CA1036718A - Separation method and device - Google Patents

Abstract

Abstract A method for separating components suspended in a liquid, in which a gas-liquid mixture is pressurised, and then is depres-surised just before being introduced in a separation device so as to obtain a substantially colloidal gas bubble mixture, the gas bubbles adhering to particles of the suspended components which are made flotating thereby, the device for executing this method comprising a liquid compression pump, a relief valve, and a nozzle opening into the separation device just behind this nozzle.

Description

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.

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-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 ~Q3671~3 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 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.

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of enhancing the separation of particles sus-pended in a carrier liquid which mixture of carrier liquid and particles constitutes the liquid material to be treated in a separation system which includes a plate separator composed of inclined parallel superposed plates forming separation passages and an associated supply chamber for the plate separator, compris-ing: introducing the liquid material to be treated to the supply chamber of the separator, forming a pressurized gas liquid mix-ture, depressurizing said gas-liquid mixture to form a mixture of gas bubbles dispersed through the liquid in a colloidal distribu-tion of gas bubbles in the liquid, introducing said depressur-ized gas-liquid mixture into the supply chamber so that the gas bubbles join with at least a portion of the particles present in liquid material to be treated for separation thereof towards the surface of the liquid to be treated present in the supply chamber, and effecting flow of the liquid material with the remaining particles therein through the plate separator to effect separa-tion of the remaining particles from said liquid material.

2. A method as set forth in claim 1 in which the gas-liquid mixture is pressurized to a pressure of between 0.5 and 1.0 Newton per square millimeter.

3. The method of claim 1 or 2, characterised in that the pressurised liquid is the treated liquid which is stripped of the suspended particles.

4. The method of claim 1 or 2, characterised in that the pressurised liquid is an additional liquid.

5. The method of claim 1 or 2, characterised in that the pressurised liquid is the suspension to be treated.

6. A method as set forth in claim 1 wherein the gas-liquid mixture and the liquid to be treated are admixed and introduced together into the supply chamber.

7. A method as set forth in claim 1 wherein the gas-liquid mixture and the liquid to be treated are separately introduced into the supply chamber.

8. The method of claim 1, characterised in that the gas is air.

9. The method of claim 1, characterised in that the gas is already present in the pressurised liquid.

10. The method of claim 1, characterised in that the gas is introduced into the liquid at the suction side of the compression pump used for pressurising the liquid.

11. A method as set forth in claim 1 wherein said pressurised gas-liquid mixture is formed by introducing the gas under pres-sure and liquid into the pressure side of a compression pump for pressurising the gas-liquid mixture.

12. The method of claim 11, characterised in that possibly appearing gas bubbles are reduced in size by means of a mixer or stirrer.

13. A method as set forth in claim 1 further including the step of storing said pressurised gas-liquid mixture in a buffer vessel to effect further intermixing of the gas in the liquid prior to introduction into said supply chamber.

14. The method of claim 1, characterised in that the suspen-sion, before being introduced into the separation device proper, is subjected to a coalescence operation.

15. A method as set forth in claim 1 wherein the gas-liquid mixture is the carrier liquid.

16. A method as set forth in claim 1 wherein the gas-liquid mixture is purified, carrier liquid.

17. A purification device for treating a liquid material in-cluding a carrier liquid having particles therein to effect sep-aration of the particles from said carrier liquid, comprising:
means forming a tank including a supply chamber for said liquid material and a discharge chamber for the carrier liquid and a portion of said particles, plate separation means positioned within said tank to receive flow of the liquid material therein and including a set of superposed parallel plates defining a plurality of separating passages communicating at one end with said supply chamber and at the other end with said discharge cham-ber, means forming a supply tube for said liquid material and in-cluding an opening communicating with said supply chamber, means forming a source of pressurized gas in a liquid and including a pump to pressurise said liquid and gas and a pressure reducing valve connected to receive flow from said pump, and injection nozzle means connected to receive flow from said valve and posi-tioned in said supply chamber whereby the pressurized gas and liquid is depressurised upon flow through the valve to form a mix-true of gas bubbles in the liquid for admixture with the liquid material in said supply chamber to remove a portion of said par-ticles prior to flow of the liquid material through said plate separator.

18. A purification device as set forth in claim 17 wherein a baffle is located in said supply tank above the opening of said injection nozzle means.

19. A purification device according to claim 17 comprising a plate separator having an input end communicating with said supply chamber to recieve a flow of liquid material from it, having an output end communicating with said discharge chamber for dischar-ging separated particles and carrier liquid into said discharge chamber, and including a set of superposed parallel plates defining a plurality of separating passages communicating at one end with said supply chamber and at the other end with said dis-charge chamber, said plates sloping downwardly from said supply chamber to said discharge chamber so that separated particles are discharged from said plate separator into said discharge chamber;
and injection nozzle means connected to receive flow from said valve and positioned in said supply chamber to provide a flow into said supply chamber for admixture with the liquid material of a mixture of gas bubbles in the liquid, whereby a portion of said particles is removed by flotation prior to flow of the liquid material through said plate separator.

20. The purification device of claim 19 wherein said injector nozzle means and said means forming a supply tube for said liquid material are located so close to each other that the liquid material emerging from said means forming a supply tube will be intermixed with the flow from said injector nozzle means.

21. The purification device of claim 20 wherein said plate separator includes an upper surface extending into said supply chamber and wherein said injector nozzle means and said means forming a supply tube for said liquid material are located above said upper surface proximate a wall of said supply chamber.