A turbomachine comprising a seal between an outer casing component and an inner casing component, and a method

Abstract

Disclosed herein is a turbomachine comprising an outer casing component and an inner casing component housed in the outer casing component and coupled to the outer casing component. A passage is provided between the inner casing component and the outer casing component and a sealing arrangement is positioned in the passage. The sealing arrangement comprises an annular seal element and a backpressure ring arranged on the low-pressure side of the annular seal element. In use the backpressure ring is in press-fit engagement with the inner surface of the outer casing component and the annular seal element is in pressure contact against the backpressure ring. Also disclosed herein is a method for mounting a sealing arrangement in a turbomachine.

Description

A TURBOMACHINE COMPRISING A SEAL BETWEEN AN OUTER CASING COMPONENT AND AN INNER CASING COMPONENT, AND METHODDESCRIPTIONTECHNICAL FIELD

[0001] The subject matter disclosed herein relates to turbomachines and components thereof. In particular, embodiments disclosed here concern turbomachines including an outer casing, an inner casing, and a seal arrangement between the inner casing and the outer casing, the inner casing housing stationary blades and a rotor of the turbomachine.BACKGROUND ART

[0002] Many existing turbomachines, such as expanders and gas turbines, include an inner casing mounted in an outer casing. The inner casing is adapted to thermally expand and contract both radially and axially with respect to the outer casing due to temperature difference between the inner casing and outer casing. The outer casing is usually split along a horizonal plane, i.e., a plane containing the rotation axis of the turbomachine. Casings made of two portions which match along a plane containing the rotation axis of the turbomachine are referred to as “horizontally split”. The two portions of the outer casing are bolted along flanges. A gas stream flowing through the inner casing has a temperature higher than a gas stream passing through an annular space between the inner casing and the outer casing. The different temperatures of the gas streams lead to different expansion rates for the inner casing and outer casing.

[0003] The annular space provided between the inner casing and the outer casing is divided in two or more annular sub-spaces at different pressures, which are separated by an inner-to-outer casing seal arrangement. Due to the above-mentioned different relative thermal expansion rates of the inner casing and outer casing, the inner-to-outer casing seal arrangement shall allow axial and radial displacements of the inner and outer casings in the area of the seal passage where the seal arrangement is positioned. Unless differently indicated, as used herein “axial” and “axially” means parallel to the rotation axis of the turbomachine; “radial”; “radial” and “radially” means orthogonal to the rotation axis.

[0004] Leaf-type or membrane-type seals are provided for this purpose.

[0005] When the outer casing is horizontally split, the leaf-type seal can easily be manufactured in the form of a continuous ring which is mounted in one half of the outer casing before the other half of the outer casing is mounted to surround and enclose the inner casing. The leaf-type seal is then housed in a tangential groove which is machined in the two portions into which the outer casing is horizontally split.

[0006] Horizontally split outer casings may suffer from some limitations and drawbacks in high pressure applications. In fact, if the gas inside the outer casing has a very high pressure, from tens of bars to hundreds of bars, the bolts that join the two halves of the horizontally split casing may fail and leakages may occur.

[0007] Recently developed oxy-fuel combustion cycles often operate with carbon dioxide in a supercritical condition (sCCh) at pressures above 50 bar, and which may reach some hundreds of bars at the point of highest pressure in the thermodynamic cycle. Horizontally split casings are unsuitable for this kind of turbomachines. The very high pressure involved in supercritical CO2 cycles require the use of so-called barrel-type casings or vertically-split casings. A vertically split casing includes two casing components which are mutually coupled by means of flanges and bolts along a plane which is orthogonal to the rotation axis of the turbomachine. In the forward section of the turbomachine the outer casing component is monolithic, i.e., in the form of a barrel having a continuous annular structure developing around the rotation axis of the turbomachine. Inner-to-outer casing seal arrangements positioned in the annular space between the barrel-type outer casing component and the inner casing component must in such case be discontinuous, i.e., must have a radial interruption, to allow mounting thereof in the monolithic barrel-type outer casing component.

[0008] Discontinuous annular seals are inefficient, since the discontinuity in the annular seal causes gas leakages from the high-pressure region towards the low-pressure region. A seal arrangement of this kind is disclosed, e.g., in US2013 / 0104565.

[0009] Improvements in inner-to-outer seal arrangements adapted to alleviate the above drawbacks would be welcomed in the art.SUMMARY

[0010] According to one aspect of the exemplary embodiment, disclosed herein is a turbomachine comprising an outer casing component and an inner casing component housed in the outer casing component and coupled to the outer casing component. A passage is provided between the inner casing component and the outer casing component and a sealing arrangement is positioned in the passage. The sealing arrangement comprises an annular seal element and a backpressure ring arranged on the low-pressure side of the annular seal element. In use the backpressure ring is in press-fit engagement with the inner surface of the outer casing component and the annular seal element is in pressure contact against the backpressure ring.

[0011] The annular seal element can be monolithic, i.e. formed as a single continuous and seamless annular member, to provide enhanced sealing efficiency. The outer casing component can be in the form of a barrel; the annular seal element and the backpressure ring can be introduced into the barrel in an aft-to-forward direction.

[0012] As understood herein, a barrel casing component is a component which has a continuous structure around an axis of the turbomachine, and is coupled with a second casing component along a plane orthogonal to the axis of the turbomachine.

[0013] According to a further aspect, disclosed herein is a method for mounting a seal between an outer casing component and an inner casing component of a turbomachine. Th method comprises the following steps: introducing an annular seal element in a passage between the inner casing component and the outer casing component; introducing a backpressure ring in the passage, in contact with the annular seal element; introducing the inner casing component in the outer casing component, the inner casing component comprising a pressure surface in contact with the annular seal element.

[0014] Further features and embodiments of the turbomachine and of the method according to the present disclosure are described below and set forth in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is now made briefly to the accompanying drawings, in which:Fig.1 illustrates a sectional view of an expander including seal arrangements according to the present disclosure;Fig.2 illustrates an enlarged partial cross-section of a seal arrangement of the expander of Fig.1 in one embodiment;Fig.3 illustrates an enlargement of a portion of the annular seal element in a front view;Fig.4 illustrates an enlarged partial cross-section of a seal arrangement of the expander of Fig.1 in a further embodiment;Fig.5 illustrates an enlarged partial cross-section of a seal arrangement of the expander of Fig.1 in a further embodiment;Fig.6 illustrates a front view of a retention ring for a seal arrangement of the present disclosure, in one embodiment;Fig.7 illustrates a front view of a retention ring for a seal arrangement of the present disclosure, in a further embodiment;DETAILED DESCRIPTION

[0016] In the following description, reference is specifically made to an expander, and more specifically to a supercritical carbon dioxide (sCO?) expander, as a possible exemplary embodiment of a power-generating turbomachine according to the present disclosure. Such expanders can be used in so-called Allam cycles, for instance. Those skilled in the art of turbomachinery will nevertheless understand that novel features disclosed herein can be used with advantage also in other power-generating turbomachines, such as expanders using a fluid other than carbon dioxide, or using carbon dioxide in a non-supercritical state, or such as gas turbine engines.

[0017] Novel features disclosed herein are particularly beneficial in expanders operating at high pressure, for instance in thermodynamic cycles where the maximum pressure point is at or above 50 barA, for instance equal to or higher than 200 barA, or equal to or higher than 300 barA, for instance equal to or less than 800 barA.

[0018] In some embodiments, the expander 3 comprises an outer casing 41,combined with a combustor 7. The combustor 7 can be housed in the outer casing 41. The combustor 7 can be a can-type combustor, an annular combustor, a can-annular combustor (aka cannular combustor), for instance. The combustor 7 can include a plurality of combustion chambers 7A arranged around an axis A-A of the expander 3.

[0019] In other embodiments, not shown, the combustor can be arranged outside the expander. In yet further embodiments, the expander may not include a combustor and can be used in a closed thermodynamic cycle, wherein heat is transferred to the process fluid through a heat exchanger, for instance.

[0020] In some embodiments, the outer casing 41 includes several casing components coupled to one another. In the embodiment of Fig.1 the outer casing 41 is a so- called vertically split casing, or barrel-type casing and includes two casing components which are coupled to one another along a separation plane P-P that is orthogonal to a rotation axis A-A of a rotor 43 supported for rotation in the outer casing 41.

[0021] A first casing component 41.1, referred to herein also as “high-pressure casing”, is coupled to a second casing component 41.2, referred to herein also as “low- pressure exhaust casing”.

[0022] The high-pressure casing 41.1 is preferably a barrel casing component, i.e., is monolithic and continuous around the axis A-A of the expander.

[0023] The low-pressure exhaust casing 41.2 can be positioned at the discharge side, i.e., the aft side, of the expander 3, i.e., opposite the combustor 7, which is located at the forward side of the expander 3. The coupling between the two components forming the outer casing, i.e. the plane P-P separating the low-pressure exhaust casing 41.2 and the high-pressure casing 41.1 from one another is thus arranged in an aft position, i.e. in an area of the expander where the pressure of the process gas expanding through the expander is substantially lower than the highest pressure of the thermodynamic cycle.

[0024] As used herein the term “forward” refers to the upstream end of the expander 3; the term “aft” refers to the downstream end of the expander 3, with respect to the direction of flow of the process gas. The pressure of the process gas therefore reduces along the expander 3 in the forward-to-aft direction. Placing the separation plane P-P near the aft end of the expander 3 is particularly beneficial, since the inner gas pressurein the region of the separation plane P-P is lower than the pressure in the forward end of the expander 3. This makes the design of the outer casing 41 easier and less challenging.

[0025] In some embodiments, the low-pressure exhaust casing 41.2 forms a discharge volute or discharge plenum 41.3, through which exhausted process gas is discharged from the expander 3.

[0026] Reference numbers 45, 47 indicate bearing arrangements, which rotatingly support the rotor 43. For instance, the bearing arrangement 45 on the side opposite the combustor 7, i.e., on the aft side, may include an axial or thrust bearing in combination with a radial bearing, or a bearing having an axial-radial bearing capability. The bearing arrangement 47 on the combustor side, i.e., on the forward side, may include a radial bearing. A reversed arrangement is also possible, with a bearing having axial load capability arranged on the combustor side. The bearing arrangements 45, 47 can be housed in bearing casings, not shown in detail.

[0027] The rotor 43 is housed in an inner casing component 51, stationarily housed in the outer casing 41 and connected thereto.

[0028] Since the plane P-P which separates the high-pressure casing 41.1 and the low-pressure casing 41.2 is positioned in the aft region of the expander, the inner casing 51 and the rotor 43 must be introduced into the outer casing in an aft-to-forward direction.

[0029] In the embodiment of Fig. 1 the expander 3 includes a plurality of stages. Just by way of example, the expander of Fig. 1 includes eight stages. The number of stages shown is merely an example. Other embodiments may include less than eight or more than eight stages.

[0030] Each stage comprises an annular row of stationary vanes or stationary blades 53, which are stationarily arranged in the inner casing component 51. Each expansion stage further includes a respective annular row of rotor blades 55, arranged downstream of the respective annular row of stationary blades 53 along the expansion flow path, which extends from the combustor 7 to the discharge plenum 41.3 in a forward- to-aft direction through the plurality of expansion stages of the expander 3.

[0031] The rotor blades 55 form part of the rotor 43, i.e., are connected thereto for co-rotation with the rotor shaft. In embodiments, each annular row of rotor blades 55 is mounted on a respective rotor disk 57.

[0032] The rotor blades 55 of each stage can be manufactured separately from the respective rotor disk 57 and mechanically mounted thereon, as schematically shown in Fig.1. In other embodiments, the rotor blades 55 and the rotor disk 57 of each stage can be manufactured as a monolithic body, for instance by additive manufacturing. In yet further embodiments, the two design options can be combined. One or some stages may include respective monolithically manufactured components including rotor blades and disks, and one or some stages may include a rotor disk and separately manufactured rotor blades mechanically coupled to the rotor disk.

[0033] In some embodiments, the rotor disks 57 are stacked and connected to one another by tie rods. In the exemplary embodiment of Fig.1 the tie rods comprise a plurality of tie rods 61 arranged at a distance from the rotation axis A-A and a central tie rod 63, which is coaxial with the rotor 43.

[0034] In other embodiments, a different arrangement of tie rods can be provided, for instance, only a single central tie rod coaxial to the rotor 43, or only a set of tie rods arranged around the axis A-A and at a radial distance therefrom can be provided. In yet further embodiments, tie rods at different distances from the rotation axis A-A can be provided. The rotor can be also assembled in a different manner, e.g., by welding adjacent rotor disks to one another or by machining a single workpiece, for instance by additive manufacturing.

[0035] In some embodiments, the rotor 43 further comprises a forward shaft portion 65 and an aft shaft portion 67. Each one of said forward shaft portion 65 and aft shaft portion 67 can include one or more sections, connected to one another, e.g., by means of tie rods, as shown by way of example for the forward shaft portion 65.

[0036] While in the embodiment shown in Fig. 1 the rotor blades are mounted on rotor disks and the rotor disks are stacked to one another between the forward shaft portion 65 and the aft shaft portion 67, in other embodiments, not shown, one or more annular rows of rotor blades can be mounted directly on (or manufactured as one piecewith) the forward shaft portion and / or one or more annular rows of rotor blades can be mounted directly on (or manufactured as one piece with) the aft shaft portion. In some embodiments, the rotor may include a forward shaft portion and an aft shaft portion, connected to one another by tie rods or the like, wherein the rotor blades of all stages are mounted on (or manufactured as one piece with) either the forward shaft portion, or the aft shaft portion, or partly on the forward shaft portion and partly on the aft shaft portion, without rotor disks in-between.

[0037] In some embodiments, a respective sealing disk 68, aka distancing disk or spacer, is positioned between each pair of consecutive (i.e., adjacent) rotor disks 57. As used herein, “torsionally connected” means a connection adapted to transmit a torque between the torsionally connected components, such that the torsionally connected components rotate as a single body around the rotation axis A-A of the rotor.

[0038] An annular space is formed between the outer casing component 41.1 and the inner casing component 51. In the embodiment of Fig.1, the annular space is divided in an annular high-pressure region 81 and an annular low-pressure region 83. A seal passage 85, herein referred to simply as “passage”, housing an inner-to-outer casing seal arrangement, to be described in more detail below, separates the annular high- pressure region 81 and the annular low-pressure region 83. In some embodiments, a tandem or dual inner-to-outer casing seal arrangement can be positioned in the passage 85. A further inner-to-outer casing seal arrangement 87 can be provided between the annular low-pressure region 83 and the discharge plenum 41.3.

[0039] Since the outer casing component 41.1 is a barrel and the separation plane P- P is in the aft region of the expander, the inner-to-outer casing seal arrangement must be introduced into the outer casing component 41.1 in an aft-to-forward direction, before the inner casing 51 and the rotor 43 housed therein are introduced in the outer casing component 41.1.

[0040] An embodiment of an inner-to-outer casing seal arrangement is illustrated in Fig.2, which shows an enlargement of the passage 85. In this embodiment the passage 85 houses a tandem or dual inner-to-outer casing seal arrangement. Each single seal arrangement is labeled 87. In this embodiment the two seal arrangements 87 forming the tandem seal arrangement are structurally and conceptually identical and differ fromone another only as far as the diameters of the components thereof are concerned. Therefore, only one seal arrangement will be described in detail.

[0041] The seal arrangement 87 comprises an annular seal element 89 having a high- pressure side 89H and a low-pressure side 89L. The high-pressure side 89H is oriented towards the forward side of the expander 3 and faces the high-pressure region 81 and the low-pressure side 89L is oriented towards the aft side of the expander 3 and faces the low-pressure region 83. The annular seal element 89 extends continuously, i.e., seamlessly, by 360° around the axis A-A without interruptions and provides therefore a continuous membrane-type or leaf-type seal. I.e., the annular seal element 89 is a continuous monolithic element.

[0042] The annular seal element 89 comprises a radially outer annular sealing area and a radially inner annular sealing area. In use, the radially inner annular sealing area of the annular seal element 89 is in pressure contact with a radially extending annular pressure surface 51S of the inner casing component 51. While in Fig. l the annular pressure surface 51S is orthogonal to the axis A-A of the expander 3, this is not mandatory. It suffices that the annular pressure surface 51S extends radially, i.e., from a radial inner circumferential edge to a radial outer circumferential edge, for instance.

[0043] The radially outer annular sealing area of the annular seal element 89 is in pressure contact with a backpressure ring 91, which is positioned adjacent the low- pressure side 89L of the annular seal element 89. The annular seal element 89 is therefore housed between the backpressure ring 91 and a shoulder S formed in the outer casing component 41.1 and projecting radially inwardly towards the axis A-A. The shoulder S can be manufactured by machining or can be formed by an annular element (in one or more segments) fastened to the inner surface 41S of the outer casing component 41.1.

[0044] Quite in the same way as the annular seal element 89, the backpressure ring 91 can be a continuous monolithic ring developing seamlessly by 360° around the axis A-A without interruptions.

[0045] In use, the backpressure ring 91 is in press-fit engagement with the inner surface 41 S of the outer casing component 41, i.e., with the surface of the outer casingcomponent 41.1 which faces the inner casing component 51.

[0046] In some embodiments, the backpressure ring 91 is made of a material having a higher coefficient of thermal expansion than a material of the outer casing component 41.1. The outer casing component 41.1 and the backpressure ring 91 can be dimensioned such that, when the expander 3 is inoperative and at room temperature, the backpressure ring 91 may have an outer diameter DI which is slightly smaller, e.g., by some tenths of a millimeter, than the diameter of the inner surface 41S of the outer casing component 41.1 at the position where the backpressure ring 91 is housed. Therefore, the backpressure ring 91 is housed with clearance in the outer casing 41.1.

[0047] If the backpressure ring 91 is made of a material having a higher coefficient of thermal expansion than the material of the outer casing component 41.1, when the expander 3 is started and hot gas flows through the expander, the backpressure ring 91 undergoes a faster radial expansion than the outer casing component 41.1. The expansion causes the backpressure ring 91 to engage in press-fit in the outer casing component 41.1. A pressure gradient between the annular high-pressure region 81 and the annular low-pressure region 83 presses the annular seal element 89 against the annular pressure surface 51S and against the backpressure ring 91. The contact pressure generated between the annular seal element 89 on one side and the surface 51S and backpressure ring 91 on the other provides a seal against gas leakages between the annular high-pressure region 81 and the annular low-pressure region 83.

[0048] If the backpressure ring 91 dimensioned such that at room temperature a clearance exists between the backpressure ring 91 in the outer casing component 41.1, removal of the backpressure ring 91, e.g., for maintenance or repairing purposes, is easier.

[0049] In other embodiments, the backpressure ring 91 may have an outer dimeter DI which is equal to or larger than the inner diameter of the outer casing component 41.1. In such case, the backpressure ring 91 can be press-fitted in the outer casing component 41.1 by applying a temperature difference between the backpressure ring 91 and the outer casing component 41.1, for instance by cooling the backpressure ring 91 and causing a thermally induced shrinkage thereof, which reduces the outer diameter of the backpressure ring 91.

[0050] In some embodiments, specifically if the backpressure ring 91 is mounted with clearance in the outer casing component 41.1, a retention device can be provided, adapted to prevent axial displacements of the backpressure ring in the outer casing component 41.1. In Fig. l the retention device can include a shear ring 93, positioned adjacent the backpressure ring 91, on a side thereof opposite the annular seal element 89, i.e. on the side of the backpressure ring 91 facing the annular low-pressure region 83 and the aft side of the expander 3.

[0051] In some embodiments the shear ring 93 can be a resilient ring in the form of a Seeger ring as shown in Fig.6, which illustrates a front view thereof.

[0052] In other embodiments, the shear ring 93 can comprise a plurality of shear ring segments, as shown in Fig.7, wherein a shear ring 93 comprising two shear ring segments 93 A, 93B is illustrated.

[0053] In some embodiments, as shown in Fig.2, the shear ring 93 is housed in an annular groove 95 machined in the inner surface 41S of the outer casing component 41.1. The depth of the annular groove 95 is smaller than thickness of the shear ring 93 in radial direction, such that the shear ring 93 projects radially outside the annular groove 95 towards the axis A-A and forms a shoulder which retains the backpressure ring 91 in a correct axial position, even if the backpressure ring 91 is mounted with clearance at room temperature in the outer casing component 41.1.

[0054] In some embodiments, if the shear ring 93 includes a plurality of shear ring segments 93 A, 93B as shown in Fig.7, resilient features 97 can be positioned between mutually facing end surfaces of the shear ring segments 93 A, 93B, to allow mounting the shear ring segments 93 A, 93B in the annular groove 95 and retaining the shear ring segments in the annular groove 95.

[0055] In some embodiments, the low-pressure side 89L of the annular seal element 89 facing the backpressure ring 91 comprises two annular ridges or projections 89.1 and 89.2. The ridges 89.1 and 89.2 define the surface of contact of the annular seal element 89 with the backpressure ring 91 and with the annular pressure surface 5 IS. The small surface of contact defined by the ridges 89.1, 89.2 provide a higher contact pressure and therefore a more efficient sealing than that achievable with a full surfacecontact of the annular seal element 89, i.e. if the annular seal element 89 had a flat side surface in pressure contact with the backpressure ring 91.

[0056] The annular seal element 89 allows axial and radial displacements of the inner casing component 51 with respect to the outer casing component 41.1 without losing the sealing efficiency. The use of ridges or projections provide enhanced contact and therefore improved sealing efficiency in case of mutual displacement of the inner casing component 51 and outer casing component 41.1.

[0057] In some embodiments, each ridge 89.1 and 89.2 has an outer convex surface which in a cross-sectional view can have the shape of a segment of a circumference. The curved and convex outer surfaces of ridges 89.1 and 89.2 provide optimal pressure contact with the backpressure ring 91 and with the pressure surface 51 S also in case of angular displacements of the annular seal element 89.

[0058] In the embodiment of Fig.2 the annular seal element 89 is broadly planar. As understood herein, planar means that the annular seal element 89 can rest on a planar, i.e., flat surface in contact therewith along at least two radially distanced circumferential lines. In the embodiment of Fig.2, the side surface of the annular seal element 89 facing the annular high-pressure region 81 is flat, i.e., planar. If the annular element 89 is planar, the two annular ridges 89.1 and 89.2 are tangent to a common geometrical plane, in the sense that, if the annular seal element 89 is placed on a planar (flat) surface with the ridges 89.1, 89.2 facing the surface, both ridges are in contact with the surface along the entire circumferential extension thereof.

[0059] In other embodiments, not shown, the annular seal element 89 can be conical, i.e., in the shape of a Belleville spring and can be flexurally deformed in a flat state when under pressure.

[0060] In use, when the expander 3 is started, the temperature of the inner casing component 51 increases at a higher rate than the temperature of the outer casing component 41.1. If the backpressure ring 91 is mounted in the passage 85 with some degree of clearance at room temperature and is made of a material having a higher thermal expansion coefficient than the outer casing component 41.1, the outer diameter of the backpressure ring 91 will increase faster than the inner diameter of the surface 4 IS,such that the backpressure ring 91 will engage under pressure the inner surface 41 S of the outer casing component 41.1 and provide a shoulder against which the annular seal element 89 can be pressed by the pressure gradient across the annular seal element 89. A pressure gradient between the annular high-pressure region 81 and the annular low- pressure region 83 will push the annular seal element 89 against the radial pressure surface 51S and the backpressure ring 91 providing an efficient sealing between the high-pressure region 81 and the low-pressure region 83.

[0061] With continuing reference to Fig.2, a further embodiment of the inner-to- outer casing seal arrangement is shown in Fig.4. The same elements already described in connection with Fig.2 are labeled with the same reference numbers and will not be described again. The embodiment of Fig. 4 differs from the embodiment of Fig.2 mainly in that an elastic member 99 is positioned between the annular seal element 89 and the shoulder S, i.e., on the high-pressure side 89H of the annular seal element 89. The elastic member 99 biases the annular seal element 89 towards the backpressure ring 91 and against the pressure surface 51 S. When the expander 3 is not operative and no gas pressure retains the annular seal element 89 in sealing contact with the backpressure ring 91 and the pressure surface 5 IS, the elastic member 99 ensures that the annular seal element 89 contacts the pressure surface 51 S and the backpressure ring 91, such that at start-up the raising gas pressure in the annular high-pressure region 81 will press the annular seal element 89 against the annular pressure surface 51S and against the backpressure ring 91, preventing pressurized gas from leaking through the annular seal element 89 towards the low-pressure region 83.

[0062] In some embodiments, in particular if the shear ring 93 comprises a plurality of shear ring segments 93 A, 93B (see Fig.7) arranged in the annular groove 95, each shear ring segment can be mechanically coupled to the outer casing component 41.1 by a plurality of fasteners. An embodiment including fasteners adapted to retain the shear ring segments 93 A, 93B in place is shown in Fig.5. The same reference numbers indicate the same or equivalent components and elements already described in Figs 1- 4, which will not be described again. The fasteners are shown at 101 and can be mounted in the inner cavity of the outer casing component 41.1 by means of screws 103, for example.

[0063] The above-described sealing arrangement includes a continuous annular seal element 89, which can be mounted in a barrel-shaped outer casing component 41.1, i.e., a casing component which extends monolithically, seamlessly around the axis A- A of the turbomachine.

[0064] If the outer diameter of the backpressure ring 91 at room temperature is smaller than the diameter of the inner surface 41S in the position where the backpressure ring 91 shall be mounted, the inner-to-outer casing seal arrangement can be assembled as follows. If an elastic member 99 is provided, the elastic member 99 is introduced first from an aft-to-forward direction and placed against the shoulder S. Next, the annular seal element 89 is introduced in the outer casing component 41.1, followed by the backpressure ring 91. These components of the sealing arrangement are then retained in axial position by the shear ring 93. If the shear ring 93 is monolithic (Fig.6), the radial dimension thereof is reduced by approaching the two ends 93 A. The shear ring 93 is introduced into the outer casing component 41.1, aligned with at the annular groove 95 and released such that it will snap-fit therein.

[0065] If the share ring 93 is formed by share ring segments (Fig.7) each shear ring segment can be introduced in the groove 95 and fastened to the outer casing component 41.1 by fasteners 101 or simply retained therein by resilient features 97.

[0066] If the sealing arrangement is double, the second sealing arrangement is mounted with the same sequence. In the embodiment of Fig.5 the shoulder S of the second (downstream) sealing arrangement is formed by annular segments or by an annular member, separate from the outer casing component 41.1 and fastened thereto before mounting the members forming the second inner-to-outer casing seal arrangement.

[0067] When the turbomachine 3 starts operation, the higher thermal expansion coefficient of the backpressure ring 91 will cause the latter to expand and become press- fitted against the inner surface 41 S of the outer casing component 41.1.

[0068] If the sealing arrangement must be removed, for instance if one or more of the components thereof shall be replaced, disassembly takes place by carrying out the same operations described above in reverse sequence. The clearance between the outercasing component 41.1 and the backpressure ring 91 at room temperature allows easy removal of the backpressure ring 91 and of the annular seal element 89.

[0069] In other embodiments, the backpressure ring 91 may have such an outer diameter as to be press fit in the outer casing component 41.1 also at room temperature. In such case, the backpressure ring 91 can be cooled below room temperature before mounting, to cause a temporary reduction of the outer diameter thereof and allow insertion into the outer casing component 41.1.

[0070] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

1. A turbomachine containing outer casing component; an inner housing component housed within an outer housing component and connected to the outer housing component; an outer housing component having an inner surface facing the inner housing component; a channel between the inner casing component and the outer casing component; an annular sealing element located in the channel; wherein the annular sealing element has a high pressure side and a low pressure side; a back-pressure ring located on the low-pressure side of the annular sealing element; wherein, in use, the back-pressure ring is in press-fit engagement with the inner surface of the outer housing component, and the annular sealing element is in clamping contact with the back-pressure ring.

2. The turbomachine of claim 1, wherein the backpressure ring is made of a material having a first coefficient of thermal expansion, the outer casing component is made of a material having a second coefficient of thermal expansion, and the first coefficient of thermal expansion is higher than the second coefficient of thermal expansion.

3. A turbomachine according to claim 1 or 2, wherein, when the turbomachine is at room temperature, the backpressure ring has an outer diameter equal to or less than the inner diameter of the outer housing component in the axial position in which the backpressure ring is located.

4. A turbomachine according to any one of the preceding claims, wherein the annular sealing element is a continuous monolithic element.

5. A turbomachine according to any one of the preceding claims, wherein the outer casing component is a cylindrical casing component.

6. A turbomachine according to any of the preceding claims, wherein the backpressure ring is a continuous monolithic ring.

7. A turbomachine according to any one of the preceding claims, wherein the annular sealing element is flat.

8. A turbomachine according to any one of paragraphs 1-6, in which the annular sealing element has a conical shape of a disk washer.

9. A turbomachine according to any of the preceding claims, further comprising a locking device configured to prevent axial displacement of the backpressure ring.

10. A turbomachine according to claim 9, wherein the locking device comprises an insert ring located in an annular groove of the inner surface of the outer casing component and projecting radially inward from the annular groove; and the insert ring is in contact with the back-pressure ring on the side of the back-pressure ring opposite the annular sealing element.

11. A turbomachine according to claim 10, wherein the insert ring is monolithic.

12. A turbomachine according to claim 11, in which the insert ring is designed to elastically engage with a snap in the annular groove.

13. The turbomachine of claim 10, wherein the insert ring comprises a plurality of insert ring segments located in an annular groove.

14. The turbomachine of claim 13, wherein the insert ring segments are mechanically connected to the outer housing component by means of a plurality of fasteners.

15. A turbomachine according to any one of the preceding claims, in which the annular sealing element comprises a radially outer annular sealing region and a radially inner annular sealing region; wherein the radially outer annular sealing region is in clamping contact with the back pressure ring; and wherein the radially inner annular sealing region is in clamping contact with a radially extending annular pressure surface of the inner housing component.

16. A turbomachine according to claim 15, wherein the radially outer annular sealing region comprises a first annular rib protruding towards the backpressure ring and in pressing contact with it.

17. A turbomachine according to claim 16, in which the first annular rib has an outer curved and convex contact surface, designed with the possibility of pressing contact with the counterpressure ring.

18. A turbomachine according to claim 15, 16 or 17, wherein the radially inner annular sealing region comprises a second annular rib projecting toward the radially extending annular pressure surface of the inner housing component.

19. A turbomachine according to claim 18, in which the second annular rib has an outer curved and convex contact surface, designed with the possibility of pressing contact with the annular pressure surface of the inner casing component.

20. A turbomachine according to any of the preceding claims, further comprising an elastic element located adjacent to the annular sealing element on its side opposite the back-pressure ring, and configured to shift the annular sealing element relative to the back-pressure ring.

21. A turbomachine according to any one of the preceding claims, wherein when using the annular sealing element on the high pressure side, the pressure present is equal to or greater than 50 bar abs. and preferably equal to or less than 800 bar abs.

22. A turbomachine according to any one of the preceding claims, wherein the inner casing component and the outer casing component are configured to be inserted into the outer casing component in a direction from the rear portion to the front portion.

23. A method for installing a seal between a component of the outer casing and a component of the inner casing of a turbomachine, comprising the steps of: insert an annular sealing element into the channel between the inner housing component and the outer housing component; insert a counter-pressure ring into the channel in contact with the annular sealing element; the inner housing component is introduced into the outer housing component, wherein the inner housing component comprises a pressure surface that is in contact with the annular sealing element.

24. The method of claim 23, wherein at room temperature the back pressure ring has an outer diameter equal to or less than the inner diameter of the inner surface of the outer housing component.

25. The method according to claim 23 or 24, further comprising the step of securing the back pressure ring to the outer housing component using a locking device to prevent axial displacement of the back pressure ring within the outer housing component.

26. The method according to claim 25, in which the locking device comprises an insert ring, and wherein the insert ring is installed in an annular groove of the inner surface of the outer housing component and protrudes from it.

27. The method according to any one of paragraphs 23-26, in which the annular sealing element, the counterpressure ring and the inner housing component are inserted into the outer housing component in a direction from the rear portion to the front.