Apparatus and method for purging a gas turbine exhaust tank to reduce warm flow leakage

Abstract

A purge box attached to the expansion joint between the exhaust diffuser and the aft diffuser can include a cover plate and a T-fairing radially adjacent to the cover plate. The inner fairing of the T-fairing can be an extension of the exhaust diffuser duct and can be attached to a flex seal at the joint. The legs of the T-fairing extend radially outward toward a cover projection extending from the aft portion of the cover plate. The purge box flow path can have at least one seal therein to reduce flow while accommodating radial and / or axial movement of the duct, cover plate, and / or T-fairing, improving turbine operating efficiency and the safety of nearby personnel.

Description

[Technical Field]

[0001] This disclosure relates generally to managing gas turbine exhaust systems, and more particularly to an apparatus and method for purging gas turbine exhaust sump tanks to reduce warm stream leakage. [Background technology]

[0002] Turbomachines can experience reduced operating efficiency due to pressure losses at various locations within the system, particularly at the joints of components that form the flow path through the turbomachine. For example, turbomachines with hot gas paths that include an exhaust diffuser feeding a transition diffuser duct or aft diffuser through a drainage basin may experience pressure losses as exhaust gases pass through seals at joints, particularly expansion joints, including drainage basins. Additionally, hot gas path components of gas turbines and aircraft engines, particularly turbine blades, vanes, nozzles, seals, and stationary shrouds, operate at high temperatures, often above 650°C. Therefore, hot exhaust gases leaking past seals at expansion joints can damage external equipment and pose a hazard to nearby personnel. Due to the potential efficiency losses and risk of injury, it may be desirable to reduce hot flow path leakage, such as by using improved seal arrangements and / or pressurizing purge cavities adjacent to expansion joints to prevent or reduce exhaust gas leakage through the expansion joints. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Chinese Patent Publication No. 104769235A Summary of the Invention

[0004] All aspects, examples, and features described below can be combined in any technically possible manner.

[0005] One aspect of the disclosure provides a purge box for a turbomachine including an expansion joint including an exhaust diffuser, an aft diffuser, and a drain sump therebetween, the purge box including: a cover plate attached to a housing of the turbomachine, a portion of the housing serving as a wall of the purge box; a flex seal at the expansion joint, the flex seal serving as an aft cover of the purge box; an inner fairing adjacent to an inner periphery of the cover plate, the inner fairing having a gap between an inner periphery of the cover plate and the inner fairing; a purge box flowpath from an interior of the purge box to the gap, the gap adjacent the exhaust diffuser; at least one seal in the purge box flowpath; and an inlet through the cover plate in fluid communication with a source of purge fluid having a pressure selected to induce a pressure in the purge box greater than the pressure in the drain sump.

[0006] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the inner fairing includes legs extending radially outward from the inner fairing adjacent the cover plate and is part of a T-fairing that forms part of the purge box flowpath.

[0007] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the cover projection extends from the rear of the cover plate parallel to the axis of rotation of the turbomachine and forms part of the purge box flowpath.

[0008] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the at least one seal includes a seal configured to reduce flow through the purge box flowpath while accommodating movement between the exhaust diffuser and the aft diffuser in a direction parallel to the axis of rotation of the turbomachine.

[0009] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the at least one seal includes a seal configured to reduce flow through the purge box flowpath while accommodating movement between the exhaust diffuser and the aft diffuser in a radial direction of the turbomachine.

[0010] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the at least one seal includes a first seal that engages a wall of the purge box flow path parallel to the axis of rotation of the turbomachine, the first seal connected to a portion of the inner fairing such that the first seal can accommodate movement between the exhaust diffuser and the aft diffuser in a direction parallel to the axis of rotation of the turbomachine.

[0011] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the at least one seal further includes a second seal that engages a wall of a radially extending purge box flowpath of the turbomachine, the second seal being attached to a portion of the inner fairing such that the second seal can accommodate movement between the exhaust diffuser and the aft diffuser in the radial direction of the turbomachine.

[0012] Another embodiment of the present disclosure includes any of the above embodiments, wherein the pressure of the purge fluid is at least 110,000 Pascals (Pa).

[0013] Another embodiment of the present disclosure includes any of the above embodiments, wherein the pressure in the purge box is at least 20 Pa higher than the pressure in the drain tank.

[0014] One aspect of the present disclosure provides an apparatus for a turbomachine exhaust system, the exhaust system including an exhaust diffuser, an aft diffuser, and an expansion joint including a sump therebetween, the apparatus including: a T-fairing including a cover plate extending radially from a housing of the turbomachine; and an inner fairing adjacent an inner periphery of the cover plate with a gap therebetween, the inner fairing extending substantially parallel to an axis of rotation of the turbomachine, the T-fairing further including legs extending radially outward from the inner fairing adjacent aft of the cover plate; and a T-fairing connected to the inner fairing and the housing of the turbomachine. a purge box including at least a cover plate, a T-fairing, the aft cover, and a housing of the turbomachine, the T-fairing together with the inner fairing and the cover plate defining a purge box flow path from an interior of the purge box, passing between the cover plate and the legs, and through a gap between the inner periphery of the cover plate and the inner fairing, at least one seal in the purge box flow path, and a purge inlet extending through the cover plate and connected to a source of purge fluid at a pressure selected to induce a pressure in the purge box that is greater than the operating pressure in the sump tank.

[0015] Another aspect of the present disclosure includes any of the aforementioned aspects, further including a cover projection extending from an aft portion of the cover plate parallel to the axis of rotation of the turbomachine, the cover projection being radially outward of and radially adjacent to the legs of the T-fairing, the purge box flow path being between the legs and the cover projection and further including a portion defined by the legs and the cover projection, and the at least one seal including a first seal between the legs of the T-fairing and the cover projection.

[0016] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the first seal includes a first tadpole seal having a head between the leg of the T fairing and the cover projection, and a tail extending radially inward from the head along the leg of the T fairing and connected to the leg of the T fairing.

[0017] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the at least one seal further includes a second seal between the cover plate and the first seal.

[0018] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the second seal includes a second tadpole seal having respective heads between the cover plate, the cover projection, and the legs of the T-fairing, and respective tails of the second tadpole seal extending from the heads and connected to the legs of the T-fairing.

[0019] Another aspect of the present disclosure includes any of the foregoing aspects, wherein the tail of the second tadpole seal extends radially inwardly around and along the outer periphery of the leg of the T-fairing.

[0020] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the second seal includes a rope seal on the cover projection, and wherein the at least one seal further includes a W-seal engaging the rope seal and connected to a leg of the T-fairing.

[0021] Another aspect of the present disclosure includes any of the above aspects, wherein the at least one seal further includes a forward seal between an inner periphery of the cover plate and the inner fairing, the forward seal positioned to at least partially close the gap.

[0022] Another aspect of the present disclosure includes any of the above aspects, wherein the forward seal is a tadpole seal having a head that engages the inner fairing and a tail that is connected to the cover plate.

[0023] Another embodiment of the present disclosure includes any of the above embodiments, wherein the temperature of the purge fluid is 40° C. or less.

[0024] Another embodiment of the present disclosure includes any of the above embodiments, wherein the pressure in the purge box is at least 20 Pa higher than the pressure in the drain tank.

[0025] Two or more aspects described in this disclosure, including those described in this Summary section, may be combined to form implementations not specifically described herein.

[0026] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description and drawings, and from the claims.

[0027] These and other features of the present disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure when taken in conjunction with the accompanying drawings which depict various embodiments of the present disclosure. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic illustration of an exemplary turbomachine in which aspects of the embodiments disclosed herein may be deployed; [Figure 2] 2 is an enlarged cross-sectional schematic view of a joint between a turbomachine exhaust diffuser and an aft diffuser of the turbomachine in which a purge box is disposed according to an embodiment of the present disclosure; FIG. [Figure 3] FIG. 2 is an enlarged view of a lower portion of a joint between a turbomachine exhaust diffuser and an aft diffuser of the turbomachine showing a sump in which aspects of the embodiments disclosed herein may be deployed; [Figure 4] FIG. 10 is an enlarged view of a portion of a purge box according to an embodiment disclosed herein. [Figure 5] FIG. 10 is an enlarged view of a portion of a purge box according to an embodiment disclosed herein. [Figure 6] FIG. 10 is an enlarged view of a portion of a purge box according to an embodiment disclosed herein. [Figure 7] FIG. 10 is an enlarged view of a portion of a purge box according to an embodiment disclosed herein. [Figure 8] FIG. 10 is an enlarged view of a portion of a purge box according to an embodiment disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0029] It should be noted that the drawings of the present disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure and therefore should not be considered limiting of the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

[0030] As an initial matter, in order to clearly describe the subject matter of this disclosure, it becomes necessary to select specific terminology when referring to and describing related components for mechanical parts within turbomachinery. Wherever possible, common industry terminology will be used and utilized in a manner consistent with its accepted meaning. Unless otherwise noted, such terminology should be given a broad interpretation consistent with the context of this application and the appended claims. Those skilled in the art will understand that in many cases, a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include, and be referred to in other contexts as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part.

[0031] Additionally, as described below, certain descriptive terms may be used conventionally herein: the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another, but do not denote the location or importance of the individual components.

[0032] The terminology used herein is merely for the purpose of describing particular embodiments and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, or that the subsequently described component or element may or may not be present, and that the description includes instances in which the event occurs or element is present, as well as instances in which it does not occur or is not present.

[0033] When an element or layer is referred to as "on," "engaged with," "connected to," or "coupled to" another element or layer, it may be directly on, engaged with, connected to, or coupled to the other element or layer, and intervening elements or layers may be present. In contrast, when an element is referred to as "directly on," "directly engaged with," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers. Other words used to describe relationships between elements should be interpreted similarly (e.g., "between" vs. "directly between," "adjacent to" vs. "directly adjacent to," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0034] 1 and 2 , embodiments disclosed herein may be implemented in a turbomachine 10 including a compressor 12 and a turbine 14 connected by a shaft 16. The compressor 12 receives intake air 1 and produces compressed air 22. A combustor 18 burns fuel 20 mixed with the compressed air 22, in response to which hot exhaust gases 24 act on blades (not shown) of the turbine 14, thereby driving the turbine 14, which in turn drives the compressor 12. After passing through the turbine 14, the exhaust gases 2 continue to an exhaust diffuser 30, which may include a manway 32 through which cooling air 37 from an air source 33 may pass to cool and purge the exhaust diffuser 30. The cooling air 37 may then pass through an aft diffuser 40, which may be connected to the exhaust diffuser 30 by an expansion joint 50. A basin 52 may be provided in the expansion joint 50 between the exhaust diffuser 30 and the aft diffuser 40 to discharge undesirable oil and other foreign matter, such as during water washing. In the illustrated example, the tub 52 may include a drain 54, such as at the bottom, through which liquids, such as liquids after a water rinse, may be collected and removed.

[0035] In embodiments, a purge box 100 may be added upstream of the expansion joint 50 to reduce or prevent leakage of exhaust gas from the tank 52 and may receive a purge fluid 101, such as air, from the air source 33 for this purpose. As seen in FIG. 2 , the expansion joint 50 may include a seal 56, such as a flex seal. Examples of expansion joint and flex seal arrangements usable in the embodiments described herein include those shown in U.S. Pat. Nos. 6,065,756, 7,793,507, and 10,830,103, the disclosures of which are incorporated by reference. The flex seal 56 may include multiple sealing layers and circumferential seal segments, which are arranged in an overlapping manner to create a tortuous leakage path for the exhaust gas. While the schematics in FIGS. 1 and 2 show the purge box 100 immediately adjacent the exterior of the expansion joint 50, it should be understood that in various embodiments, all or a portion of the purge box 100 may be within the illustrated boundaries of the expansion joint 50.

[0036] 3 and 4 , which depict the bottom of the expansion joint 50, aspects of the embodiments described herein include apparatus and methods for reducing warm flow leakage from the exhaust system of the turbomachine 10. The embodiments include a purge box 100 including a cover plate 102 extending radially from the housing 58 of the turbomachine 10, such as at the upstream end of the expansion joint 50. The purge box 100 may further include a T-fairing 104 including an inner fairing 106 adjacent an inner periphery 108 of the cover plate 102 with a gap 109 therebetween. The gap 109 is necessary to accommodate thermal expansion of the housing 58 during operation of the turbomachine 10.

[0037] In an embodiment, the inner fairing 106 may extend substantially parallel to the axis of rotation R of the turbomachine 10. The T-fairing 104 may further include legs 110 extending radially outward from the inner fairing 106 adjacent to and aft of the cover plate 102. A cover projection 112, such as a horizontal plate, may extend from the aft side of the cover plate 102 parallel to the axis of rotation R of the turbomachine 10 ( FIGS. 1 and 2 ), the cover projection 112 being radially outward from and radially adjacent to the legs 110 of the T-fairing 104. A purge box flow path 111 ( FIG. 4 ) may thereby be established from the interior of the purge box 100 between the legs 110 and the cover projection 112, between the legs 110 and the cover plate 102, and through a gap 109 between the inner periphery 108 of the cover plate 102 and the inner fairing 106. One objective of the present disclosure is to reduce or prevent the flow of hot exhaust gases through the purge box flow path 111 and reduce the temperature of such exhaust gases to reduce the potential for damage to adjacent equipment and ensure the safety of personnel working near the exhaust diffuser 30 and expansion joint 50.

[0038] The aft cover 114 may be connected to the inner fairing 106 and the housing 58 of the turbomachine 10. The purge box 100 may thereby be formed by at least the cover plate 102, the T-fairing 104, the aft cover 114, and the housing 58 of the turbomachine 10. In an embodiment, the aft cover 114 may include or be formed by the flex seal 56, although other suitable arrangements may be used. It should be noted that while the T-fairing 104 is shown in some figures as a separate part, interposed between the upstream end of the expansion joint 50 and the radial flange 60 to which the aft cover 114 / flex seal 56 is attached, in other embodiments the T-fairing 104 may include the radial flange 60 and / or be an extension of the duct 31 of the exhaust diffuser 30.

[0039] As shown in more detail in FIG. 4 , at least one seal 118 may be included in the purge box flow path 111 to reduce flow escaping from the purge box 100 during operation of the turbomachine 10. A purge inlet 116 may extend through the cover plate 102 and may be connected to a source 33, 35, or 36 ( FIG. 1 ) of purge fluid 101. The purge fluid 101 may include gas at a pressure higher than the operating pressure of the expansion joint 50. As shown in FIG. 1 , the purge fluid 101 may be air, such as from the compressor 12, the blower 35, or some other source 36. In embodiments, it may be advantageous to use the same source used to supply the cooling fluid 37 to the diffuser struts 32, although other arrangements may be used.

[0040] 4-8 , the at least one seal 118 in embodiments may include a first seal 120 between the leg 110 of the T-fairing 104 and the cover projection 112. For example, as shown in FIG. 4 , the first seal 120 may take the form of a “tadpole” seal including a head 122 between the leg 110 of the T-fairing 104 and the cover projection 112, and a tail 124 extending radially inward from the head 122 along the leg of the T-fairing 104 and connected to the T-fairing leg 110 by a bolt or the like 126. The first seal 120 so positioned within the purge box flow passage 111 may reduce flow through the purge box flow passage 111 while accommodating movement of the exhaust diffuser 30 and the cover projection 112 parallel to the rotational axis R of the turbomachine 10.

[0041] 5 , the at least one seal 118 in an embodiment may further include a second seal 130 between the cover plate 102 and the first seal 120, such as between the cover plate 102 and the leg 110 of the T-fairing 104. The second seals 130 may include, for example, second tadpole seals having respective heads 132 adjacent to or in contact with the cover plate 102 and between the cover projection 112 and the leg 110 of the T-fairing 104, and respective tails 134 of the second seals 130 extending from the heads 132 and connected to the leg 110 of the T-fairing 104. For example, the tail 134 of the second tadpole seal may extend radially inward around and along the outer periphery of the leg 110 of the T-fairing 104, which may allow the tail 134 of the second seal 130 to be attached to the leg 110 along with the tail 124 of the first seal 120 by the bolt 126. In other embodiments, a second bolt (not shown) may be used to connect the tail 134 of the second seal 130 instead of or in addition to the bolt 126.

[0042] 6 , the second seal 130 may include a rope seal 142 on the cover projection 112, and the at least one seal 118 may further include a W-seal 144 that engages the rope seal 142 and is connected to the leg 110 of the T-fairing 104 by a bolt 146 or the like. In such an embodiment, the W-seal 144 may provide a biasing force to the rope seal 142 toward the cover projection 112 to help maintain the position of the rope seal 142 thereon. The rope seal 142 so positioned may further reduce flow through the purge box flow passage 111 while similarly accommodating movement of the cover projection 112 parallel to the rotational axis R of the turbomachine 10.

[0043] To further reduce flow through the purge box flow passage 111, in the embodiment shown in FIG. 6 , the at least one seal 118 can further include a forward seal 150 between the inner periphery 108 of the cover plate 102 and the inner fairing 106, filling the gap 109. The forward seal 150 can include, for example, a tadpole seal having a head 152 that engages the inner fairing 106 and a tail 154 connected to the cover plate 102. For example, the tail 154 can extend radially inward from the head 152 along the cover plate 102 and be connected thereto by a bolt 156. The forward seal 150 thus positioned can reduce flow through the purge box flow passage 111 by filling the gap 109 while accommodating radial movement between the inner fairing 106 and the cover plate 102. The forward seal 150 can also be used in combination with other examples of the at least one seal 118, as shown in FIGS. 7 and 8 . In Figure 7, for example, forward seal 150 is used with first seal 120, and in Figure 8, forward seal 150 is used with first seal 120 and second seal 130. Forward seal 150 may also be used with the seal embodiments shown in Figures 4 and 5 to close gap 109.

[0044] As indicated above, embodiments include a source 33 ( FIG. 1 ) of purge fluid 101, which may include at least one of the blower 35, the compressor 12 of the turbomachine 10, and the turbine 14 / exhaust gas 2 of the turbomachine 10. The purge fluid 101 may be introduced into the purge box 100 via a purge inlet 116 to modify the temperature and / or pressure of the fluid within the purge box 100 and / or the drain tank 52, thereby reducing leakage from the expansion joint 50, such as through the purge box flow path 111, along with at least one seal 118. Additionally, according to embodiments provided herein, the temperature of the purge fluid 101 may preferably be 40° C. or less, and the pressure of the purge fluid may be at least 110,000 Pascals (Pa) (corresponding to 1.1 bar).

[0045] By selecting a source of purge fluid 101 to induce a pressure in purge box 100 that is higher than the operating pressure in drain tank 52, leakage from expansion joint 50 can be substantially stopped. In other words, using a higher pressure purge fluid 101 can create a pressure in purge box 100 that is higher than the pressure in drain tank 52, which can result in a positive pressure purge and prevent leakage of exhaust gas 3. In embodiments, it is advantageous to have the pressure in purge box 100 at least 20 Pa higher than the pressure in drain tank 52. Positive purging can be achieved in embodiments by using a narrower or smaller gap 109 and / or by using a higher source pressure for purge fluid 101, as may be appropriate and / or desired. Such positive purging can reduce the temperature of the leakage stream to approximately 65°C (+ / −10°C) instead of approximately 315°C, thereby reducing losses in efficiency of turbomachine 10, particularly combined cycle operation, as well as improving the safety of personnel near gap 109.

[0046] In other embodiments, partial purging can be achieved, such as by using a pressure in the purge box 100 that is equal to or slightly less than the pressure in the drain tank 52. For example, partial purging can be achieved by using a pressure in the purge box 100 that is approximately 20 Pa higher than the pressure in the drain tank 52. However, such an embodiment is less advantageous because the outlet temperature of the purge fluid 111 can be approximately 243° C. Therefore, embodiments that achieve only partial purging result in a relatively low improvement in efficiency as well as some increased risk to personnel in the vicinity of the escaping purge fluid 111.

[0047] It should be appreciated that embodiments also disclose herein a method performed on a turbomachine including an exhaust diffuser, an aft diffuser, and an expansion joint having a sump disposed between the exhaust diffuser and the aft diffuser, the method including providing a cover plate, a T-fairing having an inner fairing, legs, a cover projection, a purge box flowpath, an aft cover / flex seal, at least one seal, and a purge inlet, as described above.

[0048] The technical effect of including the embodiments disclosed herein in a turbomachine is to improve its operating efficiency while increasing safety and reducing leakage therefrom, thereby reducing the operating costs and risks associated with the turbomachine. Such technical effect may be achieved by providing positive pressure purging according to the embodiments disclosed herein.

[0049] As used herein throughout the present specification and claims, approximation may be applied to modify any quantitative expression that can vary within acceptable limits without resulting in a change in the basic function to which it relates. Thus, values ​​modified by one or more terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some instances, approximation may correspond to the precision of an instrument for measuring the value. Here, and throughout the present specification and claims, range limitations may be combined and / or substituted, and unless the context or language dictates otherwise, such ranges are identified and include all subranges encompassed therein. As used herein, "about" and "approximately" indicate + / - 10% of the stated value, or within a range of values.

[0050] The corresponding structure, material, operations, and equivalents of all means-plus-function or step-plus-function elements in the following claims encompass any structure, material, or operation for performing the function in combination with other specifically claimed claim elements. The description of the present disclosure has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the disclosed form. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described to best explain the principles and practical applications of the disclosure and to enable others skilled in the art to understand the disclosure in various embodiments with various modifications suited to the particular uses contemplated. [Explanation of symbols]

[0051] 1 Intake 2. Exhaust gas 3 Exhaust flow 10 Turbomachinery 12 Compressor 14 Turbine 16 shaft 18 Combustor 20 fuel 22 Compressed air 24 High-temperature exhaust gas 30 Exhaust diffuser 31 Duct 32 Manway 32 Diffuser strut 33 Air Source 35 Blower 36 Other Sources 37 Cooling Air 40 Rear diffuser 50 Expansion joint 52 tanks 54 Drain pipe 56 Flex Seal 58 Housing 60 Radial Flange 100 Purge Boxes 101 Purge Fluid 102 Cover Plate 104 T fairing 106 Inner fairing 108 inner circumference 109 Gap 110 Legs 111 Purge box flow path 112 Cover protrusion 114 Rear cover 116 Purge Inlet 118 stickers 120 First Seal 122 Head 124 Tail 126 volts 130 Second Seal 132 Head 134 Tail 142 Rope Seal 144 W Seal 146 volts 150 Front seal 152 Head 154 Tail 156 volts R rotation axis

Claims

1. A purge box (100) for a turbomachine (10) including an exhaust diffuser (30), an aft diffuser (40), and an expansion joint (50) including a drain tank (52) therebetween, the purge box (100) comprising: a cover plate (102) attached to a housing (58) of the turbomachine (10), a portion of the housing (58) serving as a wall of the purge box (100); a flex seal (56) attached to the expansion joint (50), the flex seal (56) serving as a rear cover (114) of the purge box (100); an inner fairing (106) adjacent to an inner periphery (108) of the cover plate (102), with a gap (109) between the inner periphery (108) of the cover plate (102) and the inner fairing (106); a purge box flow path (111) defined by at least the cover plate (102) and the inner fairing (106) from an interior of the purge box (100) to the gap (109), the gap (109) being adjacent to the exhaust diffuser (30); at least one seal (118, 120) in the purge box flow path (111); an inlet (116) through the cover plate (102) in fluid communication with a source (33, 35, 36) of purge fluid (101) having a pressure selected to induce a pressure in the purge box (100) greater than the pressure in the drain tank (52); A purge box (100) including:

2. 2. The purge box of claim 1, wherein the inner fairing is part of a T-fairing that includes legs that extend radially outward from the inner fairing adjacent the cover plate and that form a portion of the purge box flowpath.

3. 2. The purge box (100) of claim 1, wherein a cover projection (112) extends from a rear portion of the cover plate (102) parallel to the rotational axis of the turbomachine (10) and forms part of the purge box flow path (111).

4. 2. The purge box (100) of claim 1, wherein the at least one seal (118) comprises a seal (118) configured to reduce flow through the purge box flowpath (111) while accommodating movement between the exhaust diffuser (30) and the aft diffuser (40) in a direction parallel to an axis of rotation of the turbomachine (10).

5. 2. The purge box (100) of claim 1, wherein the at least one seal (118) comprises a seal (118) configured to reduce flow through the purge box flowpath (111) while accommodating movement between the exhaust diffuser (30) and the aft diffuser (40) in a radial direction of the turbomachine (10).

6. 2. The purge box of claim 1, wherein the at least one seal includes a first seal that engages a wall of the purge box flow passage that is parallel to a rotational axis of the turbomachine, the first seal being connected to a portion of the inner fairing such that the first seal can accommodate movement between the exhaust diffuser and the aft diffuser in a direction parallel to the rotational axis of the turbomachine.

7. 7. The purge box of claim 6, wherein the at least one seal includes a second seal that engages a wall of the purge box flowpath that extends radially of the turbomachine, the second seal being attached to a portion of the inner fairing such that the second seal can accommodate movement between the exhaust diffuser and the aft diffuser in the radial direction of the turbomachine.

8. The purge box (100) of claim 1, wherein the pressure of the purge fluid (101) is at least 110,000 Pascals (Pa).

9. The purge box (100) of claim 1, wherein the pressure in the purge box (100) is at least 20 Pa higher than the pressure in the drain tank (52).

10. 1. An apparatus for a turbomachine (10) exhaust system, the exhaust system comprising an exhaust diffuser (30), an aft diffuser (40), and an expansion joint (50) including a sump (52) therebetween, the apparatus comprising: a cover plate (102) extending radially from a housing (58) of the turbomachine (10); a T-fairing (104) including an inner fairing (106) adjacent an inner periphery (108) of the cover plate (102) having a gap (109) therebetween, the inner fairing (106) extending substantially parallel to an axis of rotation of the turbomachine (10), and the T-fairing (104) further including legs (110) extending radially outward from the inner fairing (106) adjacent aft of the cover plate (102); a rear cover (114) connected to the inner fairing (106) and the housing (58) of the turbomachine (10); a purge box (100) including at least the cover plate (102), the T-fairing (104), the aft cover (114), and the housing (58) of the turbomachine (10), wherein the T-fairing (104), together with the inner fairing (106) and the cover plate (102), define a purge box flow path (111) from an interior of the purge box (100) passing between the cover plate (102) and the legs (110) and through the gap (109) between the inner periphery (108) of the cover plate (102) and the inner fairing (106); at least one seal (118) in the purge box flow path (111); a purge inlet (116) extending through the cover plate (102) and connected to a source (33, 35, 36) of purge fluid (101), the purge fluid (101) being at a pressure selected to induce a pressure in the purge box (100) that is higher than the operating pressure in the drain tank (52); An apparatus comprising:

11. 11. The apparatus of claim 10, further comprising: a cover projection extending from an aft portion of the cover plate parallel to the rotational axis of the turbomachine, the cover projection being radially outward of and radially adjacent to the leg of the T-fairing, the purge box flow path being between the leg and the cover projection and further including a portion defined by the leg and the cover projection, and the at least one seal including a first seal between the leg of the T-fairing and the cover projection.

12. 12. The apparatus of claim 11, wherein the first seal comprises a first tadpole seal having a head portion between the leg portion of the T-fairing and the cover projection, and a tail portion extending radially inward from the head portion along the leg portion of the T-fairing and connected to the leg portion of the T-fairing.

13. The apparatus of claim 12, wherein the at least one seal (118) further comprises a second seal (130) between the cover plate (102) and the first seal (120).

14. 14. The apparatus of claim 13, wherein the second seal includes a second tadpole seal having respective heads between the cover plate, the cover projection, and the legs of the T-fairing, and respective tails of the second tadpole seal extending from the heads and connected to the legs of the T-fairing.

15. 15. The apparatus of claim 14, wherein the tail portion of the second tadpole seal extends radially inwardly around and along the outer periphery of the leg of the T-fairing.

16. 14. The apparatus of claim 13, wherein the second seal includes a rope seal on the cover projection, and the at least one seal further includes a W-seal engaged with the rope seal and connected to the leg of the T-fairing.

17. 11. The apparatus of claim 10, wherein the at least one seal includes a forward seal between an inner periphery of the cover plate and the inner fairing, the forward seal positioned to at least partially fill the gap.

18. 20. The apparatus of claim 17, wherein the forward seal is a tadpole seal having a head that engages the inner fairing and a tail that is connected to the cover plate.

19. 11. The apparatus of claim 10, wherein the temperature of the purge fluid (101) is less than or equal to 40°C.

20. 11. The apparatus of claim 10, wherein the pressure in the purge box (100) is at least 20 Pa higher than the pressure in the drain tank (52).

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