power plant  10 ,  100  have been previously described and specific structural components need not be described in further detail. The method of heating fuel for a power plant  200  includes heating a fluid with an exhaust gas of a turbine section of the power plant  202 . The fluid is routed to a heat exchanger  204 . A liquid fuel is also routed to the heat exchanger from a liquid fuel supply  206 , wherein the liquid fuel is heated by the fluid within the heat exchanger  208 . 
         [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.