Note: Descriptions are shown in the official language in which they were submitted.
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LARGE COMPRESSOR BUNDLE ASSEMBLY
Technical Field
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
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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
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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.
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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
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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)
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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
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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 11 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
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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
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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
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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.
