Economical heavy fuel oil finding its way into the tugboat industry

Crowley Resolve is a new 9,280-hp ATB. Crowley estimates that it cost several million dollars in additional construction costs to make the vessel capable of burning heavy fuel oil. (Courtesy Crowley Maritime)

My theory about bunker fuel is that the stuff is misnamed. Modern fuels have nothing to do with bunkers. The phrase bunker fuel, like many other phrases and words in the maritime world, harkens back to the days when coal was stored in compartments called bunkers far below the main deck.

A large steamship in the previous century might be built with a half dozen or more coal bunkers, typically located near where the coal was needed but with access to the ship’s exterior (or the main deck) for ease of loading. The infamous ocean liner Titanic, for example, carried up to 8,000 tons of coal in six separate coal bunkers.

What this has to do with the world of tugboats is that some of the largest new tugs in this country and elsewhere are beginning to burn what is known as heavy fuel oil (HFO) — a thick, black liquid that is still, annoyingly, often referred to as bunker fuel or bunker oil. These tugs, and large ships, are sometimes said to be in port for bunkers and those in the business of conveying fuel to large ships by barge are said to be in the bunkering business.

Whatever it is called, this heavy fuel is nasty stuff. Its viscosity is such that it becomes thick like tar in cooler temperatures. Thus, it is almost always kept heated, right up to the instant it is injected into the cylinders of a diesel engine or sprayed into an oil burner. It smells like tar at any temperature. And, much more than conventional diesel fuel, it makes a heck of a mess if it gets loose.

The good part about HFO is that it can be bought for considerably less than diesel fuel — anywhere from a third to half the price. For a tugboat that might have tankage for up to 150,000 gallons of fuel, that kind of savings can make a huge difference.

Unfortunately for tugboat operators everywhere, not everyone can switch to bunker fuel as a way to avoid painful fuel prices. Before it can be atomized and sprayed into the cylinders of a big diesel engine, the stuff needs to be heated, centrifuged, filtered, segregated and possibly chemically altered with additives. The complications of those processes, plus other related nuances of fuel management, make it impossible for all but the largest of tugboats to make the switch.

That’s too bad, because the cost of fuel is increasingly becoming a cause of bottom line shrinkage for anyone whose business depends on around-the-clock operation of large commercial engines. When a tank truck loaded with 10,000 gallons of diesel fuel leaves behind an invoice for $25,000 to $30,000 after emptying its cargo into a typical harbor tug, you know that the people who write the checks are looking around for an alternative fuel source. Unfortunately for most of them, there is no alternative. That good old bunker fuel, also known as bunker C or No. 6 fuel oil, remains the exclusive domain of big ships and workboats large enough to house the required fuel management infrastructure.

In the past year the tugboat industry has observed the introduction of a new generation of articulated tug-barge units (ATBs) large enough to make use of heavy fuel, and plenty more are under construction. Among the most notable are ATB Freeport (12,000 hp), introduced by U.S. Shipping Partners; and Crowley Maritime’s ATB Resolve (9,280 hp), ATB Integrity and ATB Commitment (next to be introduced). All of them are set up with Wartsila HFO-compatible engines with all the associated tankage and equipment — not to mention the extra engineer required for the crew just because of fuel-management demands.

“With the price of fuel just going up and up, we came to the conclusion that we had no choice but to switch to the less expensive heavy fuels,” said Ed Schlueter, Crowley vice president of vessel management services. While Crowley has reported that the cost of its newest ATBs is getting close to $100 million for both tug and barge, it is estimated that these construction costs might include several million extra just for design features and equipment related to HFO use.

Although the four-stroke, medium-speed Wartsila engines in these tugs can burn both diesel fuel and HFO, the two fuels are distinctly different. Diesel fuel, like gasoline, kerosene and No. 2 heating oil, are known as distillates — products of distillation in the refining process. Heavy fuel, by contrast, is known as a residual oil — a product left over after all the more valuable products have been distilled out of the crude oil.

Much of the difficulty in using HFO involves its viscosity. It is notoriously thick — so much so that if it gets below about 86 F it simply won’t pour through a funnel. At a slightly lower temperature, say 77 F, the viscosity is described as being somewhere between corn syrup and pitch.

To make this fuel fluid enough to be pumped around the engine room and to flow through a diesel engine injector, it is normally heated to 150 F or higher. Diesel fuel, by contrast, can be easily pumped around the boat at any temperature, stored almost anywhere, and fed into the engines without complications (with a few well-known exceptions).

There are different grades of HFO, and even within the same grade, each batch of the fuel is likely to have a different chemical composition, which is one reason why those individual batches must be stored in separate tanks. Grades of HFO are distinguished by the amount of marine diesel oil (MDO) mixed in. The HFO most commonly used — known as IFO 380 (IFO is intermediate fuel oil) — is a mix of 88 percent residual oil and 12 percent distillate (usually a diesel-type oil). By comparison, IFO 180 is composed of 98 percent residual oil and only 2 percent distillate.

While large oceangoing ships often get fuel delivered from barges tied up alongside while they are at anchor, smaller vessels like tugs can also get their HFO from pipelines at the same refineries or oil terminals where they might be loading or discharging product. Crowley’s new ATBs Resolve and Integrity have been delivering cargoes to chemical plants, however, so most of their refueling has been done with those possibly misnamed bunkering barges. Commitment will also be involved in the chemical trade, according to Crowley.

The ATB Freeport is powered by a four-stroke, medium-speed Wartsila HFO-compatible engine. Vessels using HFO require special heated tanks for storing and processing fuel. Despite the added cost of equipment and processing, net savings from HFO can run to 40 percent. (Courtesy U.S. Shipping Partners)

When used on land, heavy fuel is more likely to be called No. 4, 5 or 6 oil, and it is just as likely to be delivered to industrial sites and electric generating stations by tank truck or rail car. A quick check of spot fuel prices in New York on the last day of 2007 showed diesel fuel priced at $2.66 a gallon and residual fuel oil priced at $1.79 a gallon. The international publication Bunkerworld reported that in 2007 the price of marine distillate fuels in global bunkering hubs was typically 1.7 to 1.8 times higher than the price of IFO 380.

A big issue with the use of HFO is the extra tankage required to store and process the fuel, according to Robert Hill of Ocean Tug & Barge Engineering, naval architect for many ATBs under construction.

“These ATBs have more tankage to begin with because of what they do, but the HFO boats need even more tanks for a variety of reasons,” said Hill.

Among the 12 tanks included in the design of a 12,000-hp ATB currently under construction at Bender Shipbuilding in Alabama, said Hill, might be tanks for storing fuel from different sources, day tanks, settling tanks, centrifuge tanks and mixing tanks. “In addition,” he said, “you are going to have sludge tanks to handle accumulated sludge that settles out, additive tanks, and larger dirty oil tanks. Then you have to have sufficient tanks for distillate fuel to run your regular diesel engines on board and to provide a get-home fuel source in case something goes wrong with the complex HFO system.”

Tanks aboard ATBs used for storing and processing HFO fuel are heated with in-tank coils or plates, all containing a thermal fluid heated either by electricity or by on-board burners.

And to make the design process all the more complicated, according to Hill, most of the equipment involving process heat has to be segregated from the engine room. “Your viscosity control plant, your actual heaters and all the heated tanks have to be separate from the engine room. That means the tugboat needs a heck of a lot more space. For a smaller vessel like a harbor tug this would be impossible,” said Hill.

Because of all the complications of heavy fuel, a large portion of the savings from the lower price of HFO — perhaps a third or more — is soaked up by construction and operating costs related to its use.

“Still,” said Hill, “If you are burning something like 12,000 gallons of fuel a day, and you can manage a net savings of 30 to 40 percent on the cost of HFO over diesel, that amounts to a powerful incentive to go with the HFO system.”

Crowley Maritime’s Resolve and Integrity are the first of a long line of Crowley ATBs being built to burn both heavy fuel and diesel fuel. Crowley increased the size of these ATBs by eight feet — from 127 feet to 135 feet — to accommodate this new fuel. Resolve has tankage for 117,000 gallons of HFO and 42,000 gallons of diesel oil.
Currently three American companies — Crowley, U.S. Shipping Partners and Overseas Shipholding Group (OSG) — are building large barge-handling tugs with articulated coupling systems and heavy-fuel engines.

These tugs are all set up to run on both HFO and MDO with different sizes of Wartsila main engines. Other manufacturers of HFO-compatible, medium-speed diesel engines include MaK (Caterpillar) and MAN.

Switching over to diesel fuel in coastwise and in-port situations helps to keep a vessel within the realm of EPA Tier II compliance, even though such a switchover is not yet officially required in most operating areas.

Crowley’s new ATBs have tankage for 42,000 gallons of diesel fuel, which also translates into plenty of get-home fuel should the need arise.

“There are so many backup systems and redundancies that it would be an unlikely development, but if everything were to fail, you could still switch over to MDO and you’ve got plenty of fuel to get you home,” said Schlueter.

Crowley’s tugs switch over to diesel fuel any time they are approaching port or operating near coastal areas, according to Schlueter.

Making the switch from HFO to diesel could be problematic considering the dramatic differences in temperature and viscosity of the two fuels, but nowadays the switchover is managed by computers with engineers keeping track of a few switches and valves along with their computer screens.

“Years ago, it was a complex process to switch from a heavy fuel to a distillate fuel, but with today’s technology, it is all managed quite easily by computers and automatic monitoring systems,” said Schlueter.

Of course the world of bunker fuel is much bigger than the realm of a small number of tugs and workboats that might be appropriate users. Not only are there tens of thousands of large heavy-fuel using ships, but each ship has a power plant that dwarfs that of a tugboat, even a hefty ATB.

One of the largest engines of all, Wartsila’s 14-cylinder RTA96C, is rated at 95,000-hp with HFO consumption of about 1,660 gallons an hour at its most efficient power setting. Although most ship engines are not that large, virtually all of them are larger than a tugboat engine, and it is estimated that close to 300 million tons of fuel are consumed annually by the world shipping fleet, at least three quarters of that being heavy fuel.
By comparison, a 12,000-hp modern ATB might consume 35 tons of fuel per day at full operation.

Crowley first started building its fleet of ATBs in 2002. As the tugs have grown in size and horsepower, so have the barges. The 550 class of barges first introduced had a capacity of 150,000 barrels. The current 650 class of barges can carry 185,000 barrels. And beginning in 2011 will come the 750 class of barges with a capacity of 330,000 barrels.

Naturally the tugs attached to those 750-class barges will be considerably more powerful than the first ATBs. With more than 16,000 horsepower from Wartsila engines, those units will definitely be burning a lot of heavy fuel. And if they want to call it bunker fuel, no one is going to argue.

By Professional Mariner Staff