FR2746031A1 - Filtration of water leaving fish farm before returning to river - Google Patents

Abstract

A liquid is filtered through a rotating horizontal drum (1), half submerged in the liquid. A deflector (3) at the upstream end of the drum diverts the liquid flow (F1) to the sides of the drum (F2). The liquid stream is then filtered as it passes through (F3) the perforated walls of the drum and leaves (G) through its open downstream end (13).

Description

METHOD AND PLANT FOR FILTERING A LIQUID
The present invention relates to a method and an installation for filtering a liquid, and specifically a moving liquid, in the form of a current.

 This process and this installation are particularly, but not exclusively, applicable to the filtration of water leaving fish farming ponds, before discharge into the river.

 Many fish farming facilities include rearing tanks fed continuously by river water. For this, the entrance to the pools is directly connected to the river. At this level, a filter is most often positioned capable of retaining the undesirable bodies carried by the water, so that they do not enter the basins. These bodies include twigs and leaves.

 Likewise, a filter is provided at the outlet of the basins intended to retain the suspended matter in the water, in particular fish excrement, before being discharged into the river.

 A known filter consists of a cylindrical drum arranged axially with respect to the direction of the water leaving the basin. The structure of the filter is formed by an assembly of large metal rings and longitudinal profiles on which is placed externally a series of fabrics with very fine openings, for example stainless steel. The rings have a "T" section, the transverse bar of which is directed towards the inside of the drum forming the filter. The opposite edges of the same fabric bear against the transverse bars of two neighboring circles.

 The drum is rotated on its axis.

 The upstream end of the drum is open, while its downstream end is closed. Water enters the filter through the upstream end and emerges radially after passing through the filter cloths.

 The fabric necessarily having a very fine mesh opening to achieve effective filtration, the water level inside the filter is higher, for example by five centimeters, than the level outside the filter. There is therefore a pressure difference between the two sides of the filter. This results in deformations of the canvas and frequent ruptures are observed by bursting of the canvas. The suspended matter (abbreviated as "MES") then escapes to the river, polluting it, until the installation can be restored to good condition.

 In addition, hard foreign bodies such as stones are often trapped inside the filter and they are also a cause of deterioration of the fabrics.

 The present invention aims to overcome these drawbacks by providing a highly efficient filtration process, without however risking deformations and ruptures of fabrics, as in the prior art.

 It also aims to provide an installation for implementing such a process which operates in a safe manner, by operating an effective filtration of the liquid.

 The filtration method according to the invention, which uses a filter in the form of a rotary cylindrical drum, of axis XX ′ substantially horizontal, and the lower part of which is immersed in the stream of liquid to be filtered, is characterized by the fact that the liquid is circulated radially from the outside towards the inside of the drum and that the filtrate is discharged axially, by one of the two ends or base - open - of this drum.

 Thus, we no longer find ourselves facing problems of deformation of fabrics, since they are pressed against the framework of the filter under the effect of the pressure inward.

 According to one embodiment, the liquid consists of water from fish farming ponds.

 According to another embodiment, the liquid consists of water coming from a purification station.

 The invention also relates to an installation for the implementation of this method, in which the axis of the drum is disposed substantially in the direction of flow of the liquid to be filtered.

 According to the invention, there is provided, upstream of the filter, at least one deflector element capable of deflecting and directing the liquid towards the periphery of the drum. The filtrate is evacuated through the downstream (open) end of the latter.

 According to another characteristic, the deflector element has the general shape of a dihedral, of vertical edge, the faces of which diverge downstream.

 According to an advantageous characteristic, in the plane of the open downstream end of the filter is provided a sealing partition which borders the lower part of said opening.

 In this way, we are sure that the liquid escapes from the installation only after passing through the filter. However, if the liquid level accidentally exceeds (due to a flood in particular) that of the plate, it can still escape, but temporarily.

According to other advantageous but non-limiting characteristics of this installation:
- It includes cleaning means comprising a water spraying ramp arranged in the upper part, inside the drum, parallel to its generatrices, and the jets of which are directed radially against the wall of the drum;
- The drum is guided in rotation on a fixed tubular shaft, through which the water is supplied to the ramp;
- It includes a receiving gutter placed outside the drum, and adapted to collect cleaning residues.

Other characteristics of the invention will appear on reading the detailed description which follows of a particular embodiment. This description, given without limitation, will be made with reference to the accompanying drawings in which:
- Figure 1 is a general perspective view of an installation according to the invention, intended for fish farming;
- Figure 2 is a schematic top view of the installation, intended to illustrate its operation;
- Figure 3 is a diagram, also seen from above, showing the location of this installation in a fish farm;
- Figure 4 is a 1/2 front view, partial, of the filter drum;
- Figure 5 is a detail, in axial section, showing the mounting method of the canvas on the drum frame;
- Figure 6 is a cross-sectional view of the filter, along a vertical plane, intended to show means for cleaning the filter, and for recovering and removing residues.

 Referring to Figure 3 attached, there is shown the establishment of an installation according to the invention in a fish farm and the corresponding water flow.

 In a manner known per se, fishponds B are provided adjoining a river R - whose direction of flow is referenced C -, so that part of the water thereof is diverted and used for the fish farming, for example trout. A filtration device DF is provided at the entry T of the basins B capable of retaining foreign bodies such as leaves and twigs which would otherwise enter the basins.

 At the outlet S of basins, the water is discharged into the river at a point P2 located downstream of the sampling point pl, after having been filtered, so as to avoid pollution of the river water by the droppings. It is at this level that the installation according to the invention is provided.

 Referring now to Figures 1 and 2, the installation comprises a filter 1 in the form of a rotary cylindrical drum, of axis X X 'substantially horizontal.

 This drum has, for example, a diameter of 1.40 meters and a length of 3 meters.

 It is supported by an openwork metal frame 2, of generally parallelepipedal shape, consisting of an assembly of tubes or sections of stainless steel, welded to each other, which do not obstruct the circulation of the water E in which they bathe.

 The frame 2 is placed and fixed on the bottom of the outlet channel S of the fishponds. The ground is advantageously flat and regular in order to ensure the stability of the frame.

 The frame of the drum consists of transverse metal rings 10 welded to longitudinal profiles 11. At each of its ends, it comprises a set of radial arms 15 (for example four in number) which are each connected to an axial sleeve and hollow center 16.

 These sleeves are guided in rotation on a fixed shaft 100, of axis XX ', secured to the chassis 2.

 At the downstream end of the drum is mounted, attached to the last ring, a pulley 14, of cylindrical shape with an axis XX ', the wall of which is in the extension of the wall of the drum.

 As illustrated in Figures 4 and 5, the rings 10 have a particular configuration. Their section has a "T" shape, the central tab of which is directed outwards, so that the two symmetrical parts of the transverse branch constitute support and fixing surfaces - for example by gluing or welding - for the filter cloths 12.

 These fabrics can be made, as in the prior art, by a braiding of stainless steel wires, with very fine section meshes.

 As an indication, the dimensions of these meshes are 90 x 90 Fm.

 The chassis 2 supports an electric motor 5, the output shaft of which carries a drive pulley. On this passes a drive belt 6, which also passes over the pulley 14 of the drum.

 When the engine is running, it rotates the drum around its axis XX 'at uniform speed.

 As an indication, this speed is of the order of 3 to 6 rpm.

 As shown in Figure 1, the upper part of the filter drum is protected by hinged covers 4, liftable.

 The upstream end - or base - of the drum is closed off by a partition (disc) 17 (see FIG. 2). On the other hand, the opposite base 13 (downstream) is open.

 In front of the upstream end of the drum (arranged on the right side of FIG. 1) is provided a deflector element 3. It is a sheet of stainless steel, integral with the chassis 2, which affects the general shape of a dihedral, vertical edge, the faces 30 of which diverge laterally and symmetrically with respect to the axis of the drum. These faces 30 are extended by vertical flanges 31 parallel to the axis XX ', the mutual spacing of which is greater than the diameter of the drum. Thus the flow of water F1 arriving on the deflector 3 is deflected laterally at the periphery of the drum, on each of the two lateral sides of the latter (arrows F2).

 The lower part of the downstream end 13 of the drum which extends under the horizontal plane passing through the axis of the drum is bordered by a shutter partition 7, the operation of which will also be explained below.

 FIG. 6 shows only means 9 for cleaning the filter. These means include a ramp 8 which extends parallel to the upper generator of the drum, inside the latter. This ramp has several nozzles 80 for spraying water, distributed along the drum.

 The fixed shaft 100 is a tube. The ramp 8 is carried by at least one oblique tubular radial arm 81, the water supply to the ramp being made via the tubes 100 and 82.

 The direction of rotation of the drum being symbolized by the arrow K in FIG. 6, it will be noted that the ramp 8 is arranged in the descending portion of the path of the grid 12, before it dives into the water.

 The jets j produced by the nozzles 80 have the function of detaching the residues, namely the MES adhering to the fabric 12. These residues, and part of the cleaning water are recovered in a channel 90 mounted outside the drum, which discharges them to an appropriate receiving station.

 The wall of the filter is therefore washed continuously, and its meshes are always properly released.

 The operation of the installation is as follows.

 As already said above, the filter is provided at the outlet S from fish farming basins B, the drum 1 being arranged substantially in the axis of the flow F1 of the water.

 The normal water level is such that the interior half of the drum is immersed in it, without passing over the shutter partition 7.

 The deflector element 3 located in front of the upstream end of the drum deflects and directs the water towards the sides of the filter (arrows F2, Figures 1 and 2).

 Water is therefore filtered from the outside to the inside of the wall (fabrics) 12 (arrows F3). The filtered water flows towards the river, leaving it only through the open downstream end 13 of the drum, thanks to the presence of the partition 7.

 During the operation, the pressure of the liquid E tends to apply the fabrics 12 against the members of the filter. This phenomenon is illustrated in Figure 5.

 The risks of deterioration or bursting of the fabrics are therefore reduced.

These can withstand relatively high differential pressures, and it is therefore possible to use very fine mesh (low porosity). With conventional systems, in which the filtrate passes through the drum from the inside to the outside, this finesse is limited.

 In addition, hard foreign bodies such as stones are not trapped in the drum. On the contrary, they remain outside of it, at the bottom of the basin exit zone. They therefore do not attack the paintings.

 If the river becomes flooded, the water level increases, so that part of the water flows temporarily, without great damage, through the top of the partition 7 without having been previously filtered. As soon as the water level returns to normal, the system again fully fulfills its function.

 By carrying out water filtration, the outside surface of the fabrics is gradually loaded with residues, mainly excrement, which clogs the mesh.

 The washing ramp 8 is then actuated, the jets of which through the fabrics take off the residues which are stuck there.

 They are then recovered and evacuated by channel 90.

 Although the present description has been made with reference to a fish-farming installation, it is obvious that the process of the invention applies to the filtration of any liquid carrying suspended matter. It can in particular be water coming from a purification station or a liquid loaded with industrial effluents.

 The opening of the mesh of the fabrics is of course adapted to the particle size of the materials to be filtered.

Claims (9)

 1. Method for filtering a stream of liquid (E) using a filter in the form of a rotary cylindrical drum (1) with a substantially horizontal axis (XX '), the lower part of which is immersed in the stream liquid, characterized in that said liquid (E) is circulated radially from the outside to the inside of said drum, and that the filtrate is removed axially, by one of the two ends (13) - open - of it.  2. Method according to claim 1, characterized in that the liquid to be filtered (E) is water coming from fish farming ponds.  3. Method according to claim 1, characterized in that said liquid to be filtered (E) is water from a purification station.  4. Installation for implementing the method according to one of claims 1 to 3, in which the axis of the drum (1) is disposed substantially in the direction of flow of the liquid to be filtered, characterized in that there is provided, upstream of said filter, at least one deflector element (3) capable of deflecting and directing the liquid towards the periphery of the drum, the evacuation of the filtrate being effected by the downstream end (13) (open) of that -this.  5. Installation according to claim 4, characterized in that the deflector element (3) has the general shape of a dihedral, a vertical edge, the faces (30) of which diverge downstream.  6. Installation according to claim 4 or 5, characterized in that in the plane of the open downstream end (13) of the filter (1) is provided a shutter partition (7) which borders the lower part.  7. Installation according to one of claims 4 to 6, characterized in that it comprises cleaning means comprising a water spraying ramp (8) disposed in the upper part, inside the drum (1) , parallel to its generatrices, and the jets of which are directed radially against the wall of the drum.  8. Installation according to claim 7, characterized in that the drum (1) is guided in rotation on a fixed shaft (100) tubular, by which is done the water supply to the ramp (8).  9. Installation according to claim 7 or 8, characterized in that it comprises a receiving gutter (90) disposed outside the drum, and adapted to collect cleaning residues.