Surface cleaning of sea or lake waters, being polluted by oily, mineral or other products, or the recovery, through physical means, of such supernatant substances from the same waters or those located inside wells, tanks, basins, is carried out with devices based on surface adhesion or more simply by directly removing the polluted waters.

For this purpose, different types of equipment have been built (sometimes called skimmers), that can be schematically grouped into the following categories a)-disk system, b)-drum system, c)-ribbon system, d)-rope system, e)-bell system.

Background art A description of currently used systems is now given: a)-disk system The equipment comprising a set of steel disks, spaced by about 150/200 mm, with a diameter of about 500 mm and thickness of about 3 mm, is assembled on a rotating shaft.

The assembly is supported by a self-supporting steel structure, fixed or connected to floats that also ensure its horizontal stability.

The disks that are partially immersed in water rotate at a speed of 10/20 revolutions/minute.

The supernatant liquid adheres to the rotating disk surface, and is then removed by scrapers and conveyed into a tank; this equipment has a good efficiency ; however, given its great dimensions and weight, its transport is difficult, lifting means are usually required for installation and maintenance purposes, and deep waters are further required for its use.

b)-drum system The drum skimmer is a self-contained floating plant, with reduced dimensions and weight, that can be easily transported and therefore used both in a tank and in open sea.

It is built in the U. S. A. with the trademark"ELASTEC"and the commercial name of "DRUM SKIMMER".

It is composed of aligned plastic drums assembled on a metal structure.

Oil adheres to the rotating drum surfaces, and is then removed by scrapers and conveyed into a floating and atmospheric tank, adjacent and parallel to the drums, their length being greater than the global drum one, and therefrom sucked into storage tanks.

A first drawback in this plant is the system geometry favouring accumulation of floating solid materials or sludges adjacent to collecting drums, strongly decreasing the efficiency thereof.

The device, based on the scrapers operation, further removes water too, together with the product, in a strongly varying amount according to operating conditions.

Another drawback is that both collecting tank and feeding ducts are open on the top so that they easily collect water, due to wave motion or rain; this in addition to decreasing plant efficiency, can generate horizontal instability and in some rare case even the tank being sunk. c)-ribbon system It is a scarcely efficient system, that is fixed and therefore cannot be used in open sea, or even in basins with varying water levels.

It is composed of a metal plane ribbon that is pinched and squeezed between two rotating rollers, the first one of which is idle and immersed in water while the second one is driving and located outside.

The ribbon whose length is about 300 mm and whose thickness is about 0.5 mm through surface adhesion collects oily substances, that are then removed by scrapers located next to the driving drum, and then sent into a collecting tank. d)-rope system It is conceptually similar to the previous one and with similar inconveniences; a rope is used instead of the ribbon, and is"wrought"next to the upper driving drum.

e)-bell system It is composed of a"beli", located with a vertical axis and with an adjustable height, with its edges being slightly immersed under the free liquid surface at a depth that is function of the supernatant fluid thickness to be removed.

The bell connected to a suction piping is supported through a frame by floats ensuring the horizontal stability thereof.

Efficiency of this system is good only when oily substances are present with greater and constant thickness; however, given its very high weight and dimensions, it is difficult to handle, requiring lifting means to be installed and moreover it cannot be used with rough sea.

The above-described system can also be produced by methods aiming at reducing the aforementioned inconveniences, although they need an almost continuous assistance.

Summary of the invention The main object of the present invention is providing a floating equipment to recover supernatant products that can be used under extremely varying conditions with stable efficacy and efficiency that are much greater than those in pre-existing plants.

Another major object is operating in situ, that is inside the equipment, and almost completely carrying out separation between water and supernatant oily substances in order to recover only the latter ones and thereby avoid the need of further treatments.

Another object is providing an equipment that, without losing the above-mentioned advantages, can be dimensioned depending on quantitative needs for fluid to be recovered or geometric constraints being imposed by specific applications.

Another important object is providing a floating equipment that cannot be sunk and can work even in rough waters (sea, lake surfaces or the like).

Another important object is providing an equipment that can continuously operate for a long time even in sea environment or anyway in chemically aggressive environments.

Another important object is providing an equipment that can continuously operate, unattended, in stable processes, and requiring reduced operating personnel in all

other instances.

Another important object is providing an equipment that can continuously operate with very few and rare maintenance operations.

Brief description of the drawings The invention is described in detailed hereinbelow with reference to the enclosed drawings, that respectively provide Fig. 1, top view of the equipment; Fig. 2, its view from A with the positioning of the suction mouth; Fig. 3, its BB section orthogonal to view A with drums and central scraper part, and the scraper press; Fig. 4, its CC section orthogonal to BB section, wherein suction mouth and suction filter are displayed; Fig. 5, a drum assembly part; Fig. 6, display of surface currents in the above-described equipment; Fig. 7, an equipment variation, with four drums and a tank for the supernatant fluid to be removed; in this case the tank is drilled on its bottom or is even free from a bottom; the same figure displays surface currents behaviour; Fig. 8, a variation of the previous one with tank equipped with bottom including a tubular duct therein, to remove water; Fig. 9, an equipment variation with a single drum; Fig. 10, section DD referred to the previous figure where the bottomless tank is visible.

Description of the preferred embodiment The equipment shown in Fig. 1 consists in a plane rectangular structure composed of two cylindrical parallel drums 1 and a frame 2 connecting said drums; the two-drums/frame assembly delimits a room inside 3 that is open above and below, but laterally closed.

The drums oppositely rotate, each one in such a direction as to drag the floating product from outside downwards and then into the described room.

Part of the product is dragged inside the room by the mechanical operation of rotating drums, while quite a lot adheres to the drums themselves; this part, once being conveyed inside, is removed by the operation of a single central scraper 4

for both drums, the contact line with each drum being placed on a generatrix thereof next to the internal room and adequately above the waterline.

Other two scrapers 5 for each drum placed on the bases thereof next to the internal room, again with contact line above the waterline, complete the product removal operation.

In this way the product is conveyed inside the room, further reaching due to the different specific weight, a"free surface"height that is greater than the surrounding water one.

The conveyed fluid, that is placed above, but also below the free water surface, is sucked through a pump, by one 1.1 or more suction mouths.

Fluid removed by the mouths is previously filtered through a cylindrically shaped filter 1.2 in other embodiments, the filter is composed of seven drilled flat sheets.

The height reached by fluid inside the room depends both on the specific weight and on the hydrodynamical balance that is reached due to drum speed, product viscosity, amount of floating product being present in the"area", and amount being removed by the pump.

Together with the floating fluid, however, a strongly varying amount of water is inserted inside the room, due both to the mechanical conveying operation and to the adhesion to drums surface.

However, since the room inside the structure is bottom free, an almost complete and immediate separation of water from product is achieved.

Both drums and frame are made of plastic or of thermoplastic materials chosen among those creating the best surface adhesion of oily substances, such as for example polyolefins and PVC.

In an embodiment, the equipment occupies in plane view a maximum length measured onto the horizontal plane including drum axes and parallel to axes themselves that is about 1200 mm and a width measured onto the same plane and orthogonal to the same axes of about 1200 mm.

The drums, in the same embodiment, have a 450 mm diameter; for such an embodiment a recovery capacity has been proven up to 20 m3/h of oil.

Drums are rotated at a speed ranging from 4 to 20 r. p. m.; speed is function of product viscosity to be recovered (a greater viscosity corresponds to a lower

speed and viceversa) and of amount (thickness) of fluid being present next to the equipment (a greater thickness corresponds to a higher speed).

Drum motion is generated by compressed-air motors 6 either electric or hydraulic motors equipped with speed reducers.

Drums have a hollow shaft 7 on their axis; inside the hollow shaft a stainless-steel shaft 8 is located that is connected to the hollow shaft by means of a peg 9; the shaft is connected to the speed reducer through a tab 10.

In this way it is possible, through a simple operation consisting in unscrewing the screw 11 to disassemble the drums for maintenance or transport needs.

The pump is outside the floating assembly and is connected therewith through a suction piping. In other embodiments, the suction and delivery pump for floating substances that are collected inside the room, is placed on the same equipment and connected to the frame.

The scrapers composed of a plate made of plastic material can perfectly mate the drum surface by means of scraper presses 12 and springs 13.

Fig. 6 shows the flow being formed around the equipment.

In cases in which the water surface, in addition to containing the floating and polluting fluid product with different viscosity and thickness, also contains other solid floating substances, these ones could be dragged inside the described room and, if accumulated, could cause problems to drum operation and suction mouth cloggings.

In this case the equipment shown in Fig. 7 is used; this latter one is characterized by a product-collecting bottom-free tank placed centrally between drums (to allow water removal); in this case the collected fluid is only the one removed by scrapers and conveyed due to gravity into the tank through the same self- supporting structure of the equipment that is the feeding duct from scrapers to tank.

The amount of floating fluid dragged by the mechanical dragging operation is lost, but on the other hand due to the particular shape and arrangement of the central tank, the solid floating products, if dragged, are laterally discarded without interfering with drum operation.

The same Fig. 7 shows the flow thus obtained.

Fig. 8 shows a variation of the previous one with the tank equipped with a bottom; in this case a duct"draws"water from the bottom and conveys it outside through an opening placed at a convenient height from the tank bottom.

Figs. 9 and 10 show the top view and the section of an equipment variation with a single drum; in this case the tanks, being free from a bottom, are obtained below the floats by using the same geometry thereof.