Abstract:
To collect oil or other matter floating on the surface of a body of water a collection vessel ( 11 ) having a collection compartment (A) is immersed in the water. A surface layer carrying the matter to be collected is caused to flow from the area around the collection vessel into the collection compartment (A) over a vertically movable skimming weir ( 15 A) on the collection vessel. Water is discharged from the lower portion of the collection compartment such that a liquid level lower than that of the surrounding water is maintained in the collection compartment (A). Floating matter accumulated on the liquid surface in the collection compartment is removed; if the matter to be collected is low-viscosity oil, an oil-absorbing body ( 22 ) made of a hydrophobic material is used to absorb the accumulated oil from the liquid surface in the collection compartment. A dashpot damping device ( 28-30 ) dampens vertical oscillations of the skimming weir ( 15 ).

Description:
BACKGROUND OF THE INVENTION 
     This invention broadly relates to a method and an apparatus for collecting matter floating on a body of water, namely collecting such matter by skimming a surface layer carrying the matter to be collected and separating the matter from the water of the skimmed layer. Certain embodiments of the invention are specially directed to the collection of spilled oil, particularly low-viscosity oil. The invention will therefore be described with emphasis on that application, but it is also applicable to other types of floating debris. 
     According to a known skimming technique, a collection vessel is immersed in the body of water carrying the matter to be collected such that an overflow rim of the collection vessel is just beneath the surface. Water is constantly pumped out of the lower portion of the collection vessel at such a rate that the outflow from the collection vessel balances the inflow of water into the collection vessel over the rim thereof to maintain a sink—that is, an area the level of which is lower than the level of the surrounding water—in the collection vessel. The floating matter carried or entrained by the inflowing water is accumulated in the sink and can be removed continuously or intermittently. Examples of this skimming technique are disclosed in DE-B-20 30 209 and WO97/07292 (published Feb. 27, 1997). 
     This technique lends itself to a rapid and energy-efficient collection of oil or other debris floating on water, because large volumes of water can be rapidly pumped through the collection vessel at a fairly low rate of energy consumption. 
     Spillage of low-viscosity oil in waterways and other open waters occurs frequently and presents special problems. When an oil spillage is detected, it is desirable to be able quickly to take a sample of the oil so that it can be analyzed. However, low-viscosity oil forms an extremely thin layer on the water surface, and even with a very high rate of flow of water through the collection vessel it is very difficult, or even almost impossible, to collect substantial amounts of the oil using known techniques. Actually, it is hardly possible to collect even an amount of oil which is sufficient for an analysis of the characteristics of the oil. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and an apparatus for rapid and efficient collection of floating debris, such as oil and other kinds of floating matter. According to one aspect of the invention, even low-viscosity oil can be rapidly collected in amounts adequate for analysis. According to a different aspect of the invention, which is not limited to debris in the form of oil, a system for damping oscillations of the overflow rim of the collection vessel is provided. 
     The invention is advantageously applicable to the method and apparatus disclosed in WO97/07292. However, its field of application is not so limited, but extends to other methods and apparatus based on the above-described skimming technique. 
     Embodiments of the invention will now be described by way of example with reference to the accompanying drawings and to WO97/07292 the disclosure of which is incorporated herein by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view of a collecting apparatus according to the invention during collection of oil floating on a body of water; 
     FIG. 1A shows a detail of FIG. 1 drawn to a larger scale; 
     FIG. 2 is a view corresponding to FIG.  1  and shows the collecting apparatus in a position the collecting apparatus takes during a phase of its operation in which oil accumulated in a preceding phase is absorbed by an oil-absorbing body; 
     FIG. 3 is a plan view of the apparatus shown in FIG. 1; 
     FIG. 4 is a view corresponding to FIG. 1 of a modified embodiment; 
     FIG. 5 is a perspective view showing the collecting apparatus of FIG. 1 in operation in association with an oil boom. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The collecting apparatus shown in the drawings, which is generally designated by  10 , embodies the principles of operation and construction shown and explained in WO97/07292 to which reference is made for a detailed description of such principles. The embodiments of the apparatus specifically shown in the drawings and described below are designed and dimensioned primarily for use of the apparatus for collection of relatively small volumes of oil, such as for sampling purposes. 
     Accordingly, the collecting apparatus  10  comprises a substantially cylindrical, open-topped collection vessel  11  which is in upright position in operation of the apparatus. The collection vessel  11  defines a collection compartment A and includes a lower part  12  and an upper part  13 , which is telescopically slidable up and down in the lower part  12 . An outwardly directed annular flange  14  is provided at the lower end of the upper part  13  and extends to the inner side of the lower part  12  to form a seal (a perfect seal is not required) and to guide the movements of the upper part  13  relative to the lower part  12 . The major portion of the upper part  13  forms an annular buoyant body  15 , the upper end of which defines an annular skimming weir  15 A over which water can flow omnidirectionally into the collection compartment A from the surrounding body of water. 
     A bottom wall  16  of the collection vessel  11  is formed with a central opening  17  in which the impeller of an electrically driven pump  18 , namely a propeller pump, is mounted. A battery  18 A supplies the pump motor  18 B through an electronic control unit  18 C. A watertight pump housing  18 D encloses the motor  18 A, the battery  18 B and the control unit  18 C and is secured to the bottom wall  16  by means of struts  18 E, only one of which is shown in the drawings. 
     Mounted above the bottom wall  16  of the collection vessel  11  is a circular guide plate  16 A. Together with the circumferential side wall  12 A of the lower vessel part  12  this guide plate defines an annular inlet  16 B to the bottom wall opening  17 . 
     A top plate  19  is vertically spaced above the collection vessel  11 . Three lobes  19 A of the top plate  19  project horizontally beyond the circumference of the collection vessel  11 . A central circular opening  19 B in the top plate  19  accommodates a removable circular plate  20  which is held to the top plate by means of spring clips  21  and to the under-side of which a hydrophobic oil-absorbing body  22  is attached. The oil-absorbing body, which is in the shape of a generally cylindrical flat disk, can be made of any suitable material capable of absorbing oil while repelling water. Several suitable such materials are commercially available, such as the felt or cloth materials commonly used for absorbing oil in the of motor boats, an example being the material marketed by Minnesota Mining and Manufacturing Company under the designation T.151. Preferably, the oil-absorbing body  22  is formed with a plurality of narrow indents or recesses extending radially from the periphery toward the center of the body. 
     A cylindrical collar  23  concentric with and spaced radially outwardly from the oil-absorbing body  22  and spaced radially inwardly from the buoyant body  15 A extends downwardly a short distance beyond the underside of the oil-absorbing body into the upper part  13  of the collection vessel  11 . 
     The cylindrical collar  23  is integral with three circumferentially spaced-apart cup-shaped receptacles  24  positioned between the lobes  19 A of the top plate  19  and similar lobes  12 B of the lower collection vessel part  12 . Each receptacle  24  contains a water-absorbing body  25  in the lower portion thereof and a buoyant body  26 , made of expanded styrene plastic, for example, disposed between the water-absorbing body  25  and the associated top plate lobe  19 A. Tie rods  27  hold the receptacles  24  in position between the lobes  19 A of the top plate  19  and the lobes  12 B of the lower collection vessel part  12 . 
     When the apparatus  10  is placed in the water, openings  24 A formed in the bottom wall of the receptacles  24  allow water to be absorbed into the water-absorbing bodies  25 , which are made of a sponge-like material capable of rapidly absorbing substantial amounts of water. Vent passages  24 B allow air in the receptacles, such as in the water-absorbing bodies  25  to escape to the ambient atmosphere. 
     As shown in larger scale in FIG. 1A, the circumferential wall  12 A of the lower collection vessel part  12  together with the circumferential wall  13 B of the upper collection vessel part  13  and the flange  14  of the latter forms an annular variable-volume compartment  28 . A restricted passage  29  defined by the circumferential wall  13 B of the upper collection vessel part  13  and an inwardly directed flange plate  30  supported by the lobes  12 B permit restricted flow of water between the compartment  28  and the body of water in which the collecting apparatus  10  operates. The compartment  28  thus serves as a dashpot-type damping chamber to dampen vertical oscillations of the upper collection vessel part  13 . 
     Naturally, the hydraulic or dashpot damping device formed by the elements which define the annular compartment  28  and restrict the flow of water into and out of it, can also be used in the collecting apparatus disclosed in WO97/07292 and similar collecting apparatus having a collection vessel comprising a skimming weir which is vertically oscillatable in the body of water in response to variations in the flow of water into and out of the collection vessel. 
     The collecting apparatus  10  may be placed into the water, e.g. in a detected oil slick on the water, in any suitable manner, such as from a helicopter or a boat. Operation of the pump  18  may be initiated manually just before the apparatus is dropped into the water, by remote control or automatically upon immersion in the water. 
     When the collecting apparatus  10  is placed in the water the space in the receptacles  24  occupied by the water absorbing bodies  25  will immediately be filled with enough water to allow the entire apparatus to assume a position such that the collection compartment A will be filled with water. The pump  18  will tend to empty the collection compartment A through the bottom wall opening  17  of the collection vessel  11 , but the collection compartment A will be replenished with water flowing over the skimmer weir  15 A. A balance between the omnidirectional inflow of oil and water over the skimming weir  15 A and the outflow of water through the bottom wall opening  17  will be established and maintained such that a sink will be maintained in the collection compartment A. By virtue of its lower density, the oil flowing into the collection compartment A will accumulate and form a layer O in the sink as is indicated in FIG.  1 . 
     It has been found that a suitable difference H in the levels of the liquid surface of the collection compartment A and the liquid surface outside the collection compartment is about 15 mm, regardless of the rate of flow of water through the collection compartment A. Those components of the collecting apparatus, primarily the buoyant body  15 , the flange  14  and the pump  18 , which have an influence on the difference H in the levels should therefore be dimensioned accordingly. A greater difference means a higher energy consumption and should be avoided to save the battery. 
     Any tendency to disturb the balance and change the difference H in liquid levels, e.g. as a result of movements of the surface of the body of liquid, will be rapidly offset by the pump  18  increasing its throughput in response to a reduced difference or reducing its throughput in response to an increased difference and by the upper collection vessel part  13  moving upwards in response to a reduced difference and downwards in response to an increased difference. The dashpot damping arrangement which includes the annular damping compartment  28  and the restricted passage  29  prevents excessive oscillations of the upper collection vessel part  13 . 
     When the floating collecting apparatus  10  has operated as described for a predetermined period, 10 minutes for example, the control unit  18 C will switch off the pump  18 . As a result, the liquid level in the collection compartment A and the liquid level of the surrounding body of liquid will be equalized. Moreover, as shown in FIG. 2 the buoyant body  15  will rise to a position in which the skimming weir  15 A is above the water surfaces and sealingly engages a flange  23 A interconnecting the collar  23  and the receptacles  24 . The liquid level in the collection compartment A will also rise and thereby raise the accumulated layer O of oil into contact with the oil-absorbing body  22  so that the accumulated oil, or at least a substantial portion of it, can be absorbed. 
     If desired, the pump control unit  18 c can reverse the pump  18  upon completion of the collection period so that the liquid level in the collection compartment A will rise above that of the surrounding body of liquid. 
     The pump control unit  18 C advantageously is programmed to cause the pump  18  to run in opposite direction for several successive short periods after the or each collecting cycle, so that the oil-absorbing body  22  is repeatedly immersed in and raised from the liquid in the collection compartment A. It has been found that such repeated immersion and raising of the porous oil-absorbing body and the consequent filling and draining of the pores of the body with oil-entraining water greatly improves the absorption of the oil. 
     One or more additional similar collection cycles may be carried out, e.g. until the battery  18 A has become discharged. The collecting apparatus is then recovered and the oil absorbed by the oil-absorbing body  22  is extracted and subjected to analysis. 
     To facilitate visual detection of the apparatus  10  if it has been left unattended during the collection, three brightly coloured upstanding bows  32  are attached to the upper side of the top plate  19 . These bows also facilitate catching the collecting apparatus by means of hooks or other suitable implements. 
     Most of the major components of the collecting apparatus  10  can be made of plastic, e.g. by injection moulding, and the cost may be sufficiently low to warrant use of the apparatus as a disposable item. 
     The modified embodiment of the collecting apparatus  10  shown in FIG. 4 differs from the embodiment shown in FIGS. 1-3 only in respect of the arrangement of the oil-absorbing body  33 . 
     In FIG. 4, the oil-absorbing body  33  is a buoyant circular disk arranged to float on the liquid in the collection compartment A during the collection. To this end it is slidable vertically on a central guide post  34  secured to the removable plate  20 . A flange  35  secured to the lower end of the guide post  34  prevents the oil-absorbing body  33  from falling off the guide post. In this case the oil accumulating in the liquid sink maintained in the collection compartment A is continuously brought into contact with the oil-absorbing body  33  and absorbed into it. As in the embodiment shown in FIGS. 1-3, the circumferentially distributed narrow indents or recesses extending radially inwardly from the circumference of the oil-absorbing body facilitate the absorption. 
     FIG. 5 schematically illustrates how the floating collecting apparatus  10  shown in FIGS. 1-4 can be used together with a curved length of a floating oil boom  36  to collect oil floating on the water within an area defined by the boom, namely at the inner region of a small bay which is delimited by the boom and into which the oil drifts. 
     The oil boom  36  is provided with drag anchors  37  at its ends. A length of spring wire  38  connects the collecting apparatus with the arms of the boom  36  such that the collecting apparatus is kept in the inner region of the bay, i.e. near the crest  36 A of the bight formed by the boom  36 . At the same time the wire keeps the arms  36 B of the boom spread apart so that the arms can catch oil between them and guide it toward the crest area. A small sail or other suitable surface exposed to the wind applies a propelling force to the collecting apparatus  10  to orient the bighted boom  36  such that the gap between the ends of the boom  36  is in the teeth of the wind and catches the oil and guides it toward the collecting apparatus  10 . 
     If desired or required, several booms, each associated with a collecting apparatus, can be interconnected to cover a larger area.