Note: Descriptions are shown in the official language in which they were submitted.
1~4~5~;9
The present invention relates broadly to the field of
gas-liquid transfer and more particularly to a method of and
apparatus for the dissolution of gaseous oxygen in a liquid.
It is well known that oxygen is soluble in a var-
iety of liquids and that relatively pure oxygen can be util-
ized in gas-liquid contacting systems for dissolving oxygen
into liquids, including water. It is also well known that a
.. . ..
variety of processes require the dissolution of oxygen in a --
liquid and consequently efforts are being made continually to
10 improve upon existing methods and means for doing so. ~ -
Although oxygen is not generally considered-to be a
rare gas it is nevertheless an expensive gas, and therefore in
processes in which the dissolution of oxygen in a liquid is
- necessary or aesirable the overall costs involved in the oper- -
ation of the process may depend in substantial measure on the
absorption efficiency involved in the dissolution of the
oxygen in the liquid as well as the efficiency of the oxygen
generating process.
For example, many systems and processes which are
20 presently being utilized in the field of waste treatment re- `
- quire the dissolution of oxygen in the liquid undergoing treat- -
ment. In activated sludge systems it is well known that the
dissolution of oxygen is necessary to the reduction of the bio-
,
chemical oxygen demand of the waste liquid and the purification
thereof.
Some activated sludge waste treatment systems which
are found in the prior art depend upon air as a source of
oxygen in the aeration or oxygenation of the waste liquid.
Other systems use gaseous oxygen or gas which has a high oxygen
content, that is, an oxygen content in excess of that of air.
Regardless of whether air or gaseous oxygen is used
for aeration purposes the overall operating costs of the waste
--1--
,. : .
.' ' , ' ;. .
. . ~ `
569
treatment system depend in part upon the absorption efficiency
of the oxygen, that is, the amount of oxygen dissolved into
the waste liquid relative to the total amount of oxygen brought
into contact with the liquid. If a large amount of oxygen is
brought into contact with the liquid but only a very small per-
centage thereof is dissolved in the liquid then the absorption
efficiency is very low and correspondingly the operating costs
associated with the aeration stage of the purification process
will be correspondingly high. On the other hand, if a very
high percentage of the oxygen which is brought into contact
-~ith the liquid is actually dissolved in the liquid then the
absorption efficiency is high and correspondingly the operat-
ing costs with respect to aeration are relatively low.
Although the principles of the present invention find -
utility in any system or process in which gaseous oxygen is
dissolved in liquid, the present invention finds particular
utility in the field of activated sludge waste treatment sys-
tems and will generally be aescribed hereinafter in the con-
text of the aeration stage of an activated sludge waste treat-
ment system.
In the field of activated sludge waste treatmentsystems a variety of systems and apparatus have been employed
to dissolve oxygen in the waste liquid in the aeration stage
. . .
of the process for reducing the B.O.D. For example, surface
aerators which are located at the surface of the waste liquid
and which agitate the liquid in the presence of air or an
oxygen containing gas have long been used. Spargers for
bubbling up air or oxygen from below the surface of the waste
liquid have also been used in a number of installations. More
; 30 recently eductors or jet aerators utilizing ejector principles
have been employed for the purpose of dissolving oxygen in the
waste liquid by introducing a high velocity stream of liquid as
5~;9
well as a stream of air in the mixing chamber of an eductor
or jet aerator and discharging the same in the form of a high
velocity jet into the waste liquid below the surface thereof.
Other recent developments relate to the utilization of pure
gaseous oxygen or gas which includes primarily oxygen, or at
least a gas having a percentage of gaseous oxygen substan- -
tially in excess of the percentage of oxygen found in atmos-
- .
pheric air.
All of these various approaches, processes and tech-
niques are intended to reduce to the extent possible the costof dissolving oxygen in the waste liquid and, as noted, the
costs involved bear some not insubstantial relationship to
the absorption efficiency of the system as well as the energy
required to obtain such absorption efficiency. Most of the
known systems which utilize high purity oxygen or at least a
high oxygen content gas for the purpose of oxygenating a
liquid, particularly in the field of activated sludge waste
treatment systems, involve the employment of closed aeration - -~
tanks as well as seriatim staging of contacting cells to reach
a sufficiently high level of oxygen utilization. A high util-
ization factor is necessary in high purity oxygen systems to
render such systems economical and it is generally understood
that only a minor loss of oxygen can be tolerated in such sys-
tems. Transfer efficiencies of up to 90% are generally con-
sidered desirable and are presently being attributed to someclosed tank, series staged high oxygen content systems.
Apparently presently known high purity oxygen sys-
tems are not sufficiently efficient to accomplish an acceptable
absorption efficiency in a single tank or cell, and it is
apparently that fact which necessitates the staging of closed
tanks or cells in a manner so that the excess or off-gas of
the first cell is collected and introduced into a subsequent
s~9
cell for additional gas transfer and increased absorptlon eff-
iciency. Three to five stages are generally utilized in an
apparent effort to reach a desired absorption efficiency of
90% or more.
No system is believed to be known that can transfer
a high percentage of pure oxygen in an open tank, one-pass
contacting system and yet achieve a commercially acceptable -
rate of oxygen transfer at a commercially acceptable power
requirement. Systems are known which can transfer a high per-
centage of pure oxygen in an open tank, one-pass contacting
system, but these systems are extremely energy intensive and
require the use of small orifices for introducing the oxygen
which are subject to plugging, fouling, and the like. In
addition to the mechanical problems associated with these
15 systems, the capacity of the devices are limited and therefore, ~ - -
avery equipment intensive system is required to give any
appreciable transfer rate.
In addiiton, many of the existing systems which uti- -
lize either relatively pure oxygen or at least a gas having
a high oxygen content also involve moving mechanical parts
and apparatus within the aeration tank both above and below
the surface of the waste liquid. These mechanical parts are
exposed to relatively high concentrations of oxygen and are
subject to problems of corrosion and the like. Furthermore,
the existence of such mechanical equipment above the surface
of the liquid requires a relatively high tank freeboard,
generally in the range of about 3 to 5 feet, and thus far
less than the entire volume of the tank is available for the
confinement of the waste liquid. ~ ~ -
In addition, such known so-called oxygen systems
which utilize serially arranged closed systems and which are
primarily biological in nature, such as activated sludge waste
-4-
.
.
.
. ... ..
l~Z5~;9
treatment systems, involve the existence of CO2 in the aera-
tion tank between the surface of the waste liquid and the
cover of the tank by virtue of the evolution or generation of
C2 in the biological process. The existence of CO2, of
course, has a tendency to reduce the concentration o~ oxygen
and thus the absorption efficiency of the system, and tends
to increase the dissolved CO2 level in the mixed liquor solu-
tion which in turn effects pH, chemical composition and build-
up of biological waste products which can potentially adver-
10 sely affect the biological kenetics of the system. In the ~;
final stage of presently known oxygen systems concentrations
f C2 of 50% by volume quite commonly exist in the off-gas.
Although jet aerators and similar high velocity jet -;
producing devices utilizing eductor principles have been used
to accomplish oxygenation in many installations, it is believed
that none have been successfully used in systems involving
gaseous oxygen rather than air for providing the requisite
oxygenation. Jet aeration systems, as studies indicate, com-
pare extremely favorably with other oxygenation systems and
in many respect have advantages which, it is believed, other
oxygenation systems do not possess.
The present invention involves the utilization of
-~ pure oxygen or at least a substantially high oxygen content
gas for oxygenation purposes by producing at least one or more
high velocity jets comprising liquid and oxygen, which jets
are introduced into the waste liquid in a manner which differs
considerably from that of previously known air jet aeration
systems. In accordance with the information and data which
has been developed, the absorption efficiencies which are
available from this invention far exceed those which could
have been anticipated in light of the present state of the
art of jet aeration. Indeed the absorption efficiencies avail-
~. . .
11~4ZS~9able from the practice of this invention compare favorably
with other so-called "oxygen" systems but additionally this in-
vention does not require closed or covered aeration tanks,
arranged in series, and thus eliminates the difficulties which
are inherent in such known systems.
Furthermore, this invention does not involve any mov-
ing parts whatsoever within the liquid in the aeration tank or
in an atmosphere having a high oxvgen content. Initial costs
in the construction of a system embodying the principles of
this invention, relative to other "oxygen" systems, are re-
duced. Maintenance costs are also reduced by virtue of the
absence of moving parts not only within the liquid but in the
high oxygen containing atmosphere above the liquid. A greater -
portion of the aeration tanks is-utiliæed for the confinement
of waste liquid by virtuP of thé reduction of the tank free-
board to about one foot. Since the present invention does not
involve a cover for the aeration tank, the problems involved
in CO2 buildup, both within and above the liquid, are elim-
inated. In addition, since a system constructed in accordance
20 with the principles of this invention does not require any -
mechanical mixer for mixing the liquid within the aeration
tank, the potential problems relating to maintenance and down-
time are eliminated.
In accordance with the foregoing, it is an object
of this invention to increase the absorption efficiency of
oxygen dissolution systems while avoiding the necessity of
closed aeration tanks, multiple cells, mechanical liquid
stirrers or mixers, excessive tank freeboard, CO2 buildup,
and moving parts within the liquid or in a high oxygen content
environment above the liquid.
Another object of the invention is to reduce the
costs involved in dissolving oxygen into liquid, particularly
,
: . :.
., , . , . , , , ., ~ .,
:: . . ~ .
lI3~Z5~;9
in the aeration stage of activated sludge waste treatment sys-
tems, thereby improving the efficiency of such systems and
reducing the operating costs and energy requirements.
Another object of the invention is to provide a
system for increasing the oxygen content of a liquid, which
system is capable of extremely high dissolution rates at ex-
tremely high absorption efficiencies without the necessity
of utilizing enclosed oxygen pressurized serially arranged
liquid tanks or reservoirs.
Another object of the invention is to provide high
absorption efficiencies in a system which utilizes no moving ~-
parts for dissolving the oxygen in the liquid except for a
liquid pump, and the pump, instead of being located in a high
oxygen content atmosphere, is exposed only to ambient air.
Another object of the invention is to increase the
capacity of activated sludge waste treatment systems which
rely on pure or relatively pure oxygen rather than air for
oxygenation purposes in reducing the B.O.D. of the waste
liquid.
The present invention involves a method of and appa-
ratus for increasing the oxygen content of a body of liquid
by producing a stream of liquid, pressurizing the stream,
creating turbulence in the stream, introducing gaseous oxygen
into the stream and then discharging the stream through a
liquid nozzle into the body of liquid. Based upon conducted
tests, the prèsent invention has many advantages over known
methods and systems in terms of absorption ef~ioiency, ori
ginal costs, operating costs and simplicity of design, con-
struction and maintenance. All of these advantages are be-
lieved to be obtained without introducing any disadvantageswith respect to previously known oxygenation systems.
The method and the system which are involved in the
--7--
. . .
present lnvention lorld themselv~s to contlnuou~ operatlon l)y
~ich subs~ntial ~mounts of oxygen may be dlssolvod ln the
.,~,,
body of liquld nt extr~mely high absorptlon efficlencles in
comparison to other well known ~o~called "oxygen" systems of
water treatment and purlflcation.
In the preferred embodiment an In~ector, which
is completely void of moving parts, is utilized as the instru-
mentality by which the oxygen ls introduced into the liquid. A
pump is used to circulate liquid from the body to be oxygenated,
through a conduit arrangement and back to the body of liquid, -;
As the liquid is circulated through the conduit the oxygen is
introduced into the liquid by means of the injector in the form
of a stream. Preferably the oxygen stream is introduced into
the liquid stream on the inlet or upstream side or low pressure
side of the pump, merely to utilize the pump as a mixer, but -
tests indicate that the oxygen may be introduced on the dis-
charge side of the pump without losing any of the enhanced
characteristics of the system and without suffering any
significant reduction in absorption efficiency.
The method and system of the present invention
lend themselves not only to new construction but to modifications ~ - -
of existing waste treatment and water purification facilities,
The absorption efficiencies and total reductions in energy
requirements which inure to the present invention do not depend
upon the size of the aeration system, as a consequence of which
the principles of the present invention find utility in very
small oxygenation systems and activated sludge waste treatment
systems as well as in very large systems that are employed, for
example, ln the maJor metropolitan areas. `
In one particular aspect the present inventi;on
provides a method of dissolving gaseous oxygen into liquid
oomprising the steps of; confining a body of liquid into which
~a~eous oxygen iB to be discolved, continually removing a portion
Jl/~ 8_
A;~ ., ,
. ~ . ,~ , . . .
5~i9
o the llquid rrom sald con~incd body, prcssuri7ing ~hc llquld
~emoved from 9aid confincd body, lnJectln~ gn8eoUS oxygcn -~nto
~ald pressurl7.ed llguld to oxygenate said liquid, causing said
oxyeenated ].lquid to reside ln a pressurized state for at least
about five second while removed from said conflned body, and
returning said oxygenated liquid to said confined body and
causing it to be discharged into said confined body through a
discharge nozzle while undergoing a pressure drop in the range
of approximately 5 to 12 psia, -
In another aspect the present invention provides ~--
apparatus for dissolving gaseous oxygen in a liquid comprising
in combination, reservoir means for confining a body of liquid
into which gaseous oxygen is to be dlssolved, circulating means
comprising hydraulic circuitry connected to said reservoir means
and including fluid conduit means externally of said reservoir
means, fluid flow and pressure producing means connected in -~
said fluid conduit means externally of said liquid confining
means for circulating and pressurizing liquid from said confined ~ :
liquid body through said fluid conduit means and returning said
removed fluid back to said reservoir means, injector means ~ :
connected in said fluid conduit means for in~ecting gaseous
oxygen into the liquid in said fluid conduit means to oxygenate
said liquid, said circulating means further including nozzle
discharge means disposed within said reservoir means for dis-
charging the oxygenated liquid from said hydraulic circuitry
into said confined liquid body, said fluid flow means and
hydraulic circuitry being operative to maintain said oxygenated
liquid within said circuitry for a minimum period of approx~
lmstely five seconds prior to discharge through said nozzle
discharge means, said nozzle discharge means being adapted to
effect a pressure drop of between approximately 5 to 12 psia as
sald oxygenated liquid ls discharged into said confined liquid
body,
_8a-
~ ~ , ` - `
. :, .,, :. . ..
: . ~ . ' ~ . " : ' :
Z5¢9
^~ Many feattlles~ advnntages and obJects of the
resent inven~ion in addltion to the foregoing will become
manlfest to those versed in the art by making reference to the
detailed
~ '
_8b- ~
~ ~ t ~ . .
~ ,
1~4ZS~;9
description which follows and the accompanying sheets of draw-
ings, in which a preferred structural embodiment incorporating
the principles of the present invention is shown by way of
illustrative example only.
FIG. 1 is a graph which discloses the absorption
efficiency of a typical prior art aeration system using conven-
tional jet aeration equipment, at various levels of submergence.
FIG. 2 is a graph which illustrates the absorption
efficiency of a conventional prior art jet aeration system,
at a constant submergence, both when air and when high purity
oxygen are used as the source of oxygen.
FIG. 3 is a graph which illustrates the absorption
efficiency of a conventional prior art jet aeration system and
of a system which embodies the principles of the present inven-
tion, when high purity oxygen i8 used in systems as the source
of oxygen, the submergence levels of both systems being the
same.
FIG. 4, which appears on the sheet of drawings bearing
FIG. 1, is a schematic or diagrammatic illustration of a conven-
tional prior art ~et aeration system.
; FIG. 5 is an enlsrged sectional view of the jet
aerator utilized in the ~et aeration sy3tem shown in FIG. 4.
FIG. 6 is a schematic or diagrammatic illustrationof a ~et aeration system constructed in accordance with the
prlnciples of the present invention. `
FIG. 7 is an enlarged sectional view of the eductor
utilized in the system shown in PIG. 6.
FIG. 8 is a graph which discloses the manner in
which the absorption efficiency of the present invention varies
3~ in accordance with variations in jet submer~ence levels.
FIG. 9 is a curve which discloses the absorption
efficiency of a system embodying the principles of the pres-
jb/~,~
, . . . ................................. : . .
. .
5~9
ent invention operated over a range of jet pressure drops.
FIG. 10 is a graph which discloses the effect of var-
iations in liquid residence time on the absorption efficiency
of a system constructed in accordance with the principles of
the present invention.
FIG. 11 is a graph which discloses the absorption
efficiency of a system embodying the present invention operated
both with and without shrouds to produce secondary delivery
jets from the liquid jet nozzles submerged within the body of
10 liquid being oxygenated.
FIG. 12 is a graph which compares the oxygenation
capacity of a conventional prior art jet aeration system
using both air and high purity oxygen as the source of oxygen
and a system constructed and operated in accordance with the
15 principles of the present invention, all at various oxygen-
to-liquid flow ratios. ~.-
As noted, aeration systems which utilize eductors
or jet aerators embodying eductor principles have long been
known in the prior art. Generally, waste liquid is pumped
20 from an aeration tank, through hydraulic conduits, to the
liquid nozzle of a jet aerator or eductor. The jet aerator
is furnished with a mixing chamber into which the waste liquid
from the liquid nozzle issues and connected to which is a ~
source of pressurized or aspirated air. The admixture of ~ -
25 waste liquid and air is then discharged from the jet aerator
or eductor in the form of a high velocity jet into the aera- ;
tion tank below the surface of the liquid.
- The curves shown in FIG. 1 were developed from test
data relating to a previously known aeration system utilizing
30 conventional jet aeration equipment. FIG. 1 illustrates that
- such systems are capable of achieving a relatively high absorp-
~ "...~ ~ ... .
tion or transfer efficiency when air (as contrasted with high
--10--
,
1~4~S~;9
purity oxygen) is utilized in the gas-liquid contacting
process. As a matter of fact the curves shown in FIG. 1 ill-
ustrate that the absorption efficiencies of jet aeration sys-
tems compare favorably with those available from any other
aeration system, that is, one which utilizes air rather than
oxygen in the oxygen transfer process.
On the other hand, the curves shown in FIG. 1 dis-
close absorption efficiencies which would not be commercially
feasible or acceptable, from an operating cost standpoint, in
identical systems in which high purity oxygen were substituted
for air as the source of oxygen.
The curves shown in FIG. 1 suggest, however, that
if high purity oxygen is substituted for air and if, in addi-
tion, experimentation were conducted to optimize the percent
ransfer of the high purity oxygen, acceptable absorption
efficiencies could possibly be attained. The fact that a
substantially pure oxygen bubble will have a higher partial
pressure of oxygen than will an air bubble and will not be
subject to dilution of the percent oxygen content as oxygen
is transferred into solution may well suggest to those skilled
in the art a higher transfer efficiency than that which has
been obtained with air, even without optimization.
In the course of the investigations which resulted
in the present invention, the inventor experimented with the
- 25 utilization of high purity oxygen instead of air in conven-
tional prior art jet aeration systems. In the course of the
investigations and experiments, the parameters whioh effect
absorption efficiency were varied in an effort to maximize
absorption efficiency.
The most favorable results obtained from this exper-
imentation are shown in FIG. 2. The two curves shown therein
were derived from test data concerning the same prior art jet
--11--
.
.
~4;~ 9
aeration system, but the curve entitled "Jet Aeration" re-
sulted from the use of air as the source of oxygen, whereas
the curve entitled "Jet Oxygenation" resulted from the use of
high purity oxy~en. A comparison of the curves shown in
FIG. 2 illustrates quite clearly that conventional jet aera-
tion systems previously known in the prior art are probably
not commercially feasible when high purity oxygen is substi-
tuted for air, since the absorption efficiencies of such sys-
tems do not increase substantially as a consequence of such
10 substitution. - ~
In the course of these investigations, experimenta- - -;
tion was conducted with numerous modifications in conventional
jet aeration equipment. In each case the improvements in ab- ~-
sorption efficiency using high purity oxygen instead of air
were only marginal, resulting in most instances in not more
than a two to three percent increase in transfer or absorp-
tion efficiency. Even when the gaseous oxygen application ~ -
rates were reduced or backed off to such an extent that the
oxygen which went into solution was not even sufficient to
saturate the motive liquid stream, absorption efficiency did
not improve in any substantial degree.
It was as a consequence of the foregoing experimen-
tation and the failure of conventional jet aeration equipment
to produce high absorption efficiencies when utilizing high
purity oxygen that consideration was given to alternative sys-
tems. One possible system considered involved the pre-injec-
tion of gaseous oxygen into a pressurized liquid motive
stream. However, based upon information which is presently
known to those skilled in the art of gas-liquid contactors and
- 30 gas-liquid trans~er, such a system should not produce favorable
absorption efficienceis since (1) the benefits which are known
to derive from gas-liquid contacting at the nozzle of the jet
-12-
..,. . . ~ .: .. :
~4ZS~;9
aerator would be completed eliminated, (2) the amount of oxygen
that could be transferred into the motive liquid stream would
be limited by the motive stream flow rate and its saturation
value, and (3) any gaseous oxygen that carries through the
motive stream cycle may exit in a state of dispersion which
is unfavorable for mass transfer.
Notwithstanding the foregoing it was decided to
develop a prototype and conduct tests of such a system. The
results were completely and unexpectedly favorable. FIG. 3
illustrates the substantial increase in absorption efficiency
of an aeration system embodying the principles of the present
invention and utilizing high purity oxygen as contrasted with
a conventional jet aeration system also using high purity
oxygen. The curve entitled "Jet Oxygenation" corresponds to
the similarly entitled curve shown in FIG. 2. On the other
hand, the curve entitled "Pre-injection Jet Oxygenation" dis- -
closes the much higher absorption efficiencies available from
a jet aeration system constructed in accordance with the prin-
ciples of the present invention. Both curves illustrate the
variation in absorption efficiency which results from varia-
tions in the mass-flow ratio of gaseous oxygen and waste
liquid.
FIG. 4 illustrates a conventional prior art jet
aeration system and corresponds to the system which was used
in developing the curves shown in FIG. 1, the curve entitled
"Prior Art Jet Aeration"shown in FIG~ 2 and the aurve entitled
"~et Oxygenation" shown in FIG. 3. The system includes a
large aeration tank or reservoir indicated generally at ref-
erence numeral 10 which contains a body of liquid 11 being
oxygenated. The surface of the liquid 11 is shown at refer-
ence character lla and it is noted that the surface of the
liquid may very closely approach an open upper end 12 of the
, ': ' ' ' ': ' . .. . .
. . .. . . . . .
'; . '
:, : .
1342S~9
aeration tank 10. A side wall 13 of the tank 10 is, in the
illustrated embodiment, cylindrically shaped, but it will be
appreciated that the particular configuration of the tank 10
is not critical to the present invention. Unlike presently
known high purity oxygen systems, however, the top 12 of the
tank 10 is not closed or covered but instead is fully open
to the atmosphere surrounding the tank 10.
A jet aerator 14 is located within the aeration
tank 10 below the surface of the liquid 11. In the system
which was actually used in the course of these investigations
and experiments, the jet aerator 14 comprised a single unit
(which may be referred to as a jet cluster) having a plur- ~ :
ality-of liquid nozzles 15 arranged radially about a verti-
-al axis and communicating with a common manifold 16 to which --
is connected a conduit 17 which extends through the side wall
13 of the tank 10 and to a discharge side 18 of a liquid pump
19. Another condu.t 20 is connected at one end 21 there^f to
the suction or inlet side of the pump 19, whereas an opposite
end 22 communicates with the interior of the tank 10.
valve 23 is mounted in the high pressure liquid conduit 17
whereas a similar valve 24 is mounted in the low pressure
liquid conduit 20.
Re~erring again to the jet aerator 14, a series of
gas-liquid nozzles 26, corresponding in number and location
to the liquid no~zles 15, communicate with an air manifold 27
to which is connected an air conduit 28 which extends through
the side wall 13 of the aeration tank 10 to an air blower
( not shown).
In the operation of the conventional jet aeration
- 30 system shown in FIG. 4, liquid 11 from the aeration tank 10
- is pumped through the conduit 20 by the liquid pump 19 and
conducted through the conduit 17 to the liquid nozzles 15 of .
-14-
.:
.:
~Z569
the jet aerator 14. Liquid ~rom the nozzles 15 issues in the
form of high velocity liquid jets and mixes with air being con-
ducted through the conduit 28 to the manifold 27 surrounding
the liquid nozzles 15. The admixture of liquid and air then
issues in the form of high velocity jets from the air-liquid
nozzles 26 extending radially about the axis of the jet aera-
tor 14.
While the illustrated embodiment of the jet aerator
14 includes a plurality of liquid and air-liauid nozzles, the
principles of the conventional jet aeration do not require a
multi-nozzle jet aerator or cluster and in 'act many systems
utilize one or more jet aerators, each of which comprises
only a single liquid nozzle surrounded by an air-liquid
nozzle.
FIG. 6 illustrates an aeration system embodying the
principles of the present invention and a comparison of FIGS.
~ and 6 illustrates .he essential similari ~i25 O' an~ distinc-
tions between the two systems. Those parts or components of
the system shown in FIG. 6 which correspond to those shown in
FIG. 4 are identified with the similar reference characters,
and it is noted that the system shown in FIG. 6 does not
utilize an air conduit 28. As a consequence the jet aerator
chamber 27, which previously served as an air manifold, is
now in direct communication with the liquid 11, and the air-
liquid nozzles 26 merely serve to produce secondary liquidjets surrounding the jets which issue from the liquid nozzles
lS.
In the system shown in FIG. 6 a conduit 30 has been
added to interconnect the high pressure liquid conduit 17 and
the low pressure conduit liquid 20. In the illustrated em-
bodiment the diameter of the conduit 30 is significantly less
than the diameter of either the conduit 17 or the conduit 20,
' ` . '" `', ' : `
.
,
.: .
1~25~9
and mounted in the conduit 30 is an eductor 31, as well as a
pair of valves 32 and 33 mounted on the opposite sides of the
eductor 31. Another conduit indicated at reference numeral
34 is connected to the eductor 31 and has mounted therein a
valve 36. The conduit 34 is connected to a source of high
purity oxygen (not shown) although the principles of the
present invention are applicable even though the percent of
oxygen in the gas is substantially less than 100%.
Referring to FIG. 7, the eductor 31 comprises a
liquid nozzle section 37, a mixing chamber 38 and a diffuser
section 39. The precise embodiment of the eductor 31 is not
critical to the present invention, however, and indeed it is
not necessary that an eductor be used for the purpose of -.
introducing the oxygen into the liquid. What is important --. --
is that the oxygen be introduced into the liquid in the form
of fine bubbles, and for that purpose an eductor 31 is par- `- ~.
ticularly well suited. - ~`
.
In operation of the system disclosed in FIG. 6, the
liquid pump 19, which is connected to an electric motor l9a,
draws liquid from the tank 10 through the low pressure con-
:-: duit 20 and discharges the liquid back into the tank 10
through the high pressure liquid conduit 17 and the liquid
nozzles 15. A small poriton of the liquid being circulated
: through the pump 19 and being discharged back into the tank
10 through the high pressure liquid conduit 17 is by-passed
thorugh the conduit 30 back to the low pressure liquid con-
duit 20. As this small portion of the liquid stream is con-
ducted through the conduit 30, relatively high purity oxygen ~
is introduced into the liquid by virtue of the eductor 31. : - -
30 Thus in the embodiment shown in FIG. 6, the oxygen is added . .
to the liquid stream on the suction side rather than the dis-
charge side of the liquid pump 19.
- -16-
, ~ .
i~42S~9
In the test facilities in which the investigations and
experimentations were undertaken, the eductor or injector 31
produced oxygen bubbles in the order of about 2 millimeters or
less in diameter, resulting in a specific interfacial area of
about 30,000 cm /liter of gas. Based upon these investigations,
it is believed that the very high absorption efficiencies resul-
ting from the present invention may be obtained regardless of
whether the oxygen is introduced into the low pressure liquid
conduit 20 on the suction side of the pump 19 or in the high
pressure liquid conduit 17 on the discharge side of the pump 19,
and it is also believed that absorption efficiencies in the same
order of magnitude as those achieved in the specific test fac-
ility utilized can be obtained regardless of the manner in which
the oxygen is introduced into the conduits 17 and 20, provided
the specific interfacial area of the oxygen to the liquid is
about 30,000 cm2/liter or gas, or greater.
That hydraulic circuitry, including the liquid nozzles
15, the high pressure liquid conduit 17, the liquid pump 19 and
.the low pressure liquid conduit 20, by which the liquid 11 is
circulated from the tank 10, through the circuitry and then
back to the tank 10, is indicated generally at reference num-
eral 36. -
It is apparent that the principles of the present
invention do not require any specific geometry or configura-
tive relationships with respect to the hydraulic circuitry36. Nor is it required that the oxygen be introduced at any
particular point in the hydraulic circuitry 36 as long as it
is subjected to a minimum residence time therein. What is
apparent, however, is that the liquid stream in the hydraulic
circuitry 36 must be in a state of turbulence upstream of the
liquid nozzles 15 to provide mixing of the oxygen bubbles in
the liquid stream. By turbulence is meant a state of distur-
bance of the liquid stream to produce relatively violent agi-
-17-
. . . . .
. . . . . . . . .
-. . ~ .
,. ~
.
. .
.. . . .
,
1~4ZS69
tation or perturbation of the liquid.
It has been estimated that the Reynolds number of
- the hydraulic circuitry 36 in the test facility was probably
between 200,000 and 400,000. In the course of these inves-
tigations, however, a considerable effort was made to varythe Reynolds number, and upon observation it was noted that
there was no appreciable variation in absorption efficiency
as a consequence of variation in Reynolds number. As noted,
it is only necessary that the liquid stream be maintained in ` -
a state of turbulence upstream of the liquid nozzles 15, but
it is anticipated that, ~ith respect to any particular system,
and depending upon the diameter of the pipes, the number of
elbows and other fittings and the like, some adjustment with
respect to the valves 23 and 24 and other experimentation
may be required in order to obtain the maximum absorption
efficiency.
The curve snown in FIG. 8 illustrates variation in
absorption efficiency of the system shown in FI~.6 as the
level of submergence of the jet aerator 14 is varied. The ~ -
tests in connection with which this curve was developed were
conducted at a fixed gas flow rate of 5 lbs. per hour per
liquid iet nozzle 15. Actually, the jet aerator indicated at
reference numeral 14 which was used in the test facility
.
diagrammatically indicated in FIG. 6 comprised a total of 12
- 25 liquid nozzles 15 extending radially outwardly from a single
casing. Experimentation indicates, however, that the absorp-
tion efficiencies available from the invention do not depend
upon the numbex of liquid jet nozzles involved, although it
is apparent that the total rate of dissolution of oxygen in
the liquid will vary in accordance with the number of liquid
jet~.
FIG. 8 indicates that the absorption effiaiency of
-18-
,
. . . ~ , .
: .,.. ,...... , . . ~ . . , ~ .
1¢~4;~
the invention approaches almost 50~ even when the liquid jet
approaches the very surface lla of the liquid 11 in the tank
10. Absorption efficiency increases upon an increase in
li~uid jet submergence level and very nearly 100~ absorption
efficiency was obtained when the liquid jets were located
approximately 20 feet below the surface lla of the liquid 11.
In the course of the tests the liquid 11 in the tank
10 was tap water at standard conditions, but based upon com-
parative test data the greatly increased absorption effic-
iencies which the invention is capable of producing are alsoobtainable in the waste liquid introduced into the aeration
tanks of activated sludge waste treatment systems. Beyond
that, however, it would,appear as though the principles of
the invention are applicable in any situation in which it is
desirable to dissolve a gas into a liquid at greatly enhanced
absorption efficiencies.
Based upon the results of these investigations, var-
iations in the pressure drop across the liquid nozzles 15 ~'~
shown in FIG. 6 have a definite effect on the absorption '
20, efficiency of the system. As illustrated in the curve shownin FIG. 9, the absorption efficiency of a system constructed
in accordance with the principles of the invention probably
requires a liquid nozzle pressuredrop of about 5 psia in order '
to provide a viable or practically commercial system, and the ', ~ ,
pressure may be advantageously increased to about 10-12 psia.
Further pressure drop, however, does not appear to enhance
absorption efficiency to any significant degree and, on the
other hand, requires the expenditure of additional energy.
Tests were conducted in an effort to determine
whether the residence time of the liquid within that hydraulic
circuitry bears some significant relationship to absorption
efficiency. FIG. 10 discloses a curve which indicates varia- -
--19--
.,;' ~, . ,, , ' .
1~4Z5~9
tions in absorption efficiency with variations in liquid res-
idence time, that is, the time which elapses from the time
that the liquid in the hydraluic circuitry 36 is first in-
troduced to the gaseous oxygen until the liquid is discharged
from the liquid nozzles 15 into the body of liquid 11. This
curve indicates that, within limits, an increase in residence
time produces an increase in absorption efficiency, but it -~
also indicates that a residence time of at least about five
seconds is required to produce a co~mercially acceptable ab-
sorption efficiency.
It will be understood, of course, that with respect
to any given system it may be desirable to adjust flow rates
of the gaseous oxygen and-of the recirculated liquid to pro-
vide maximum absorption efficiency for that system in accor-
dance with the principles of the invention described herein,but these adjustments fall within the purview of one having
ordinary skill in the art. --
Tests were also conducted in which the liquid nozzles
15 discharged directly into the liquid 11 both with and with- -
out the benefit o the gas-liquid nozzles 26 surrounding the
liquid nozzles 15. FIG. 11 illustrates that absorption
efficiency is somewhat enhanced when the high velocity jets
issuing from the liquid nozzles 15 are surrounded by the noz-
zles 26 which, in the embodiment shown in FIG. 6, merely serve
as shrouds to produce secondary liquid streams surrounding the
jets issuing from the nozzles 15. Since the cost involved in
providing the shrouds of nozzles 26 is quite nominal, the
preferred embodiment should include the nozzles 26 to in-
crease the absorption efficiency as the curve shown in FIG.
11 would indicate.
In the tests, the mean velocity of the liquid stream
in the hydraulic circuitry 36 was between the range of about
-20-
, .; . . : .
. .
~42S69
4 to 8 feet per second. It would appear that variations in
liquid mean velocity may produce some variations in absorp-
tion efficiency, but once again it is apparent that the only
requirement relating to velocity is that it be sufficient to
produce a state of turbulence of the liquid within the hydrau-
lic circuitry so that the gaseous oxygen is mixed with the
liquid.
It will be understood by those skilled in the art
that any aeration system which can be considered commercially
acceptable and economical must, in addition to providing
acceptable absorption efficiencies at acceptable gas trans-
fer rates, also be capable of producing such absorption effi-
ciencies and gas transfer rates at acceptable energy require-
ments. . ;
FIG. 3 discloses that the present invention is cap-
able of producing extremely high absorption efficiencies at -~-
economically acceptable sas .rar,sfer rates. FIG. 12 discloses
that these high absorption efficiencies and rates are obtain- -
- able at relatively low and entirely acceptable energy require-
ments. Indeed FIG. 12 discloses that the present invention
requires much less energy for dissolution of the oxygen in
the liquid than does the conventional jet aeration system,
regardless of whether air or high purity oxygen is utilized
as the oxygenation medium.
In comparing the absorption efficiencies of systems
constructed and operated in accordance with the principles
of this invention with the absorption efficiencies a pre-
viousl~ known "oxygeD~' s~stems which require a succession of
completely enclosed tanks or cells, it is apparent that the
30 present invention compares favorably in terms of efficiencies, -
but in addition attains such efficiencies in an open tank,
one-pass contacting system.
-21-
2569
In FIG. 5 the details of the jet aerator 14 are
shown in greater detail. The air conduit 28 is shown con-
nected to jet aerator 14 in the manner illustrated in FIG. 4,
but in the system shown in FIG. 6 the conduit 28 is elimin-
ated, as mentioned hereinabove. Again it should be empha-
sized that while the embodiment of the jet aerator 14 illus-
trated herein comprises a plurality of liquid jet nozzles
arranged in a "cluster" form, the principles of the invention
are equally applicable to systems in which individual and dis-
tinct liquid jet nozzles are used for producing the.high velo-
city jets in the aeration tank 10.
Although minor modifications might be suggested by . ~
those versed in the art, it should be understood that in- ~. ; . .
cluded within the scope of the patent warranted hereon all
such modifications as reasonably come within the scope of t.he
present contribution to the art.
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..
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