Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process of and
a device for saturating a liquid with a gas.
Various processes and devices have been employed
for the saturation of liquids with gases; for example, DOS
2 612 255 utilizes injectors in a circulation trough. The
economic advantage of such apparatus and process depends upon
the rate of saturation of the liquid by the gas.
Through-flow saturation using steady flow transi-
tion phenomena, such as a ring jump, has been shown to be an
extremely suitable process for saturating a liquid with a gas,
for example, in the most common case saturating water with
air oxygen.
The amount of gas dissolved in the liquid is limited
by the saturation concentration of such liqu.id with the gas
under given conditions. The rate of dissolving of the gas is
defined as the ratio of the amount of dissoLvecl g~s to the
total amount of gas supp~ied to the liquid. Such rate d~pen~
most importantly among other factors upon the gas-liquid dis-
charye ratio, that is, the ratio of the discharges of the
gaseous and liquid components, in the through-flow mixing, and
is limited by it. The rate of dissolving of the gas in the
liquid can be increased by decreasing the gas-liquid discharge
rate. This can be accomplished by the method and apparatus
of the present invention without any perceptible loss of the
energy required for dissolving the gas in the liquid.
According to the present invention, there is pro-
vided a process for increasing the rate of solution of a yas in
a liquid in through-flow mixing, comprising clrculating a mix-
ture of a liquid and a gaseous component formed by dissolved
gas together with other gases into an elongated circulation
oxidation ditch in the direction of the longitudinal axis of
such ditch, reducing the gas-liquid discharge ratio in such
manner that the discharge of the liquid component emerging
from a primary mixing conduit is increased by the part of the
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licluid discharge ~hich circulates in the circulation ditch,
introducing the discnarge of liquid and gaseous component
emerging from the primary mixing conduit directly into a
secondary mixing channel which directly joins the circulation
so that the transfer process which starts directly in the
primary mixing conduit continues in the secondary mixing
channel.
According to the present invention, there is also
provided a device for increasing the rate of solution of a gas
and a liquid in a primary through-flow mixing conduit, com-
prising a reaction tank formed by at least one circulation
oxidation ditch, a channel of secondary mixing in the circu-
lation ditch, said seconclary mixing channel immediately join-
ing the primary mixing conduit and belng in the shape o~ a
covered channel :into which a mixture o~ liquid and CJa5 1~ .E~
ThereEore, in accordance with the prese~t invention
the liquid in which the g~s is to be dissolved is circulated
in an elongated endless circulation ditch, there being a pipe
feeding a mixture of -the liquid and the gaseous component
having an outlet disposed in the inlet part of the covered
secondary mixing channel or trough ditch, the inlet ener~y of
such gas-liquid mixture inducing circulation of the liquid in
the ditch. The mixture of the liquid and gaseous component
may be formed by steady flow transition phenomena, for example
by a ring jun-lp. The gas-llquld mixture is leacl to the
covered trough of a secondary mixing means which is preEer-
ably disposed in the circulation ditch. As above-noted, the
discharge energy of the gas-liquid mixture into the liquid in
the ditch maintains the circulation of such liquid, as well as
causing the gas-liquid mixture to be mixed with the liquid in
the ditch. The rate of dissolving of the gas in the liquid
increases with a decrease of the gas-liquid discharge ratio.
When the saturated liquid is not lead directly and
is repumped, the inflow of the repumped liquid to the pump
-- 2 --
leads inwardly through a hole in a hydrodynamically designed
bottom sill in the channel while maintaining the flow veloc-
ities in the ditch. When a plurality of circulatlon ditches
are employed for mixing, they can be interconnected in parallel
or in series depending upon -the nature o:E the saturation pro-
cess used.
The invention will be more readily understood upon
consideration of the accompanying drawings, in which:
Fig. 1 is a schematic view in side elevation oi a
portion of the apparatus of the invention including a through-
flow mixer disposed in a circulation oxidation ditch;
Fig. 2 is a foreshortened view in plan of an instal-
lation incorporating a plurality of circulation oxidation
ditches each of which incorporates two through-flow mixers in
~5 accordance with the inventlon; and
Figs. 3 and 4 illustrate respective alt~rna~ivc~
desiyns of a secondary mixing channel hy its beincJ recessecl
under the bottom level of the oxidation ditch, the construc-
tions of Figs. 3 and 4 being suitable for use in a shallow
oxidation ditch.
Turning first to Fig. 1, in a continuous recircula-
tion ditch 1 containing a liquid which extends to a level L
near the top thereof. In such portion of the ditch 1 there is
an inflow pipe ~ extending from the bottom of the dikch up-
wardly to a pump 5, the inflow pipe 4 having its lower inletend disposed within an opening or recess 6 in a streamlined
bottom sill portion 7 of the ditch.
The pump 5 is provided with an exhaust manifold 9
from which there extend a plurality of laterally spaced dis-
charge pipes 2 which extend horizontally for a short distance,then extend downwardly at 11 and finally are curved at the
bottom so that such curved lower end 12 thereof lies within a
laterally extended covered trough 3. As shown, discharge
from the lower ends of the pipes 2 travel in the same direc-
tion as the general flow of recirculating liquid in the ditch1. Near the top of eaeh of the pipes 2, adjaeent the dis-
eharge manifold 9, there enters a vertieal gas-conducting pipe
10. The vertical portion of the pipe 2 is of somewhat larger
diameter than the upper and lower end portions thereof, pipe
11 eonstituting a mixer for the liquid which has been fed
thereto from the diseharge manifold and the gas whieh has been
introduced thereinto through the pipe 10.
Turning now to Fig. 2, a plurality of recirculation
oxidation ditches 1 are shown, such ditches being fed with the
main body of liquid through a pipe 8 having entry ports 15
leading to the respective recirculation ditches; the ditches
1 and outlets 14 are thus eonneeted in series by the eonduits
8.
In eaeh of the reeireulation ditehes 1 -two pum~ ancl
mixer units as shown in l~ig. 1 are disposed in oppos:L~
relationship adjaeent the opposite ends of the reci.reulation
ditch. It will thus be seen that in each of ditehes 1 the
main body of liquid in the ditch i.s driven in a generally
eloekwise direetion b~ the gas-liquid mixture introdueed
therein by the pump and mixer unit, the resulting mixture of
the main body of liquid and the introduced gas~liquid mixture
being eonstrained to travel lenyth~ise along one side of the
diteh in the sub-diteh formed between the side oE the tan)c or
diteh-forming member and a longitudi.nal dividing partition 13.
The gas-liquid mixture then travels around the end of the
dividing partition, flows longitudinally of the diteh in a
direction opposite that of the first longitudinal flow thereof
and finally travels around the other end of the dividing
partition 13.
~ he process and the device of the invention can be
used to advantage in the chemieal and other industries, in
water management, and partieularly in waste water treatment by
oxidation as in the biological treatment of sewage.
In a preferred embodiment of the device of the
invention the circulation ditch of a waste water treatment
plant has a volume of 760 cubic meters, the water in the ditch
moves longitudinally thereof with a velocity of 0.7 meters per
second, the through-flow mixers 5, 9, lO/ 11 repump a mixture
of liquid and gas into the main body of liquid in the ditch
at the rate of 2 x 0.175 cubic meters per second, that is, in
the ditch a discharge of 6.7 cubic meters per second is
recirculated and the added amount of dissolved oxygen and the
transfer rate per required unit of power are increased by 56%
over a known comparable prior art device.
Parts in Figs. 3 and 4 which are the same as those
in Figs. 1 and 2 are designated by the same reference charac-
ters as in the earlier figures. As above stated, the devices
of Figs. 3 and ~ are suitable for use in a shallow oxidation
ditch .
In the embodiment shown in E'ig. 3, the bottom :L6 o.E
ditch l slants at 17 at a relatively small angle with respect
to the horizontal level surface 18. The lower end 12 of
mixing pipe is disposed at the left hand end (the beginning
of level surface 18). Somewhat to the xight of end 12 of pipe
ll, and adjacent the right hand end of channel 3, the bottom
l~ of ditch l slants shallowly upwardly to rejoin the level 16
of the general bottom of the ditch l.
In the embodiment of Fig. ~, the bottom 16 slants
sharply downwardly at 20, and slants shallowly upward at 21 to
regain the general level 16 of d.itch l. The outlet 12 of pipe
ll is disposed within the space provided between the right
hand end of surface 20 and the left hand end of surface 21.
The reaction ditch with longitudinal flow, in which
circulates the saturated liquid e.g. the treated water with
activated sludge that is brought into longitudinal movement by
the outflow from one or more aeration devices from which the
mixture of recirculated liquid and air (or another gas) flows
'
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into the reaction ditch in longitudinal direction in such a
way, whereby the improvement lies in the withdrawal of water
for recirculation from the reaction ditch by means of a
hydraulically shaped bottom sill and by situating the covered
canal of secondary mixing into the bottom pa~t of the ditch,
whereby the aerator mixing tube opens into this canal, ~hus
creating a triple successive mixing, first in the mixing tube,
then in the covered canal of secondary mixing and finally in
the ditch as such and that with electric energy saving, and
these improvements incorporate:
(A) the hydraulically-shaped upward convex bottom sill
situated on the reaction ditch bottom and ~n its upstream side
it has the opening 6 that does not interfere with the upper
convex part of the sill and into which is joined the tube 4,
leadin~ to the pump 5, whereby the concave curve of the sill
is designed so that during the inflow of the recircu~ated part
o.~ th~ uid fQr the given liquid discharcJ~ abov~ th~ bottom
sill no marked head loss occurs,
(B) a low-pressure pump whose inlet is connected by the
pipe 4 with the bottom sill and the outlet is connected with
the aeration device that is open into the mixing tube 11,
(Ct a covered secondary mixing channel 3, situated in
the bottom part of the reaction ditch, whereby the covering of
this channel is formed 1) by a horizontal separating wall
situated above the reaction ditch bottom, or 2) by a horizon-
tal or a slightly slanting separating wall situated flush with
reaction ditch floor or below .it, whereby under the separating
wall the reaction ditch bottom is gradually lowered 50 that a
secondary mixin~ channel is thus formed under the separating
wall, whereby the secondary mixing canal pro~ile and its
location to the outlets of the primary mixing pipes 11 is
chosen in such a way that turbulence created in the mixing
tube 11 is maintained, whereby the length of the secondary
mixing canal is only such, that the homogeneous bubble mixture
37
of the gaseous component in the liquid is maintained in the
secondary mixing channel, and
(D) an aeration device joined by its liquid inlet to the
pump and by its outlet to the mixing tube 11 with its lower
end 12 open into the secondary mixing canal 3, into which it
brings the recirculated liquid-air mixture which flows in the
secondary mixing canal together with the respective part of
the recirculated flow, whereby this arrangement
a) forces the liquid in the reaction ditch to move
in a longitudinal movement,
b) creates a triple successive mixing with varying
concentration gradients and that: the first mixing in the
aerator and mixing tube 11, second mixing in the covered
channel of secondary mixing 3 and the third mixiny at the
outlet from this canal, where the liquid from the canal ~ets
mixed with the other liquid, ~lowing in the ditcl~ in th~
conformable direction,
c) it prolongs the total contact time of the gas
bubbles with the liquid without creating undesirable air
cushions or separating the phases,
d) the mixing in the secondary mixing canal takes
place in the point of the highest hydrostatical pressure
without requiring for this effect a special device or con-
structional modifications,
e) although for this solution, an aerator of the
ring-jump type is most advantageous also another aeration
~evice type can be used, this arrangement means an essential
energy saving.
Although the invention is ~llustrated and described
with reference to a plurality of embodiments thereof, it is to
be expressly understood that it is in no way limited to the
disclosure of such embodiments but is capable of numerous
modifications within the scope of the appended claims.
