Abstract:
A steam cycle power plant includes a gas turbine, a gas turbine intercooler, a steam turbine, and a heat recovery steam generator (HRSG). The gas turbine intercooler recovers unused heat generated via the gas turbine and transfers substantially all of the recovered heat for generating extra steam for driving the steam turbine.

Description:
BACKGROUND 
       [0001]    This invention relates generally to gas turbine engines, and more particularly, to a system and method for extracting and using heat from a gas turbine&#39;s intercooler in a steam cycle. 
         [0002]    Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high-pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometime collectively referred to as the core engine. At least some known gas turbine engines also include a low-pressure compressor, or booster, for supplying compressed air to the high pressure compressor. 
         [0003]    Gas turbine engines are used in many applications, including aircraft, power generation, and marine applications. The desired engine operating characteristics vary, of course, from application to application. More particularly, within some applications, a gas turbine engine may include a single annular combustor, including a water injection system that facilitates reducing nitrogen oxide (NOx) emissions. Alternatively, within other known application, the gas turbine engine may include a dry low emission (DLE) combustor. 
         [0004]    Gas turbines alone have a limited efficiency and a significant amount of useful energy is wasted as hot exhaust gas is discharged to the ambient. To improve the efficiency of a gas turbine power plant and use this heat for further power generation, many gas turbines are equipped with a heat recovery steam generator and a steam cycle. This is known as a combined cycle. 
         [0005]    Inter-cooled gas turbine engines may include a combustor that may be a single annular combustor, a can-annular combustor, or a DLE combustor. While using an intercooler facilitates increasing the efficiency of the engine, the heat rejected by the intercooler is not utilized by the gas turbine engine, and the intercooler heat from an intercooled gas turbine or compressor is usually wasted. In some applications, a cooling tower discharges intercooler heat to the ambient at a low temperature level. 
         [0006]    There is a need for a system and method for extracting and using heat from a gas turbine&#39;s intercooler in a steam cycle. 
       BRIEF DESCRIPTION 
       [0007]    According to one embodiment, a combined gas and steam turbine power plant comprises: 
         [0008]    a gas turbine; 
         [0009]    a gas turbine intercooler; 
         [0010]    a steam turbine; and 
         [0011]    a heat recovery steam generator (HRSG) configured to generate steam for driving the steam turbine in response to heated fluid received from the gas turbine intercooler. 
         [0012]    According to another embodiment, a combined gas and steam turbine power plant comprises: 
         [0013]    a gas turbine; 
         [0014]    a gas turbine intercooler; 
         [0015]    a steam turbine; and 
         [0016]    a heat recovery steam generator (HRSG) connected downstream from a low-pressure gas turbine compressor and upstream from a high-pressure gas turbine compressor in a steam cycle, wherein the HRSG is configured to generate steam for driving the steam turbine in response to a heat transfer medium received via the gas turbine intercooler. 
         [0017]    According to yet another embodiment, combined gas and steam turbine power plant comprises: 
         [0018]    a gas turbine; 
         [0019]    a gas turbine intercooler; 
         [0020]    a steam turbine; and 
         [0021]    a heat recovery steam generator (HRSG), 
         [0000]    wherein the gas turbine intercooler is configured to recover the intercooling heat and use substantially all of the recovered heat to produce hot water and steam for driving the steam turbine. 
     
    
     
       DRAWINGS 
         [0022]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawing, wherein: 
           [0023]      FIG. 1  is a block diagram of a gas turbine engine including an intercooler system; and 
           [0024]      FIG. 2  illustrates a combined cycle power plant according to one embodiment. 
       
    
    
       [0025]    While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. 
       DETAILED DESCRIPTION 
       [0026]      FIG. 1  is a block diagram of a gas turbine engine  10  including an intercooler system  12 . Gas turbine engine  10  includes, in serial flow relationship, a low pressure compressor or booster  14 , a high pressure compressor  16 , a can-annular combustor  18 , a high-pressure turbine  20 , an intermediate turbine  22 , and a power turbine or free turbine  24 . Low-pressure compressor or booster  14  has an inlet  26  and an outlet  28 , and high-pressure compressor  16  includes an inlet  30  and an outlet  32 . Each combustor can  18  has an inlet  34  that is substantially coincident with high-pressure compressor outlet  32 , and an outlet  36 . In another embodiment, combustor  18  is an annular combustor. In another embodiment, combustor  18  is a dry low emissions (DLE) combustor. 
         [0027]    High-pressure turbine  20  is coupled to high-pressure compressor  16  with a first rotor shaft  40 , and intermediate turbine  22  is coupled to low pressure compressor  14  with a second rotor shaft  42 . Rotor shafts  40  and  42  are each substantially coaxially aligned with respect to a longitudinal centerline axis  43  of engine  10 . Engine  10  may be used to drive a load (not shown) which may be coupled to a power turbine shaft  44 . Alternatively, the load may be coupled to a forward extension (not shown) of rotor shaft  42 . 
         [0028]    In operation, ambient air, drawn into low-pressure compressor inlet  26 , is compressed and channeled downstream to high-pressure compressor  16 . High-pressure compressor  16  further compresses the air and delivers high-pressure air to combustor  18  where it is mixed with fuel, and the mixture is ignited to generate high temperature combustion gases. The combustion gases are channeled from combustor  18  to drive one or more turbines  20 ,  22 , and  24 . 
         [0029]    The power output of engine  10  is at least partially related to operating temperatures of the gas flow at various locations along the gas flow path. More specifically, in the exemplary embodiment, an operating temperature of the gas flow at high-pressure compressor outlet  32  is closely monitored during the operation of engine  10 . Reducing an operating temperature of the gas flow entering high-pressure compressor  16  facilitates decreasing the power input required by high-pressure compressor  16 . 
         [0030]    To facilitate reducing the operating temperature of a gas flow entering high-pressure compressor  16 , intercooler system  12  includes an intercooler  50  that is coupled in flow communication to low pressure compressor  14 . Airflow  53  from low-pressure compressor  14  is channeled to intercooler  50  for cooling prior to the cooled air  55  being returned to high-pressure compressor  16 . 
         [0031]    During operation, intercooler  50  has a cooling fluid  58  flowing therethrough for removing energy extracted from the gas flow path. In one embodiment, cooling fluid  58  is air, and intercooler  50  is an air-to-air heat exchanger. In another embodiment, cooling fluid  58  is water, and intercooler  50  is an air-to-water heat exchanger. Intercooler  50  extracts heat energy from compressed air flow path  53  and channels cooled compressed air  55  to high-pressure compressor  16 . More specifically, in the exemplary embodiment, intercooler  50  includes a plurality of tubes (not shown) through which cooling fluid  58  circulates. Heat is transferred from compressed air  53  through a plurality of tube walls (not shown) to cooling fluid  58  supplied to intercooler  50  through inlet  60 . Accordingly, intercooler  50  facilitates rejecting heat between low-pressure compressor  14  and high-pressure compressor  16 . Reducing a temperature of air entering high-pressure compressor  16  facilitates reducing the energy expended by high-pressure compressor  16  to compress the air to the desired operating pressures, and thereby facilitates allowing a designer to increase the pressure ratio of the gas turbine engine which results in an increase in energy extracted from gas turbine engine  10  and a high net operating efficiency of gas turbine  10 . 
         [0032]    In an exemplary embodiment, feedwater is flowing through intercooler  50  for removing energy extracted from gas flow path  53  and functions as the cooling fluid  58 . The feedwater is being heated or turned into low-pressure (LP) steam, or a combination thereof as described in further detail herein. In this fashion, the extracted heat, if extracted at a higher temperature, ideally approaching that of the hot compressed inlet air, can be a useful contributor to a bottoming cycle generating electricity. 
         [0033]    Whether feedwater heating only or steam generation is preferable depends on the bottoming cycle configuration, required feedwater mass flows and intercooler temperatures. Exergy considerations suggest that intermediate or high-pressure feedwater heating can yield the highest available work from the intercooler heat; however, the amount of feedwater to be heated may be more than the bottoming cycle requires and may compete with HRSG economizers. Low-pressure preheating and steam generation is the alternative. The exergy portion can be more than twenty (20) % of the available intercooler heat under typical conditions. 
         [0034]    Intercooler  50  may comprise a high efficiency counterflow or cross-counterflow heat exchanger to gain useful heat from intercooling air with feedwater applications. One suitable configuration may include, for example, a serpentine coil fin-tube heat exchanger enclosed within a pressure shell. 
         [0035]    According to one aspect, intercooler  50  may be used to generate hot feedwater or saturated steam by utilizing a significant fraction of the available heat from the hot air in a suitable heat exchanger. This hot feedwater or saturated steam, at low-pressure to facilitate evaporation at temperatures as low as about 100° C., is fed into an evaporator (if hot feedwater) or a superheater (if saturated steam) in a heat recovery steam generator (HRSG) described in further detail herein with reference to  FIG. 2 , and admitted to a low-pressure turbine, also described in further detail herein. The extra steam then generates additional electricity. 
         [0036]      FIG. 2  illustrates a combined cycle power plant  100  according to one embodiment. The power plant  100  comprises a high pressure gas turbine system  10  with a combustion system  18  and a turbine  20 . The gas exiting turbine  20  may be at a pressure, for example, of about 45 psi for one particular application. The power plant  100  further comprises a steam turbine system  110 . The steam turbine system  110  comprises a high pressure section  112 , an intermediate pressure section  114 , and one or more low pressure sections  116 . The low pressure section  116  exhausts into a condenser  120 . 
         [0037]    The steam turbine system  100  is associated with a heat recovery steam generator (HRSG)  104 . According to one embodiment, the HRSG  104  is a counter flow heat exchanger such that as feedwater passes there through, the water is heated as the exhaust gas from turbine  16  gives up heat and becomes cooler. The HRSG  104  has three (3) different operating pressures (high, intermediate, and low) with means for generating steam at the various pressures and temperatures as vapor feed to the corresponding stages of the steam turbine system  110 . The present invention is not so limited however; and it can be appreciated that other embodiments, such as those embodiments comprising a two-pressure HRSG will also work using the principles described herein. Each section of the HRSG  104  generally comprises one or more economizers, evaporators, and superheaters. 
         [0038]    The HRSG  104  uses the heat of the turbine  20  exhaust gas to produce three (3) steam streams, a high pressure steam stream  128 , an intermediate pressure stream  130 , and a low pressure steam stream  132 . These three steam streams enter the high, intermediate and low pressure steam turbines  112 ,  114 ,  116  to produce power. A high pressure steam stream extracted from the high pressure steam turbine  112  is injected to the gas turbine combustor  18 . 
         [0039]    Subsequent to exiting the low pressure steam turbine  116 , the steam stream enters the condenser  120  where the steam is condensed into liquid water. The liquid water exiting the condenser  120  along with make-up water  122  and residual water from the HRSG  104  enters a water collector  124 . 
         [0040]    An appropriate amount of water is pumped from the water collector  124  to the HRSG  104  where the water absorbs the heat from the high pressure gas turbine exhaust to generate the requisite steam streams. The three steam streams enter the steam turbines  112 ,  114 ,  116  to complete the bottoming cycle. 
         [0041]    According to one embodiment, combined cycle power plant  100  further comprises a gas turbine intercooler  50  that operates as described herein before with reference to  FIG. 1 . Intercooler  50  may comprise, for example, a high efficiency counterflow or cross-counterflow heat exchanger as stated herein, to generate hot feedwater or saturated steam  126  by utilizing a significant fraction of the available heat from the hot air stream  53 . This hot feedwater or saturated steam  126 , at low pressure to facilitate evaporation at temperatures as low as about 100° C., is fed into an evaporator (if hot feedwater) or a superheater (if saturated steam) in the HRSG  104 , and subsequently admitted to the low-pressure turbine  116 . The extra steam then generates additional electricity, as stated herein. In this way, system efficiency is advantageously increased while simultaneously decreasing the size of the cooling system. 
         [0042]    In summary explanation, a system and method have been described herein for harvesting a significant amount of intercooler heat and generating additional electricity therefrom in a gas turbine bottoming cycle, thus substantially eliminating wasted heat. Since the heat is integrated into the bottoming cycle in the form of steam hot feedwater, no major additional investment is required. The present inventors recognized the foregoing advantages even though intercooler heat has been rarely employed due to the corresponding low temperature(s) and regardless of the low numbers of large gas turbines that employ intercoolers. 
         [0043]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.