TECHNICAL FIELD
Exemplary embodiments relate generally to compressors and, more
specifically, to the provision of thermal barriers for ensuring the smooth operation of ,
a compressor over a wide temperature range.
BACKGROUND
A compressor is a machine which increases the pressure of a
compressible fluid, e.g., a gas, through the use of mechanical energy. Compressors
are used in a number of different applications and in a large number of industrial
processes, including power generation, natural gas liquification and other processes.
Among the various types of compressors used in such processes and process plants
are the so-called centrifugal compressors, in which the mechanical energy operates on
gas input to the compressor by way of centrifugal acceleration, for example, by
rotating a centrifbgal impeller.
Centrifugal compressors can be fitted with a single impeller, i.e., a
single stage configuration, or with a plurality of impellers in series, in which case they
are frequently referred to as multistage compressors. Each of the stages of a
centrifugal compressor typically includes an inlet conduit for gas to be compressed, an
impeller which is capable of providing kinetic energy to the input gas and a diffuser
which converts the kinetic energy of the gas leaving the impeller into pressure energy.
A multistage compressor 100 is illustrated in Figure 1. Compressor
100 includes a shafi 120 and a plurality of impellers 130. The shaft 120 and impellers
130 are included in a rotor assembly that is supported through bearings 190 and 190'
and sealed to the outside through sealings 180 and 180'.
The multistage centrifugal compressor operates to take an input
process gas from an inlet duct 160, to increase the process gas pressure through
operation of the rotor assembly, and to subsequently expel the process gas through an
outlet duct 170 at an output pressure which is higher than its input pressure. The
process gas may, for example, be any one of carbon dioxide, hydrogen sulfide,
butane, methane, ethane, propane, liquefied natural gas, or a combination thereof.
Between the impellers 130 and the bearings 1 90 and 190', the sealings 1 80 and 1 80'
are provided to prevent the process gas from flowing through to the bearings.
Each of the impellers 130 increases the pressure of the process gas.
Each of the impellers 130 may be considered to be one stage of the multistage
compressor 100. Additional stages, therefore, result in an increase in the ratio of
output pressure to input pressure.
Compressors in oil and gas industries and power plants are operated
with different gas temperatures. The temperature varies from cryogenic to very high
temperature. The internal surfaces in boiled off gas application (BOG) compressors
are subjected to cryogenic temperature while the outer surfaces of the compressor are
exposed to atmospheric temperature. Due to the cryogenic temperature, thermal
contraction occurs in the components. The contraction is not uniform due to variation
in temperature on different parts. The non-uniform contraction reduces clearance
and/or creates interference between the adjacent components and affects performance
of the compressors. In BOG compressors, the differential thermal contraction
between the sealings 180 and 180' (in general, mechanical seals or dry gas seal type
or DGS), the end head 140 and 140' (which could also include heated seal carrier), the
bearings 190 and 190' and the shaft 120 creates interference between them and affects
normal operation of the compressor.
In order to remove or reduce thermal tension across the operating
temperatures involved, dry gas seals 180 and 180' are encapsulated in heated seal
carriers 140 and 140' that also act as thermal shields.
It would be desirable to minimize thermal tension and stress on the dry
gas seal and the end head by introducing a thermal barrier around the DGS to ensure
smooth operation of the BOG compressor.
SUMMARY
Systems and methods according to these exemplary embodiments
provide radial and axial thermal barriers to minimize thermal tension and stress on a
mechanical seal and an end head by introducing a thermal barrier around the
mechanical seal to ensure smooth operation of the BOG compressor.
According to an exemplary embodiment, a compressor end head for
providing a thermal barrier near a mechanical seal includes an inner end head and an
outer end head. The outer end head includes an opening in the center for enclosing
the inner end head, an outlet and grooves along side surfaces radially adjacent the
opening. The inner head has an opening in the center, an inlet, grooves in the opening
for enclosing an end portion of a compressor shaft and a flow path along an outer
surface.
According to another exemplary embodiment, a compressor end head
for providing a thermal barrier near a mechanical seal includes an inner end head and
an outer end head. The inner head includes an opening in the center, an inlet, grooves
in the opening for enclosing an end portion of a compressor shaft. The outer end head
includes an opening in a center for enclosing the inner end head, an outlet, grooves
along side surfaces radially adjacent the opening, an inlet chamber connected to the
inlet, an outlet chamber connected to the outlet and axial channels connecting the inlet
chamber and the outlet chamber.
According to a further embodiment, a compressor includes a shaft, a
plurality of impellers, a plurality of seals, an inner end head and an outer end head
adjacent the seals. The outer end head includes an opening in the center for enclosing
the inner end head, an outlet and grooves along side surfaces radially adjacent the
opening. The inner head has an opening in the center, an inlet, grooves in the opening
for enclosing an end portion of a compressor shaft and a flow path along an outer
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate exemplary embodiments,
wherein:
FIG. 1 illustrates a multistage compressor;
FIG. 2 illustrates a dry gas seal end head according to exemplary
embodiments;
FIGS. 3 and 4 illustrate a cut view of a dry gas seal end head according
to exemplary embodiments;
FIGS. 5 and 6 illustrate inner and outer sides of an outer end head
according to exemplary embodiments;
FIG. 7 illustrates a cut view of an outer end head according to
exemplary embodiments;
FIGS. 8 and 9 illustrate internal and external cut views of an inner end
head according to exemplary embodiments;
FIG. 10 illustrates an oil flow path in an inner end head according to
exemplary embodiments;
FIG. 11 illustrates an oil flow path in an end head according to
exemplary embodiments;
FIGS. 12 and 13 illustrate a cut view of a dry gas seal end head
according to exemplary embodiments;
FIG. 14 illustrates a cut view of an outer end head according to
exemplary embodiments; and
FIGS. 15 and 16 illustrate a cut view of an inner end head according to
exemplary embodiments.
DETAILED DESCRIPTION
The following detailed description of the exemplary embodiments
refers to the accompanying drawings. The same reference numbers in different
drawings identifl the same or similar elements. Also, the following detailed
description does not limit the invention. Instead, the scope of the invention is defined
by the appended claims.
In exemplary embodiments, interference between a mechanical seal
and an end head is prevented by providing axial thermal barriers around the
mechanical seal to ensure smooth operation of a BOG compressor.
For BOG applications, the mechanical seal (such as sealings 180 and
180' of FIG. 1) may include a dry gas seal encapsulated in a heated seal carrier as is
known. The dry gas seal closes the compressor to seal the compressor from the
outside.
A dry gas seal may be in contact with an end head 140 and 140' at the
end of the compressor. Referring to FIG. 2, end head 200 may includes an inner end
head 210 and an outer end head 220. Each or both of the end heads 210 and 220 may
be circular or may be some other shape but are illustrated as being circular in
exemplary embodiments. End head 200 may be formed by, for example, welding the
inner end head and outer end heads 2 10 and 220 in some embodiments.
A circular or ring shaped outer end head 220 is illustrated in FIGS. 5
and 6. Outer end head 220 may include a circular opening 221 in the center within
which inner end head 2 10 may be is circumferentially enclosed or fitted (as illustrated
in FIG. 2).
Referring to FIG. 2, outer end head 220 includes a hot oil outlet 224 on
an inner side surface 222. Outer end head 220 also includes a circular groove 225
surrounding the circular opening 221 where the inner end head 210 may be welded
with the outer end head 220 to form the circumferential enclosure. Outer end head
220 may include grooves 225 along both side surfaces (i.e. inner side surface and
outer side surfaces). Inner end head 210 includes a hot oil inlet 21 3.
Cut section views of the outer and inner surfaces of inner end head 2 10
are illustrated in FIGS. 8 and 9. Inner end head 210 includes a circular opening 21 1 in
the center. As illustrated in FIG. 8, inner end head 2 10 includes a plurality of grooves
212 within the opening for facilitating the placement and sealing of the end portion of
a compressor shaft.
The diameter of inner end head 2 10 may be approximately equal to the
diameter of circular opening 221 of outer end head 220 in order to facilitate the
enclosure of inner end head 210 within outer end head 220.
As illustrated in FIG. 9, inner end head 210 may also includes an oil
flow path 214 along an outer swface. Flow path 214 may be a helical flow path.
Flow path 214 along the outer surface may be formed between the grooves 212 which
are on the inner surface of inner end head. That is, the helical path 214 on the outer
surface may correspond to the raised portion of the inner surface of the inner end head
between the grooves 212 (path 214 may be positioned on the outer surface
corresponding to the raised portions between grooves 212 on the inner surface of the
inner end head 210). In some embodiments, flow path 214 may correspond to the
grooves 212. When the inner end head 210 is welded to outer end head 220, flow
path 2 14 may provide a path for hot oil or gas to flow from inlet 2 13 to outlet 224.
End head 200 of FIGS. 3 and 4 illustrates a helical flow path 214 and
hot oil or gas outlet 224. When viewed in conjunction with FIG. 2, hot oil or gas
entering inlet 21 3 of inner end head 210 flows through helical flow path 214 to outlet
224 of outer end head 220.
The outer surface of inner end head 210 may includes the helical flow
path 214 as described above and illustrated in FIG. 10. The flow path may be similar
to a spiral path providing an axial thermal barrier as illustrated in FIG. 1 1. The flow
path as described herein provides a thermal barrier between the end head and DGS.
In some embodiments, an additional thermal barrier may also be
provided. Referring to FIG. 7, a hot oil/gas chamber 223 proximate the outer side
surface of outer end head 220 (nearer to DGS) reduces the thermal differential further.
In this embodiment, oil in helical flow path 214 flows into chamber 223 and to outlet
224.
In order to prevent leakage from the helical flow path, a light
interference fit may be made between the inner end head 21 0 and the outer end head
220 in some embodiments. The inner and outer end heads can also be bolted to the
compressor housing in some embodiments.
In some embodiments, the helical flow path may be substituted with
straight holes in the outer end head to provide heating to the inner end head so that
inner end head and the dry gas seal can be maintained at required temperature to avoid
interference between the dry gas seal and end head when the compressor handles or
processes gas at cryogenic temperatures.
Refemng to FIGS. 12 and 13, an end head 300 includes inner end head
3 10 and outer end head 320 (corresponding to inner end head 21 0 and outer end head
220 of end head 200 as described above). Inner end head 3 10 includes a hot oil inlet
3 13. Outer end head 320 includes hot oil outlet 324 and groove 325 for facilitating
welding of inner end head 3 10 to outer end head 320. Outer end head also includes an
inlet gas or oil chamber 326 and an outlet gas or oil chamber 327.
Chamber 326 is provided near the inner head hot oil inlet 313 for
receiving the oil fiom inlet 3 13. A plurality of passages 328 in the outer end head 320
(illustrated in FIG. 14) facilitates oil flow from inlet chamber 326 to outlet chamber
327. Outlet chamber 327 is connected to oil outlet 324. In exemplary embodiments,
there may be four passages (or channels or holes) 328.
Chambers 326 and 327 may be connected with each other via straight
holes 328 in outer end head 320 in order to facilitate uniform hot oil flow along the
axis of the inner end head 3 10.
Inner end head 310 may be in the form as illustrated in FIGS. 15 and
16. Inner end head 3 10 may also facilitate oil flow along its outer surface 3 15 from
inlet 3 13 to outlet 324 of outer end head 320. Inner end head 3 10 may provide a
labyrinth seal.
The term "inner side surface" of an outer end head (or the inner end
head) as used herein may refer to the side of the end head that is facing an impeller
(i.e. between an impeller and end of the shaft). The term "outer side surface" as used
herein may refer to the side of the end head that is on a side not facing an impeller
(i.e. side of the end head that faces toward the outside of the casing).
The outer surface of the outer end head is adjacent the mechanical seal.
The mechanical seal may be a dry gas seal (DGS). The inlet, the outlet, the chamber
(of FIG. 7) and the flow path may be for hot oil or gas.
The inlet chamber 326 and the outlet chamber 327 provide a radial
thermal barrier. Channels or passages 328 (of FIG. 12) may be axial channels and
provide an axial thermal barrier.
Exemplary embodiments as described herein provide multiple
advantages. A heating system according to exemplary embodiments provides a radial
and axial thermal barrier. The thermal barrier reduces heat transfer between inlet and
the zone surrounding the DGS leading to a smooth operation of the BOG compressor.
The optimized flow path provides gradual change in temperature in radial and axial
directions around the DGS and also reduces internal thermal stress. In addition, the
heating system according to exemplary embodiments prevents interference between
DGS and the end head. The system is simple and compact. The system also prevents
interference and provides smooth operation of the BOG compressor at cryogenic
temperatures.
Exemplary embodiments as described provide an axial thermal barrier
or an axial and a radial thermal barrier for handling temperature gradients in boiled
off gas applications. The end head may be bolted to the compressor. The inner and
outer heads may also be interference fitted to form the end head.
The above-described exemplary embodiments are intended to be
illustrative in all respects, rather than restrictive, of the present invention. Thus the
present invention is capable of many variations in detailed implementation that can be
derived from the description contained herein by a person skilled in the art. All such
variations and modifications are considered to be within the scope and spirit of the
present invention as defined by the following claims. No element, act, or instruction
used in the description of the present application should be construed as critical or
essential to the invention unless explicitly described as such. Also, as used herein, the
article "a" is intended to include one or more items.

WE CLAIM :
1. A compressor end head (200) for providing a thermal barrier to a mechanical
seal, the end head (200) comprising:
an inner end head (21 0) having an opening (2 1 1) in a center, an inlet (2 13),
grooves (2 12) in the opening (2 1 1) for enclosing an end portion of a compressor shaft
and a flow path along an outer surface; and
an outer end head (220) having an opening (221) in a center for enclosing the
inner end head (210), an outlet (224) and grooves (225) alongside surfaces radially
adjacent the opening (22 1).
2. The end head of claim 1, wherein the outer end head fixther comprises a
chamber adjacent to the groove along an outer surface.
3. The end head of claim 1 or claim 2, wherein the outer swface of the outer end
head is adjacent the mechanical seal.
4. The end head of any preceding claim, wherein the mechanical seal is a dry gas
seal (DGS).
5. The end head of any preceding claim, wherein a diameter of the inner end
head is approximately equal to a diameter of the opening in the center of the outer end
head.
6. The end head of any preceding claim, wherein the flow path on an outer
surface of the inner end head corresponds to the grooves on an inner surface of the
inner end head.
7. The end head of any preceding claim, wherein the inlet, the outlet, the flow
path and the chamber are for hot oil or gas.
8. The end head of any preceding claim, wherein the flow path is connected to
the inlet and the outlet.
9. The end head of any preceding claim, wherein the flow path is a helical flow
path and provides at least an axial thermal barrier to the mechanical seal.
10. The end head of claim 9, wherein the flow provides a radial thermal barrier to
the mechanical seal.
1 1. The end head of any preceding claim, wherein the inner end head is welded to
the outer end head along the grooves of the outer head.
12. A compressor end head (200) for providing a thermal barrier to a mechanical
seal, the end head (200) comprising:
an inner end head (2 1 0) having an opening (2 1 1) in a center, an inlet (2 13) and
grooves (2 12) in the opening for enclosing an end portion of a compressor shaft; and
an outer end head (220) having an opening (221) in a center for enclosing the
inner end head (210), an outlet (224), grooves (225) alongside surfaces radially
adjacent the opening (221), an inlet chamber (326) connected to the inlet (213), an
outlet chamber (327) connected to the outlet (224) and axial channels (328)
connecting the inlet chamber (326) and the outlet chamber (327).
13. The end head of claim 12, wherein the inlet chamber is connected to the inlet
of the inner end head and the outlet chamber is connected to the outlet.
14. The end head of claim 12 or claim 13, wherein a heating substance flows from
the inlet to the inlet chamber and from the inlet chamber to the outlet chamber via one
of the channels.
15. A compressor (1 00) comprising:
a plurality of impellers (130);
an inner end head (2 10) having an opening (2 1 1) in a center, an inlet (2 13), a
plurality of grooves (2 12) along a surface adjacent the opening (2 1 1) for enclosing an
end portion of the shaft and at least one flow path along a radially outward surface;
an outer end head (220) having an opening (221) in a center for enclosing the
inner end head (2 1 O), an outlet (224) and grooves (225) along an inner surface and an
outer surface radially adjacent the opening (22 1).