Waste fuel recovery - an industry standard overnight?

May 01 2014

Alfa Laval is seeing increasing take up of its PureDry separator system. Orders have now been placed by leading shipowners in nearly every vessel category, including the tanker segment.

Since 2008, MARPOL rule MEPC.1/Circ.642 has allowed the recovery and reuse of the heavy fuel oil (HFO) percentage of waste oil as engine fuel. Thus far, however, only Alfa Laval’s PureDry system has been developed to take advantage of this waste oil possibility, the company said.

This separator lets vessels recover nearly all of their fuel oil losses, which range from 0.5 to 2% of their total fuel consumption.

“In general, I can only think of this as an excellent idea,” said Jacob Norrby, newbuilding project manager for Stena. “We recover something that is normally wasted, and that we sometimes have to add energy to in order to burn it.”

The Gothenburg-based company is installing the systems on board the Stena Weco 50,000 dwt MR series of Eco tanker newbuildings. In general, the larger the installed power on a vessel, the more savings can be made by using PureDry, Alfa Laval explained.

Stena is just one of the leading shipping companies who together have ordered around 120 PureDry systems for their newbuildings.

In the tanker sector, joining Stena in ordering systems, is Frontline, while other owners  include Carnival Corp, MSC, Norwegian Cruise Line and Wallenius. All of their vessel designs were modified by the shipyard to segregate fuel and lube oil waste. This marked a paradigm shift, as vessel design changes were made to accommodate the new separation technology, Alfa Laval said.

Previous attempts with traditional separators have marginally reduced waste volumes, but process water and discharge losses have allowed a large amount of waterlogged, fuelcontaining waste to remain. “The treatment and disposal aspect was normal, in that it’s been addressed over the years,” said JS Narayanan, manager newbuilding projects for Frontline. Naranayan had expressed surprise to learn of a solution that gets fuel out of the sludge, rather than simply reducing its volume.

“This is new,” he said, “the recovery of fuel from what was previously thrown out.”

 “Knowing that there’s 1-2% fuel (losses) in the sludge, it’s not surprising that this application should develop,” said Norrby. “But what’s encouraging is that we see PureDry as a quality product. It’s engineered well, and the technology Alfa Laval has built on is good.”

Breakthrough technology

PureDry is a hybrid technology: a high-speed disc-type centrifugal separator with a solid bowl, yet one that is also self-cleaning.

As the name suggests, PureDry requires no process water and leaves no liquid in the solid waste. Nor does it have a bowl aperture, or hydraulics. Norrby explained; “The separator looks fairly simple, which is some of the beauty of it.” Alfa Laval said that the only major moving parts are an outer bowl and a separator insert, which rotate at slightly different speeds. Attached to the insert is the XCavator, a patented spiral device that transports the separated, super-dry solids into a container at PureDry’s base.

Yet another departure from traditional selfcleaning separators claimed by the company is the way that maintenance is performed.

PureDry relies on maintenance and service by exchange, whereby the separator insert and XCavator are replaced at fixed intervals. “This is attractive, because the crew on board are not high-tech experts,” said Narayanan. “The complete renewal of the rotating assembly makes maintenance simpler and easier, so we don’t expect much workload on the crew.” The systems are skid mounted for ease of installation.

By using PureDry, virtually all of a vessel’s fuel oil losses can be recovered to ISO 8217 quality. The elimination of this energy leak has a strong environmental implication, but above all it makes for a bullet proof business case, the company claimed. Norrby said; “These two things go hand in hand. This is not a cheap investment, so it’s nothing you just run out and buy. You have to support the purchase.”

For many shipowners, there is also a strong business case in minimising the sludge volumes, which PureDry is claimed to reduce by 99%. PureDry leaves just 5-10 kg per day of non-pumpable, super-dry solids, which are landed simply as dry waste. All of the water, with an oil content of around 100 ppm, is passed on to the bilge water system. This negates the necessity of offloading waste to a barge.

Alfa Laval said that if there is anything to complicate the PureDry business case, it is thefact that modifications in  vessel design are needed to achieve all the benefits. On the one hand, PureDry makes it possible to reduce sludge tank holding capacities by at least 50% under current legislation. But to recover fuel in addition to reducing waste, the streams of waste fuel oil and waste lube oil must be segregated.

Segregating the tanks, rather than demonstrating PureDry’s effectiveness, has thus far been the main hurdle, the company said. For a newbuildings, the procedure is easier, since the changes can be made on the drawing board. Yet for shipyards unfamiliar with waste fuel recovery, even this has led to some discussion. “The product is unique, so there was no challenge in selecting it,” said Frontline’s Narayanan.

“The challenge was making the shipyard understand the simplicity of it. But once it has been done with one shipyard, others can simply follow.” As shipyards grow more familiar with the application and with PureDry itself, smoother integration can be expected.

With the savings documented thus far, it is hardly surprising that there is talk of waste fuel recovery as a new standard, Alfa Laval said.

Leaving the last words with the tanker owners, Fronline’s Narayanan said; “We welcome anything that can lead to savings in our fuel use and the reduction of emissions. We welcome the new technology.”

“If we expect to recoup 1% of the bunker consumption, that’s on the margins of what is possible to measure. But we believe in the technology. And we expect it to work as intended in regard to performance and maintenance,” said Stena’s Norrby.

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