Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-04-13
2003-01-28
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S196020, C204S196030, C204S196370
Reexamination Certificate
active
06511586
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an antifouling system for preventing marine organisms from attaching to surfaces of a structure exposed to seawater and, more particularly, to an antifouling system capable of generating oxygen by the agency of an electrical catalyst provided on a surface of a structure exposed to seawater in order to prevent marine organisms from attaching to the surface of the structure exposed to seawater.
BACKGROUND ART
In some power plant that uses seawater as cooling water, blue mussels, barnacles, hydrozoans or marine plants, which will be inclusively referred to as “marine organisms”, tend to attach to an inlet and an outlet pipe plates for heat-exchanger-holding heat transfer pipes. These marine organisms block up end parts of the heat transfer pipes so that passage of a cleaning sponge through the heat transfer pipes is obstructed and/or that insides of the heat transfer pipes are narrowed. Therefore, the power plant is frequently forced to stop its operation unavoidably to remove the marine organisms. These marine organisms are liable to attach to pipe plates and/or heat transfer pipes that are made of titanium and that have corrosion-resistance in seawater, more than to pipe plates and heat transfer pipes made of a copper alloy.
In a steel water chamber lined with a rubber lining, larvae of marine organisms passed through a strainer net may attach to the rubber liner, and the larvae of marine organisms repeats growing on the rubber lining and falling off the rubber lining. This may clog heat transfer pipes for cooling.
Measures taken to exterminate the marine organisms and to prevent attachment of the marine organisms to the structure (hereinafter referred to as “antifouling measures”) include pouring chlorine or chlorine compound into the ambient region of the sea around the structure, coating the structure with antifouling paint containing toxic-ion-producing pigment and producing of toxic ions such as chlorine ions or copper ions by electrolysis of seawater.
Although these antifouling measures exercise effective antifouling functions, amount and concentration is not easy to be managed, and the concentration is liable to be excessively increased in anticipation of reliable antifouling effect. Consequently, it is highly possible that the antifouling measures cause environmental pollution. Therefore, it is recent trend that use of such antifouling measures is inhibited or controlled.
Recently, many research workers and engineers are engaged in development of antifouling measures that do not use toxic substances. For example, antifouling silicone paints are nonpolluting and nontoxic but have antifouling effect. However, antifouling silicone paints have not been prevalently used because their drawbacks including shortening of service life of antifouling silicone paints by contact with foreign matters such as shells, high costs of work for application of the antifouling silicone paints, difficulty in finding suitable applying means capable of simply and easily applying the antifouling silicone paints to structures having a large surface area and/or existing structures, and reduction of the antifouling effect of antifouling silicone paints when flow of seawater is stopped.
A method mentioned in JP-B No. Hei 01-46595 forms an electrical catalyst film, mainly consisting of a mixed crystal of metals of platinum group or a mixture of oxides of those metals, on the surface of a titanium heat exchanger or the like to be exposed to seawater, and generates a sufficient amount of oxygen substantially without generating chlorine gas by electrolysis using the titanium heat exchanger as an anode to control attachment of marine organisms to the heat exchanger or formation of scales on the heat exchanger.
However, since this prior art method forms the electrical catalyst film over the surfaces of titanium structural members to be exposed to water or seawater and uses the titanium structural members as an anode, other metallic members, such as a water chamber or pipes that are usually made of steels and lined with rubber linings, of the heat exchanger electrically connected to the titanium structural members are similarly loaded as the anode. If, by any chance, the rubber linings or the like should be damaged, a current flows through a part of the metallic members corresponding to a damaged part of the rubber linings so that a structural member of a metal other than titanium may be subject to abnormal corrosion.
Moreover, this prior art method conducts an electrical resistance heating process at temperatures in the range of 350 to 450° C. for several hours for activation of the electrical catalyst. This electrical resistance heating process is possible to damage the structure by generated heat and/or thermal stresses, and requires an enormous cost. Accordingly, this prior art method has not been prevalently practiced.
DISCLOSURE OF THE INVENTION
As mentioned above, the prior art technique mentioned in JP-B No. Hei 01-46595 coats the titanium members of a heat exchanger directly with the electrical catalyst film, heats the titanium members at temperatures in the range of 350 to 450° C. for several hours by means of an electrical resistance heating or the like for the thermal activation, and uses the same as an anode. Therefore, it is possible that the structure is damaged by heat applied thereto and/or thermal stresses induced therein. In addition, such electrical resistance heating requires an enormous cost.
Generally, in the titanium heat exchangers, only the heat transfer pipes and the pipe plates are titanium members, but the body, the water chamber, suction pipes for carrying seawater to the heat exchanger and discharge pipes for discharging used seawater into the sea are made of steels. Since the steel water chamber, the steel suction pipes and the steel discharge pipes are electrically connected to the titanium members, the same are subject to galvanic corrosion when exposed to seawater and may be heavily corroded. Therefore, the surfaces of the steel members that may be wetted with seawater are coated with rubber linings for preventing corrosion.
If, by any chance, a rubber lining of a steel member is damaged, the titanium member electrically connected to the steel member must be cathodically loaded by a cathodic protection method that lowers potential of the steel member to a protection potential thereof. However, since the aforesaid prior art technique uses the titanium member as an anode, the steel water chamber, the suction pipes and the discharge pipes connected therewith are anodically loaded, and hence the cathodic protection method cannot be applied in principle so that a current flows through a part of the steel member corresponding to a damaged part of the rubber lining and that the steel member is abnormally corroded.
It is an object of the present invention to provide an antifouling system capable of easily forming an electrical catalyst on a surface of a titanium pipe plate or the like of a heat exchanger, without applying heat to the titanium pipe plate or the like by electric resistance heating or the like, capable of electrically isolating the electrical catalyst from structural members such as the titanium pipe plates, and capable of preventing abnormal corrosion of a part of a metal member corresponding to a damaged part of a rubber lining or the like coating the metal member, by employing a cathodic protection method even when the rubber lining or the like is damaged by some rare accident.
According to the present invention, an antifouling system that generates oxygen on a seawater-exposed surface of a structure to be exposed to seawater to prevent attachment of marine organisms to the seawater-exposed surface of the structure comprises: an anode forming member bonded to the seawater-exposed surface of the structure to be exposed to seawater via an insulating adhesive; an electrochemically active and stable electrical catalyst coated on the anode forming member; a conductive member disposed so as to be wetted with seawater; a
Inagaki Shuichi
Kajiyama Takahiro
Nakashima Shoji
Oba Tadahiko
Sakurada Shigeru
Bell Bruce F.
Foley & Lardner
Kabushiki Kaisha Toshiba
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