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Introduction to Anti-Biofouling Electrodes
Seawater is used for a number of purposes in a ships engine room, with the most important function being to supply such components as the main oil and water coolers through a system of pipework, using seawater cooling pumps.
One of the problems associated with the sea water cooling systems is biofouling of the internal surfaces that is normally taken care of by the mixing and injection of chemicals to the seawater inlet chests. However this is a very laborious procedure, requiring the storage and handling of hazardous containers of chemicals.
An innovative system using electrolysis has been developed to produce sodium chlorite, a known anti-biofouling agent, which can be pumped directly into the shipside sea water inlet sea chest.
This is a marine article on the use of titanium electrodes in the production of sodium chlorite, and we begin with an overview of an engine room cooling system using seawater from the shipside inlet chests, being circulated through the various components by the cooling water pumps.
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Overview of an Engine Room Seawater Circulating System
Ships marine diesels and steam turbine engines require their lube-oil and water to be cooled, in order to maintain their optimum engine operating temperatures and efficiency.
This is achieved by circulating seawater around various coolers, steam condensers and freshwater generators by dedicated seawater cooling pumps.
To keep all these components operating efficiently, the accumulation of biofouling consisting of slime, mussels, and barnacles, must be eliminated. (Single or multiple biofoulers are capable of impeding the flow of seawater through the seawater cooler tubes, plates, and system piping.)
This is achieved by the direct injection of hypochlorite that is produced by an electrochlorination unit into the seawater inlet sea chests as described in the next section.
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Electrochlorination Using Anti Biofouling Titanium Electrodes
A typical modern electrochlorination plant is a self-contained unit usually mounted on a steel skid ready for installation in an engine room.
It consists of a plate electrolyzer, with the main unit containing the anode and cathode plate titanium electrodes. The anode electrodes are coated with a catalyst containing mixed metal oxides, essential for the production of chlorine by hydrolysis.
The electrical power to the titanium electrodes is controlled by electrical panels, AC/DC transformer/rectifiers, and current regulators. The mechanical equipment includes metering and injection pumps, sampling elements, piping, valves, and the hypochlorite storage vessel.
I have illustrated these components in a sketch of the unit in the image section at the end of the article.
In operation, the electrochlorinator cell is supplied with seawater from the engine sea water cooling system that passes through the titanium anode and cathode electrodes which have a DC current supplied. This promotes the action of electrolysis of the sodium chloride contained in seawater, forming hypochlorous ions through hydrolysis.
These hypochlorous ions react with the bromides that are also contained in seawater to produce hypochlorite. This is then injected into the sea water cooling water pumps shipside seawater suction chest using a metering pump, which can be adjusted to alter the regular or intermittent dosing of the seawater intake.
On the ships cooling water discharge pipe, a small bore bleed-off pipe supplies the electrochlorinators skid with sea water which is constantly monitored, and the dose of hypochlorite adjusted automatically as required.
1. cathelco - electrochlorination of seawater
2. c-a-m - descriptions and illustrations of electrochlorination units
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Advantages of Using Anti biofouling Titanium Electrodes Technology on Ships
The advantages of using an anti-biofouling titanium electrodes technology system, as opposed to bulk chemical treatment in a ship’s engine room sea water cooling system are noted below:
- Effective against all biofouling, injection pumps can deliver continuous or pulse dosing, directly to the shipside seawater suction chest.
- Eliminates the need to store and handle containers of hazardous chlorine chemicals.
- Suitable for disinfection of fresh water generators produced drinking water against bacteria, as well as biofouling of the operating components surfaces.
- Very little environmental impact uses seawater to produce the hypochlorite.
- Accurately controls and monitors amount of hypochlorite injected by sampling seawater discharge conditions.
- Produces various amounts of sodium hypochlorite that is one of the most effective oxidizing biocides used to eliminate all types of marine growth caused by the constant use of sea water.
- The modern ectrochlorination skid is supplied as a complete package, ready to install, and which connects to the ship's engine room piping and electrical supplies.
Reference Web: cathelco - benefits of using an electrochlorination plant on ships