Note: Descriptions are shown in the official language in which they were submitted.
1 334822
The present invention relates to a method for
aeration of liquids.
BAG~ROU~D OF THE IDV~NTION
Aeration of liquids i5 required in numerous
industrial processes. For example, water treatment
systems use oxygenation to remove iron, manganese and
gases from water. Oxidization forms iron into ferric
oxide (Fe203), and triggers a further reaction with
10 water (H20) to form the precipitate ferric hydroxide
lPe2(0~)3. Oxidization forms manganese into manganese
dioxide (MnO2). Manganese dioxide acts as a catalyst to
oxidize iron and M~ng~nese into their respective oxides.
The~e precipitates are then captured in a filter medium
15 and ~ ,v d from the water. The efficiency of the water
treatment system is, therefore, dependent upon the
amount of oxygen which the water i8 capable of
absorbing.
There are four accepted approaches used to increase
the absorption capacity of a liquid. One approach is
known as the "gravity" method. With this method
droplets of liquid are dropped through the air. Another
approach is "mechanical" aeration. With this method the
25 liquid is violently agitated. Another approach is the
"spray" method. With this method liquid is forced
through a nozzle and sprayed through the air. Another
approach is through the use of "diffusers", which mix
the liquid by diffusion. All methods attempt to
30 decrease the interfacial films between the liquid and
gas molecules.
SU~aRY OF T~E INV~NTION
What is required is a method of increasing the
35 efficiency of aeration.
2 1 334822
According to the present invention there is
provided a method of aeration of liquids which is
comprised of the following steps. Firstly, injecting a
gas into a flowing liquid stream whereby a plurality of
bubbles are formed, the gas being of lesser density than
the liquid. Secondly, directing the liquid stream
through a restriction whereby the gas bubbles pass more
quickly through the restriction pneumatically
accelerating the liquid.
The described "pneumatic acceleration" occurs in
two way~. The liquid in front of the bubbles is pushed
through the restriction and the liquid following the
bubbles accelerates due to a decrease in resisting
15 pressure.
Although beneficial results may be obtained through
the use of the described method, the e~h~nced spray
obtained by virtue of the pneumatic acceration can be
20 combined with mechanical aeration means. Even more
beneficial results may therefore be obtained if the
liquid stream is directed at an impaction target thereby
creating a pneumatic hammering effect.
Although beneficial results may be obtained through
the use of the described method, it is preferred that
the gas bubbles be of a substantially consistent size.
Even more beneficial results may therefore be obtained
if the liquid stream is directed through a conduit
30 having a bend, such that small gas bubbles adhere to the
wall of the conduit in the vicinity of the bend and
amalgamate to form bubbles substantially consistent in
size prior to being swept by the liquid stream through
the restriction.
36
~ 3 l 334822
Although beneficial results may be obtained through
the use of the described method, even more beneficial
results may be obtained if the bubbles are substantially
the same size as or larger than the restriction.
Although beneficial results may be obtained through
the use of the described method, it is preferred that
there be a spacial separation between the bubbles as
they go through the restriction. Even more beneficial
10 results may therefore be obtained if the liquid stream
is directed d~ - rdly through a vertically aligned
conduit prior to flowing through the restriction, such
that a spacial separation of the bubble~ occurs.
Although beneficial results may be obtained through
the u~e of the described method, by controlling the
atmospheric pressure the absorbtion capacity of the
liquid can be increased. Even more beneficial results
may therefore be obtained if the restriction is housed
20 in a pressure vessel.
Although beneficial results may be obtained through
the use of the described method, if the difference in
density between the gas and the liquid can be used to
25 ~nh-n5e acceration. Even more beneficial results may
therefore be obtained if the impaction target is at the
top of the pressure vessel such that the buoyancy of the
air bubbles results in an acceleration of the bubbles
prior to impacting upon the target.
Although beneficial results may be obtained through
the use of the described method, it is preferred that
aeration methods be combined to create a synergistic
mixing effect. Even more beneficial re~ults may
`~ 4 l 334822
therefore be obtained if the pressure vessel is a tower
such that the liquid stream strikes the impaction target
and then by force of gravity cascades through the gas in
the pressure ves~el to further impact upon liquid
accumulated in the pressure vessel.
BRIEF ~ PTPTION OF THE DRAWINGS
These and other features of the invention will
become more apparent from the following description in
10 which reference is made to the appended drawings,
wherein:
FIGURE 1 is a perspective view of a water treatment
system con~tructed in accordance with the teachings of
the preferred method.
FIGURE 2 is a longitudinal section view of an
apparatus for the aeration of liquids taken along
section lines 2-2 of FIGUR~ 1.
FIGURE 3 is a section view taken along section
lines 3-3 of FIGURE 1.
FIGURE 4 is a detailed view of a portion of FIGURE
2.
~T~r~n D~SCRIPTION OF THE PREF~RR~D ~MBODIMENT
The preferred method will now be described with
25 reference to the apparatus illustrated in FIGURES 1
through ~. The apparatus are components of a water
treatment system developed for intermixing oxygen with
water, but the method described is equally applicable to
the intermixing of other gases with other liquids.
Referring to FIGUR~ 1, the components of the water
treatment system consist of a venturi air injector 10, a
fluid conduit 12, a tower-like pressure vessel 14, a gas
eliminator 16, and a filter 17. Although the described
35 components are well suited for use in accordance wi~h
~- 5 1 334822
the preferred method which will hereinafter be
described, it must be recognized that other
configurations could be adapted for use in accordance
with the teachings of the preferred method. Referring
to FIGURE 2, pressure vessel 14 has a top 18, a bottom
20, an interior cavity 22, interior side walls 23 and an
exterior 24. Liquids have access to interior cavity 22
through an inlet 26 and C~r~ from interior cavity 22
through an outlet 28. Both inlet 26 and outlet 28 are
10 positioned adjacent bottom 20. A cylindrical conduit 30
extends substantially vertically in interior cavity 22.
Conduit 30 has a first end 32 coupled by a "T" joint 31
with inlet 26 and a second end 34 di~u_ed immediately
adjacent top 18 forming a cylindrical flow restriction
15 gap 19. Referring to FIGURE 3, a plate 35 with a
plurality of openings 37 i8 spaced from top 18 of
pressure vessel 14. Referring to FIGURE 1, liquid flow
conduit 12 has a substantially horizontal portion 36, a
portion with a bend 38, and a substantially vertical
20 portion 40. Horizontal portion 36 has a first end 42
and a second end 44. Portion with a bend 38 has a first
end 46 and a second end 48. Vertical portion 40 has a
first end 50 and a second end 52. First end 42 of
connecting portion 36 is secured to first end 46 of
25 portion with a bend 38. Second end 48 of connecting
portion 36 is adapted for connection to a source of
liquids under pressure ~not shown). First end 50 of
vertical portion 40 is connected to second end 48 of
portion with a bend 38 at a height of approximately 2/3
30 of the height of pressure vessel 14. Second end 52 of
vertical portion 40 is connected by an 90 degree elbow
25 to inlet 26 of pressure vessel 14. Gas injector 10
is secured to horizontal portion 36 of liquid flow
conduit 12.
` 6 l 334822
The preferred method of aeration of liquids will
now be described with reference to the cc ~ n~nts
illustrated in FIGUReS 1 through 4. In its most
fundamental form the method consists of only two steps.
Firstly, injecting a gas into a flowing liquid stream to
form a plurality of gas bubbles in the flow stream. The
gas should be of lesser density than the liquid.
Secondly, directing the liquid stream through a
restriction gap whereby the gas bubbles pass more
10 quickly through the restriction pneumatically
accelerating the liquid. In the preferred method those
fundamental steps have been combined with additional
steps which through experimentation it has been found
e~hAnce the desired aeration. In addition some
15 conventional gravity, spray and mechanical aeration
techniques have been incorporated in the preferred
method. The inter- i~ing takes place in a pressure
vessel to further increase the absorption capacity of
the liquid. The preferred method, therefore, consists
20 of the following described steps.
Firstly, injecting a gas via gas injector 10 into a
flowing liquid stream in horizontal portion 36 of liquid
flow conduit 12 to form a plurality of gas bubbles (not
shown). This is illustrated in FIGURE 1. The gas must
25 be of lesser density than the liquid. In the
illustrated application air is being injected into
water, however with other applications care must be
taken to ensure the liquid is not so viscose as to
prevent the desired pneumatic acceleration from
30 occurring.
Secondly, directiny the liquid stream through
portion with a bend 38 of liquid flow conduit 12. When
this is done it has been found that small gas bubbles
adhere to the upper wall of portion with a bend 38 and
35 amalgamate to form a pocket of air. This pocket of air
1 334822
surrenders air bubbles which are relatively consistent
in size, which are swept away by the liquid stream. The
size of the bubbles produced is depe~Aent upon the size
of the air pocket and the velocity of the liquid stream.
The bubbles enh~nce the desired pneumatic acceleration,
as will be hereinafter explained. The bend in portion 38
is illustrated as being at 90 degrees, but it has been
determined that a much less severe bend will also be
operable. However, with a less severe bend it is more
10 difficult to produce bubbles of a consistent size.
Thirdly, directing the liquid stream do.. -~dly
through vertical portion 40 of liquid flow conduit 12.
The air bubbles have a ten~ncy to rise in vertical
portion 40. This te~ency keeps the air bubbles
15 accumulating to form an air pocket in portion with a
bend 38, prior to bubbles being swept down vertical
portion 40 by the liquid stream. As the bubbles descend
down vertical portion 40 they become evenly spaced,
which i~ important to avoid amalgamation. The height of
20 vertical portion 40 must be sufficient to achieve the
desired spacing. A rule of thumb developed by the
Applicant is that the height of vertical portion 40
should be approximately 2/3 of the height of pressure
vessel 14, this will be hereinafter further explained in
25 relation to the studies made on the prototype.
Fourthly, directing the liquid stream through a
cylindrical restriction gap 19 formed between second end
34 of conduit 30 and top 18 of pressure vessel 14. This
is illustrated in FIGURE 4. The gas, being of lesser
30 density, passes more quickly through the restriction.
This pneumatically accelerates the liquid in front of
the bubbles, as the bubbles "push" the liquid through
the restriction. Liquid following the bubbles also
accelerates due to a localized decrease in resisting
35 pressure. As the liquid exit restriction gap 19 it
` 8 l 334822
pneumatically hammers Ag~inst top 18 of pressure vessel
14 which serve as an impaction target and side walls 23.
The size of restriction gap 19 required is dependent
upon the size of bubbles that are produced. The
5 variables on bubble Yize and the flow of the bubbles
through restriction gap 19 will be hereinafter explained
in relation to the studies made on the prototype. After
striking top 18 and side walls 23, the liquid stream, by
force of gravity, cascades through the gas in pressure
10 vessel 14 to further impact upon plate 35. The liquid
stream then passes through openings 37 in plate 35 and
by force of gravity ca~cades through the gas in pressure
vessel 14 to further impact upon bottom 20 of pressure
vessel 14. As pressure vessel 14 continues to be used
15 liquid accumulates at bottom 20 of pressure vessel 14,
and it is primarily UpOA this liquid that the liquid
stream impacts. Outlet 28 provides a means for removing
liquid and gas from interior cavity 22 of pressure
vessel 14, but interior cavity is always partially
20 filled during use. In this particular water treatment
application the liquid stream continues on from outlet
28 to gas eliminator 16, where gases are vented, and
then on to filter 1~ where the precipitates ferric
hydroxide Fe2(OH)3 and m~ng~nese dioxide ~MnO2) are
25 removed.
The presence of plate 35 serves a dual purpose. It
provides an impaction surface as described, but it also
serves to prevent a portion of the liquid stream from
30 running down the side walls 23 of interior cavity 22,
thereby avoiding the desired intermixing. The pressure
level in pressure vessel 14 is maintained at 3
atmosphere. As a general rule the greater the
atmospheric pressure the greater the ability of the
liquid to absorb the gas; in this case the water to
- 9 1 334822
absorb the oxygen. The effect of a variation in the
size of the restriction between second end 34 of conduit
30 and top 18 of pressure vessel 14 must be noted. If
the distance is too large the impaction is diminished.
If the distance is too small, although there is good
impaction, you lose your flow rate, open the possibility
of clogging, and create too great of a pressure loss
across the restriction. It will be noted the multiple
impaction points in the described apparatus. The more
10 of these impaction points the thinner the interfacial
films between the water and the air; the thinner the
interfacial films the faster the transfer of oxygen.
When passing the liquid stream through the described
apparatus the water should be cool as heat tends to
15 lower the maximum amount of gas soluble in the water,
thereby preventing the desired aeration. The velocity of
the liquid flow stream as it passes through the
apparatus is approximately 9 feet per second. If the
flow is too slow, it diminishes the force of the impact
20 upon top 18. If the flow is too fast the consistency of
the size of bubbles downstream i5 adversely effected as
excess turbulence tends to rip the bubbles apart. The
applicant recommends A~ing to the water treatment
~ystem illustrated filter 17, preferably in the form of
25 a regenerating catalyst, to facilitate the removal of
iron and m~ng~nese. The applicant also recommends
adding to the water treatment system illustrated a
magnetic or alloy based fluid stabilizing unit after
filter 17, in order to prevent calcium scale build up on
30 equipment downstream.
As a general rule, the more turbulence created the
greater the degree of gas transfer. The Applicant has
ascertained that the presence of air bubbles of a
35 consistent size assists in e~ncing turbulence at
1 334822
restriction gap 19. However, as will be apparent from
the description of the test apparatus which follows, in
order for the preferred method to be operable the
turbulence within liquid flow conduit 12 must be
carefully controlled to ensure the bubbles are not
ripped apart prior to reaching restriction gap 19.
The Applicant built a test apparatus out of
transparent material in order that the method could be
10 studied and photographed. The flow in substantially
horizontal portion 36 of conduit 12 was studied to
determine the effect of the alteration of the distance
between air injector 10 and bend 38 and other variables.
The Applicant discovered that air injected by air
15 injector 10 formed bubbles of relatively small random
sizes. The rate at which these bubbles would amalgamate
into larger bubbles in the flow stream and the size of
the bubbles formed was dependent upon the size, length,
and flow rate of liquid within horizontal portion 36.
20 Also of importance was the air to fluid ratio. As more
air was injected into the flow stream, there was an
increase in the rate at which the smaller bubbles
amalgamated and the size of the bubbles formed. As the
distance from air injector 10 to bend 38 was increased
25 the bubbles became larger due to increased time for the
amalgamation. The flow rate effected the amalgamation
rate as the slower the bubbles travelled along
horizontal portion 36 the more time they had to
amalgamate. As the speed of the flow stream was
30 increased, the turbulence in horizontal portion 36
similarly increased. The turbulence tended to rip the
larger bubbles apart forming smaller bubbles and
prevented the smaller bubbles from re-amalgamating.
Regardless of which variable was altered the bubbles
35 remained of random size.
1 334822
In studying the flow around bend 38 it was
determined that the smaller the radius of bend 38 the
more mixing of the air and the fluid occurred. This is
not, however, the primary purpose of bend 38. Bend 38
serves to collect most incoming bubbles into an air
pocket located at the top of the bend. It is
significant that the bubbles which are cut away by the
fluid stream from the air pocket are of a relatively
consistent size. The size of the pocket will vary,
10 largely dependent on the velocity of the fluid flow
stream. The air pocket is continuously generated and as
the air pocket increases in size it impinges upon the
flow stream. The impingement eventually becomes so great
that the flow stream separates and entrains a plurality
15 f air bubbles from the pocket. The pocket will then
again increase its size to the point where another
portion of the pocket will be separated and entrained.
There is a consistent pattern to this building and
separating of a portion of the pocket. The faster the
20 velocity of the flow stream the smaller the bubbles
formed will be. There is, however, a limiting factor in
that there has to be enough air injected in the flow
stream to accommodate pocket formation. If the air to
fluid ratio is too low, the bubbles will have a te~ency
25 to stay entrained in the flowing stream.
In order for the bubbles from the entrained pocket
of gas to be swept down vertical portion 40, the
velocity of the fluid has to be greater than the
30 buoyancy forces attempting to force the bubble in the
opposite direction. As a bubble flows down vertical
portion 40, a flattening of the bubble occurred. This
causes a ixing and a transfer of gases from the water
to the air and vice versa. The bubbles also separate
~_ 12 1 334822
and space themselves evenly as they flow downwardly.
The length of vertical portion 40 should be long enough
to accommodate this bubble separation. Vertical portion
40 of the Applicant's prototype was 32 inches with a
pipe having a 0.8 inch inside diameter. The velocity of
the flow stream was maintained at 9 feet per second. As
the Applicant increased the length of vertical portion
40, the contact time with the water was increased but
the desired bubble separation was not substantially
10 effected. As the Applicant shortened vertical portion
40 the bubble separation diminished. The diminishing of
the bubble separation was viewed as being undesirable,
a~ this allowed for amalgamation of the bubbles into
larger bubbles. Amalgamation is undesirable for reasons
15 which will be hereinafter explained.
When flowing through 90 d~ elbow 25 and "T"
joint 31, the bubbles generally did not amalgamate into
larger bubbles. Thi~ was attributed to the separation
20 between the bubbles. Elbow 25 caused turbulence which
increased oxygen transfer; the smaller the radius of the
elbow the greater the turbulence. When a tee was
substituted for elbow 25 for this redirection and
turbulence function, the bubbles tended to amalgamate
25 and separate into more random sizes. The velocity of the
water as it flowed through elbows 25 and 31 proved to be
important. Slower moving water permitted the bubbles to
amalgamate and faster flowing water broke up the bubbles
prematurely. "T" joint 31 caused turbulence in the
30 fluid, much the same as the elbow 25. Howeverj more
turbulence was created, due to the apparent short radius
as compared to a typical elbow of the same size. This
increased the oxygen transfer rate. The use of "T"
joint 31 to redirect the fluid flow from horizontal to
35 an upward flow did not have negative effects, unlike the
~_ 13 1 334822
substitution of a "T" joint for elbow 25.
As the bubbles flowed up conduit 30 they assumed a
more spherical shape and raced towards the restriction
and impaction target. The velocity of the bubbles was
greater than that of the flowing water due to buoyancy.
As the bubbles reached top 18 of pressure vessel
14, they impacted upon top 18 with the water causing a
10 localized high pressure zone. This zone crushed the
bubble to a smaller size. This caused an increase in
bubble pressure and increased the oxygen transfer rate.
The greater the speed of the water the greater the
crushing effect. These bubbles were then swept way by
15 following water causing the bubble to exr~n~ to its
approximate original size. Some bubbles broke up due to
this violent action. This is not viewed by the
Applicant as being a desirable effect for reasons which
will be hereinafter explained, however, it does cause
20 considerable gas transfer. The contracting and
~xpAn~ i ng of the bubble due to turbulence, causes a
thi~ning of interfacial films on both the water and gas
side.
The impacted bubbles and non impacted bubbles then
travel over to restriction gap 19. Here the bubbles
will begin to flow through restriction gap 19 in various
areas. The water in front of the bubble is pushed
forward at increased velocity by the following gas,
30 because of the ability of the gas to travel faster
through restriction gap 19. This water sprays against
interior walls 23 of interior cavity 22 of pressure
vessel 14 causing intimate mixing with the gas contained
in pressure vessel 14. The oxygen transfer rate is
35 e~hAnce due to a "misting" of the fluid. The fluid
` ~_ 14 1 334822
following the bubble also increases in velocity due a
decrease in pressure caused by the faster travelling
bubble. When the water reaches restriction gap 19 it
then rapidly reduces its velocity and causes as
localized high pressure zone. Any bubbles in the
immediate vicinity are compressed, and then eYrAn~. The
incrca3cd local pressure will cause spraying of water
into the bubble travelling restriction gap 19. The
compressing and expanding increase turbulence. This
10 will then equate to more gas transfer to and from the
liquid. Restriction gap 19 used by the Applicant had a
cylindrical peripheral edge. This cylindrical edge was
preferred as the liquid sprayed in all directions. The
greater the diameter of the cylindrical peripheral edge
15 the more area which was provided for spraying. However,
the greater the diameter, the closer end 34 of conduit
30 had to be positioned to top 18 of pressure vessel 14.
The relationship between restriction gap 19 and bubble
size is important. In order to maintain this
20 relationship it is required that the bubbles be of
uniform size. The use of bend 38 to form bubbles into
pockets is critical to the formation of bubbles of
uniform size. The bubbles should be large enough so
that they occupy the height of the restriction gap 19.
25 This is so that the restriction force is at a minimum,
causing greater velocity changes in the liquid before
and after the gap. The bubbles should also be numerous
80 that the effect can be spread around the cylindrical
peripheral edge of restriction gap 19. This will have
30 the effect of creating numerous violent small jets of
spray around restriction gap 19.
The water leaving restriction gap 19 impinges on
interior walls 23 and cascade down to baffle plate 35.
35 Water striking baffle plate 35 streams through openings
~ 15 l 33482~
37 the surface of water in vessel 14. The faster the
water i`mpinges on the water surface the more the gases
can transfer to and from the liquid. Also the faster
the water impinges on the surface of the fluid in the
vessel the higher the fluid level will become. This i8
due to the formation of very small bubbles which have
very little buoyant forces acting upon them. This
allows them to be swept away out the drain of the
vessel, thus removing vessel gas. Having the vessel
10 under pressure also helps in oxygen transfer. This i8
due to an increase in partial pressure of each of the
individual gases in the vessel and bubbles.
It will be apparent to one skilled in the art that
modifications may be made to the preferred method and to
the preferred apparatus without departing from the
spirit and scope of the invention. For example, it is
beneficial, but not essential, that the method and
20 apparatus also include other types of gravity and
mechanical aeration techniques.
