NL2008390C2

NL2008390C2 - Filtration appliance and filtration installation comprising such an appliance.

Info

Publication number: NL2008390C2
Application number: NL2008390A
Authority: NL
Inventors: Philip Jackson
Original assignee: Beaudrey & Cie
Priority date: 2011-03-04
Filing date: 2012-03-01
Publication date: 2013-08-14
Also published as: FR2972116B1; GB2488656A; NL2008390A; FR2972116A1; GB201203544D0; GB2488656B

Description

No. NLP190912A

Filtration appliance and filtration installation comprising such an appliance

The present invention relates generally to screens with a filter element that are usually installed in water intakes, whether these are river or sea water intakes, for retaining debris and particles carried by the abstracted 5 water.

In such a screen, that is normally placed downstream of a grid composed of bars placed a few centimetres apart and protecting it from debris of large dimensions (either in isolation or in association with one 10 or more other screens of the same type belonging to the same screening station), the filter element, the mesh of which has apertures of only a few millimetres, is mobile to enable the removal of debris and particles which, since their dimensions are greater than those of its mesh, 15 progressively obstruct all of the apertures, causing clogging.

Such a mobile filter element can constitute a panel capable of being lifted in its own plane, alternately with another panel of a similar type placed parallel to the 20 previous one and at a distance therefrom.

Moreover, this mobile filter element can also constitute an endless loop with an elongated cross section, in order to constitute a travelling band screen, or with a circular or polygonal cross section, in order to constitute 25 a drum screen.

Regardless of its form, such a filter element passes cyclically from an immersed position, in which it is progressively laden with various debris and particles, to an emerged position, in which it is subjected to the action 30 of pressurized backwash water jets in order to remove the 2 particles and debris attached to its surface and thus make it capable once again of carrying out its filtration function during its subsequent immersion.

The particles and debris thus entrained by the wash 5 water have up to the present time usually all been collected together in a trough provided for the purpose, and thereby discharged to a drain.

The fact that these debris and particles were of mineral and vegetable origins, or that they contain living 10 elements, in particular fish, does not appear to have been given attention up to the present time.

This is no longer the case today, when there is increasing anxiety to protect nature generally, particularly for the protection of living elements in an 15 aqueous environment, when greater quantities of water are drawn from rivers or the sea, particularly those required by nuclear power plants, and the current trend to install high-capacity water intakes in estuaries or coastal areas aggravates the problem. The living elements carried by the 20 corresponding water do not have the benefit in these installations of the benign influence of a possible current which advantageously would limit their entrainment, unlike the situation in some river water intakes which are sensibly arranged for this purpose.

25 It appears that such living elements (particularly fish), when trapped and entrained by the filter element of a screen at such a water intake are inevitably subjected to : - an often lengthy period out of water during the 30 emerging phase of the filter element, - the action of the wash water jets applied to the filter element, which is often brutal, - and as a result being violently thrown into the trough provided for collecting all of the particles and 35 debris that temporarily clogged the filter element in question.

Of course, various devices have already been 3 proposed that are intended for installation on a screening station for water intakes with the aim of ensuring the safeguarding of the living elements and particularly of fish that are carried by the extracted water.

5 However, in implementations of this type known up to the present, these are either special filters that by themselves only ensure the safeguarding of fish, without any general screening function, or conventional screening filters that impose on the collected fish a period out of 10 water.

The only viable solution proposed up to the present is that described in French patent No. 2396123 that relates generally to making it possible to ensure both the desired screening and the safeguarding of fish.

15 More specifically, a subject of this system is any screen having a mobile filter element for water intakes, whether this is a filter panel screen, a travelling band screen, or a drum screen. This screen is characterized in that, for the protection of any living elements, 20 particularly fish, carried by the water intake, a safeguarding device is associated therewith containing, slightly below the low water level, a collection trough extending transversally facing said filter element, on the upstream side of the latter and opposite to the inlet water 25 passing through this element. The concave portion of this collection trough is turned towards said filter element and is subjected to low-pressure means capable of causing, at the level of said trough, a reverse flow of water through said filter element that is sufficient to entrain the 30 living elements captured thereby.

The low pressure means to be used can result very simply from the fact that the head of water in the collection trough is kept lower than that on the downstream side of the filter element.

35 However created, the reverse current circulation resulting therefrom at the level of the collection trough is sufficient to detach from the filter, without brutality, 4 the living elements, and particularly fish, entrained thereby to that point, while these living elements are still immersed in their original medium. These living elements, accompanied by some quantity of debris of small 5 dimensions that is easily detachable, are carried by the collection trough to their original medium, either directly, or via a collection sump provided for this purpose, still without brutality and in their natural medium. In the case where a collection sump is present, 10 they can, after recovery, be sent back unharmed to their original medium using any suitable device, such as an Archimedes screw, fish lift, discharge valve, or any other appliance, particularly according to the location of the screening station concerned in relation to said original 15 medium.

Apart from the essential advantage of thus ensuring the desired protection of the elements carried by the extracted water, this safeguarding device also has the advantage of accommodating to the current technology in the 20 field of screens with a filter element for water intakes, whatever the nature of this filter element.

This system, which is extremely effective, can even provide survival rates for fish and other aquatic organisms that exceed eighty percent for most species. These survival 25 rates relate to the elements captured by the filter element of the rotary screen before the element passes in front of the suction nozzle that removes and carries away the captured elements. The nozzle is situated just below low-water level in order not to dry up at this level. If the 30 water level is higher, a portion of the water passes through the filter element above the nozzle. The living elements captured by the filter element pile up to the level at which high-pressure jet washing takes place, thus destroying them. The overall survival rate is reduced 35 accordingly.

The proportion of the total flow that passes through the filter element above the nozzle increases the 5 higher the water level and the larger the filtration surface area. If the unscreened water is relatively debrisladen, the filter element before the nozzle is significantly clogged, while the filter element just after 5 the nozzle is very clean, increasing the proportion of the flow treated on the portion of the screen situated after the nozzle.

It should be noted that the immersed backwash satisfactorily cleans the filter element. Assuming that the 10 filter element arriving in front of the nozzle is completely clogged and leaves clean, to the extent that the water level is substantially above the nozzle, the detritus-removing capacity of the mechanical screen is almost doubled. This constitutes a remarkable advantage in 15 the case of massive and generally short-lived arrivals of algae, leaves, shellfish or other unwanted organisms and detritus.

The purpose of the invention is to overcome at least one of the above-mentioned drawbacks by proposing an 20 appliance for filtering a fluid flow laden with solid bodies, containing: - a filtration device comprising a plurality of mobile filter elements, - drive means of the plurality of filter elements 25 for moving them particularly from bottom to top, characterized in that the appliance contains at least one additional protection device comprising at least two separate portions, - a lower portion comprising at least one suction 30 unit and capable of adopting a suction position arranged opposite at least one filter element close thereto and at least one retracted position distanced from said at least one filter element, said at least one suction unit being made to pass from the suction position to a retracted 35 position under the action of the insertion of large-volume bodies between said at least one filter element and said at least one suction unit when in its suction position, 6 - an upper portion situated above said at least one suction unit, comprising at least one element forming a barrier, placed opposite filter elements that are on a higher level than that of said at least one suction unit.

5 The additional protection device makes it possible in particular to protect fish carried by the water flow while preventing them from reaching a washing station situated on the upper portion of the filtration device.

More particularly, the element forming a barrier 10 prevents the water laden with bodies, such as fish, to be protected from reaching the filter elements without passing through the inner part of the device where the aspiration of the filter elements takes place.

In fact, in the absence of such a barrier, insofar 15 as the aspirated filter elements are raised, the water laden with bodies reaches the filter elements which have been aspirated and which will then be washed in the upper portion.

A risk then exists that the washing jet or jets 20 will injure or even kill the fish.

It will be noted that the upper portion of the additional device is arranged immediately above said at least one suction unit in the sense that the distance between the lower end of the upper portion and the upper 25 end of said at least one suction unit must be sufficiently small to prevent solid bodies, such as fish, from passing between the two and therefore reaching the filter elements cleaned by the suction unit or devices.

Moreover, the lower portion of the additional 30 protection device is retractably mounted so as to allow bodies of large dimensions to pass between the suction unit and the filter element opposite, when the dimensions of the bodies are too large to be able to pass between the suction unit, in its suction position, and the filter element 35 opposite.

The fact that the additional protection device is in two separate parts allows only one of these two parts to 7 be made mobile, namely the suction unit, and not the whole of the device.

In fact, for a filtration device with large dimensions, for example several metres, or even for some 5 applications more than 20 metres in height, a device made in a single piece would give rise to great difficulties if it needed to be moved in order to clear the way for large debris to pass.

With the invention, only the lower portion of the 10 additional protection device is mobile, the upper portion itself remaining fixed.

Moreover, inasmuch as the upper portion of the additional device must be sufficiently rigid to withstand the pressure of a fluid, particularly water, that increases 15 with the height of the filtration device, the weight of this part would mean that is would be very difficult to move .

It will be noted that the various bodies and particularly fish which are captured by the filter elements 20 are aspirated by the suction unit or appliances for collection purposes.

According to a possible feature, said at least one element forming a barrier contains a lower portion that is mobile between a first, lower position situated close to 25 said at least one suction unit when the latter is in the suction position and a second, raised position, called the high position, that is achieved under the action of passing said at least one suction unit from the suction position to a retracted position.

30 By thus extending the barrier downwards until it comes very close to the suction unit, it is then possible to close the access to the filter elements already aspirated and situated at a level higher than that of the suction unit with respect to the laden fluid placed 35 upstream of the barrier.

The distance between the mobile lower portion in the low position, particularly its free end, and the 8 suction unit is calculated so that the bodies (particularly fish) cannot enter in between the two elements.

Moreover, this mobile lower portion can also be folded back in order to free space for the clearance 5 necessary for the suction unit to clear the filter elements for the passage of large-volume bodies.

According to a particular possible feature, the mobile lower portion is a flap hinged on said at least one element forming a barrier.

10 It will be noted that the mobile lower portion extends generally along the entire width of the filtration device or over a portion of this width only in the case in which the filtration appliance contains at least two additional protection devices that are for example arranged 15 in parallel fashion.

According to a particular possible feature, said at least one element forming a barrier has at least one opening and at least one mobile closing member of said at least one opening, said at least one closing member being 20 designed to move away from said at least one opening as soon as a predetermined fluid pressure difference is established between one side and the other of the filtration device in the lower area of the latter situated opposite said at least one suction unit.

25 Said at least one closing member is thus mobile between a closed position where it is against said at least one element forming a barrier in order to close said at least one opening and a distanced position from said at least one element forming a barrier in order to clear said 30 at least one opening.

When the lower area of the filtration device which is situated facing the suction unit is heavily clogged by various debris, the headloss between upstream and downstream of the filtration device reaches a value that is 35 too high (predetermined pressure difference) . It is then provided to allow a determined fluid flow to pass through the barrier in order to allow fluid to pass through the 9 filter elements that have already been aspirated and are situated in a high position (at a higher level than that of the suction unit).

This arrangement makes it possible to temporarily 5 reduce the prevailing headloss between upstream and downstream of the filtration device.

It will be noted that no manual involvement is required for the closing member to move away from the opening, this movement taking place naturally when the 10 pressure of fluid built up upstream of the barrier (the closing member being placed downstream of the barrier) is sufficient to cause this displacement.

This arrangement thus makes it possible to lighten the load imposed by the mass of fluid on the structure of 15 the appliance, particularly on the structure of the filtration device and the additional protection device or devices .

Moreover, the ability to lighten the load to which the structure is subjected ensures that it is unnecessary 20 to overdimension the barrier, particularly in terms of thickness and therefore weight.

According to a possible feature, said at least one element forming a barrier has several openings distributed according to the height of the barrier and several mobile 25 closing members each arranged to close an opening.

The presence of several closed openings that can be freed according to a given headloss makes it possible to distribute the stream passing through the barrier in comparison with a situation where the barrier has only one 30 opening.

For example, the openings are placed one above another. For the same level, several openings can also be provided in order to cover a large portion of the surface of the barrier.

35 According to a possible feature, the additional protection device extends over the entire width of the filtration device or over a portion of this width only in 10 the case where the appliance contains at least two additional protection devices.

For example, the width of the filter elements corresponds to the width of the filtration device and the 5 additional protection device extends over the entire width of said elements or only over a portion thereof in the case of a plurality of devices.

It will be noted that the additional protection device extends to a level above that of the portion of the 10 filtration device that is immersed when the level of fluid (e.g.: water) is at its highest. Generally, the additional device does not extend over the entire height of the filtration device.

According to a possible feature, said one element 15 forming a barrier contains an upper portion forming an extension hinged in the direction of the filter elements, closing the space comprised between the wall and these latter and being temporarily folded back during the passage of a large-volume body captured by a filter element, the 20 upper portion returning to its original closed position after the body has passed through.

According to a possible feature, said at least one suction unit is connected to a pump designed to aspirate the various bodies and debris collected on the filter 25 elements as well as the elements of aquatic life, without killing or injuring them.

This pump thus makes it possible, using a suction unit or appliances, to aspirate the fish captured by the filter elements and then return them to their natural 30 medium.

Said at least one suction unit is for example a suction nozzle.

According to a possible feature, said at least one element forming a barrier is a wall arranged above said at 35 least one suction unit.

The wall can be, for example, rectilinear or curved, for example domed, with its concavity oriented 11 opposite the filter elements (or more generally orientated downstream with respect to the direction of flow of the fluid) in order to better withstand the pressure of the fluid.

5 According to a possible feature, the filter elements of the plurality of filter elements are arranged in relation to each other so as to form a closed filtration enclosure that rotates on itself.

This plurality of filter elements thus arranged 10 form a continuous or almost continuous filtration surface that is closed in on itself.

For example, it can take the form of a wheel rotating about its centre of rotation or adopt a form similar to that of a conveyor belt rotatably mounted around 15 two shafts placed at the two opposite ends of this belt.

According to a possible feature, the filtration device is a drum screen containing two filtration chambers, an additional protection device being arranged inside each chamber .

20 Alternatively, the additional protection device or devices is or are arranged outside the drum if the flow through the latter takes place from the outside to the inside .

Generally, the two chambers or half-drums are 25 separated from each other by a median plane in which a peripheral rim and spokes are placed radially with respect to this rim.

According to a possible feature, the filtration device is a travelling band screen.

30 It will be noted that in the different filtration device examples previously mentioned the drive means of the plurality of filter elements have the effect of displacing them in a cyclical movement, from bottom to top, then from top to bottom.

35 A subject of the invention is also a filtration installation comprising: 12 - a channel in which a fluid laden with solid bodies flows, - a filtration appliance installed in the channel so as to filter the flowing fluid and collect the solid 5 bodies captured by the appliance.

The filtration appliance is according to the appliance described briefly above.

Moreover, said at least one additional protection device is arranged upstream of the filtration device with 10 respect to the direction of flow of the fluid through the filter elements.

According to a possible feature, where the fluid is water, said at least one suction unit is placed immediately below the low water level.

15 This arrangement makes it possible to ensure that the suction unit is always able to aspirate the debris captured by the filter elements of the filtration device, even in the case of a drop in the water level in the channel.

20 Moreover, said at least one element forming a barrier extends following a height of the filtration device such that the upper end of said at least one element forming a barrier is placed above the high water level.

This makes it possible to ensure that in case of a 25 significant rise in the water level in the channel, the laden water will not pass above the barrier. This would allow the fish to escape from the lower aspiration area and therefore to reach the level of the washing station of the aspirated filter elements.

30 According to a feature, the channel is defined by lateral walls, said at least one additional protection device being fixed to one of the walls.

Other features and advantages will become apparent during the following description, given by way of non-35 limitative example only and with reference to the attached drawings in which: 13 - Figure 1 shows a vertical section CC of the installation according to the invention; - Figure 2 shows the installation in Figure 1 along a horizontal half-section AA and a half-section BB; 5 - Figure 3 shows the mechanism of the installation allowing it to be adapted to large debris; - Figure 4 is a partial enlarged view of the area of the suction nozzle in Figure 1; - Figure 5 is a sectional view along BB of the 10 installation in Figure 1; - Figure 6 is a sectional view along AA of the installation in Figure 1; - Figures 7 and 8 are successive views of the installation in Figure 1 with different water levels; 15 - Figures 9 to 11 are of the diagrammatic views of variants where the filtration device is a travelling band filter.

The application of the invention to a filtration installation comprising a drum screen with the water 20 flowing from the inside to the outside will now be described.

The filtration installation shown in Figures 1 and 2 comprises a channel 2 in which water laden with various debris and living organisms such as fish flows. The channel 25 2 is delimited by lateral walls 3 and 4 between which the water flows. A filtration appliance 5 is installed in the channel so as to filter the laden water and collect the solid bodies captured by the appliance.

The appliance 5 comprises a filtration device, here 30 a drum screen 20, installed between two parallel walls 11 and 12 joined by a transverse wall 13. The water arrives via water ways 14 And 15, enters the drum through the inlets (water intake flow areas) 16 in the direction of the arrow F4. The minimum level of the water or low water level 35 is marked Ni. The maximum level or high water level is marked N2.

14

The drum screen comprises a shaft 21 rotating on two bearings 22 fixed to the civil work. This shaft 21 contains at its centre a hub 23 onto which are fixed spokes 24 supporting a peripheral rim 25 onto which cross members 5 34 are perpendicularly fixed. Filter elements 26 are mounted on the cross members 34 over the entire outer periphery of the drum of so as to form a closed filtration enclosure that is cylindrical overall and rotates on itself about a horizontal axis. The shaft 21 of the drum is driven 10 in rotation in the direction of the arrow Fi by the pinion 27 engaging with a peripheral toothed crown wheel (not shown) . A motorization of a type known per se drives the pinion in rotation. These elements constitute drive means of the mobile filter elements 26.

15 Peripheral seals 28 known per se (Figure 2), avoid any possibility of the water and debris by-passing the filter elements. The water enters via the intake flow area 16 within each half-drum or filtration chamber. Each chamber is separated from the other by a median plane in 20 which the rim 25 and the spokes 24 are arranged. The water flows in the direction indicated by the arrows F2 in Figure 1 and passes through the filter elements 26 from the inside to the outside of the drum. The screened water flows out of the drum in the direction indicated by the arrow F3 (Figure 25 2) , without the debris and living organisms that are captured on the filtration surface of the drum. The water then drains into the downstream portion of the channel on the right in Figure 2.

This filtration surface or enclosure is divided 30 into substantially equal compartments 29 by solid partitions 30 mounted radially following the generatrices of the cylinder towards the inside thereof. In the absence of another system, the dirty filter elements 26 are backwashed by jets 31 mounted on a tubular wash water 35 manifold 32 that is generally placed on the upper portion of the drum. The detritus and fish are roughly thrown into 15 the troughs 33 so as to be returned to their natural medium.

In order to collect fish and other living organisms accumulated on the surface of the filter elements 26, a 5 suction unit such as a suction nozzle 40 is installed within the half-drum shown in the half-section BB in Figure 2. More particularly, the nozzle is installed such that the opening 41a provided on the inlet face 41 is arranged tangentially to the inner edges of the partitions 30.

10 This nozzle is installed just below the level Ni so that it is always primed and aspirates the compartments 29 in turn as they pass from bottom to top in front of the opening 41a of the nozzle. For this purpose the nozzle is connected to a special pump 42 capable of aspirating and 15 pumping fish and other living organisms without selection via a conduit 43. It will be noted that in Figures 1 and 2 this nozzle adopts a so-called aspiration position in which its aspiration opening 41a is arranged facing a compartment 29 and therefore a filter element. The nozzle is mobile and 20 is thus capable of adopting a retracted/ position. This clearance movement is caused by the insertion a large-volume body or item of debris between the nozzle and the opposite filter element. The nozzle can pivot about the horizontal axis 44 and move away from the opposite filter 25 element 26 in order to avoid blocking the rotation of the drum in the case where an item of debris of larger dimensions is caught in a compartment 29. The raised position is shown in Figure 3 (arrow E) . It will be noted that there exists a plurality of retracted positions 30 according to the size of the debris/bodies and that the nozzle returns to the suction position (under the action of the weight of the upper mobile portion itself) when the debris/bodies are no longer there (Figure 4). Moreover, lifting the nozzle can also be manually controlled.

35 As shown in Figure 5 (sectional view along the section BB in Figure 1), the filtration appliance comprises two suction units (nozzles) 40A and 40B, each installed in 16 one of the chambers of the drum in order to be able to serve the entire filtration surface of the filter elements. Each appliance thus extends over a half-width of the drum. A corresponding special aspiration pump 42A, 42B is also 5 provided. The features and functions of the suction units 40A, 40B and of their associated pumps 42A, 42B are identical to the previous description of the suction unit 40 and of the pump 42. The remainder of the description applies to this double arrangement but in the interest of 10 simplicity refers only to the suction unit 40 and its pump 42 .

It goes without saying that in the absence of any other element, as soon as the intake level in the drum rises above the level Ni, the water laden with detritus and 15 fish is intended to pass through the filter elements 26 comprised between the nozzle 40 and the water level of the upstream side of the cleaned filter elements (at a higher level than that of the nozzle) . The living organisms thus caught are subjected to the washing by the jets 31 and the 20 great majority of them are therefore killed.

In order to avoid this performance failure in the safeguarding of fish, the present invention provides for installing upstream of the filter elements at least one element forming a barrier such as a wall 50, above the unit 25 40. This wall is arranged almost abutting the upper end of the face 41 of the nozzle 40 (Figures 1 and 4). The height of this wall reaches the high water level N2 and extends opposite filter elements 26 that are at a higher level than that of the unit 40 and that have therefore been aspirated. 30 The upper end of the wall is situated above the level N2 in order to avoid any overflow.

In the type of drum described, with water flow from the inside to the outside, the debris captured on the filter elements 26 in the compartments 29 have a tendency, 35 due to the overhang of the wall 50, to fall back into the water the nearer they get to the wash water station 31, often even before being caught in the trough 33. An 17 inclined flap 58 is provided in order to prevent them falling back and remaining between the wall 50 and the opposite filtration surface 26. This flap (mobile upper portion) is hinged horizontally on the shaft 59 situated at 5 the upper end of the wall 50. In the normal position, the upper edge of the flap 58 is closest to the edges of the solid partitions 30 of the compartments 29. If an element of large size spills over from a compartment 29, the flap 58 will push it back (when the compartment rises) and will 10 fall to its normal position immediately thereafter. As the flap 58 is inclined and kept wet by the splashing caused by the wash water manifold 32, any debris falling thereon will slip and return to the intake raw water area situated upstream of the wall 50, and not into the space between the 15 wall and the filtration surface of the drum.

The wall forming a barrier can be produced from several elements assembled together on site, for reasons of ease of manufacture and transport (taking account of the large dimensions that such a wall can have of several 20 metres or even about ten metres) . The wall can alternatively be domed with its convexity oriented upstream so that it can better withstand the fluid pressure. As shown in a top view in Figure 2, the wall 50 has opposite flanges. A first flange 50a extends upstream along the wall 25 3 of the channel and is fixed by known means to this wall.

The flange 50a extends over substantially the entire height of the wall 50 and reinforcing ribs 51 are provided on the upstream side between the wall 50 and its flange acting as a mounting base. A second flange 50b extends downstream 30 along the median plane of the drum defined by the rim 25 and the spokes 24, almost in abutment with this plane in order to prevent any passage of unscreened water towards the filtration drum. The second flange 50b extends up to the filtration drum. It will be noted that in a top view 35 the wall 50 equipped with its flanges is generally Z-shaped, the base being more elongated than the head. This wall therefore prevents the laden water from being screened 18 in the portion of the filter elements situated above the nozzle. The fish are therefore all collected by the nozzle and the pump, thanks to this barrier.

It will be noted that a wall 50A, 50B identical to 5 the wall 50 is placed above each respective suction unit 40A, 40B as shown in Figure 6 (sectional view along the section AA in Figure 1).

This additional protection device, as described above (suction unit in the lower portion and, separate from 10 the latter, at least one element forming a barrier in the upper portion), although satisfactory, can nevertheless be improved. In fact, the headloss due to clogging of the filter elements 26 which, in the absence of the partition 50, are distributed homogenously and symmetrically over the 15 whole of the immersed portion, is no longer applied to the portion masked by the partition 50. The resultant of the forces is then no longer vertical but inclined, stressing the bearings and their fastening to the structure in a manner that becomes more difficult to contain, the greater 20 the headloss and the forces thereby generated. It can thus be sought to reduce these non-vertical forces to a minimum. It will be noted that in practice the rotary screens operate over 98 percent of the time with very low headlosses (less than 20 cm) . In this respect, it is 25 possible to install on the wall 50, in which through-holes are made in the thickness, mobile members for closing the openings (ballast valves) 52 that are normally closed and therefore in contact with the wall 50 (Figures 1 and 7) on the downstream side of the latter. These members 52 open 30 only if the headloss across the drum increases beyond a predetermined value that is low but rarely reached in service (20 cm, for example) . In the embodiment, several openings 47 are provided, some above others, and are distributed according to the height of the wall 50 in order 35 to carry out the distribution taking account of the headloss when the level rises. This allows a more homogenous and less turbulent distribution of the stream in 19 front of the filter elements 26. It will be noted moreover that providing several closing members makes it possible to simplify the manufacture of the wall when it is composed of several elements (each element is thus provided to have an 5 opening and accept a closing member). These members or valves include a (dome-shaped or dished) shutter or cover 55 hinged horizontally about a shaft 54 attached to the wall. A counterweight 53 is fixed to the shutter 55 and is calculated so that the opening of the valve begins as soon 10 as the previously-chosen headloss prevails on both sides of the drum in a lower area of the latter situated facing the suction unit 40, or even below the latter. This headloss indicates a large accumulation of debris on the filter elements 26 situated in this area. This or these mobile 15 closing member or members (valves) then open for a short period when fish contained in the unscreened water are subjected to the high-pressure washing in the upper portion. This period is very short and limited to the periods of excessive concentration of debris in the water 20 and therefore excessive clogging of the filter elements 26. This passage of water however makes it possible to recover the above-described additional screening capacity and to ensure continuity in the supply of screened water.

Figures 7 and 8 show the increase in the fluid 25 level upstream of the wall 50 following the beginning of clogging of the filtration drum. In Figure 7 the fluid level is normal and no closing member is open. Conversely, in Figure 8, a predetermined headloss level has been reached, as the filtration surface in the lower portion is 30 significantly laden with various debris and a first closing member 52 (the lowest) moves away from the wall in order to allow the water to pass momentarily through the corresponding opening 47.

If the water level increases and the headloss stays 35 above the predetermined level, upper closing member or members in turn are activated in order to decrease the built-up weight of water upstream of the wall.

20

As shown in Figures 3 and 4, it is provided for the horizontal lower portion 56 (e.g.: flap) of the wall 50 to be hinged along a horizontal axis 57 with respect to the remainder of the wall situated above. This thus allows the 5 mobile portion 56 to be raised (retracted position) from its low position (Figure 4) in the case where a large-size item of debris having caused the nozzle 40 to move away by pivoting (following the arrow E in Figures 3 and 4) obstructs this portion. In the low position the mobile 10 portion 56 is kept inclined in the direction of the filter elements by an element forming a stop (not shown) that prevents it coming into alignment with the vertical wall 50.

As shown in Figures 3 and 4, the hinged lower 15 portion 56 pivots upwards and towards the face of the wall 50 oriented downstream, following the direction of the arrow F so as not to obstruct the moving away (by pivoting) of the suction unit 40 in the direction E. It will be noted that the displacement of the unit 40 causes the 20 displacement of the portion 56. Alternatively, the displacement of the portion 56 can be caused by a large-volume item of debris/body passing through.

When constituted in this way, the safeguarding device (additional protection device) makes it possible to 25 avoid obstructing the operation of the drum while safeguarding the increased debris capacity in the periods when this is required. Moreover, the presence of the mobile closing members (valves) limiting the pressure exerted on the wall 50 in case of an increase in the headloss reduces 30 the weight and the cost of said wall 50 as well as the lateral stresses on the bearings 22.

As already mentioned above, the filtration appliance comprises two additional protection devices (suction unit and at least one element forming a barrier 35 above), one per half-drum or chamber.

It goes without saying that the application of this method associated with the aspiration of fish on filter 21 elements is not limited to a drum screen with the water flow from the inside the outside only. It can, in fact, be applied to drums with the reverse direction of water flow. It can also be used on travelling band screens of different 5 types such as so-called through-flow band screens, where the water arrives over the entire width of the upstream panels installed across the total width of the water way, or rotating travelling band screens that are installed across the water way, and have one side of the filter apron 10 that descends while the other ascends after having travelled via the lower portion. Double-flow band screens with water circulation from inside to outside can beneficially be equipped therewith, the wall being installed above the nozzle on the ascending end of the 15 filter element in order to occlude the latter.

Figure 9 shows very diagrammatically a filtration appliance 90 according to the invention in which the device 92 is a through-flow band screen of a known type.

The installation comprising the channel or raceway 20 94 in which the appliance is installed is shown in Figure 10.

The filter 92 symbolized by broken lines extends across the opposite walls 96 and 98 of the channel.

An additional protection device 100 is arranged 25 upstream of the filter 92 and contains a lower portion containing two suction units 102, 104 (e.g.: nozzles) placed side by side in order to cover the entire width of the filter. Alternatively, a single suction unit could replace these two appliances but for reasons of simplicity 30 and space occupied two appliances are preferred. These two appliances are each connected to a pump or both to a single pump.

The description of the features, advantages and operation of the appliance in Figures 9 and 10 as well as 35 that in Figure 11 hereinafter, is identical to the description made with reference to the previous Figures.

22

The device 100 also comprises a separate upper portion 106 containing an element forming a barrier in the form of a wall. It will be noted that this wall can be composed of several elements forming a barrier and mounted 5 in relation to each other in order to form a wall extending over the entire width of the filter.

It will be noted that the barrier can be divided into two elements, each extending over a portion of the width of the filter.

10 Two closing members 108 and 110 have been shown in dotted lines.

In Figure 10 which is a top view, the barrier 106 has been removed in the interest of clarity.

Figure 11 shows a filtration appliance 120 15 installed in a race 122 delimited by two lateral walls 124, 126 and comprising a filtration device 128 which is a double-flow band screen of known type.

The screen 128 is mounted on two transverse walls 130, 132 fixed to the two walls 124, 126.

20 On the ascending side of the screen an additional protection device 134 is positioned, identical to the device 100 in Figures 9 and 10. Only the suction units 136 and 138 have been shown, in the interest of clarity.

Claims

A filtering device for filtering a liquid stream loaded with solid bodies, comprising: - a filtering device (20) comprising a plurality of displaceable filter elements (26), - driving means (27) for driving the plurality of filter elements to move it, in particular from low to high, characterized in that the device comprises at least one additional safety device which comprises at least two separate parts, - a lower part (40) which comprises at least one suction member (40) ) and which is adapted to assume a suction position which is positioned opposite at least one filter element and in its vicinity, and at least one retracted position at a distance from the at least one filter element, the at least one one suction member is adapted to move from the suction position to a retracted position under the action of introducing large volume bodies between the at least one filter element and the at least one suction member when it is in the suction position, - an upper part (50) which is placed above the at least one suction member, comprising at least one element forming a barrier that is positioned opposite filter elements which be at a level higher than that of the at least suction device.

A filter device according to claim 1, characterized in that the at least one element forming a barrier 30 comprises a lower part (56) movable between a first, lower position which is placed close to the at least one suction member (40) when it is in the suction position, and a second, raised position, so-called the high position, which is achieved under the action of moving the at least one suction member from the suction position to the retracted position.

3. Filtering device as claimed in claim 2, characterized in that the movable lower part is a valve (56) which is hingedly connected to the at least one element that forms a barrier.

A filter device according to any one of claims 1 to 3, characterized in that the at least one barrier-forming element has at least one opening (47) and at least one movable closing member (52) for the at least one opening, the at least one closing member is adapted to move away from the at least one opening at the moment that a predetermined liquid pressure difference is obtained between one side and the other of the filter device in a lower region of that opposite the at least one suction device is located.

5. Filtering device as claimed in claim 4, characterized in that the at least one element which forms a barrier has several openings which are distributed over the height of the barrier, and several movable closing members which are each adapted to close an opening.

6. A filter device according to any one of claims 1 to 5, characterized in that the additional protection device extends over the entire width of the filter device or, only in the case where the device comprises at least two additional protection devices, over a part of this width.

A filter device according to any one of claims 1 to 6, characterized in that the at least one suction member is connected to a pump (42).

A filter device according to any one of claims 1 to 7, characterized in that the at least one suction member is a suction nozzle (40).

A filter device according to any one of claims 1 to 8, characterized in that the at least one element that forms a barrier is a wall.

10. A filter device according to any one of claims 1-9, characterized in that the filter elements of the plurality of filter elements are positioned relative to each other such that they form a closed filter enclosure that rotates on its own.

A filter device according to any one of claims 1 to 10, characterized in that the filter device is a drum filter (20) comprising two filter chambers, an additional safety device being placed in each chamber.

A filter device according to any one of claims 1 to 10, characterized in that the filter device is a band filter.

13. A filter device according to any one of claims 1 - 12, characterized in that the at least one element that forms a barrier comprises an upper part (58) which forms an extension which hinges in the direction of the filter elements that the space between the wall and the latter closes and is temporarily folded back during the passage of a large volume body trapped by a filter element, the upper part returning to the original closed position after the body has passed through it.

A filtering installation comprising: - a channel (2) into which a liquid-laden liquid flows, - a filtering device (5) installed in the channel for filtering the flowing liquid and collecting the solids trapped by the device, characterized in that the filter device is in accordance with any of claims 1 to 13, wherein at least one additional safety device is positioned upstream of the filter device relative to the direction of flow of the liquid through the filter elements.

A filter installation according to claim 14, characterized in that the liquid is water, wherein the at least one suction member is placed directly below the lowest water level (NI).

A filter installation according to claim 14 or 15, characterized in that the liquid is water, wherein the at least one element that forms a barrier extends above the highest water level (N2).

17. Filter installation as claimed in any of the claims 14-16, characterized in that the channel is defined by side walls (3, 4), wherein the at least one additional security device is attached to one of these walls. -o-o-o-o-o-o-o-