FR2472943A1 - Floating decanter with tubular risers to clarify river water etc. - pumps water ashore from collecting tank above risers - Google Patents

Abstract

Installation is for clarifying water taken from a river etc. by passing the water through a floating decanter. The installation is of the type which comprises a float supporting a submerged enclosure. The enclosure contains a set of parallel riser passages, open top and bottom and set at an angle between horizontal and vertical. Water passes up the riser passages, depositing solid impurities en route. The open tops of the risers deliver into a reception tank. The lower ends of the risers are now divided into a number of groups. Each group is provided with a common, vertical entry channel extending below the risers. The reception tank overflows into a surrounding channel which supplies the inlet of a delivery pump. Preclarification of turbid water from rivers etc. to be further purified for drinking. Clarification of turbid water for irrigation, factory processes and services. Adaptable for wide range of capacities e.g. between 5,000 cubic metres/day and 25,000 cubic metres/day. The plant can handle water contg. originally between 1500 and 5000 mg/l of suspended solids.

Description

The present invention relates to the supply of drinking water and industrial water, as well as irrigation, and in particular relates to a floating installation for clarifying or purifying water by precipitation or despite particles in suspension at location of the surface water intake. Such an installation is of particular importance during the preclarification of highly turbid waters used in the production of drinking water.

 At the present time, the prelarification of water by precipitation of the solid particles in suspension is carried out in water treatment works on the edge, or "earthworks", such as decanters, clarifiers, drum filters, microfilters etc.

 The preclarification of water in riparian works is linked to the problem of the accumulation, treatment and use of mud, as well as to the construction of mud accumulators to dehydrate the mud, and to the setting at the point of systems allowing the reuse of decanted water in the mud accumulator.

 Normally no clarification of water is used where it is taken from a surface source.

As a result, the solid particles suspended in the water stream cause wear by abrasion of the pumps with which the water intake devices are fitted. The same cause is causing the clogging of free flow (gravity) and distribution pipes as well as reception chambers installed in riparian water treatment works. This occurs in particular when the water taken is characterized by a high content of suspended particles, which requires additional repair work on pumps and pipes.

In order to be able to clarify the water where it is taken from a surface source, it has been proposed to use immersion decanters (see ESPosgate "Submerged Enclosures May Help Sink Plant Problems", "Water and Wastes Engineering ", Vol. 14, NO 9, pp 127133, 1977).

Such a settling tank is incorporated in a tank in the form of a vault immersed in a basin and maintained at a prescribed depth by cables fixed to the bottom of said basin. A clarification of the water takes place in the decanter, which is then routed to the neighboring water treatment works for its subsequent clarification.

 The use of this type of decanter gives rise to considerable difficulties. First, in order to protect the vault-shaped tank against destruction due to the effect of hydraulic shocks, it must be permanently supplied with air, hence the need for the water treatment plant. be equipped with compressors.

 Secondly, to periodically remove the sludge accumulated at the bottom of the tank, suction dredgers must be used, which complicates the operation of the water treatment unit and makes this treatment more expensive.

 Thirdly, maintenance and repair operations on the decanter require the intervention of divers equipped with appropriate tools.

Fourth, although the volume of such decanters is large, their yield remains relatively low.

Taking into account the aforementioned factors, immersion decanters have not in practice found application in water treatment techniques.

A floating installation is also known for clarifying water (see United States patent No. 3613889), which comprises a floating means on which a decanter and a pipe for the evacuation of the water are mounted. clarified water. The decanter is incorporated in an envelope and comprises pipes arranged at an angle to the horizontal and forming several parallel channels. These channels are open at their two ends to allow the passage of an ascending stream of liquid, in particular waste water. The pipes are fixed to the envelope by their upper ends so as to form the bottom of this envelope, which allows the clarified water to accumulate there.

 The installation is placed in a fixed tank into which the water to be treated comes from a basin. During the passage of water in laminar mode through the decanter pipes, a phase separation occurs by gravity: the solid particles in suspension separate from the water and settle on the lower internal surface of the pipes. The deposit formed slides against the current (relative to the direction of the water flow) to the bottom of the tank. The clarified water is evacuated from the envelope by a pipe which carries it out of the tank, to the post-treatment stations.

The practical use of such an installation gives rise to certain difficulties.

 Due to the fact that the clarified water is sampled locally in the envelope, i.e. in the area of the inlet opening of the discharge pipe, the regular water withdrawal clarified of all the channels of the settling tank is not ensured, which results in different speeds of the water currents in these channels. This results in a reduction in the clarification rate of the water and an irregular distribution of the load exerted by the mud on the pipes of the settling tank, which prevents the regular evacuation of the mud from these pipes.

 The irregular nature of the water withdrawal is accentuated with the decrease in the height of the water column in the envelope above the surface of the decanter and with the increase in the surface of the latter.

When the water level in the tank changes, there are sudden changes in the height of the water column and the water flow in the drain. This disrupts the hydrodynamic regime in the decanter channels, so that the precipitated particles are entrained from the different channels to the area of the clarified water. These factors prevent the normal process of clarifying the water and affect its quality.

 It should be noted, moreover, that this installation does not solve the problem of clarifying the water at the point of its intake from the basin, since it is designed to operate in a fixed reservoir built on the shore and being part of all the water treatment works. In addition, to be able to evacuate the sludge from the reservoir, treat it and use it, it is necessary to have appropriate technical means, such as those provided for in the known water clarification works on riverside.

 Since the sludge goes from the settling tank to the tank and accumulates at the bottom of the latter, the volumetric utilization rate of the whole "floating tank installation", that is to say the ratio between the volume of l clarified water and the total volume of the whole, is relatively small.

When using the installation directly in an open current, for example in a river, the following difficulties arise. Since the speed of the current in the river significantly exceeds (by 30 to 40 times) the speed at which the water rises through the channels of the decanter, there is a swirling of the current in the vicinity of the inlet openings of these channels, which prevents the uniform distribution of currents between the channels.

 In an open stream of water, we can see that the inlet openings of the canals are blocked by small objects (pieces of wood, branches, algae, etc.) as well as by small fish, which leads to a reduction in the decanter performance and decommissioning.

For this purpose, the installation is placed in a closed tank, and not in a basin.

The object of the invention is to overcome the drawbacks mentioned above.

The invention therefore aims at a floating installation for clarifying water, which grates over the creation of a system for supplying water in separate streams to the settling tank and at a regular withdrawal of water from the surface of the latter, would clarify the water directly at the point of its intake from the water source.

 This problem is solved by means of a floating installation for clarifying water, containing a floating means on which are mounted a decanter incorporated in an envelope and equipped with several parallel channels arranged at an angle to the horizontal and open at their two ends to allow the upward flow of water from the basin and the deposition on their walls of solid particles suspended in said current followed by the sliding of the deposits of particles (mud) in the basin, and d ured evacuation of clarified water, said installation being characterized, according to the invention, in that it is provided with vertical partitions in order to ensure the supply of water to the decanter in separate streams, said partitions being attached to the lower part of the decanter casing and used to divide it into cells placed in communication with the inlet openings of the decanter channels, and of a collector allowing the withdrawal regular water leaving the decanter, said collector being constituted by a system of horizontal channels meeting in a single channel communicating with said pipe.

The cells formed in the lower part of the decanter envelope ensure a stable hydrodynamic regime of supply of the water current to all the channels of the decanter and prevent the formation of swirls of the water current at the channel inlet openings. . In the area of the cells, the solid particles suspended in the current collide with the mass of mud leaving the channels, so that a layer of suspended particles is formed in this area and that when they pass through this layer the new solid particles arriving with the current agglomerate with the particles of the layer in suspension. This intensifies the precipitation process of solid particles and, therefore, accelerates the water clarification process.

The regular removal of water from the surface of the decanter using a collector allows the evacuation of clarified water from all the channels of the decanter at the same speed. There is thus obtained a regular character of the precipitation of solid particles in all the channels.

Thanks to the regular removal of water from the surface of the decanter, a clarified water column of constant height is formed above it, allowing a stable flow of water in the evacuation pipe, whatever variations in the water level in the basin.

It is advantageous for the collector mentioned to be formed by an annular partition disposed inside the casing of the decanter, along the perimeter thereof, and by said casing.

Such a design of the installation, which is relatively simple to carry out, is suitable for a water treatment plant with average output (from 5 to 25,000 m3 / åouA
It is advantageous to produce the collector mentioned in the form of troughs or the like distributed over the surface of the decanter, above the outlet openings of these channels.

 The floating installation thus designed is suitable for a water treatment plant with a low yield and even a high yield (more than 25,000 m3 / day). It is advantageous to use such an installation with a relatively large area decanter in order to facilitate the removal of clarified water from the surface of the decanter.

 It is also possible to design a floating installation in which the collector would be produced in the form of perforated pipes distributed over the surface of the decanter, above the outlet openings of its channels. Such an installation is suitable for a low-yield factory (up to 5,000 m3 / day), with very irregular daily water consumption.

The invention will be better understood and other objects, details and advantages thereof will appear better in the light of the explanatory description which will follow of different embodiments given only by way of nonlimiting examples, with references to the drawings. nonlimiting annexed in which
- Figure 1 schematically shows a floating installation for clarifying water, produced according to a first embodiment, in which the collector is in the form of an envelope and an annular partition placed inside this (in this figure and in the figures which follow, the directions of movement of water and mud are indicated by arrows);
- Figure 2 is a plan view, partially broken away, of the installation shown in Figure 1; ;
- Figure 7 is a perspective view of the decanter of the floating installation;
- Figure 4 shows another embodiment of the invention, in which the collector is made in the form of troughs (for clarity, the floating means is not shown);
- Figure 5 is a plan view, partially broken away, of the assembly shown in Figure 4;
- Figure 6 shows another embodiment of the invention, in which the manifold is made in the form of perforated pipes (for clarity, the floating means is not shown);
- Figure 7 is a plan view, partially broken away, of the assembly shown in Figure 6 ;;
- Figure 8 shows schematically the process of formation of a layer of particles in suspension in the cells of the envelope).

 The floating installation for clarifying the water contains a floating means 1 (FIG. 1) on which are mounted a pump 2 and a decanter 3 placed in an envelope 4. The decanter 3 is connected to the suction pipe of the pump 2 via a line 5 for discharging clarified water. The discharge pipe of the pump 2 is connected by a pipe 6, via a hinge 7, to the pipe 8 for supplying clarified water to the bordering or riparian works.

 The hinge 7, by ensuring a flexible connection between the installation and the riparian structures, allows the latter to function normally in the event of variations in the water level in the river 9. Instead of the hinge, it is possible to use in the same purpose a flexible hose.

 The installation according to the invention is provided with a collector 10 for the regular withdrawal of clarified water.

This collector is in the form of a system of horizontal channels joining in a single channel connected to the pipe 5.

 In the embodiment shown in FIGS. 1 and 2, this collector is formed by an envelope 4 and an annular partition II arranged inside of it, along the perimeter of the decanter 3. Around the decanter 3 are thus formed peripheral channels 12 (FIG. 2) meeting in a single discharge channel 13.

 The partition It serves to separate the zone 14 for evacuating the clarified water (FIG. 1) from the zone 15 for withdrawing said water and allows the formation of a constant column of water above the surface of the decanter. , whatever the variations in the water level in the river.

 The height of the partition II is chosen as a function of the surface area of the settling tank 3 and the desired yield of the installation.

 The decanter 3 (FIG. 3) is produced in the form of a set of U-shaped blades 16, arranged in the casing 4 parallel to each other and at an angle to the horizontal, so as to form channels 17 between them. These channels are open at their two ends to allow the updraft of the water of the watercourse 9. The best results are obtained in the case where the blades 16 are arranged at an angle of 450 to 650 relative to the horizontal. The chosen angle of inclination of the channels 17 allows their permanent self-cleaning.

 The decanter 3 is arranged, relative to the floating means 1, so that the outlet openings of the channels 17 are arranged lower than the water level in the basin when the installation is immersed in it.

Of course, instead of the blades 16, one can use in the decanter other elements which can form the channels of any section. For example, the decanter 3 can be made in the form of a set of pipes (not shown).

In the lower part of the envelope 4 are fixed the vertical longitudinal and transverse partitions 18-dividing it into cells 19 communicating with the inlet openings (lower in the drawing) of the channels 17. The height of the partitions 18 is chosen sufficient to form in cells 19 a layer of solid particles in suspension, of a minimum height, in the stream of water.

The partitions 18 not only ensure a stable hydrodynamic regime of the supply of water to the channels 17, but make the construction of the decanter 8 more rigid and serve, if necessary, as support for grids preventing the passage of fish. These grids are used in the case where water is taken from basins intended for nursery.

Besides the. variant shown in FIGS. 1 and 2, the collector 10 can be produced for example in the form of troughs 20 (FIGS. 4 and 5) or perforated pipes 21 (FIGS. 6 and 7) distributed over the surface of the decanter 8, au- above the outlet openings of the channels 17.

 The troughs 20 (FIG. 4) and the annular partition II (FIG. 1) can be made with a smooth or toothed edge as shown in FIG. 4. In the latter case, during sudden variations in the water level in the river, one obtains self-regulation of the water flow from the decanter 3, while retaining, above the openings of the channels 17 of the decanter 3, a column of water of minimum height making it possible to ensure the regular departure of the water.

The installation described works as follows.

The installation is placed in a river 9 or in a watercourse of any water basin, and is put in communication by pipes to the riparian water treatment works.

The pump 2 being started, the water level in the casing 4 drops relative to the level of the river 9. The difference in these levels increases all the more as the flow of water sucked increases .

The difference in the water levels in the river 9 and in the envelope 4 advances the updraft water through the cells 19 through the inclined channels 17 of the decanter 3 (see FIG. 8). The cells 19 formed in the lower part of the envelope 4 prevent the swirling of water at the entrance to the channels 17. In this way, the water arrives in the channels 17 in the form of a calm, laminar current, the speed practically does not exceed 0.01 m / s, while the speed of the current in the river can reach 2 m / s and even more.

 During the laminar current movement of the water in the channels 17, there is a regular precipitation of the suspended solid particles, which slide on the walls of the channels through the cells 19 in the river 9 and are carried away by it. this. This prevents the accumulation of excess mud on the bottom of the basin where the installation works.

Given the opposite movement of the river current, due to the arrival of water in the cells and the sliding of the mud from the inclined channels 17, it is constantly formed in the area between the partitions 18, a layer 22 of solid particles in suspension. The formation of such a layer promotes the aggregation of solid particles, entrained in the cells 19 by the water of the river, with those of the layer. Thanks to this aggregation, the solid particles arriving in the channels 17 are deposited more quickly, which improves the clarification rate of the water.

 The process described above accelerates when the river water contains clay particles having adsorbent properties (montmorillonite or other bentonitic clays); This makes it possible to use the installation both in rivers with a low content and in a high content of suspended particles, since the rate of clarification of the water increases with the increase in the amount of particles suspended in water.

 The clarified water leaving the channels 17 arrives in the upper part of the casing 4 (FIG. 1), forming above these openings a column of water (zone 15 for collecting the clarified water). Then, the clarified water arrives regularly in the collector 10, then it is discharged by the pump 2 in the pipes 5 and 6 towards the riparian works for its subsequent treatment or for its direct use.

 In the variant of the installation shown in FIGS. 1 and 2, the clarified water flows from the zone 15 through the annular partition II in the peripheral channels 12 and then arrives, via the evacuation channel 13, in driving 5.

In the variants shown in FIGS. 4 and 6, the water leaving the casing 4 arrives respectively in the troughs 20 through their edges, or else in the pipes 21 through the openings of the latter, after which it is brought into driving 5.

 it should be noted that, whatever the variant of the installation proposed, the height of the water column formed above the outlet openings of the channels 17 remains invariable during variations in the water level in the basin and of the clarified water flow.

The collector 10 produced in the form of a system of horizontal channels covering the entire surface of the decanter 3 allows the regular removal of the clarified water from the entire surface mentioned, which makes it possible to equalize the speed of the water stream in all the channels 17 of the settling tank 3 and to obtain a uniform distribution of the mud load to which the latter is subjected.

The supply of water from the river to the decanter 3 in several currents through the cells 19 and the regular withdrawal of the water clarified by the collector 10 make it possible to obtain a stable hydrodynamic regime of the operation of the installation and d '' consequently increase its reliability, while ensuring the desired rate of water clarification.

In view of the fact that the speed of the current of water passing through the cells 19 in the channels 17 is significantly lower than that of the current in the river, the aspiration of small fish in the installation is excluded.

 The choice of the most suitable variant of the installation depends on the desired yield of the water treatment plant, the morphological characteristics of the water source and the daily water consumption regime.

 Thus, in the case of a low-yield water treatment plant (in particular up to 5,000 m3 / day), of a slight turbidity of the water (for example of a water whose particle content in suspension can reach 1,500 mg / l), and with a very irregular daily water consumption, an installation according to the variant shown in Figures 6 and 7 should be used. -the water pressure in the manifold 10 and in the line 5 must not exceed 1.5in2.0 m of water column.

In the case of a medium-yield water treatment plant (in particular from 5,000 to 25,000 m3 / day), with high turbidity of the water surface (for example from 1,500 to 5,000 mg / l and more), it There is an advantage in using the variant shown in Figures 1 and 2.

 For a high-yield plant (over 25,000 m3 / day) with a large surface settling tank, it is advantageous to use the variant shown in Figures 4 and 5, because in this case the regular sampling of clarified water from the entire surface requires less energy consumption than in the variant shown in Figures 1 and 2.

The proposed floating installation, whatever the variant of its realization, is suitable for various technological schemes of water treatment.

 Research carried out in the field of clarification of water taken from a river containing from 1,200 to 5,200 mg / l of suspended particles shows that, for a specific yield of the installation ranging from 20 to 30 m3 / h per m2 of surface area of the decanter, the water clarification rate constitutes from 40 to 75%. It has been established that the greater the quantity of suspended particles, the more effective the clarification. The highest clarification efficiency is obtained in water preferably containing suspended particles whose hydraulic dimension is equal to or greater than 0, 2 mm / s.

 it should be noted that in the case where water is taken from a river, the sand particles are practically driven out of the treated water, which avoids their abrasive effect on the organs of the pump which is fitted with the device. hydrant.

If the floating installation is used for irrigation purposes, where the requirements for the quality of the clarification are significantly less stringent than those required in the field of water supply (from 20 to 25%) the specific yield of the installation reaches 75 m3 / h per m2 of decanter surface. In this case, the area of the passage section of the decanter channels must be chosen so that the Reynolds number does not exceed 500.

The described construction of the floating installation ensures a high rate of volumetric use of this (from 0.85 to 0.90), as well as a stable withdrawal of water at the same depth, while ensuring the rate clarification required, regardless of the variations in the water level in the source or its morphological characteristics.

 The use of the proposed floating installation avoids the construction of riparian works for water pretreatment, dewatering and evacuation of mud, reduces water consumption for the specific needs of water treatment works which increases consumers' water supply.

 At the same time, the operation of water treatment works becomes simpler and the area of the land necessary for the construction of the works can be reduced.

 The installation described makes it possible to avoid the sudden discharge of the mud into the river, which is particularly important for the protection of the environment against pollution.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are executed according to the spirit and implemented within the framework of protection, as claimed.

Claims (4)

 1.- Floating installation for clarifying water, of the type comprising a floating means on which are mounted: a decanter placed in an envelope and equipped with several parallel channels arranged at an angle to the horizontal and open to their two ends to allow the upward passage of water from a source of water to be clarified, such as a watercourse, basin, pond or the like, and the deposition, on the walls of said channels, of solid particles suspended in said stream, followed by the sliding of the deposited particles, or mud, in said stream; and a clarified water evacuation pipe, characterized in that it comprises vertical partitions for the arrival of water in the decanter in several separate streams, said partitions being fixed on the casing of the decanter, in the lower part of the latter, and sharing the latter in cells or sections placed in communication with the inlet openings of the decanter channels, and a collector for the regular withdrawal of water from the decanter, said collector being constituted by a system of horizontal channels joining in a single channel communicating with said pipe.  2.- Installation according to claim 1, characterized in that said collector is formed on the one hand, by an annular partition disposed in the casing of the decanter, along its perimeter, and on the other hand, by said casing. 3.- Installation according to claim 1, characterized in that said collector is produced in the form of troughs distributed over the surface of the decanter, above the outlet openings of its channels. 4.- Installation according to claim 1, characterized in that said collector is produced in the form of perforated pipes distributed over the surface of the decanter, above the outlet openings of its channels.