Fouling is the undesired growth of micro organisms like bacterial slimes, algae, mussels, barnacles etc. within water systems, i.e. heat exchangers, condensers, cooling towers, piping, filters and storage tanks. The high temperatures and continuous supply of nutrition at water inlets results in a rapid accession of fouling. The fouling contaminates the water system resulting in:
- Reduced heat transfer in heat exchangers or condensers
- Increased pressure drop in pipelines leading to a higher pump load
- Inevitable system cleaning which is usually inconvenient and expensive
- Evolution of corrosive gasses like CO2 or H2S
For these reasons anti fouling treatment is deemed necessary in industrial cooling water and other service water systems.
For anti fouling a number of methods are available. Chlorine dosing is the most well-known method which is accompanied with the following problems:
- Special safety measures for storage and transport of chlorine gas
- Often complicated dosing installations
- Regular maintenance necessary
The Vandervelde Protection anti-fouling system is an effective method without these disadvantages. The system is based on the same principle as the well-known anti fouling paints.
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How it works
The Vandervelde Protection anti-fouling system is based on the controlled continuous dissolution of copper located in the water intake of the system. With this system metallic cupper is oxidised to cupro ions (Cu+). These cupro ions dissolve and create a temporary toxic medium for fouling, because they hinder the growth and development of micro organisms. Therefore cupro ions are effective in anti fouling. The cupro ions are also unstable. They rapidly react with oxygen dissolved in water to cupper(I)oxides and oxidise in water spontaneously further to the inert and non-toxic cupri-oxides or cupper(II)oxides. The cupri-oxides are less soluble and precipitate. Research measurements in a fish pool with the cupper-sensitive trout have proven that there were no hazardous effects.
The concentration of dissolved cupper is relatively small, circa 0,01 ppm, which is effective as anti fouling. This gives e.g. for a cooling water flow of 600 m3/h a consumption rate of 75 – 90 kg cupper per year.
System design and description
The system consists of the following components:
- Electrical control panel (transformer/rectifier)
- Terminal box
- Anode/cathode unit
The anode/cathode unit can be designed and built to suit any particular physical circumstance. The system is suitable for use in fresh, brackish and seawater cooling devices and is often used on a great number of suction dredgers operating all over the world and on off-shore platforms in the North Sea and the Middle East. These anti fouling systems can be used on the following structures:
JETTIES – DRILLING PLATFORMS – OIL RIGS – POWERSTATIONS REFINERIES – CHEMICAL PLANTS – PIPELINES – STORAGE TANKS – CONDENSORS – COOLERS – COOLING TOWERS – FILTERS – DREDGERS
One of the most commonly used units is fitted inside a caisson (stilling tube) and attached underneath a submersed pump. The screen type unit is yet another design which has been specially developed for use in the water inlet into the chest of a ship or dredger.
An anode/cathode unit containing copper anodes (some units are fitted with copper and aluminium anodes) is placed in the intake which ensures that all water entering a system will have to pass through it. The possibility of “secondary infection” in the water being treated must be avoided. The copper (and aluminium) anodes will slowly dissolve as a result of the DC current passing through them. This current may vary in capacity during pump running or pump standby conditions and water flow intake rates.
Since the anodes gradually dissolve in the passing water stream, the anode/cathode unit will need to be replaced eventually. The anodes are dissolved at levels measured in micrograms per litre, which enables lifetimes of up to 5 years. However, most units are designed for a lifetime to coincide with standard service and overhaul periods.
Maintenance and control
After installation, the system is free of maintenance. The system can simply be monitored by the weekly recording of the ammeter on the rectifier unit.
Where fire fighting pumps are concerned the system will be based on an operation time of only 30 – 60 minutes/week at maximum output. Where service water pumps and/or cooling systems are concerned the systems will be calculated for operation at full load during the total lifetime.
|screen protection||All steel in the direct vicinity of and in electrical contact with the anode/cathode unit will also be automatically protected with CP|
|no danger of pollution||The system is quite safe since the dissolved copper is either precipitated or where it remains soluble it is rapidly diluted to a safe level.|
This shows that the Vandervelde Protection anti-fouling system efficiently and effectively deals with fouling.