Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SUBMERSIBLE MIXING IMPELLER
Field of the Invention
The invention pertains to a device for
introducing and dispersing a fluid in a liquid. More
specifically, it relates to a submersible fluid mixing
impeller for introducing and dispersing a fluid, such as a
gas or liquid, into a liquid. Preferably, the device is
used as an aerator for aerating liquid-solid organic waste
mixtures in order to accelerate the decomposition of the
organic matter.
Background of the Invention
Submersible mixing impellers are known devices
with a wide variety of applications for introducing a
fluid, such as a gas or liquid, into the liquid in which
the device is submerged. For example, they are used to
draw air from the atmosphere into a liquid to aerate the
liquid.
In the field of organic waste treatment, decompo-
sition of organic matter, such as vegetable wastes and
sewage, can be effected by introducing suitable bacteria
into a tank containing a slurry of the organic matter in
water, while aerating and mixing the slurry. Thorough
aeration of the slurry, in the form of fine air bubbles
dispersed throughout the slurry, accelerates such decompo-
sition by providing ample oxygen to the bacteria.
Slurries of organic matter typically contain
solid matter, namely the organic matter itself or trash
such as wrapping materials, which are frequently made of
plastic, that accompany the waste. To prevent blockages
within the aerator, it is important that it function in a
manner which does not draw the slurry into the aerator
during the aeration process. It is also desirable for the
aerator to draw sufficient air into itself for aeration of
the slurry by the simple rotation of the aerator, without
the need for any external pump to supply air to the
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aerator. It is also desirable for the aerator to disperse
the drawn air into the slurry as fine bubbles. A need
therefore exists for an improved aerator for use in aerat-
ing waste slurries.
Summary of the Invention
It is an object of the invention to provide a
rotatable mixing impeller to be submersed in a liquid, the
device having peripheral blades extending outwardly from
the body of the device with fluid exit ports immediately
rearward of such blades which are shielded by the blades as
the device rotates in the liquid so that the partial vacuum
produced by the rotating blades prevents liquid from
entering the ports.
The mixing impellers of the present invention are
of the type that are submerged in liquid at the end of a
hollow shaft and draw gas or liquid down the shaft as they
are rotated, by means of the vacuum drawn by the device.
They have a rotatable body which ejects the fluid drawn
down the hollow shaft of the device into the liquid in
which they are submerged through ports at the circumference
of the body, said ports being positioned immediately
rearward of outwardly projecting, rearwardly inclined
blades. The inventor has found the devices of the present
invention, when used as aerators, highly effective in
aerating liquid-solid slurries. It is believed that the
effectiveness is due to the creation of a strong partial
vacuum immediately behind the projecting portion of the
blades as the aerator rotates, producing a pocket of water
vapor into which air is ejected through the air exit ports
before dispersing in the body of the liquid.
According to one aspect of the invention, there
is provided an aerator to be submerged in a liquid for
introducing and dispersing air in the liquid. The aerator
has a lower body, an upper body and a plurality of blades
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disposed between the upper and lower bodies. The lower and
upper bodies are generally circular in horizontal cross-
section and are rotatable, together with the blades, as a
unit. The blades are spaced apart from each other and have
a portion which projects outwardly and rearwardly with
respect to the intended direction of rotation of the
aerator. The upper body has an axial bore to engage with
a rigid air conduit which is open to the atmosphere at its
intake end. The axial bore interconnects with spaces
between the blades which form air exit conduits. The
aerator is submerged in a liquid and is rotated by means of
rotating the air conduit. This causes air to be drawn
through the air conduit into the aerator and to be ejected
and dispersed into the fluid, without intake of the liquid
into the air exit conduits.
According to a preferred embodiment of the
invention, the blades are removable and replaceable. The
blades include a body portion which is positioned between
the upper and lower bodies of the aerator. Preferably, the
upper body of the aerator is in the shape of an inverted,
truncated cone.
According to a further aspect of the invention,
the upper body of the aerator extends outwardly over the
projecting portion of the blades, and acts as a deflector
to prevent air bubbles that are rising from the aerator
from being drawn around the blades as the aerator rotates.
According to a further aspect of the invention
there is provided an aerator having an axially rotatable
hollow shaft which has an air intake at its upper end and
which has a plurality of symmetrically disposed tubes
extending radially outward from the shaft. Connecting
members extend between the outer ends of the radially
extending tubes. Blades project outwardly and rearwardly
proximate the outer ends of the radially-extending tubes
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and air exit ports are disposed immediately rearwardly of
said blades. When the aerator is submerged in liquid and
is rotated by rotation of the shaft air is drawn down
through the hollow shaft, through the radially-extending
tubes and is ejected into the liquid through the air exit
ports.
Brief Description of the Drawings
Fig. 1 is a perspective view of a first embodi-
ment of an aerator according to the invention;
Fig. 2 is a top view of the aerator of Fig. 1;
Fig. 3 is a horizontal cross-section on the line
3-3 of Fig. 1;
Fig. 4 is a vertical cross-section through the
aerator with an air conduit attached, on the line 4-4 of
Fig. 3;
Fig. 5 is a perspective view of a second embodi-
ment of an aerator;
Fig. 6 is a perspective view of a third embodi-
ment of an aerator;
Fig. 7 is a bottom cross-section view of the
embodiment of Fig. 6; and
Fig. 8 is a cross-section view on the line 8-8 of
Fig. 6.
Detailed Description of the Preferred Embodiment
Referring to Fig. 1, the first preferred embodi-
ment of the aerator 8 has an upper body 10, lower body 12
and a set of replaceable blades 14. The upper body 10,
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lower body 12 and blades 14 are fastened rigidly together
as a unit by means of bolts 80, as described below.
The upper body 10 has the external shape gen-
erally of an inverted, truncated cone. It is radially
symmetrical about its vertical axis. It has an outer wall
22 and circumferential rim 68 at its lower edge. Axial
bore 16 opens at the upper end of the upper body 10 and is
threaded to receive and securely engage a threaded
rotatable air tube 74, shown in cross-section in Fig. 4,
having a hollow passage therein, which conducts air into
the aerator. The air tube 74 is preferably a rigid metal
tube.
Referring to Fig. 4, which shows the internal
structure of the aerator, axial bore 16 has shoulder 18
therein. When the air tube 74 is threaded into the axial
bore 16, the lower end of the air tube abuts against
shoulder 18. Below shoulder 18, the inner wall 20 of upper
body 10 tapers downwardly and outwardly, meeting rim 68 at
circumferential edge 24 of the upper body.
Referring to Figs. 1 and 4, the lower body 12 is
generally radially symmetrical about its vertical axis. It
has a circumferential rim 70, which has the same circumfer-
ence as circumferential rim 68 of the upper body 10. Below
rim 70, outer side wall 26 tapers inwardly in the downward
direction, ending in rounded bottom end 28. The upper
surface 30 of the lower body 12 has projection 32 in its
centre and slopes downwardly and outwardly to meet rim 70
at circumferential edge 34.
As shown in Figs. 1 and 3, blade 14, of which
there are four in the first preferred embodiment, has a
body portion 36 and a projecting portion 38. Body portion
36 has a forward edge 40, an inner edge 42, a rear edge 44
and an outer edge 46. The radius of curvature of the outer
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edge 46 is the same as that of rim 68 of upper body 10 and
rim 70 of lower body 12. The outer edge 46 and rims 68 and
70 are therefore aligned, as best seen in Fig. 1. Projec-
ting portion 38 of the blade 14 extends outwardly beyond
outer edge 46 at the rear edge 44 of the blade 14. The
trailing side 48 of the projecting portion 38 is contiguous
with and in the same plane as rear edge 44. Projecting
portion 38 is angled rearwardly at an angle of approximate-
ly 20.1 1.5' with respect to a radius of the arc described
by outer edge 46 of the blade body 36. The length of the
blade body 36 along said arc, from the intersection of said
arc with edge 40 to the intersection of said arc with
projecting portion 38 is preferably 4.00 .05 inches.
Projecting portion 38 has upper edge 50, lower
edge 52, outer edge 54, and inner edges 56, 58. The height
of projecting portion 38 is greater than that of body 36 so
that the plane of upper edge 50 is aligned with the top of
rim 68 and lower edge 52 is aligned with the bottom of rim
70. The length of projecting portion 38 from inner edges
56, 58 to outer edge 54 is preferably 1.688 f.125 inches.
Upper body 10, lower body 12 and blades 14 are
assembled in the following manner. Referring to Figs. 3
and 4, upper body 10 and lower body 12 each have eight
vertical bores 60 and 62 respectively therein, and each of
blades 14 have two bores 64 therein. Bores 60 are threaded
to engage a bolt. Bores 62 open on the sides of lower body
12 at countersunk openings 66. When the upper and lower
bodies and the blades are assembled, bores 60, 62, and 64
align with each other. Bolts 80 are inserted through
opening 66 and extend through bores 62, 64 and 60, engaging
the threads in bores 60, to securely attach the upper body,
lower body and blades together, with the inner edges 56, 58
of the projecting portions 38 abutting rims 68 and 70
respectively.
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The assembled aerator has air channels 72 formed
between the inner wall 20 of the upper body 10 and the
upper surface 30 of the lower body 12. Air channels 72
extend from axial bore 16 between the blades 14 and open at
the sides of the aerator 8 between the blades 14 at air
exit ports 78. The width of each air exit port 78, as
measured along the arc described by rim 68 or 70, is
preferably 1.5 .05 inches.
In use, the aerator is affixed to air tube 74 in
a tank (not illustrated) in which an organic waste slurry
is to be treated. The slurry preferably contains up to
about 11% of solid organic matter. Within the tank, the
air tube 74 extends downwards from the top of the tank,
supported as required along its length for rotation, by
conventional supports and bearings, and holds the aerator
near the bottom of the tank. The air tube is open to the
atmosphere at its upper end above the surface of the
slurry. The air tube 74 is rotated by conventional means,
such as an electric motor positioned above the tank,
rotating the aerator in the direction shown by the arrows
in Figs. 1, 2 and 3. The aerator is preferably rotated at
about 1500 rpm for the four-blade embodiment having the
preferred dimensions stated above, resulting in a speed of
rotation at the tips of the blades of about 69.5 feet/sec.
The spinning causes a vacuum to be drawn down the passage-
way in air tube 74, through air channels 72 and to be
expelled through air exit ports 78 and into the slurry as
fine bubbles. In relatively deep tanks, for example where
the depth of the slurry is over about twelve feet, it is
preferable to have supplementary mixing of the slurry
beyond that provided by the aerator, for example by means
of rotating paddles.
The first embodiment of the invention has been
illustrated with four blades. However, the aerator may
have other numbers of blades, for example six blades or
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eight blades. The preferred dimensions for the blades,
blade angle, exit port width and blade tip speed for such
embodiments is the same as those set out above as preferred
for the four-blade aerator. To achieve the same blade tip
speed, the speed of rotation for the six blade aerator
would accordingly be about 1000 rpm, and for the eight-
blade embodiment about 750 rpm.
Referring next to Fig. 5, there is shown an
embodiment of the invention in which the upper body of the
aerator extends outwardly over the blades. This aerator
comprises principally upper body 110, lower body 112 and
replaceable blades 114, of which there are three in the
embodiment illustrated, though the aerator can have more or
fewer blades. Upper body 110 has an axial bore (not shown)
therein which is threaded to a rigid rotatable air tube 74
having a hollow passage therein. Upper body 110 is larger
in diameter than the circumference defined by the outer
edges 154 of the blades 114 and extends over and radially
outward of them. The lower rim 113 of the upper body 110
abuts the upper edge 150 of the projecting portion 138 of
the blades 114. The upper body 110 has a circumferential
shoulder 168 which abuts upper inner edge 156 of the
projecting portion 138. Lower body 112 of the aerator has
outer circumferential rim 170 which abuts lower inner edge
158 of the projecting portion 138 of the blades 114. Lower
body 112 is held to upper body 110 by means of bolts in
bores 166, in the same way as in the first embodiment.
Lower body 112 has an upper surface (not shown) the same as
the upper surface of lower body 12 of the first embodiment,
and slopes downwardly and outwardly to meet rim 170 at
circumferential edge 134. Air channels are present extend-
ing from the air tube 74 through to the air exit ports 178
between body portion 136 of each blade and projecting
portion 138 of the adjacent blade, as with the first
embodiment.
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The purpose of having an upper body 110 which
extends outwardly beyond the ends of the blades is to
deflect air bubbles rising from the aerator from being
drawn down onto the blades as the aerator rotates. By
deflecting air bubbles away from the blades, liquid unmixed
with air is drawn to the blades from below as air rises
from the aerator, producing smoother rotation of the
aerator. It is possible to achieve the same result by
modifying the first embodiment of the aerator by adding
thereto a circumferential ring extending over the project-
ing portion of the blades. Thus, although it is preferred
that the deflector be integral with the upper body, as in
the embodiment of Fig. 5, it can be a separate component
attached to the upper body or affixed between the blades
and the upper body.
In the aerator of Fig. 5, the length of the
projecting portion 138 of the blades, the rearward angle of
the projecting portion, the length of the body portion of
the blades and the tip speed of the blades when the aerator
is rotated, are preferably the same as for the embodiment
of Figs. 1-4.
Referring next to Figs. 6-8 which illustrate a
third embodiment of the invention, the aerator comprises a
wheel-like structure in which the air is dispersed at the
rim of the wheel as the aerator is rotated. This form of
aerator is intended to be substantially larger than the
first and second embodiments. For example, the diameter of
the third embodiment may be about 10 feet, for use in a
tank about 14 feet in diameter.
The aerator has a rigid hollow shaft 200 open at
its upper end 202 and closed at its lower end by plate 204.
Shaft 200 is threaded on its inner wall and is intended to
be connected to extension shafts as required to make a
shaft of the desired length, i.e. sufficient to extend
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above the surface of the liquid in which the aerator is
submerged. Four tubes 206 extend radially outward from
shaft 200 at the lower end thereof. Tubes 206 are circular
in cross-section adjacent shaft 200 and are flattened
somewhat, outward of the point marked 203 in Fig. 6, in
order to reduce the resistance of the tubes 206 in the
liquid as the aerator is rotated.
Connecting member 208 extends circumferentially
between the outer ends 210 of tubes 206. As shown in Figs.
7 and 8, shaft 200, radial tubes 206 and connecting member
208 are hollow with a passage therethrough.
At the end of each radial tube 206 there is, in
connecting member 208, an air exit port 210, axially
aligned with each of tubes 206. Blades 212 are bolted to
the wall of connecting member 208 and have a projecting
portion 214 which projects through air exit port 210
radially outwardly and rearwardly with respect to the
intended direction of rotation of the aerator, which is
indicated by the arrow in Figs. 6 and 7. Deflectors 216
are affixed to the connector member 208 and extend radially
outwardly therefrom immediately above each of the blades
212 and air exit ports 216, extending outward beyond the
outer edge 218 of blades 212.
In use, the aerator of Figs. 6-8 is open to the
atmosphere when submerged in liquid in a tank by means of
hollow shaft 200 and one or more extensions thereto, of
sufficient length to extend above the surface of the
liquid. The aerator is mounted in the tank with the
rotatable shaft 200 and extensions thereto supported by
suitable and conventional mountings and bearings for
rotation about a preferably vertical axis by an electric
motor situated above the tank. The aerator is preferably
rotated at a speed such that the speed of the blade tips is
about 69.5 feet per second. This causes air to be drawn
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from the atmosphere down through shaft 200, through radial
tubes 206 and to be ejected into the fluid through air exit
ports 210. Deflector plates 216 deflect air bubbles in the
fluid immediately above the aerator from being drawn down
about the blades as the aerator rotates. This reduces the
vibration of the aerator.
In the embodiment illustrated, connector tube 208
is a hollow tube. However, the aerator also functions
satisfactorily with no air passage through the connector
tube between adjacent radial tubes 206, since each air exit
port 210 is fed directly by a radial tube 206. However, if
desired, additional air exit ports and blades can be
positioned about the periphery of the connector tube, at
positions other than the ends of the radial tubes 206, and
in such case the connector member 208 must have an air
passage therethrough to permit air to flow from the radial
tubes 206 to such ports. Connector member 208 can also
conveniently be square or rectangular in cross-section.
The aerator of Figs. 6-8 can have various numbers
of radial tubes 206 rather than the four shown. Such tubes
should be symmetrically disposed about shaft 200 so the
aerator is balanced during aeration. The length of the
projecting portion of the blades, the rearward angle of the
projecting portion, and the size of the exit ports are
preferably the same as for the embodiment of Figs 1-4.
The apparatus of the invention has been described
herein principally for use as an aerator for example for
introducing air into a liquid solid slurry of organic waste
in water. However, it is equally applicable for mixing any
gas or liquid with a liquid and can be used in a wide
variety of applications where such mixing is required.
