Oil Collecting Apparatus

The present invention relates to an apparatus for collecting pollution, especially oil, from a surface contaminated liquid.

There is an increasing demand for means capable of removing pollution from surface contaminated liquids. Particularly, oil discharges into seas, rivers and lakes are serious environmental problems. To prevent such oil from spreading over a vast area of the water surface it may be encircled by floating barriers defining an area in which there commonly is a relatively thin layer of oil floating on the water surface. It is difficult to remove this thin oil layer without simultaneously removing a considerable amount of water.

In the Swiss Pat. No. 510,792 there is suggested an arrangement in which a vortex is formed in surface contaminated water. Oil flows into the cavity formed in the centre of the vortex, where there is accumulated a volume of oil which is sufficiently large to be removed without simultaneously removing any substantial amount of water. However, this arrangement has certain drawbacks. Thus, for example, the shape and position of the accumulated oil volume varies with the heave of the sea, whereby the removing of oil is less efficient.

An apparatus according to the invention includes a submerged, rotationally symmetrical shaped vortex chamber with inlet and outlet for the liquid, means for bringing liquid within the vortex chamber into a horizontally rotating vortex movement, and a pollution outlet tube arranged above the vortex chamber. According to the invention the efficiency is considerably improved in that a rotationally symmetrical shaped stator is arranged at the level of the liquid surface, the stator having a collecting cavity which opens downwards in a central part of the stator, said pollution outlet tube being connected to the collecting cavity. The stator has a lower end surface which slopes downwards and inwards through the liquid surface to the opening of the collecting cavity, the stator being arranged in a concentric manner with respect to the vortex chamber. The vortex chamber may comprise the interior of a hollow rotor having an upper threshold inlet and vaned inner pump means in the rotor interior for recirculating a portion of the liquid near the bottom of the rotor back toward the inlet to support the liquid vortex.

The invention is further described below with references to the drawings, in which:

FIG. 1 is a side view, partly in section, of an embodiment of the invention;

FIG. 2 is a top view of the arrangement of FIG. 1 cooperating with floating oil barriers; and

FIG. 3 is a schematical side view, in section, with reference to which the operative function of the stator is explained below.

In FIG. 1 there is shown an apparatus for collecting oil from oil discharges at sea. The apparatus includes a rotationally symmetrical stator 1 and a rotor 2. The stator 1 is rigidly connected to a framework 3 which includes float bodies 4 being arranged in such a manner that the apparatus floats steadily in a correct floating position. The rotor 2 is mounted on a shaft 5, which is driven by a motor 7 through a gear box 6. The motor 7 and the gearbox 6 are rigidly connected to the framework 3 through a shield 8.

In the central part of the stator 1 there is provided a collecting cavity 9, which is open downwards and has an outlet tube 10 in its upper part. The lower end surface 11 of the stator 1 slopes downwards and inwards through the water surface and partly into the interior of rotor 2 to the opening of the collecting cavity 9.

The rotor 2 confines a vortex chamber 12 and is open upwards. It has a cylindrical side wall 13 terminating somewhat below the water surface level CWL. Thus, the surface layer including the oil floating on the water is free to enter the vortex chamber 12 through the threshold inlet formed by the upper edge of cylindrical side wall 13. In a lower part of the cylindrical side wall 13 and around its periphery there are provided a plurality of outlet openings 14. Above the outlet openings 14 annular plates 15 and 16 are arranged around the periphery of the side wall 16. Between the plates 15 and 16 an inner plate 16a and a plurality of radial vanes 16b are provided whereby a multi-chambered inner radial pump is formed having inlets 17 and an outlets 18. An outer multichambered radial pump 19 with inlet 20 and outlet 21 is formed on the outside of the cylindrical side wall around its periphery. Outside the outlet 21 guide vanes 22 are mounted on the framework 3.

The method of operation of the apparatus is described below with reference also to the schematical view in FIG. 3 for explaining the operative function of the stator 1. It is presumed that the apparatus is operating in a water area which has been polluted by oil, which is prevented from spreading by means of floating oil barriers 23 (FIG. 2). The apparatus is floating in such a manner that the water surface level CWL is above the upper edge of the cylindrical side wall 13 permitting the surface layer to enter the vortex chamber 12.

The motor 7 brings the rotor 2 to rotate. Thus, a vortex is established in the vortex chamber 12, i.e. liquid in the chamber is rotating around the shaft 5. It is essential that the liquid rotates properly in the volume below the lower end surface 11 of the stator 1. In a cylindrical liquid volume below the collecting chamber 9 rotation is not important. In the layer immediately adjacent to the lower end surface 11 of the stator 1 there occurs a so-called boundary layer phenomenon due to the fact that the particles in this layer are retarded by friction against the stator 1, whereby their rotational velocity is reduced. For particles in the boundary layer the horizontal pressure gradient force acting towards the centre of rotation is thus larger than the centrifugal force acting in the opposite direction. Due to this excess pressure force these particles move inwards along the lower end surface 11 of the stator in towards the collecting cavity 9. Such boundary layer flux is well known in the art of hydrodynamics.

As oil is floating on the water surface, oil will be present in the boundary layer adjacent to the stator 1. Thus, oil is transported within this boundary layer into the collecting chamber 9, wherefrom it is pumped away through the outlet tube 10 by a pump (not shown) to suitable subsequent treatment.

The water floating out through the pump outlet 18 has a rotary movement around the shaft 5. The object of that water flow is to support the rotation motion of the liquid in the vortex chamber 12. Excess water leaves the vortex chamber through the outlet openings 14.

The purpose of the outer radial pump 19 is to provide a flow of water in towards the apparatus in a water layer adjacent to and below the polluted surface layer. This water flow is comparatively strong and interacts with the polluted surface layer in such a manner that oil flows with increased velocity in towards the apparatus from a comparatively large area around the arrangement. Thus, the inlet 20 of the pump 19 is situated on such a level below the water surface that oil from the surface layer will not be sucked into the pump. The flow of water from the turbine outlet 21 is directed radially outwards and downwards below the float bodies 4 by means of the guide vanes 22.