Combined cycle power augmentation by efficient utilization of atomizing air energy

A combined cycle power plant includes a gas turbine having a first compressor, a second compressor downstream of the first compressor, and a regenerative heat exchanger between the first and second compressors. A steam generator is downstream of the gas turbine and receives exhaust from the gas turbine. A closed loop cooling system through the regenerative heat exchanger and the steam generator transfers heat from the regenerative heat exchanger to the steam generator. A method for operating a combined cycle power plant includes compressing a working fluid in a compressor and cooling the compressed working fluid with a regenerative heat exchanger so as to create a cooled compressed working fluid. The method further includes transferring heat from the regenerative heat exchanger to a steam generator.

FIELD OF THE INVENTION

The present invention generally involves a power plant that combines a conventional gas turbine with a heat recovery system to improve the overall efficiency of the combined cycle power plant. Specific embodiments of the present invention may include a regenerative heat exchanger that transfers heat from the gas turbine to the heat recovery system.

BACKGROUND OF THE INVENTION

Gas turbines are widely used in industrial and power generation operations. A typical gas turbine includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and stationary vanes and rotating blades in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases flow to the turbine where they expand to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.

The combustion gases exit the turbine, and, if released immediately to the environment, would result in wasted energy generated by the gas turbine that does not produce work. Therefore, a heat recovery system is often connected downstream of the turbine to receive the exhaust combustion gases from the turbine. The combination of the gas turbine and heat recovery system is commonly referred to as a combined cycle power plant. The heat recovery system typically includes a steam generator, a steam turbine, and a condenser. The exhaust combustion gases flow to the steam generator where they heat water to generate steam. The steam then flows through the steam generator where it expands to produce work. For example, expansion of the steam in the steam turbine may rotate a shaft connected to a generator to produce electricity. The shaft and generator may be the same shaft and generator connected to the gas turbine, or the gas turbine and heat recovery system may operate using separate shafts and generators. The condenser downstream of the steam generator condenses the steam to condensate, and condensate pumps direct the condensate back to the steam generator. The heat recovery system thus captures energy from the exhaust combustion gases before they are eventually released to the environment, thus increasing the overall efficiency of the combined cycle power plant.

The steam generator is typically located in or upstream of a vertical stack that allows the exhaust combustion gases to naturally rise across tubes in the steam generator to enhance steam generation. In some instances, a customer may limit the height of the vertical stack, resulting in a corresponding limit in the size of the steam generator and the amount of steam that it may produce. In addition, the gas turbine often includes one or more heat exchangers associated with auxiliary components, and the heat removed by these heat exchangers is often not recaptured, thus reducing the overall efficiency of the combined cycle power plant. Consequently, there is a need for systems that makes more efficient use of the heat extracted by the heat exchangers of auxiliary components while increasing steam generation, particularly in systems having vertical stacks of limited height.

BRIEF DESCRIPTION OF THE INVENTION

One embodiment of the present invention is a combined cycle power plant that includes a gas turbine having a first compressor, at least one combustor downstream of the first compressor, a turbine downstream of the combustor, and a second compressor downstream of the first compressor. A regenerative heat exchanger is between the first and second compressors, and a steam generator is downstream of the turbine and receives exhaust from the turbine. A steam turbine is downstream of the steam generator, and a condenser is downstream of the steam turbine and upstream of the steam generator. A first condensate pump is between the condenser and the steam generator and in fluid communication with the regenerative heat exchanger.

Another embodiment of the present invention is a combined cycle power plant that includes a gas turbine having a first compressor, a second compressor downstream of the first compressor, and a regenerative heat exchanger between the first and second compressors. A steam generator is downstream of the gas turbine and receives exhaust from the gas turbine. A closed loop cooling system through the regenerative heat exchanger and the steam generator transfers heat from the regenerative heat exchanger to the steam generator.

The present invention also includes a method for operating a combined cycle power plant that includes compressing a working fluid in a compressor and cooling the compressed working fluid with a regenerative heat exchanger so as to create a cooled compressed working fluid. The method further includes transferring heat from the regenerative heat exchanger to a steam generator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a simplified block diagram of a combined cycle power plant10according to one embodiment of the present invention. The combined cycle power plant10generally includes a gas turbine12connected to a heat recovery system14as is known in the art. For example, as shown inFIG. 1, the gas turbine12includes a first compressor16, at least one combustor18downstream of the first compressor16, and a turbine20downstream of the combustor18. As used herein, the terms “upstream” and “downstream” refer to the relative location of components in a fluid pathway. For example, component A is upstream of component B if a fluid flows from component A to component B. Conversely, component B is downstream of component A if component B receives a fluid flow from component A. The first compressor16produces a compressed working fluid22which flows to the combustor18. The combustor18generally combines the compressed working fluid22with a supply of fuel24and/or diluent26and ignites the mixture to produce combustion gases28. The supplied fuel24may be any suitable fuel used by commercial combustion engines, such as blast furnace gas, coke oven gas, natural gas, vaporized liquefied natural gas (LNG), propane, and any form of liquid fuel. The diluent26may be any fluid suitable for diluting or cooling the fuel, such as compressed air, steam, nitrogen, or another inert gas. The combustion gases28flow to the turbine20where they expand to produce work.

The heat recovery system14generally includes a steam generator30, a steam turbine32, and a condenser34. The steam generator30is located downstream from the turbine20, and exhaust combustion gases36from the turbine20flow through the steam generator30to produce steam38. The steam turbine32is located downstream of the steam generator30, and the steam38from the steam generator30expands in the steam turbine32to produce work. The condenser34is located downstream of the steam turbine32and upstream of the steam generator30and condenses the steam38from the steam generator30into condensate40which is returned to the steam generator30. A first condensate pump42between the condenser34and the steam generator30is in fluid communication with the steam generator30to provide condensate40from the condenser34to the steam generator30. In addition, a second condensate pump44may be present to increase the pressure of the condensate40supplied to subsequent stages of the steam generator30.

Returning to the gas turbine12portion of the combined cycle power plant10, the gas turbine12may further include a second compressor46downstream of the first compressor16and upstream of the combustor18. The second compressor46receives a portion of the compressed working fluid48from the first compressor16and increases the pressure of the compressed working fluid48from the first compressor16. The typical increase in pressure provided by the second compressor46is approximately 30 to 70%, although the actual increase in pressure is not a limitation of the invention unless recited in the claims. The output of the second compressor46may be referred to as atomizing air50and is injected into the combustor18with the fuel24and/or diluent26to atomize the mixture to enhance the efficiency of the combustion.

The portion of the compressed working fluid48supplied by the first compressor16to the second compressor46typically has a temperature on the order of 650 to 900° F. A closed loop cooling system between the gas turbine12and the heat recovery system14may be used to reduce the temperature of the portion of the compressed working fluid48supplied by the first compressor16. As used herein, “a closed loop cooling system” is defined as any cooling system in which at least some coolant in the system flows in a repeating loop, including a system in which coolant is added to or removed from the loop. Specifically, a regenerative heat exchanger52may be located between the first and second compressors16,46to remove heat from the portion of the compressed working fluid48supplied by the first compressor16to the second compressor46. As used herein, the regenerative heat exchanger52includes any heat exchanger in which the heat removed by the heat exchanger is transferred to another component for use prior to release to the environment. The closed loop cooling system provides a fluid communication for a coolant, such as the condensate40, to flow through and between the steam generator30and the regenerative heat exchanger52. For example, as shown inFIG. 1, the first condensate pump42may supply the coolant (e.g., the condensate40) through piping to the regenerative heat exchanger52. As the coolant flows through the regenerative heat exchanger52, it removes heat from the portion of the compressed working fluid48flowing through the regenerative heat exchanger52to the second compressor46. For example, the regenerative heat exchanger52may reduce the temperature of the compressed working fluid54supplied to the second compressor46to less than 400°, 350°, 300°, or 250° F., as desired. After leaving the regenerative heat exchanger52, at the point indicated by reference number56, the coolant may then flow to the second condensate pump44, at the point indicated by reference number58. The second condensate pump44increases the pressure of the coolant and supplies the coolant to the steam generator30. In this manner, the closed loop cooling system transfers heat from the regenerative heat exchanger52to the steam generator30, thereby increasing the overall efficiency of the combined cycle power plant10. In some embodiments, the amount of heat transferred from the regenerative heat exchanger52to the steam generator30may be capable of generating more than 200 to 650 kW of power.

One of ordinary skill in the art will readily appreciate that the combined cycle power plant10described and illustrated inFIG. 1provides a method for operating the combined cycle power plant10at an improved efficiency. Specifically, the method includes compressing the working fluid in the first compressor16and cooling the compressed working fluid48with the regenerative heat exchanger52so as to create the cooled compressed working fluid54. The method further includes transferring heat from the regenerative heat exchanger52to the steam generator30so that the heat removed by the regenerative heat exchanger52may be used to generate steam38and perform work. The steam38may then be condensed into condensate40and pumped through the closed loop cooling system through the regenerative heat exchanger52and steam generator30. The cooled compressed working fluid54may be further compressed and supplied to the combustors18to atomize the fuel24and/or diluent26with the cooled compressed working fluid50. Depending on the particular design needs, the method may result in transferring more than 200 to 650 kW of power from the regenerative the exchanger52to the steam generator30.