Note: Descriptions are shown in the official language in which they were submitted.
~569~4
MIXING APPARATUS
1. Background of the Invention
1. Field of use: While the invention is subject
to a wide range of applications, it is especially suited for
use in a system for mixing oxygen with industrial waste and
will be particularly described in that connection.
2. Description of the prior art: Mixing apparatuses
biochemically treat BOD-containing waste water, such as munici-
pal sewage, by oxygenation. This has customarily been accom-
plished by providing a sparge ring in a tank beneath an
10. impeller. The impeller circulates the sewage and the sparge
ring introduces the oxygen into the tank to be mixed. For
example, see U.S. Patent No. 3,227,701 to Pennington and U.S.
Patent No. 3,547,813, to Robinson, et al.
In one known biochemical oxidation process, sewage is
mixed with oxygen-containing gas, such as air, and activated
sludge. The latter consists essentially of aerobic organisms
which have the ability in the presence of sufficient dissolved
oxygen to absorb and assimilate the biochemically oxidizable
organic material of the municipal sewage, thereby converting the
20. organic material to forms which can be separated readily from
the purified water. Under normal conditions the bacteria
multiply rapidly in the aeration tanks during this treatment
step. When the requisite period of BOD conversion is complete,
the mixed liquor is settled, the purified affluent decanted to
receiving waters, and sludge is withdrawn from the bottom of a
clarifier.
AS pointed out above, it is known to use a sparge
ring to supply oxygen-containing gas to the waste water. The
sparge ring would be placed beneath a circulating impeller
30. with the gas traveling to the suction side of the impeller.
The impeller generally rotates at a fixed speed. When the
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lOS~964
1. sparge ring is supplying gas to the tank, the impeller is
drawing a gassed power. When the sparge ring is not supplying
gas to the tank, the impeller is drawing an ungassed power.
The ratio of ungassed power to gassed power is known as the K
Factor. Generally, the K Factor is quite low since the system
draws more power when ungassed. This is because it requires
more torque to rotate the impeller through liquid than through
liquid and gas. Therefore, if a motor for the impeller is
designed to operate at a given gassed power, and someone
10. accidentally turns off the gas, the power drawn increases and
the motor may be damaged.
It is an object of the present invention to provide
an apparatus for mixing a liquid with a gas.
It is a further object of the present invention to
provide a mixing apparatus than can operate in a gassed or
ungassed condition without concern for overloading the motor
that drives the impeller.
It is a further object of the present invention to
provide an apparatus for mixing a liquid with a gas at a higher
20. power level to increase the mass transfer rate.
It is a further object of the present invention to
provide an apparatus for mixing a gas with a liquid being
circulated by a radial flow turbine.
S~mmary of the ~nvention
In accordance with the present invention, an apparatus
mixes a liquid with a gas in a vessel such as a tank. Means,
such as a submerged impeller driven by a motor, circulates the
liquid in the tank. A sparge ring introduces the gas into the
tank. The sparge ring i~ beneath the impeller and includes a
30. supply means, such as a plurality of holes spaced ahout the top
surface of the sparge ring. The supply means are located to
prevent the gas from entering the suction side of the impeller
1056964
1. and insure a good mass transfer rate. 'h
For a better understanding of the present invention,
together with other and further objects thereof, reference is
made to the following description, taken in connection with the
accompanying drawings, while its scope will be pointed out in
the appended claims.
Brief Description of the Drawings
Figure 1 is a diagrammatic, cross-sectional view of
the mixing apparatus of the present invention;
10. Figure 2 is a bottom view of an impeller used in
the present invention;
Figure 3 is a top view of a sparge ring used in
the present invention; and
Figure 4 is a cross-sectional view illustrating the
relationship of the sparge ring and the impeller in the present
invention.
Description of the~Preferred-Emb-odiment
In accordance with the present invention, an apparatus
mixes a liquid L with a gas G. The apparatus includes a tank 10
20~ with the liquid L therein. A means 20 circulates the Liquid L
in the tank 10. A sparge ring 40 introduces gas G into the
tank 10. Sparge ring 40 introduces the gas away from a suction
area 21 of the circulating apparatus 20 so that the circulating
apparatus 20 encounters only liquid resistance.
Referring to Figure 1, there is shown a cross-sectional
view of an apparatus in accordance with the present invention.
The apparatus includes the tank 10 having side walls 12, end
walls ~not shown) and a base 14. The tank is generally con-
structed of concrete. Inlet conduit 16 supplies the liquid L,
30. such a municipal or industrial waste, to tank 10. Outlet
conduit 18 is provided for supplying liquid L to an additional
apparatus, such as a clarifier, after the liquid has been
105f~964
1. oxygenated.
Circulating apparatus 20 may be any suitable sub-
merged impeller-type mixer, preferably one having curved blades,
such as Model No. 89Q125 sold by the Mixing Equipment Company,
Rochester, New York. It includes a motor 22, such as, for
example, a 125 horsepower, induction motor, for rotating a
drive shaft 24. On the bottom end of drive shaft 24 is a
collar 26, which is mounted to a disc 28 by several bolts,
two of which are shown at 30 in Figure 4. Impeller or turbine
10. blades 32 are rigidly connected to disc 28 by any suitable
means such as bolts or welds (not shown). Figure 2 is a bottom
view of the disc 28 with impeller or turbine blades 32 mounted
thereon. Shaft 24, disc 28, and blades 32 may be made of any
suitable material, such as stainless or galvanized steel.
Blades 32 are oriented on disc 28 so that the liquid L is
circulated substantially radially as it leaves impeller blades
32. While circulating apparatus 20 has been illustrated as
being top-entering, a bottom-entering apparatus may also be
used. Also, stabilizing rings or devices to limit radial shaft
20. motion have not been illustrated but they may be used.
Referring again to Figure 1, gas G is supplied to
tank 10 via sparge ring 40 that is fastened to tank 10 by any
suitable means, such as brackets (not shown) attached to base
14. The gas is pumped to sparge ring 40 through a gas supply
line 38 by a suitable pump means 36. As shown diagrammatically
in Figure 1, the gas enters an annular hollow portion 41 of
sparge ring 40 from gas supply line 38 and leaves sparge ring
40 through a set of apertures 42 extending about the top
surface 43 of sparge ring 40.
30. It has been customary to place a sparge ring beneath
the impeller blades so that the gas from the sparge ring is
delivered to the suction area of the blades. This reduces
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~056964
1. the density of the medium being circulated by the blades. The
medium, being of lower density, offers less resistance to blade
rotation. Since the power drawn by the motor rotating the
impeller is directly proportional to the resistance offered by
the medium, the motor draws less power when gas is delivered
to the suction area of the blades. This might seem desirable
except that the mass transfer rate decreases as the power
drawn by the motor decreases.
In accordance with the present invention, the sparge
10. ring introduces gas away from the suction area of the blades so
that the blades encounter only liquid resistance. This is
accomplished by locating the sparge ring so that it discharges
gas within a volume V (shown as dashed lines in Figure 4).
Volume V comprises a ring having a radial dimension a and an
axial dimension b. Radial dimension a extends from 1 to 1.5
time the diameter Dt of the blades. Axial dimension b extends
downward from the disc 28 a distance approximately equal to the
height of blades 32. As long as gas is introduced within
volume V, the gas will not enter the suction area of the
20. blades. Figure 4 illustrates this relationship for sparge
ring 40', but it should be understood that the principal is
applicable to other sparge rings, such as sparge ring 40 in
Figure 1. Preferably, the diameter Ds of the sparge ring
at the apertures is approximately 1.2 times the diameter Dt
of the turbine blades so that the gas is introduces at this
location.
As used in this disclosure, the diameter Ds is taken
at an imaginary circle that is formed by the radially innermost
point of each aperture in a set of apertures such as imaginary
30. circle C for apertures 42'. The diameter Dt referred to herein
as the diameter of the blades, is actually the diameter of a
circle formed by the outer tips of the rotating blades. By
1056~64
1. positioning the apertures radially outward of the turbine
blades, the turbine blades, as they rotate, encounter only
liquid resistance. This draws more power and therefore
increases the mass transfer rate. If gas is introduced
radially outwardly of volume V, the mass transfer rate
decreases significantly.
If gas is introduced above the volume V, the mass
transfer rate will decrease. If gas is introduced below the
volume V, gas may drift into the suction area of the blades
10. and reduce the power drawn. Freferably, the gas in introduced
at approximately the midpoint of the blade (axially) for best
mass transfer.
Referring to Figure 3, there is shown a top view of
a modified sparge ring 40', also made in accordance with the
present invention. The sparge ring 40' differs from sparge
ring 40 in that it contains two sets of apertures. A first
set of apertures 42' is spaced about top surface 43' of sparge
ringe 40'. A second set of apertures 44' is also spaced about
top surface 43'. The second set is radially outward of the
20. first set. As shown, each set of apertures lies along a circle
in the top surface of the sparge ring, but this is a matter of
convenience as long as the gas is directed away from the
suction area of impeller blades 32.
Referring to Figure 4, the use of the two sets of
apertures will become more clear. Sparge ring 40' includes
an annular divider 46 for separating the interior of the
sparge ring into two distinct hollow portions 41' and 41n.
Gas may be introduced into either Lor both~ hollow portion.
If the interior hollow portion 41' is used, gas is delivered
30. to the tank through apertures 42'. If the outside hollow
portion 41" is used, gas is delivered to the tank through
apertures 44'. Therefore, the diameter Ds may be changed
~: : . . .
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1056964
1. from Ds(l) to D (2)~ depending on which of hollow portions
41' or 42" are supplied with gas from line 38.
It should be noted that an annular slot (or slots)
may be used in place of a set of apertures. Further, while
it is convenient to make the sparge ring rectangular in cross-
section, any cross-sectional shape may be used. It i9 also
possible to use a divided sparge ring, such as the one shown
in Figure 3 and 4, to mix more than one gas with a liquid.
EXAMPLE
10. A rectangular tank approximately 38 feet by 40 feet
by 30 feet in depth contained approximately 20 feet of water.
A 125 horsepower induction motor rotated a steel disc at less
than 100 revolutions per minute. Each blade had a radius of
curvature of approximately 38 inches and each blade was approxi-
mately 35 degrees from a radial line from the outer edge of the
blade. Gas was supplied at a flow rate of approximateIy 3,000
standard cubic feet per minute through a sparge ring having a
diameter Ds of approximately 7 feet. This diameter Ds com-
prised 24 aperatures each approximately 3/4 inches in diameter
20. with a pressure drop of about 1.5 pounds per square inch across
the aperture. The top surface of the sparge ring was approxi-
mately 6 inches below the disc. The gassed horsepower drawn
was approximately 93 1/2, and the ungassed horsepower was
approximately 91 1/2, for a K Factor of appraximately 1.02.
One skilled in the art will realize that there has
been disclosed a mixing apparatu~ including a sparge ring
that provides a high K Factor and a high mass transfer rate.
While t~ere has been described what is at pres~nt
considered to be the preferred emhodiment of the inYention! it
30. will be obvious to those skilled in the art that Yax~ous changes
and modifications may ~e made therein without departing from
the invention, and it is, therfore, aimed in the appendea
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- lOS6964
1. claims to cover all such changes and modifications as fall
within the true spirit and scope of the invention.
10.
20. ;~
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30.
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