NO761396L - - Google Patents

Description

The invention relates to seawater intakes for devices in which seawater (or in some cases brackish water) containing marine life which can cause fouling is used or consumed.

As examples of devices in which seawater is used and

which can be located on land or on ships, can be mentioned heat exchangers in which seawater is used for cooling, electrochemical cells

clay for the production of chlorine and/or hypochlorite from seawater for industrial purposes or for water purification purposes, and desalination devices in which seawater is converted to fresh water. Marine life in such seawater causes fouling not only of the devices themselves, but also of lines, channels and gutters and similar devices in which the seawater is transported from its source to the device, and of the intake sieves used to prevent marine waste, fish and similar sea creatures from entering. Examples of marine life that can cause fouling include bacterial

sludge, algae, clams, duck shells and similar sea creatures.

Due to the fact that fouling can reduce the efficiency of use for such devices or sometimes even make them unusable, previous attempts have been made to reduce fouling due to marine life to a minimum in order to prevent such fouling. As examples of these attempts, the devices and methods described in US patent documents No. 3,520,790, No. 3,458,413 and No. 3,530,051 can be mentioned which, although they are all effective to varying degrees, are still burdened with disadvantages which limits their .applicability.

It should be particularly noted that in US patent no.

3 520 .7 90 where the use of copper ions leached from copper

anoas arranged in seawater heat exchangers or pipes to

prevent the attachment and growth of sea animals, no precaution has been taken to prevent fouling of the seawater intake strainer, and an effective effect against fouling seems to require that the copper anodes extend in the same direction as the wire surfaces.

In US patent no. 3 458 413 where the use of electrodes in the intake part of a seawater passage (intake between ship's side and sea valve) and using an electrolysis current of 0>06 - 1 A/m<3> seawater flowing through the passage per hour, is described, there is no device to protect the passage from marine debris, and the intake and the passage up to the location of the electrode will be exposed to fouling by marine organisms.

Finally, it should be noted that in US patent no.

3 530 051 where a complex seawater inlet opening is described which consists of an intake line strainer surrounded by a number of electrode units in which a central anode in each unit is closely surrounded by a series of cathode rails, the investment costs and operating costs will be high due to the loss of chlorine to the sea caused by the arrangement of the electrode units at a distance from the seawater intake lines. Moreover, such a complex inlet opening will be exposed to damage by marine debris and cannot be used with a cathode current density of less than 3 A/dm 2 if clogging of the short distance between the anode<p>g cathode due to mineral deposits is to be prevented.

The invention therefore aims to provide a device which prevents or inhibits fouling due to marine life of equipment in which seawater is consumed or used (including associated transport lines for seawater) and which reduces to a minimum or is not affected by the shortcomings with which the previously used devices are affected.

The invention specifically aims to provide a seawater intake for such equipment and for auxiliary pipelines and which provides strong protection against fouling on

(marine life filter, which is simply designed and has a simple construction, yet robust, which sifts out seawater waste and wreckage without being fouled with marine organisms, which can be used within a.wide range for the supply rates of

seawater without being clogged with mineral deposits, and which is efficient during operation.

The invention thus relates to a seawater intake for an apparatus in which seawater containing marine life capable of causing fouling is used, and the seawater intake is characterized in that it comprises (a) a line for transporting water to the apparatus and with an inlet submerged in the sea, (b) a metallic corrosion-resistant, electrocatalytically active, anodic screen covering the line inlet, (c) a cathode located in the sea near the anodic screen, and (d) an electrical insulator located in the sea between the anodic screen and the cathode.

When seawater is taken in through the intake, an electric current is periodically or continuously caused to pass between the anodic strainer and the cathode, thereby developing chlorine at the anodic strainer and which prevents fouling of the intake, the line and the equipment in which seawater is consumed, due to marine life.

The present seawater intake will be described in more detail-- -

know with reference to the drawing where .

fig. 1 and 2 are side views, partly in section, of two embodiments of the seawater intake according to the invention, and

fig. 3 is a perspective side view of a further

embodiment which is also shown partially in section.

On. the figures show three different embodiments of the seawater intake according to the invention, and in these figures the same numbers have been used to denote the same elements. It appears from these figures that the intake consists of an anodic strainer 1 which is corrosion resistant to seawater and which has a surface of which at least part is electrocatalytically active, which is attached to and covers the inlet end 2 of a line 3 for transporting seawater to an apparatus in which seawater is consumed, a cathode 4 arranged near and at a distance from the anodic sieve towards the sea side in relation to the inlet end 2 of the line 3, and an electrical insulator 5 arranged between the anodic sieve 1 and the cathode 4. The anodic sieve 1 (the anode sieve) and the cathode 4 is supplied with electric current from a direct current power source (not shown) via respectively an anode wire 6 and a cathode wire, 7.

In the seawater intake according to fig. 1 where the wire 3 is shown made of metal, the anode sieve is attached to and electrically isolated from the wire 3 by means of a retaining ring 8 of a dielectric material, such as rubber or plastic, while the cathode 4 is attached to an electrical insulator 5 which is dielectric, cylindrical plastic sleeve that protects and surrounds the anode sieve 1 and is attached to the wire 3 by means of a spacer ring 9.

In the seawater intake according to fig. 2 where the line 3 consists of a rigid, dielectric material, such as PVC, fiberglass-reinforced polyesters or similar dielectric material, the cathode 4 is kept at a distance from the anode sieve 1 by means of the spacer and holder ring 10 which is attached to the line 3 and on the same manner as this is made of a dielectric material, such as PVC, rubber or a similar dielectric material. The electrical insulator or 5 is either a dielectric sleeve that is attached to a dielectric coating that covers the entire surface 11 of the cathode 4 that faces the anode cell 1, and the electrical insulator can be made of any dielectric material, such as e.g. rubber,

plastic or a ceramic material.

In a similar way, the line for the seawater intake consists according to fig. 3 of a rigid, dielectric material, such as a plastic or similar dielectric material. According to this embodiment, the cathode 4 and the insulator 5 are held below the anode sieve 1 and at a distance from each other by means of a support rail 12 which also

is made of a rigid, dielectric material and which is attached to the wire 3.

As shown for the embodiment according to fig. 3, it is not necessary for the insulator in the seawater intake according to the invention to be located close to the cathode. The only requirement is that the insulator must be arranged in such a way that it will prevent any mineral deposits (which are assumed to consist mainly of calcium and magnesium hydroxides) that accumulate on the cathode, from forming a bridge across the space between the cathode and the anode cell.

Although the invention has been explained with reference to the three embodiments shown in fig. 1, 2 and 3, A person skilled in the art will also understand that the invention is not limited to these particular embodiments of the intake or to the

elements and materials used for this.

Thus, the wire may be of any desired size and cross-sectional shape, and may be arranged in any desired direction (when enclosed) and may be made of any material, such as plastic, metal , concrete or similar material.

The only requirement is that the line must be resistant to seawater and to the electrolysis products on the anode sieve, and that when the wire is electrically conductive, it must be isolated from the anode sieve. The seawater intake according to the invention can thus be used in connection with enclosed lines, such as pipelines, pipes and gutters, or in connection with open lines, such as troughs, channels or even pits in the ground when large volumes of seawater are required.

It should also be noted that although an anode sieve with a truncated cone shape has been shown, the geometric shape of the anode sieve is not of decisive importance. It is only necessary that the anode sieve has a geometric shape that provides a sufficient area for the development of a quantity of chlorine sufficient to

provide the desired inhibition of fouling due to marine life. The physical form of the anode is also not of particularly decisive importance as long as it provides the transparency necessary for

to achieve a substantially unobstructed intake of water and to

filter out unwanted marine waste and unwanted marine animals, and it is structurally strong enough to withstand the conditions of use to which it is subjected. As examples of perforated anodes that can be used as an anode sieve, mention can be made of a wire cloth sieve, wire mesh, expanded sheet metal cloth, perforated metal plates, grids of rods and similar devices that can be used alone or in combination with each other.

The construction material used for the anode sieve

is similarly not of particularly decisive importance.

It is only necessary that it is electrically conductive, resistant to corrosion due to sea water and electrocatalytic. Although a number of materials will satisfy these requirements, the materials known as "dimensionally stable anodes" (DSA) are particularly effective. A DSA consists mainly of

of a corrosion-resistant substrate, usually a friendly

til metal (titanium, tantalum, niobium or zirconium) or a ven til metal alloy, and with at least part, but preferably all, of its surface coated with an electrically conductive, electrocatalytic coating consisting of a metal from the platinum group (platinum, ruthenium , palladium, iridium, rhodium or osmium), an alloy of a metal from the platinum group, an oxide of a metal from the platinum group or a mixture thereof, or a solid solution of one or more oxides of metals from the platinum group and one or more oxides of other metals, Due to the fact that they are inexpensive, electrochemically* efficient and durable, coatings of solid solutions containing one or more oxides of a metal from the platinum group and one or more oxides of a valve metal are particularly preferred, and in particular coatings consisting of titanium dioxide and ruthenium oxide in a molar ratio of 1.5:1 - 2.5:1. Materials and methods for producing DSA with coatings of this type are well known and described in more detail in US Patents No. 3, 632,498, No. 3,711,385, No. 3,840,443 and No. 3,853,739. Coating of this preferred type for DSA and which is even more affordable and has similar or even far better usage properties and duration, is a coating in which up to 60 mol%

of the oxide of the metal from the platinum group is replaced with cobalt metatitanate, as described in US patent document no.

3,778,363, or coatings comprising titanium dioxide and ruthenium dioxide

oxide in a molar ratio of 1.5:1 - 2.5:1 and in which 35 - 50 mol% of the ruthenium dioxide is replaced with tin dioxide, as described in US patent document no. 3 776 834. When the seawater intake is to be used in seawater at a temperature of approx. 15° C or below,

it has been found that DSA coatings described in US Patent No. 3,793,164 and in which iridium oxide constitutes the main or only oxide of a metal from the platinum group used, give an improved service life and are therefore preferred. The currently preferred DSA coating for use in cold water is a solid solution of 70.40% by weight SnO 2 . 7.53% by weight antimony oxide, calculated as Sb2O3, 20.76% by weight IrQ2 and 1.31% by weight TiO2 - By using these preferred anode silic coatings, current yields of approx. 85% or more in terms of chlorine development, and thereby the energy requirement is greatly reduced.

On the other hand, the cathode in the present seawater intake can be made of any electrically conductive metal or any electrically conductive metal alloy which is preferably corrosion resistant to seawater, such as stainless steel or alloys of nickel, titanium or a similar metal. The nickel alloy "Hastelloy C-276" has been found to be particularly useful. For some intakes, however, metals or metallizations that are exposed to corrosion due to seawater can be used as cathode, such as e.g. in a ship's intake for seawater where the hull near the intake forms the cathode and the intake's anode filter is isolated from the hull with a dielectric material, as the part of the hull used as the cathode will be cathodically protected from corrosion. The cathode can generally have any desired size, shape and physical embodiment. It can thus be fixed or perforated and can be used in the form of plates, rods, sieves and a similar device. For practical reasons, it is preferred that the cathode has such a size that the area supplied by its electricity that comes into contact with the seawater will usually amount to at least approx. 10% or more of the electrocatalytic area of the anode, thereby reducing the voltage requirement of the seawater intake. When lower voltages are not important, even smaller cathodes can be used. Conversely, cathodes with an effective area of approx. 50% or more of the anode's electrocatalytic area when the electrical voltage supplied to the intake must be kept as low as possible. When mineral deposits on the cathode are to be kept as low as possible, the cathode will have such a size that the current density of the cathode will be approx. 3 A/dm<2> or above, as described in US Patent No. 3,530,051.

As shown in the drawing and explained above, the cathode 1 of the present seawater intake is arranged at a distance from the anode sieve in the direction towards the sea, but close to the anode sieve. Although the distance between the cathode and the anode is not of particularly decisive importance, for practical reasons this will mainly depend on the design of the intake and will normally vary from 2.54 cm to 61 cm. Although even greater distances can be used, for practical reasons the intake will be designed so that the distance and thereby the required voltage for the intake are as low as possible. The design of the intake will similarly determine the placement of the cathode in the seawater in relation to the anode sieve. The position of the cathode can be below, next to or even above the anode sieve. It has been shown that by placing the anode in the direction towards the sea in relation to the anode sieve, the accumulation of mineral deposits on the cathode is greatly reduced. It is believed that this is because the cathode is thereby exposed to natural sea currents and to the influence of waves and tides. It has also been shown that this placement of the cathode towards the sea did not significantly increase the voltage

beyond a certain maximum, although it did lead to an increase in the voltage requirement for the seawater intake, and this is believed to be due to the wide electrical conduction path obtained due to the large volume of seawater surrounding the cathode.

As explained and shown above, the electrical insulator in the seawater intake according to the invention is placed between the anode sieve and the cathode in such a place that seawater minerals which accumulate on the cathode are prevented from bridging the space between the anode sieve and the cathode. Such bridging of mineral deposits can have the harmful effect of introducing unwanted mineral impurities into the inlet water. or even occasionally that the anode-in filter's effective intake area is reduced. Because of this, the seawater intakes according to the invention are not subject to limitations regarding the water intake speed, as is the case for some known seawater intakes (e.g. for those described in US patent document no. 3 530 051), where the cathode current density (and thus the volume of the ingested water that can be treated) must be kept below or above a certain value if destructive accumulations of mineral deposits on the cathode are to be prevented. Taking this into account, the electrical insulator may be attached to the cathode close to or at a distance from it, and the electrical insulator may be of any size and shape which will achieve this purpose. In a number of cases, a good design will require that the insulator is arranged closely together with the cathode surface facing the anode sieve, and that it has the same general area and the same geometric design as this cathode surface, while the electrical insulator in other cases, such as .ex. for an intake for a ship where, as previously described, the ship's hull is used as the cathode, will simply be placed between the anode screen of the intake and the cathode. The electrical insulator can be made of any dielectric material which is stable in seawater and which will not significantly lose its dielectric properties. The insulator in the intake can, depending on the structural requirements placed on it, be flexible or rigid and can take the form of a coating, a film, a plate or even a structural support part, as shown in the intakes according to fig. 1 and 3. As examples of dielectric materials that can be used, mention can be made of natural rubbers and synthetic rubbers, plastics based on synthetic resins, such as PVC, fluorocarbon resins, phenolic resins, melamine resins, epoxy resins, polyester resins and similar synthetic resins, and insulating ceramic materials .

As shown for the seawater intake according to fig. 1 and 2. the seawater intake according to the invention can be designed in such a way that the anode sieve can be shielded and protected against marine debris and wreckage by the insulator and/or cathode being arranged around and beyond the anode sieve. This optional feature is particularly useful when less robust anode filters, such as wire cloth and wire mesh anodes, which are more susceptible to damage by marine debris, are used. In contrast, a more robust anode sieve, such as a sheet of stretched sheet metal, grids of metal rods and a similar device, will not need a cathode shielding and/or insulator shielding.

Electrical power is usually supplied to the seawater intake from a direct current power source, such as an accumulator, rectifier or generator, only when seawater is taken in. However, when a cathode is used which is subject to corrosion, it may occasionally be desirable to supply electric current to the intake in a sufficient amount to provide cathodic protection for the cathode,

even when no seawater is taken in. When the intake is used, the supplied amount of electricity (ampere-hours) will be adjusted in relation to the amount of chlorine that is necessary to be developed at the anode filter, and this in turn will vary with the amount of sea water that is taken in, the amount of fouling marine life that is present in the seawater, the temperature of the seawater, the desired degree of inhibition of fouling and similar factors. The an-

depending on these interdependent factors, usually sufficient electricity is converted so that at least 0.25 part and at most 6 parts chlorine will be developed per million parts of water flowing into the seawater intake. In the preferred embodiments of the present seawater intake, i.e. where DSA anodes are used, 1 g of chlorine can be developed by supplying an amount of electricity of approx. 0.85 amp hours. For a number of applications, the preferred amount of chlorine to achieve adequate protection against fouling will usually lie within the narrow range of 1-4 ppm chlorine. Although these amounts of chlorine are usually obtained by continuously supplying electrical current to the seawater intake when the water is taken in, it will be understood that there may be cases when electrolysis of the ingested seawater can best be carried out by periodic supply of electricity in periods which in relation to the amount of seawater ingested will give an average amount of chlorine with the typical values described above.

Example

An electrochemical cell for the production of hypochlorite from seawater which was fed to the electrochemical cell through a 701 m long PVC line with a diameter of 5.1 cm, and with a filtering screen arranged between the electrochemical cell and the line was operated for 2 months. During this time had to

the cell filter strainer is cleaned at least once a day to remove slimy deposits. The deposits could only be removed with difficulty by backwashing and sometimes could not be removed at all, and the filter screen had to be replaced. In addition, duck shells and other forms of marine life attached themselves to the inside of the wire and caused an approx. 50% narrowing of the seawater pipeline.

A seawater intake with a similar design as shown

on fig. 1 was then attached to the PVC line's seawater inlet, and when seawater entered the line, electrical current was continuously supplied to the seawater inlet in such a quantity that approx.

4 ppm chlorine was formed. In the seawater intake, the anode sieve was one

cylindrical sheet of stretched titanium plate (with an internal diameter of 6 cm and a height of 19 cm and with the bottom 15 cm coated with an electrocatalytic coating consisting of titanium dioxide and ruthenium dioxide in a molar ratio of 2.5:1), while the cathode was

a cylindrical ring of a stainless steel sheet (with a diameter of

20 cm and a height of 15 cm) which was arranged laterally and concentrically in relation to the anode sieve on the outside of a PVC cable sleeve (with an internal diameter of 15 cm) which was also arranged concentrically in relation to the anode sieve and which stretched approx. 61 cm outside this.

It was observed that the seawater intake prevented marine plants, algae and marine waste from entering the line, and the anode strainer remained essentially clean presumably because of: the washing effect of the sea and because marine life no longer adhered to the strainer. Growth of duck scales in the PVC line ceased, and duck scales that were previously present and had not been removed by mechanical cleaning of the line were moved and flushed through the line to the cell filter screen where they could be removed.

It was no longer necessary to carry out a daily backwash

of the cell filter strainer, and it was possible to carry out a cleaning at intervals of 2 weeks. Even after 2 weeks a backwash could be carried out more easily as deposits of marine life no longer appeared to grow on the strainer and appeared to be of a different type.

The intake water was found to be free of appreciable amounts

of precipitated minerals. It was calculated that the seawater intake could be operated with an average electricity yield of approx. 90%

what mattered the development of chlorine.

Although the above description and example for the sake of simplicity and clarity have been described with chlorine as an antifouling agent, the person skilled in the art will understand that the chlorine formed on the anode will react with water to form hypochlorous acid and/or sodium hypochlorite as in reality acts as the agent that prevents fouling of marine life.

This is evident from the drawing, description and example

that the seawater intake according to the invention offers the following advantages: a simple and reasonable construction, robustness, ability to filter out marine waste and marine life without even being fouled or clogged by the growth of marine life, a strong protection against fouling by marine life by equipment that consumes seawater, and of h-jelpel lines for the transport of seawater, ability to be used within a wide range of intake rates for seawater without

become clogged with mineral deposits, a high electrical yield

and thereby low operating costs and a long service life with minimal maintenance.

Claims (14)

1. Seawater intake for a device in which water is used that is taken from a sea containing marine life that is capable of causing pollution, characterized in that it includes (a) a line for transporting the water to the device and with an inlet submerged in the sea, (b) a metallic, corrosion-resistant, electrocatalytically active anode screen covering the line inlet, (c) a cathode arranged in the lake near the anode cell and (d) an electrical insulator arranged in the lake between the anode cell and the cathode. 2. Seawater intake according to claim 1, characterized in that the electrical insulator is arranged close to the surface of the cathode which faces the anode sieve. 3. Seawater intake according to claim 1, characterized in that the electrical insulator extends in the same direction as the surface of the cathode facing the anode sieve. 4. Seawater intake according to claim 1, characterized in that the electrical insulator surrounds and extends beyond the anode strainer to shield it from marine waste" 5. ' Seawater intake according to claims 1-4, characterized in that the cathode surrounds and extends beyond the anode sieve to shield it against marine debris. 6. Seawater intake according to claim 5, characterized in that the electrical insulator extends in the same direction as the surface of the cathode facing the anode sieve. 7. Seawater intake according to claims 1-6, characterized in that the anode seal comprises an electrically conductive, metallic substrate which is corrosion-resistant to seawater and which is provided on at least part of its surface with a coating consisting essentially of a valve - metal oxide and an oxide of a metal of the platinum group. 8. Seawater intake according to claim 7, characterized in that the anodesil substrate comprises a valve metal. 9. Seawater intake according to claim 7, characterized in that the coating essentially consists of titanium dioxide and ruthenium dioxide in a molar ratio of 1.5:1 - 2.5:1. 10. Seawater intake according to claim 9, characterized in that the anode substrate comprises a valve metal. 11. Seawater intake according to claim 7 or 8, characterized in that the coating essentially consists of titanium dioxide, ruthenium dioxide and tin dioxide in a molar ratio of Ti02:Ru02 and Sn02 of 1.5:1 - 2.5:1, and that the tin dioxide amounts to 35 - 50 mol% of the combined ruthenium and tin dioxides. 12. Seawater intake according to claim 11, characterized in that the anodesil substrate comprises a valve metal. 13. Seawater intake according to claim 7 or 8, characterized in that the coating essentially consists of a mixed oxide coating of 30 - 90% by weight Sn02 , 1.0 - 10% by weight anti-mpnoxide, calculated as Sb2C>2> 1.0 - .50% by weight of at least one oxide of a metal from the platinum group and 0.5 - 30% by weight of titanium dioxide, the molar ratio between the tin dioxide and the antimony oxide being 85:15-95:5. 14. Seawater intake according to claim 13, characterized in that the oxide of the metal from the platinum group is iridium oxide and that the anodesil substrate comprises a valve metal.