U.S. patent number 3,741,676 [Application Number 05/188,199] was granted by the patent office on 1973-06-26 for surge control for fluid compressors.
This patent grant is currently assigned to Barodyne, Inc.. Invention is credited to Stanley J. Minton, David Harold Silvern.
United States Patent |
3,741,676 |
Silvern , et al. |
June 26, 1973 |
SURGE CONTROL FOR FLUID COMPRESSORS
Abstract
A control means for preventing surging under changing or low
flow conditions in a fluid compressor such as an air compressor
which includes a rotor and diffuser and at least two stages of
compression is disclosed. Compressed air from the n+1 stage of the
compressor is injected into the diffuser of the nth or lower stage
of the compressor through a collection chamber which is disposed
about the diffuser.
Inventors: |
Silvern; David Harold (Los
Angeles, CA), Minton; Stanley J. (Woodland Hills, CA) |
Assignee: |
Barodyne, Inc. (Los Angeles,
CA)
|
Family
ID: |
22692148 |
Appl.
No.: |
05/188,199 |
Filed: |
October 12, 1971 |
Current U.S.
Class: |
415/58.1; 415/11;
415/58.4; 415/147; 415/149.1; 415/179; 415/27; 415/122.1; 415/148;
415/175; 415/914 |
Current CPC
Class: |
F04D
29/684 (20130101); F04D 27/0238 (20130101); F04D
25/02 (20130101); F04D 25/163 (20130101); F04D
27/0215 (20130101); Y10S 415/914 (20130101) |
Current International
Class: |
F04D
27/02 (20060101); F01d 001/12 () |
Field of
Search: |
;415/11,27,28,45,52,147,DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Husar; C. J.
Claims
I claim:
1. In a centrifugal fluid compressor such as an air compressor
having a plurality of stages of compression at least one of which
includes a diffuser, surge control means for controlling surging in
the compressor comprising:
a manifold coupled to said diffuser of one stage of compression
defining a volume which communicates with said diffuser through
orifices, said manifold including an inlet such that inlet fluid to
said inlet enters said diffuser through said orifice;
a line coupled between said inlet of said manifold and a higher
stage of compression than said one stage of compression such that
fluid may be removed from said higher state of compression and
injected into the diffuser of said one stage of compression.
2. The means for controlling surging defined in claim 1 wherein a
control means, for controlling the flow of fluid in said line, is
coupled to said line.
3. The means for controlling surging defined in claim 1 wherein
said orifices are disposed such that fluid entering said diffuser
from said volume is injected in the direction of the prevailing
flow direction in said diffuser.
4. The means for controlling surging defined in claim 3 wherein
said orifices are tangentially disposed through said diffuser.
5. In a centrifugal air compressor which includes a plurality of
stages of compression, each stage comprising a rotor and diffuser,
surge control means comprising:
a manifold defining a collection chamber disposed about the
diffuser of one stage of compression said manifold having an inlet,
and said collection chamber communicating with said diffuser
through a plurality of orifices;
a line for transporting air, coupled between said manifold inlet
and a stage of compression higher than said one stage of
compression such that air from said higher stage of compression may
be injected into the diffuser of said one stage of compression,
and
control means for controlling the flow of air in said line as a
function of the output flow of air from said compressor.
6. The surge control means defined in claim 5 wherein said orifices
are disposed such that fluid entering said diffuser from said
collection chamber is injected in the direction of the prevailing
flow in said diffuser.
7. The surge control means defined in claim 6 wherein said orifices
are tangentially disposed into said diffuser.
8. The surge control means defined in claim 7 wherein said
compressor has two stages of compression.
9. The surge control means defined in claim 6 wherein said control
means includes a valve disposed in said line.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to means for controlling surging in
centrifugal compressors.
2. Prior Art
Centrifugal compressors which utilize rotors and diffusers to
compress fluids such as air are well known in the art. While these
devices are efficient for a constant predetermined flow they
exhibit undesirable characteristics such as surging when the flow
drops below the predetermined level. For example, in some
centrifugal compressors surging occurs when the flow through the
compressor drops below 80 percent of the compressor's predetermined
or optimum flow. The surging results from the building up and
breaking down of various boundaries and layers of fluid within the
compressor. The surging is an undesirable characteristic since it
results in an uneven flow of air from the compressor.
Numerous attempts have been made in the prior art to control
surging. One method for controlling surging is to permit the
compressor to operate at its predetermined or optimum flow level
independently of the demand for fluid from the compressor. This is
generally accomplished by discharging the high pressure fluid at
the outlet of the compressor when the fluid is not being used. An
obvious disadvantage to this method is the fact that the work
performed on the fluid in compressing it is wasted when the high
pressure fluid is discharged.
Another method for controlling surging is that described in U.S.
Letters Patent No. 2,660,366. In this patent compressed fluid such
as air is recirculated through the compressor by injecting it into
the stream of air before that stream contacts the compressor
rotor.
It appears from a review of the prior art techniques for preventing
surging that the principal efforts have been directed towards
preventing surging caused by the compressor rotor. Tests have
indicated that in many centrifugal compressors the rotor is more
tolerable of low flow conditions than is the diffuser. For example,
in some instances it has been found that a reduction of flow of
about 20 percent will cause surging in a compressor and that the
cause of surging was attributable to the flow of air in the
diffuser and not the flow of air in the rotor. On the same
compressor it was found that a decrease of flow of about 60 percent
was required before surging problems attributable to the flow of
air in the rotor could be detected. Thus, the prior art attempts to
solve surging by injecting air upstream of the rotor have been
somewhat misdirected since these attempts are aimed at preventing
flow problems in the rotor area, when in fact the cause of the
surging is first attributable to problems within the diffuser.
SUMMARY OF THE INVENTION
A surge controlling means for a centrifugal compressor having at
least two stages, each of which comprise a rotor and diffuser is
described. Air from one stage of the compressor is directed into
the diffuser of a lower stage of the compressor through a
collection chamber disposed about that diffuser. Control means are
provided within a line which couples the collection chamber to a
higher stage of compression to selectively allow the flow of air
from the higher stage to the lower stage when the flow of air to
the compressor drops below a predetermined value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates one prior art technique for preventing surging
in a centrifugal compressor; said compressor is illustrated in a
partial cutaway view;
FIG. 2 is a plan view of a two-stage compressor utilizing the surge
control means of the present invention;
FIG. 3 is a partial cutaway view of the portion of the compressor
shown in FIG. 2 generally along section line 3--3; and
FIG. 4 is a sectional view of the collection chamber, diffuser and
rotor of the compressor illustrated in FIGS. 2 and 3.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a typical centrifugal compressor for
compressing a fluid such as air is illustrated along with a means
used in the prior art for preventing surging. The compressor
illustrated in FIG. 1 includes a first stage of compression 10 and
a second stage of compression 20. The air or other fluid to be
compressed enters the compressor through inlet 12, is then
compressed within the first stage of compression 10, leaves the
first stage of compression through outlet 16 and then enters the
interstage heat exchanger 17. The air is typically cooled in
between stages of compression and as illustrated in FIG. 1, the air
leaving the heat exchanger 17 enters the second stage inlet 18
where it is compressed by the second stage of compression 20. The
outlet air from outlet 19 of the second stage of compression 20 may
then be used to perform numerous tasks as is presently done in the
art such as driving pneumatic tools or may be compressed in
additional stages of compression.
The first stage of compression 10 includes a rotor 14 and a volute
diffuser 15. Likewise the second stage of compression 20 includes a
rotor 22 and a diffuser 21. Both rotors 14 and 22 are directly
connected to a drive shaft 28 which is rigidly coupled to a pinion
gear 27. The power for the compressor is obtained from a motor 23
which is coupled to pinion gear 27 through bull gear 24, pinion
gear 25 and bull gear 26.
The prior art surge control means illustrated in FIG. 1 includes an
inlet valve 13, an outlet control valve 30, recirculating control
valve 31 and a recirculating line 11. The recirculating line 11
interconnects the outlet 19 of the second state of compression 20
with the inlet 12 of the first stage of compression 10. Valve 11
disposed within the recirculating line 11 controls the amount of
outlet air which is recirculated within the compressor. The inlet
valve 13 controls the amount of air which enters the compressor
while the outlet valve 30 is used to control the outlet flow of air
from the compressor.
Centrifugal compressors such as the one illustrated in FIG. 1 have
a high efficiency while operating at a predetermined or optimum
flow rate. In many applications a constant demand for air is not
required and thus the flow of air from outlet 19 is not a constant.
For example, where the air from the compressor is utilized to drive
a plurality of pneumatic tools, the demand for air will be a
function of the number of tools in operation and will be a
variable. As previously explained, when the flow through the
compressor is decreased below a predetermined value surging occurs.
In the prior art method for preventing surging illustrated in FIG.
1, air from the outlet 19 is fed into the compressor at the inlet
to the first stage of compression 10. Typically control means sense
the demand for air and as the demand decreases, valve 30 prevents
all the air compressed by compressor stage 20 from leaving the
compressor. Simultaneously valve 31 opens, allowing some of its air
to enter the inlet of compressor stage 10 through line 11. Also the
inlet air to compressor stage 10 is throttled by valve 13.
The surge control means illustrated in FIG. 1 has the disadvantage
of wasting the energy utilized to compress the air in compressor
stages 10 and 20. The high pressure air from outlet 19 when
recirculated into the inlet 12, expands and is again recompressed
within the compressor. Additionally, as previously explained, the
injection of air by line 11 into the rotor 14 is intended to
present the compressor surging associated with the rotor. Tests
have indicated that in a typical centrifugal compressor the rotor
is more tolerable to low flow conditions than is the diffuser.
Thus, the prior art surge control technique illustrated in FIG. 1
has not provided a satisfactory surge control.
Referring to FIGS. 2 and 3, a compressor of substantially the same
construction as the compressor of FIG. 1 is again illustrated but
with a surge control means built in accordance with the present
invention. The compressor comprises a first stage of compression 40
and a second stage of compression 50. Inlet air to the compressor
enters through inlet 44, is then compressed by the first stage of
compression 40, and is then delivered to the inlet 46 of the second
stage of compression through line 45. Typically, a heat exchanger
is coupled into line 45 so that the heat of compression from the
first compression state 40 may be removed before the air is
recompressed within the second stage of compression 50.
The first stage of compression includes a rotor 41 and a volute
diffuser chamber 42 defined by manifold 52. The second stage of
compression likewise includes a rotor and diffuser 43 which for the
sake of clarity have not been illustrated in detail in FIGS. 2 or
3. The second stage of compression may be similar to the first
stage of compression 40.
The driving means for the compressor includes a motor 64 which is
directly connected to a bull gear 65. Bull gear 65 cooperatively
engages and drives a pinion gear 66 which is axially mounted on a
common shaft with a bull gear 67. Bull gear 67 cooperatively
engages a pinion gear 68 which in turn drives drive shaft 69. The
drive shaft 69 is coupled directly to the rotor 41 of the first
state of compression 40 and may also be coupled to the rotor of the
second stage of compression 50.
The compressor and in particular the rotor and diffuser may be
built utilizing standard prior art techniques. While in FIGS. 2
through 4 the surge control means of the present invention is
described in conjunction with a volute diffuser such as the one
defined by manifold 52, it will be obvious to one skilled in the
art that other types of diffusers such as a spiral diffuser may be
utilized with the presently disclosed surge control means.
Referring to FIGS. 2, 3 and 4, a collection chamber 70 defined by a
manifold 71 is axially disposed about one side of diffuser manifold
52. As best illustrated in FIG. 3, the collection chamber 70 is
partly defined by the outer surface of manifold 52 and by manifold
71. Manifold 71 abuts an inner radius of manifold 52. Orifices 63
disposed through manifold 52 allow the collection chamber 70 to
communicate with the diffuser chamber 42. Referring particularly to
FIG. 4, the orifices 63 are generally tangentially disposed through
manifold 52 such that the air entering the diffuser chamber 42 will
be injected into that chamber in the same direction as the
direction of air forced into the chamber by rotor 41; that is, the
air is injected into the chamber in the direction of the prevailing
flow.
An inlet 54 formed by a portion of the collection chamber manifold
71 allows the inlet 54 to communicate with collection chamber 70.
The diffuser return line 60 interconnects the outlet 62 of the
second stage of compression 50 with the inlet 54 of the collection
chamber 70. A valve 61 which is disposed within line 60 is used to
throttle the air or other fluid which will flow from outlet 62 to
the inlet 54.
The collection chamber 70 defined by manifold 71 with its inlet 54
may be an ordinary metal part manufactured utilizing known
techniques. The line 60 and valve 61 may be standard components
known and used in conjunction with fluid compressors.
When the compressor illustrated in FIGS. 2 through 4 is operating
at its optimum or predetermined flow the valve 61 disposed within
line 60 may be completely closed so that no air will flow from
outlet 62 into inlet 54. As the flow from outlet 62 decreases below
its optimum or a predetermined value, valve 61 opens, allowing air
from the outlet 62 to flow into the collection chamber 70. The
amount of air which is allowed to flow through line 60 is regulated
by valve 61, and as the demand for air from the compressor is
decreased more air is allowed to flow into the collection chamber
70. As the air enters the collection chamber 70 it is directed
through the orifices 63 into the diffuser chamber 42 since it is at
a higher pressure than the air in that chamber. It has been found
that the injection of air into the diffuser will greatly decrease
the effects of surging. Known means and techniques may be utilized
to control valve 61 as a function of the outlet flow from the
compressor. For example, a Pitot tube may be inserted within outlet
62 and utilized to operate valve 61.
While in FIGS. 2 through 4 the chamber 70 and orifices 63 are
illustrated disposed along an inner radius of the diffuser
manifold, it is of course within the scope of the present invention
to place such chamber and orifices along the side of the diffuser
or at any convenient location. Additionally, while the presently
preferred embodiment has been illustrated as a two-stage compressor
having stages of compression 40 and 50, it is within the scope of
the present invention to utilize the presently disclosed surge
control means with a compressor having any number of stages of
compression. In such cases the air from any stage of compression
except the first stage may be injected into the diffuser of any
lower state of compression, as taught by the present invention.
Also, in some applications it may be desirable to use the surge
control means illustrated in FIGS. 2 through 4 in combination with
some prior art surge control means such as the one illustrated in
FIG. 1.
Thus, a surge control means for use with a centrifugal compressor
has been disclosed wherein air from a higher stage of compression
is injected into the diffuser of a lower stage of compression
thereby preventing surging.
* * * * *