FR2778121A1 - Cyclonic flotation device for use in systems for treatment of industrial waters - Google Patents

Abstract

Flotation device has new construction. The device comprises tank into which water to be treated and eventually flocculating agent are delivered through pipe, system for collection and removal of foam formed on the surface of flotation bath in the tank, and collector of clarified water, under flotation bath. The device comprises cylindrical flotation pipe (3), penetrating vertically the bottom (11) of the tank (2) and extending up to the level of flotation bath (8), with the pipe (5) delivering water to be treated opening tangentially into lower part of flotation pipe (3). The latter is disposed coaxially with tank, and the collector of clarified water (4) is disposed in annular manner around the flotation pipe (3), below the bottom (11) of flotation tank (2). Device also comprises separator element (6) positioned outside and around the upper end of flotation pipe (3) and extending up to a small distance (e) from internal wall of the tank (2). Water feeding pipe (5) comprises depressurizing valve (12), and water to be treated and/or flocculent do not contain dissolved gas downstream of this valve. Feeding connector (13) is linked to feeding pipe (5) through annular vessel (14) in which holes (15) are pierced through to (5). Turbulence device may be provided inside feeding pipe (5) in proximity of flotation pipe (3). Upward slope of the part of feeding pipe (5) downstream the depressurizing valve (12) is preferably at an angle 7 deg .

Description

CYCLONIOUE FLOAT

  The present invention relates to the treatment of water, in particular industrial waste water, by flotation. It relates more particularly to a device specially designed for this treatment called a float, and in particular operating by depressurization of the gases dissolved in the water to be treated. Flotation or aeroflotation is a process for purifying water, in particular waste water, consisting in bringing the surface of the flotation bath up

  elements to be separated which are in colloidal or suspended form.

  These elements are entrained towards the surface by the presence of bubbles or micro-

  bubbles present in the water to be treated. These bubbles or micro-bubbles are brought by a pressurized gas which is blown into the water supplying the float, they can also result from the depressurization of gas dissolved in the water supplying the float. They can finally be generated by electrolysis

partial of the water to be treated.

  In a known manner, a float consists of a reservoir into which a supply pipe introduces the water to be treated and optionally one or more chemical reagents, a device for collecting and discharging the foams formed on the surface of the flotation bath contained in the tank and a clarified water collector giving into the tank. The water to be treated in which the elements to be separated are located and the bubbles or micro-bubbles and possibly the chemical reagent (s) enter the reservoir, via the supply line. The elements in suspension are entrained by the bubbles towards the surface of the bath at the level of which a foam is created formed by the accumulation of these elements and by the air escaping from the bath. These foams are collected and disposed of by the device provided for this purpose. The clarified water reaching the collector is evacuated as the water to be treated is supplied to the tank. In practice, the

  tank in question is an open concrete, steel or plastic basin.

  Generally, the ratio between the hourly flow to be treated and the flotation surface is between 2 and 20 m / h, which can lead to implementation - 2 -

  very bulky installations when it comes to high flows.

  The goal set by the applicant is to offer a float having a capacity

  greater purification than known floaters.

  This object is perfectly achieved by the float of the invention which comprises the structural elements described above for the known float and which is characterized in that it comprises a cylindrical flotation pipe, penetrating vertically into the bottom of the tank up to the level of the flotation bath and in that the supply line for the water to be treated in which the elements to be separated are located, the bubbles and possibly the chemical reagent (s)

  opens tangentially in the lower part of the flotation tube.

  Due to this tangential supply of water to be treated in the cylindrical pipe, a helical updraft is created inside the flotation pipe up to the flotation bath. When the water to be treated passes from the supply line into the flotation pipe, its movement is slowed down by the frictional forces of the water against the interior wall of the flotation pipe. This results in a shear stress which improves the capture of the elements in suspension by the air bubbles and, in the presence of chemical reagents their coagulation and their flocculation. This improvement combined with the stability of the movement of water in the flotation pipe has the effect of significantly increasing

  the efficiency of water purification by the float.

  In a preferred embodiment, the flotation pipe is arranged axially with respect to the tank and the clarified water collector is arranged

  annularly around the flotation pipe under the bottom of the tank.

  In a preferred variant, the flotation device comprises a separating element which extends externally around the upper end of the flotation pipe up to a reduced distance from the interior wall of the tank. It is in the gap between the interior wall of the tank and the separating element that the clarified water, free of water, can escape below the flotation bath.

suspended elements.

  - 3 Advantageously, the separating element is a frustoconical plate

flaring down.

  As it relates more particularly to a flotation device operating by depressurization of the gases dissolved in the water to be treated, preferably the supply line of this flotation device comprises a depressurization valve; in addition, a supply pipe for flocculating agents and / or water to be treated, not comprising dissolved gas, opens into the supply line downstream of said valve. Thus, according to this particular arrangement, the mixing of the water to be treated with the flocculating agent takes place immediately after the depressurization and therefore the formation of bubbles and micro-bubbles, which makes it possible to obtain a particularly homogeneous mixture of the flocculating agent with the water to be treated saturated with air bubbles. In addition, the shear stress occurs on the mixture of water to be treated with the flocculating agent, which further improves flocculation and increases the efficiency.

water purification.

  In order to further improve the action of the flocculating agent on the elements in suspension, the flotation unit may further include a swirl device installed in the supply line near the flotation pipe. It may in particular be a body placed inside the supply duct and

  locally narrowing the water passage section.

  2 o A particular difficulty may arise, namely the formation of deposits in

  the supply line between the depressurization valve and the flotation pipe.

  These deposits are undoubtedly caused by accumulation of flocculated suspended matter. To overcome this drawback, the float according to the invention is characterized by the upward inclination of the portion of the supply duct downstream of the depressurization valve. Due to this upward inclination, the flocculated material carried upwards by the air bubbles can no longer

  accumulate on contact with the interior wall of the supply line.

  It is however noted that it is preferable to limit the angle of inclination of the portion of this supply pipe to approximately 7 'so as to comply with the conditions desired for the helical ascending current inside the pipe

flotation.

  The present invention will be better understood on reading the description which will

  be made of a preferred example of a cyclonic float illustrated by the accompanying drawing in which Figures 1 and 2 are schematic sectional views

  transverse for Figure 1 and in top view for Figure 2 of the float.

  The float 1 has as main parts: the tank 2, the flotation pipe 3, the clarified water collector 4, the supply pipe 5 and the cone

separator 6.

  o10 The supply conduit 5 opens tangentially into the lower part 3a of the flotation pipe 3, which opens into the bottom 11 of the tank 2, its upper edge 7 being below the flotation bath 8 when the float is in operation. The flotation bath 8 is constituted by the portion of water to be treated which comprises the accumulation of flocculated matter or suspended matter which is carried to the surface of the water by the air bubbles. It is on the surface of the flotation bath 8 that the foams 9 are located which are collected and discharged

  by a known device not shown.

  The separating cone 6 is a downwardly flared plate which is fixed along the upper edge 7 of the flotation pipe 3 and which extends to a reduced distance e

  2 o of the internal wall of the tank 2.

  The collector 4 of clarified water is constituted by an annular chamber arranged around the flotation pipe 3 and opening in the upper part on an opening 10

  made in the bottom 11 of the tank 2.

  In the preferred embodiment which is illustrated, the float 1 of the invention operates by depressurization of the gas dissolved in the water to be treated. To obtain this depressurization, a throttling valve 12 is disposed on the supply line 5. In addition, downstream of this valve 12 is provided a manifold 13 for admitting a chemical reagent, that is to say an agent which performs the precipitation or agglomeration of suspended matter to be eliminated. This tubing is, in the example illustrated, terminated by an annular endpiece 14, holes 15 drilled in the supply pipe 5 at the level of said annular endpiece 14 allowing the injection of the flocculating agent in a distributed manner the section of

the supply line 5.

  A buffer tank 7 is disposed on the discharge pipe 17 connected to the collector 4 of clarified water. More precisely, the clarified water is evacuated by overflow in the downstream part 17b of the evacuation pipe from the buffer tank 16 which is filled by the play of the communicating vessels by

  through the upstream portion 17a of the discharge pipe 17.

  The operation of the float 1 is as follows. The water to be treated under pressure, saturated with dissolved air, passes through the depressurization valve 12. After passage of the throttle and the fact that the float is open to the open air, the dissolved air is released in the water to be treated in the form of tiny bubbles in the supply line 5. When the water in treating saturated with bubbles passes through the holes 15 through which the chemical reagent is injected, the said agent is mixed with water. This mixture is brought by the supply line 5 into the flotation pipe 3, tangentially thereto. This tangential supply gives a general rotary movement of the liquid contained in said flotation pipe 3,

  so that this rotary, helical upward movement quickly stabilizes.

  Going upwards, the mixture passes into the flotation bath 8. The length and diameter of the flotation pipe 3 are chosen so as to ensure total interaction of the flocculating agent with the suspended matter and the bubbles. In the flotation bath 8, the air bubbles and the flocculating materials rise to the surface and form the foam layer 9, the upper part of which is removed by a device not shown. It should be noted that the foam layer is naturally renewed as the flotation unit operates. The water separated from the suspended matter, that is to say the clarified water goes towards the outside of the tank 2, beyond the separating cone 6, in the interval between the flared lower part thereof. and the tank wall 2 and enters the manifold 4. In the buffer tank 16, the upper end 18 of the downstream portion 17b of the evacuation pipe 17 is at the level desired for the flotation bath 8 The evacuation of the clarified water coming from the buffer tank 16 is therefore obtained by overflow as the float 1 operates. To avoid the risk of deposits in the supply line 5, between the holes 15 of injection of the flocculating agent and the flotation tube 3, the supply line 5, after the depressurization valve 12 is inclined upward by an angle of the order of 7 '. This angle is not such as to disturb the cyclonic operation of the float 1 at the level of the flotation tube 3, an operation which combines the shearing effects at the level of the wall of the float and centrifugal effects due to the rotary movement of the movement of the mixture injected into the bottom of the flotation tube 3. The flocculated materials or flocs that form in the lower part of the flotation tube 3 are less dense than water, being moreover entrained by air bubbles, so that under the centrifugal effect induced by the free vortex created by the tangential feed, these flocs gather in the center of the vortex and tend to agglomerate going up in the flotation tube, thus forming particularly stable macro-flocs, this who

  considerably increases the efficiency of the float.

  In a specific embodiment, given by way of nonlimiting example, the flotation tube 3 had a diameter of 250 mm, for a height of 1,200 mm. The clarified water collector 4 was an annular chamber, arranged around the flotation tube 3, 50 mm wide. The separating cone formed an angle of about 60 e with the axis of the float, its diameter in the widest lower part was 700 mm. The tank 2 was of square section, 150 mm sides. The bottom 11 of the tank was pierced with a 10 mm orifice 20 mm wide. This bottom 11, as it appears clearly on examining FIG. 1, was partially inclined downwards in the portion arranged below the separating cone 6. The bottom 4a of the manifold was also inclined -7 towards the down in the direction of the evacuation pipe 17. Purge valves were arranged in the lower part of the flotation tube 3 and of the upstream portion 17a of the evacuation pipe 17. With the flotation thus produced, it was possible to treat 6 t / h of wastewater, which compared to a conventional flotation device constituted an increase in efficiency greater than 500%. The present invention is not limited to the embodiment which has just been described in a preferred manner. The cyclonic operation of the float, thanks to the tangential supply of the mixture in the flotation tube, can also be used in the case where the formation of micro-bubbles is not obtained by

o depressurization.

  More advantageously, the end piece 14 can be used for feeding not only the chemical reagent but also a portion of water to be treated beforehand mixed with the chemical reagent. In this way of operating, the quantity of water to be treated is reduced in which it is necessary to dissolve gases under pressure. The particular arrangement of the supply of this water between the depressurization valve and the entry into the flotation tube makes it possible to produce a perfectly homogeneous mixture. This further reduces the cost of operating the float, since it reduces the volume of water to be subjected to pressurization. 2 o Furthermore, the structure of the device can be simplified compared to the embodiment described: the separator cone is not essential. In addition, the tank can consist of a simple extension of the flotation pipe; in other words, the upper part of the flotation pipe can act as a reservoir according to the invention. In this case, the clarified water collector can be arranged annularly around the flotation pipe, the clarified water entering the

  manifold through holes in the pipe.

Claims (8)

  1. Float comprising a tank into which a supply pipe introduces the water to be treated and optionally a flocculating agent, a device for collecting and evacuating the foams formed on the surface of the flotation bath contained in the tank and a collector clarified water giving into the tank, under the flotation bath, characterized in that it comprises a cylindrical flotation pipe (3), penetrating vertically in the bottom (11) of the tank (2) up to the level of the bath flotation (8) and in that the supply pipe (5) of the water to be treated opens tangentially in the lower part of the tube (3) of flotation.   2. Float according to claim 1 characterized in that the flotation pipe (3) is arranged axially relative to the tank and the clarified water collector (4) is arranged annularly around the flotation pipe (3) under the bottom (11) of the tank (2).   3. Float according to one of claims 1 or 2 characterized in that it   has a separating element (6) which extends externally around the upper end (7) of the flotation pipe up to a reduced distance (_)   of the inner wall of the tank (2).   4. Float according to claim 3 characterized in that the separating element   (6) is a frustoconical plate which widens downwards.   5. Float according to one of claims 1 to 4 operating by   depressurization of the gases dissolved in the water to be treated, characterized in that the supply line (3) comprises a depressurization valve (12), and in that a tube (13) for supplying flocculating agents and / or water to be treated which does not contain dissolved gas opens into the downstream supply line (5) of said valve (12).   6. Float according to claim 5 characterized in that the supply pipe (13) is connected to the supply line (5) by an annular end piece (14) and in that holes (15) are drilled in the supply line (5) at said 9- end cap (14).   7. Float according to one of claims 5 or 6 in that it comprises a   swirl device installed in the nearby supply line (5) flotation pipe (3).   8. Float according to one of claims 5 to 7 characterized by the inclination   towards the top of the portion of the supply duct (5) downstream of the   depressurization (12) preferably at an angle of around 7.