Patent Application
20180066548
Embodiments of the present specification relate to gas turbines, and more particularly to a heat recovery steam generator and an integrated recuperator for use in combined cycle power plants.
Combined cycle power plants are being increasingly used for power generation. Typically, the combined cycle power plant includes a gas turbine and a steam turbine. The gas turbine is used to generate electrical power by combusting a mixture of compressed air and natural gas. Further, exhaust heat from the gas turbine is captured via use of a Heat Recovery Steam Generator (HRSG). The HRSG creates steam from water using heat from the gas turbine exhaust and delivers the steam to the steam turbine. The steam turbine in turn is used to generate additional electrical power via use of the steam.
Moreover, a recuperator is used in the combined cycle power plant to enhance the efficiency of the combined cycle power plant. In particular, the recuperator uses the exhaust gases from the gas turbine to pre-heat the compressed air received from a compressor of the gas turbine. The pre-heated compressed air is mixed with natural gas for combustion in the gas turbine to generate the electrical power. Consequent to the use of the pre-heated compressed air, the requirement of natural gas for combustion in the gas turbine to generate electrical power is reduced.
However, using the recuperator in the combined cycle power plant results in a reduction in the efficiency of the steam cycle due to the non-availability of high-temperature exhaust gas for superheating and reheating the steam. Moreover, use of the recuperator in the combined cycle power plant leads to additional pressure losses in the exhaust gas flow, which in turn reduces the efficiency of the gas turbine. Furthermore, the recuperators used in the combined cycle power plants are bulky and expensive.
Briefly, in accordance with one aspect of the present specification, a combined cycle power plant is presented. The combined cycle power plant includes a gas turbine, which in turn includes at least a compressor and a combustor. Furthermore, the combined cycle power plant includes a heat recovery steam generator disposed in fluid communication with the gas turbine, where the heat recovery steam generator includes steam heater units. Moreover, the combined cycle power plant includes a recuperator unit, where the recuperator unit is integrated with the heat recovery steam generator, and where the recuperator unit is configured to use gas turbine exhaust from the gas turbine to preheat compressor discharge air from the compressor and supply the preheated compressor discharge air to the combustor, where a first subset of the steam heater units is disposed in parallel to the recuperator unit, and where a second subset of the steam heater units is disposed in series with the first subset of the steam heater units and the recuperator unit with respect to a direction of flow of gas turbine exhaust.
In accordance with another aspect of the present specification, a heat recovery steam generator is presented. The heat recovery steam generator includes one or more steam heater units. Also, the heat recovery steam generator includes a heat recovery steam generator duct. In addition, the heat recovery steam generator includes a recuperator unit, where the recuperator unit is integrated with at least one of the one or more steam heater units, where the recuperator unit is configured to use gas turbine exhaust from the gas turbine to preheat compressor discharge air for the compressor and supply the preheated compressor discharge air to the combustor, where a first subset of the one or more steam heater units is disposed in parallel to the recuperator unit, and where a second subset of the one or more steam heater units is disposed in series with the first subset of the one or more steam heater units and the recuperator unit with respect to a direction of flow of the gas turbine exhaust.
In accordance with yet another aspect of the present specification, a combined cycle power plant is presented. The combined cycle power plant includes a gas turbine comprising at least a compressor and a combustor. Further, the combined cycle power plant includes a heat recovery steam generator disposed in fluid communication with the gas turbine, where the heat recovery steam generator includes one or more steam heater units, a heat recovery steam generator duct disposed in fluid communication with the gas turbine. In addition, the combined cycle power plant includes a recuperator unit configured to use gas turbine exhaust from the gas turbine to preheat compressor discharge air from the compressor and supply the preheated compressor discharge air to the combustor, where the recuperator unit is integrated with at least one of the one or more steam heater units of the heat recovery steam generator such that a plurality of recuperator tubes in the recuperator unit is disposed perpendicular to a direction of flow of the gas turbine exhaust in the heat recovery steam generator duct; and where the recuperator unit is arranged in a parallel configuration with the at least one of the one or more steam heater units such that a first smaller portion of the gas turbine exhaust discharged by the gas turbine is channeled over the at least one steam heater unit and a second larger portion of the gas turbine exhaust is channeled over recuperator unit. Also, a first subset of the one or more steam heater units is disposed in parallel to the recuperator unit, and where a second subset of the one or more steam heater units is disposed in series with the first subset of the one or more steam heater units and the recuperator unit with respect to a direction of flow of the gas turbine exhaust. The combined cycle power plant also includes a steam turbine operatively coupled to the heat recovery steam generator and configured to generate additional electrical power,
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 drawings in which like characters represent like parts throughout the drawings, wherein:
Embodiments of various systems and methods presented herein provide enhanced efficiency in combined cycle power plants. Use of these systems circumvents the need for expensive extra ducting and other structures in a heat recovery steam generator (HRSG) in the combined cycle power plants. Additionally, these systems and methods result in enhanced combined cycle efficiency of a recuperated gas turbine as hot exhaust gas is available for steam superheating, reheating, and recuperation.
The gas turbine 102 is used to generate electrical power using a gaseous or liquid fuel. In one embodiment, the gas turbine 102 includes at least a compressor 112, a combustor 114, and a diffuser 116. The compressor 112 is configured to receive air 118 from the atmosphere and compress the air to a determined pressure to generate compressed air 120. The compressor 112 is also configured to convey the compressed air 120 to a recuperator unit 106 of the HRSG 104.
Moreover, the HRSG 104 is configured to recover heat from a hot gas stream and use the recovered heat to produce steam. This steam may be used to drive a steam turbine 130 to generate additional electrical power. In one embodiment, the HRSG 104 includes a HRSG duct 108. In a presently contemplated configuration, the HRSG duct 108 is in fluid communication with the gas turbine 102. In one embodiment, the HRSG duct 108 may have a rectangular cross-section. Furthermore, the HRSG 104 further includes one or more steam heater units that may be located within the HRSG duct 108. For ease of illustration, a single stage HRSG 104 is depicted in
A recuperator unit is employed to preheat the air supplied to the combustor using heat from hot gas turbine exhaust. In conventional combined cycle power plants that include a heat exchanging unit such as the recuperator unit, the heat exchanging unit is located external to and upstream of the HRSG. Such embodiments typically include bulky recuperators and have a drawback of reduced efficiency of the steam cycle due to the non-availability of high-temperature exhaust gas for superheating and reheating.
These shortcomings of conventional combined cycle power plants or previous concepts of recuperated gas turbines are circumvented via use of the combined cycle power plant 100 presented in
In accordance with aspects of the present specification, the recuperator unit 106 is integrated with the HRSG 104. More particularly, in certain embodiments, the recuperator unit 106 is integrated with the HRSG duct 108 of the HRSG 104. In certain embodiments, the recuperator unit 106 is a gas-gas heat exchanger and is configured to preheat the compressed/compressor air 120 generated by the compressor 112 of the gas turbine 102 to generate preheated compressed air 122. In accordance with aspects of the present specification, the recuperator unit 106 is configured to use hot gas turbine exhaust 124 to preheat the compressed air 120 discharged from the compressor 112 of the gas turbine 102 to generate preheated compressor discharge air 122. In addition, the recuperator unit 106 is configured to convey the preheated compressor discharge air 122 to the combustor 114 in the gas turbine 102. In one embodiment, the recuperator unit 106 may include a plurality of recuperator tubes. Further, in certain embodiments, the plurality of recuperator tubes is disposed in a direction perpendicular to the direction of flow of the gas turbine exhaust 124 in the HRSG duct 108. It may be noted that the terms gas turbine exhaust, exhaust gas, and exhaust gas flow have been used interchangeably. Also, the terms compressor air, compressed air, and compressor discharge air may be used interchangeably. In a similar fashion, the terms preheated compressed air, preheated compressor air, and preheated compressor discharge air may be used interchangeably.
Preheating the compressor discharge air 120 generated by the compressor 112 and supplying that preheated compressor discharge air 122 to the combustor 114 aids in lowering the amount of fuel used for combustion in the combustor 114, thereby enhancing efficiency of the combined cycle power plant 100. The recuperator unit 106 will be described in greater detail with reference to
Referring again to the gas turbine 102, the combustor 114 is used to combust a mixture of the fuel and the preheated compressor discharge air 122. To this end, the combustor 114 is supplied with a determined quantity of the fuel from a fuel reserve (not shown). In one embodiment, the fuel may include natural gas. Upon combustion of the mixture of the fuel and the preheated compressor discharge air 122, energy is extracted from the gas turbine 102 and may be used to generate electrical power using a power generator 126.
With returning reference to the HRSG 104, the HRSG 104 is used to generate steam using the heat of the gas turbine exhaust 124. The steam generated by the HRSG 104 is used to drive a steam turbine 130 for generating additional electrical power via a generator 132.
As previously noted, the HRSG 104 includes one or more steam heater/generator units. These steam heater units are configured to receive feed water 134 and convert the feed water 134 to steam via use of the heat recovered from the gas turbine exhaust 124. In certain embodiments, the HRSG 104 may include a steam super heater unit 136 and a steam reheater unit 138. In one embodiment, the steam super heater unit 136 and/or the steam reheater unit 138 may include a plurality of steam heater tubes. Also, in certain embodiments, the steam heater tubes in the steam super heater unit 136 and/or the steam reheater unit 138 may include finned tubes. Additionally, these steam heater tubes may be disposed in the HRSG duct 108 between the gas turbine 102 and an HRSG exhaust outlet stack 146. Also, the HRSG 104 may also include an economizer unit 140 and an evaporator unit 142 that are configured to aid in converting the feed water 134 into steam via use of the heat recovered from the gas turbine exhaust 124.
As previously noted, the recuperator unit 106 is configured to extract heat from the gas turbine exhaust 124 to preheat the compressor discharge air 120 prior to combustion by the combustor 114. In accordance with aspects of the present specification. A first subset of the one or more steam heater units in the HRSG 104 is disposed in parallel to the recuperator unit 106 and a second subset of the one or more steam heater units is disposed in series with the first subset of the one or more steam heater units and the recuperator unit 106 with respect to a direction of flow of the gas turbine exhaust 124 (see
Moreover, in accordance with aspects of the present specification, the recuperator unit 106 may be integrated with one or more of the steam heater units of the HRSG 104. In a presently contemplated configuration, the recuperator unit 106 is integrated with the super heater unit 136 and/or the reheater unit 138 in a parallel configuration. More specifically, the recuperator unit 106 may be arranged such that the plurality of recuperator tubes is disposed in a parallel configuration with respect to the plurality of steam heater tubes in the super heater unit 136 and/or the steam reheater unit 138 (see
Additionally, the recuperator unit 106 and the super heater unit 136 may be arranged such that the corresponding tubes are oriented in parallel to a shorter side of the HRSG duct 108, such as the width of the HRSG duct 108. Moreover, the other steam heater units are positioned downstream of the recuperator unit 106 and the super heater unit 136 in the HRSG duct 108 such that corresponding tubes are oriented parallel to a longer side of the HRSG duct 108 and perpendicular to the tubes in the upstream units.
Consequent to the extraction of heat from the gas turbine exhaust 124 by the super heater unit 136 and the recuperator unit 106, cooled gas turbine exhaust 144 is generated. The cooled gas turbine exhaust 144 is conveyed over the tubes in the remaining steam heater units 138, 140, 142 situated downstream in the HRSG 104 towards the stack 146. Moreover, the cooled gas turbine exhaust 144 after passing through the HRSG 104 is channeled towards the stack 146, and the cooled gas turbine exhaust 144 is dispersed into the atmosphere via the stack 146.
Implementing the combined cycle power plant 100 where the integrated recuperator unit 106 is integrated with the HRSG 104 as described hereinabove facilitates enhanced efficiency of the combined cycle power plant 100 as the gas turbine exhaust 124 from the gas turbine 102 facilitates preheating of the compressor discharge air 120 prior to combustion in the gas turbine 102 in addition to generating steam using the HRSG 104. Use of the preheated compressor discharge air 122 reduces the quantity of fuel required for combustion, thereby further improving the efficiency of the combined cycle power plant 100.
Also, as previously noted, the tubes corresponding to the other steam heater units in the HRSG 104 are oriented parallel to the longer side of the HRSG duct 108 and perpendicular to the tubes in the upstream units. This arrangement allows a reduction in the number of tubes, thereby lowering associated costs of the HRSG 104, while promoting natural circulation in the evaporator unit in the HRSG 104. Furthermore, the presently contemplated configuration of
Moreover, in the embodiment of
Additionally, in the example of
Furthermore, this exemplary configuration circumvents the need for extra ducting, flow split baffles and related structures to split and guide two separate exhaust gas streams for steam generation and recuperation that are typically used in the currently available combined cycle power plants with recuperators. Also, the arrangement of
As noted with reference to
In the embodiment of
Thus, in the example embodiment of
Moreover, in certain embodiments, all the steam heater units 204, 206, 208, 210 are made of finned tubes. Also, these steam heater units are housed in a large HRSG duct 226. Reference numeral 228 is representative of a length of the HRSG duct 226, while a width of the HRSG duct 226 is represented by reference numeral 230. Also, a height of the HRSG duct 226 is represented by reference numeral 232.
Furthermore, the recuperator unit 202 is configured to preheat compressor discharge air 214 (via use of hot gas turbine exhaust 212) prior to the compressor discharge air 214 being supplied to the combustor 114. Also, the steam heater units 204, 206, 208, 210 of the HRSG 200 use both the hot gas turbine exhaust 212 and exhaust gas that has been cooled after exchange of heat with the recuperator unit 202 (cooled gas turbine exhaust 224) to preheat, boil and superheat feed water 218 to generate steam.
As previously noted and shown in
In the example of
Accordingly, in certain embodiments, the recuperator tubes of the recuperator unit 202 and the steam heater tubes of the super heater unit 204 are substantially similar. By way of example, the tubes used in the recuperator unit 202 and the hottest section of the HRSG 200 such as the super heater unit 204 may have substantially similar dimensions, shapes, lengths, diameters, circumferences, sizes, or combinations thereof. In one embodiment, the dimensions, shapes, lengths, diameters, circumferences, sizes, or combinations thereof of the recuperator tubes may be identical or equal to the corresponding dimensions, shapes, lengths, diameters, circumferences, sizes, or combinations thereof of the steam heater tubes of the super heater unit 204. Moreover, in some embodiments, the outer dimensions of the recuperator tubes of the recuperator unit 202 and the steam heater tubes of the super heater unit 204 may be similar. Also, in this example, wall thickness of the recuperator tubes and the steam heater tubes may be similar. In alternative embodiments, the wall thickness of the recuperator tubes and the steam heater tubes may be different. In addition, in some embodiments, the tubes in the recuperator unit 202 and the super heater unit 204 may be formed using the same material. However, in some other embodiments, different materials may be used to form the recuperator tubes and the steam heater tubes.
Furthermore, the recuperator tube are installed in a counter-cross flow arrangement with the gas turbine exhaust 212. Additionally, in the embodiment of
Moreover, as depicted in
The preheated compressor discharge air 216 may then be conveyed to the combustor 114 of the gas turbine 102 (see
Also, as previously noted, the recuperator unit 202 and the hottest sections 204 of the HRSG 200 such as the super heater unit 204 have tubes oriented in parallel to the shorter side 230 of the HRSG duct 226 and the remaining steam generator sections 206, 208, 210 have tubes oriented parallel to the longer side 232 of the HRSG duct 226. Further, consequent to the heat exchange in the super heater unit 204, the first portion of the hot gas turbine exhaust 212 is cooled as the gas turbine exhaust passes over the super heater 204. Similarly, the second portion of the hot gas turbine exhaust 212 is cooled consequent to the heat exchange in the recuperator unit 202.
The cooled first and second portions of the gas turbine exhaust are subsequently channeled over the steam heater tubes in the remaining sections of the HRSG 200 towards the stack 146. Reference numeral 224 is generally representative of gas turbine exhaust that has been channeled through the HRSG 200.
Further, the steam tube modules in the other sections of the HRSG 200 such as the units 206, 208, 210 have the tubes typically oriented parallel to the longer side 232 of the HRSG duct 226 and perpendicular to the tubes in the tube modules upstream. This arrangement of the tube modules promotes natural circulation in the evaporator unit 208. Additionally, the arrangement of the tube modules depicted in
Moreover, feed water 218 is provided to the HRSG 200. In the example depicted in
Furthermore, the steam or feed water 218 in most of the steam heater units of the HRSG 200 predominantly flows in a counter cross-flow direction to the gas turbine exhaust 212. Since the tubes in super heater unit 204 are perpendicular to the tubes in the remaining steam heater units downstream, any temperature difference in exhaust gas streams leaving the recuperator unit 202 and super heater unit 204, which result from a difference in the corresponding amounts of heat recovered from the gas turbine exhaust 212 will not cause differences in the duty of individual tubes of the downstream steam heater units.
The cooled gas turbine exhaust 224 flows over the tubes in the remaining steam heater units situated downstream in the HRSG 200. Subsequently, the cooled gas turbine exhaust 224 after passing through the HRSG 200 is channeled into the stack 146 and dispersed into the atmosphere via the stack 146.
Implementing the HRSG 200 having an integrated recuperator unit 202 as depicted in
As previously noted, in accordance with aspects of the present specification, the recuperator unit 106 is integrated with one or more steam heater units of the HRSG 104.
In the presently contemplated configuration of
The recuperator unit 302 includes a plurality of recuperator tubes 310. Also, two or more recuperator tubes 310 of the plurality of tubes 310 may be bundled together to form one or more recuperator tube modules or bundles. In one example, the recuperator tubes 310 are coupled together to form a tubular recuperator unit 302. Moreover, the recuperator tubes 310 may be arranged along one or more rows. In certain embodiments, the recuperator tubes 310 may include external fins. Furthermore, these tube modules are installed in a counter-cross flow arrangement with respect to a flow of hot gas turbine exhaust 312 from a gas turbine such as the gas turbine 102.
Moreover, in accordance with aspects of the present specification, the recuperator unit 302 is integrated with the super heater unit 306 such that the recuperator unit 302 and the super heater unit 306 are in a parallel configuration with respect to each other and share a common cross-sectional axis 314. In one example, the steam heater tube modules of the super heater unit 304 and/or the reheater unit of the HRSG 300 are installed in parallel to the recuperator tube modules of the recuperator unit 302 and share a common frontal area after the diffuser 114 and the HRSG duct 340.
Additionally, in some embodiments, the recuperator unit 302 is integrated with the super heater unit 306 such that the recuperator unit 302 is disposed perpendicular to a direction of flow of the gas turbine exhaust 312 from the gas turbine 102. Consequently, the recuperator unit 302 is disposed such that the recuperator tubes 310 are arranged along an axis 316. This axis 316 is generally representative of a shorter side such as the width 344 of the HRSG duct 340. In particular, since the recuperator tubes 310 are arranged in parallel to the shorter side 344 of the HRSG duct 340, tubes of shorter length may be used in the recuperator unit 302 in comparison to the tubes in the other steam heater units of the HRSG 104. This arrangement aids in reducing pressure loss of the air inside the recuperator tubes 310.
In the embodiment where the recuperator unit 302 is integrated with the super heater unit 306, both the super heater unit 306 and the recuperator unit 302 are mounted such that the plurality of recuperator tubes 310 and the plurality of steam heater tubes 308 corresponding to super heater unit 306 are positioned horizontally along the axis 316. Additionally, in this example, other steam heater units of the HRSG may be positioned such that steam heater tubes corresponding to these other steam heater units are mounted vertically an axis 318. This axis 318 is generally representative of a longer side such as the height 346 of the HRSG duct 340. Furthermore, as the super heater unit 306 and the recuperator unit 302 share the common cross-sectional axis 314, the super heater unit 306 and the recuperator unit 302 are in the parallel configuration with respect to one another and the direction of flow of the gas turbine exhaust 312. This configuration of the recuperator unit 302 and the super heater unit 306 allows the gas turbine exhaust 312 to simultaneously pass through the recuperator unit 302 and the super heater unit 306 in a perpendicular direction to the tubes 308, 310.
Moreover, the gas turbine exhaust 312 that passes over the plurality of recuperator tubes 310 of the recuperator unit 302 allows exchange of heat between the gas turbine exhaust 312 and the compressed air 320 in the recuperator unit 302. This exchange of heat aids in heating the compressed air 320 in the recuperator unit 302 to generate preheated compressed air 326. In particular, the compressed air 320 is heated towards the temperature of the gas turbine exhaust 312 as the compressed air 320 is circulated through the recuperator tubes 308 to generate the heated compressed air 326. The heated compressed air 326 is channeled out of the recuperator unit 302 and conveyed to the combustor 112 of the gas turbine 102. It may be noted that in other examples, the location of supply of the compressed air 320 and the location of the egress of the heated compressed air 326 may be interchanged.
Furthermore, the gas turbine exhaust 312 that passes over the steam heater tubes 308 of the super heater unit 306 facilitates exchange of heat between the gas turbine exhaust 312 and the 322 to generate high temperature steam 328. This high temperature steam 328 may also be referred to as super-heated steam 328. Also, the super-heated steam 328 is conveyed out of the super heater unit 306 to the steam turbine 132 for generating additional electrical power.
As previously noted, a first, smaller portion 330 of the gas turbine exhaust 312 is channeled over the super heater unit 330 and other steam heater units, while a second, larger portion 332 of the gas turbine exhaust 312 is channeled over the recuperator unit 302. Consequent to the heat exchange between the first portion 320 of the hot gas turbine exhaust 312 and the steam 322 in the steam heater tubes 308, the temperature of the first portion 330 of the gas turbine exhaust 312 is reduced. Reference numeral 334 is generally representative of a cooled first portion of the gas turbine exhaust. Similarly, the temperature of the second portion 332 of the gas turbine exhaust 312 is reduced due to the heat exchange between the second portion 322 of the hot gas turbine exhaust 312 and the compressed air 320 in the recuperator tubes 310. Reference numeral 336 is generally representative of a cooled second portion of the gas turbine exhaust. Also, the first and second cooled portions 334, 336 of the gas turbine exhaust may be combined to form a cooled gas turbine exhaust 338.
The cooled gas turbine exhaust 338 flows over the tubes in the remaining steam heater units situated downstream in the HRSG 104 towards the stack 146. Moreover, the cooled gas turbine exhaust 338 after passing through the HRSG 104 is channeled into the stack 146 and dispersed into the atmosphere via the stack 146.
Moreover, as will be appreciated, it is desirable to maintain a desired flow ratio of the first, smaller portion 330 of the gas turbine exhaust 312 that passes over the steam heater tubes 308 in the super heater unit 306 and/or the reheater unit and the second, larger portion 332 of the gas turbine exhaust 312 that passes over the recuperator tubes 310 in the recuperator unit 306. In accordance with aspects of the present specification, the desired flow ratio may be maintained by varying/adjusting a plurality of HRSG parameters. More particularly, one or more of the plurality of HRSG parameters may be adjusted to maintain the desired flow ratio of the gas turbine exhaust 312 passing over the recuperator unit 302 and the super heater unit 306. Some examples of the HRSG parameters include, but are not limited to, number of rows of steam heater tubes in each stage of the HRSG 104, number of steam heater tubes per row in the HRSG 104, spacing between the steam heater tubes, and a number of external fins on each steam heater tube.
In one example, if the number of rows of steam heater tubes 308 and recuperator tubes 310 and the number of external fins on the steam heater tubes 308 and recuperator tubes 310 in the super heater unit 306 and the recuperator unit 302 are the same, the flow ratio of the gas turbine exhaust 312 in each of the super heater unit 306 and the recuperator unit 302 is dependent on a ratio of a number of tubes in each row of the super heater unit 306 and the recuperator unit 302. However, if the number of rows of tubes in each heat recovery stage, number of tubes in each row, and the number of external fins on each tube in the super heater unit 306 and the recuperator unit 302 are different, then the super heater unit 306 and the recuperator unit 302 are designed such that for a determined flow rate a gas turbine exhaust pressure loss in the super heater unit 306 and the recuperator unit 302 are the same.
It is to be understood that a skilled artisan will recognize the interchangeability of various features from different embodiments and that the various features described, as well as other known equivalents for each feature, may be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this specification. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Various embodiments of systems and methods described hereinabove present a combined cycle power plant with enhanced efficiency. The combined cycle power plant includes a recuperator unit that is integrated with an HRS G. The exemplary configuration increases the efficiency of the combined cycle power plant as a gas turbine exhaust from a gas turbine in the combined cycle power plant is available for steam generation using the HRSG and also for recuperation using the recuperator unit. Furthermore, the recuperator unit that is integrated with at least one of the heat recovery stages of the HRSG facilitates preheating of compressed air prior to combustion in the gas turbine. Use of the preheated compressed air reduces the quantity of fuel required for combustion of the preheated compressed air, thereby improving the efficiency of the combined cycle power plant.
Moreover, the recuperator unit is integrated with at least one of the heat recovery stages and in a parallel configuration with respect to a super heater unit of at least one heat recovery stage. This configuration of the recuperator unit reduces pressure losses of the gas turbine exhaust during operation of the combined cycle power plant as only a single gas turbine exhaust used for both steam generation and recuperation. The exemplary configuration of the combined cycle power plant 100 also obviates the need for extra ducting, flow split baffles, and/or other related structures to split and guide two separate exhaust gas streams for steam generation and recuperation that are typically required in alternative concepts of the combined cycle power plants with recuperators. Also, embodiments of the combined cycle power plant presented herein result in reduced cost of the HRSG that includes the recuperator unit as the recuperator unit is formed using tubes that are typically used in the HRSG. Moreover, the exemplary recuperator unit may be retrofit to existing HRSGs for improving the efficiency of existing combined cycle power plants.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
