Note: Descriptions are shown in the official language in which they were submitted.
CA 02393162 2002-07-15
"Modular Gas Diffuser"
Background of The Invention
I . Field of the Invention
This invention relates in general to gas diffusers and more particularly to an
improved gas
diffuser for use in aquaculture.
2. Prior Art
Diffusers are used in many water treatment applications including aquaculture,
wastewater treatment and other water treatment applications, such as stripping
of
dissolved gases or pH adjustment. A variety of gases may also be used in
diffusers
including, but not limited to, air, oxygen, ozone or carbon dioxide.
In aquaculture applications, the application of each gas used is as follows:
air and oxygen
are used to increase the oxygen content of the water, carbon dioxide is used
for
anesthetizing aquatic species and ozone is used top disinfect water.
When using a pure gas, such as oxygen ui an aquaculture application, it is
very important
that the diffuser bubble size is as tine as possible. Smaller bubble size
increases gas
transfer rate and gas transfer efficiency in two ways:
1 ) Smaller bubbles rise slower, increasing their residence time.
2) Smaller bubbles have a higher surface area for a given volume of gas,
increasing the rate at which gas is transferred to the water.
CA 02393162 2002-07-15
C~trently, there are a variety of diffusers available, including: air stones,
disk diffusers,
tube diffusers, porous tubing and rectangular diffusers. A variety of
materials may be
used as diffusion media including porous ceramic, rubber or plastic. The
diffusion media
and type of diffuser selected is application dependent.
Large disk and tube diffusers are have been well developed and can be
exemplified by
U.S, Pat. Nos. 4,046,845, 6,244,574 B I, 4,865,778, 6,367,783 B 1, 4,118,447,
5,788,847,
3,977,606 and 4,243,616. The large disk and tube diffusers generally produce
relatively
large bubbles and are used extensively for wastewater treatment as well as for
aeration of
lakes and ponds. This style of diffuser is not useful in most aquaculture
applications for
the following reasons: the bubble size is too coarse for use with pure gases
such as
oxygen and the diffusers do not present a low enough profile to be useful in
culture or
transport tanks.
Air stones are generally rectangular or tubular in shape and are constructed
of fused silica
or plastic beads. Air stones produce relatively coarse bubbles and for that
reason are
unsuitable for use with pure gases such as oxygen.
Porous tubing includes: drilled ("leaky") pipe, porous rubber tubing and
porous plastic
tubing. Porous tubing, like air stones, produces relatively coarse bubbles and
is generally
considered unsuitable for use with pure gases.
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Plate diffusers consist of a very fine porous ceramic or porous plastic plate,
bonded to a
plastic or aluminum support frame using an adhesive such as epoxy. Porous
ceramic is
the preferred material because it tends to produce finer bubbles than porous
plastic and is
more robust. Plate diffusers are used extensively in aquacultare to dissolve
pure gases
such as oxygen and carbon dioxide. The fine pore structure of plate diffusers
creates a
cloud of bubbles, generally 10 - 500 ~m in diameter, which allows higher gas
transfer
efficiencies than for other diffusers with coarser bubbles.
Plate diffusers are generally rectangular and are supplied in a variety of
lengths
depending on the required gas flow. The main disadvantages of ceramic plate
diffusers
are that if even a small part of the ceramic plate cracks, the entire diffuser
must be
discarded also, if additional diffusing capacity is required, more diffusers
must be added
to increase capacity. To help mitigate the cost involved when a single, large
diffuser
breaks, a large number of smaller diffusers may be used. The use of smaller
diffusers is
undesirable, however, because they are unwieldy and inconvenient. Another
disadvantage
of the plate diffusers is that there is no ability to easily adjust weight
with ballast. In some
applications, it is desirable to maximize the diffuser weight (for example in
fast flowing
water so that the diffuser doesn't move). In other applications (stagnant
water) it is
desirable to minimize the diffuser weight to increase ease of handling.
It is therefore an object of the invention to provide a device to diffuse
small gas bubbles
into a liquid wherein the said device consists of a number of interlocking
diffuser
elements, each of which is replaceable, should it fail. It is also an object
of the present
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CA 02393162 2002-07-15
invention to provide such a device, which is of simple and inexpensive
construction.
Another object is to provide such a device that can easily be disassembled for
cleaning
and is of modular construction so that a diffuser of the desired capacity may
be easily
assembled from the component parts. A further object is to provide a diffuser
where the
weight of the component parts can easily be adjusted to achieve the desired
buoyancy for
the specific application.
Summary of The Invention
The above objects are satisfied with a diffuser made in accordance with the
present
invention. The diffuser generally includes three component parts: an inlet end
piece, a
diffuser element and a cap end piece.
The inlet end piece consists of a molded housing containing an inlet fitting
for connection
to the gas supply line and an outlet, which provides a pressure tight
connection with a
diffuser element, or cap end piece. The inlet fitting may consist of, but is
not limited to:
either a threaded metallic insert or a "push to-connect" fitting. A cavity in
the interior of
the inlet end piece allows a ballast of the desired density to be added. A
bottom plate
attaches to the end piece to contain and protect the ballast. On the side of
the inlet end
piece with the outlet, two dovetail connectors, one male and one female, allow
the inlet
end piece to mechanically connect to a diffuser element, or cap end piece. Two
small
locking tabs on the outlet side of the inlet end piece ensure that the
mechanical
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connection will not unintentionally disengage. Vertical holes through the
inlet end piece
allow attachment to a tank floor with screws or bolts.
The diffuser element consists of a molded housing containing a cavity on the
upper
surface where a porous material is attached to the housing. The porous
material may be
bonded to the housing using an adhesive, such as epoxy or it may be attached
by
mechanical means using a retaining ring and a rubber seal. The upper cavity is
designed
to allow unimpeded gas flow while providing sul$cient support for the porous
material.
A cavity in the lower interior of the diffuser element allows a ballast of the
desired
density to be added. A bottom plate attaches to the diffuser element to
contain and protect
the ballast. The diffuser element contains an inlet and outlet. The inlet
consists of a
female socket that fits the outlet of another diffuser element or the outlet
of the inlet end
piece and the outlet provides a pressure tight connection with the inlet of
another diffuser
element or a cap end piece. On the ends of the diffuser element with inlet and
outlet
fittings, there are two dovetail connectors, one male and one female on each
end, which
allow the diffuser element to mechanically connect to another diffuser element
or to the
appropriate end piece. Two small locking tabs on the each of the inlet and
outlet ends of
the diffuser element ensure that the mechanical connections will not
unintentionally
disenga~.
The cap end piece consists of a molded housing containing an inlet that
connects to the
fitting of a diffuser element. A cavity in the interior of the cap end piece
allows a ballast
of the desired density to be added. A bottom plate attaches to the cap end
piece to contain
CA 02393162 2002-07-15
and protect the ballast. On the end of the cap end piece with the inlet, two
dovetail
connectors, one male and one female; allowing the cap end piece to
mechanically connect
to a diffuser element. Two small locking tabs on the outlet side of the cap
end piece
ensure that the mechanical connection will not unintentionally disengage.
Vertical holes
through the cap end piece allow attachment to a tank floor with screws or
bolts.
Sloped sides on the inlet end piece, diffuser element and outlet end piece
allow
unimpeded fluid flow over a diffuser assembly and helps prevent sediment from
building
up on the upstream side of the diffuser assembly.
An assembled diffuser consists of one inlet end piece to which is attached a
plurality of
diffuser elements to which is attached a cap end piece. During operation, the
inlet end
piece is connected to a gas supply line and pressurized gas travels through
the assembled
diffuser by means of the inlet and outlet connection on each of the component
parts. The
cap end piece prevents gas leakage from the diffuser assembly. Once the
pressure within
the diffuser assembly has reached a threshold value, which depends on the pore
diameter
of the porous material, gas travels through the porous material in each
diffuser element
and diffuses into the process liquid. The dovetail connectors allow the
diffuser assembly
components to quickly be assembled and disassembled without tools.
Further details and advantages of the present invention will become apparent
to those
skilled in the art upon review of the following detailed description, claims
and drawings.
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Brief Description of the Drawings
FIG. 1 is a diagra~nrr~atic, fragmentary sectional elevation through a fish
culture tank
depicting the manner in which plate diffusers are typically installed.
FIG. 2 is a perspective view of an assembled four-element diffuser.
FIG. 3 is a perspective view of a diffuser element.
FIG. 4 is a perspective view of an inlet end piece.
FIG. 5 is a perspective view of a cap end piece.
FIG. 6 is a cross-sectional view of a single element diffuser.
FLG. 7 is a cross-sectional view of an alternative embodiment of the single
element
diffuser depicted in FIG. 6, showing an alternative means of securing the
porous material.
Detailed Description of the Preferred Embodiments
FIG. 1 illustrates a perspective view of a typical plate diffuser 3
installation in a fish
culture tank 1. The diffusers 3 are typical of plate diffusers currently used
in aquaculture
applications and are connected to a main gas supply by means of supply lines
2. The gas
used
FIG. 2 illustrates a perspective view of an assembled diffuser containing four
diffuser
elements. The diffuser is connected to a main gas supply by means of a supply
line 2. The
diffuser assembly is comprised of three component parts: an inlet end piece 4,
a plurality
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of diffuser elements 5 and a cap end piece 6. Each of the component parts
attaches to an
adjoining part by means of male and female dovetail connectors 7 allowing a
"twist-and-
lock" method of assembly. Sloped sides 8 streamline the diffuser assembly and
allow
water and debris to flow over the diffuser without obstniction. Mounting holes
9 in each
of the end pieces allow the diffuser assembly to be bolted to a mounting
surface, if
desired. A gap filling adhesive 10 is used to secure the porous media to the
diffuser
element housing and provide a pressure-tight seal. A plate of porous media 11
allows gas
bubbles to diffuse into the process liquid when the diffuser is pressurized.
FIG. 3 shows a perspective view of a single diffuser element. A female
dovetail
connector 12 and male dovetail connector 13 on the mating ends of the diffuser
element
allow connection with other component parts using a "twist-and-lock" motion.
Detent 16
and indent 17 locking tabs prevent mating parts from unintentionally
disengaging. The
gas outlet 14, allows gas to flow to adjoining diffuser elements. Dual o-rings
15 on the
gas outlet prevent gas leakage when the diffuser element is pressurized.
FIG. 4 shows a perspective view of an inlet end piece. A female dovetail
connector 12
and male dovetail connector 13 on the mating end of the inlet end piece allows
connection with a diffuser element using a "twist-and-lock" motion. Detent 16,
and
indent 17 locking tabs prevent the connection from unintentionally
disengaging. A "push
to-connect" fitting 18 provides a means whereby the inlet end piece may be
connected to
a gas supply line. The outlet 14, equipped with sealing o-rings 15 provides a
pressure-
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tight connection to a connected diffuser element. A mounting hole 9 provides a
means
whereby the inlet end piece may be attached to a mounting surface.
FIG. 5 shows a perspective view of a cap end piece. A female dovetail
connector 12 and
male dovetail connector 13 on the mating side of the cap end piece allows
connection
with the outlet side of a diffuser element using a "twist-and-lock" motion.
Detent 16, and
indent 17 locking tabs prevent said connection from unintentionally
disengaging. The
inlet 19 is a blind hole which, when connected to the outlet of a diffuser
element, blocks
it and prevents gas from escaping. A mounting hole 9 provides a means whereby
the cap
end piece may be attached to a mounting surface by means of bolts.
FIG. 6 shows a cross sectional view of an assembled, single-element diffuser.
Bottom
plates 20 and 21 contain the ballast 23. The housing of the diffuser element 5
contains a
series of ridges 24 and 25, which support the porous element. The inner ridge
24 is not
continuous so that it does not impede gas flow. A cavity 26 beneath the porous
media
allows gas to flow through the diffuser element and into the porous media.
FIG. 7 shows an alternative embodiment of the diffuser element. In this case,
the porous
material 11 is attached to the housing 5 by means of a mechanical seal. The
mechanical
seal consists of a threaded retaining ring 26 and a rubber seal 27.
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