EP0140732A1 - Device for picking up a polluting layer from the water surface - Google Patents

Abstract

The device can be used for removing pollution from stretches of the sea. It consists of a hull (12) fitted with means for propulsion and having a central part (10) which bows out towards the front with respect to two lateral sections (11). These lateral sections, together with the central part, define channels leading to the separators. The central part has deflecting elements, such as vanes (17), to create eddies whose orientation tends to reduce the separation of the surface flow around the hull. Each lateral section defines, in a portion located in front of a first capture threshold (18), an open channel letting communication at depth persist. This allows water to flow from one side of the side hull to the other. The front end of each side hull is connected to a blade (14) for connection to the submerged part of the central hull in front of the stem (13) of the side hull. This blade is designed to deflect the flow of the deep layers towards the bottom and towards the outside. <IMAGE>

Description

The invention relates to a device for the selective sampling of a layer of pollutant, such as a hydrocarbon, floating on the surface of a sheet of water capable of being subjected to swell, a device which can be used in particular for cleaning up covered areas. of a layer of oil following accidental spills.

The patent application WO 83 01799 of the applicants describes such a machine of the type which comprises a hull provided with propulsion means making it possible to keep it in flight, the hull having a central part projecting forward with respect to two parts lateral which delimit, with the central part, supply conduits to separators and the central part having deflector means, such as wings, to create vortices whose orientation tends to reduce the divergence of the surface flow around the hull. The deflector means make it possible to sweep the sea between two current lines which, upstream of the machine, have a spacing much greater than that which they would have in the absence of these means, and cause a thickening of the polluting layer at the entrance to the separator supply conduits. However, this thickening remains insufficient for the separators to receive a mixture containing a sufficient content of pollutant. To increase the thickening of the polluting layer throughout an open vein flow to the separators, it is proposed, in patent application WO 83 01799, to carry out the collection of liquid between the lateral parts and the part central, using an offset profile floor whose leading edge protrudes in front of the conduits, intended to slow the flow upstream of the leading edge. This solution gives satisfactory results when the level variations above the floor remain limited. In fact, in view of the request WO 83 01799, the captured flow is limited by decreasing the depth at the level of the capture threshold formed by the floor and, simultaneously, the speed is reduced above of this threshold to maintain a river flow, which requires a Froude v / Vgh number less than 1. But it remains difficult to achieve this slowdown while completely eliminating a local divergence of the surface flow.

• - une captation superficielle ou cloisonnement, consistant à couper la surface libre de la nappe d'eau par l'étrave des parti-es latérales, présentant dans leur surface avant une profondeur inférieure à celle de la partie centrale, ce qui constitue pour la nappe polluante une barrière,mais laisse subsister une communication profonde permettant des écoulements d'eau d'un côté à l'autre de la coque latérale,
• - une captation définitive, à partir du bord d'attaque d'un plancher immergé qui relie la coque centrale à la coque latérale, mais loin derrière l'étrave de cette dernière.

The invention aims in particular to provide a machine of the type defined above in which a progressive thickening of the polluting layer is caused without any divergence of the current lines on the surface. For this, the capture function is broken down into two operations:

• - A surface capture or partitioning, consisting in cutting the free surface of the water table by the bow of the side-es, having in their front surface a depth less than that of the central part, which constitutes for the water table polluting a barrier, but leaves a deep communication allowing water flows from one side to the other of the lateral hull,
• - a definitive capture, from the leading edge of a submerged floor which connects the central hull to the lateral hull, but far behind the bow of the latter.

By giving the bottomless channel delimited by the external wall of the central part and the internal wall of the lateral hull, upstream of the submerged floor, a regularly decreasing width, one obtains a progressive thickening of the polluting layer and a withdrawal of water from the channel, by oblique bypass flow from the bottom of the side hull.

Such an arrangement, used in isolation, would not make it possible to avoid a divergence of the surface flow upstream of the lateral bow and the separations.

Consequently, the invention proposes in particular to provide the front part of each lateral hull, immediately behind its bow, with a connecting vane with the submerged part of the central hull, in front of the bow of the lateral hull, drawn to deflect the flow of deep layers down and out. This dawn can be constituted, on the major fraction of its length from the central part, of a wing in arrow of constant cord made up of identical profiles with flat lower surface (profile NACA 4515 for example), whose lower surface is wound in helix on a quarter of cylinder of revolution, the lower surfaces profiles constituting generators of the cylinder. The deflection of the flow then strongly depends on the angles α and pfaits by the axis of the cylinder with the horizontal plane and the vertical plane of symmetry of the machine. This wing-shaped fraction is connected to the front of the lateral part by a descending extension of this lateral part.

It should be noted in passing that the dawn, intended to avoid a divergence of surface flow, has a shape and a role completely different from those of the proposed wing, among other solutions, to counterbalance the effect of a floor of capture the leading edge of which projects forward from the lateral parts in application WO 83 01799.

Advantageously, the submerged floor ensuring final capture will be given a form of fairing with a convex underside. The leading edge of this floor will advantageously have a first horizontal shape with a strong arrow from the central part of the hull, then a decrease in the angle of the arrow and, at the same time, an upward slope for that the leading edge is connected to the apparent vertical contour line of the lateral part of the hull, which curves down to join the floor.

This arrangement allows the blade to be placed at a significant depth, since there is no longer any attempt to limit the flow which passes over it. The flow which is the subject of surface capture is greater than in the case of application WO 83 01799, but this flow is gradually reduced by the draw-off flow caused by the carrier dawn on the one hand, the floor spoiler on the other hand. These elements generate, in the deep part of the flow which has been the subject of the surface capture, a flow with vertical downward component and with lateral component directed towards the outside which facilitates the bypassing of the lateral part of the hull by below. In In the end, we can easily reduce the flow after final capture to a fraction of 20 to 25% of the flow that passes over the dawn, which allows to deeply immerse it over most of its scale. Because the deep racking takes place after superficial capture, there is no loss of pollutant, nor spillage around the bow of the lateral part.

The angles α and 8 will be chosen so as to avoid a significant divergence upstream of the bow of the lateral part, which implies giving a and / or θ a positive value, sufficiently limited however so that the dawn does not not disturb the flow to the free surface. Frequently, values of "and s near 24 ° and 18 ° can be adopted, respectively.

The agitation of the surface of the water, in particular by the swell and the blades, results in another problem which must also be resolved. This is the risk of rising surges in the capture channels, between the central part and the lateral parts of the hull. This problem was eliminated, in the object of application WO 83 01799, by placing a weir on the flow path between the capture and the discharge. However, this solution requires pumps capable of operating under very variable load and power. The invention also aims to provide a solution making it possible to use, for propulsion, pumps which, in steady state, operate at constant speed and power.

To do this, the final collection flow is divided into three separate flows by two thresholds added to the first threshold constituted by the front part of the floor.

The second threshold, which begins with a leading edge arranged horizontally, is placed so that the main fraction of the flow (generally 65 to 70% of the average final capture flow) falls below this threshold. This main fraction leads directly to a propulsion pump which runs at constant power and speed in steady state. This main fraction therefore represents a practically constant flow during a swell period.

The third threshold is placed so that the fraction of the flow which passes over the free surface above represents a few percent of the sampling flow. This fraction of the flow rate, which contains the pollutant, is injected into a separator which can be of the type described in patent application WO 83 01799.

The flow that goes on charge between the second and third thresholds bypasses the feed flow rate of the separator. It ends up, in the form of a blade passing over a tangential weir, in the well of a swell compensator. The decontaminated flow coming from the separator is advantageously returned, by a second weir, in the same well.

• - la perte de charge qu'elles introduisent en régime permanent ne doit représenter qu'une faible fraction de la pression dynamique de référence aV²/2, où V désigne la vitesse de l'engin ;
• - l'inertie de la colonne de liquide doit être suffisamment faible pour que les différences de pression engendrées entre les extrémités de la conduite par les accélérations de l'écoulement correspondant aux variations de débit restent faibles devant la pression dynamique de référence _PV²/2.

Under the effect of the swell and the blades, the relative movement of the sea with respect to the ship causes, in the channel delimited by the parts of the hull, a periodic variation of the loading height, at the period of the apparent swell . To avoid the reflection of the compression zones which descend the channel when the head height varies at the entrance of it, it is necessary that the total flow collected increases fairly quickly depending on the head height at the rear of the channel . The first of the three flow fractions being constant, the variation of the captured flow as a function of the head height must be entirely and instantly ensured by the other two flow fractions. This assumes that the pipes supplying the weirs opening into the compensator well meet two conditions:

• - the pressure loss they introduce steady should represent a small fraction of the reference dynamic pressure aV ^2/2, where V denotes the velocity of the device;
• - the inertia of the liquid column must be low enough so that the pressure differences generated between the ends of the pipe by the flow accelerations corresponding to the flow variations remain low compared to the dynamic reference pressure _P V ² / 2.

This double objective can be achieved by adopting a passage section sufficient for the pipes. The variations in level and load height are then practically in phase between the two ends of each pipe for the swell periods encountered in practice.

The law of variation of the flow over a weir makes it possible to easily obtain a sufficiently high value of the derivative dq / dz ₀ of the flow q par. relative to the head height z ₀ = z + v ² / 2g (v being the water flow speed): in fact, the flow rate is proportional to the power 3 half the thickness of the overhanging blade. It suffices in practice that the head height downstream of the weir, that is to say in the receiving well of the variable flow taken between the second and third thresholds always remains low enough for the Froude number above the weir remains greater than about 0.5.

For the weir to be effective, it is obviously necessary to evacuate the variable flow which enters the well by maintaining at each instant, in the latter, a level such that there is a pouring blade. Sometimes, to achieve this result, it is enough to connect the bottom of the well to the sea by a spiral pipe, the ejection orifice being directed towards the rear. The movement of the ship is sufficient to generate a flow in the well. However, the recovery of kinetic energy in the spiral may be insufficient to keep the level low enough and it is preferable to amplify the rotational movement generated by the tangential injections above the weirs by a rotor driven by a motor.

However, the required energy supply from the rotor remains moderate insofar as the average ejection speed chosen is significantly lower than the speed of the ship. The rotor, which operates at variable flow and may even be partially exposed, must be of robust constitution. It can be constituted by an axial pump driving the flow downwards. But it can also be very rudimentary, given the low power it has to develop. One can in particular use a simple wheel with longitudinal vanes which does not have risk of cavitation. In practical here, the total flow poured into the swell compensator well can vary, during a swell period, between 10 and 40% of the average flow captured during a period, while 75% of the flow medium are ejected by the propulsion pump.

• - la Figure 1 est une vue en perspective montrant la moitié gauche de la coque de l'engin, sur laquelle a été indiqué un maillage suivant des couples et des lignes de niveau à un écartement de 30 cm ;
• - la Figure 2A est une vue en coupe à la flottaison (niveau 28) sur laquelle apparaît également la section des conduits au niveau z₆ de la Figure 1 ;
• - la Figure 2B, similaire à la Figure 2A, est une vue en coupe au niveau z₄ de la Figure 1 ;
• - la Figure 3 est une vue en coupe suivant le couple X₃₆ de la Figure 1, montrant également les formes au niveau couple 38 ;
• - les Figures 4 et 5, similaires à la Figure 3, sont des coupes suivant les couples X₄₀ et X₄₆ de la Figure 1, montrant également les formes au niveau des couples X₄₂ et X₄₈, respectivement ;
• - la Figure 6 est une vue en élévation de l'engin, montrant une répartition possible des éléments internes ;
• - la Figure 7 est un schéma montrant un dispositif de décantation utilisable pour accroître la concentration en polluant.

The invention will be better understood on reading the following description of a machine which constitutes a particular embodiment thereof, given by way of nonlimiting example. The description refers to the accompanying drawings, in which:

• - Figure 1 is a perspective view showing the left half of the hull of the machine, on which has been indicated a mesh according to couples and level lines at a spacing of 30 cm;
• - Figure 2A is a sectional view at the waterline (level 28) on which also appears the section of the conduits at level z ₆ of Figure 1;
• - Figure 2B, similar to Figure 2A, is a sectional view at level z ₄ of Figure 1;
• - Figure 3 is a sectional view along the couple X ₃₆ of Figure 1, also showing the shapes at the torque level 38;
• - Figures 4 and 5, similar to Figure 3, are sections along the pairs X ₄₀ and X ₄₆ of Figure 1, also showing the shapes at the pairs X ₄₂ and X ₄₈ , respectively;
• - Figure 6 is an elevational view of the machine, showing a possible distribution of the internal elements;
• - Figure 7 is a diagram showing a settling device which can be used to increase the concentration of pollutant.

The device which will now be described by way of example is intended for interventions either in coastal regions, or with the logistical support of a transport building for several devices of this type, provided for the intermediate storage of the pollutant sampled and collection. The machine can have a length of about twenty meters and a width of about seven meters. Because of this short length, the ratio between its draft, generally Lement of the order of 3.50 m to take into account the expected swells, will be much lower than that encountered on a deep sea craft with high storage capacity and great length.

The machine comprises a hull 12 comprising a central part 10 and lateral parts 11 whose facing surfaces delimiting the grip channels have a general spiral shape (Figure 2). The lateral surfaces constituting the wall of the central part are substantially vertical, as shown in Figure 1. This wall is designed to limit as much as possible the wave of bow which would generate turbulence.

• - Le débit d'eau prélevé par captation superficielle est progressivement réduit à 20 à 25% de son débit primitif par déviation des couches profondes, avant captation définitive.
• - Le débit ayant fait l'objet d'une captation définitive au-dessus d'un plancher constituant un premier seuil est à son tour soumis à fractionnement. La partie profonde de l'écoulement, représentant 65 à 70% du débit moyen de captation définitive, est prélevée en charge entre le premier seuil et un second seuil placé au-dessus et en arrière. Cette fraction du débit arrive à une pompe de propulsion qui travaille ainsi, en régime permanent, à vitesse et puissance constantes. Le débit, de valeur instantanée très variable, qui passe au-dessus du second seuil, est à son tour séparé par un troisième seuil. La partie passant entre les deux seuils, représentant 20 à 30% du débit de captation définitive, arrive par un syphon au déversoir destiné à éviter la remontée des ondes déferlantes, d'où il est renvoyé à la masse d'eau.

The machine has a general constitution similar to that already described in patent application WO 83 01799 to which reference may be made. However, it is intended to ensure gradual capture and then fractionation:

• - The water flow taken by surface capture is gradually reduced to 20 to 25% of its original flow by deflection of the deep layers, before final capture.
• - The flow having been the subject of a definitive capture above a floor constituting a first threshold is in turn subject to fractionation. The deep part of the flow, representing 65 to 70% of the average final capture rate, is sampled between the first threshold and a second threshold placed above and behind. This fraction of the flow arrives at a propulsion pump which thus works, in steady state, at constant speed and power. The flow, of highly variable instantaneous value, which passes above the second threshold, is in turn separated by a third threshold. The part passing between the two thresholds, representing 20 to 30% of the final collection flow, arrives by a siphon at the weir intended to prevent the rising of the breaking waves, from where it is returned to the body of water.

Finally, the flow passing above the third threshold, representing a few percent of the flow of water captured, is subjected to centrifugal separation in separators which can be of the same type as those described in patent application WO 83 01799, l clean water taken from the base of the separators joining the water taken between the second and third thresholds.

We will now describe the means which allow the thickening of the layer of polluting liquid, then the fractionation of the sampled flow. The components involved will be described in the order in which they appear from front to rear.

Front deflector means: In the case illustrated in FIG. 1, these means comprise a jagged front wing 17 of "wound" shape, of the type already described in application WO 83 01799 to which reference may be made.

• La captation superficielle est assurée par l'étrave 13 de chaque partie latérale 11 et par l'aube 14 qui lui est associée.

Means of layer thickening and capture:

• The surface capture is ensured by the bow 13 of each lateral part 11 and by the blade 14 which is associated with it.

It can be seen in FIGS. 1, 2, 3 and 6 that the front of each lateral part 11, just behind the stem 13, extends downwards by a twisted zone of connection to the blade 14 which joins the bottom of the central part 10 very in front of the bow 13. The blade 14. intended to deflect the downward and outward flow, has a constant chord wing profile with flat underside. This lower surface is wound in a helix on about a quarter of a cylinder of revolution (not shown) whose axis makes angles _a and with the horizontal plane and with the vertical plane of symmetry. The leading edge 15 of the blade 14 is first horizontal from the central part 10, with a large arrow, typically about °. Then the arrow decreases at the same time as the leading edge rises to connect to the apparent contour line of the vertical part 11. In its zone of connection to the central part, the blade ₁ 4 is at a maximum depth close to of the draft of the machine (Figure 3), since we no longer seek to limit the flow which passes over this dawn.

The cooperation of the blade 14 and the stem i3 of the lateral part causes a deflection of the deep layers indicated by the arrows f ₀ in FIGS. 2B and 3, deflection which reduces the rate of final capture to a fraction less than 25 % of the input flow in the section delimited by the parts of the hull and the blade.

The final capture takes place above the first threshold 18 which is connected to the lateral part 11 between the pairs X ₃₇ and X ₃₈ (Figure 3). As already indicated, this threshold is constituted by the front part of a floor 19. A second threshold 20, placed above the first, having a leading edge 21 behind that of the first threshold (Figures 1 and 2B) , ensures a first fractionation of the final collection flow. We see in Figure 4 that this threshold is placed between the pairs X ₄₀ and X ₄₂ , that is to say far behind the first threshold. Line 22, thus delimited, supplies a main propulsion pump 23 placed in a cavity 24 (Figures 2B and 6). This propulsion pump discharges water through an exhaust pipe 26 opening to the rear of the ship.

A third threshold 27 placed at a level higher than that of the second threshold, between the levels z ₅ and z ₆ in the case shown, ensures a fractionation of the flow not sampled by the pipe 22. The surface flow, representing a few percent of the total flow taken above the threshold 18, is sent to a centrigure separator 28 with tangential injection which appears in Figures 2A and 2B at two different levels. We see appear in Figure 4, the pipe 29 for supplying the separator, at the top of the latter, and the pipe 30 for the removal of depolluted water at the bottom. The pollutant taken from the upper part and from the center of the vortex produced by injection and tangential extraction in the separator is then sent to storage means which will be described later.

The pipe 30 for evacuating clean water from the separator 28 feeds as well as the water taken between the second and third thresholds 20 and 27, a swell compensator 31. This compensator comprises a substantially cylindrical vertical well (FIGS. 2A, 2B , 5 and 6) provided with two weirs 32 and 33 of tangential feed (Figures 2A and 5). The weir 32 is supplied by 1 ₁ pipe 34 which opens upstream between the thresholds 20 and 27. The oblique weir 33 is supplied by the depolluted water outlet pipe 30 which rises from the bottom of the separator, near the plane of symmetry of the machine, then emerges obliquely relative to the weir 33. A rotor 35, shown only on the Figure 6, is placed in the well of the swell compensator 31 to maintain the level in the well at a value low enough that there is always a flooded overflow blade. The water escapes tangentially to the lower part of the swell compensator well 31 towards the rear of the machine.

It is sufficient to apply moderate power to the rotor, which gives it a constant speed of rotation, so that the flow ejected by the pipe 36 increases rapidly as soon as the level of the free surface rises in the well, which tends to limit the level variations. If the latter drops until the rotor is partially uncovered, the water which leaves through the spiral pipe 36 can entrain air in the form of small bubbles, which does not present any drawbacks insofar as the nozzle d ejection from line 36 is short and has a horizontal or slightly rising ceiling.

As indicated above, the rotor can be of very rudimentary construction and be limited to a wheel with longitudinal vanes.

The extraction of all the pollutant from the centrifugal separator 28 requires a high proportion of water to be taken at the same time which can subsequently be partially separated by decantation. For this, one can use the arrangement shown in Figure 7. Each tank 40 for storing water loaded with pollutant from the separator 28 is provided with a discharge pipe 41 and a dip tube 42 for injecting the water at the bottom of the tank in order to push back the upper layers rich in polluting by the pipe 41. A connection 43 on the tube 42, provided with a stop valve and with an extraction pump 44, then makes it possible to discharge the pollutant-free water into the water table. When the machine is planned to operate with the logistical support of a large tonnage building, the tube 42 and the pipe 41 can be simply provided with connection fittings. the power required for operation being supplied by the support vessel. the device can be completed by a vacuum connection 45 on the separator sampling tube 28, allowing the sampling of polluted water to be initiated.

The distribution of the various components in the machine can be that shown diagrammatically in FIG. 6, which shows the locations 49 reserved for the storage of charged water and the drive means of the propulsion pumps 35. These means consist of a generator group 46 and an electric motor 47 per pump. Jet reversing flaps 48 can be provided on the ejection pipes 26 to allow the machine to be braked or to be steered. Vertical fixed planes 50 can be provided at the rear of the machine to stabilize the latter in yaw.

Claims (7)

1. Apparatus for selective sampling of a layer of pollutant, such as a hydrocarbon, floating on the surface of a sheet of water capable of being subjected to swell, comprising a hull provided with propulsion means and having a central part (10) which projects forward with respect to two lateral parts (11) which delimit with the central part of the supply channels to separators (28), the central part having deflector means, such as wings (17), to create vortices whose orientation tends to decrease the divergence of the surface flow around the hull, characterized in that each lateral part delimits, in a portion situated in front of a first threshold of capture (18), an open channel leaving a deep communication allowing water flows from one side to the other of the side hull and in that the front end part of each side hull is connected to a blade (14 ) of connection with the submerged part of the central hull, in front of the bow (13) of the lateral hull, a blade designed to deflect the flow of the deep layers downwards and outwards. 2. Machine according to claim 1, characterized in that the blade is made up, over the major fraction of its length from the central part (10), of a substantially constant chord wing of rope made up of intrados profiles flat, the lower surface of which is wound in a helix on a quarter of a cylinder, the lower surfaces of the profiles constituting the generatrices of the cylinder. 3. Machine according to claim 2, characterized in that the angles made by the axis of the cylinder with the horizontal plane and the vertical plane of symmetry of the machine are positive. 4. Machine according to any one of the preceding claims, characterized in that the first. threshold (18) is constituted by the front part of a submerged final capture floor in the form of a fairing with a convex lower face, the leading edge of the threshold having a strong arrow in the region close to the central part (10) of the shell. 5. Machine according to any one of the preceding claims, characterized in that the flow between the central part (.10), each lateral part (11) and the corresponding first threshold (18) is divided by a second threshold and a third threshold placed above and behind, the fraction taken between the first and the second threshold (18, 21) representing 65 to 70% of the average final capture flow being directed to a propulsion pump (23), the flow passing between the second and third thresholds (21, 27) being directed towards a swell compensator and the fraction of the flow passing above the third threshold (27) being directed towards the separator (28). 6. Device for selective sampling of a layer of pollutant, such as a hydrocarbon, floating on the surface of a sheet of water capable of being subjected to swell, comprising a hull provided with propulsion means and having a central part (10) which projects forward with respect to two lateral parts (11) which delimit with the central part of the supply channels to separators (28), the central part having deflecting means, such as wings (17), to create vortices whose orientation tends to decrease the divergence of the surface flow around the hull, characterized in that each duct (16) has a floor starting with a first threshold (18) and in that a second and a third threshold are placed above and behind the first threshold to split the flow taken, the fraction of the flow between the second and the third threshold (27, 21 ) being directed towards a swell compensator and the fraction of the flow passing above the third threshold (27) being directed towards the separator (28). 7. Machine according to claim 5 or 6, characterized in that the swell compensator is constituted by a well provided with a tangential overflow inlet of the fraction d _? the flow taken between the second and third thresholds, an outlet pipe (36) opening out at the rear of the machine and a rotor (33) provided with drive means to a speed such that it keeps the level in the well low enough so that there is always a pouring blade.

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