Ballast water treatment: The third way

It is likely that the IMO Ballast Water Management Convention will come into force this year or early 2016. There will be many a furrowed brow as owners, operators and agents decide exactly which system is best for their fleet.

Before Coldharbour Marine designed its ballast water treatment (BMT) system, chief executive officer Andrew Marshal ordered an audit of customers’ views. “Customers told us they were thinking beyond installation costs but were also working to identify the best option for their particular fleet,” says Marshall. “They were worried about staff training, about system reliability and functionality, about running costs and about the impact of a newly installed system on the rest of their vessel especially when managing port operations.”

Marshall believes that there is no simple solution to preventing foreign organisms being transported thousands of miles in ballast water to contaminate virgin environments. As vessels vary in size and capacity, so too does the space available for a new installation. The waters that ships cross, and in which they collect or discharge ballast water, also vary. “One size does not, and never can, fit everything,” says Marshall.

In discussions with customers Coldharbour identified 14 criteria that an ideal BWT system must achieve:

• No disruption to normal operations, especially ballasting and de-ballasting
• Allow for gravity ballasting and de-ballasting
• No need for upgrades to ballast pumps or pipes
• No ballast water filtration requirement
• No need for upgrades to on-board power generation capacity
• A small footprint
• Low running costs
• Robust, reliable and suitable for life on-board
• No specialist maintenance requirement
• Simple to use
• Safe for crew and the environment, particularly in the event of accidental misuse
• Ideally not use chemicals or active substances (IMO G8 approval preferred)
• Able to deal with any regrowth in the ballast tanks
• Future proof and able to respond to tightening regulations worldwide

Marshall explains that Coldharbour Marine’s BWT system was based upon these criteria. The company has a long history in the manufacture and supply of inert gas generators producing super-clean, very low oxygen inert gases used to blanket cargoes in tankers, LNG and LPG carriers and floating production, storage and off-loading vessels (FPSOs). Coldharbour decided to focus on those vessels to design and develop an in-tank solution to serve their needs. The company’s design engineers then set down a set of challenges that their system had to overcome.

Design challenge

First, the treatment had to cope with the high ballast water volumes and flow rates depended upon by tanker operators, with a minimum of 6,000–8,000m/hr of water being pumped and volumes of 100,000m3 or greater being used. Those are big quantites for systems relying on filtration, and equipment which would cause pressure drops or impede ballasting must be avoided. Large volumes also bring up issues of regrowth on longer voyages.

Second, a system should not demand ballast water management at port - the critical time for any ship operator. With personnel busy managing ballasting and deballasting, taking on stores, transferring cargo and liaising with Customs, avoiding the need to manage ballast during port time has obvious appeal.

The final demand was the need to minimise the footprint of any equipment that needed to be installed. With its design challenges established, Coldharbour Marine developed its system using an inert gas generator linked to simple GLD (gas lift diffusion) units mounted inside ballast tanks.

The GLDs use natural fluid dynamics to stir inert gasses through the ballast water and ensure thorough treatment. Marshall explains that the inert gases reduce the oxygen content of the ballast water (hypoxia), while the elevated CO2 levels in the inert gas reduce its pH (hypercapnia). Gasses leaving the GLD device generate an ultrasonic frequency which physically disrupts the cell walls of any organism living in the water, while gas micro-bubbles amplify and enhance these in-tank ultrasonics. Organisms are thus killed in three ways.

Marshall believes the Coldharbour system delivers a number of benefits. One is simplicity. The inert gas generator has no burner cone, demister pads or steam injector while the treatment itself has no need for filters, membranes, active substances or electrical connections. There are no filters to get blocked and pump sizes and flow rates are as irrelevant.

Doubling up

The system can be operated when the ship is underway, meaning staff can focus on other tasks when in port. The units inside the ballast tanks require no power, giving the overall system a small footprint. The inert gas generator also doubles up to produce gasses for blanketing cargo. “Being based upon well understood marine inert gas technology and with a minimum of moving parts, the Coldharbour system requires minimal maintenance or staff training,” adds Marshall.

Coldharbour’s system was IMO certified under the UK Maritime and Coastguard Agency, supervised by Lloyds Register. For testing, the system was retrofitted onto a VLCC during a normal dry-docking period. Marshall notes that in the 24 months since installation, the operator has reported no disruption to normal ballasting and deballasting. The system proved immune to changes in water salinity and temperature, no additional power generation was needed and the ballast water was cleaned in voyage when power demands were a minimum. There were no problems with regrowth since the organisms had been killed in the tanks, meaning it was always safe to deballast.

The GLD system also handled silts, sediments and turbid water as easily as clean water, says Marshall. And since there are no active ingredients nor chemicals involved, there was no damage nor corrosion in the ballast tanks themselves - Jotun and International Paints independently verified reduced ballast tank corrosion tests, bringing savings in tank repair costs and vessel downtime.

Despite the apparent effectiveness of the system, Marshall does not expect the Coldharbour system to approve to all operators. “The in-tank system is not the cheapest option,” he admits. “It works very well and offers particular advantages to tanker owners operating large vessels with significant ballast flows and water volumes.

“Owners of vessels using smaller volumes of ballast should balance the cost savings gained from specifying an alternative system against the difficulties of managing a power-hungry system relying on UV, active agents, filters and maintenance. One size does not fit all.”

• See The Motorship's February issue, out now, for an in-depth report on ballast water treatment systems. To subscribe, click here.