FR2501073A1 - DEVICE FOR FLOATING GAS BUBBLES OF MATERIALS SUSPENDED IN A LIQUID - Google Patents

Abstract

DEVICE FOR TREATMENT OF A LIQUID BY FLOTATION, INCLUDING A FLOTATION ZONE 2, A DUCT 16 FOR DELIVERY OF LIQUID TO BE TREATED, MEANS 15, 17 FOR SATURATION AT HIGHER PRESSURE OF THE LIQUID WITH GAS, A DUCT 11 CONNECTED TO THESE MEANS, EQUIPPED WITH A RELIEF VALVE 12 AND OPENING NEAR THE BASE OF ZONE 2, SO THAT THE BUBBLES, PRODUCED BY THE RELAXATION, ADHER TO THE PARTICLES IN SUSPENSION IN THE LIQUID; MEANS 7, 9 FOR EVACUATION OF A LAYER 6 FORMED BY THE SEPARATE FLOATING COMPONENTS AND THE REMAINING LIQUID ARE PROVIDED. THE DEVICE APPLIES TO THE TREATMENT OF LIQUIDS CONTAINING PARTICLES OR AGGREGATES, IN PARTICULAR IN A BIOLOGICAL TREATMENT SYSTEM.

Description

The present invention relates to a device

  flotation, by means of gas bubbles,

  components suspended in a liquid.

  We know various processes, as well as

  sitives of implementation of these processes, for the separation

  tion of components suspended in a liquid, for example-

full of waste water.

  A known method consists in causing the float

  tion of suspended particles, by fixing small gas bubbles, and in particular air bubbles, to these particles so that they become lighter than the liquid. After flotation, a floating layer of foam is thus obtained which can, for example, be removed by means of a scraper. This process is particularly suitable

  lb for the separation of components formed from particles

  laterally small, whose settling or flotation would therefore be carried out relatively slowly * Indeed, the smaller particles have a better surface / volume ratio

  that of larger particles, so that the resistance

  tance encountered as they move through the liquid

  surrounding, crott correlatively. Therefore, the above-

  Pensions of small particles are relatively stable.

  This separation process is also well suited for Particles whose density differs only slightly from

that of the liquid.

  Such gas bubbles are obtained by saturation.

  tion of a liquid, under higher pressure, with the

  chosen gas and introduction of the mixture, after a sudden

  tent, in a separation space in which the liquid to be treated is located. After decompression, the liquid mixed with the gas becomes supersaturated and a large number of very small gas bubbles are formed, having an almost colloidal distribution, these bubbles easily adhering to the particles.

  eWsiuspension and this effect being further improved by the re-

  fine and uniform partition of these bubbles in the liquid. We can, in this regard, refer to NL patent applications

73 17 649, 79 05 328 and 78 07 081.

  If the particles, whose flotation is obtained,

  bare as described above, consist of solid material or a liquid immiscible with the carrier liquid, the floating layer contains only relatively little carrier liquid, so that the separated material can be freed of the remains of carrier liquid

  fairly simple way, for example by drying, post-separation

ration, etc.

  However, sometimes the particles above

  board in the liquid to be treated themselves contain relatively a lot of liquid, for example in the case

  microorganisms whose cells contain li-

  that cell. It is, for example; danila mud's case

  in excess produced in a biological treatment of a li-

  what to purify using microorganisms, treatment

  during which microorganisms multiply.

  te that the mud must be extracted regularly for main-

  keep the amount of biological material at a suitable level

nable.

  If this material is separated from the liquid,

  particular by separation by means of gas bubbles, the material

  separate container still contains liquid inclusions

  which cannot be removed by treatments u-

  separation altars. This liquid often needs to be removed

  before rejection, storage, treatment or destruction of the material

  solid. Drying in the open air usually lasts too long, often causes inconvenience due to the decomposition of organic matter and drying is hampered if the material to be dried contains liquid included * Drying by heating is generally expensive. It exists

  therefore a demand for means making it possible to reduce

  The liquid content of the separated material is further enhanced. The present invention relates to a device for treating a liquid, in which the floating of the particles in suspension in this liquid is caused.

  by fixing small gas bubbles. This device com-

  takes a flotation zone, a pipe for supplying the liquid to be treated near the base of this zone, means for saturation at higher pressure of a liquid with a gas, a pipe starting from these said means and provided an expansion valve or the like, this pipe opening into the flotation zone near its base in order to allow the gas bubbles produced

  in this area when you want to join the

  the suspended particles present in this zone, and means for evacuating the flotation zone on the one hand from a layer comprising the separate components which float on the liquid present in said zone and on the other hand the remaining liquid. According to the invention, the device is characterized in that the pipe for supplying the liquid to

  to be treated is connected to the suction of the

  pressure, so as to saturate the liquid to be treated itself with the gas, and in that the pipe which opens into

  the flotation zone and which is fitted with a valve

  tent serves at the same time to bring the liquid into the

flotation area.

  Since it is the liquid to be treated which is itself

  even saturated with pressurized gas, the included liquid is also pressurized and can even absorb gas from the surrounding liquid. During the sudden relaxation

  liquid under pressure, said included liquid is also subjected to

  Lent a trigger and the gases dissolved in this liquid are therefore released. As a result, the envelope that encloses

  amounts of liquid is broken and the liquid is

  béré. The remaining material is then made buoyant by the adhesion of gas bubbles in the flotation zone, and it can be removed as a floating layer.

  with a lower liquid content.

250 107 5

  More particularly, for example as described in the aforementioned patent application NL 73 17 649, if a

  mixing tank is interposed between the compressor pump

  liquid and the expansion valve, an independent pump

  gas compression pendant being used to provide

  the gas to be mixed with the liquid at least at the pressure of the

  quide, said mixing tank further comprising means for improving the mixture of gas and liquid, the

  line connected to the discharge of the compressor pump

  gas sion can, according to the invention, lead directly-

  in the mixing tank. This tank is then used

  to mix the gas and the liquid. Preferably, the gas line extends inside the mixing tank and leads to one or more distribution nozzles,

  so that the gas to be mixed under pressure is found

  gone substantially uniformly through the liquid.

  In addition, the mixing tank can be designed to maintain, above the liquid, a buffer volume of gas under pressure, the pipe fitted with the expansion valve then opening below the lowest level of liquid in the tank. mixture. In particular, the various compression pumps can be controlled so as to maintain a determined pressure in the tank

  gas buffer and a certain level of liquid.

  If the liquid trapped in the material above

  board in liquid to be treated contains dissolved components which cannot be removed by flotation

  with air bubbles which contaminate the liquid

  cue from the flotation zone, the latter liquid must be

  be directed to post-processing, in particular a stage

  biological treatment, in order to eliminate the so-called

posing.

  In a device in which the liquid to be treated

  ter is subjected to separation by means of gas bubbles in a pre-separator before being sent to a biological treatment stage and in which the excess sludge

  this biological treatment is recycled to the same pre-

  separator in order to separate this mud by flotation

  at the same time as the components suspended in the liquid

  the liquid compression pump and the expansion valve according to the invention can be incorporated

  in the recycling of excess vow.

  The invention will be better understood in light

  ueAa description of its embodiment, not limited to

  tive, shown in the accompanying drawings.

  Fig. 1 is a very simplified diagram of a device

  positive according to the invention, and FIG. 2 is an even more simplified diagram of

  such a device included in a milking installation

ment of a liquid.

  The device represented in FIG. 1 comprises a separator 1, in the form of a flotation tank which can in particular be constructed as described in the

  above-mentioned patent applications NL 73 17 049 and 79 05 328.

  This basin includes a chamber 2 for feeding or

  flotation separated by an inclined partition 3 of a chamber

  bre 4 of post-separation which aims to separate the com-

  layers, not separated in bedroom 2, by flotation or decantation as appropriate. As described in the requests

  above, a plate separator, not shown

  felt in FIG. 1, can be provided in room 4.

  The components separated by flotation from the liquid 5 combine to form a floating layer 6, which can be evacuated by means of a weir 7 to an evacuation chute 8, if necessary using a scraper device, not represented. Below the

  floating layer 6, an outlet 9 for purified liquid communicating

only with room 4.

  A nozzle 10 for the supply of liquid to be purified is provided near the bottom of the chamber 20 This nozzle is connected to a line 1i in which is provided an expansion valve 12, this line coming from a tank

mixing 13.

  In the tank 13 there is a pipe 14 connected

  dedicated to a liquid compression pump 15 which can

  pump the liquid to be treated from a supply line

  ment 16. The pump 15 can discharge the liquid under

pressure in the tank 13.

  On the other hand, an az compressor 17 makes it possible to discharge ambient air, or another suitable gas, to an inlet nozzle 18, under a pressure which is at least

  equal to the pressure supplied by the pump 15.

  The nozzle 18 can for example be constructed in the form of a boot or a perforated tube, so as to distribute the gas as uniformly as possible through the liquid. The gas rises in the form of small bubbles and collects, for the part which is not dissolved, in a gas buffer volume 19, at the upper part of the tank 13. If necessary, an agitator 20 can be used.

  to better mix the gas with the liquid.

  A level detector 21 is connected to the pump

  , as shown schematically in 22, so as to stop

  ter this pump as soon as a determined level of liquid is

  achieved. In addition, this detector, or an additional detector

  mentary, can be used to control, as shown schematically in 22 ', the gas compressor 17 when the air buffer 19 becomes too large or too small. If desired, other modes of regulation can also be used.

  Line 11 opens into tank 13 above

  below the liquid level, so that the gas is never

  but introduced into line 11. The liquid is discharged into line 11 at the pressure prevailing in space 19 and this liquid is substantially saturated with gas at this

pressure.

  This pressure is suddenly reduced to a value

  their close to ambient pressure, passing through valve 12, so that the liquid becomes very supersaturated

  in gas. The gas then separates in the form of small bul-

  them, with a substantially colloidal distribution. These bubbles adhere to suspended particles entrained in the liquid, so that these particles become lighter than the liquid and rise in the chamber.

  flotation 2, towards layer 6. The possible particles-

  The remaining parts can be separated in room 4, if necessary in a plate separator which can be

  arranged in this chamber, by decantation or flotation.

  The difference with the known gas bubble flotation devices is that, according to the invention, it is the liquid to be purified itself which is mixed under pressure with a gas and not a relatively pure auxiliary liquid.

  such as, for example, the purified liquid to be treated.

  Another consequence of saturation under pres-

  of the liquid to be treated with a gas is that the particles

  those in suspension containing an included liquid explode

  almost all of them during their sudden expansion in the valve 12. They then lose the liquid included, so that the

  separate material is drier and therefore requires less

  drying energy. This applies primarily to the mid-

  cro-organisms made up of cells comprising a cavi-

  tee filled with liquid. When the liquid is compressed and saturated with a gas in the tank 13, the cell cavities are also pressurized and, in addition, the gas diffuses inward through the cell. By decompression, and in particular under the effect of gas

  released in the cavities, the cells are destroyed.

  A similar phenomenon can occur in

  particle aggregates with intermediate cavities

  res in which the liquid is trapped. During decompression, this liquid can also be released, which

  which destroys the cohesion between the particles.

  If the flotation is caused, by means of the bul-

  gas, debris from the particles broken in this way and they thus reach the floating layer 6, an effective purification of the liquid is obtained. The ingredients

  separated health are also freed of liquid,

  that the substance of the evacuated floating layer has a

  higher solid content.

  However, if the liquid trapped in the particles or aggregates of particles or otherwise contained in these particles, may contaminate the treated liquid discharged in 9, for example in the case of organic substances dissolved in the cellular material or in the liquid in the cavities of microorganisms, these substances must be eliminated from the treated liquid. That

  can be done in further processing, e.g.

  ple in a biological treatment stage. If the liquid supplied in 16 already comes from biological treatment,

  it can be used for this purpose.

  FIG. 2 is a diagram, by way of example,

  a combined device comprising a stage 23 for milking

  biological. This device includes the float basin

  tation 1 and the mixing tank 13 with their as-

  companies, as in the case of figure 1. The liquid to be treated

  ter is brought by a pipe 24 opening at 25 into the flotation chamber 2 of the basin 1, more particularly near the nozzle 10 of the pipe 11 equipped with the expansion valve 12. The pipe 16 is connected to a pipe

  26, by which the sludge is removed from the biological treatment

  that 23. Part of the sludge is returned by a pump 27 to the biological treatment, at 28. The pumps 15 and

  27 are determined so as to obtain such a distribution

  that the quantity of mud returned by the pump 27 is sufficient to maintain the concentration of mud in the biological treatment 23 at the desired level, the pipe 16 then discharging the excess mud. This is saturated under

  pressure with the gas, in the mixing tank 13. After de-

  tent in valve 12, it is introduced at 10 into the flotation chamber 2, in which the air bubbles produced cause the flotation not only of the

  mud particles but also suspended particles

  sion introduced in 25. The pipe 9 leaving the basin

  1 returns to biological treatment 23, in which the

  non-separated and in particular dissolved components are subjected to a biological purification treatment. The purified liquid

  is rejected in 29. This combined device corresponds sensi-

  wholly to that described in the patent application NL 77 01 608 except in that, in the present case, it is the recycled sludge itself, and not part of the liquid

  pretreated in tank 1, which is saturated with gas.

  As described in the aforementioned patent application,

  holds a floating layer 6 by joint flotation of the particles suspended in the inlet liquid and in the mixture of recycled mud, this layer containing less liquid and therefore more solid matter than

  in the case of separate flotation.

  As shown in 24 ', we can also

  put the liquid to be treated towards the pump 15 in order to

  also to gas gas, which can be advantageous if this liquid also contains particles or aggregates

  particles with trapped liquid. Of course

  of, we can also saturate only the liquid with

  gas and return the recycled sludge directly to the chamber.

bre 2.

  If, during the bursting of the particles in sue-

  pension or particle aggregates due to the de-

  compression, debris of these particles arriving in the floating layer 6 can be further dissociated and generate, during drying or other treatments,

  unwanted decomposition products it can be

  advantageous to post-treatment the

  material of the floating layer. If a biological treatment

  that is suitable, it can be carried out in a separate stage of biological treatment but it is also possible to use for this the treatment device 23. The ma-

  float layer can be steered from the gou-

  monkfish 8 to a storage bin 31, in order to temporarily store it there and send it at the appropriate time to the

  biological treatment 23 via a

  pick 32, for example while no liquid is brought in through line 24, which may be the case during weekend vacations and other work interruptions when there is no production of liquid to be treated . An advantage of this arrangement is that the microorganisms can thus be kept alive in

the device 23.

  It is understood that modifications of detail can be made in the form and construction of the device according to the invention, without departing from the scope thereof. The device shown in Figure 1 can also be incorporated in different ways in

  existing liquid processing systems.

Claims (8)

Claims   1. Device for processing a liquid, in the-   which the flotation of particles in suspension in a liquid is caused by the fixing of small gas bubbles, comprising a flotation zone (2), a pipe for supplying the liquid to be treated near the base of this zone, means of saturation under increased pressure of a liquid with a gas, these means comprising a pump (15) for compressing the liquid, a pipe (11) connected   to these means and provided with an expansion valve (12) or   gane analog and opening near the base of the flotation zone so that the gas bubbles produced in / the   liquid during relaxation can adhere to particles   present in said zone and in suspension in the introduced liquid, and means (7,9) for evacuating from the flotation zone on the one hand a layer (6) which comprises the separate components floating on the present liquid   in zone (2), and on the other hand the remaining liquid, charac-   terized in that the line (16) for supplying the liquid to   to be treated is connected to the suction of the   pressure (15), so as to saturate the liquid with a gas   to process itself, and in that the pipe (11), which   mouth in the flotation zone (2) and includes a   trigger (12), serves at the same time to bring this line in the flotation area.   2. Device according to claim 1, wherein a mixing tank (13) is interposed between the pump   compression of the liquid and the expansion valve, a compressor   gas drainer (17) being provided and determined to introduce the gas to be mixed with the liquid into said tank, at least at the pressure of the liquid, this tank being provided with means (20) which promote mixing of the gas with the liquid, characterized in that the pipe connected to the discharge of the gas compressor opens into the mixing tank,   this being designed for mixing gas and liquid that under pressure.   3. Device according to claim 2, character-   laughed at the fact that the gas line ends, inside   of the mixing tank, by one or more distribution nozzles (18) by means of which the gas to   mixing under pressure is distributed substantially uniformly even through the liquid.   4. Device according to claim 2 or 3, ca-   characterized in that the mixing tank is designed in such a way   to maintain above the liquid a buffer volume (19) of gas under pressure and in that the line (11) provided with the expansion valve opens into the mixing tank   below the lowest liquid level.   5. Device according to claim 4, character-   laughed at in that it includes control means (21, 22,   22 ') of the compression pumps, so that a level   liquid calf is kept in the mixing tank.   6. Device according to any one of the claims.   cations 1 to 5, characterized in that the means (9) of   evacuation of the treated liquid from the flotation zone   provide with a post-processing device, in particular   Particular biological treatment (23), the latter being intended to remove the components which remain in this liquid.   7. Device according to claim 6, danslle-   which liquid to be treated is subjected to a gas bubble flotation treatment in a pre-separator (1) before being sent to a post-treatment stage (23), the excess sludge produced in this post-treatment being recycled to the same separator (1) in order to separate the components of this sludge by flotation at the same time as the components in suspension in the liquid to be treated,   characterized in that the liquid compression pump (15)   quide and the expansion valve (12) are placed in the con-   waste recycling sludge.   8. Process for the treatment of liquids containing   suspended particles and / or aggregates of particles   them, characterized in that the liquid is treated in a   device according to any one of the claims   previous, so that the particles or aggregates are broken during the expansion and that the liquid included in   these particles or aggregates is released.