OCTOBER 15, 2014 — A breakthrough ballast water treatment system developed by Danish company Bawat A/S is soon to enter the market. It has successfully completed all IMO-mandated tests, as verified by DNV GL, and is expected to soon receive final certification from the Danish Maritime Authority. It will then be submitted for U.S. Coast Guard AMS certification and full U.S. testing and certification.
What's different about the Bawat system, which is aimed primarily at the tanker and bulk carrier markets, is that it is an in-tank recirculation system that can treat ballast water at sea, saving time and money compared to in-line systems where treatment must be carried out in port. Instead of filters, UV radiation or chemicals, the Bawat system uses deoxygenation and pasteurization to bring the concentration of living organisms down to well below the regulation requirements.
Bawat is a technology company and systems integrator and the system uses existing, off the shelf, marine components, such as plate heat exchangers, from suppliers with good track records and service locations in various locations worldwide supports.
"Operating the system is simple," says Bawat CEO Kim Diederichsen, "and easy for the crew to handle onboard the vessel, while there is hardly any maintenance."
The system employs two distinct process principles in a circulation procedure: De-oxygenation and pasteurization. The ballast water (BW) is circulated in a circuit from the top of the BW tank, treated and re-introduced into the tank through jet nozzles close to the tank bottom.
The de-oxygenation process effectively eradicates zooplankton and the pasteurization process reduces phytoplankton and bacteria concentrations to levels below the IMO D2 requirement. As an extra benefit the deoxygenation of the BW causes a substantial reduction in BW tank corrosion.
The process principles are outlined in the figure below:
Treatment is initiated when the ship has left the ballasting position and is on voyage.
BW is pumped from just below the water surface in the BW tank through the Pasteurizing Unit.
In the Pasteurizing Unit the BW is heated to a specified temperature (typically 72 °C). In the Retention Section it is held at this temperature for a specified period of time (typically 1 min.).
The heating takes place in one or two plate heat exchangers and the heat is provided by surplus heat sources – e.g. main engine jacket cooling water or exhaust heat economizers through steam or thermal oil systems.
In the regeneration section of the Pasteurizing Unit, the out-going water is preheating the in-coming water
After pasteurization, nitrogen under pressure is injected into the water flow. The nitrogen is release as mini bubbles at the BW Tank bottom and through the surface of the bubbles the dissolved oxygen in the BW is replaced by nitrogen.
The circulation is performed a specified number of times the exact number depending on the BW Tank’s construction (typically 4 to 8 times).
No further treatment is necessary before re-ballasting.
Bawat's system offers several technical and operational advantages.
Cargo and ballast operation are as usual. The system treats the ballast water after cargo operations are completed and does not impact or disrupt activity while the vessel is in port, nor does it alter the vessels existing ballasting or cargo handling equipment or procedures.The Bawat BWT system simply requires 36-96 hours of available treatment time after the vessel has left port.
With the Bawat system, gravity assisted ballast operations are possible – often important in the large vessel segments. This addresses energy costs, and more importantly, the limit of maximum available power capacity during cargo operations. Bawat is a non-additional power consumption technology allowing for partial gravity ballasting.
Many vessels have waste or excess energy available from main engine cooling water and exhaust gases. The Bawat’s technology is the only BWT technology based on the utilization of excess heat sources within the treatment process while using very limited electrical power solely to run the system’s circulation pump. The low overall energy consumption is considered a main competitive advantage compared to the competition.
The Bawat system offers low installation and operating costs, with no upgrade of ballast water pumps, pipes or power generators being necessary.
With non-skidded components Bawat BWTS is flexible for implementation in almost any type and size engine or pump room and is well suited to retrofit applications.
Examples of the estimated total foot print required are
Bulk Carrier: 25,000 DWT with 10,000 cu.m BW: capacity: 6 sq.m
Oil Tanker: 50,000 DWT with 20,000 cu m BW: capacity: 6 sq.m
Bulk Carrier: 135,000 DWT with 55,000 cu.m BW: capacity: 12 sq.m