U.S. patent application number 11/734116 was filed with the patent office on 2008-10-16 for gas compressor with pulsation absorber for reducing cylinder nozzle resonant pulsation.
Invention is credited to Eugene L. Broerman, Ralph E. Harris, Mitchel A. Smolik.
Application Number | 20080253900 11/734116 |
Document ID | / |
Family ID | 39853880 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253900 |
Kind Code |
A1 |
Harris; Ralph E. ; et
al. |
October 16, 2008 |
GAS COMPRESSOR WITH PULSATION ABSORBER FOR REDUCING CYLINDER NOZZLE
RESONANT PULSATION
Abstract
A method for reducing pulsation effects associated with the
compressor nozzle of a positive displacement compressor system. A
pulsation absorber, having a design like that of a side branch
absorber, is installed on the cylinder valve cap or on the cylinder
nozzle. The acoustic dimensions and placement of the pulsation
absorber are designed to reduce the amplitude of the pulsations
associated with the peak resonant frequency of the compressor
nozzle response.
Inventors: |
Harris; Ralph E.; (San
Antonio, TX) ; Broerman; Eugene L.; (San Antonio,
TX) ; Smolik; Mitchel A.; (San Antonio, TX) |
Correspondence
Address: |
BAKER BOTTS L.L.P.;PATENT DEPARTMENT
98 SAN JACINTO BLVD., SUITE 1500
AUSTIN
TX
78701-4039
US
|
Family ID: |
39853880 |
Appl. No.: |
11/734116 |
Filed: |
April 11, 2007 |
Current U.S.
Class: |
417/312 |
Current CPC
Class: |
Y10T 29/49238 20150115;
F04B 39/0066 20130101; F04B 39/0055 20130101; F04B 39/0061
20130101 |
Class at
Publication: |
417/53 |
International
Class: |
F04B 39/08 20060101
F04B039/08 |
Claims
1. A method of reducing pulsations associated with the compressor
nozzle of a positive displacement compressor, comprising:
determining the resonant frequency of the pulsations; placing a
side branch absorber on the cylinder valve cap; wherein the side
branch absorber has a surge volume and a choke tube; wherein the
side branch absorber has the following dimensions operable to
reduce the peak pulsation amplitude of the resonant frequency:
volume of the surge volume, length of the choke tube, and diameter
of the choke tube.
2. The method of claim 1, wherein the side branch absorber has an
acoustic frequency that splits the cylinder nozzle frequency
response.
3. The method of claim 1, wherein the pulsation absorber is placed
at a location such that a gas velocity "maximum" is generated at
the location where a velocity "minimum" would typically form when
the pulsation absorber is not installed.
4. A method of reducing pulsations associated with the compressor
nozzle of a positive displacement compressor, comprising: measuring
the resonant frequency of the pulsations; placing a side branch
absorber on the cylinder nozzle; wherein the side branch absorber
has a surge volume and a choke tube; wherein the side branch
absorber has the following dimensions operable to reduce the peak
pulsation amplitude of the resonant frequency: volume of the surge
volume, length of the choke tube, and diameter of the choke
tube.
5. The method of claim 4, wherein the side branch absorber has an
acoustic frequency that splits the cylinder nozzle frequency
response.
6. The method of claim 4, wherein the pulsation absorber is placed
at a location such that a gas velocity "maximum" is generated at
the location where a velocity "minimum" would typically form when
the pulsation absorber is not installed.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to large positive displacement
compressors for transporting fluids, and more particularly to an
improved method for reducing cylinder nozzle pulsations in large
positive displacement compressors.
BACKGROUND OF THE INVENTION
[0002] Most natural gas consumed in the United States is not
produced close to where it is used. To transport gas from
increasingly remote production sites to consumers, pipeline
companies operate and maintain hundreds of thousands of miles of
natural gas transmission lines. The gas is then sold to local
distribution companies, who deliver it to consumers, using a
network of more than a million miles of local distribution lines.
This vast underground transmission and distribution system is
capable of moving billions of cubic feet of gas each day.
[0003] To provide force to move the gas, operators install large
gas compressors at transport stations along the pipelines.
Reciprocating compressors are a type of positive displacement
compressor that compress gas by using a piston in a cylinder and a
back-and-forth motion. A suction valve in the cylinder receives
input gas, which is compressed, and discharged through a discharge
valve. Reciprocating compressors inherently generate transient
pulsating flows, and various devices and control methods have been
developed to control these pulsations. A proper pulsation control
design reduces system pulsations to acceptable levels without
compromising compressor performance.
[0004] The state of the art in pulsation design and control
technology has evolved as compressor technology has changed.
Designs for low-speed compressors are more mature, with fewer
critical issues. However, relatively recent high-speed,
high-horsepower compressor designs are placing significant
challenges on pulsation control design.
[0005] Cylinder nozzle pulsations are one challenge to
high-horsepower, high-speed, variable-speed units. The cylinder
nozzle is the section of pipe that connects the cylinder to the
suction or discharge side of the compressor, typically to a filter
bottle. This section of pipe can provide significant resonance
responses.
[0006] Currently, one solution to attenuating cylinder nozzle
pulsations is the installation of an orifice in the cylinder
nozzle. For example, a plate with a flow restricting hole may be
placed across the circumference of the nozzle. However, a downside
of the orifice is that it causes a pressure drop that requires the
supply of additional horsepower. This burden can be significant on
large horsepower units.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
[0008] FIG. 1 illustrates an integrated (low speed) compressor
system.
[0009] FIG. 2 illustrates a separable (low or high speed)
compressor system.
[0010] FIGS. 3A and 3B illustrate a nozzle pulsation absorber
installed at alternative locations.
[0011] FIG. 4 illustrates test data of cylinder nozzle pulsations
without a nozzle pulsation absorber.
[0012] FIG. 5 illustrates test data of cylinder nozzle pulsations
with a nozzle pulsation absorber installed on the valve cap.
[0013] FIG. 6 illustrates test data of cylinder nozzle pulsations
with a nozzle pulsation absorber installed on the cylinder
nozzle.
[0014] FIGS. 7-9 illustrate how the cylinder nozzle resonance is
altered when the pulsation absorber is installed near the
compressor valves.
DETAILED DESCRIPTION OF THE INVENTION
[0015] As explained in the Background, large reciprocating
compressors used in the gas and processing industries generate
cylinder nozzle pulsations that can cause poor compressor
performance, poor valve life, and significant vibration issues. The
conventional approach to reducing nozzle pulsation is the
installation of an orifice.
[0016] The following description is directed to a "nozzle pulsation
absorber" which when properly designed, can significantly reduce
the cylinder nozzle resonant pulsations. The nozzle pulsation
absorber can absorb cylinder nozzle resonant pulsations such that
the maximum pulsations are drastically reduced, eliminating the
need for an orifice. Unlike a conventional orifice, the nozzle
pulsation absorber does require additional horsepower.
[0017] Similar to the conventional orifice, the nozzle pulsation
absorber can be easily installed on an existing system at valve up.
It can also be installed in the cylinder nozzle near the cylinder
flange, but for existing systems this is a more costly
alternative.
[0018] FIG. 1 illustrates a reciprocating gas compressor system
100. Compressor system 100 is an "integrated" compressor system in
the sense that its engine 11 and compressor 12 share the same
crankshaft 13. The engine 11 is represented by three engine
cylinders 11a-11c. Typically, engine 11 is a two-stroke engine. The
compressor 12 is represented by four compressor cylinders 12a-12d.
In practice, engine 11 and compressor 12 may each have fewer or
more cylinders.
[0019] FIG. 2 illustrates a reciprocating gas compressor system 200
in which the engine 21 and compressor 22 are separate units. This
engine/compressor configuration is referred to in the natural gas
industry as a "separable" compressor system. The respective
crankshafts 23 of engine 21 and compressor 22 are mechanically
joined at a coupling 24, which permits engine 21 to drive the
compressor 22.
[0020] As indicated in the Background, a typical application of gas
compressor systems 100 and 200 is in the gas transmission industry.
System 100 is typically a low speed system, whereas system 200 can
be a low or high speed system. The trend in the last decade is
toward separable (high speed) systems, which have a smaller
footprint and permit coupling to either an engine or electric
motor.
[0021] Both systems 100 and 200 are characterized by having a
reciprocating compressor 12 or 22, which has one or more internal
combustion cylinders. Both systems have a controller 17 for control
of parameters affecting compressor load and capacity. Both systems
can exhibit the residual frequency problems discussed above.
[0022] As shown in FIG. 1, the compressor systems operate between
two gas transmission lines. A first line, at a certain pressure, is
referred to as the suction line. A second line, at a higher
pressure, is referred to as the discharge line. Typically, the
suction pressure and discharge pressure are measured in psi (pounds
per square inch).
[0023] The following description is written in terms of the
separable system 200. However, the same concepts are applicable to
system 100; as indicated in FIGS. 1 and 2, the same controller 17
may be used with either type of system.
[0024] FIGS. 3A and 3B illustrate a nozzle pulsation absorber 30
installed at alternative locations, namely, the cylinder valve cap
32 (FIG. 3A) and the cylinder nozzle 35 (FIG. 3B). Only a single
cylinder 31 is represented, shown as an elevation view toward its
valve cap 32. Cylinder 31 could be one of the cylinders from either
system shown in FIG. 1 or FIG. 2.
[0025] The cylinder nozzle 35 is the section of pipe that connects
the cylinder 31 to the discharge or suction side of the compressor.
In the embodiment of FIGS. 3A and 3B, the cylinder nozzle 35 is
labeled on the discharge side of the compressor, and the nozzle
pulsation absorber 30 is on the discharge side of cylinder 31.
However, the nozzle pulsation absorber 30 may be on either the
suction or discharge side of the cylinder 31.
[0026] In the embodiments of FIGS. 3A and 3B, the cylinder 31 is
connected to filter bottles 33 and 34 at both the suction input and
discharge outlet. These filter bottles 33 and 34 are installed as a
common method for pulsation control, and are placed between the
compressor and the attached piping systems. These filter bottles 33
and 34 operate with surge volumes, and are commonly implemented as
volume-choke-volume devices. They function as low-pass acoustic
filters, and attenuate pulsations on the basis of a predetermined
Helmholtz response.
[0027] Each nozzle pulsation absorber 30 operates like a side
branch absorber, and has a choke tube 30a and surge volume 30b.
Choke tube 30a is a span of piping connecting the valve cap 32 or
cylinder nozzle 35 to the surge volume 30b. In accordance with the
invention, nozzle pulsation absorber 30 reduces pulsations by
altering the frequency of the responses in the cylinder nozzle
35.
[0028] As is known in the art of side branch absorbers (also known
as Helmholtz resonators) for other applications, the physical
dimensions of choke tube 30a and surge volume 30b are not the same
as their acoustic dimensions. The desired acoustic dimensions and
the resulting physical dimensions are determined by various known
calculation and acoustic modeling techniques.
[0029] The acoustic dimensions of pulsation absorber 30 vary
depending on the pulsation frequency to be dampened. The resonant
frequency to be damped may be determined by various measurement or
predictive techniques.
[0030] The connecting piping 30a is attached to the valve cap 32 or
nozzle 35, such that pulsations corresponding to the acoustic
natural frequency of the pulsation absorber 30 are absorbed from
the compressor system. The diameter and size of the connecting
piping 30a and the size of the surge volume 30b determine the
acoustic natural frequency of the pulsation absorber 30.
[0031] Advantages of the above-described nozzle pulsation absorber
30 are that it controls cylinder nozzle pulsations, with
significant reduction of peak pulsation amplitudes and pulsations
at resonance. Its design is simple, and it is easy to install on an
existing system.
[0032] FIG. 4 illustrates test data from a compressor having a 8.5
inch bore and 3 inch stroke, running at 500 to 1000 rpm, without a
nozzle pulsation absorber. As illustrated, the cylinder nozzle
response has a significant peak at approximately 50 Hz.
[0033] FIG. 5 illustrates test data from the same compressor, under
the same operating conditions as FIG. 4, but with a nozzle
pulsation absorber 30 installed on the valve cap 32. As
illustrated, the cylinder nozzle response is split, to
approximately 43 and 58 Hz.
[0034] FIG. 6 illustrates test data from the same compressor, under
the same operating conditions as FIG. 4, but with a nozzle
pulsation absorber 30 installed on the cylinder nozzle 35. As
illustrated, the cylinder nozzle response is split, to
approximately 42 and 56 Hz.
[0035] FIGS. 7-9 illustrate how the cylinder nozzle resonance is
altered when the pulsation absorber is installed near the
compressor valves. FIG. 7 depicts the velocity profile that is
typically associated with a cylinder nozzle resonance. FIG. 8
depicts the velocity profile that is typically associated with a
side branch resonator. As shown in FIG. 9, by installing the
pulsation absorber near the compressor valves, a gas velocity
"maximum" is generated at the location where a velocity "minimum"
would typically form when the pulsation absorber is not
installed.
* * * * *