Note: Descriptions are shown in the official language in which they were submitted.
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LOW-TURBULENT AERATOR AND AERATION METHOD
FIELD
[00011 The present disclosure relates to a vertically oriented aspirating type
low-
turbulent aerator and an aeration method for supporting aquatic environments
by maintaining
dissolved oxygen requirements. The aerator and aeration method can be
incorporated into
many applications such as in: aquaculture, aeroponics and hydroponics as well
as lagoon,
sewage and water treatment.
BACKGROUND
[00021 Dissolved oxygen (DO) is an essential requirement to maintain viable
biochemical processes required for water treatment and in maintaining healthy
aquatic
environments.
[00031 There exist today a plenitude of aeration devices (aerators) and
aeration
methods, principally evolved from and designed for applications within the
field of
wastewater treatment. Many of these aeration devices and methods have been
introduced into
other fields of application such as aquaculture for supplying the requirements
of dissolved
oxygen. Aerators in addition to providing a source of oxygen to be transferred
into water also
induce turbulent mixing. This turbulent mixing action can in certain
applications result in
adverse complications, along with increased energy consumption, operational
and
maintenance needs with a subsequent increase in overall cost.
[00041 The two principle types of processes employed for aeration are
subsurface
aeration and surface aeration. Each type has a number of technologies and
variants that
perform the task of transferring air into water.
[00051 Subsurface or pressure aeration employs a blower or compressor to
deliver
oxygen under pressure to some form of air transferring device located at a
specified depth
within the water column. Bubbles that are formed under pressure ascend quickly
and
generate mixing conditions within the water column. Because pressurized
bubbles rise to
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surface quickly it becomes imperative that pressure type aerators are placed
at a sufficient
depth within the water column in order to provide adequate gas transfer.
[0006] Surface or mechanical aeration, involves rigorous surface agitation
forming a
water spray of small water droplets wherein oxygen is transferred into the
water.
[0007] Aspirating type mechanical aerators introduce oxygen into the water by
drawing atmospheric air through a draft tube or gas conveyance tube via the
action of a
rotating propeller. The action of the propeller creates a highly turbulent
mixing environment
that maintains particles to be in suspension. Propeller type aspirating
aerators typically are
positioned within the water at a depth between 60 to 120 centimeters and
placed at an angle
between 25 and 30 degrees.
[0008] Other aspirating type aerator variants, which are incorporated below
for
reference, have been introduced recently they are vertically oriented,
partially submerged
typically to a depth ranging from 20 to 50 centimeters and are equipped
with'the impeller
positioned adjacent to the bottom bubble discharge end of aerator.
[0009] Patent 6,884,353 B2, Jerard B Hoage, discloses an aeration apparatus to
produce small bubbles for use in a septic tank and the like, comprising of an
orifice plate
having small holes and slots within the air transfer tube and above the
impeller.
[0010] Patent 7,306,722 B1, Jerard B Hoage, discloses an aeration apparatus to
create
small bubbles for use in industrial type wastewater that comprises a rotating
disc having
louvered openings.
[0011] Patent 7,651,075, Samuel S Rho and Jae-Hak Eom, discloses an aeration
apparatus to produce small air bubbles for use in septic tank wastewater and
comprises an
aeration disk having angle blades and incorporating an arcuate wall having
several slots.
[0012] The operating principles of the prior art aspirating type aerators
referenced
above are similar and rely upon a rotating impeller to produce an area of
lower pressure or
vacuum allowing atmospheric gas to be drawn into contact and mixed with
liquid.
[0013] Bubble formation is a product of high shear forces from the rotating
impeller.
As gas is drawn into the liquid the air-liquid mixture is subject to the
shearing forces
imparted by the rotating impeller where bubbles are formed at the trailing
edge. These
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bubbles will vary in diameter and are subject to bubble coalescence when
discharged,
wherein bubbles unite to form larger bubbles that will ascend quickly and
reduce gas-hold up
or residence time. When the ratio of large bubbles, greater than 1 millimeter
in diameter, are
high the bubbles generate an uplifting effect as well as changing the liquid
density wherein
fine to micro sized gas bubbles will rise at a faster rate. This creates the
need to have
increased gas input volume to offset the loss of oxygen discharged to the
atmosphere at the
liquid gas boundary thereby reducing aeration efficiency.
100141 The position of the impeller (aeration disk - Rho and Eom), of the
prior arts,
adjacent to bottom end of the aerator produces a large percentage of gas
bubbles that are
predominantly greater than one millimeter in diameter having a high ascent
rate. A high
percentage of quickly ascending bubbles will cause small bubbles of
predominantly less than
1 mm in diameter to rise at a higher ascent rate thereby reducing their
residence time. In
addition the proximity of the impeller at the bottom end of aerator generates
radial and
helical turbulence that is transferred directly into the liquid body. In the
event the aerator is
placed within a liquid body containing large amounts of solids there is an
increased potential
of debris entering the impeller.
[00151 It therefore becomes apparent that improvements are required with
respect to
vertical aspirating aerators wherein aeration efficiency, bubble residence
time are increased,
turbulent energy transfer is reduced and impeller impacts are prevented.
SUMMARY
100161 There is described an aspirating type low-turbulent aerator introduced
into a
body of liquid and comprising of. an air transfer tube having a gas inlet end
and a gas outlet
end; a gas-liquid mixture chamber incorporating; at least one impeller affixed
to a rotatable
shaft, at the least one gas intake opening and at the least one gas-liquid
discharge opening at
or near bottom end of gas-liquid mixture chamber.
[00171 Rotation of the impeller creates a low-pressure or vacuum zone allowing
gas
to be drawn into rotating impeller, whereby bubbles are formed at the trailing
edge of
impeller. Gas-liquid mixture chamber confines gas bubbles thereby allowing the
action of
impeller shearing force to produce micro-sized gas bubbles of predominantly
less than 0.85
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millimeters that are discharged into the surrounding liquid body with minimum
turbulence.
The micro-sized gas bubbles generated have an long residence or gas hold up
time within the
body of liquid, wherein gas within bubble can, based on a concentration
gradient, diffuse into
liquid thereby providing the capacity to provide a high gas (oxygen) transfer
rate.
[0018] There is also described an aeration method wherein a liquid conveyance
conduit is incorporated in combination with aerator. Liquid conveyance conduit
can convey
liquid directly into the gas-liquid mixture chamber via a liquid intake or
into a liquid transfer
conduit positioned below and proximal to bottom of aerator. The method in
combination with
aerator can increase oxygen transfer via the introduction of liquid having a
lower dissolved
oxygen concentration as well as providing a method of controlled non-
aggressive mixing.
BRIEF DESCRIPTION OF DRAWINGS
[0019] These and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
[0020] Figure 1 illustrates a sectional side view of aerator
[0021] Figure 1-A illustrates a cross-sectional bottom view of impeller
[0022] Figure 2 illustrates a sectional side view of aerator that incorporates
impeller
shaft within gas conveyance tube
[0023] Figure 3 illustrates a sectional view of aeration method in combination
with
liquid conveyance conduit connected to liquid intake fitting intersecting
bottom end of gas-
liquid mixture chamber.
[0024] Figure 4 illustrates a sectional view of aeration method in combination
with
liquid conveyance conduit connected to liquid transfer conduit positioned
proximal to liquid
intake fitting intersecting bottom end of gas-liquid mixture chamber.
[0025] Figure 5 illustrates a sectional view of fully submerged aerator
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DETAILED DESCRIPTION
[0026] Figure 1 and 1-A illustrates aerator 110 and impeller 110-a wherein the
rotation of impeller 112 housed within gas-liquid mixture chamber 130 produces
a low-
pressure zone or vacuum that draws gas introduced into gas inlet end 122 of
gas conveyance
tube 124 such that gas is brought into contact with impeller 112 via gas
intake opening 132 in
communication with gas outlet end 126.
[0027] Shaft 114 is housed within shaft protection sleeve 118 and supported
via shaft
bearing bushings 120. Shaft 114 intersects upper end of gas-liquid mixture
chamber 130 and
impeller 112 is attached to shaft 114 via attachment nut 116.
[0028] Rotation of shaft 114 can be via a variety of submerged or non-
submerged
motive means such as an electric, hydraulic or pneumatic motor powered by
grid, solar or
hybrid energy source. Additionally rotation can be continuous or intermittent.
[0029] Rotation of impeller 112 creates a gas-liquid mixing zone at the
interface of
the impeller wherein leading edge of impeller 112-A generates a shearing force
that moves
gas-water mixture to move across top and bottom surfaces whereby bubbles are
formed at the
trailing edge 112-B of impeller.
[0030] The bubbles are then forced downward in a radial and helical motion
within
gas-liquid chamber 130 where liquid 140 drawn into gas-liquid mixture chamber
130 is of a
greater pressure than the internal internal pressure of the formed gas
bubbles.
[0031] The gas-mixture chamber 130 allows bubbles 136 to be confined within
the
gas-mixture chamber 130, wherein the increased shearing action of impeller 112
and
incoming liquid 140 produce micro-sized gas bubbles of predominantly less than
0.85 mm to
be ultimately discharged from gas discharge opening 134 of gas-liquid chamber
130.
[0032] Gas introduced into gas inlet end 122 of gas conveyance tube 124, as
described above, is not limited to only atmospheric gas and alternatively gas
supplied can be
pressurized and introduced into gas conveyance tube 124 at gas inlet end 122
such that the
vacuum induced via rotating impeller 112 draws the introduced gas to come into
contact with
impeller 112 via gas intake opening 132 of gas-liquid mixture chamber 130.
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[0033] Figure 2 illustrates aerator 210, which is a variant of aerator 110,
wherein gas
conveyance tube 224 comprising of a rigid tube and incorporating internally:
impeller 212,
shaft 214, and shaft support bushing 220.
[0034] Gas drawn into or introduced into gas conveyance tube 224 is drawn into
contact with impeller 212 via gas intake opening 232 in communication with gas
outlet end
226.
[0035] The gas-mixture chamber 230 allows bubbles to be confined within gas-
liquid
chamber 230, wherein the shearing forces of impeller 212 and incoming liquid
240 produce
micro-sized gas bubbles of predominantly less than 0.85 nun to be ultimately
discharged
from gas discharge opening 234 of gas-liquid chamber 230.
[0036] Rotation of shaft 214 can be via a variety of submerged or non-
submerged
motive means such as an electric, hydraulic or pneumatic motor powered by
grid, solar or
hybrid energy source. Additionally rotation can be continuous or intermittent.
[0037] Gas introduced into gas inlet end 222 of gas conveyance tube 224, as
described above, is not limited to only atmospheric air and alternatively gas
supplied can be
pressurized and introduced into gas conveyance tube 224 at gas inlet end 222
such that the
vacuum induced via rotating impeller 212 draws the introduced gas to come into
contact with
impeller 212 via gas intake opening 232 of gas-liquid mixture chamber 230.
[0038] Figure 3 illustrates a sectional view of aeration method; wherein
aerator 310 is
operated in combination with a liquid conveyance conduit 350 that comprises a
liquid inlet
end 352. Liquid inlet end 352 can be connected to a liquid conveyance pump
(not shown)
that introduces liquid into liquid conveyance conduit 350 such that conveyed
liquid
discharges from liquid conveyance outlet end 354 into liquid intake opening
342 of gas-
liquid mixture chamber 330. The liquid can be a liquid having low dissolved
oxygen, low
total solids and/or contain bio-augmentation, biocatalysts and/or soluble
ionic compounds.
[0039] Operation of aerator 310 functions similarly as that of aerator 210
illustrated
and described in figure 2 wherein, rotation of impeller 312 housed within gas-
liquid mixture
chamber 330 produces a vacuum that allows gas introduced into gas inlet end
322 of gas
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conveyance tube 324 to be brought into contact with impeller 312 via gas
intake opening 332
in communication with gas outlet end 326.
[00401 The gas-mixture chamber 330 allows bubbles to be confined within gas-
liquid
chamber 330, wherein the shearing forces of impeller 312 and incoming liquid
340 produce
micro-sized gas bubbles of predominantly less than 0.85 mm to be ultimately
discharged
from gas discharge opening 334 of gas-liquid chamber 330.
[0041] Rotation of shaft 314 can be via a variety of submerged or non-
submerged
motive means such as; an electric, hydraulic or pneumatic motor powered by
grid, solar or
hybrid energy source. Additionally rotation can be continuous or intermittent.
[00421 Gas introduced into gas inlet end 322 of gas conveyance tube 324, as
described above, is not limited to only atmospheric air and alternatively gas
supplied can be
pressurized and introduced into gas conveyance tube 324 at gas inlet end 322
such that the
vacuum induced via rotating impeller 312 draws the introduced gas to come into
contact with
impeller 312 via gas intake opening 332 of gas-liquid mixture chamber 330.
100431 Figure 4 illustrates a sectional view of another variant of aeration
method
wherein aerator 410 is operated in combination with liquid conveyance conduit
450
connected to a liquid transfer conduit 456 positioned below and proximal to
bottom of gas-
mixture chamber 430.
[00441 Liquid conveyance conduit 450 comprises liquid inlet end 452 and a
liquid
outlet 454 wherein liquid conveyed into liquid conveyance inlet 452 via a
conveyance pump
(not shown) discharges liquid from liquid conveyance outlet 454 into liquid
transfer conduit
456.
[00451 Liquid transfer conduit 456 comprises of an open upper end 458 and a
closed
bottom end 460. Conveyed liquid introduced into liquid transfer conduit 456 is
discharged
from open upper end 458 whereby liquid is than drawn into liquid intake 442
via a central
suction vortex generated via rotation of impeller 412. The liquid can be a
liquid having low
dissolved oxygen, low total solids and/or contain bio-augmentation,
biocatalysts and/or
soluble ionic compounds.
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[00461 Aerator variant 410 is similar to aerator 110 described and illustrated
in figure
1 wherein gas conveyance tube 424 and shaft 414 are segregated such that each
is separately
connected and in communication with gas-mixture chamber 430.
100471 Operation of aerator 410 functions similarly as that of aerator 110
illustrated
and described in figure 1 wherein, shaft 414 housed within shaft protection
sleeve 418 is
supported via shaft bearing bushing 420. Shaft 414 intersects upper end of gas-
liquid mixture
chamber 430 and is attached to impeller 412 via attachment nut 416.
[00481 Rotation of impeller 412 housed within gas-liquid mixture chamber 430
produces a vacuum that allows gas introduced into gas inlet end 422 of gas
conveyance tube
424 to be brought into contact with impeller 412 via gas intake opening 432 in
communication with gas outlet end 426.
[00491 Gas-mixture chamber 430 allows bubbles produced via rotating impeller
412
to be confined within gas-liquid mixture chamber 430, wherein the shearing
forces of
impeller 412 and incoming liquid 440 produce micro-sized gas bubbles of
predominantly less
than 0.85 mm to be ultimately discharged from gas discharge opening 434 at or
near bottom
end of gas-liquid mixture chamber 430.
[00501 Rotation of shaft 414 can be via a variety of submerged or non-
submerged
motive means such as an electric, hydraulic or pneumatic motor powered by
grid, solar or
hybrid energy source. Additionally rotation can be continuous or intermittent.
[00511 Gas introduced into gas inlet end 422 of gas conveyance tube 424, as
described above, is not limited to only atmospheric air and alternatively gas
supplied can be
pressurized and introduced into gas conveyance tube 424 at gas inlet end 422
such that the
vacuum induced via rotating impeller 412 draws the introduced gas to come into
contact with
impeller 412 via gas intake opening 432 of gas-liquid mixture chamber 430.
[00521 Figure 5 illustrates a sectional view of a fully submerged variant of
aerator
510, wherein, as part of one embodiment, a submersible motor 550 is housed
within gas
intake conduit 524.
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100531 Activation of motor 550 rotates impeller 524 via shaft 522, wherein as
impeller rotates gas is drawn form gas intake conduit 524 into gas-liquid
mixing chamber
530 via gas intake opening 532.
[00541 Gas supply into gas intake conduit 524 is via gas conveyance tube 560.
Gas
conveyance tube 560 can be connected to a blower or air compressor for the
supply of
pressurized gas into gas intake conduit 524. Gas supply can be continuous or
intermittent.
100551 The distance from impeller 524 to gas bubble outlet holes 534 within
gas-
liquid mixing chamber will determine the dwell or residence time the gas-
liquid mixture is
under the influence of the impeller shear force. The overall submergence depth
of aerator
will determine the amount of gas pressure is required.
[00561 As micro-sized gas bubbles are discharged from outlet holes 534 liquid
540 is
drawn into gas liquid mixture chamber via liquid intake opening 542.
[00571 All aeration devices can be measured for their capability of
transferring
oxygen into a liquid and more specifically water via the following standards
of measures:
a) Oxygen Transfer Rate, which is the measure of mass transfer of oxygen
within a
specified volume of water over a specified time and
b) Aeration Efficiency, which includes the energy input (motor current draw)
requirements.
[00581 Oxygen transfer into water is governed by several parameters. The two
most
important factors governing oxygen transfer is bubble size and residence time.
This can be
understood with greater clarity with the following brief description related
to bubble size.
[00591 The greater interfacial area of smaller bubbles increases the
volumetric area of
contact with water boundary films, which increases oxygen transfer. Oxygen
transfer is
affected by density and viscosity wherein rise velocity of gas bubbles is
inversely affected.
Cold water is denser therefore gas bubble rise velocity is slower and oxygen
transfer rate is
greater.
[00601 Smaller bubble diameter reduces gas bubble rising velocity allowing
greater
residence or gas hold-up time for the oxygen to dissolve and diffuse.
Diffusion increases with
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temperature rise. The diffusivity of the gas out of the bubble film allows the
gas bubble to
shrink as it slowly ascends and depending on the bubble diameter and depth
within the liquid
the gas bubble will collapse releasing the full content of gas.
[00611 Another parameter that is important with respect to oxygen transfer is
the
oxygen concentration difference between oxygen within the gas bubble and that
within the
liquid body. As the difference in oxygen concentration decreases between gas
bubble and
liquid oxygen concentration air transfer rate degreases from an aeration
device and therefore
aeration efficiency is also reduced.
100621 Without imparting complex details and theory of fluid mechanics it
should be
understood that a self inducing aspirating type aerator is influenced greatly
by impeller
design: pitch ratio, thrust; radial, axial or combine, shape of leading and or
trailing edge,
rotation speed and submergence depth.
[0063] It has been discovered that an increase in micro-bubble production of
less than
0.85 mm, along with, a reduction of helical turbulence is achieved by
providing a gas-liquid
mixture chamber having a depth of 7 cm below impeller wherein bubbles
generated at the
trailing edge of impeller are prevented from being quickly discharged by
allowing a dwell
time within the gas-liquid mixture chamber, thereby gas bubbles are further
affected by the
impeller shearing force as well as the pressure differential between the gas
pressure within
the bubble and that of the water pressure. The above described results where
achieved with
the use of an aerator having a 5 cm diameter gas conveyance tube, a 4.3 cm
diameter four
bladed impeller having an angle of 6 degrees with an outward curved leading
edge and an
inward curved trailing edge, a shaft speed of 3250 rpm and aerator submerged
to a depth of
30 cm.
[00641 Other impeller designs incorporating straight leading edge and trailing
edge,
as well as in combination with another impeller having principally vertical
oriented blades
and positioned below the primary vacuum inducing impeller, also achieved
similar results.
However these alternate impeller types required greater power draw due to
increase
resistance or drag forces.
[00651 Aerator performance is a product of the impeller pitch ratio or pitch
angle and
gas-bubble residence time within the gas-liquid mixture chamber. Understanding
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relationship of impeller design characteristics allows the aerator to be
placed at greater
depths than the aerator characterized above and thereby discharge micro-sized
gas bubbles
deeper within the water column. The key parameters to consider are the
relationships
between; a) pitch angle, rotation speed, torque and b) gas bubble residence
time within gas-
liquid mixture chamber, which is controlled by distance from impeller gas-
liquid interface
and to gas-bubble discharge point.
[00661 A fundamental characteristic benefit with the use of the gas-liquid
mixture
chamber is that when the gas introduced into gas conveyance tube is
pressurized and
introduced above and proximal to impeller the gas-liquid mixture chamber
provides a
distance and residence time that enables the gas-bubble internal pressure to
be lower than that
of the liquid at the point of discharge from the gas-liquid mixture chamber.
This process of
using pressurized air allows the aerator to be of a submersible type and
positioned deeper
into the water column. In addition impeller pitch angle and torque
requirements are similar as
those applied with the low-submerged depth aerator. Tests have revealed that
impeller pitch
angle can be reduced since suction draw requirement are minimized with the use
of
pressurized gas.
[00671 The aeration method, as described in combination with aerator,
increases
oxygen transfer via the introduction of liquid having a lower dissolved oxygen
concentration.
Liquid can be conveyed directly into aerator or proximal to bottom of aerator.
In addition can
provide a method of controlled non-aggressive liquid mixing. Liquid conveyed
can be
intermittent and in addition transport various soluble carriers such as ionic
compounds, bio-
active agents and/or catalyst.
[00681 In this patent document, the word "comprising" is used in its non-
limiting
sense to mean that items following the word are included, but items not
specifically
mentioned are not excluded. A reference to an element by the indefinite
article "a" does not
exclude the possibility that more than one of the element is present, unless
the context clearly
requires that there be one and only one of the elements.
[00691 The following claims are understood to include what is specifically
illustrated
and described above, what is conceptually equivalent, and what can be
obviously substituted.
Those skilled in the art will appreciate that various adaptations and
modifications of the
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described embodiments can be configured without departing from the scope of
the claims.
The illustrated embodiments have been set forth only as examples and should
not be taken as
limiting the invention. It is to be understood that, within the scope of the
following claims,
the invention may be practiced other than as specifically illustrated and
described.
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