Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Canada Dkt. 32
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BRIEF DESCRIPTION OF THE INVENTION
AND SUMMARY OF THE INVE~TIO~:
The invention relates to an improved method,
and submerged system for efficiently mixing gas with
waste water.
Industrial waste, sewage and ~he like are
commonly purified by pumping the liquid into a large
pond or basin where a bacteria population consumes the
inorganic and organic material. Because the
dissolved oxygen in the waste water is usually insuf-
ficient to support the required population of bacteria,
the water must be aerated. This can be done with a
surface aerating machine which has beaters extending
into the waste water from above the water surface to
agitate the water and incorporate air. Alternatively,
air can be diffused through the bottom of the basin, e.g.,
through a porous medium. Surface aerators are not
efficient and cause certain mechanical problems. The
energy loss of diffusing air is also great and a
diffused system is not suitable for installation in
an existing pond.
The waste water can also be aerated by pumping
through submerged tubes with Venturi openings
through which air is drawn or pumped into the tubes
to create turbulent mixing.
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The present invention relates to an improved
method and system for mixing a gas such as oxygen or
air with waste water. The system includes a plurality
or mixing chambers which are disposed below the surface
of the waste water and through which the water is
pumped from an inlet to an outlet. A suitable gas,
such as oxygen or air containing oxygen, is in~ected
into each of the mixing chambers at a step surface to
form parallel streams of air and water in an extending
chamber. As the two streams move down the extending
chamber, the interface between the two streams becomes
unstable and waves form which attach to the sides of
the chamber. This causes large frictional stresses,
creating tiny bubbles which mix with the water.
Since the water and air essentially ~low in the same
direction, no energy is wasted in turbulence and the system
is energy efficient.
This system can be quickly and easily installed
in any existing aeration pond without the need for the
system to be shut down for an extended period and
without the need for the pond to be drained, a
project which is dlfficult or impossible in most instances.
The system can, in fact, be installed and operating
within a few minutes. Incomparison with diffused air
~ 25 type devices and surface aeration systems, the energy
; required to incorporate a given amount of oxygen into
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the water is much less. Because lit~le energy is wasted
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in turbulent mixing , the present invention is more energy
efficient than Venturi, jet or impingement type systems
which depend on turbulent mixing. Further, ~he bubbles
which are produced are tiny, thus creating a good
environment ~or efective use of the oxygen by the
bacteria within the pond or basin. Many of the other
disadvantages of surface aerators and difusion type
devices are also avoided.
Other objects and purposes of the invention wi
be clear from the following detailed description of the
drawings.
BRIEF DESCRIPTION OF T~E DRAWTNGS:
FIGURE 1 shows a schematic side view of the
system of the present invention in use;
FIGURE 2 shows a planar view o~ the system
of FIGURE l;
FIGURE 3 shows a sectional view of a mixing
; chamber of the present invention without helical
vanes;
FIGURE 4 shows a front view of a mixing chamber
with helical vanes;
FIGURE 5 shows a partial sectional view of the
mixing chamber of FIGURE 4;
FIGURE 6 shows a schematic view of another
embodiment;
FIGURES 7 and 8 show a further embodiment.
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DETAILED DESCRIPTION OF THE DRAWINGS:
.
Reference is now made to FIGURES 1 and 2
which schematically illustrate one embodiment of
the present in~ention. In the embodiment of FIGURES
1 and 2, a plurality of circumferen~ially disposed mixing
chambers 20, each preferably identical to the othex,
are circularly disposed around a dome manifold 22
which includes an upper section 24 into which water
is pumped and a lower section 26 connected to a source
of air or oxygen at a suitable pressure. Each of the
mixing chambers is of the type shown in detail in
FIGURES 3-5 and discussed in detail below.
A plurality of conduits 30, each formed of a
metal segment 32 and a plastic segment 34, connect
section 24 to each mixing chamber 20 so that wat~r is
continuously pumped through each chamber 20. A
similar series of conduits 40, each formed of a metal
portion 42 and a plastic portion 44, connect section 26
to each of the mixing chambers 20. Each of the mixing
chambers 20 forms parallel streams of air and gas
which interact within an extending passage in the
mixing chamber to form tiny bubbles which efficiently
mix with the pumped waste water as it passes between
an inlet and outlet.
Manifold 22 is suspended from a fibreglass
floating work platorm 50 by means of guide bars 52, 54,
and two bars behlnd bars 52 and 54. Industrial air
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piping conduit 60 is attached to guide bar 54 for
supplying air to section 26. Cable 62 connects
the manifold 22 to a frame 64 on platform 50 for
lifting manifold 22 and holding manifold 22 in
position for maintenance.
Submerged pump 66 is mounted above mani-
fole 22 and includes a self-cleaning strainer has-
ket 67 over the pump intake which keeps most debris
from entering the pump~ For many installations the
basket can be omitted and the debris which collects
in the pump back-flushed as described below. When
a basket is used, the small particles which accumu-
late on the outside of basket 67 are removed by
flushing. Conduit 68 connects pump 66 to section 24.
Platform 50 is provided with suitable rail-
ings 7G of a height so that the unit can be lifted to
; a level for convenient work on the mixing chambers 20
and pump 66. An on-shore air pumP 74 is schemati-
cally shown as connected to line 60 for pumping air,
oxygen or other gas to section 26 for mixing with the
pumped waste water.
When it is desired to clean the inevitable
particles and debris which sill accumulate on basket
- 67, within pump 66 and within mixing chambers 20,
pump 66 can simply be turned off while the air pump
74 continues forcing air into mixing chambers 20.
Surprisingl~, instead of moving out of the outlet
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on each chamber, the air will pump waste water back
through the inlet, opposite to the direction of flow
during aeration, through conduits 34 and 32 into sec-
tion 22, through conduit 68 and through pump 66,
blowing off the debris which has accumulated on the
outside of strainer basket 67. This occurs because
the water pressure at the level of the strainer bas-
ket is lower than the water pressure at the level of
the mixing chambers 20. :~
Alternatively, flushing can be accomplishad
by operating a valve 76 in a line 78 which connects
to conduit 68. The debris will now be blown into
the air and since the pressure differential is greater,
the force produced, by the air which works as an
air hammer, will blow the debris tnrough the system
and back-flush all of the material in a few minutes.
FIGURES 3-5 illustrate two embodiments of
the unique mixing chamber 20 of the present inven-
tion. Waste water flows from the inlet through passage
lO0 into the extending chamber 102. At the inter-
section between passage lO0 and section 102, a step
surface lO4 is provided at which a plurality of
bores terminate. The bores inject gas at an angle
between roughly ll and 22-l/2. To keep the vortices
within chamber 102 at high air pressures, a chamber
110 with helical vanes 106 as shown in FIGURES 4
and 5 creates greater wave generating conditions, as
the water enters an extending chamber (not shown)
similar to the chamber shown in FIGURE 3.
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Thus, two parallel streams of gas and waste
water are created as shown in FIGURE 3. As the
streams move along the chamber 102, the friction
between them causes waves to form and air thus
trapped in the waves to disperse into tiny bubbles.
Since the air and gas streams move in the same direc-
tion, effective mixing is achieved at minimum
energy consumption. It is desirable that under most
conditions the mixing take place within chamber 102
and for tha* reason the chamber is slightly tapered
inwardly within the portion llO with the cross-
section decreasing in the direction from inlet to
outlet and more radically tapered inwardly within
portion 112 at a rate greater than ~or section 110.
These tapers extend the maximum air flow rate with
which the system will operate by several times
without substantial loss of efficiency.
The helical gulde vanes 106 provide a twist-
ing motion to the air and thus create more waves which
also help the interface break up more quickly by
creating instability.
The mixing chambers can be made of any suit-
able materials such as stainless steel, aluminum or
plastic.
FIGURE 6 shows another embodiment in which
the submersible pump is replaced with a conventional
waste water pump 200 mounted beside tank 202 and
connected to manifold 204 by line 206. Pump 200
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has an inlet 207. A plurality of mixing chambers 208
are mounted about manifold 204 and can be any suit-
able mixing device such as a jet, vortex, Venturi or
impingement type device. Aix pump 21Q is also mounted
beside tank 202 and is connected to manifold 204 by
line 212. Valve 214 can be opened to back flush waste
water as described above while pump 200 is turned off
and pump 210 continues to ~orce gas into the mixing
chambers 208. The gas then pumps the waste water
back through manifold 204 and line 212 where it leaves
via valve 214. The waste water returns to the tank
and the debris is caught in strainer 216 if desired.
FIGURES 7 and 8 illustrate yet another
embodiment of the invention which utilizes mixing
chambers as described above. In the arrangement of
FIGURES 7 and 8j water in a suitable tank 300 is
pumped through a straight line pipe 302 by a pump 304.
A plurality of mixing chambers 306 extend outwardly
from pipe 302 at separated locations as shown in
FIGURE 7. Air is supplied to a second pipe 308 which
extends above and parallel to pipe 302. Alternatively~
one pipe can be within the other. Pipe 308 is connec-
ted to the individual mixing chambers for injecting
air into those chambers. Pipes 302 and 308 prefer-
ably extend along the center of tank 300 parallel
to the edges so as to cause a fa~orable pattern of
water flow from one side to the other using a minimum
amount of energy to create maximum flow and aeration.
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The system is flushed by opening valve 310 while pump
304 is turned off and air continued to be supplied to
chambers 306.
Many changes and modifications in the above-
described embodiments of the invention can, of cour e~
be carried out without departing from the scope of
the invention. The system can be used with non-
aqueous liquids and gas other than air, such as pure
oxygen, can be added. Accordingly, that scope is
intended to be limited only by the scope of the
appended claims.
