This invention relates to reciprocating compressors for transporting natural gas, and more particularly to an improved method for controlling pulsation associated with such compressors.
Most natural gas consumed in the United States is not produced in the areas where it is most needed. 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. This gas is then sold to local distribution companies, who deliver gas 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. To provide force to move the gas, operators install large compressors at transport stations along the pipelines.
Reciprocating gas compressors are a type of compressor that compresses 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. An ideal pulsation control design reduces system pulsations to acceptable levels without compromising compressor performance.
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:
In the example of
The following description is written in terms of the “generic” compressor system 100. However, the same concepts are applicable to other compressor configurations.
A typical application of compressor system 100 is in the gas transmission industry. It operates between two gas transmission lines. A first line, at a first pressure, is referred to as the suction line. A second line, at a second pressure, is referred to as the discharge line. Typically, the suction pressure and discharge pressure are measured in psi (pounds per square inch). The suction and discharge lines are also referred to in the industry as the “lateral piping”.
Side branch absorber (SBA) 16 reduces residual low frequency pulsations by altering the amplitude of the responses in the lateral piping. SBA 16 may be installed on piping 19 on either the discharge or suction side of the compressor. SBA 16 comprises a choke tube 16a and surge volume 16b. Choke tube 16a is a span of conduit connecting the lateral piping to a surge volume 16b.
Compressor system 100 may also have filter bottles 18a and 18b. Filter bottles 18a and 18b are used to reduce compressor system pulsations. These filter bottles are placed between the compressor and the lateral piping, on the suction or discharge side or on both sides.
The effectiveness of SBA 16 and filter bottles 18a and 18b is dependent on their size and configuration and the pulsation frequencies that are to be controlled due to the speed of the compressor. Controller 17 is used for control of parameters affecting compressor load and capacity.
Pulsation filter bottles 32 and 33 are “internal choke tube” filter bottles. The filter bottles have two or more internal chamber volumes, separated by baffles, and pair of chamber volumes having a choke tube for carrying gas from one chamber to the other. In other embodiments, filter bottles may have external choke tubes, also implemented as volume-choke-volume devices. Both types of filter bottles function as low-pass acoustic filters, and attenuate pulsations on the basis of a predetermined response.
The low frequency sound reduction required for gas compressor piping requires high mass reactance to reduce suppression equipment cavity volume. Low mass reactance requires ¼ wave length side branch to generate out-of-phase wave cancellation. The side branch length is equivalent to a mechanical spring; the longer the side branch the lower the spring constant. In the example of
Further reduction of the resonant frequency of the SBA of
Decreasing the resonator stiffness by increasing the resonator volume increases the size of the SBA, which is not acceptable. More efficient means of increasing the resonator mass is needed to reduce the size of pulsation equipment in gas compressor piping installations.
In the example of
Application of a hyperbolic horn to increase mass reactance to reduce suppression device volume is applicable to other gas compressor pipe line pulsation suppression devices in addition to SBA's.
A filter bottle may alternatively have an external rather than internal choke tube. In this configuration, the two volumes are physically separate but connected by a choke tube. A hyperbolic horn in each volume is structured similarly to those of
Another application of a hyperbolic horn is with distributed SBA's, which are acoustic liners comprised of a resistive face sheet backed by a horn fitted resonator volume and distributed along the pipe line. The gas flow is confined to the transmission pipe and not routed through the acoustic liner, thereby greatly reducing the pressure drop experienced by conventional reactive volume-choke-volume resonators. This type of SBA's would look similar to the SBA of
Number | Name | Date | Kind |
---|---|---|---|
2570241 | Hutchinson | Oct 1951 | A |
2936041 | Sharp et al. | May 1960 | A |
5005353 | Acton | Apr 1991 | A |
5040495 | Harada et al. | Aug 1991 | A |
5354185 | Moringo | Oct 1994 | A |
5760349 | Borchers et al. | Jun 1998 | A |
5957664 | Stolz et al. | Sep 1999 | A |
20030136119 | Marks et al. | Jul 2003 | A1 |
20040234387 | Marshall et al. | Nov 2004 | A1 |
20060275158 | Nagao et al. | Dec 2006 | A1 |
20070154325 | Grant | Jul 2007 | A1 |
20070272178 | Brun | Nov 2007 | A1 |
Number | Date | Country | |
---|---|---|---|
20090155108 A1 | Jun 2009 | US |