HEAT EXCHANGER TUBE BUNDLE AND RELATED HEAT RECOVERY STEAM GENERATOR

Abstract

A heat exchanger tube bundle of horizontal gas path design is presented, the tube bundle comprising a sequence of bottom headers and corresponding top headers, wherein each unit of the sequence comprises a row of tubes, wherein each bottom header-is fluidly connected to a corresponding top header-via at least two similar tube rows for passing a fluid in a first direction between the bottom header and the top header, respectively, and wherein each unit of the sequence further comprises at least one further tube row in fluid connection with one of said bottom or top header, wherein the further tube row is further fluidly connected to a header of a subsequent unit, and wherein the further row's tubes are configured for passing the fluid in a second direction opposite to the first direction. Moreover, a related heat recovery steam generator-and combined cycle power plant are presented.

Claims

1-13. (canceled)

14. A heat exchanger tube bundle of horizontal gas path design, the tube bundle comprising a sequence of bottom headers and corresponding top headers, wherein each unit of the sequence comprises a row of tubes, wherein each bottom header is fluidly connected to a corresponding top header via at least two similar tube rows for passing a fluid in a first direction between the bottom header and the top header, respectively, and wherein each unit of the sequence further comprises at least one further tube row in fluid connection with one of said bottom and top header, wherein the further tube row is further fluidly connected to a header of a subsequent unit, and wherein the further row's tubes are configured for passing the fluid in a second direction opposite to the first direction.

15. The heat exchanger tube bundle according to claim 14, comprising only two similar tube rows and only one further tube row.

16. The heat exchanger tube bundle according to claim 14, wherein the heat exchanger tube bundle is configured for only one fluid pass per tube row.

17. The heat exchanger tube bundle according to claim 14, wherein the similar row's tubes are configured for an upflow fluid pass, and the further row's tubes are configured for a downflow fluid pass.

18. The heat exchanger tube bundle according to claim 14, wherein the similar row's tubes and the further row's tubes are all of similar dimension.

19. The heat exchanger tube bundle according to claim 14, wherein the similar row' tubes and the further row's tubes are all of equal cross section.

20. The heat exchanger tube bundle according to claim 14, wherein the similar row's tubes are of equal dimension and a cross section of the further row's tubes differs from that one of the similar row's tubes.

21. The heat exchanger tube bundle according claim 20, wherein the cross section of the further row's tubes is smaller than that one of the similar row's tubes.

22. The heat exchanger tube bundle according to claim 14, comprising more than two similar tube rows per unit.

23. The heat exchanger tube bundle according to claim 14, comprising more than two further tube rows per unit.

24. The heat exchanger tube bundle according to claim 14, being free of partition plates, crossovers and/or external piping.

25. A heat recovery steam generator of horizontal gas path design comprising the heat exchanger tube bundle according to claim 14, wherein the heat exchanger tube bundle is functionally set up for transferring heat from a flue gas to a feed water or condensate when passing it through the tube bundle.

26. A combined cycle power plant comprising the heat recovery steam generator according to claim 25, wherein the heat exchanger tube bundle is applied in an economizer and/or an evaporator of the power plant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further, features and advantageous embodiments become apparent from the following description of the exemplary embodiment in connection with the Figures.

[0025] FIG. 1 shows a simplified perspective view on a heat exchanger design as economizer of the prior art.

[0026] FIG. 2 shows a simplified side view of another heat exchanger design as economizer of the prior art.

[0027] FIG. 3 indicates, similarly to FIG. 2, a simplified side view of a heat exchanger tube bundle of the present invention.

[0028] FIG. 4 indicates in a simplified sketch a combined cycle power plant, along with an inventive heat exchanger as shown in FIG. 3 being functionally integrated to the power plant process.

DETAILED DESCRIPTION

[0029] Like elements, elements of the same kind and identically acting elements may be provided with the same reference numerals in the Figures. The Figures are not necessarily depicted true to scale and may be scaled up or down to allow for a better understanding of the illustrated principles. Rather, the described Figures are to be construed in a broad sense and as a qualitative base which allows a person skilled in the art to apply the presented teaching in a versatile way. The term and/or as used herein shall mean that each of the listed elements may be taken alone or in conjunction with two or more of further listed elements.

[0030] FIG. 1 shows a known principle of a heat exchanger, particularly an economizer 10 for a heat recovery steam generator (HRSG) application in a horizontal gas path design. The heat exchanger as shown preferably relates to a so-called harp design. The component 10 comprises a plurality of such harps or racks, wherein two racks are exemplarily depicted in FIG. 1 in a series connection, which are connected to each other by means of external piping elements 6, also called crossovers. In order to maximize a heat transfer-effective surface for each rack, several rows of tubes 3 are connected to inlet and outlet collecting headers 2a, 2b, respectively.

[0031] For the sake of simplicity, tubes 3 are only depicted schematically, wherein the dashed lines shall indicate an interspace and/or separation between different tubes in a row.

[0032] Reference numeral 4 as used herein shall particularly denote a so-called upflow tube, whereas reference numeral 5 shall indicate a downflow tube, all of which characterizing the horizontal path design of heat recovery steam generators for the related heat exchanger section.

[0033] During an operation of the economizer, incoming water (not explicitly indicated) is fed to the parallel tubes 3 through the respective inlet header and collected in the corresponding outlet header (cf. as well arrows in the Figures indicating flow direction of the feed water during an intended operation).

[0034] In order to ensure a favorable feed water velocity partition plates 9 (only partially indicated in the Figures) are welded inside the headers 2, which effectuate creation of a number of subsequent or separated water circuitsalso called passes per row or tube passes. According to this embodiment of the economizer, the partition plates 9 force the feed water to pass several times, e.g. twice, through the same rack in up and down flow direction. Thus, for each rack, a number of tubes are grouped in the design of the heat exchanger as shown in FIG. 1.

[0035] Furthermore, numeral 7 indicates a general feed water inlet, whereas numeral 8 indicates a related water outlet in the depicted tube bundle 10. Depending on the intended fluid flow direction, an inlet may principally relate to an outlet, and vice versa.

[0036] A main technical drawback of this configuration is its quite complex design and relatively low effectiveness in exchanging heat with the exhaust gas, the course of which is indicated by the larger arrow and numeral G. In fact, since not all exhaust gas G can be exposed to the coldest, i.e. upstream, feed water, also not the whole share of heat of gas G can be extracted by the heat exchanger 10 and transferred to the feed water. In other words, the gas can in this way not be cooled to the lowest possible temperature; or as the case may be, the water heated to the maximum possible temperature. Consequently, heat exchange is reduced due to this less favorable crossflow geometry, as compared to the inventive design as shown in FIGS. 3 onwards, for instance.

[0037] FIG. 2 shows an alternative (known) heat exchanger concept that may pertain to a so-called harmonica-type of economizer used for horizontal path HRSG applications. Therein, single, parallel tube or tube rows 3 are arranged in a series and each of which (or each row) connected to a top header 2a and an bottom header 2b. Each bottom header 2b is preferably fluidly connected via an upflow tube 4 with the corresponding top header 2a. Such a sequential unit 1 of the whole component 10 is encircled by a dashed square. In total, six sequential units or tube elements are shown connected in series. The larger square (not explicitly indicated) between the headers 2a, 2b indicates an exhaust or flue gas channel, the economizer is, preferably subjected to in its intended operation, such as an operation of a related steam generator. Again, the arrow G indicates a possible direction of exhaust gas for the expedient heat transfer.

[0038] As compared to the harp-design of FIG. 1, this concept stands out for a higher heat transfer efficiency due to a lack of cross flow loops. However, a main disadvantage relates to the constructability and/or a less compact design which increases the overall costs. Another disadvantage compared to the harp design is the impossibility to tune feed water velocity and a related flow stability, for an acceptable pressure drop, due to a lack of partition plates or similar measures.

[0039] FIG. 3 illustrates a simplified sketch of a heat exchanger design featuring a tube bundle according to the present invention. Said heat exchanger 10 may as well be set up for heat recovery steam generators (cf. FIG. 4 below). This tube bundle 10 comprises a sequence 1 of bottom headers 2b and corresponding top headers 2a, wherein each unit 1a of the sequence comprises a row of tubes, wherein each bottom header 2b is fluidly connected to a corresponding top header 2a via at least two similar tube rows 3 for passing a fluid in a first direction between the bottom header 2b and the top header 2a, respectively. The presented heat exchanger 10 is further characterized in that each unit of the sequence further comprises at least one further tube row 3 in fluid connection with one of said bottom and top header, wherein the further tube row is further fluidly connected to a header of a subsequent unit 1b. The further row's tubes 3 are configured for passing the fluid preferably in a second direction opposite to the first direction (cf. again arrows indicating the flow directions of a fluid guided through the tube rows in an operation of the heat exchanger 10). As shown in FIG. 1, this configuration of heat exchanger tube bundle comprises a number of only four connected serial header units.

[0040] In contrast to the known bundle configuration as described by way of FIG. 2, particularly two upflow tubes 4 (each of which shall indicate a whole row of tubes connecting the bottom header and the top header in FIG. 3) are arranged in fluid communication for a fluid or feed water flow from a given bottom header 2b to the top header 2a, respectively.

[0041] Preferably, as indicated in FIG. 3, the tube bundle 10 comprises only two upflow tubes 3, 4 and only one downflow tube 3, 5 per unit. It is further shown that the tube bundle 10 is configured such that it allows for only one fluid or water pass per tube or tube row.

[0042] Of course, it is contemplated by the present invention, that the fluid flow direction could as well be established vice versa, i.e. such that there are two (similar) downflow rows 3, 5 per unit and e.g. only one (further) row set up for an upwardly guided fluid.

[0043] In a preferred embodiment of the present invention, the similar row's tubes 3, 4 and the further row's tubes 3, 4 are all of similar dimension, particularly of similar or equal cross section.

[0044] Alternatively and deviating from the indication of FIG. 3, it is contemplated that only the similar tube rows 3, 4 (pointing upwards) are of equal dimension and e.g. a cross section of the further tubes 5 (pointing downwards) differs from that one of the similar tubes. More particularly, it may be advantageousfor optimization of the fluid flow and the avoidance of flow instability in any type of exchanger applicationthat e.g. the downflow tube's cross section(s) is/are smaller than that one of the upflow tubes 4. This advantageously allows to keep the downflow velocity at an optimum and/or a related downflow throughput (through the tubes) at a minimum, like in case of heat exchangers applied in an industrial economizer and/or evaporator. In turn, thereby instabilities in the feed water flow are reliably avoided.

[0045] Preferably, the inventive heat exchanger is free of any partition plates, crossovers and/or external piping, thereby maintaining a compact layout.

[0046] As well, the design of the inventive tube bundle may be configured such that it comprises more than two similar up- or downflow tubes 3 or related tube rows connecting a given bottom header 2b and the corresponding top header 2a.

[0047] Conditionally, the inventive advantages may also manifest in a design with a plurality of further up- or downflow tubes (or related rows) per header unit. This would, however, most probably imply as well a plurality, particularly a larger number, of the respectively other type of tube rows.

[0048] The inventive design stands further out for an optimized number of top headers 2a and bottom headers 2b. As shown by way of example only, the depicted heat exchange tube bundle 10 comprises a number of four bottom headers 2b and/or a number of four, top headers 2a. It is emphasized that the technical advantages are preferably intrinsic to the described configuration, e.g. number and size, of headers, upflow and downflow tube rows with which fluid flow properties may be tailored better than with any known heat exchanger design to the respective application.

[0049] The inventive heat exchanger may relate to a so-called Accordion economizer design, advantageously combining the design compactness and constructability of the harp design and the effectiveness of a harmonica design. Moreover, it allows to effectively avoid downflow instability by allowing a specific design of the downflow row's tube size, i.e. independently from the other tube rows. This results in a more compact, robust and easily constructed bundle with a far greater potential of heat recovery in the operation of related steam generators or a higher-ranking power plant (cf. FIG. 4 below). Particularly, as compared to the design shown in FIG. 1, the inventive concept excels in a better heating surface effectiveness andat the same timein a simpler construction due to a lack of crossover connections. Both advantages, in turn, result also in a cost advantage.

[0050] As compared to the harmonica design as illustrated in FIG. 2, furthermore, a bundle compactness is increased due to a lower number of headers, and to a shorter module depth. Consequently, the steam generator's overall dimension can also advantageously be reduced and shop constructability improved.

[0051] FIG. 4 shows a simplified sketch of at least parts of a combined cycle power plant 100 illustrating the basic principle of its assembly, e.g. comprising a heat exchanger 10, such as the inventive heat exchanger configured for an application of heat recovery steam generator 40. Also an evaporator assembly 20 as well as a superheater 30 are shown. All of these components are preferably functionally coupled in an expedient way. Moreover, the plant 100 may comprise or be connected to the flue gas path of a gas turbine GT via which an exhaust gas G is exposed to the superheater 40 (or vice versa). Then the superheater 30 is connected or coupled to a hot steam path-fed in by a steam drum 21 of the evaporator section 20. The steam ST is then expediently provided to a steam turbine of the plant 100, or to another facilty. Downstream of the superheater assembly 30also comprising dedicated tube bundles for steam generation and/or heat transferthe exhaust gas G enters the tube bundle of the evaporator 20. Later, in a rather low temperature section, the gas G finally arrives at the economizer tube bundle 10 for efficient heat transfer operation of the plant 100. However, the assembly could also be different, such as using the heat exchanger 10 in another setup, like in a configuration for a heat transfer from any kind of waste heat and the generation of related process steam (without any superheater or turbines involved). Thus, besides the above-described (plant) applications, the improved heat exchanger design imparts the outlined technical advantages as well to other application, such as downscaled and/or domestic application of heat exchangers.