Abstract:
A dual-fluid heat engine having a gas turbine and an open cycle steam turbine. The gas turbine has a compressor for compressing a first working fluid, the compressor having a compressor outlet. The gas turbine has a combustion chamber in fluid communication with the compressor outlet. The turbine portion of the gas turbine has an inlet in fluid communication with the combustion chamber for performing work by expansion of the first working fluid, and a gas turbine exhaust. A heat recovery exchanger is coupled to the gas turbine exhaust having a heat recovery inlet and an outlet for heating a second working fluid, water. The water is converted into steam in the heat recovery exchanger. A pump increases the pressure of the water prior to entrance in the heat recovery exchanger. An atmospheric exhaust expansion steam turbine extracts energy from the heated second working fluid to drive an electrical generator. An exhaust chimney takes the gas turbine exhaust and the steam turbine exhaust and rejects it into the atmosphere.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 60/263,936, filed Jan. 24, 2001. The entire contents of the above application are incorporated herein by reference in entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The generation of electrical power is a complex matter which is dependent in part on the amount of power required on the grid. Therefore, the amount of power being generated varies widely depending on the time of day, day of the week, and atmospheric conditions such as cold spells and heat waves. While the amount of power varies, it is recognized that maximum efficiencies are achieved by operating power generation systems at a steady state or near steady state conditions. With this in mind, there has been an increased use of gas turbine systems that may be added online to the grid to provide additional power in that gas turbine systems typically are well suited for ease of being brought online quickly therefore being either in a standby or running mode. However, gas turbines are recognized as being not as efficient as other plant systems such as large steam plants because of the gas turbine system being an open cycle where approximately 60 to 70 percent of the energy is lost in waste heat energy. 
     One method of increasing efficiency that has been recognized is a combined cycle power plant in which a gas turbine, also referred to as a topping cycle, transfers its exhaust waste heat through a heat recovery system to a closed cycle heat engine such as a steam turbine. To capture the exhaust steam energy in these steam turbines, the steam turbine operates in a closed cycle that adds a circulating water system, a condensate water system, and a large cooling trap to reject the low energy heat. 
     SUMMARY OF THE INVENTION 
     The invention relates to a combined cycle system having an open cycle system using a fuel to create power and expending an exhaust with a waste heat. The system has a heat recovery exchanger for transferring heat from the exhaust with waste heat to the heat exchange fluid. A second open cycle system uses the heat exchange fluid to create power and expend the heat exchange fluid. 
     In one embodiment, the first open cycle system is a gas turbine, the second open cycle system is a steam turbine. The heat exchange fluid is water in a fluid and gaseous state. A pump moves and pressurizes the water to the heat recovery exchanger. 
     In one embodiment, an exhaust system combines the exhaust from the first open cycle and the heat exchange fluid from the second open cycle. 
     In one embodiment, the heat recovery exchanger is a once-through exchanger. In another embodiment, the heat recovery exchanger is a drum boiler. A purifier cleans the water prior to entering the heat recovery exchanger to remove dissolved minerals. 
     The steam turbine in the combined cycle system produces power in a range of between 30 to 45 percent of the power produced by the gas turbine. In one embodiment, the power produced is approximately 35 percent of the power produced by the gas turbine. 
     A dual-fluid heat engine has a gas turbine and a steam turbine. The gas turbine has a compressor section, a combustion chamber section, and a hot expansion turbine section. The compressor section compresses a first working fluid. The combustion chamber section is in fluid communication with the compressor outlet and mixes the air with the fuel to ignite and produce a hot first working fluid. The turbine section of the gas turbine has an inlet in fluid communication with the combustion chamber section for performing work by expansion of the first working fluid. In addition to producing mechanical energy, the gas turbine expends an exhaust fluid. 
     The steam turbine is an atmospheric exhaust expansion steam turbine. The steam turbine extracts energy from the heated second working fluid, steam, to drive a shaft to produce mechanical energy. 
     A heat recovery exchanger is coupled to the gas turbine exhaust and has a heat recovery inlet and an outlet for heating the second working fluid, water. The heat recovery exchanger extracts heat from the gas turbine exhaust to heat the water to produce water in a gaseous state, steam. A pump increases the pressure of the second working fluid prior to entrance into the heat recovery exchanger. 
     The steam turbine, likewise expends an exhaust in addition to producing mechanical energy. An exhaust chimney takes the gas turbine exhaust and the steam turbine exhaust, steam, and combines and rejects the exhausts into the atmosphere. The mechanical energy produced by both the gas turbine and the steam turbine drive electric generators. 
     The foregoing and other features and advantages of the system and method of the invention will be apparent from the following more particular description of preferred embodiments of the system and method as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 is a schematic of a combined cycle plant according to the invention; 
     FIG. 2 is a schematic of a gas turbine; 
     FIG. 3 is a schematic of a steam turbine; 
     FIG. 4 is a schematic of a drum heat exchanger; and 
     FIG. 5 is a schematic of a once-through counter flow heat exchanger. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings in detail, where like numerals indicate like elements, there is illustrated a combined cycle plant according to the invention generally referred to as  10 . 
     Referring to FIG. 1, the combined cycle plant  10  in one embodiment has a gas turbine  12  that receives air  50  and fuel  14  and produces a rotation force to a shaft  16  to drive an electric generator  18 . In addition, the gas turbine  12  creates an exhaust gas  20 . In one embodiment, as discussed below, the exhaust gas  20  is at a flow of 2,367,000 lbs/hour at a temperature of 1000° F. 
     The exhaust gas  20  is used to heat a heat exchange fluid  21  in a heat recovery steam generator  22 . In one embodiment, the heat exchange fluid  21  is water. The water in a liquid state  24  is sent to the heat recovery steam generator  22  from a water supply  26 . 
     The water in the liquid state  24  prior to the heat recovery steam generator  22  is treated to remove dissolved minerals from the water, such as iron, calcium, and silicon. 
     The water supply  26  can include a de-mineralization system, an acid/caustic system or other systems to treat the water. 
     The combined cycle plant  10  has a pump  28  to move the water  24  from the water supply  26  to the heat recovery steam generator  22 . The pump  28  in addition pressurizes the heat recovery steam generator  22 . 
     The liquid water  24 , the heat exchange fluid  21 , is converted to water in gaseous state, steam  30 , in the heat recovery steam generator  22 . The steam  30  is sent to a steam turbine  32 . 
     In the steam turbine  32 , the energy of the pressurized steam is extracted to rotate a shaft  34 . The shaft  34  drives a second electric generator  36 . It is recognize that both the shaft  16  of the gas turbine  12  and the shaft  34  of the steam turbine  32  can drive a single electric generator. 
     The exhaust gas  20  from the gas turbine  12  after passing through the heat recovery steam generator  22  and a steam exhaust  38  from the steam turbine  32  are mixed to form an exhaust gas/steam mixture  40 . The exhaust gas/steam mixture  40  is mixed and vented to atmosphere through an exhaust stack  42 . 
     In the past few years the electrical infrastructure of the industrialized nations has experienced shortfalls in the generation, transmission and distribution of electricity into the rapidly growing urban areas. These areas have very limited space available for locating new power plants and transmission lines and in many cases the better option is to quickly upgrade existing local community plants so the power can go directly to the distribution system, thus, bypassing the overloaded transmission lines. This invention provides for an economical and quick upgrade of any simple cycle gas turbine or reciprocating engine power plant. Improvement in power and heat rate up to approximately 35% can be achieved without subjecting the existing engine to any increased loads, forces or stresses. Also, this plant upgrade puts no additional burden on the local fuel delivery infrastructure unlike the fuel requirements of an added new power plant. All of the additional electric power is produced with no increase in the emissions of harmful gases and also, the total power plant heat rejection is reduced. While a gas turbine  12  is shown with respect to FIGS. 1 and 2, it is recognized that the invention can be used with other open cycle systems. For example, the invention can work with a reciprocating engine power plant, such as a diesel. 
     With the combined cycle plant  10  described and some of the benefits, individual components of the combined cycle plant  10  are described. Referring to FIG. 2, the gas turbine  12  of the combined cycle plant has a compressor  48  that compresses air  50 . The air  50  and the fuel  14  are mixed in a combustion chamber  52  of the gas turbine  12 . The mixture is ignited and burned to produce a hot working fluid  54 . The working fluid  54  pushes a series of blades in a turbine  56  of the gas turbine  12 . This produces a rotational force that spins the compressor  48  in addition to rotating the shaft  16  connected to the electric generator  18 , as seen in FIG. 1, to produce electric power. In addition to rotating the shaft  16  that is connected to the electric generator  18 , a product of the combustion of the fuel and the air in the gas turbine  12  is the hot exhaust gas  20 . The hot exhaust gas  20  is directed from the gas turbine  12  through the heat recovery steam generator  22  that is described in greater detail in FIGS. 4 and 5. 
     Referring to FIG. 3, the steam turbine  32  of the combined cycle plant  10  is shown. The steam turbine  32  is an open cycle system in that the exhaust steam  38  is vented to atmosphere. This is in contrast to a closed cycle in which the dynamic fluid does not enter or leave the system but is used over and over again such as in a closed cycle steam turbine. In addition, in closed cycle systems, the exhaust steam is captured and returned to the heat recovery steam generator  22 . This increases the complexity, cost and maintainability because of the addition of steam condenser, circulating water system, condensate water system, and a large cooling tower to reject the low energy heat. 
     Still referring to FIG. 3, the steam turbine  32  has a turbine  60 . The turbine receives the steam  30  from the heat recovery steam generator  22  and rotates the series of blades in the turbine  60  to rotate the shaft  34  connected to the electric generator  36  to produce electric power. The steam exhaust  38  is sent to the exhaust stack  42  to mix with the exhaust gas  20 . 
     In the heat recovery steam generator  22 , the heat of the exhaust gas  20  is transferred to water to produce steam. The water to the heat recovery steam generator  22  is provided by the water supply  26 . The water  24  is pumped to the heat recovery steam generator  22  by the pump  28 , which in a preferred embodiment is an electric driven centrifugal pump. In the heat recovery steam generator  22 , the exhaust gas  20  from the gas turbine  12  passes around a plurality of tubes carrying the water  24  to convert the water to steam. 
     Referring to FIG. 4, a drum heat recovery steam generator  64  is shown. The drum generator  64  has an economizer  65  that receives water in a liquid state  24  from the water supply  26 . The exhaust gas  20  passes over the tubes of the economizer  65 . The water  24  that passes through the economizer  65  is preheated to near the saturation temperature prior to being feed into the steam generator drum  68 . Water  24  flows down from the steam generator drum  68  in at least one down feed tube  69  to a blow-down drum  66  and then flows up through a plurality of steam generating tubes  70  to the steam generator drum  68  by natural circulation. The exhaust gas  20  passes over the tubes  70  to change the pressurized water  24  into a saturated steam  30 . The steam  30  passes from the steam generator drum  68  through a plurality of superheater tubes  72  to raise the temperature of the steam  30  above the saturation temperature. The super heated steam  30  is sent to the open cycle steam turbine  32 . 
     FIG. 5 shows a section of an alternative heat recovery steam generator  22 . The generator  22  is a once-through exchanger  76 . The exchanger  76  has a plurality of tubes  78  for the heat exchange fluid  21 , water  24 . In the embodiment shown, the exhaust gas  20  flows in one direction and the heat exchange fluid  21  flows in the other. The heat exchange fluid  21 , water  24 , changes to steam  30  as it absorbs heat energy from the exhaust gas  20  in the heat recovery steam generator  22 . As the water flows through the tubes  78 , different segments of the tubes  78  act as the economizer, evaporator and superheater. 
     The water generally needs to be of a better quality in the once-through exchanger  76  then in the drum generator  64 . The drum generator  64  has blow-down capability to clean impurities, which is not possible in the once-through exchanger  76 . 
     While two styles of the heat recovery steam generators  22  are shown, it is recognized that other style heat exchangers or heat recovery steam generators can be used. For example, other styles of the heat recovery steam generators  22  include force circulation steam generators or kettle boilers. 
     The exhaust steam  38  from the steam turbine  32  is released at atmospheric pressure to the exhaust stack  42  as seen in FIG.  1 . In addition, the exhaust gas  20  from the gas turbine  12  after passing through the heat recovery steam generator  22  to produce the steam exits from the heat recovery steam generator  22  to the exhaust stack  42 . 
     The steam turbine  32  and the heat recovery steam generator  22  need to be sized relative to the gas turbine  12  of the combined cycle plant  10  in order to operate efficiently. In that the gas turbine  12  typically operates at its base rating, the plant designer knows the power rating of the turbine and its exhaust gas flow rate and temperature. The designer can take the exhaust gas flow temperature and rate to determine what size heat recovery steam generator  22  is needed and how much steam can be produced at a certain pressure, such as 700 PSI at a desired flow rate. The designer with the known flow rate and temperature and pressure of the steam generated by the heat recovery steam generator  22  can size the steam turbine  32  to efficiently convert this energy into rotational energy to drive the electric generator  36  of FIG.  1 . 
     In that the combined cycle plant  10  exhausts both the exhaust gas  20  and the exhaust steam  38  directly to atmosphere, this dual open cycle system simplifies that power plant design from the prior art and reduces maintenance and installation cost. In addition, it improves the reliability of the power plant over the previous combined cycle plants. 
     Over the past 35 years, gas turbines have been increasingly used to generate electric power because of their low cost, short installation time and the high availability of clean burning oil and natural gas fuels. Many different manufacturers through out the world have installed thousands of engines as simple cycle power plants. Most of these plants operate at a fuel efficiency of 25% to 35%. One of the most popular large engines is General Electric Company&#39;s Frame 7 that was first commercialized in 1969. The current version of this model is the Frame 7EA with a power rating of 85,000 kilowatts. It has an exhaust gas flow of 2,367,000 lbs/hour at a temperature of 1000° F. The heat energy in this exhaust gas can be converted in a heat recovery steam generator to produce over 350,000 lbs/hour of high and low pressure steam. This will generate 30,000 kilowatts of power when expanded through an atmospheric discharge, backpressure steam turbine. Any simple cycle gas turbine plant can achieve similar results by installing a heat recovery steam generator  22 , a steam turbine/generator set  32  and  36  and a water purifier  26 . 
     The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.