Embodiments of the subject matter disclosed herein generally relate to rotary machines, in particular centrifugal compressors, as well as systems and methods for assembling them, in particular for the insertion/extraction of a large diaphragm bundle into/from a barrel casing.

Related art

A centrifugal compressor is composed by an external casing having an internal cylindrical cavity that accommodates a cylindrical diaphragm bundle. The diaphragm bundle includes rotor and stator with their impellers, seals, fluid channel and balance pistons. In a compressor having a so called barrel casing, i.e. a casing that is radially split, during assembling or disassembling of the compressor the diaphragm bundle is inserted axially in the cylindrical cavity of the barrel casing through one of its open ends. The insertion or extraction of the bundle from the casing is a difficult and complicated task when dealing with large size compressors. The diaphragm bundle and the barrel casing should never come in contact during this operation because of the very high risk of damaging their surfaces due to wear / galling phenomena. When assembling large diaphragm bundles, typically heavier than -10 tons, the probability to damage both casing and bundle surfaces, either due to the very high contact pressure developed at the time the bundle gets to his centering location inside the casing, or to possible casing / bundle misalignments at assembly, is very high and definitely not acceptable. The clearance between the outer surface of the bundle and the inner surface of the casing is very small in order to avoid leakage of the compressed fluid, thus even a small tilt of the bundle during insertion or extraction can result in an interference with the internal surface of the casing that can be seriously damaged thus impairing the airtightness. On the other hand it is impractical or very difficult to use external vertical supports by two sides of the center of gravity of the bundle since this center is located inside the cavity. On top of this the external surface of the bundle and the internal surface of the casing present stepped portions i.e. they have sections of different diameters. Thus the problem to avoid galling or other type of damage due to the contact between casing and bundle while this is sliding inside the cavity is very difficult to solve. A technique to solve this problem, at least partially, consists in providing the casing or the diaphragm bundle, or both, with rollers on which the diaphragm bundle can slide inside the casing cavity. The position of the rollers mounted on the diaphragm bundle that is normally adjusted through shims or other similar means before the bundle is installed inside the casing, cannot be adjusted anymore once the bundle is in. When the rollers are mounted on the casing their height can be adjusted by means of screws or similar devices, they can also be provided with means to correct the tilting. According to this prior art technique, besides not being able to handle possible misalignments that may occur during the bundle installation phase, these internal rollers are not able to support the bundle once it reaches its final centering zones inside the casing cavity, therefore the bundle, in its final motion, directly slides and finally rests on the casing surface at gaskets location. Another consequence of possible bundle misalignments, not mitigated by the presence of the above internal rollers, is the seizure, due to the high contact forces generated during a possible hard contact, of large areas of both diaphragm bundle and casing, even in areas different from the centering stretches, wherein gaskets are located. To minimize the above risks of sizing the bundle / casing alignment is continuously monitored and frequent adjustments are required on the installation fixture. This technique is also time consuming and it requires a highly skilled operator turning the screws to adjust the height of the external fixture rollers to maintain the right casing / bundle alignment, and still a high probability remains that the screws are turned when the damage has already been done. Besides, till now, an easy way to repair the casing or the bundle in the event of remaining damaged during this process has not been found. Neither methods to reduce casing/bundle local contact pressure are known, nor methods to prevent the casing internal sealing surface getting in direct contact with the external surface of the diaphragm bundle. Therefore, a reliable system for supporting a diaphragm bundle during its insertion into or removal from the casing that is capable of supporting a heavy weight bundle and that can assure a controllable and precise movement of the bundle relative to the casing without causing damages, is highly needed.

Summary

Therefore, there is a general need to provide an arrangement that can facilitate the insertion into or the removal from a barrel casing of a heavy compressor diaphragm bundle without causing damage to the surface of the bundle and/or the casing.

Therefore, at the light of the above objectives, a first aspect of the present invention is a rotary machine, in particular a centrifugal compressor.

According to embodiments thereof, a rotary machine comprises a barrel casing having a cylindrical internal surface, and a diaphragm bundle having a cylindrical external surface wherein the diaphragm bundle during assembly of the compressor is insertable in axial direction into the casing with its external surface in mating relation with the internal surface of the barrel casing, and wherein the diaphragm bundle comprises sliding means attached to its external surface bearing the whole diaphragm bundle weight while preventing any direct contact between the casing internal surface and the diaphragm bundle external surface both during assembly of the compressor and with the bundle in operating position.

It is to be noted that a "sliding motion" is lateral motion of two solid surfaces in contact. Therefore, the above mentioned "sliding means" are designed to bear the whole diaphragm bundle weight but also to allow a sliding motion of the diaphragm bundle on the casing. According to the present invention, the sliding means are typically sliding pads, and are advantageously made of self-lubricant material like cast iron, bronze, or other lubricant filled materials.

According to another feature of the present invention, the sliding pads, as well as the steps inside the casing, may have blended surface portions to minimize Hertzian contact pressure while the bundle is approaching the internal diametric steps possibly existing inside the casing housing.

A second aspect of the present invention is a system for assembling a rotary machine. According to embodiments thereof, a system for assembling a rotary machine comprises a barrel casing having a cylindrical internal surface, and a diaphragm bundle having a cylindrical external surface, wherein the diaphragm bundle during assembly of the compressor is insertable in axial direction into the barrel casing with its external surface in mating relation with the internal surface of the barrel casing, and wherein the diaphragm bundle comprises sliding means attached to its external surface bearing the whole diaphragm bundle weight while preventing any direct contact between the barrel casing internal surface and diaphragm bundle external surface both during assembly of the centrifugal compressor and when the diaphragm bundle is in its final operating position.

A third aspect of the present invention is a method for assembling a rotary machine.

According to embodiments thereof, a method for assembling a rotary machine comprises a barrel casing having a cylindrical internal surface, and a diaphragm bundle having a cylindrical external surface, wherein the diaphragm bundle during assembly of the compressor is inserted in axial direction into the barrel casing with its external surface in mating relation with the internal surface of the barrel casing, and wherein the diaphragm bundle comprises sliding means attached to its external surface; the diaphragm bundle during assembly of the rotary machine is inserted in axial direction into the barrel casing said sliding means bearing the whole diaphragm bundle weight while preventing any direct contact between the barrel casing internal surface and diaphragm bundle external surface during assembly of the rotary machine and when the diaphragm bundle reaches its final operating position.

Brief description of the drawings

Other objectives, features and advantages of the invention will be more evident by a detailed description of a preferred, but not exclusive, embodiments illustrated as a non-limited example with the help of the accompanying drawings, wherein:

Fig. 1 represents a cross sectional longitudinal view of a compressor showing the barrel casing and the diaphragm bundle after assembling;

Fig. 2 represents a perspective view of the compressor mounted on the assembling structure; Fig. 3a represents a particular of the bundle position during installation phase;

Fig. 3b represents a particular of the bundle/casing at the final installation position;

Fig. 4 represents a perspective view of a sliding pad mounted on the external surface of the bundle;

Fig. 5 represents particular of the casing internal surface, of the bundle external surface and of the sliding pad at the final centering position; and

Fig. 6 represents a particular of the diaphragm bundle with a series of sliding pads inserted along its the external surface; Detailed description of the preferred embodiment(s) The following description of exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The invention, mainly applicable to large / very heavy centrifugal compressors equipped with barrel casing, provides the installation of sliding pads at several convenient locations, typically in the areas adjacent the external gasket, on the outer diaphragm bundle periphery. The sliding pads will be bearing the whole diaphragm bundle weight preventing it from touching the casing cavity after the bundle reaches its final location inside the casing. The sliding pads will also prevent during the assembly phase, when the bundle is supported on rollers, that any direct contact can occur between casing and diaphragm bundle due to misalignments or other possible installation errors. Another advantage of the present invention is the easy replacement of possible damaged pads instead of having to manage costly and time consuming repairs on heavy compressors parts, considering also the costs due to machine unavailability. Fig 1 illustrates a particular of a large rotary machine, in particular a large barrel centrifugal compressor generally designated 100 with the barrel casing 1 and the diaphragm bundle 2. Fig. 2 illustrates the same compressor mounted on his baseplate together with the assembling structure. The barrel casing 1 includes a general cylindrical cavity into which the diaphragm bundle 2 can accommodate, the internal surface 6 of the casing 1 forming the cylindrical cavity mating with the external surface 7 of the generally cylindrical diaphragm bundle 2. Both internal surface 6 of the barrel casing 1 and external surface 7 of the diaphragm bundle 2 are stepped and present portions having different diameters. The barrel casing 1 may be provided at its end with a flange 5 while it is open for the insertion of the diaphragm bundle 2 at the other end. The diaphragm bundle 2 has a known basic configuration and includes the stator, the flow path 1 1 with the suction channels 14-15 and the discharge channels 21 -22, and a rotor 16 with the rotating shaft 17 and a plurality of impellers 18. The rotor 16 is driven at high rotational speed by a motor and the fluid, supplied through the suction nozzle/s 14-15 is compressed stepwise by the rotor and stator blades and discharged through the discharge nozzle/s 21 -22. The barrel casing 1 must contain the very high pressure created inside. The air sealing between the possible different compression sections that are made up in the barrel casing cavity is normally obtained through a series of gaskets 8 (Fig. 5) positioned between the internal cavity surface 6 of the barrel casing 1 and the external diaphragm bundle surface 7. In order to achieve a precise centering of the diaphragm bundle 2 inside the casing 1 while preventing the gaskets extrusion, very little clearance is left between the diaphragm bundle external surface 7 and the casing internal surfaces 6. The diaphragm bundle 2 is inserted into the casing 1 by sliding it into there through the opening provided at the end of the casing cavity. A proper apparatus generally designated 200 as shown in Fig. 2 is provided for facilitating the insertion and/or extraction of the diaphragm bundle 2 from the barrel casing 1 . The apparatus 200 includes a member 201 for supporting the barrel casing 1 and the bundle 2 (when inside the casing 1 ) during the insertion/extraction. Outside the casing 1 , the diaphragm bundle 2 is supported, through the fixture 202, by external rollers 203. Given the close tolerance between the external surface 7 of the diaphragm bundle 2 and the mating inner surface 6 of the barrel casing 1 , it is very difficult to avoid contact between these two surfaces during insertion/extraction of the diaphragm bundle 2 from the into/from the barrel casing 1 . The diaphragm bundle 2 is directly centered inside the casing 1 at gaskets 8 location. Fig. 3a shows the diaphragm bundle 2 position during the installation phase. The bundle at this stage is supported by internal rollers 19. Fig. 3b shows the diaphragm bundle final installation position when the internal rollers 19 mounted on the diaphragm bundle 2 do not support it anymore once it reaches its final centering location inside the casing 1 . Risk of galling is then very high because of the huge contact forces developed between barrel casing 1 and diaphragm bundle 2 surfaces at the moment the bundle 2 reaches its centering location and loses both external and internal rollers support. To solve this problem, according to the present invention, sliding pads 9 are provided at several convenient locations, typically in the areas adjacent the external gaskets 8, around the external surface 7 of the diaphragm bundle 2. In Fig. 1 sliding pads 9 are shown positioned at the two longitudinal extremities of the diaphragm bundle 2 near the position that is generally occupied by the gaskets 8. In the same figure other sliding pads 9 are mounted at the interphase gasket position.. At insertion the bundle is initially aligned with the casing by means of the external fixture rollers 203 in such a way that its axis is parallel to the casing 1 and it is pushed inside the casing 1 cavity while being supported on both the internal 19 and external 203 sets of rollers. All along this phase the sliding pads 9 ensure that no contact can occur between casing and bundle due to possible tilting of the latter. Once the bundle reaches its final operating position these pads 9 provide that a small clearance of around 100 microns is however maintained between the diaphragm bundle external surface 7 and the barrel casing 1 centering stretches at gasket location so preventing that the casing and diaphragm bundle come in contact at any time. According to the prior art normally the two mating surface are in direct contact. Fig. 4 shows such a sliding pad according to a preferred embodiment. The pads 9 can present a relatively large contact surface to minimize contact pressure while the diaphragm bundle 2 reaches its final destination. For the same reason the shape of the pads is adapted to the curvature of the casing surface. The pads have substantially the shape of a section of a cylinder that copies the mating barrel casing 1 inner surface 6, and a longitudinal dimension parallel to the bundle circumference greater than the transverse dimension. The typical dimensions of a pad 9 according to the invention are, as shown in Fig.5 where it is represented a particular of the bundle 2 at its final position inside the casing 1 :

- longitudinal length between D/35 and D/15, where D is the internal diameter of the barrel casing 1

- thickness between D/120 and D/60

Fig. 6 shows the installation of the pads along a circumference of the bundle external surface 7. The pads 9 are positioned on the bundle surface interspersed around its circumference. The number of pads along a circumference can be of the order of 10. The pads, see Fig.4,5,6 are inserted and kept in position by screws 10 in a recess 20 formed on the surface 7 of the diaphragm bundle 2 in such a way that they can protrude from the surface 7of the diaphragm bundle 2 for few mm more specifically from 2 to 10 mm. Besides the surface 12 (see Fig. 4 and 5) of the pads 9 is blended, as well as the steps inside the casing, in order to minimize the Hertzian contact pressure while the bundle during insertion into the casing approaches the diametric steps inside the casing housing, see Fig. 5, where in greater details it is shown the casing internal surface profile and the diaphragm bundle 2 external surface profile at the centering location. Finally considering the need to guarantee an easy and accurate pad installation, shim pack 9a (see Fig. 4 and 5) have been built in the sliding pad design. To facilitate their function the sliding pads are made of self-lubricating material such as cast iron or other graphite or other lubricant filled materials, like graphite filled nickel. The locations of the pads on the outer bundle surface 7 in the direction of the longitudinal axis of the bundle and all around a circumference of the bundle 7 are chosen in such a way to prevent contact between bundle and casing at any time. This invention prevents that barrel casing 1 and diaphragm bundle 2 could ever be in contact either during the installation phase or after the bundle assembly completion. Thanks to this invention the galling phenomena, that is quite frequent on diaphragm bundles weighing more than 10 tons and that often involves very expensive and time consuming repairs activities is eliminated as the very opportunity to get to a hard contact between casing and diaphragm bundle at the moment they center each other is totally avoided. Another important consideration is that even though a damage could occur, in the invention application scenario, it would likely involve just the pads, that could be easily replaced. This invention would ensure that no damages on casing and bundle diametric sealing faces, involving significant compressor performance losses, could be generated during the diaphragm bundle installation or removal from the casing. This problem, much more likely to happen as the compressor size increases, would be particularly severe once the machine is located on site. The damages created inside the casing in particular, could very hardly be repaired and could require the machine removal from its location with important production losses for the users. Spare sliding pads could also be available to quickly replace the ones damaged.