Electrochemical technique adapted for subsea raw water injection
EctoSys, a new electrochemical method of water treatment, has several potential applications in the offshore oil industry. It is currently part of a system under development in Norway for the subsea injection of raw seawater. It can also be used topside for cleaning process water on offshore production facilities and ballast water on offshore vessels.
EctoSys, RWO’s electrochemical method of water treatment (at rear), incorporated into the Clean Ballast! system.
EctoSys was originally developed in Sweden by Permascand, part of the Akzo Nobel group, but it was acquired recently by Germany’s RWO GmbH Marine Water Technology, a subsidiary of the Veolia Water Solutions & Technologies group. The Swedish office of RWO plays a leading role in developing and marketing EctoSys.
The technique involves treating water electrochemically through use of electrodes with a high-oxygen over potential. The special electrode type makes it possible to electrolyze the water so that different short-lived highly reactive disinfectants, such as hydroxyl radicals, are produced, which inactivate micro-organisms and bacteria. No chemicals are added to the water prior to treatment.
This advanced system makes it possible to control whether residual disinfection effects will remain or not, says Lars Nyman, business manager of EctoSys. Thus, it can be used in a range of applications such as aquaculture, where no residual effects are wanted, or ballast water and injection water, where some residual effects are advantageous.
The electrolytic process takes place within the pipe. A contaminated water stream is fed to the electrolytic cell, which contains pairs of electrodes angled perpendicularly to the flow. A direct current is passed between the electrodes. The system can treat up to 500 cu m/hr (17,657 cu ft/hr) in a single module, and several modules can be connected in parallel to increase the overall capacity.
EctoSys is very compact, Nyman says. Each module has a footprint of less than 1 sq m (10.7 sq ft) and is accompanied by a rectifier occupying the same space. Module and rectifier weigh a combined 300-500 kg (661-1,102 lb) and require a power supply of 5-8 kW per 500 cu m (17,657 cu ft) for seawater electrolysis.
EctoSys is integrated into RWO’s new ballast water treatment system CleanBallast! for use on ships, of which a full-scale version is in operation in Bremerhaven harbor, northern Germany. It has also been incorporated into a subsea water injection and treatment system developed by Well Processing AS in Norway. The system reduces solids content and sterilizes the seawater prior to injection into a reservoir. EctoSys works especially well in saltwater, which is one reason why it is suitable for raw seawater injection.
For more information contact Lars Nyman, RWO GmbH Marine Water Technology. Tel +46 691 66 35 80, fax +46 691 66 35,[email protected], www.rwo.de
