FR3048690A1 - DISSOLVED AIR FLOTTER WITH INPUTS AND MULTIPLE OUTPUTS - Google Patents

Abstract

This installation for clarification by dissolved air flotation comprises a tank (1), means for supplying the tank (1) with water to be treated, at least one clarified water collector (5) capable of collecting the water clarified, extending in the vicinity of the bottom of the tank (1), means (7) for discharging the clarified water collected by the at least one collector (5). This installation also includes. At least one box (2) immersed under the surface of the water, said box (2) being closed at the bottom and open at the top and extending substantially in one of the dimensions of the tank (1); Water supply means to be treated and pressurized water extending inside the box (2); Said at least one clarified water collector (5) is situated substantially towards the bottom of the tank (1) and substantially under the caisson (2). This installation is intended for the clarification of water charged with suspended matter.

Description

TECHNICAL FIELD The invention relates to an installation for the separation of suspended solids present in a liquid (usually water), using the technique of dissolved air flotation. In current practice, this type of installation is called a "dissolved air float". It can be used for clarification of drinking water or wastewater.

PRIOR ART

The technology of dissolved air flotation clarification uses microbubbles of air (or other gas) that adhere to solid particles (suspended solids) present in the water to bring them to the surface. Thus, the polluting solids are separated from the water, which is therefore clarified. Each dissolved air float is composed of two main elements. • A first element consisting of a microbubble production system which is the core of each dissolved air flotation clarification plant. Most often, the microbubbles are obtained by recycling a portion of the clarified water through a pressurizing pump and a device for dissolving air under pressure. The return to atmospheric pressure of this pressurized water enriched with dissolved air generates the release of the dissolved air in the form of microbubbles. • a second element consisting of a tank in which physically separates the pollutants from the water.

There are many constructions implementing different hydraulic concepts. The most widespread use circular tanks with water inlet to be treated in the center, and recovery of clarified water to the periphery, or rectangular tanks with water inlet to be treated on one side, and outlet of clarified water to the opposite side.

Without going into the details of each of the existing hydraulic concepts, it can be said that the aim pursued remains the same, namely to ensure the least turbulent flow possible of the water between the inlet and the outlet so that the process of separating pollutants from water can be carried out under the conditions closest to the laminar regime, which are obviously the most favorable for the course of the clarification process, but which is most often fragile and delicate.

The closest known concept of the installation according to the invention is illustrated schematically in Figure 1, showing a vertical longitudinal section of a clarification tank. The water to be treated, previously mixed with pressurized water carrying microbubbles, enters a tank through an inlet (20). In some cases, the pressurized water can be injected separately by a device (21) into the contact zone (22). The mixture of water to be treated / pressurized water then passes into a clarification compartment (27), in which the pollutants are separated. Thanks to the air bubbles, said pollutants are raised to the surface to be evacuated by a suitable device, well known, for example a motorized surface scraper (28), or by simple overflow. The clarified water descends towards several collectors (23) located towards the bottom of the tank, and which receive the clarified water relatively homogeneously under the entire flotation surface, and discharge it through a manifold (29) to a weir (25), the purpose of which is to regulate the liquid level in the tank. After said weir, the clarified water leaves the plant through an outlet (24), and the floated sludge is discharged through an outlet (26).

The concept thus implemented therefore comprises a multitude of clarified water recovery collectors (23), which ensure a relatively uniform collection on the outlet side of the clarified water. This minimizes the turbulence caused by the preferred currents, inevitably created in clarifiers having only one exit point in front of the input. Nevertheless, two hydraulic problems still persist: the turbulence created by the inlet current located on one side of the tank, which move the water in the direction of the arrows V, thus disturb the clarification in the upper part of the flotation compartment ; in installations of relatively large size (length), the distribution of microbubbles with respect to the flotation surface is unbalanced because said microbubbles tend to rise as soon as the water enters the flotation compartment, by thus more and more rare towards the opposite side of the tank.

DISCLOSURE OF THE INVENTION The plant according to the invention combines a multitude of collection points for clarified water with a multitude of entry points of the water to be treated. It thus makes it possible to perfectly homogenize the conditions of clarification over the entire surface of the flotation zone, and consequently to substantially reduce the turbulence caused by the horizontal input current (and thus to operate at a higher hydraulic load in the flotation zone); to increase the size of the flotation tank (and thus the treatment capacity of the installation) by overcoming the problem of the unbalanced distribution of microbubbles along the length.

BRIEF DESCRIPTION OF THE FIGURES

The manner in which the invention can be realized and the advantages which result therefrom will emerge more clearly from the following exemplary embodiments, given by way of non-limiting indication, in support of the appended figures.

FIG. 1 represents a longitudinal vertical section of a prior art dissolved air flotation device equipped with multiple clarified water collectors.

FIGS. 2a and 2b diagrammatically illustrate two vertical sections of a first embodiment of an installation according to the invention, in two perpendicular vertical planes relative to one another, with injection of the mixture of raw water and pressurized water , Figure 2c illustrating a view similar to Figure 2b of an alternative embodiment;

FIGS. 3a and 3b schematically illustrate two vertical sections of a second embodiment of an installation according to the invention, according to again two vertical planes perpendicular to each other, with separate injection of the water crude and pressurized water, Figure 3c illustrating an alternative embodiment.

Detailed description of the invention

According to a first embodiment of the invention, more particularly described in connection with FIGS. 2a, 2b and 2c, the installation comprises a dissolved air float comprising a rectangular tank (1). This installation comprises: at least one box (2) immersed under the surface of the water present in the tank (1), said box (2) being closed at the bottom and open at the top and extending substantially over the entire width of the tank (1) (see Figure 2a), that is to say, according to substantially all one of the dimensions of the tank, higher than the height ;; means for supplying (14) and dispensing (4) the mixture of water to be treated and pressurized water, equipped with orifices (40) allowing a homogeneous distribution of the water over the entire length of the box (2), the means dispensing device (4) extending inside the box (2) substantially in the vicinity of the bottom of said box (2); at least one clarified water collector (5) located substantially towards the bottom of the tank (1), and substantially under the caisson (2), said collector (5) covering substantially the entire surface of the flotation zone and being equipped orifices (50) capable of relatively homogeneously collecting water over the entire length of said collector (5); means (7) for discharging the clarified water, for maintaining and regulating the level of liquid (8) in the tank (1), and for leaving (9) the clarified water; means (10) and (11) for collecting the floated sludge (13) and evacuation (12) of said floated sludge

According to a variant not shown, the boxes (2) do not extend along the entire width of the tank, but at a smaller distance.

This version of the device according to the invention operates as follows: The water to be treated is mixed with the pressurized water in the pipework (14), and is introduced into the at least one box (2) via the pipes (4) through the orifices (40). The mixture of water to be treated and pressurized water leaves the box (2) through the open upper part of said box, and opens at a certain depth below the surface of the water. Arriving to the surface of the water, the vertical flow of water entering the flotation zone is divided into two horizontal components, and each of these components meets the (opposite) one of the neighboring caisson, when they exist. a. This splitting of the points of introduction of the water over the entire flotation surface, as well as the creation of small surface currents opposed to one another, makes it possible firstly to attenuate these small currents more easily, and moreover to minimize the resulting turbulence compared to those created by a single powerful input current, as in the case of the known device of Figure 1. The distribution of pressurized water is also homogeneous over the entire flotation surface.

From the upper part of the flotation compartment, the water descends between the caissons (2) towards the collectors (5) in the direction of the arrows VI. This descent is substantially vertical and according to a substantially homogeneous hydraulic load, so optimal. Thus the clarified water is collected by the collectors (5) through orifices (50) and discharged through the pipe (7) to the weir (8) and the outlet (9).

The floated sludge (13) is scraped by a scraper (10) towards the compartment (11) and then discharged through the outlet (12).

This first embodiment of the installation according to the invention can also be performed in a circular tank with one or more distribution boxes (2) and one or more clarified water collectors (5) oriented radially, the feed and the collection of water from the center to the periphery, or even from the periphery to the center, or the food from the center and the collection of clarified water from the periphery or still the opposite. The installation can also be equipped with a device for collecting floating sludge (13) by simply overflowing.

The orifices (40) for dispensing the water to be treated can be oriented upwards, downwards or to the side. It is the same for the orifices (50) which are provided with the collectors (5) of clarified water.

The device according to the invention can also be equipped with a bottom scraper of the tank (1) to collect any decanted sludge, or simple receptacles in the shape of an inverted pyramid filling, in a manner known in the field considered, the same function.

The distribution box (s) (2) and the clarified water collector (s) (5) can be oriented in the same direction or can be oriented in two different directions, for example perpendicular to one another.

The means (7) for discharging the clarified water can be located on both sides of the collector (s) (5), as shown in Figure 2b or on one side.

Finally, if necessary, the collector (s) (5) clarified water can be replaced by simple orifices (55) positioned in the walls of the tank (1) instead of said collectors (5) and a level less than that of the box or caissons (2). (see Figure 2c).

These orifices (55) are able to evacuate the clarified water to the means (7) for discharging said clarified water. This solution constitutes a technological compromise because the collection of the clarified water is less homogeneous than during the implementation of the collector (s) (5), but this collection can however be carried out in combination with the caissons (2).

According to a second embodiment of the invention, more particularly described in relation to FIGS. 3a, 3b and 3c, the installation comprises a dissolved air float comprising a rectangular tank (1). This installation comprises: at least one box (2) immersed under the surface of the water, said box (2) being closed at the bottom and open at the top; it extends substantially over the entire width of the tank (1) (see Figure 3b); water supply means (14) to be treated and distribution (4) of the water to be treated, equipped with orifices (60) allowing a homogeneous distribution of water over the entire length of the box (2), the means (4) extending inside the boxes (2); means for distributing the pressurized water (15) and (3), distinct from the water supply means to be treated, and provided with orifices (30) allowing a homogeneous distribution of the pressurized water over the entire length of the box (2), the means (3) extending inside the box (2); at least one clarified water collector (5) located substantially in the vicinity of the bottom of the tank (1) and substantially under the caisson (2), said collector (5) covering substantially the entire surface of the flotation zone; it is provided with orifices (50) allowing a relatively homogeneous collection of water over the entire length of said collector (5); means (7) for discharging the clarified water, maintaining and regulating the liquid level (8) in the tank (1), and output (9) of the clarified water; means (10) and (11) for collecting the floated sludge (13) and evacuation (12) of said floated sludge

This second embodiment of the installation according to the invention operates as the first, but the mixture raw water / pressurized water is directly in the box (2) and no longer upstream of the latter.

In the example described, the means (3) for dispensing the pressurized water are located below the means (4) for dispensing water to be treated within the caissons (2). However, it can be considered the opposite, namely that the means (3) for dispensing pressurized water are located above the means (4) for dispensing water to be treated within the caissons (2). The installation according to this second embodiment of the invention can also be performed in a cylindrical vessel, with distribution boxes (2) and clarified water collectors (5) oriented radially, as well as the means for supply of water to be treated and pressurized water. Water supply and collection takes place from the center to the periphery, or from the periphery to the center. Food can also be made from the center and the collection of clarified water from the periphery, or even the opposite. The installation can also be equipped with a device for collecting the floated sludge (13) by simple overflow.

The orifices (60) for dispensing the water to be treated may be oriented upwards, downwards or to the side. It is the same for the orifices (50) which are provided with the collectors of clarified water (5).

The device according to the invention can also be equipped with a bottom scraper to collect any decanted sludge or simple reversed pyramids fulfilling the same function.

The distribution casing (s) (2) and the clarified water collector (s) (5) may be oriented in the same direction, or may be oriented in two different directions, for example perpendicular to each other .

The means (7) for discharging the clarified water can be located on both sides of the collector (s) (5), as shown in Figure 3b or on one side.

Finally, if necessary, the collector (s) (5) clarified water can be replaced by simple orifices (55) positioned in the walls of the tank (1) instead of said collectors (5) (see Figure 3c ).

These orifices are able to evacuate the clarified water to the means (7) for discharging said clarified water. This solution constitutes a technological compromise because the collection of the clarified water is less homogeneous, than in the presence of said collectors (5), but it can be performed in combination with the distribution boxes (2).

Claims (10)

1. Installation for clarification by dissolved air flotation comprising a tank (1), means (14) for supplying the tank (1) with water to be treated, means (7) for discharging the clarified water collected in the tank, characterized: - in that the pressurized water is conveyed into the tank (1) by the feed means (14) in water to be treated; and - in that the installation further comprises: at least one box (2) immersed in the tank (1) under the surface of the water, said box (2) being closed at the bottom and open at the top; means (4) for dispensing the mixture of water to be treated and pressurized water inside the tank, connected to said supply means (14), said dispensing means (4) extending to the inside the at least one box (2) and being provided with orifices (40, 60) able to allow a homogeneous distribution of said mixture over the entire length of said at least one box (2). 2. Installation according to claim 1, characterized in that the pressurized water is conveyed into the tank (1) by means (15), distinct from the feed means (14) of the water tank to be treated, said means supplying pressurized water (15) being connected to pressurized water distribution means (3), extending inside the at least one box (2) and being provided with apertures (30) capable of to allow a homogeneous distribution of pressurized water over the entire length of said at least one box (2). 3. Installation according to one of claims 1 and 2, characterized in that the at least one box (2) extends substantially in one of the dimensions of the vessel (1). 4. Installation according to claim 1, characterized in that the orifices (40) which are provided with the dispensing means of the mixture of water to be treated and pressurized water are oriented downwards, upwards or towards the sides of the at least one box (2). 5. Installation according to claim 2, characterized in that the orifices (60) which are provided with the dispensing means (4) of the water to be treated are oriented downwards, upwards or to the sides of the caissons (2). ). 6. Installation according to one of claims 2, 3 and 5, characterized in that the means (3) for dispensing pressurized water are located above the means (4) of water distribution to be treated within at least one casing (2). 7. Installation according to one of claims 2, 3 and 5, characterized in that the means (3) for dispensing pressurized water are located below the means (4) of water distribution to be treated within at least one casing (2). 8. Installation according to one of claims 1 to 7, characterized in that it further comprises at least one clarified water collector (5) capable of collecting clarified water, extending in the vicinity of the bottom of the tank (1) and connected (s) to the evacuation means (7) clarified water, or said collectors (5) extending under said at least one box (2). 9. Installation according to claim 8, characterized in that the tank (1) is substantially cylindrical in shape, and in that the water supply means to be treated and pressurized water, as well as the at least one box ( 2) and the at least one clarified water collector (5) is oriented substantially radially. 10. Installation according to one of claims 1 to 7, characterized in that it further comprises orifices (55) positioned within the walls of the tank (1), and able to collect clarified water, and connected the evacuation means (7) clarified water, said orifices (55) being located at a level lower than that of the caissons (2).