BWT simplified for versatility and retrofitting

The C2E disinfection unit The C2E disinfection unit
Industry Database

Norwegian ballast water treatment (BWT) company OceanSaver says that its Mark II system offers high-end technology to different sizes and types of vessels, while saving energy and simplifying retrofitting.

As the IMO BWT requirements enter into force the industry expects demand to be strong, both from newbuildings and from retrofit orders. When this will be is still not certain; the required number of IMO member states which have ratified the Convention, representing a percentage of world tonnage, has still not been met. But the industry anticipates that this will happen sooner rather than later, and this will cause a surge in demand, as recently-built ships will be forced to install suitable systems. The class societies have been recommending for the past two years or so that builders make provision in newbuildings for fitting BWT equipment, but the desire to cut costs, to maximise cargo space, and the age of many basic designs mean that this has not always been fully considered at the build stage.

As outlined in this issue by Malin Marine Consultants, retrofitting a BWT system is not necessarily a straightforward matter. As well as finding space in the vessel for the equipment itself, considerable rearrangement of existing pipework, and addition of new pipework, is likely to be required. Also, pumping capacity may have to be increased and this in turn may demand an upgrade to electrical generating systems.

Such was the thinking behind OceanSaver’s development of its next-generation system, which it has named the ‘Mark II’. The existing type-approved Mark I system is still available, and is still being sold and delivered – 22 systems for tankers were contracted in 2010 alone - but the Mark II aims to both simplify the installation and reduce energy requirements with minimal compromise on performance.

The Mark II BWT system is a specifically tailored version of the Mark I model, but with the most 'energy demanding' features of the original removed. The Mark II model is able to do this by introducing better performing filtration technology.

Sales and marketing director Tor Atle Eiken said: "we are sharpening the already proven OceanSaver technology with our new Mark II ballast water treatment system, this will widen our core market segments, reduce installation time and complexity for retrofit and newbuilding projects and at the same time continue to be a high quality supplier".

The company’s systems were previously targeted at the larger sized vessel segment, particularly tankers, but it believes the introduction of the Mark II technology opens up the medium sized newbuild market, as well as retrofits, thanks to reduced installation time and complexity.

In fact it is the retrofit market that OceanSaver will provide increased focus, in addition to the fairly stable newbuilding market. The major difference between the two generations of system is that the Mark II is able to dispense with the Mark I’s cavitation units, so a significant amount of piping is not needed. In addition, no further treatment is required at the de-ballasting stage, again reducing installation work, space requirement, complexity and cost. The energy required for the complete system and related equipment is said to be some 50% less for the Mark II than for the first generation system, which Oceansaver estimates will, in the majority of installations, avoid having to upgrade the ballast pumps.

The company says that the technology behind the Mark II has been the result of many years of development at its own laboratories; it claims to be one of the few, if not the only, market players with its own facilities dedicated to BWT development and testing. The concept is based on the technology found in Mark I which already has full type approval. However, the new technology has undergone a separate testing programme, and full type approval for the Mark II is anticipated soon. The system is also suitable (and, in the case of the Mark I, approved) for installations in gas hazardous areas, a prerequisite for tanker applications.

The Mark II is basically a two-step system. Ballast water is pumped onboard by the ballast pumps and filtered by a mechanical, fully automatic back-flushing filter. The filter is self cleaning with a 40μm screen. The filter is used at uptake and will when in use, automatically backflush all organic material back to the water at the inlet, where it was taken up by the ballast pumps.

The next step, disinfection, injects an in-line produced disinfectant (C2E) into the water. The disinfectant is produced onboard in a water activation unit, using  an electro-dialytic process. Only about 1.6% of the total ballast water flow is fed through the C2E unit and thereafter injected into the main flow. The C2E unit, which has a very small footprint, can be located remotely from the ballast line, requiring only small-diameter piping and an electrical supply. The electrodialytic process can work at very low salinity level, but in cases where vessels are operating in brackish or low salinity waters (e.g. river water) the aft peak tank (or any other suitable tank) is used as a storage tank for normal seawater to feed the C2E unit.

A further stage, optional in the Mark II isystem, is nitrogen supersaturation. This is carried out by patented OceanSaver technology, and is not actually part of the ballast treatment process, but minimises corrosion in the ballast system. It offers ship owners the potential for reduced vessel maintenance costs through the improved corrosion performance of ballast tanks and coatings and is particularly suited to newbuildings or high specification, specialist vessels.  The nitrogen gas is produced onboard by means of a nitrogen generator driven by an air compressor. Both the superaturation unit and the gas generator can, like the C2E unit, be installed remotely from the ballast line - in any suitable area onboard – and connected with small-diameter piping and power cable. The compressor can serve as a working air compressor, and the nitrogen generator may be used for other application when required; ships with suitable air supply and nitrogen systems can use these for the supersaturation stage.

The OceanSaver ballast water treatment system has demonstrated compliance with the intentions of the IMO Performance Standard for Protective Coatings (PSPC).

"The Mark II system is extremely compact and flexible. Standard systems are available for flow rates from 2 x 500m3/h up to 2 x 3.000m3/h and customised systems unlimited in capacities," says Eiken.

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