U.S. patent application number 13/879833 was filed with the patent office on 2013-10-03 for multi-stage centrifugal compressor and return channels therefor.
The applicant listed for this patent is Hiromi Kobayashi, Hideo Nishida, Kazuyuki Sugimura, Manabu Yagi. Invention is credited to Hiromi Kobayashi, Hideo Nishida, Kazuyuki Sugimura, Manabu Yagi.
Application Number | 20130259644 13/879833 |
Document ID | / |
Family ID | 45975206 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130259644 |
Kind Code |
A1 |
Kobayashi; Hiromi ; et
al. |
October 3, 2013 |
MULTI-STAGE CENTRIFUGAL COMPRESSOR AND RETURN CHANNELS THEREFOR
Abstract
A multi-stage impeller is configured in a multi-stage
centrifugal compressor by fixing and attaching a plurality of
centrifugal impellers to one rotating shaft. Diffusers and return
channels are provided in order downstream from each impeller. The
centrifugal impellers, the diffusers and the return channel are
housed within a compressor casing. The return channels have a
plurality of vanes positioned at intervals from one another in a
circumferential direction, and at least two stages are provided.
The vane exit angles monotonically increase toward the downstream
stage.
Inventors: |
Kobayashi; Hiromi;
(Kasumigaura, JP) ; Nishida; Hideo; (Kasumigaura,
JP) ; Sugimura; Kazuyuki; (Hitachinaka, JP) ;
Yagi; Manabu; (Tsuchiura, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kobayashi; Hiromi
Nishida; Hideo
Sugimura; Kazuyuki
Yagi; Manabu |
Kasumigaura
Kasumigaura
Hitachinaka
Tsuchiura |
|
JP
JP
JP
JP |
|
|
Family ID: |
45975206 |
Appl. No.: |
13/879833 |
Filed: |
October 17, 2011 |
PCT Filed: |
October 17, 2011 |
PCT NO: |
PCT/JP2011/073876 |
371 Date: |
June 3, 2013 |
Current U.S.
Class: |
415/68 |
Current CPC
Class: |
F05D 2250/70 20130101;
F04D 17/122 20130101; F05D 2240/122 20130101; F04D 29/444
20130101 |
Class at
Publication: |
415/68 |
International
Class: |
F04D 17/12 20060101
F04D017/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2010 |
JP |
2010-233576 |
Claims
1. A multi-stage centrifugal compressor comprising: a multi-stage
impeller configured by fixing and attaching a plurality of
centrifugal impellers to one rotating shaft, diffusers and return
channels formed in order downstream from each impeller, and a
casing housing the centrifugal impellers, the diffusers and the
return channels, wherein the return channels have a plurality of
vanes circumferentially arranged with spacing, and wherein the
vanes have exit angles monotonically increased toward the
downstream stage.
2. A multi-stage centrifugal compressor according to claim 1,
wherein the more downstream impeller has the larger or equal blade
angle with respect to a radial direction at an exit of the
impeller.
3. A multi-stage centrifugal compressor comprising: a multi-stage
impeller configured by fixing and attaching a plurality of
centrifugal impellers to one rotating shaft, diffusers and return
channels provided in order downstream from each impeller, and a
casing which houses the centrifugal impellers, the diffusers and
the return channels and in which a plurality of compressor groups
are configured by forming a plurality of inlet channels, wherein in
at least one of the plural compressor groups, the return channels
have a plurality of vanes circumferentially arranged with spacing
and are provided at least in two stages, and wherein the vanes have
exit angles monotonically increased toward the downstream
stage.
4. The multi-stage centrifugal compressor according to claim 3,
wherein in each group, the more downstream impeller has the larger
or equal blade angle with respect to a radial direction at an exit
of the impeller.
5. A return channel for use in multi-stage centrifugal compressor
which is used in at least more than one stage of the multi-stage
centrifugal compressor having a plurality of impellers attached to
one shaft and which includes a plurality of vanes circumferentially
arranged with spacing and attached in a channel formed between
opposite flat plates, wherein of the plural vane exit angles with
respect to a radial direction, an exit angle of the vane used in an
upstream stage is equal to or less than an exit angle of the vane
used in a downstream stage.
6. The return channel according to claim 5, wherein the vane of the
uppermost return channel has an exit angle substantially equal to
zero.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multi-stage centrifugal
compressor and a return channel thereof. More particularly, the
invention relates to a uniaxial multi-stage centrifugal compressor
having a plurality of impellers fixedly attached to one shaft as
well as a return channel thereof.
BACKGROUND ART
[0002] An example of a conventional multi-stage fluid machine is
set forth in Patent Literature 1. The multi-stage pump disclosed in
this patent publication has such a structure as to attain high
efficiency but not for a partial discharge range and attain a good
H-Q characteristic at the partial discharge range. That is, a
return channel is provided with a return guide vane, a trailing
edge of which is located outwardly of a leading edge of an impeller
blade in a radial direction of a rotating shaft. Further, flow
guide plates that extends from the trailing edge of the return
guide vane toward the rotating shaft are formed within a part of
the return channel.
[0003] Examples of the conventional multi-stage centrifugal
compressor improved in the performance of the return channel are
set forth in Patent Literatures 2 and 3. A multi-stage centrifugal
compressor disclosed in Patent Literature 2 has a structure in
which a return vane has a leading edge portion and a trailing edge
portion configured to conform to the flow. That is, a central
portion of the return vane in a width direction (axial direction)
is configured such that a leading edge thereof stands up while a
trailing edge thereof is inclined in a direction opposite to the
rotation of the impeller. A multi-stage centrifugal compressor
disclosed in Patent Literature 3 has a structure in which the
return channel is provided with movable return vanes on an upstream
side thereof and stationary return vanes on a downstream side
thereof.
[0004] [Citation List]
[0005] [Patent Literature]
[0006] JP-A No.2005-330878
[0007] JP-A No.1997-203394
[0008] JP-A No.1996-200289
SUMMARY OF THE INVENTION
[0009] [Technical Problem]
[0010] The centrifugal compressors such as a process centrifugal
compressor are often required of high efficiency and wide operating
range. In a case where the centrifugal compressor includes multiple
stages of centrifugal compressors to meet the requirements, the
individual stages are so designed as to achieve the highest
efficiency at a flow rate at a specified point. Therefore, if the
compressors are operated at flow rate other than that at the
specified point, the individual stages may encounter flow
mismatching.
[0011] This flow mismatching is explained as below with reference
to characteristic curves of a multi-stage compressor shown in FIG.
3 and FIG. 4. FIG. 3 shows a characteristic of the first-stage
compressor of the multi-stage compressor. FIG. 4 shows a
characteristic of the last-stage compressor of the multi-stage
compressor. The low flow operation limit of the compressor is
dependent upon the occurrence of surging. On the other hand, the
high flow operation limit is dependent on the occurrence of
choking.
[0012] In actual operation, the compressor is operated with an
operating range (WR) defined by a flow rate range between (Qs) and
(Qc). It is noted that a surge point (Ps) means a point at which
the surging occurs; (Qs) means a flow rate at which the surging
occurs; (Pc) means a point at which the choking occurs; and (Qc)
means a flow rate at which the choking occurs. A specified point
(P.sub.Des) as a design point is at the intermediate point of the
operating range. With a flow rate (Q.sub.Des) at this specified
point (P.sub.Des) as the boundary, a flow rate range between the
surge flow rate (Qs) and the specified point flow rate (Q.sub.Des)
is referred to as "surge margin SM" and a flow rate range between
the choke flow rate (Qc) and the specified point flow rate
(Q.sub.Des) is referred to as "choke margin CM". In a case where
the first-stage compressor is operated at the specified point flow
rate (Q.sub.Des) (volume flow ratio=1.0), the last-stage compressor
is also operated at the specified point flow rate (Q.sub.Des).
[0013] On the other hand, if the flow rate for the first-stage
compressor is increased to a high flow point (A) so as to increase
the flow rate, the head (H) of the first-stage compressor decreases
to (H.sub.A), which is lower than the head (H.sub.Des)
corresponding to the specified point (P.sub.Des) Namely, the
working gas is less compressed than when the first-stage compressor
is operated at the flow rate of the specified point (P.sub.Des).
Therefore, the downstream impellers are operated at point of higher
volume flow ratio. Consequently, the last-stage compressor is
operated at a higher flow operation point (A') in terms of volume
flow ratio. Namely, the last-stage compressor is operated at a
point significantly deviated from the specified point flow rate
(Q.sub.Des).
[0014] Conversely if the first-stage compressor is operated at a
lower flow operation point (B) than the specified point
(P.sub.Des), the head (H.sub.B) thereof is higher than the head
(H.sub.Des) corresponding to the specified point (P.sub.Des).
Therefore, the working gas is more compressed so that the
downstream compressors are operated at a lower flow operation point
in terms of volume flow ratio. The last-stage compressor, for
example, is operated at a lower flow operation point (B') close to
the surge point (Ps).
[0015] As described above, the operating range of the multi-stage
compressor strongly depends upon the operating range of the
downstream compressors or more particularly, upon the operating
range of the last-stage compressor. In order to construct the
multi-stage compressor featuring the wide operating range,
therefore, it is necessary that the more downstream compressor is
configured to have the wider operating range. However, the
impellers alone can only achieve limited expansion of the operating
range, which limits the operation of the multi-stage
compressor.
[0016] The above fluid machine disclosed in Patent Literature 1
suggests improvement in the return channel of the multi-stage pump,
achieving improved stability at the partial discharge range.
However, this machine is not the multi-stage centrifugal compressor
and hence, the fluid passes through the individual stages at
substantially the same volume flow rate. That is, difference in
working flow rate of the individual impellers forming the
individual stages is not considered.
[0017] The above multi-stage centrifugal compressors disclosed in
Patent Literatures 2 and 3 can be improved in efficiency because
the return vanes in the return channels are so configured as to
conform to the gas flow moving through the return channels.
However, enormous amounts of labor and knowledge are necessary for
forming the return vanes in conformity to the flow of gas into the
return channels. What is more, the individual stages have
complicated structures, resulting in an increased number of
manufacture steps and complicated control.
[0018] In view of the above-described problems of the related art,
the invention seeks to provide a multi-stage centrifugal compressor
that can achieve, on the whole, higher efficiency and wider
operating range than the conventional machines without sacrifice of
the efficiency. Another object of the invention is to achieve the
above object in a simple construction.
[0019] [Solution to Problem]
[0020] According to an aspect of the invention for achieving the
above objects, a multi-stage centrifugal compressor including: a
multi-stage impeller configured by fixing and attaching a plurality
of centrifugal impellers to one rotating shaft, diffusers and
return channels formed in order downstream from each impeller, and
a casing housing the centrifugal impellers, the diffusers and the
return channels is characterized in that the return channels have a
plurality of vanes circumferentially arranged with spacing, and
that the vanes have exit angles monotonically increased toward the
downstream stage. It is preferred in the above characteristics that
the more downstream impeller has the larger blade angle with
respect to a radial direction at an exit of the impeller.
[0021] According to another aspect of the invention for achieving
the above objects, a multi-stage centrifugal compressor including:
a multi-stage impeller configured by fixing and attaching a
plurality of centrifugal impellers to one rotating shaft, diffusers
and return channels provided in order downstream from each
impeller, and a casing which houses the centrifugal impellers, the
diffusers and the return channels and in which a plurality of
compressor groups are configured by forming a plurality of inlet
channels is characterized in that in at least one of the plural
compressor groups, the return channels have a plurality of vanes
circumferentially arranged with spacing and are provided at least
in two stages, and that the vanes have exit angles monotonically
increased toward the downstream stage. It is preferred in the above
characteristics that in each group, the more downstream impeller
has the larger blade angle with respect to a radial direction at an
exit of the impeller.
[0022] According to still another aspect of the invention for
achieving the above objects, a return channel for use in a
multi-stage centrifugal compressor which is used in at least more
than one stage of the multi-stage centrifugal compressor having a
plurality of impellers attached to one shaft and which includes a
plurality of vanes circumferentially arranged with spacing and
attached in a channel formed between opposite flat plates is
characterized in that of the plural vane exit angles with respect
to a radial direction, an exit angle of the vane used in an
upstream stage is equal to or less than an exit angle of the vane
used in a downstream stage. In the above characteristics, the vane
of the uppermost return channel may have an exit angle
substantially equal to zero.
[0023] [Advantageous Effects of the Invention]
[0024] According to the invention, the multi-stage centrifugal
compressor can achieve, on the whole, the high efficiency and the
wider operating range than the conventional machines because the
vane exit angles of the return channels of the multi-stage
centrifugal compressor are progressively increased toward the
downstream. stage. The invention only needs the setting of the vane
exit angles. Hence, the compressor having the simple structure can
achieve the high efficiency on the whole and provides the wider
operating range than the conventional machines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] [FIG. 1]
[0026] FIG. 1 is a vertical sectional view showing a multi-stage
centrifugal compressor according to one embodiment of the
invention;
[0027] [FIG. 2]
[0028] FIG. 2 is a view showing return channels of the multi-stage
centrifugal compressor of FIG. 1 in an overlapping relation as seen
in P-direction;
[0029] [FIG. 3]
[0030] FIG. 3 is a graph illustrating a characteristic of a first
stage of the multi-stage compressor;
[0031] [FIG. 4]
[0032] FIG. 4 is a graph illustrating a characteristic of the last
stage of the multi-stage compressor;
[0033] [FIG. 5]
[0034] FIG. 5 is a graph showing one example of exit angles of
vanes of the return channel according to the invention;
[0035] [FIG. 6]
[0036] FIG. 6 is a graph showing another example of the exit angles
of the vanes of the return channel according to the invention;
[0037] [FIG. 7]
[0038] FIG. 7 is a graph showing still another example of the exit
angles of the vanes of the return channel according to the
invention; and
[0039] [FIG. 8]
[0040] FIG. 8 is a set of graphs showing still another example of
the exit angles of the vanes of the return channel according to the
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] A multi-stage centrifugal compressor and a return channel
for use therein according to the invention will be described as
below with reference to the accompanying drawings. FIG. 1 is a
vertical sectional view showing a multi-stage centrifugal
compressor 10 according to one embodiment of the invention.
Further, return channels 3 of the multi-stage centrifugal
compressor 10 shown in FIG. 1 are illustrated in FIG. 2 in an
overlapping relation as seen in P-direction.
[0042] The multi-stage centrifugal compressor 10 includes a
plurality of impellers (1a to 1e) fixedly attached to one rotating
shaft (8) and diffusers (2a to 2e) disposed downstream from the
impellers (1a to 1e) respectively. Return channels (3a to 3d)
interconnecting the diffusers (2a to 2e) and the subsequent
impellers (1b to 1e) are disposed downstream from the respective
diffusers (2a to 2d except the last one. The impellers (1a to 1e),
the diffusers (2a to 2e) and the return channels (3a to 3e) are
housed in a compressor housing (6), where an inlet casing (4) is
disposed upstream of the first impeller 1a and an outlet casing (5)
is disposed downstream from the last diffuser (2e).
[0043] The multi-stage compressor (10) shown in FIG. 1 is a 5-stage
compressor. A working gas from outside the multi-stage compressor
(10) is first introduced into the machine through the inlet casing
(4) as a flow (9) moving radially inwardly. The flow enters the
first impeller (1a) and is increased in pressure while passing
through the respective impellers (1a to 1e), diffusers (2a to 2e)
and return channels (3a to 3d). After flowing through the last
diffuser (2e), the flow is discharged from the machine through the
outlet casing (5).
[0044] In a case where the multi-stage compressor (10) includes
five stages, four return channels (3a to 3d) are provided. The
return channels (3a to 3d) each include a portion disposed
downstream from the diffuser (2a to 2d) and having a U-turn bend in
section, and a ring-like portion having a plurality of vanes (13a
to 13d) circumferentially arranged with spacing (see FIG. 2) and
between opposite planes defined by wall surfaces of the compressor
casing (6). According to this embodiment, the more downstream is
the compressor, the larger exit angles (.beta..sub.3a to
.beta..sub.3d) have the vanes (13a to 13d) of the return channels.
As shown in FIG. 5, for example, the vanes (13a to 13d) of the
individual stages exhibit an angle distribution such that the vane
exit angles increase by a given angle for each addition of stage.
It is noted here that the vane exit angle (.beta.) is an angle
formed between the radial line and the vane surface at vane
exit.
[0045] In the return channels (3a to 3d) of the embodiment
configured in this manner, the following merits occur if the return
channels (3a to 3d) are increased in the vane exit angles
(.beta..sub.3a to .beta..sub.3d) . Namely, the return channels (3a
to 3d) having the vanes (13a to 13d) increased in the exit angles
(.beta..sub.3a to .beta..sub.3d) thereof and the subsequent
impellers (1b to 1e) connected to the return channels (3a to 3d)
via the flow paths obtain the following merits.
[0046] Specifically, pre-rotation remains in the flow entering the
subsequent impellers (1b to 1e) and hence, the flow into the
impellers (1b to 1e) is decreased in relative inlet velocity. It is
therefore expected that the flow in the impellers (1b to 1e) is
decreased in relative velocity of diffusion and an increased surge
margin (SM) results. If the return channels are progressively
increased in the vane exit angle (.beta.) toward the downstream
stage, the impellers (2) connected to the flow path of their
corresponding return channels are relatively increased in surge
margin (SM). This suggests that the magnitude of surge margin (SM)
of the entire compressor machine depends upon the impellers on the
downstream side. Accordingly, the surge margin (SM) of the entire
compressor machine can be increased by increasing the surge margin
(SM) of the downstream impeller.
[0047] The second merit is that the vanes (13a to 13d) of the
return channels (3a to 3d) reduce the turning angle of the flow so
that the vanes (13a to 13d) themselves are decreased in loss. The
vanes (13a to 13d) normally work to turn swirl flow in an axial
direction (reducing the exit angle to (.beta.=0.degree.)), the
swirl flow formed at exits of the diffusers (2a to 2d). As a
result, the flow along the vanes (13a to 13d) is turned greatly so
that the vanes (13a to 13d) encounter significant flow loss, which
is difficult to reduce.
[0048] The embodiment is adapted to allow the swirl component to
remain in an exit flow from the vanes (13a to 13d) of the return
channels (3a to 3d) or particularly the exit flow from the
downstream vanes (13a to 13d) and to enter the subsequent impellers
(1b to 1e) as the pre-rotation. Hence, the vanes (13a to 13d) have
smaller turning angles. Thus, the load on the vanes (13a to 13d)
can be reduced so that the flow loss at the vanes (13a to 13d) is
reduced.
[0049] The third merit is a uniformalized flow distribution. If the
load on the vanes (13a to 13d) of the return channels (3a to 3d) is
reduced, as described above, the flow distribution of the exit flow
from the return channels (3a to 3d) is reduced in flow
non-uniformity so as to be more prone to uniformalization. This
leads to improved performance of the impellers that are connected
to the return channels and designed based on receiving uniform
inlet flow.
[0050] This embodiment is configured to allow the swirl component
to remain in the exit flow from the return channels (3a to 3d) or
particularly the exit flow from the downstream return channels and
to allow the exit flow to enter the subsequent impellers.
Therefore, the head is lowered as compared with a case where the
flow without containing the swirl component or the pre-rotation is
allowed to enter the subsequent impellers. In the design of the
downstream impellers, rotation speed and outside diameter of the
impellers are designed to recover this head decrease into
consideration.
[0051] In a case where the characteristics of the downmost stage or
the stage just prior to the downmost stage significantly affect the
overall surge margin, it is preferred to increase the exit angles
of the vanes (13b to 13d) of only the stages having the significant
influence, as shown in FIG. 6. In the example shown in FIG. 6, the
vanes (13a, 13b) of the first and second stages have such exit
angles (.beta..sub.3a, .beta..sub.3b) as not to allow the swirl to
remain in the flow, while the vane (13c) of the stage just prior to
the downmost stage and the vane (13d) of the downmost stage have
such exit angles (.beta..sub.3c, .beta..sub.3d) as to allow the
swirl to remain in the flow. In this configuration, the exit angle
(.beta..sub.3d) of the downmost vane (13d) more affecting the surge
margin has a larger increment than the exit angle (.beta..sub.3c)
of the vane (13c) just prior to the downmost vane (13d) . The
downmost stage and/or the stage just prior to the downmost stage
exhibit a noticeable head decrease but the head decrease is
insignificant at the other stages. Hence, the head decrease of the
entire compressor can be reduced and besides, the compressor can
ensure a required surge margin.
[0052] The above are the examples of the 5-stage centrifugal
compressor. An example of a multi-stage centrifugal compressor (10)
having a larger number of stages is illustrated in FIG. 7. The
multi-stage centrifugal compressor (10) shown in FIG. 7 is a
9-stage machine in which the stages are divided into pairs and the
exit angle (.beta.) for each pair is changed incrementally. The
preceding stage of the pair has the same vane exit angle (.beta.)
as that of the subsequent stage of the preceding pair. At the
subsequent stage, the vane exit angle (.beta.) is increased by a
predetermined amount.
[0053] For example, the second stage is paired with the third
stage. The exit angle (.beta..sub.3b) of the second vane (13b) is
equal to the exit angle (.beta..sub.3a) of the first vane (13a),
while the exit angle (.beta..sub.3c) of the third vane (13c) is
increased by a predetermined increment from the exit angle
(.beta..sub.3b) of the second vane (13b). If the vane exit angle
(.beta.) is thus changed incrementally and the amount of
pre-rotation entering the subsequent impeller is previously
determined from the flow at the vane exit angle (.beta.), it is
easy to grasp performance and make design decision.
[0054] FIG. 8 shows vane angle distributions of the return channels
of a multi-stage centrifugal compressor according to still another
embodiment of the invention. In this embodiment, two inlet channels
are provided in one compressor casing. The machine is adapted for a
case where, for example, the compressed working gas flows out of
the machine in midstream for intercooling purpose and after cooled,
flows back into the compressor again. The compressor is divided
into two groups by the inlet channel. The first group includes five
return channels while the second group includes four return
channels.
[0055] The return channels of the compressor stages constituting
each group have the exit angles (.beta.) progressively decreased
toward the inlet side, or progressively increased toward the outlet
side. Namely, the return channels are configured such that the vane
exit angles progressively or monotonically increase in order from
the inlet side. If the return channels provided at the respective
stages have the exit angles (.beta.) set this way, the working gas
flows through the respective groups the same way as in the above
embodiments. Therefore, the operating range and performance of the
machine is changed or improved as described above. As for a pattern
of changing the exit angles of the return channels toward the
downstream stage, the patterns shown in FIG. 6 and FIG. 7 are also
applicable to this embodiment.
[0056] An alternative structure, the illustration of which is
omitted, may also be made in which the return channels are
configured as described above and the impeller is configured to
include impeller units progressively decreased in the impeller exit
angle toward the downstream stage. That is, the more downstream
impeller unit has the wider surge margin (SM). Having such a
structure, the multi-stage compressor as a whole can attain a wider
surge margin (SM).
[0057] While the above embodiments have been described by way of
examples of the 5-stage machine and 9-stage machine, it is needless
to say that the invention is not limited to these stage numbers.
The invention is applicable to any multi-stage centrifugal
compressors that include two or more return channels. The setting
of the vane exit angle is exemplified by the case where the exit
angle is proportionally increased, the case where only the two
downstream stages are increased in the exit angle and the case
where every other stage is increased in the exit angle. The setting
of the vane exit angle is not limited to these examples and various
setting methods are applicable. However, it is preferred that the
vane exit angle monotonically increases toward the downstream
stage.
[0058] [Reference Signs List]
[0059] 1a-1e: Impeller
[0060] 2a-2e: Diffuser
[0061] 3, 3a-3h: Return channel
[0062] 13a-13h: Vane
[0063] 4: Inlet casing
[0064] 5: Outlet casing
[0065] 6: Compressor casing
[0066] 7: Bearing
[0067] 8: Rotating shaft
[0068] 9: Inlet flow
[0069] 10: Multi-stage centrifugal compressor
[0070] A, A': High flow operation point
[0071] B, B': Low flow operation point
[0072] CM: Choke margin
[0073] H: Head
[0074] Ps: Surge point
[0075] Q: Volume flow ratio
[0076] Qc: Choke flow rate
[0077] Qs: Surge flow rate
[0078] SM: Surge margin
[0079] WR: Operating range
[0080] .beta..sub.3a to .beta..sub.3d: Vane exit angle
* * * * *