US3894610A

US3894610A - Gas stream silencer

Info

Publication number: US3894610A
Application number: US498984A
Authority: US
Inventors: Edmund John Halter; John Charles Lanpher
Original assignee: Burgess Industries Inc
Current assignee: Burgess Manning Inc
Priority date: 1974-08-20
Filing date: 1974-08-20
Publication date: 1975-07-15
Anticipated expiration: 1992-07-15
Also published as: DK140181B; SE7507131L; DK140181C; JPS51128501A; DE2534556B2; GB1466512A; FR2282533A1; ES435717A1; NO751949L; FR2282533B1; CA1026239A; DE2534556A1; DK247275A

Abstract

Noise and noise potential in a gas stream are controlled by series step treatment, each step accomplishing diffusion and smoothing of the flow with overall absorption of sound. The first stage provides a sturdy shock absorbing cushion to receive and mitigate rough blast while subsequent stages successively moderate and smooth the flow of the gas stream and absorb sound energy. Design criteria maximize diffusion and sound absorption while avoiding the creation of secondary noises within the unit.

Description

United States Patent [191 Halter et a1.

[ GAS STREAM SILENCER [75] Inventors: Edmund John Halter; John Charles Lanpher, both of Irving, Tex.

[73] Assignee: Burgess Industries Incorporated,

Dallas, Tex.

[22] Filed: Aug. 20, 1974 [21] App]. No: 498,984

[52] [1.8. CI i. 181/50; 181/57 [51] Int. Cl. t l t ..F01n 1/10 [58] Field of Search 181/49 50, 53, 57, 58

[56] References Cited UNITED STATES PATENTS 759964 5/1904 Bonar i i l 181/57 992.839 5/1911 Wolle et al. 181/57 X 2.640.557 6/1953 Gaffney l l l i i i i l 181/50 2.764250 9/1956 Jeffords 181/50 [451 July 15, 1975 1196,977 7/1965 Sanders 181/50 Primary ExaminerJoseph W. Hartary Assistant Examiner-.lohn F. Gonzales Attorney, Agenl, or FirmDarbo, Robertson &

Vandenburgh [57] ABSTRACT Noise and noise potential in a gas stream are con' trolled by series step treatment, each step accomplishing diffusion and smoothing of the flow with overall absorption of sound. The first stage provides a sturdy shock absorbing cushion to receive and mitigate rough blast while subsequent stages successively moderate and smooth the flow of the gas stream and absorb sound energy. Design criteria maximize diffusion and sound absorption while avoiding the creation of secondary noises within the unit.

10 Claims, 9 Drawing Figures FMEWEUJUL 1 5 ms SHEEI 1 GAS STREAM SILENCER BACKGROUND AND SUMMARY OF THE INVENTION The history of noise control has been a story of stepby-step technological improvement with concurrent progressive realization of the physiological, psychological and sociological importance of minimizing the levels of noise to which people are exposed. The scientific principles involved in the art are drawn and combined from the fields of acoustics, pneumatics and hydraulics. As in the mechanical arts, known physical expedients are combined in new relationships with dimensional and other design criteria discovered to provide the ever sought improved results.

In the particular field of the treatment and control of gas streams, especially pulsating or pressure and/or velocity disordered flow, it is necessary to deal with complicated problems of eliminating or at least greatly attenuating sonic frequency systems as well as smoothing and otherwise altering the flow to avoid the generation of noise directly upon discharge to the atmosphere or indirectly by causing noise creating vibrations of mechanical apparatus. At the same time, the production of secondary noise in the silencer, itself, or other treating device must be avoided.

The object of the present invention is to provide a silencer for controlling the noise. existing or potential, of a gas stream and which is capable of absorbing noise created upstream and smoothing disordered flow to avoid the creation of noise downstream while avoiding the creation of secondary noise within the silencer, it self. The device is capable of handling streams having a wide range of pressure and velocity flow characteristics, including surges of blast proportions.

A further object is to provide such a silencer which has a long and dependable useful life. Another object is to provide such a plural stage silencer to which an additional stage or stages may be added to provide more complete silencing as noise pollution standards become more strict. Another object is to provide such a silencer which has a very high performance/size ratio.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a typical silencer of the invention.

FIG. 2 is a longitudinal view, in cross section, of the silencer of FIG. 1.

FIG. 3 is an enlarged detail view showing structure and indicating action in the shock absorbing section of the unit.

FIGS. 3A and 3B are detail views showing the perforation patterns of the inner shells and of the diffusers, respectively, full size.

FIGS. 4 and 5 are detail views in cross section showing alternative forms of vibration isolating connection of adjacent sections of the silencer, the structure of FIGS. 1 and 2 being that illustrated in FIG. 4.

FIG. 6 is an exploded view of an add-on unit.

FIG. 7 is a side view of a modified form of a silencer.

DESCRIPTION OF SPECIFIC EMBODIMENTS The silencer illustrated in FIGS. 1-4 is a two-section unit comprised of cylindrical shells I and 2, the inlet end being closed by head 3. First stage diffuser tube 4 is welded to the head structure and a standard connecting flange 5 is welded to the exposed inlet end of the diffuser tube. The cylindrical walls of the tube are perforated, the pattern being shown, full size, in FIG. 38. An orifice plate 6 having an orifice 7, the purpose of which will be described hereinafter, is shown lying against the face of flange 5.

The contiguous ends of shells l and 2 are provided with

flanges

8 and 9. A partition I0 having a central opening II and a peripheral flange 12 is mounted at the junction of the first and second stages of the silencer by means of the peripheral flange. Elastomeric spacers I3 are sandwiched between flange I2 and

flanges

8 and 9 before the joint is drawn up tight by bolts [4, the function of the elastomeric spacers being to prevent the transmission of vibration between the shells connected at the joint.

Inner cylindrical shells I5 and I6 are mounted by means of rings 17 in spaced relation to shells I and 2. The inner shells are perforated, as shown. to provide access from the interior of the silencer to the material packed into the spaces between the inner shells and the silencer shells. The nature and function of these materials will be described hereinafter. The perforation pattern of the inner shells is shown, full size. in FIG. 3A.

A second stage diffuser tube I8 is mounted in opening II of partition I0. This tube, like the first stage diffuser tube, is perforated, as shown.

Desirably, a perforated inner head 19 is mounted in spaced relation to head 3 and the space thus provided is filled with sound absorbing material such as a pack of copper or steel fibers. Also, shell I of the first section of the silencer is double wrapped with a shell vibration dampening material such as lead or asbestos sheet 21. A sheet metal covering is provided.

While the gas stream silencer of the invention may be connected in line;" that is, connected at its inlet end to receive gases from a conduit and connected, also, at its outlet end with a conduit, the device shown in the drawing is designed to terminate the gas flow conduit. The inner and outer shells at the outlet end 22 of the silencer are open to the atmosphere.

The gas stream, the characteristics of which may vary from a relatively smooth flow to violently pulsating flow, is directed into first stage diffuser tube 4. Since the downstream end of the tube is closed, the gases are forced to flow radially outwardly through the tube perforations. For the duration of each pulse, the gases are directed in a multiplicity of individual jets toward inner shell IS. The space 23 surrounding the diffuser tube is filled with a durable type of material, such as metal turnings or copper scrubble, which provides a body having interconnecting voids. While serving to contribute to the absorption of sound vibrations in the gases from upstream sources, the principal function of this body is to receive and cushion the impact of the jet streams issuing from diffuser tube 4. Otherwise stated, while sound absorption is a desired characteristic of the material contained in space 23, this characteristic is somewhat sacrificed to achieve resistance to disintegration by the gases flowing at high velocity through the perforations of inner shell 15 and into the voids in the body. The space 24, which is downstream from the diffuser but still a part of the first, shock section of the silencer, is preferably filled with the durable type of sound absorbing material. Sound energy is absorbed by the material in

spaces

23 and 24 and also by the sound absorbing material 20 which is also exposed to the space within the first stage of the silencer.

The accomplishment of the flow treatment in the first section of the silencer is a partial but substantial smoothing of the flow of the gases following exposure to the shock and sound absorbing bodies.

The second stage of the silencer is designed to further damp pulsations and absorb sound energy still existing in the stream of gases as it fiows from treatment in the first stage into the second stage diffuser tube I8. While treatment action in the second stage is similar in nature to that brought to bear in the first stage of the silencer, the emphasis is changed from mitigation of shock flow to sound absorption with continued smoothing of the flow to prepare the stream for emission to the atmosphere with minimum noise-creating impact. Sound energy is absorbed by a more efficient sound absorbing material than that contained in the first section, such as punched hairfelt or glass fiber. contained in the spaces 25. Noise having their sources upstream from the silencer and noise that may be created in the gas system within the silencer are absorbed to an acceptable level before reaching the outlet of the silencer.

The gas stream silencer must be designed, not only to absorb so far as possible noise energy reaching it from upstream sources and smooth the flow to avoid the creation of noise at or beyond the outlet of the silencer, but also to avoid the creation of noise within the silencer itself. The generation of low frequency flow noise which tends to occur when a relatively high velocity stream flows into a large volume, such as emission of a stream from an inlet conduit into a relatively large silencer chamber, is avoided in the silencer herein described. The inlet stream is divided into a multiplicity ofjets 26 (FIG. 3) and the shock absorbing material is .arranged somewhat beyond the jet cores as represented at 27 in the enlarged detail view of FIG. 3. The preferred distance between inlet tube 4 and perforated inner shell is from four to times the diameter of the perforations in the diffuser tube. With this configuration. damage to the shock absorbing material by the high velocity jet cores is avoided and the gases are received and treated without the generation of low frequency noise. This distance may be somewhat less or may be greater with some sacrifice of useful life of the shock absorbing material or acoustic performance of the silencer, but the dimension specified represents optimum design.

Following treatment of the gas stream in the first, shock, stage of the silencer, the gases flow into the second stage diffuser tube 18 and radially therefrom through the perforations therein. Preferably, the perforations in the second stage diffuser tube are somewhat smaller and the tube somewhat longer as compared with the corresponding dimensions of the first stage diffuser. This results in smaller and more numerous jets. While the second stage diffuser tube effects further smoothing of the flow, the primary emphasis in the second treatment stage is acoustical; that is, the absorption of sound waves traveling in the gas stream. The spaces are packed with an efficient sound absorbing material, such as hairfelt or glass fiber. As is shown in FIG. 1, the exposed area of the sound absorbing material is extended well beyond the closed downstream end of the diffuser tube to provide continued absorption of sound energy as the stream consolidates for exit to the atmosphere at relatively low and steady velocity through the open downstream end of the silencer.

The silencer must necessarily be designed to handle a predetermined maximum flow of gases. While a valve in the upstream conduit leading to the silencer may be provided to limit the flow, secondary noises are likely to be generated downstream from the valve. This can be avoided by employing an orifice plate 6 at the inlet to the first stage diffuser tube. The amount of open area provided by the totality of perforations in the diffuser tube is related to the size of orifice 7. In general, this area should be approximately three times the area of the orifice. If, as is preferred, the perforations in the second stage diffuser tube are somewhat smaller than those in the first diffuser tube, the total open area for flow through the perforations in the second tube may be approximately the same as that of the first tube for optimum results since the flow of the stream into the second diffuser tube is substantially smoother.

Normally, it is necessary to provide means for preventing the radiation of noise to the atmosphere from the shell of the first or shock stage, only, of a two-stage silencer. This is done by surrounding the shell 1 with vibration damping layers, as above described. Transmission of the vibration of the first stage shell I to shell 2 of the second stage is largely avoided by the interposition of the elastomeric material at the joint as above described and the relatively smoother flow of the gas stream into and through the second stage does not normally create troublesome vibration of the shell.

An alternative form of vibration isolating joint is shown in FIG. 5. In this arrangement, the ends of shells la and 2a overlap and are fastened together with an elastomeric spacer 13a sandwiched between as a vibration barrier.

Although it is generally more desirable from both cost and performance efficiency standpoints to construct the silencer with cylindrical shells, they may, alternatively, be conical as shown in FIG. 7. Design considerations described with reference to the silencer of FIGS. 1-4 are applicable to the unit shown in FIG. 7 which differs essentially only in that the shells are conical instead of cylindrical.

The trend over the years has been to require better and better silencing to reduce noise pollution. What is acceptable and tolerated today is inadequate to meet the more stringent standards of tomorrow. In recognition of this trend and the likelihood that it will continue in the future, the invention contemplates the possible future addition of one or more gas stream treatment stages to the initially installed silencer which may comprise only two stages. This concept is illustrated in FIG. 6 wherein the initial two-stage unit is provided with a connecting flange 28. An add-on" stage 29, comprising shell 30 having a lining of sound absorbing material 31, diffuser tube 32 and connecting elements, is shown in position for connection to the outlet end of the initial two-stage unit. If desired at a later date, an additional stage or stages may be inserted between the initial unit and the terminal stage 29.

The silencer shown in FIG. 6 illustrates a further alternative feature of construction. To still further enhance the quieting of the gas stream, a sound absorbing body 33, contained between inner solid tube 34 and outer perforated tube 35 is provided as an extension of diffuser tube 32. Extended sound absorption is effected by passage of the stream through the annular passageway defined by the sound absorbing body surfaces.

The silencer of this invention is very flexible in its useful applications. While the taming of relatively violent flow is its forte, it is effective in pressure reduction applications, such as the quiet exhausting of steam under pressure to the atmosphere.

We claim:

1. In a plural stage gas stream silencer having circular shell means defining a plurality of treatment sections connected in series for the flow of a gas stream there through, each section having a central inlet opening therein and at least the side walls of the shell means having their internal surfaces covered with a layer of sound absorbing material held in position by perforated inner shell means; the improvement wherein a diffuser tube is mounted in each inlet opening and extends downstream therefrom into but not through the associated treatment section; each said tube being open at its upstream end, closed at its downstream end and having its side walls perforated; the distance from said perforated side walls to the perforated inner shell means surrounding the same being greater than four times the diameter of the perforations in said side walls; the sound absorbing material of the layer surrounding said diffuser in the treatment section at the inlet end of the silencer consisting of a durable material such as metal turnings; the layer of sound absorbing material of succeeding treatment sections comprising material having high sound absorption capability such as punched hairfelt or glass fiber.

2. Structure in accordance with claim 1 wherein the distance from the perforated side walls to the perforated inner shell means surrounding the same is from four to twenty times the diameter of the perforation in said side walls.

3. Structure in accordance with claim 1 and including a layer of vibration damping material surrounding the shell means defining the treatment section at the inlet end of the silencer to minimize the radiation of noise from said shell means to the atmosphere.

4. Structure in accordance with claim 1 wherein the shell means defining adjacent sections are connected together with resilient material sandwiched between and separating contiguous shell means structure whereby to minimize the transmission of vibration from the shell means of one section to the shell means of the adjacent section.

5. Structure in accordance with claim 4 wherein the joints connecting adjoining treatment sections comprise flanges mounted upon the respective shell means. a layer of resilient material arranged between said flanges. and fastening means drawing and holding the flanges together with said layer sandwiched therebetween.

6. Structure in accordance with claim 4 wherein the joint connecting adjoining treatment sections comprise spaced telescoping end portions of the shell means and a layer of resilient material filling the space between said telescoping end portions. and means fastening said telescoping end portions together with said resilient material sandwiched therebetween.

7. Structure in accordance with claim 1 wherein the outlet end of the final treatment section of the silencer is provided with means for connection thereto of an additional treatment section whereby the degree oftreatment of the gas stream may be increased at some time after the initial installation and use of the silencer.

8. Structure in accordance with claim I and including a downstream extension of a diffuser tube. said extension having a layer of sound absorbing material exposed to the gas stream and defining with the inner shell an annular passageway for the gas stream.

9. Structure in accordance with claim 8 wherein the extension of the diffuser tube in in the final treatment section of the silencer.

10. Structure in accordance with claim 1 wherein the shell means in conical, the small end being the inlet end of the silencer and the large end being open to the atmosphere.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,894,610

DATED July 15, 1975 INVENTOWS) i Edmund John Halter; John Charles Lanpher It rs certrfred that error appears rn the ahove rdentrfied patent and that said Letters Patent are hereby corrected as shown below:

Col. 3 line 38 6 line 15 6 line 33 line 36 C01. C01. C01. 6

[SEAL] Attest.

RUTH C. MASON Arresting Officer Signed and Scaled this fourzeentir Day Of October 1975 C. MARSHALL DANN Commissioner nfPaIenls and Trademarks

Claims

1. In a plural stage gas stream silencer having circular shell means defining a plurality of treatment sections connected in series for the flow of a gas stream therethrough, each section having a central inlet opening therein and at least the side walls of the shell means having their internal surfaces covered with a layer of sound absorbing material held in position by perforated inner shell means; the improvement wherein a diffuser tube is mounted in each inlet opening and extends downstream therefrom into but not through the associated treatment section; each said tube being open at its upstream end, closed at its downstream end and having its side walls perforated; the distance from said perforated side walls to the perforated inner shell means surrounding the same being greateR than four times the diameter of the perforations in said side walls; the sound absorbing material of the layer surrounding said diffuser in the treatment section at the inlet end of the silencer consisting of a durable material such as metal turnings; the layer of sound absorbing material of succeeding treatment sections comprising material having high sound absorption capability such as punched hairfelt or glass fiber.

5. Structure in accordance with claim 4 wherein the joints connecting adjoining treatment sections comprise flanges mounted upon the respective shell means, a layer of resilient material arranged between said flanges, and fastening means drawing and holding the flanges together with said layer sandwiched therebetween.

6. Structure in accordance with claim 4 wherein the joint connecting adjoining treatment sections comprise spaced telescoping end portions of the shell means and a layer of resilient material filling the space between said telescoping end portions, and means fastening said telescoping end portions together with said resilient material sandwiched therebetween.

7. Structure in accordance with claim 1 wherein the outlet end of the final treatment section of the silencer is provided with means for connection thereto of an additional treatment section whereby the degree of treatment of the gas stream may be increased at some time after the initial installation and use of the silencer.

8. Structure in accordance with claim 1 and including a downstream extension of a diffuser tube, said extension having a layer of sound absorbing material exposed to the gas stream and defining with the inner shell an annular passageway for the gas stream.