Anchor for underwater electrodes

Abstract: The invention relates to an anchor (1), comprising a cavity structure (10) with a top surface (2) and essentially vertical wall means (4) extending downwards from said top surface (2) to form a cavity (10). The anchor has at least one sealable opening (5) in its top surface, and it is provided with means (8) for allowing supply of low density fluid, e.g. gas, to the interior of said cavity structure. It further comprises a bottom surface (3) with an opening (6) or openings for enabling sea water to enter said cavity (10) when the anchor is immersed. The top surface (2) extends in the horizontal plane beyond the periphery of said wall means (4) to form a circumferential flange (11). There is provided a similar flange (12) at the lower end of said wall means (4), said wall means (4) and said flanges (11, 12) thereby forming a receiving portion (13) on said anchor for receiving a windable member (14) therein. It also relates to an electrode station comprising an anchor and electrodes wound onto said anchor.

Description: Technical Field of the Invention This invention relates in general to anchoring of submarine structures, and in particular to an anchor device for safe anchoring of underwater electrodes for use in HVDC transfer across water. Technical Background It is known to anchor under-water structures of various types, e.g. electrodes for HVDC transfer, by using concrete structures having windows for transport of electrolyte to electrochemically active elements located inside such structures. Other methods of anchoring is e.g. to place rocks or concrete blocks on mat electrodes (e.g. such as disclosed in WO 89/12334, corresponding to SE-460 938) extending over the sea bottom. These known devices suffer from a number of disadvantages, namely in that the design with windows there occur unnecessary voltage drops due to the contraction of the conducting cross section. In addition thereto the circulation of electrolyte is limited, and design of anodes become restricted. The system according to WO 89/12334 suffers from high installation costs at larger depths. Summary of the Invention The present invention sets out to solve the problems with the prior art devices. These problems are solved by the anchor as defined in claim 1. Advantageously the anchor of the invention is utilized as an anchor for electrodes suitable for HVDC transfer across water, by providing a recesslike receiving portion for receiving such electrodes in a wound fashion. Such an anchor provided with an electrode rolled thereon is very easy to transport and to deploy inthe sea. In a preferred embodiment the anchor is provided with a valve means, e.g. a gas coupling for pressurized air such that the interior of the anchor may be filled with low density medium, such as air, thus facilitating floating and lifting of the anchor out of the water. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus not limitative of the present invention, and wherein Figure 1 illustrates an anchor according to the invention in a perspective view; Figure 2 shows a cross section through the center of the anchor of Fig. 1; Figure 3 shows an embodiment wherein the anchor is enclosed in a diaphragm; Figur 4 shows an embodiment without bottom surface. Detailed Description of Preferred Embodiments An anchor according to an at present preferred embodiment of the invention is shown in Fig. 1, and is generelly designated with reference numeral 1. In a preferred embodiment the anchor is made of glass fibre reinforced concrete, although other construction materials are conceivable. The shown embodiment of the anchor according to the invention comprises a top surface 2, a bottom surface 3, vertical wall means 4, said wall means in the preferred embodiment being cylindrically shaped and forming a cavity 10. However, other shapes such as square or rectangular are conceivable. The top surface 2 is provided with a plurality of holes 5 for enabling sea water to flow through the entire structure when it is immersed in the sea. In the shown embodiment also the bottom surface 3 is provided with a plurality of holes 6, also for facilitating filling of the cavity with water during immersion of the structure 1. It is possible to refrain from a bottom surface entirely and to just let the cylindrical walls end in an opening 7 (see Fig. 4). This may be advantageous i.a. from a manufacturing aspect. The anchor is furthermore provided with means 8 for supplying gas or other low density fluid to the interior of the anchor. Such means may be in the form of a standard type gas coupling, but should preferably be made of corrosion resistant material, e.g. titanium. However, any material that can withstand as much as several tens of years of under-water location without significant deterioration is conceivable. The anchor is also preferably provided with one or more lifting eye bolts 9 to enable its immersion in and recovering from the sea respectively. These could also be made of e.g. titanium. When the anchor is to be used for anchoring an HVDC electrode on the bottom of the sea, said top surface preferably extends in the horizontal plane beyond the periphery of said wall means to form a circumferential flange 11. There is also provided a similar flange 12 at the lower end of the wall means 4, said wall means and said flanges thereby forming a recess-like receiving portion 13 on said anchor for receiving said electrode in the form of a mat 14 or a cable having electrochemically active segments. A suitable electrode mat is the previously mentiond one, disclosed in WO 89/12334. It is within the inventive concept to use any electrode structure that may be wound onto the anchor. Metal mesh structures of various filament thickness and various mesh sizes may be applied depending on the current densities required in a specific case. Of course such electrode structures will have catalytic coatings appropriate for the specific conditions at hand. I.e. anodic or cathodic operation, varying salt concentration in the sea water etc. will affect the choice. Conductive polymer mats or mesh is also possible to use as electrodes. The recesslike receiving portion 13 must be of sufficient size such that there will be adequate convection of electrolyte due to streaming water, in order to avoid development of elementary chlorine. Also, the electrode surface must be of such size that the buffer capacity of the sea water is not exceeded by the production of reaction components, i.e. there must not occur a lowering of the pH, and the forming of hypochlorite takes place in the alkaline region. Furthermore, the receiving portion should preferably be coated with an inert material for protection purposes, since reaction products at the electrode, such as hypochlorite, might be deleterious to the concrete. Suitable materials for coating are e.g. polypropylene, high density polyethylene, Halar, or FEP, but preferably polyesters of the bisphenolic type are used, the latter preferably being sprayed onto the surface. Plastic paint of high quality is also a possible choice. The important aspect is the ability to protect the concrete from attack by hypochlorite that might be produced. A practical size of one anchor element is 2-3 m diameter and height 1-1,5, e.g. 1,2 m, although both smaller and larger sizes could be used. However, the size must be sufficient for enabling enough gas, preferably air, to be supplied to the interior to make the apparent density of the assembly suffiently low to faciltiate floating or at least lifting thereof. In a further embodiment the anchor with its interior cavity is enclosed inside an inert diaphragm 15, e.g. made of fluorocarbon polymers or other inert polymer, which however becomes electrically conductive on impregnation with electrolyte. This embodiment may be very desirable in cases where it is essential to control the electrochemistry at the electrode, especially where there are very strict requirements of chlorine-free conditions. Thereby there is also provided means 16a , e.g FEP or tubing of suitable type for introducing and means for removing synthetic electrolytes containing reducing species to the "reaction chamber", i.e. to the receiving portion 13 where the electrode structure is located. The introducing means 16a is preferably connected to a perforated PEM tube 16b located along the periphery of the lower flange 12. The removing means, e.g suitable tubing, may be connected to a pump for drawing the electrolyte through the interior of the diaphragm at a suitable rate. Synthetic electrolytes may be a reducing solution, comprising e.g. bisulfite, hydrogen peroxide or the like in proportion to the current. In another embodiment the electrodes in the form of mats or the like may be of alternating anodic and cathodic type, i.e there may be concentric layers of anodic and cathodic elements. Thereby the assembly may be used as a bipolar type electrode. The anchor is used as follows in HVDC applications. A suitable electrode, e.g. the aforementioned mat, is wound in several layers on the anchor in the receiving portion and secured e.g. by clamping or any other convenient means. The hook or a plurality of hooks of a lifting crane or other lifting device is secured to one or several eye bolts on the anchor, and lowered in the sea. Thereby water will fill the cavity by virtue of the openings in the top surface not being sealed. When the anchor is positioned on the bottom at the desired location, divers place suitable plugs in the holes in the top surface. This operation does not necessarily have to be carried out on deployment of the assembly, but instead one can wait until that point in time when it is desired to lift the anchor out of the sea agian in a future. However, it could be advantageous to do it on deployment since the hole surfaces are virgin and thus may be easier to seal than after say 30 years of under-water operation. The invention being thus described, it will be obvious that the same may be varied in many ways within the scope of the following claims.

Claims: An anchor (1), comprising a cavity structure (10) with a top surface (2) and essentially vertical wall means (4) extending downwards from said top surface (2) to form said cavity (10), and having at least one sealable opening (5) in said top surface (2), said anchor being provided with means (8) for allowing supply of low density fluid, e.g. gas, to the interior of said cavity structure (10). The anchor of claim 1, further comprising a bottom surface (3) with an opening (6) or openings for enabling sea water to enter said cavity (10) when the anchor is immersed. The anchor of claim 1 or 2, wherein said top surface (2) extends in the horizontal plane beyond the periphery of said wall means (4) to form a circumferential flange (11), and wherein there is provided a similar flange (12) at the lower end of said wall means, said wall means (4) and said flanges (11, 12) thereby forming a receiving portion (13) on said anchor for receiving a windable member (14) therein. The anchor of any preceding claim, wherein said sealable opening(s) (5) in said top surface (2) is(are) conicial and has(have) a smooth surface for facilitating sealing with a soft material. The anchor of any preceding claim, wherein said cavity (10) has a volume such that the overall density of the anchor when said cavity is filled with low density fluid becomes less than the density of the surrounding medium, e.g. sea water. The anchor of any preceding claim, wherein said wall means (4) are vertical and cylindrical. An electrode station suitable for use as one pole in HVDC transfer across water, comprising an anchor as claimed in any of claims 1-6, provided with electrode means for HVDC transfer in water in the form of a mat or a cable or the like. The electrode station as claimed in claim 7, wherein alternating anodic and cathodic type electrodes are arranged in said receiving portion (13), i.e as concentric layers of anodic and cathodic elements, whereby the assembly is usable as a bipolar type electrode assembly. The electrode station of claim 7 or 8, enclosed in an inert diaphragm (15) having the property of becoming electrically conductive when it becomes impregnated with electrolyte. The electrode station of any of claims 7-9, comprising means (16a,16b) for supplying and removing synthetic electrolyte to and from the interior of said diaphragm (15). The electrode station of any of claims 7-10, wherein alternating anodic and cathodic type electrodes are arranged in said receiving portion (13), i.e as concentric layers of anodic and cathodic elements, whereby the assembly is usable as a bipolar type electrode assembly.

Inventors: CARLSSON HANNA, KROON MARTIN, ULLMAN ANDERS, CARLSSON, HANNA, KROON, MARTIN, ULLMAN, ANDERS
Applicants: PERMASCAND AB
Application year: 1996
Main classification: H01R3
IPC codes: H01R3