Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.
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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
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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
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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.
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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
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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.
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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
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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.
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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
15
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
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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
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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.
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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
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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
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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.
30
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