EP0093759A1

EP0093759A1 - Device for selectively removing a light liquid layer at the surface of a water sheet.

Info

Publication number: EP0093759A1
Application number: EP82903459A
Authority: EP
Inventors: Henry Benaroya
Original assignee: CADOUX JEAN ELIE
Current assignee: CADOUX JEAN ELIE
Priority date: 1981-11-23
Filing date: 1982-11-23
Publication date: 1983-11-16
Also published as: DK331983D0; NO157342C; DE3268897D1; DK331983A; JPS58502010A; NO832660L; EP0093759B1; BR8207983A; US4491518A; NO157342B; WO1983001799A1

Abstract

Un engin de dépollution d'une nappe d'eau comprend une coque ayant une partie centrale (10) en saillie par rapport à deux parties latérales (11) qui délimitent avec la partie centrale des conduits d'amenée à des séparateurs. La partie centrale présente une aile (17) de création de tourbillons dont l'orientation diminue la divergence de l'écoulement en surface. Chaque conduit (16) a un plancher à profil déporteur à bord d'attaque en saillie pour ralentir l'écoulement et épaissir la couche polluante. Une cloison verticale sépare chaque conduit (16) en deux sous-canaux dont un communique en aval avec le séparateur et dont l'autre s'ouvre à l'arrière de l'engin dans une pompe (53).A machine for depolluting a body of water comprises a hull having a central part (10) projecting with respect to two lateral parts (11) which delimit with the central part supply ducts to separators. The central part has a wing (17) for creating vortices whose orientation reduces the divergence of the surface flow. Each duct (16) has a protruding leading edge spoiler floor to slow the flow and thicken the pollutant layer. A vertical partition separates each duct (16) into two sub-channels, one of which communicates downstream with the separator and the other of which opens at the rear of the vehicle into a pump (53).

Description

Device for selective sampling of a layer of light liquid on the surface of a sheet of water

The present invention relates to a device for selective sampling of a layer of light liquid, such as a hydrocarbon, floating on the surface of a sheet of water likely to be subjected to swell, usable in particular for depolluting areas covered with a layer of oil following accidental spills.

It should first of all be recalled what are the problems encountered in the production of a pollution control device to be used at sea.

The polluting hydrocarbon is in the form of a thin layer (of the order of a millimeter) consisting of a hydrocarbon phase which can be very viscous as a result of the evaporation of the light components or by a multiphase hydrocarbon emulsion with seawater and / or air, following the mixing caused by the blades.

The machine must be designed to clean up on each pass over a width as large as possible. The water inevitably withdrawn at the same time as the pollutant must represent as small a fraction as possible of the extracted and stored part. Obtaining this latter result is thwarted by the very low ratio between the thickness of the pollutant layer and that of the water layer which it is necessary to capture because of the level variations due to particular to swell.

Patent application FR-A-2467769 describes a machine of a 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 lateral parts which delimit with the central part of the conduits for supplying separators and the central part having deflecting means, such as wings, to create vortices whose orientation tends to reduce the divergence of the surface flow around of the hull.

The deflector means achieve a double result. On the one hand, the craft and sweeps the sea between two current lines, upstream, ^' have a much larger spread than they would have in the absence of these means; correlatively, there is a thickening of the layer of light liquid at the inlet of the supply conduits. Because the sample is taken in flight, the wake of the ship dampens the swell.

It is thus possible, between the open sea upstream of the vehicle and the inlet water intakes of the conduits 16, to thicken by a factor of the order of 2.5. In practice, it is possible to achieve, thanks to the convergence of the current lines, a rate of thickening ent of the layer of hydrocarbon of the order of 2.5.

Such thickening remains very insufficient, however, to enable a separator, in particular centrifugal, to be supplied under conditions such that the ratio between pollutant and water in the flow rate sampled is acceptable. The invention aims in particular to provide a sampling device in which a progressive thickening of the layer of light liquid is carried out throughout a flow in an open vein until separation by a vortex process with a free surface, vertical axis and central sample.

This thickening must be carried out very gradually from the bow of the central part to the sampling by axial dip tube. Indeed, the equilibrium of a layer of light liquid of variable thickness involves entrainment of this liquid by water resulting from a speed discontinuity at the interface with a tangential constraint proportional to the gradient of the square thickness; this equilibrium becomes unstable beyond a limit value of this constraint, therefore also of this gradient or of the speed discontinuity.

To this end, the invention provides a machine of the type defined above, characterized in that each duct or channel comprises a floor with offset profile, the leading edge of which projects in front of the ducts, intended to slow the flow upstream of the leading edge and to cause a gradual thickening of the layer, and in that it is separated by a partition approximately vertically on a part of its height ending a dis- tance ^• a horizontal limit of the water blade into two sub-channels one of which communicates with the upstream-inlet duct and, downstream, with the separator, and the other of which, separated from the first by the partition, opens downstream into pumping and discharge means at the rear of the machine.

The partition is advantageously swollen at its lower part, located at a distance from the floor, in order to limit the curvature of the paths of the liquid which passes from one subchannel to the other; the total section of the two sub-channels is substantially constant in the direction of flow, the section of the first sub-channel decreasing while the other increases.

Thickening is thus carried out by three successive phenomena in a vein with a free surface:

- a free vortex with a horizontal axis and approximately parallel to the plane of symmetry of the ship, generated by the deflector means, typically by a submerged bearing wing connected to the bottom of the central part of the hull and beyond the bow towards the before. This tour¬ bill superimposes, on the divergent velocity field generated by the central part, velocity components converging towards the plane of symmetry at the level of the free surface and causes a progressive thickening of the sheet by convergence at constant speed (rate of thickening on the order of 2.5);

- An obi ical and approximately horizontal tourbi1 Ion due to the offset profiled floor forming the bottom of each duct and whose leading edge has a negative arrow, at least near the central part of the hull. The vortex induces velocity components on the surface which gradually slow the flow upstream of the leading edge of the floor at the cost of a very moderate divergence. This results in a slowing down of the sheet, at almost constant width, and a further gradual thickening (rate of the order of 2);

- a withdrawal of the major fraction of the flow collected in the duct above the leading edge of the floor and which remains completely separated from the outward flow _. laughing machine until its final ejection after pa ^ s é in a pump, this configuration allows better control of the gradual withdrawal of almost the entire flow rate. For this, practically from the entry of the conduit and up to the injection into the vortex of the separator, the conduit is separated into two sub-channels by the substantially vertical partition, oblique to the median plane of the machine. , which cuts the water line and descends a short distance from the floor. The sum of the areas of the cross sections of the two sub-channels 0 remaining substantially constant, that of the discharge (or withdrawal) sub-channel increases from 0 to approximately 9/10 of the total area, while that of the sub-channel supply which initially receives all the captured flow, decreases by as much. As a result, the velocity component parallel to the plane of symmetry remains approximately constant in the supply sub-channel, both for water and for the polluting layer which thickens progressively (rate of thickening of the order of 10). This arrangement can also be reversed, the supply sub-channel 0 being supplied over the partition, which forms a weir. The channel floor is advantageously constituted by a thick partition whose sections by vertical planes parallel to the plane of symmetry of the hull are offset profiles, therefore having a very convex lower face 5. Usually, the underside descends approximately to a depth equal to the draft and then rises backward. The upper face will then have a horizontal threshold parallel to the leading edge and submerged to a depth equal to approximately 0 x 1/3 of the draft and, behind this threshold, will descend to the compatible limit depth with the thickness required for the mechanical strength of the board the initial increase in ^the depth of the duct has simplified the trust problem of the loss of useful cross section 5 due to the partition between the two subchannels SINCE it compensates for this loss by increasing the total cross-section available.

At the rear, the vertical partition joins the inner side wall of the supply sub-channel. _/ TlR The leading edge of the partition definitively separates the supply sub-channel, which therefore acts as an injection gutter for the vortex in the open vein of the separator, from the discharge sub-channel which becomes a simple exhaust channel, the entire flow of which is sucked in by a pump which can be a means of propelling the machine.

It is necessary to avoid the formation in the biphasic flow of surges or projections. This problem is made particularly acute by the fact that the machine must be designed to work in rough waters, for example subject to swell or a sea of wind. We already know the conditions to be fulfilled, in the event of a permanent flow, to avoid passages of torrential flow to a river flow which give rise to a jump. Theoretical considerations make it possible to identify, in the event of a periodic regime and even when the flow has parts under load where the periodic stresses result in periodic compression waves, the conditions to be fulfilled to avoid breaking waves in the two-phase flow and the shuffling they cause.

Model experience confirmed these considerations, which were by no means obvious to those skilled in the art, accustomed to considering only permanent flows. They lead to the provision of a damping of the swell coming from the rear in the form of a leak by means of a submerged rear wing which, moreover, unexpectedly brings additional favorable properties. In addition, it is desirable to interpose ^one in the downstream discharge subchannel of the partition in the direction of flow generally a dip weir which locally causes a transition flow supercritical, subcritical flow and forming a projection and surges at a well-localized location where this phenomenon has no drawbacks and avoids the formation of new surges further upstream.

In a particular embodiment, the subchannel of the machine which opens into the pumping means

O successively has a fraction constituting a damping bowl, then a loaded portion opening into the pumping means. The sub-channel is full-walled, so that the pumps can only suck water that has entered the sub-channel by passing above or below the partition.

Given that the flow rate sucked by the pumping means is substantially constant, or at least varies little, while the flow rate sampled by each supply duct varies periodically, for example due to the swell, the volume of water contained in the bowl limited upstream by the partition varies as a function of time. It is necessary to prevent the low level of the free surface in the bowl from falling below a limit value for which the pumping means will suck in air, which would risk damaging them. ^' This result can be achieved by giving significant plan dimensions to the bowl. But, when the machine is designed to operate in swells having a large hollow, we arrive at unacceptable plan dimensions of the bowl. To allow operation in conditions such that the flow rate varies significantly, without requiring a damping bowl (I have large dimensions, the subchannel which opens into the pumping means is advantageously provided with water supply means from the water table provided to provide an additional flow to the pumping means, at least when the level in this channel drops to or exceeds a determined level.

These means for providing a make-up flow can be limited to an opening for communication with the sheet of water formed in the wall of the sub-channel, advantageously in the floor. This opening will generally be placed at the entrance to the part in charge of the subchannel which opens into the pumping means or immediately upstream. The entry of the loaded part may constitute a threshold projecting downward relative to the downstream portion, so as to better avoid the aspiration of air towards the pumping means. The invention will be better understood on reading the following description of particular embodiments

given by way of nonlimiting examples. The description refers to the accompanying drawings, in which:

- Figure 1 is a block diagram showing the plan shape of the buoyancy device and a possible shape of the front wing for creating vortices and the rear wing for damping the swell;

- Figure 2 is a schematic perspective view showing the hull and the wings of the machine of Figure 1;

- Figures 3 and 4 show, respectively in plan and elevation, the arrangement of a wing before creation. deflection vortices;

FIGS. 5 and 6 show, respectively in plan and in elevation (line VI-VI of FIG. 5), a possible form of wing and wing for raising the rotation;

- Figures 7 and 8 show, respectively in plan and in the direction VIII of Figure 7, a wing shape constituting a variant of that of Figures 5 and 6; - Figure 9 is a diagram showing the general shape of the floor of an intake duct, in section along a vertical surface

- Figures 10A to 106 are cross-sectional views showing a possible development of the shape of the floor and the vertical wing located at the intake orifice; - Figure 11 is a perspective diagram showing the splitting of the duct into two sub-channels by an oblique partition;

- Figure 12 is a block diagram, in section along a vertical plane, showing the appearance of a centrifugal separator with free surface fed by one of the subchannels of Figure 11;

- Figure 13 is a section, similar to Figures 10, showing the shape of the profile of the rear wing;

FIGS. 14 and 15 are block diagrams, respectively in plan and in elevation, showing a constitution of the second subchannel so as to avoid surges in the conduit;

- Figure 16 shows a possible constitution of an annular wing to further increase 1 thickening of the layer of light liquid upstream of the conduits;

Q PI - Figures 17 and 18 schematically show another alternative embodiment, respectively in top view and in section along the line XVII-XVII;

- Figure 19 is a curve showing the variation of the feed rates of a subchannel and suction by the pump as a function of time;

- Figure 20 is a block diagram, in vertical section, showing the variations in the water level in the damping chamber, in the case of an arrangement of the kind shown in Figure 11; - Figure 21, similar to Figure 20, corresponds to a mode of ^r embodiment of the invention.

Before describing the craft, it should be remembered that it constitutes a vessel which moves on the surface of the sea and that the initial movement of the light liquid with respect to this vessel is that of a thin layer, of unlimited width at the scale of the ship animated by a uniform horizontal movement of movement, to which the movement due to the swell is superimposed.

If, as is the general case, the final operation of extraction of the light liquid is carried out, in a separator using centrifugal forces, using a central tube, it is desirable to bring the lines of current to gradually bend to pass from a uniform trans¬ lation upstream of the machine to a convergent movement towards the vertical axis of the separators with a radial component of speed. The most rational solution for this consisted in giving the light liquid current lines a shape which, initially rectilinear, turns into a logarithmic spiral in the vicinity of the sampling tube. For this, the central part 10 and the lateral parts 11 of the shell 12 have surfaces which delimit the flow along internal spirals 13 and external spirals 14 and meet at a cusp point 15 (FIG. 1). In this case, the lateral surfaces must extend approximately vertically, at least up to a depth which is chosen according to the maximum wave trough for which the machine is designed. In practice, this verticality is ensured up to a depth which is of the order of half the draft D of the machine. The surfaces 13 are thus formed by the wall of the central part 10 of the hull, starting from the bow which must be designed to limit as much as possible the bow wave which creates turbulence. Each external surface 14 is materialized by the internal wall of a lateral part 11, from the bow 30 of the latter, which will be hampered. Payment located mid-length of the hull. Figure 1 shows that one thus arrives at a shape which, between the bow of the central part 10 and a point approximately half-length of the ship, corresponds to the forward half of a conventional ship hull. Between each bow of a lateral part 11 and the stern, the water line corresponds substantially to the rear half of a monohull ship having a master torque greater than that of the central hull 10.

The overall shape parameters of the machine (and in particular the total length L, the overall width 21_ and the grip width 2 j) must be proportional to each other to ensure satisfactory flow. In practice, the ratio L / 21_ will remain between approximately 3.6 and 4. The ratio 1 / lc will be between 1.5 and 2.5, a value of the order of 2 being generally satisfactory.

A third important parameter is the ratio D / L ^" of the draft to the length. But the choice of this ratio must take into account different requirements depending on whether it is a machine intended to work offshore or in the immediate vicinity of the coast.

In the first case, the length L will generally be greater than 75 m and D / L will then be determined by the maximum value that can be given to D for a pollution control work, generally less than 12 m: we arrive at a value less than 0.1, that is to say a very flat machine.

On the contrary, the most frequent devices intended to operate near the coasts will have a length of less than 75 m and, in this case, a value of D / L can be adopted between 0.14 and 0.16.

As for the D / lc ratio, which is also important, it will also be very different depending on whether it is a deep sea craft, where we will have D / lc ~ 0.9, or coastal, where we will have D / lc ≈ 2.25.

In all cases, it can be seen that, when the machine advances in the direction of arrow V, the layer of water carrying a layer of pollutant can bypass the central part 10 and rush into the conduits or channels 16 delimited by surfaces 13 and 14, the grip orifice of which generally has a width of the order of a quarter of the overall width 2i_ of the machine. We can immediately see that the flow entering each duct 16 is huge. On average, it is a sheet of water and pollutant whose thickness will be approximately equal to half the draft D, whose speed is of the order of that of the ship and whose width is about half the width j_ to the master couple.

The flow rate sampled by the separator dip tube must be at least two orders of magnitude less than this inlet flow rate, which leads to the search for thickening of the layer of light liquid before admission to the separators. This thickening will be carried out in several stages, under the action of components placed in series and which will be successively described.

Front deflector means: As in the case of the machine described in document FR-A-2467769, deflector means are provided for converging the threads of liquid on the surface, without however causing phenomena of surge or jump.

In the case illustrated in FIGS. 1 and 2, these means comprise a jagged front wing 17, provided with fins 18 directed upwards, the feet of which converge forward and whose role will be explained below. This is an arrangement which differs from that of document FR-A-2467769 only by the presence of the ailerons, The wing 17, with positive lift, creates vortices causing convergence on the surface.

This provision is not the only one possible; before describing variant embodiments, it is preferable to analyze the role of the deflector means and to deduce therefrom the characteristics to be sought and the manner in which to obtain them.

When the deflector means consist of a wing, the latter must generate marginal eddies whose efficiency (measured by the relative transverse displacement of the water streams which it causes on the surface) is as high as possible without causing surges in surface, for a given speed of the machine.

The transverse displacement is proportional to the circulation of the vortex created by the wings. It increases with the distance, projected on the longitudinal axis, which separates the stem 30 from the lateral part of the origin of the vortex, as well as with the distance which separates the vortex from the plane of symmetry.

5 The influence of the depth of the wing is less marked: if the efficiency of a vortex passes through a maximum when the depth of the wing, equal to the draft, is equal to 1a / 2 (figures 3 and 4), this maximum is fairly flat.

10 To increase the distance between the bow of the lateral hull and the origin of the vortex, it is necessary to move the wing 31 forwards, which leads to placing the leading edge of the wing 31 in front of the point where the bow 20 cuts the water line, therefore increasing the length above all

15 of the craft. It can be noted that this increase in length only occurs with respect to the water line 32 of the boat, the bow possibly protruding in the shape of a spur below the water line, as will be seen. further.

20 If we want to increase the distance which separates the origin of the vortex from the plane of symmetry, we are practically limited to adopt 1a = 1, no sailor willingly accepting that the live works of the boat have a greater lateral dimensions than those of the parts visible from the bridge.

25 The efficiency of the marginal vortex, which gathers all the circulation of a sheet of free vortices discharged by the wing, is equal to the circulation around the profile at its root, itself proportional to the lift of the profile. It is therefore desirable to increase this

30 tance, but this increase will come up against other imperatives which must also be respected.

To increase the lift from an initial profile indicated in solid lines in Figure 4, which leads to a depth h _Q from the highest point, we can increase

35 the incidence of the wing or its camber. In both cases, the highest point is located at a shallower depth, h ₁ or h ~. The overspeed coefficient also increasing with traffic, the number of Froude F = v / <fg \. (v being the maximum surface speed) therefore increases for a given speed V of the machine when the lift is increased. However, to avoid the surface surge, the condition F -J 1 must be respected, which limits the acceptable lift. In addition, the above considerations do not take account of the presence of the central part 10 of the hull which causes surface speed disturbances (under speed in the vicinity of the bow 20, overspeed downstream). It is the result of disturbances

10 due to the wing and disturbances due to the hull, which _. intervenes to define the value of ^ â not to be exceeded. It is therefore advantageous to make the point where the stem 20 intersects the free surface of the water table coincide, as far as possible, with the point where the upper surface of the profile

15 wing. Passes by the highest point (Figure 4).

As in addition, it is necessary to ensure a robust mechanical connection between the central part 10 of the hull and the wing 31, it is desirable to extend the stem 20 towards 1 ′ -forward under the free surface, to constitute

20 a spur provided with a bulb for connection with the wing. Figures 5 and 6, where the shape of the central part 10 at the free surface is shown in thick lines, while the shape at the location of the connection with the wing is shown in thin lines and a line of

25 intermediate level in dashes, shows an arrangement which has proved particularly satisfactory.

However, an isolated wing gives the vortices a marginal vortex immersion depth which is greater than the optimal value mentioned above, even in

30 the case of a relatively flat machine, for which D / 1 is of the order of 0.9, and a fortiori in the case of machines with a deep draft (D / l _c of the order of 2.25).

It is therefore desirable to raise the level of the peat lion. 35 In the case of a relatively flat machine, this résul¬ tat can be achieved by providing each wing 31 with a fin 32 practically vertical. To take into account the deflection of the water nets caused on the surface by the central part 10 of the hull, it is desirable to give the vertical bisector plane to the trailing edge of the fin 32 a significant inclination relative to the median plane, typically 30 to 35 °. This result can be obtained either with a profile with low camber and high incidence, as indicated in the case of FIG. 5, or with an average incidence and a high camber.

Another solution, shown in FIGS. 7 and 8, consists in giving the end portion of the wing 31 a "rolled up" shape: this latter solution will generally be preferable in the case of machines with a deep draft. Again, the bisector plane of the terminal part of the wing, having a large dihedral, must be strongly inclined on the median plane of the ship (Figures 7 and 8).

Slowdown and thickening of the layer at the setting orifice:

The production of gripping means, at the entry of conduits or channels, poses various problems, the most important of which are to avoid the formation of surges or projections and rejection, outside the lateral bows 30, d 'a fraction of the light liquid.

The risk of breaking out appears if we study the situation immediately upstream of the threshold of the intake orifice, width 1 in the presence of level oscillations due for example to swell. Denoting by D the depth of the duct of the threshold and v the velocity above this threshold, the water thickness above the threshold will be the ^'passage of the trough of a wave amplitude

AT :

The corresponding Froude number will be F = v / - / ^" gϋ This Froude number must not exceed 1, which means that the immersion depth D„ of the threshold in calm water must be

D _c * A + v ² / g.

In addition, it is necessary to give to D_ the smallest possible value, to minimize the average flow of water collected, which is equal to n _c D _C V.

We see the advantage of obtaining a value of _y_ significantly lower than the speed V of the ship, for example of the order

WIPO - 14 - from 0.5 to 0.6 V, therefore slowing the flow of the liquid immediately upstream of the threshold. However, it is necessary at the same time to avoid an appreciable local divergence of the polluting layer, which would reduce the capture width and the thickness of this layer.

In practice, as indicated above, it is sought to give the threshold a depth D of the order of one third of the draft D of the ship and this choice is only possible with a significant slowdown. This slowdown can be obtained by delimiting the open lavatory below by a floor 33 having a general shape of a horizontal wing with negative lift. The general shape of the profile, along the dashed line in FIG. 1, can then be that shown in FIG. 9. The wing has a wingspan equal to 1. Its leading edge is at a depth of the order of D / 2 if the threshold is at a level of D / 3. Behind a threshold, at depth D / 3, the upper face of the wing descends to increase the depth of the duct, then rises while the upper surface descends to ^" a depth, substantially equal to the drawing d If used in isolation, such a form of floor effectively slows down, but it creates a marginal vortex which tends to go back up inside the bow of the lateral part 11 and cause the seed to sink. outer layer of pollutant.

Various solutions can be used to overcome this drawback.

A first palliative consists in extending the floor forwards beyond the bow 20 and in giving its leading edge 30 a shape having, at least near the central part 10, an inverted arrow. In FIG. 1, the leading edge has, on most of its development from the central part an inverted arrow, while the external part 34 has a notable arrow, from a point which is located slightly inside the bow in the transverse direction. The vortices created by the reverse arrow portion cause the light liquid layer to converge towards the central part 10, which is favorable. But the vortices due to the other party, as well as the vertical vorticity due to the tip, tend to cause divergence.

This residual divergence can be largely compensated by the addition to the floor of a vertical wing 35 directed downwards, of the kind shown in phantom in Figure 9. If it were isolated, this wing would release a marginal vortex in a direction tending to make the fluid threads converge at a depth of the order of D / 2, as well as an antagonistic marginal vortex with no effect on the surface flow, at depth D. When such a wing 35 is assembled to the floor, and if the two profiles are chosen so as to create comparable circulations, the vortex created by the wing 35 compensates for the vortex created by the part 34 of the floor and, therefore, the vertical vortex at the tip disappears.

By way of example, there are shown in FIGS. 10A to 10G successive profiles of the floor 33. In these figures, the profile of the central part 10 of the shell at the location of the cut is indicated in solid lines, while the master couple is indicated in dashed lines.

Figure 10A shows a section along plane A of Figure 1, immediately behind the tip of the floor. We see the vertical wing 35 and a fragment, of small width, of the floor. Figures 10B, 10C and 10D are sections in planes staggered from that of Figure 10A to the bow 30 of the side part (Figure 10D). FIG. 10E shows the evolution of the cross section immediately behind the bow, and in particular the thickening of the lateral hull 11. Finally, FIGS. 10F and 10G are sections approximately at the level of the planes F and G of FIG. 1 In FIG. 10 G, it can be seen that the lateral shell 11 is progressively increasing upwards. This form corresponds to an embodiment in which the partition between the two sub-channels constitutes a weir,

CÎ.'PI a small fraction of the captured flow discharging from the conduit into a supply sub-channel of the separator. There is shown in dashes in FIG. 10G the general appearance taken by the partition 36 behind the section along the plane G. Progressive withdrawal:

As already indicated above, it is necessary to direct most of the water captured to a discharge channel to a depth approximately 10. equal to the half draft of the craft. . This resul¬ tate can be achieved by racking below a partition. Provided that. the pollutant captured is not entrained - by the downward movement of the water to pass under the partition, the layer of light polluting liquid 15 thickens as one approaches the separator.

The problem to be solved is then the organization of an open vein flow in the conduits compatible both with the necessary stability of the water-light liquid interface, even in the presence of swell, with withdrawal of almost all of the liquid flow initially captured in the conduit

To better understand the withdrawal mechanism and the role of the various elements which come into play to carry it out, reference will be made to FIG. 11 which schematically shows the arrangement of the transverse partition which separates each conduit progressively into two sub-channels.

Figure 11 shows a constant section supply duct, which will be assimilated to the channel delimited by surfaces 13 and 14 and the floor 23 in Figure 1. The partition 37 is placed obliquely to the direction of the duct , so as to progressively reduce the passage section offered to a subchannel 38 which goes towards the separator. This partition ends upwards above the free surface and below it at a distance from the bottom of the channel. A fraction of the flow is thus gradually drawn off from the bottom in a volume constituting a damping bowl 39, which is extended by a discharge subchannel 40 whose external wall 41 is constituted by the inner wall of the lateral part of the hull. This external wall of the exhaust sub-channel is shown rectilinear in FIG. 11. In practice, it will obviously be shaped to correspond to the shape of the shell.

The flow towards the bowl 39 implies a change of orientation of the fluid threads. To avoid turbulence, this change. orientation is helped by vanes 42 which, at the same time, support the partition 37. In addition, the partition is thick so that the orientation change¬ ment is gradual. The reduction in cross section which results from the presence of the partition is offset by the fact that the bowl represents an increase in the passage section. In the approximately triangular bowl 39 and the subchannel 40 which follows it downstream, the water level may vary. However, this variation must remain in an area that is lowered by the risk of air entering the rejection pump and, above all, by the presence of a load lower than the upstream load. If the pump rotates at constant speed, which will be the general case, the flow rate which it takes in the bowl 39 decreases when the level drops, even in the case of a constant section at ejection. Although this variation in flow rate is not in phase with that of the flow rate received by the bowl 39, it contributes to reducing the buffer volume offered by the bowl which is necessary. In an alternative embodiment, the ejection orifice is provided with section adjustment means, for example using a flap controlled by a jack. In this case, it is possible to asser¬ the cylinder to modulate the ejection section as a function of the height of water in the bowl, which makes it possible to obtain larger variations in flow and whose phase is better. adapted, therefore to reduce the minimum buffer volume required of the bowl. Centrifugal separator:

The two-phase current supplied by the supply subchannel, in which the thickness of the layer of light liquid is approximately ten times greater than at the beginning from the duct, is admitted tangentially into a centrifugal separator with an open vein. In this separator, the flow in an open supply stream must give rise to two flows in a closed stream, one consisting of a discharge flow escaping from the bottom of the separator to an extraction pump. , the other by a sample flow sucked by pumping means towards storage containers.

The light liquid is often an extremely viscous hydrocarbon, it is necessary to warm it.

This reheating is almost impossible to achieve in

^" open vein. It will therefore take place in the flow in closed sampling vein, which begins at the entrance of a vertical tube plunging into the mass of liquid, to a depth in which there is permanently pollutant .

Before describing the particular embodiment of a separator which is shown diagrammatically in FIG. 12, it should be remembered that the operation of an open vein separator is very different from that of a closed vein separator, where we can easily obtain values of the tangential component of the high speed, which provide a radial acceleration much greater than the acceleration of gravity. Indeed, in an open vein flow, the free surface takes a slope proportional to the square of the tangential speed, and a too high value of the latter would result in an excessive digging of the central region of the mass of liquid. Furthermore, if the radial and vertical components of the speed are very small (and they will always remain an order of magnitude lower than the tangential component), the interface between the layer of light liquid and the water remains substantially parallel to the free surface if the tangential speed remains constant over the entire height of the body of water.

To obtain a thickening, provision will be made for means which give the tangential speed a decreasing value from the surface towards the bottom, with radius around the axis of the constant separator. - 19 - In the embodiment shown in FIG. 12, this result is obtained by constituting the separator by a cavity 45 with a vertical axis 46 into which a dip tube 47 enters. The supply sub-channel 38 opens out

5 tangential to the upper part of the cavity 45 to maintain the rotational movement. The retarding effect of friction on the central tube 47 gives the free surface 48 a shape of the kind indicated in FIG. 12 and causes a thickening of the layer of liquid.

10 light, as shown by the shape of the upper and lower borders 49 of the interface in FIG. 12. In practice, the maximum thickness of polluting layer that can be reached around the tube 47 is limited only by the risk entrainment of the pollutant downwards by the flow

15 of discharge.

In practice, it is easy to obtain a thickness of layer of light liquid of the order of half the radius of the vortex at the feed orifice, which generally corresponds to a thickness of about one hundredth of the

20 overall length of the craft.

The separator shown in Figure 12, which can be considered as a section along a plane substantially parallel to the median plane of the machine, has a thick horizontal plate 50 of partition pierced with a hole

25 approximately circular central and centered on the axis 46. The plate 50 limits a supply chamber into which opens the supply sub-channel 38 which maintains the vortex flow and whose wall has an approximately cylindrical shape whose

30 director is a spiral. The discharge chamber placed below the plate 50 is delimited downwards by a floor 51. It opens by a tangential exhaust channel 52. The flow in this chamber and the diverging exhaust channel has a wide symmetry

35 with the supply flow. The angular momentum of the discharged water mass is preserved, except for pressure drops. The corresponding energy can be recovered in a vortex placed downstream or the exhaust channel 52 can lead directly into an extraction pump,

y o. τι which can moreover be confused with the propulsion pump 53 (FIG. 1) which receives the flow coming from the subchannel 40. It should be noted that, except in the central region of the vortex, the level of the free vein will exceed that of the buoyancy due to the conservation of the energy of the flow and it is necessary to take into account the weight of the corresponding volume of water in the longitudinal equilibrium of the machine.

The tube 47 must suck all the flow of light polluting liquid which arrives at the separator, which implies that it sucks at the same time a flow of water sufficient to entrain the pollutant even if the viscosity of the latter is so high that it occurs in lumps. To prevent the pollutant from progressively obstructing the dip tube 47 by sticking along its internal wall, the tube 47 shown in FIG. 12 is double-walled and has an internal conduit 54 for supplying steam which escapes to the top by a series of holes 55 formed in an internal rim of the tube, at the bottom of the latter. This steam injection heats the pollutant at the same time and makes handling easier. It should be noted in passing that the drive water sucked in by the dip tube tends to occupy the central part of the tube and that consequently the injection of steam at the periphery preferably heats the pollutant. To prevent the steam from coming out of the holes 55 at too high a speed, it is possible to see on the duct 54 calibrated inlet throttles: the corresponding rolling is adiabatic and does not appreciably modify the heat supply of the vapor On sees that the layer of light polluting liquid is concentrated in the separator to form a core whose thickness and volume correspond to a balance between the. flow aspirated by the tube 47 and an injected flow which can vary very quickly, since it is substantially proportional at each instant to the thickness of the layer of polluting liquid, itself roughly fifty times greater than the average thickness of the polluting layer at the level of the bow 20. This core constitutes a buffer volume It is normally maintained between determined limits - by controlling the pump (not shown) for suctioning the light liquid by a relay actuated by means for determining the level of the interface, indicated schematically at 56. These means can be constituted in particular by a cell electric or by a float whose average density is between that of water and that of light liquid, connected to a control relay of the pump motor.

All of the light polluting liquid must be sucked through the tube 47. To fulfill this condition for sure, while the flow of this liquid undergoes variations which are impossible to measure, a proportion of water must be admitted into the flow sucked , which as a rule will be less than two thirds. This proportion ^" 15 is low enough that the residual water can be removed by a conventional centrifugal separator (not shown) operating in a closed vein, interposed between the tube 47 and the suction pump.

The light liquid finally obtained will be stored. This 2o storage can be carried out in tanks placed on board the pollution control device, whence the pollutant will be transferred to tanks placed on the ground. It is however possible, especially in the case of small machines, to store the pollutant in containers which are closed and ballasted. These containers are then submerged as they are filled in locations marked with buoys. The containers are then recovered by non-specialized vessels.

It should be noted that the buffer volume represented by the core will generally be sufficient to authorize a temporary stop of the suction pump for the time necessary for a change of container for storing light polluting liquid.

Hitherto, it has essentially been a question of the means making it possible to thicken the thickness of the polluting layer, then to extract it at the same time as the lowest possible flow of water. These are the means whose role is essential in calm water. However, in working conditions at sea, it is also necessary to avoid the surge and the formation of projections at locations where they risk causing a mixing harmful to the separation, in particular in. conduits and their entry constituting outlet orifice. A first remedy consists in reducing the amplitude of the swell coming from the rear in the appearance of a leak, during its journey along the hull before it reaches the grip orifices. In the embodiment shown in Figures 1, 2 and 3, the machine comprises a rear wing 57. It is preferable that this wing does not project beyond the machine towards the rear. The thickness of the flange 57 increases from the rear forwards and the wing is positioned at a slightly lower _^ deur profon¬ the draft of the craft. In the form of a leak compared to the swell, especially on very long vehicles, the wing 57 dampens the absolute movement of the swell in a dark area which covers all the flow in free vein before entering the orifices for collecting conduits.

In addition, on very long gear, the wing reduces the amplitude of the pitch. On short vehicles, it dampens the relative movement of the ship relative to the sea, especially if it has a positive lift. The wing finally plays the role of anti-roll keel. A second remedy takes into account that the most dangerous disturbances from the point of view of the risk of surge are those which go up the general flow. Such disturbances can appear in the conduits as a result of the reflection of the waves which descend the conduit, then the exhaust sub-channel towards the part in charge of the latter.

This result can in particular be achieved thanks to a geometry of the evacuation sub-channel which leads to a surge located behind the partition 37 (in the general flow direction) and in the immediate vicinity of this partition and to an order propulsion pump, in order to maintain in the bowl 39 a sufficiently low head height to ensure a torrential flow.

The conditions to be established will appear better if we analyze the evacuation flow to the subchannel 40 on a simplified diagram of the conduit 16, of the bowl 39 and of the subchannel 40, which passes under load downstream of the bowl. Figures 14 and 15 show these components of the installation in alignment to facilitate analysis. ^*

The flow suction pump which runs through the subchannel 40 is controlled so that this subchannel remains under load and there is no air admission into the pump and also so as to maintain immediately upstream a speed and a height of water such that the flow is of the fluvial type, that is to say with a Froude number less than 1. The bowl 39 is given a width 1 ~ greater than the width 1 of the duct and a submerged weir 59 is placed there which reduces the depth and, correspondingly, causes a local increase in speed. The widening lp / li ^and ** •• - ** height of the weir 59 are chosen so that the variations undergone by the flow from upstream to downstream are as follows. In the duct 16, upstream of the partition 37, the flow speed and the depth h. are such that the flow is fluvial (Froude number less than 1). In the upstream part of the bowl, this fluvial character is further increased due to the decrease in speed caused by the increase in width. On the other hand, the depth h ₂ of the flow at the right of the weir becomes such that the Froude number becomes equal, then greater than 1. It remains greater than 1, then the flow becomes fluvial again with the formation of a projection 60 which is likely to move longitudinally in a limited area. The disturbances propagating from upstream to downstream cross the jump and can be reflected on the entry of the subchannel under load 40. But the reflected disturbances cannot cross the jump and come to disturb the flow in the conduit.

The invention is not limited to the particular embodiments given by way of examples but, on the contrary is susceptible of numerous variant embodiments It can in particular be noted that means other than the vertical wings 35 shown in FIGS. 1 and 10 can be used. FIG. 16 shows by way of example a wing 67 of annular shape capable of being used at the front of the floor 33. This wing is connected to the floor 33 by a profile which can be similar to that shown in FIG. 10G then l 'wing turns forward to connect to the central part 10 of the hull by a profile close to the horizontal, as indicated by a cut folded in dashes. At its root on the floor 33, the wing has a shorter length than in the case of FIG. 10 and a higher incidence, so that the wing 61 does not descend below the draft of the shell. This arrangement brings a double advantage.

The annular wing, embedded at its two ends, has greater rigidity and resistance than a cantilever wing; we remove the free vortices that escape from a wing of the kind shown in Figures 1 and 10, vortices which can be in some cases annoying although they are released at significant depth. The floor 33 of the embodiment shown in Figures 1, 2 and 9 is full. Despite the slowing down of the flow upstream of the capture, it limits the speed at which the machine can move, since it is necessary to avoid a spill. In the variant embodiment shown in FIGS. 17 and 1, this limitation is largely removed by effecting the capture (that is to say the separation between the polluted flow sampled and the water returned to the ambient water table). ) in two steps. The vein of liquid sampled by the lateral shell 11, placed obliquely, is first closed laterally, and then the vein is closed by the expensive plane 33 downstream from the bow of the lateral shell. In its upstream part, the floor 33 is limited to inclined blades 65 and 66, connecting the two shells and of progressively decreasing depth (Figure 17). The purpose of these blades is to eject downward and outward, under the side shell 11, the lower part of the flow water from the vein, part which does not contain pollutant. The front part of the side hull will in this case have a depth of between half and a third of the draft. The non-rejected part of the vein is directed to the pumps.

The curve in solid line in FIG. 19 shows the variation of the supply flow supplied to a subchannel opening into pumping means as a function of time, in the presence of a swell of period T. This supply flow is pours into a damping bowl 39 (FIG. 20) communicating with the pumping means 53 via a charge pipe 40. The pumping means 53 are provided for sucking in an approximately constant flow rate (dashed line in FIG. 19) which corresponds at the average feed rate. The level of the mass of water contained in the bowl therefore varies as a function of time, the difference between the average volume and the minimum volume of water in the bowl being represented by the hatched area in FIG. 19. At each value of this difference in volume corresponds to a difference between the average level πii of the water in the bowl (downstream of the projection 60 due in particular to the presence of the flooded weir 59) and the low level. This difference is all the greater the smaller the surface area of the bowl 39.

It is necessary to prevent the pumping means 53 from sucking air, which imposes prohibiting at the low level of descen¬ dre below a limit _1_ beyond which the tunnel 40 is no longer in charge . It should be noted that any suction of air by the pump amplifies the phenomenon because the ejection channel in which the pump is placed then partially empties of the water it contains, which tends to rele¬ 'rear of the machine and, in particular, the threshold of the overflow 59, hence a further decrease in the feed rate.

The risk of dewatering the pumping means 53 is avoided by providing the sub-channel with water supply means from the water table in which the machine circulates. In the embodiment shown in FIG. 21, the means for supplying the subchannel with make-up water consist of an opening 62 formed in the floor to achieve permanent communication between the subchannel and the sea. The opening shown is placed in the front part of the loaded tunnel 40. The ceiling of this front part has a threshold 61 projecting downward, making it possible to further decrease the risk of air suction. For the average level ni, the flow of the water streams at the bottom of the subchannel takes place along the floor upstream and downstream of the opening 62 (arrow f _n ). When the level drops due to a decrease in the feed rate, there is suction of water from the ambient water table (arrow f _j ). It is thus possible, for the flow rate which corresponds to the limit in the case of FIG. 20, to maintain in the bowl 39 a low level b_ sufficient to avoid any aspiration of air. It is easy to determine experimentally the optimum dimensions to be given to the opening 62. As a general rule, this opening will either be at the entrance to the loaded part 40, or immediately upstream, partly below the threshold 61 When the water level in the damping bowl 39 is higher than the average level, there is ejection of water through the opening 62: this ejection is without drawback, this flow of water being free of pollutants.

Depending on the relative position in height and angle of incidence of the leading edge 63 downstream of the opening 62 and the trailing edge 64 upstream, the additional flow rate towards the pumping means 53 can be given a value time-averaged which is positive, zero or even negative, when the machine moves at its normal operating speed, the make-up flow being always positive in the case of a zero speed. If, for example, provision is made for opening 62 so that it provides an average make-up flow of 10 to 20% of the total flow sucked by the pumping means 53, we can obtain a maximum flow of l 'order of 50% of the flow sucked by the pump, which clearly shows a very significant impact on maintaining the level in the damping bowl 39 at a sufficient height.

The inlet opening of a supply flow can be fitted with oscillating flaps preventing the ejection of a frac-

WIPO tion of the flow which crossed the flooded weir. These flaps can be fitted with jacks which keep them closed when the machine moves without operating to take a layer of light liquid, for example to go to a place of intervention.

Claims

1. Apparatus for selective sampling of a layer of light liquid floating on the surface of a sheet of water capable of being subjected to swell, comprising a hull

5 provided with propulsion means making it possible to keep it in flight, the hull having a central part (10) which projects forward relative to two lateral parts (11) which delimit with the central part of the conduits (16 ) leading to separators and the central part

10 line having deflector means, such as a wing (17), for creating vortices whose orientation tends to reduce the divergence of the surface flow around the hull, characterized in that each duct (16) comprises a spoiler profile floor whose edge

15 leading protrudes upstream of the inlet of the conduits, floor intended to slow the flow upstream of the leading edge and to cause a gradual thickening of the layer of light liquid and in that a partition (37) approximately vertical and ending

20 at a distance from the upper or lower limit of the sheet of water which traverses the conduit separates the latter, over a fraction of its height, into two sub-channels (38, 40) one of which communicates downstream with the separator and the other of which opens downstream into means (53) for pumping and

25 rejects and water at the rear of the machine to cause a propulsive effect.

2. Machine according to claim 1, characterized in that the partition (37) ends at a distance from the floor and is swollen in its lower part to limit the curvature

30 of the liquid streams which pass from the conduit and from the first sub-channel (38) to the second sub-channel (40), the total section of the two sub-channels being substantially constant along the flow and the section of the subchannel going towards the separator decreasing while the other increases. 5 3 _* Machine according to claim 1, caracté¬ ized in that the floor has a wing shape whose leading edge has a negative arrow near the central part of the hull.

4. Machine according to claim 3, characterized in that the outermost fraction (34) of the leading edge of the floor has a positive arrow to the right of the stem (30) of the lateral part (11) of the hull and in that the floor carries , near the leading edge, an approximately vertical wing (35) for compensating for the effects of surface divergence due to the leading edge of the floor.

5. Machine according to claim 1, characterized in that the floor has a cambered profile directed downwards, the lower surface of which has a threshold at a depth substantially equal to half the draft of the boat, then a deepening up to the maximum distance compatible with the mechanical strength of the floor.

6. Machine according to claim 1 or 5, characterized in that the deflector means consist of a posi¬ tive lift wing whose leading edge is located in front of the point where the bow (20) of the central part (.10) of the cut shell. the water line, the span of the wing being substantially equal to the overall width of the hull.

7. Machine according to claim 6, characterized in that the wing (17) is at a depth of the same order as the draft of the hull to avoid surges and in that the wing carries substantially vertical fins , having significant convergence forward, projecting upward from the wing near the ends thereof to raise the vortices.

8. Machine according to claim 1 or 6, characterized in that the wing has a depth of the same order as the draft from the hull to the plinth and a part wound to present a dihedral pro¬ gressively increasing towards its extremities.

9. Machine according to claim 1, characterized in that the bow (20) of the central part (10) forms, below the water line, a bulbous spur connecting with the wing.

10. Machine according to claim 1, characterized in that the subchannel which

OLC-I opens into the pumping means comprises a flooded weir intended to cause the surge of disturbances which go up the flow.

11. Machine according to claim 1, characterized in that it comprises a rear wing immersed at a depth of the same order as the draft of water from the hull, intended to weaken the swell in the appearance of a leak and to reduce disturbances, at the entrance to the pipes.

12. Machine according to claim 1, characterized in that each separator comprises a cavity (45) of vertical axis (46) separated by a horizontal plate (50) pierced with a central hole in a supply chamber. into which opens the subchannel (38) and a discharge chamber opening into a tangential escape channel (52), the separator further comprising a central tube (47) dipping into the upper part of the eddy flow with free surface in the supply chamber and communicating with a light liquid suction pump.

13. Machine according to claim 12, characterized in that the tube (47) is double walled and has an internal duct (54) for supplying steam which escapes upwards through holes made in an internal rim of the tube at the bottom of it.

14. Machine according to claim 1, characterized in that the subchannel which opens into the pumping means is provided with means for supplying water from the water table provided to provide an additional flow to the means pumping, at least when the level in this channel drops to a certain height and exceeds it.

15. Machine according to claim 14, characterized in that the means for supplying an additional flow consist of an opening (62) formed in the wall of the subchannel.

16. Machine according to claim 1, characterized in that the floor (33) is constituted in its front part by vanes (65,66) each connecting the part central (10) to one of the lateral parts (11) and in that each lateral part is extended forward in said front part and has, in its part connected to the blades, a depth of between one third and half of the tie rod water from the craft.

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