GB2257984A - Electrolytic cell for antifouling treatment of fresh water - Google Patents

Abstract

A cell for producing copper and/or aluminium hydroxide and/or iron oxide floc in fresh water flowing through the cell to combat the settlement of mussels, barnacles, clams and algae includes anode elements of copper and/or of aluminium or iron in the form of plates, and ferrous metal cathode elements of plate form spaced from the anode elements at a spacing between 3 mm and 15 mm by an insulating spacing element. Annular copper or aluminium anode 112 is spaced by annular spacer 110 from steel disc cathode 114 provided with a plurality of flow passages 115 (see Fig. 5 not shown) so that the water passes through the cell in labyrinthal fashion. The spacer may have circular cross-section (Fig. 8 not shown). <IMAGE>

Description

Anti fouling apparatus The invention relates to antifouling apparatus.

It is well known to use an antifouling apparatus for producing copper and aluminium hydroxide floc in the sea-chest of an ocean going vessel in order to combat the settlement of mussels, barnacles, clams and algae or the like in the sea-chest and in water systems drawing water from the sea-chest. In such an apparatus a current is applied to anodes of copper and aluminium, the sea-chest constituting the cathode and the sea water constituting an electrolyte through which an electric current can pass relatively easily.

However, a problem exists when it is desired to use such apparatus in a vessel in a fresh water lake because fresh water does not provide an electrolyte through which an electric current can easily be passed. The present invention has for its object to provide apparatus by means of which the problem referred to will be at least alleviated.

According to the invention, there is provided an assembly for the production of copper and/or aluminium hydroxide and/or iron oxide floc, the assembly including at least one cell unit including an anode element in the form of a plate of copper or of aluminium or iron, a cathode element in the form of a plate of ferrous metal, a spacer element made of an electrically non-conductive material and acting to space the anode and cathode surfaces apart at a spacing between 3 m m and 15 m m, means for passing water through the assembly, and means for passing an electric current through the water between the two plate elements.

The assembly may include a plurality of cell units each being constituted by an anode element in the form of a plate of copper or of aluminium or iron, a cathode element in the form of a plate of ferrous metal, and a spacer element made of an electrically non-conductive material disposed between the anode and cathode elements. The plurality of cell units may be of generally circular shape, and the anode element of each cell unit may be of annular shape; the cathode element of each cell unit may be of annular shape for water passing through a central flow passage of the assembly to act directly against radially inner portions of the anodes and cathodes.

Alternatively, in each cell unit one of the anode and cathode elements may have a central flow passage and the other may be in the form of a plate with a plurality of flow passages extending through it in outer regions thereof radially spaced from said central passage for water passing through the cell to flow in labyrinthal fashion through said flow passages of the two elements and across their intervening faces. The plurality of cell units may have annular anode elements made alternately of copper and of aluminium or iron.

The plurality of cell units may be arranged in a vertical stack and successive elements of the stack may rest upon each other with non-conductive spacers between them, so that the spacing between the elements of each cell unit will remain constant throughout their useful life.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which:- Figure 1 is a semi-diagrammatic view of antifouling apparatus embodying the invention, Figure 2 is a part sectional side view of a treatment cell forming part of the apparatus of Figure 1, Figure 3 is a view, drawn to a somewhat larger scale than Figure 2, of a single unit of the treatment cell of Figure 2, Figure 4 is a view similar to Figure 3 and illustrating a possible modification, Figure 5 is a perspective view of a cathode forming part of the treatment cell of Figure 4.

Figure 6 is a perspective view of some component parts of a different arrangement of anti fouling apparatus, Figure 7 is a scrap plan view, Figure 8 is an axial section through the component parts of Figure 6, and Figure 9 is a view on the line 9-9 in Figure 8.

Referring now to Figure 1 of the drawings, the apparatus there illustrated is constituted by a water treatment cell, generally indicated 100, shown to be drawing water from a fresh water lake and to be returning it to the lake after treatment.

The construction of the treatment cell is illustrated in Figures 2 and 3. It includes a plurality of generally cylindrical cell units generally indicated 102, arranged end to end with pipe connecting flanged plates 104 at the opposite ends of the assembly. The assembly is connected together by a plurality of longitudinally extending rods 106 with nuts 108 on their screwthreaded end portions.

Each cell unit 102 includes an annular spacer element 110 (see Figure 3) made of a synthetic plastics material, an annular anode element 112 made either of copper or aluminium and housed within the spacer element, and a further spacer element 114 which constitutes a cathode element made of steel. The annular spacer element 110 has a narrow register 111 against which the anode element can abut, as shown. A synthetic plastics ring 113 is provided to abut against the other side of the anode. The outside diameter of the spacer element 114 is the same as that of the spacer element 110 and the bore of the spacer element 114 is of the same diameter as the bore of the anode element 112. Felt pads 116 flank the anode element 112.

The arrangement is such that the rods 106 can extend through aligned holes 118 which extend through the spacer elements 110 and 114. When the cell units have all been clamped together as shown in Figure 2, the felt pads 116 fill the annular spaces between the adjacent side surfaces of the anode elements 112 and cathodes 114, except for relatively small radially inner areas which, as shown in Figure 3, remain open.

As shown in Figure 2, the spacer elements 114, constituting the cathodes, and the flanged plates 104, are all electrically connected together by connections 117. The flanged plates are electrically connected one to the other by means of the rods 106. The spacer elements 114 and said flanged plates are connected to an electric current controller, generally indicated 21, by means of an electric lead 120. The anodes of copper and of aluminium are arranged alternately. The anodes made of copper are all electrically connected together, and the anodes made of aluminium are all electrically connected together; the anodes of copper and aluminium are connected to the electric current controller 21 by means of respective electric leads 122 and 124. The manner in which the electrical connections to the anodes are made is by means of respective metal pins 123 extending through the plastics spacer elements 110 and into the anodes, being either a tight drive fit in radial holes therein or having threaded engagement therein. Radial holes in the plastics spacer elements through which the metal pins extend will of course be spaced from the holes 118 through which the rods 106 extend.

In use of the treatment cell, the water passing through the cell is able to act directly against the radially inner portions of the anodes and cathodes, that is to say initially against the originally machined bore of each element and the radially inner side surfaces. However, as the anode materials wear away, the radially inner portions of the anodes will assume the shape indicated in chain-dotted lines in Figure 3, but the anode and cathode surfaces are maintained at relatively close spacing throughout. Floc is thus produced despite the fact that the water passing through the cell is fresh water.

It will be understood that in this construction of cell it is very easy to increase the capacity of the treatment cell by the simple expedient of including a greater number of cell units and using longer rods 106. It is also very easy to replace the anodes when they have become unduly worn away.

As the anodes become worn, the effective distance between the anode and cathode surfaces does not increase very substantially. In addition, whatever increase there is in the effective spacing of the anode and cathode surfaces is countered by the fact that the effective areas of the anodes being acted on by water passing through the cell becomes progressively increased because of the gradually increasing diameter of the flow passage therethrough.

Referring now to Figure 4, this illustrates a possible modification of the construction of cell just described with reference to Figures 2 and 3.

The modification resides in the fact that in each cell unit the felt pad has been discarded and the spacer element 114, which constitutes the cathode, has been made as a disc with a plurality of flow passages 115 extending through it in radially outer regions as shown in Figure 5. The arrangement is such that the water passing through the cell is caused to flow in labyrinthal fashion through the centre of each anode, through the flow passages of each cathode element and across the intervening faces of said anode and cathode elements. The spacing of the anode and cathode surfaces as already described makes this possible, that is to say, the fact that each anode element 112 is of lesser thickness than the spacer element 110 within which it is centrally located.

Referring now to Figures 6 to 9, a different arrangement of antifouling apparatus embodying the invention includes a plurality of generally cylindrical cell units in a vertical stack within a synthetic plastics body part 242, each cell unit being constituted by an annular anode element 222 made either of copper or of aluminium, a disc element 224 made of steel and constituting a cathode element, said disc element having a plurality of flow passages 226 extending through it in radially outer regions thereof, and respective synthetic plastics spacers 228 (see Figure 8) of circular cross section interposed between the various element of the cell.The synthetic plastics body part is provided at its opposite ends with pipe connecting flanged plates at its opposite ends, similar to the flanged plates 104 of the previously described embodiment, one of these being shown in ghosted outline in Figure 6.

Flexible electrical connections are provided to the anode and cathode elements. Each element has a plastics boss 236 at its periphery with a flexible wire 238 sealed in it and contacting the metal beneath. The plastics boss of each element is located in a longitudinally extending slot 240 within the body part 242 (see Figure 7), the arrangement being such that the anode and cathode elements are held against rotation during transit and each flexible wire, passing through the wall of the plastics body part as shown in Figure 7, is sufficiently long to allow some axial movement of the respective element within the body part throughout the life of the unit.

The arrangement is such that a variable current can be applied to the anodes for the production of copper and aluminium hydroxide floc, respectively, as fresh water is pumped, as indicated by the arrows, through the spaces extending through and flanking each anode. The continuous circulation of water through the unit flushes out the relatively narrow spaces so that they do not become blocked by floc. In addition, bubbles of hydrogen which are produced during the process are flushed out of the apparatus.Depending on where the apparatus is installed, the copper and aluminium hydroxide floc may be distributed through pipework and/or seachests of a vessel requiring protection from marine growth or the apparatus may, for example, be used as shown in Figure 1 for the floc to be mixed with water being drawn from a freshwater lake which has become contaminated with mussels or the like in some way, the water being drawn from the lake for cooling purposes or for use in some industrial process for example. As in the previously described embodiment, the surfaces of the anode and cathode elements are maintained at relatively close spacing throughout the life of the apparatus by settlement of the various elements of the cell units as the anodes wear away. Floc will thus be produced at a substantially constant rate despite the fact that the water passing through the cell may be fresh water.If the apparatus is used for marine applications, that is to say where water passing through it will be sea water, a reduced voltage may be applied to the apparatus to limit the production of floc and of course to extend the useful life of the anode elements.

The required spacing of the surfaces of the anodes and cathodes, and their effective surface areas for the production of a sufficient quantity of copper and aluminium floc without an excessive electric currrent requirement, can be determined by trial and experiment. However, it is believed that the spacing of the anodes and cathodes will need to fall within the range of 3 mm to 15 mm. A spacing less than 3 mm is likely to interfere with the free flow of floc from the surfaces of the anodes.

A spacing greater than 15 mm would require an electrical voltage which could possibly be dangerous. It is thought that the optimum spacing of the anode and cathode surfaces will be 5 mm.

Purely by way of example, it may be noted that in the illustrated embodiment just described the anode and cathode elements are all of 216 mm outside diameter, the initial bore diameter of each annular anode element is 38 mm, the six flow passages extending through each disc element 224 are each of 16 mm diameter, the initial thickness of each anode element is 28 mm and the synthetic plastics spacers 228 are 5 mm thick. However, it is thought that the thickness of the spacers could be varied within the range of 3 mm to 15 mm.

In the illustrated embodiment just described, which has two copper anode elements and two aluminium anode elements, a flow rate of 17 gallons/minute with the apparatus operating at 2.5 amps, 30/40 volts DC, has been found to produce 290 ppb at the outlet. An increase of flow rate to 2500 gallons/minute will reduce floc production to 2 ppb at a similar current input.

In the operation of this particular form of apparatus, as the surfaces of the anode elements gradually wear away, the stack of elements will settle. The spacing of the anode and cathode elements will therefore remain substantially constant throughout the effective life of the anode elements. When the anode elements eventually need to be replaced, it is a relatively simple operation to strip down the apparatus and to insert new anode elements in place of those which have become almost worn away.

It is not essential for the cell units to be of generally cylindrical shape although for ease of manufacture and assembly they will preferably be of cylindrical shape. The aluminium anode elements could be replaced by soft iron elements.

Claims (8)

CLAIMS:

1. An assembly for the production of copper and/or aluminium hydroxide and/or iron oxide floc, the assembly including at least one cell unit including an anode element in the form of a plate of copper or of aluminium or iron, a cathode element in the form of a plate of ferrous metal, a spacer element made of an electrically nonconductive material and acting to space the anode and cathode surfaces apart at a spacing between 3 mm and 15 mm, means for passing water through the assembly, and means for passing an electric current through the water between the two plate elements.

2. An assembly according to claim 1, including a plurality of cell units each being constituted by an anode element in the form of a plate of copper or of aluminium or iron, a cathode element in the form of a plate of ferrous metal, and a spacer element made of an electrically non-conductive material disposed between the anode and cathode elements.

3. An assembly according to claim 2, in which the plurality of cell units are of generally circular shape, and the anode element of each cell unit is of annular shape.

4. An assembly according to claim 3, in which the cathode element of each cell unit is of annular shape for water passing through a central flow passage of the assembly to act directly against radially inner portions of the anodes and cathodes.

5. An assembly according to either one of claims 2 and 3, in which in each cell unit one of the anode and cathode elements has a central flow passage and the other is in the form of a plate with a plurality of flow passages extending through it in outer regions thereof radially spaced from said central passage for water passing through the cell to flow in labyrinthal fashion through said flow passages of the two elements and across their intervening faces.

6. An assembly according to any one of claims 2 to 5, in which the plurality of cell units have annular anode elements made alternately of copper and of aluminium or iron.

7. An assembly according to any one of claims 2 to 6, in which the plurality of cell units are arranged in a vertical stack and successive elements of the stack rest upon each other with non-conductive spacers between them, so that the spacing between the elements of each cell unit will remain constant throughout their useful life.

8. An assembly for the production of copper and/or aluminium hydroxide and/or iron oxide floc, the assembly being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 3, or Figures 4 and 5, or Figures 6 to 9 of the accompanying drawings.