Note: Descriptions are shown in the official language in which they were submitted.
1~3671~
For separating components suspended in a liquid, which
components may be heavier or lighter than this liquid, various
kinds of separation devices are known, in particular so-called
plate separators in which the liquid is led through passages de-
fined between superposed parallel and in particular corrugated
plates. The separation effect depends, inter alia, on the size
of the suspended particles and on the difference in specific
weight between these particles and the carrier liquid. In order
to promote the separation it can be favourable to bring about
particle growth beforehand.
Apart from or instead of by means of preceding particle
growth, the separation can also be enhanced by introducing air or
another gas into the liquid so as to obtain a flotation effect
by adhesion of gas to the particles to be separated. The inven-
tion provides a method and a device by means of which this can
be effectively realised.
To that end, according to the invention, a liquid mixed
with a gas or a substance vaporising at the prevailing tempera-
ture is pressurised and introduced into the supply chamber of the
separation device, which gas-liquid mixture is depressurised just
before introduction into the separation device so that a more or
less colloidal gas bubble mixture is obtained in which components
pres~nt in the liquid in this supply chamber are made flotating
by adhering gas bubbles.
Dependi~.g on the circumstances the said liquid is the
liquid to be treated itself or a liquid mixed with gas which is
supplied to the supply chamber separately from the liquid to be
treated, in particular the carrier liquid stripped of suspended
components obtained at the outlet of the separation device.
As a rule air is used as the gas, but in some cases use
can be made of a gas already present in the liquid or of an eva-
porating substance.
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103~j718
The invention will be elucidated below by reference to
a drawing showing in:
Figure 1 a schematic representation of a separation device
according to the invention;
Figure 2 a simplified view of an injection nozzle for this
device; and
Figure 3 another embodiment of a part of this device.
The device shown in Figure 1 comprises a tank 1 from
which is separated, by means of a partition 2, a supply chamber
3 and a discharge cham~er 4. A second partition 5 constructed
as an overflow weir separates from the tank 1 a discharge chamber
6 for the separated components which can flow off over the weir 6.
In the chamber 3 a plate assembly 7 is provided which bears on a
sloping wall 8 of the tank 1, the lower end of the upper wall 9
of this assembly joining the partition 2. The lower side of the
discharge chamber 4 merges with a sediment discharge 10, and
means not shown for discharging the cleaned liquid connect with
the upper side of the chamber 4.
The liquid to be treated is supplied by means of a duct
11 which terminates in a nozzle 12 situated in the triangular
space between the partition 2 and the upper wall 9 of the assem-
bly 7. This nozzle is, in particular, formed by a tube extending
across the full width of this space and provided with a longitu-
dinal slot which is, in particular, shaped so as to ensure that
the liquid will uniformly emerge. Possibly already separated
flotating components will immediately rise towards the surface
of the liquid in the chamber 3, which liquid will then flow on
through the plate assembly 7, in which remaining flotating and
possibly also sedimentating components are separated. The li-
quid stripped of these components then flows upwards into thechamber 4 and is discharged, and sediment slides downwards from
the plates of the assembly 7 and arrives in the collecting fun-
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1(136718
nel 10. The flotating components slide upwards along the platesand will float on the liquid in the chamber 3.
Below the supply nozzle 12 a second nozzle 13 is located
communicating with a duct 14. This duct co~prises a throttle or
relief valve 15 and leads to the pressure side of a compression
pump 16. ~t the suction side of this pump a duct 17 is connected
by means of which liquid can be sucked in from the discharge cham-
ber 4. ~loreover an air duct 18 opens in the duct 17 50 that air
is sucked in from the surroundings and is mixed with the liquid.
This air is thoroughly mixed with the liquid in the pump 16 which
is generally a centrifu~al pump, and possibly occurring air bub-
bles are disrupted by the pump vanes. The pump 16 is adapted to
produce in the duct 14 before the throttle valve 15 a considerable
pressure, e.g. of 0,5...1 N/mm .
In view of static pressure differences it can sometimes
be advisable to include in the air duct 18 an auxiliary pump for
introducing the air at a certain pressure into the liquid.
The pressurized liquid which contains a considerable
amount of air, and is, in particular, saturated therewith, is
suddenly relieved behind the valve 15, so that, then, a super-
saturated condition is obtained manifesting itself in a more or
less colloidal distribution of small air bubbles injected by the
nozzle 13 i~nto the space above the plate assembly 7. These bub-
bles rise and mix with liquid introduced by the nozzle 12 into
this space, and the air bubbles will adhere on particles suspend-
ed therein, which thus become lighter and are entrained towards
the liquid surface.
Figure 2 shows an embodiment of this nozzle 13 which ex-
tends across substantially the whole width of the chamber 3, and
is provided with a longitudinal slot 19 through which the supplied
liquid can emerge. In order to obtain a uniform distribution of
the emerging liquid, this slot is made convergent in the flow
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sense. Also the supply nozzle 12 can be constructed in the same
manner. In particular the slot 19 is directed downwards in order
to obtain a better distribution of the appearing air bubbles
which, moreover, can be promoted by arranging a guiding baffle 20
above the tube 13. It is also possible to make the tube 13 ro-
tatable on its own axis in order to allow the outflow direction
to be adjusted at will. Also the auxiliary baffle 20 can be made
adjustable, and it is also possible to arrange this bafffe in
another place, for instance above the nozzle 12.
Figure 3 shows another embodiment in which air is supp-
lied at the pressure side of the pump 18 by means of an addition-
al pump 21 providing the required pressure. In this manner often
a better saturation with air can be obtained. Since the intro-
duced air then does no longer arrive in the liquid pump, general-
ly additional means are to be provided for disrupting air bubbles.
To that end a mixing vessel 22 in which a stirrer 23 is arranged
is included in the duct 14, by means of which the air bubbles can
be reduced. In particular it is possible to construct this ves-
sel 22 as a buffer vessel in which the liquid can be stored for
some time so as to promote the mixing. Such a buffer vessel can
be used, of course, also in the case of Figure 1.
It can sometimes be favourable to subject the liquid
supplied by the duct 11 previously to a coalescence treatment so
as to bring about a certain particle growth. Apparatuses for
that purpose are known.
Such a coalescence apparatus can be positioned also in
the triangular space between the partition 2 and the upper wall.
In that case the injection of the air-liquid mixture will take
place at the inlet end of this coalescence apparatus. For the
rest this can also take place in a coalescence device located
outside the separation device proper.
Furthermore it is also possible to use only one injection
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nozzle, in which case the ducts 11 and 1~ are interconnected
before this common nozzle, and it is also possible to use a mix-
ing nozzle which, for instance, consists of nozzles 12 and 13
surrounding one another.
In particular a simple nozzle can be used if the liquid
to be treated itself is pressurised and mixed with air by the
pump 16, and the duct 17 is then connected to the liquid supply.
Of course this is only possible if the character of the suspen-
sion is so that the pump 16 and the relief valve 15 are not sub-
stantially soiled thereby, or if this can be taken into the bar-
gain.
Instead of air also any other gas can be supplied of
course. In some cases the liquid to be treated comprises a gas
or a substance which is highly volatile at the prevailing tempera-
ture, so that, if this liquid is pressurised, no separate gas
needs to be supplied.
Furthermore it is possible to add additional substances
promoting the separation or particle growth in any point of the
duct mentioned above. It will be clear that for providing the
gas-liquid mixture also a liquid may be used which is not origin-
ating from the system itself, if this liquid is compatible with
the remaining liquids, for instance tap-water when the carrier
liquid of the suspension is water.
In the manner described above it becomes possible to
improve considerably the separation of often difficulty to be
separated components. Within the scope of the invention many
modifications are possible.
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