Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
2000-03-23
2002-02-05
Nappi, Robert E. (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
C181S210000
Reexamination Certificate
active
06343672
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device that reduces noise arising from venting at high pressure of a high mass flow rate stream of fluid, to an environmentally acceptable level, and releases the resulting jet at subsonic velocity. In a number of industries, high pressure fluid systems, typically gaseous, 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 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 silencers for jet noise, in particular, for high flow rate releases from high pressure fluid facilities.
A need clearly exists for a device inhibiting 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 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. Pat. No. 5,036,948, issued August 1993, U.S. Pat. No. 1,425,637 issued April 1890, U.S. Pat. No. 1,666,257 issued Apr. 17, 1928 and U.S. Pat. No. 4,953,659 issued Sep. 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 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.
The alternative approach is to pass the fluid through one or more perforated plates as illustrated by U.S. Pat. No. 5,266,754 issued Nov. 30, 1993 and U.S. Pat. No. 3,889,776 issued Jun. 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 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 streams in radial and tangential directions along an energy adsorbing surface and then subsequently through a tightly packed layer of granular material.
The present invention seeks to provide a rugged and simple jet noise inhibition device which may be used with jets vented at high flow rate from a high pressure fluid facility.
SUMMARY OF THE INVENTION
The present invention provides a fluid jet pressure and velocity reducing and noise suppressing device, comprising in cooperating arrangement, an inlet, an annular base, an annular cylindrical dissipative swirling member, a dissipative annular shroud member and a diffuser. The inlet is adapted to cooperate with and receive a fluid stream from a stack of a high pressure system. There is an annular base for receiving the inlet.
The annular cylindrical dissipative swirling member, has an internal diameter at least equal to or larger than the diameter of the inlet and an external diameter less than the diameter of the base. The swirling member comprises an annular array of enclosed radially outwardly extending swirling channels, wherein 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 walls defined by a set of vanes mounted on the base around the inlet, to deflect, swirl and discharge the fluid stream in a radially outward and tangential manner.
The dissipative annular shroud member comprises: (i) a housing mounted on the base, having an internal diameter larger than the external diameter of the swirling member and (ii) an inner core mounted on the top of the annular dissipative swirling member, the inner core comprising a first part in the form of a cylindrical segment with a diameter substantially the same as the external diameter of the annular dissipative swirling member, and a second part in the form of a conical segment having a diameter at its base substantially equal to the diameter of the cylindrical segment.
The diffuser is mounted upon the housing and has an opening at its lower end at least as large as the diameter of the external housing and has 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 the diffuser is atmospheric and the velocity of the fluid jet is subsonic. The diffuser is tightly packed with discrete particulate packing and the diffuser has first and second grates to retain the particulate packing in the diffuser.
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 dividing the inlet stream into a plurality of streams and deflecting the resulting streams 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 direction of flow to reduce further the resulting exiting jet to subsonic flow conditions.
REFERENCES:
patent: 1425637 (1922-08-01), Eschholz
patent: 1666257 (1928-04-01), Furnivall
patent: 3889776 (1975-06-01), Postma
patent: 4953659 (1990-09-01), Norris
patent: 5036948 (1991-08-01), Henn
patent: 5166479 (1992-11-01), Gras et al.
patent: 5266754 (1993-11-01), Swift
patent: 5962822 (1999-10-01), May
patent: 6202785 (2000-03-01), Hilling et al.
patent: 6161646 (2000-12-01), Curl
Jungowski Wiktor
Petela Grazyna
Bereskin & Parr
Lockett Kim
Nappi Robert E.
NOVA Gas Transmission Ltd.
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