CA2233072C - Blowdown and venting jet noise suppressor - Google Patents

Abstract

The present invention relates to a noise suppressor capable of reducing the noise of a fluid vented at high pressure and high mass flow rate from an industrial source, to the environmentally acceptable noise level. The invention combines two principles of dissipation of fluid stream energy: first, stream pressure is reduced by passing the stream through a swirler to split the stream into a number of smaller tangential streams which dissipate their energy along the spiral flow path due to friction; and next, the resulting streams pass through a tightly packed granular bed to reduce further the pressure and velocity of the exiting jet to atmospheric pressure and subsonic velocity, respectively. Such jet will generate much lower noise level, as compared to high pressure jet with cellular structure and supersonic velocity.

Description

SLOWDOWN AND \/ENTING JET NOISE SUPPRESSOR
FIELD OF THE INVENTION
The present invention relates to a device that reduces high pressure of a high mass flow rate stream of fluid, to atmospheric pressure level, and releases the resulting jet at subsonic velocity. In a number of industries high pressure fluid systems, typically gaseous, 1o need to be vented. There are a number of constraints on such systems. In an emergency situation (e.g. fire at a compressor station for a pipeline) the fluid venting time must be very short. Additionally, the noise of the venting jet has to be reduced to the level that complies with environmental noise control standards.
BACKGROUND OF THE INVENTION
Many industrial processes require the release of high pressure fluid, such as gas, into the atmosphere. This type of release may occur through, for example, stacks or vents equipped with safety or relief valves which are installed in compressor stations, gas metering stations, cryogenic facilities and power plants. Typically, without any additional noise suppression devices, such releases will result in a supersonic or sonic jet causing significant noise pollution. Generally, in 3o industrial facilities, such a jet will have a noise level of at least about 120 decibels (dB), measured at app. 50 m from the source, similar to the noise of a jet engine. There are a number of laws and regulations to protect workers and the general public against noise pollution.
Therefore, there is an increasing need for effective and inexpensive M:\TREVOR\TTSpec\9147can.doc 2 silencers for jet noise, in particular, for high flow rate releases from high pressure fluid facilities.
A need clearly exists for a device preventing excessive noise generation (i.e. a device which reduces the amount of noise generated to the acceptable level but does not necessarily prevent all noise).
Such device should be effective, simple to construct, robust, and of a so relatively compact size so that it may be transported, or even constructed as a portable one, (e.g. for the blowdown of a pipeline for routine maintenance).
Generally, mechanical silencers or mufflers seek to throttle the exhaust fluid jet to reduce jet pressure and velocity. This can be accomplished when the jet is passed through a porous packing such as sinter or sponge, as disclosed in U.S. patent 5,036,948, issued August 1993, U.S. patent 1,425,637 issued April 1890, U.S. patent 1,666,257 issued April 17, 1928, and U.S. patent 4,953,659 issued Sept. 4, 1990. However the porous materials used in the above inventions are suitable for low mass flow rates of the attenuated fluid.
Based on similar principle is the concept of flow through metal discs with expanding passage grooves, which is utilized in the commercially 3o available "atmospheric resistors", sold by Control Components Inc. of California, U.S.A. However, in this case, the fabrication of the disks is very expensive and the disk stacks are large and very heavy. These limitations are avoided by the hemispherical "excessive noise preventer", in which fluid is throttled by a granular layer of spherical particles, as disclosed in Canadian Patent Application 2,082,988.
M:\TREVOR\TTSpec\9147can.doc 3 The alternative approach is to pass the fluid through one or more perforated plates as illustrated by U.S. 5,266,754 issued Nov. 30, 1993 and U.S. 3,889,776 issued June 17, 1975. This approach seeks to also break up the stream into a number of smaller streams, but the perforated plates are not sufficiently effective in noise suppression.
The mufflers which utilize a combination of the perforated plates and l0 sound attenuating lining, are also commercially available from e.g.
American Air Filters and Acoustic Lining Co., but these devices have extremely large dimensions and are very expensive.
None of the art teaches or suggests the use of "swirler" to break up the stream and concurrently direct a number of radially tangential streams along an energy adsorbing surface and then subsequently through a tightly packed layer of granular material.
The present invention seeks to provide a rugged, simple and transportable jet noise suppressor effective with jets vented at high flow rate from high pressure fluid facility.
SUMMARY OF THE INVENTION
The present invention provides a fluid jet pressure and velocity reducing and silencing device, comprising in cooperating arrangement:
3 o A. an inlet adapted to cooperate with and receive a fluid jet from a stack of a high pressure system;
B. an annular base receiving said inlet;
C. an annular cylindrical dissipative swirling member, having an internal diameter equal to the diameter of the inlet and an external diameter less than the diameter of the base, comprising M:\TREVOR\TTSpec\9147can.doc 4 an annular array of enclosed horizontal radially extending swirling channels, provided the sum of the minimum cross section areas of the channels is not less than the cross section of the inlet, said charnels having vertical walls defined by a set of equi-length vanes mounted on the upper surface of said base around the inlet, to deflect, swirl and discharge the fluid stream so in a radial and horizontal manner;
D. a dissipative annular shroud member comprising:
(i) a cylindrical external housing mounted on said base, having an internal diameter equal to the diameter of said base;
(ii) an inner core mounted on the top of the annular dissipative swirling member, said inner core comprising a lower part in the form of a cylindrical segment with a diameter essentially the same as the external diameter of said annular dissipative swirling member, and an upper part in the form of a conical segment having a diameter at its base essentially equal to the diameter of the cylindrical segment and a height to bring the height of the so inner core to essentially the height of the external housing, the angle of the surface of said conical segment off vertical being less than 45°; and E. upwardly extending diffuser being mounted upon the external housing and having an opening at its lower end of the same diameter as the internal diameter of said external housing and M:\TREVOR\TTSpec\9147can.doc 5 having one or more outwardly sloping walls defining a final opening of a size so that the pressure of the fluid jet at the exit of said diffuser is atmospheric and the velocity of the fluid jet is subsonic, said diffuser being packed with discrete particulate packing and having grills at its exit and inlet to retain said particulate packing.
1o The present invention also provides a process to vent a fluid under pressure up to 15,000 kPa, to atmospheric pressure at a subsonic velocity within a period of time adequate for an emergency shut down of the high pressure fluid system, which comprises passing said one or more jets of said fluid through one or more devices as described above.
Further, the present invention provides a process to reduce the pressure and velocity of a sonic or super sonic fluid jet. The process comprises restructuring the said jet into the stream which is split and deflected so that the resulting streams are directed into contact with one or more high friction surfaces to dissipate the energy of the resulting streams and passing the resulting streams through a layer of granular packing having an increasing cross section area in the 3o direction of flow to reduce further the resulting exiting jet to subsonic flow conditions.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic sectional view of a suppressor in accordance with the present invention.
M:\TREVOR\TTSpec\9147can.doc Figure 2 is a side view of a swirler in accordance with the present invention.
Figure 3 is a sectional top view through A-A of the swirler of figure 2.
Figure 4 shows the results of the suppressor prototype performance testing and compares noise spectra and overall noise so levels generated by a free unsilenced jet exiting the stack in the absence of the suppressor, with the noise generated by the jet exiting the suppressor installed on the 2" stack.
BEST 61lIODE
The suppressor of the present invention is useful in association with the high pressure, high flow rate discharge of a supersonic or sonic fluid, generally gaseous, jet. Generally, the jet will be released at flow rate up to 600 kg/sec from facilities with fluid pressure up to 15,000 kPa (about 2,175 psi). Although the suppressor may be used for other applications it is particularly useful in a pipeline environment and in particular a natural gas (methane) pipeline.
In the device of the present invention noise suppression is based on the two equally important principles: firstly, to reduce stream pressure by 3o restructuring stream aerodynamics into a swirl and to dissipate its energy along the spiral flow path due to friction, and secondly, to reduce the stream velocity to a subsonic level by forcing the swirled flow through the layer of granular material.
This process of pressure and velocity reduction occurs in the noise suppressor of the present invention, which consists of the M:\TREVOR\TTSpec\9147can.doc 7 following parts: the swirler, which restructures the stream into a number of swirling streams; the annular shroud, preferably having the inner walls threaded to increase friction and to dissipate energy of the swirled stream; and the exit diffuser which contains, between its perforated bottom and top grates, a layer of tightly packed granular material which creates a tortuous path for the flowing swirled steam 1o and reduces further the exiting jet pressure to an ambient level and jet velocity to a subsonic level at the diffuser outlet.
One embodiment of a noise suppressor in accordance with the present invention will now be described in conjunction with figure 1.
The noise suppressar of figure 1 comprises the following elements. The noise suppressor is mounted on a vent from a high pressure vessel or line (not shown in the drawing), using a flange member 2. The flange member is annular in shape having an internal opening of a size to accommodate the inlet 1, which is a pipe segment.
Flange member 2 is adapted to cooperate with a corresponding flange member at or adjacent to, the exit of the stack (not shown). While a flange member 2 is shown in the drawing, other means for attaching the noise suppressor to the stack could be used. For example the inlet 1 could fit snugly either over or in the vent, or the inlet could be welded to the vent. A number of other mechanical equivalents will be obvious to those of skill in the art. The inner diameter of the inlet 1, is not smaller than that of the stack or vent from the high pressure fluid system.
M:\TREVOR\TTSpec\9147can.doc The inlet 1 passes into or through the annular base 13 of the suppressor. The inlet i opens into a swirler 3 in the interior of the suppressor, in accordance with the present invention. The swirler has an internal diameter equal to the external diameter of the inlet 1 and an external diameter less than the diameter of the annular base 13. The swirler comprises an annular array of enclosed horizontal radially extending swirling channels, provided the sum of the minimum cross section areas of the channels is not less than the cross section area of the inlet. The channels have vertical walls defined by a set of equi-length vanes mounted on the upper surface of said annular base around the inlet, to deflect, swirl and discharge the fluid stream in a radial and horizontal manner. Preferably the vanes are uniformly spaced in a radial manner around the inlet. The swirler 3 may be fabricated in any number of ways. It could be formed by attaching a number of vanes to the base 13 or it could be formed by casting, milling or welding vanes, to provide the enclosed channels. That is the channels have a base, which may be the upper surface of the base 13 or a part of a molded, milled or welded component walls which are the vanes, and a closed top which defines the upper surface of the 3o channel. The top may be an integral part of the swirler (e.g. cast or machined or a welded part) or it may be attached to or dependent from the base of the inner core 12. The vanes may be straight or curved or may be in the form of wedges. The vanes must be such that the channels deflect the resulting streams in a radially tangentially outward manner. The channels preferably deflect the streams in a horizontal M:\TREVOR\TTSpec\9147can.doc manner but they might be inclined at an angle of up to 15° up from the horizontal. Most preferably, the vanes have a deflective angle of greater than 5°. That is the angle of the vane from the radius is greater than 5°, typically from 5 to 25°. One of the possible means to construct the swirler is shown in Figures 2 and 3, where the swirler is cast with the annular base 'I 3, vanes 3, and the upper top 15 as so integral parts.
The streams from the swirler are discharged into a dissipative annular shroud member generally indicated as 4. The annular dissipative shroud member comprises a cylindrical external housing 11, having an internal diameter essentially the same as the diameter of the base 13, and an inner core having a lower part in the form of a cylindrical segment 12 and an upper part in the form of a conical segment 5. The cylindrical external housing 11 may be attached to the annular base 13 by a number of means. For example, the base could have external threads and the cylindrical external housing could have internal threads to engage the annular base. The swirler 3 could be welded or riveted or bolted, or even be an integral part of the annular base 13, as is shown in figure 2. The cylindrical segment 12 of the 3 o inner core may be mounted on the swirler, if the swirler is a unit construction or mounted directly on top of the vanes. The cylindrical segment may be attached to the vanes of the swirler by any conventional fixing means (e.g. welded, bolts or riveted, etc.). The upper conical segment 5 may be an integral part of the inner core or may be a separate part attached on top of the cylindrical segment 12.
M:\TREVOR\TTSpec\9147can.doc 1 O

The base of the conical segment 5 has a diameter the same as the diameter of the cylindrical segment 12. The angle of the surface of the conical segment off vertical is generally less than 45°, typically from to 30°. In a preferred embodiment of the invention, the internal surface of the cylindrical housing 11, and/or the external surface of the inner core (either or both of the cylindrical segment 12 and conical segment so 5), may be threaded to provide an increased friction surface that the stream has to pass over. The threads, if present, may have a depth from 5-8 mm.
The downstream end of the shroud inner core, shaped in the form of a conical segment 5, ensures gradual expansion of the shroud cross section area from the annular shape to the full circle. The geometry of the conical segment, characterized by 'the angle a,, which should not be larger than 45°, ensures a smooth flow transition between the annular and circular passage areas. Larger a angles may create flow disturbance and separation of the swirled stream from the core wall at the shroud exit.
The major function of the dissipative shroud 4 is to dissipate jet energy and to promote a large pressure drop. This is achieved by increasing friction along the threaded shroud walls, and by lengthening 3o the flow path with the swirling motion of the stream.
In the embodiment shown in figure 1 there is a flange 10 mounted externally at the upper end of the dissipative shroud member.
The flange is illustrative of one of the means to mount and attach the diffuser 6 on top of the dissipative shroud member. The diffuser 6 could be attached to the upper end of the dissipative shroud member M:\TREVOR\TTSpec\9147can.doc 11 by a number of mechanical equivalents such as by welding, bolts or rivets.
The diffuser comprises an inverted truncated cone 6. The angle of the wall of the truncated cone off vertical may be from 10° to 50°.
Other shapes, for example square, could also be used for the diffuser.
In the figure 1 the base of the inverted truncated cone is attached to a to flange 9. The flange 9 attaches to flange 10 at the upper end of the annular dissipative shroud. In figure 1, the cone walls of the diffuser 6 do not project to the exit of the annular dissipative shroud. However, this was done only for ease of fabrication and it represents an optional feature, because the truncated diffuser cone 6 could extend to the outlet of the dissipative shroud member.
In accordance with the invention there are grates at the inlet and at the exit of the diffuser 6, to provide opening for fluid flow and to contain packing. In the emfoodiment shown in figure 1 there is the plate 7 having a grating therein. The grating provides an opening for the fluid flow from the dissipative annular shroud member. In figure 1 the plate 7 is held in place by the diffuser flange 9 and the dissipative shroud flange 10. At the upper end of the inverted truncated cone 3 o diffuser is a rim 14. On the top of rim 14 is a second upper grate 8. In the figure 1, the upper grate was welded on to the rim. The rim was used to provide for ease of welding the grate to the diffuser and it represents an optional feature, because the grate 8 could be fixed directly to the top of the diffu$er. The diffuser is tightly packed with granular packing 15. The size of the perforation in both plates should M:\TREVOR\TTSpec\9147can.doc 12 be sufficiently large to provide no flow restriction for the stream, but also sufficiently small to contain the smallest pieces of the granular packing. The granular packing or particulates 15 may be of regular shape such as spheres as shown in the drawing. While spheres are shown, other regular shapes could be used. The granular packing could be irregularly shaped. Gravel provides cheap granular packing.
to The granular packing in the diffuser creates the tortuous path for the flow of the stream, which results in a further pressure and velocity reduction of the fluid. The achieved reduction depends on the thickness of the granular layer and on the angle (~i) of the wall of the conical diffuser off vertical.
The diameter or size of the opening at the exit of the diffuser is such that at the exit there is no constraint on the flow of the fluid out of the suppressor and the velocity of fluid is subsonic. The height of packing to obtain a pressure drop to atmospheric pressure may be calculated based on principles for fluid (gas) flow through a packed granular bed. Once the bed height is determined and the size of the exit from the diffuser is calculated, the angle of the wall of the diffuser is determined as a 'Function of the exit opening and the bed height (e.g. for a given inlet diameter or size and outlet or exit diameter or size and bed height, the uniquely defined angle will give the required dimensions).
3o The operation of the suppressor will now be described.
A high pressure fluid (gaseous) stream vertically enters the inlet of the suppressor, and flows into i:he swirler. The fluid is there divided among the swirler channels into the smaller streams, which are discharged horizontally from the channel exits into the dissipative shroud, at radial angles consistent with the curvature of the swirling vanes.
M:\TREVOR\TTSpec\9147can.doc 13 The swirling streams, after impinging and mixing at the bottom of the shroud, flow upwards through the annular cross section of the shroud. The increased flow path, due to a swirling motion of stream and the increased friction along the threaded walls of the shroud, results in substantial pressure losses.
The stream exits the shroud and enters the diffuser through the bottom Zo perforated grate. It flows through the increasingly large cross sections of the granular bed, which creates the tortuous path for the flow. As a result, the stream is throttled and dissipated into even smaller streams, which are of low turbulence, low velocity, and they experience further pressure losses combined with the simultaneous velocity reduction. The jet flow exits the diffuser through the top perForated grate, at the atmospheric pressure and with a subsonic velocity. Accordingly, noise generated by the jet is significantly reduced.
Example The present invention will now be illustrated by the following non-limiting example.
A prototype according to the present invention was constructed and installed on a 2" vent stack at a natural gas compressor station, in order to 3o reduce the level of the venting noise. The jet noise suppressor was similar to the one shown in figure 1, vvith the dimensions given below.
(a) The inlet was a segment of 2" pipe, having an inner diameter of about 52.5 mm.
(b) The swirler was a fabricated part (cast) and had the following dimensions: the annular base diameter was 200 mm; the outer M:\TREVOR\TTSpec\9147can.doc 14 diameter of the swirling vanes was 100 mm; the diameter of upper plate was 100 mm; and the height of the swirling vanes was 21 mm.
(c) The dissipative shroud was made of an NPS-8/schedule-80 pipe segment, with the inner diameter of 194 mm; the inner core of the shroud was made of NPS-4 pipe having an outer diameter of 100 mm.
The interior walls of the shroud were threaded approximately 5 mm to deep. The conical segment of the inner core had an angle off vertical of 45° and a height of 120 mm.
(d) The conical diffuser had a granular bed height of 300 mm and the angle off vertical was 30°. The cylindrical diffuser base had diameter of 362 mm, to accommodate the shape of the conical diffuser shown with the dotted line "c" in figure 1, and to ease manufacturing. The height of the diffuser rim was 50 mm.
(e) The perforated grates that constituted bottom and top grills of the diffuser, had a multiplicity of 4 mm in diameter holes with staggered centers. The thickness of the bottom plate was approximately 25 mm, while the thickness of the upper plate was approximately 12.7 mm.
(f) The conical diffuser of the suppressor was filled with satellite shaped (i.e. a cylindrical middle and two hemispherical ends) alumina 3 o granules.
Natural gas at a mass flow rate of 16.0 kg/s, at stagnation pressure of approximately 6000 kPa and at temperature 10~C, was vented through the above described suppressar.
The testing was carried out with two sizes of granular fillings. The first filling was of uniform granules having an average diameter of 9 mm. The M:\TREVOR\TTSpec\9147can.doc 15 second filling contained a mixture of approximately equal amounts of granules having an average diameter of 6 mm and 9 mm.
The noise level generated by the venting was significantly reduced by the device in comparison to the free venting in the absence of the noise suppressor. The suppressor containing the mixture of two sizes of granular filling in the diffuser provided noise attenuation from overall sound pressure so level (OSPL) of 118 dB, measured at 45 m, by more than 40 dB, to almost background noise, as shown in figure 4. This result was approximately 3 dB
better than the noise attenuation obtained with the suppressor with uniform larger filling. The levels (SPL) of all noise components in the spectrum were significantly suppressed, what indicates effective suppressor performance in the entire frequency range, up to 20 kHz.

M:\TREVOR\TTSpec\9147can.doc 16

Claims (27)

1. A fluid stream pressure and velocity reducing and silencing device comprising in cooperating arrangement:
A. an inlet adapted to cooperate with and receive a fluid jet from a stack of a high pressure system;
B. an annular base receiving said inlet;
C. an annular cylindrical dissipative swirling member having an internal diameter equal to the diameter of the inlet and an external diameter less than the diameter of the annular base, comprising an annular array of enclosed horizontal radially extending swirling channels, provided the sum of the minimum cross section areas of the channels is not less than the cross section of the inlet, said channels having vertical walls defined by a set of equi-length vanes mounted on the upper surface of said base around the inlet, to deflect, swirl and discharge the fluid stream in a radial and horizontal manner;
D. a dissipative annular shroud member comprising:
(i) a cylindrical external housing mounted on said annular base, having an internal diameter equal to the diameter of said base;
(ii) an inner core mounted on the top of the annular dissipative swirling member, said inner core comprising a lower part in the form of a cylindrical segment with a diameter essentially the same as the external diameter of said annular dissipative swirling member, and an upper part in the form of a conical segment having a diameter at its base essentially equal to the diameter of the cylindrical segment and a height to bring the height of the inner core to essentially the height of the external housing, the angle of the surface of said conical segment off vertical being less than 45°; and E. upwardly extending diffuser being mounted upon the external cylindrical housing and having an opening at its lower end of the same diameter as the internal diameter of said external housing and having one or more outwardly sloping walls, defining a final opening of a size so that the pressure of the fluid jet at the exit of said diffuser is atmospheric and the velocity of the fluid jet is subsonic, said diffuser being tightly packed with discrete particulate packing and having grills at its exit and inlet to retain said particulate packing.

2. The device according to claim 1, wherein said diffuser is tightly packed with regularly shaped particles

3. The device according to claim 2 wherein said diffuser is tightly packed with spherical particles.

4. The device according to claim 1 wherein said diffuser is tightly packed with irregular particulate packing.

5. The device according to claim 4 wherein said diffuser is tightly packed with gravel.

6. The device according to claim 1, wherein the angle of the walls of said diffuser is from 10° to 50° off vertical.

7. The device according to claim 6, wherein said upwardly extending diffuser is an inverted truncated cone.

8. The device according to claim 7, wherein in the diffuser the angle of the surface of said upper truncated cone off perpendicular is from 10° to 50°.

9. The device according to claim 1, wherein in said annular dissipative swirling member said vanes are uniformly radially spaced.

10. The device according to claim 9, wherein said vanes have a deflective angle between 5° and 15°.

11. The device according to claim 10, wherein said vanes have straight parallel deflective edges.

12. The device according to claim 10 wherein said vanes are wedged shaped.

13 The device according to claim 10, wherein said vanes are curved.

14. The device according to claim 1, wherein the internal surface of the external housing has threads having a depth from 5 to 8 mm.

15. The device according to claim 1, wherein the external surface of the inner core member has threads having a depth from 5 to 8 mm.

16. The device according to claim 14, wherein the external surface of the inner core member has threads having a depth from 5 to 8 mm.

17. The device according to claim 1 wherein at least one grill on said diffuser is removable.

18. A process to vent a fluid under pressure up to 15,000 kPa to atmospheric pressure at a subsonic velocity within a period of time adequate for an emergency shut down of the high pressure fluid, which comprises passing one or ore streams of said fluid through a device according to claim 1.

19. A process according to claim 18 wherein said time is less than 5 minutes.

20. A process to vent a fluid from a system under pressure up to 15,000 kPa, to atmospheric pressure at a subsonic velocity within a period of time adequate for a planned shut down of the high pressure fluid system, which comprises passing said one or more jets of said fluid through one or more devices according to claim 1.

21. The process according to claim 18 wherein said fluid under high pressure is in a pipeline.

22. The process according to claim 19 wherein said fluid under high pressure is in a pipeline.

23. The process according to claim 20 wherein said fluid under high pressure is in a pipeline.

24. The process according to claim 21 wherein said fluid is natural gas.

25. The process according to claim 22 wherein said fluid is natural gas.

26. The process according to claim 23 wherein said fluid is natural gas.

27. A process to reduce the pressure and velocity of a sonic or super sonic fluid jet which comprise restructuring the jet into the stream which is next split and deflected so that the resulting streams are directed into contact with one or more high friction surfaces to dissipate the energy of the resulting stream and passing the resulting stream through a layer of granular packing, having an increasing cross section area in the direction of flow to reduce further the exiting jet to subsonic flow conditions.