TECHNICAL FEATURE

Different Fuels, New Systems—the Future Is Coming Soon

Article Written in 2008

What will propel the vessels of tomorrow? It is too early to be sure but candidates are becoming visible. Combination of fuels and various mechanisms assembled into hybrid systems will be common but not necessarily universal. Electricity is a thread common to many of the systems—as one tugboat expert summarized the future, “It’ll be diesel and electricity.” He may be right.

This article will focus largely on systems usable by harbor tugs, ferries, and other craft with similar duty cycles—that is, much idling, some transit time, and periods using short bursts of maximum power. (As an example of what is meant by “short,” full-throttle operation of the Caterpillar main engines in two modern East Coast tractor tugs occupies a mere 2% of total engine hours.) Descriptions as to what is happening out there are often short of real information, excessively vague, or close-held by the developers but enough is known to take a first-look at what’s out there. Let’s examine fuels first, and then briefly visit some of the systems coming along.

What about the anti-pollution regulations? As of January 1, 2007, all new marine engines and about 3/4 of all remanufactured engines had to comply with Tier 2 requirements. Tier 3 requirements are basically similar to those of Tier 2 but tougher in some respects. Tier 4 emission standards will be phased-in over the period of 2008-2015 and require that emissions of PM and NOx be further reduced by about 90%. Such emission reductions can be achieved through the use of control technologies—including advanced exhaust-gas aftertreatment such as particulate (soot) filtering and catalytic converters.

What is driving the switch from good-old everyday diesel oil? Two factors: its cost as world demand for petroleum products causes skyrocketing prices, and the general feeling that the world has become intolerable dirty and must become cleaner; pollution is driving the creation of increasingly tighter regulations.

Will diesel fuel continue to be available? Sure but at increasing cost and perhaps derived from unusual sources, such as the oil shales of Colorado or the oil sands of Canada. But not all diesel oil need be made from petroleum—more on that later.

Are bio-fuels the answer? Maybe. Maybe not. For the purposes of this article, biofuels can be said is to fall into two categories: alcohols and biodiesel. Both can be derived from vegetation but, as the world population increases, the ever-present question arises: Can Mother Nature grow enough vegetation to make lots and lots of biofuel and still feed everyone? That answer is not yet clear.

• Alcohol powers many racecars and dragsters and an ethanol/gasoline blend probably is in your vehicle’s gas tank. Ethanol produced from corn is much in the news nowadays and comparisons of its environmental/economic value and true cost are the subjects of much controversy. But ethanol can be produced from other vegetation: Shell, the world’s leading biofuel distributor, recently received an $80 million dollar US government grant to build a facility in Idaho that will produce ethanol from plant waste and straw. And, in Brazil sugarcane-based ethanol is widely used due that nation’s vast farming areas, favorable climatic conditions, and extensive production of sugarcane. (It has been reported that the exhaust fumes from alcohol-fueled vehicles in Brazilian traffic jams tend to leave everyone with a slight buzz.)

But ethanol has a potential competitor. It is butanol, also known as buytl alcohol, and it could be in large-scale production by 2012. Butanol is less-corrosive on engines than ethanol, easier to mix with gasoline (and probably diesel oil), and, unlike ethanol, can be transported via a pipeline. Unfortunately, it is more expensive than ethanol. Butanol usually made from fossil fuels and ends up as a solvent but biobutanol used to be and will be produced by bacteria feeding on feedstocks (a process called fermentation) such as wheat, paper-pulp-derivatives, and even the corn waste from making ethanol!

• Biodiesel produces less CO2 than petroleum-based fuels, can be safer to handle, and its exhaust fumes are easier to live with. It may also make engines run quieter and regular diesel can still be substituted when necessary. Negatives are lower economy, gelling in cold weather, and increased production of NOx emissions. The most-common method of producing biodiesel is to react animal fat or vegetable oil with methanol in the presence of sodium hydroxide (lye or caustic soda). Vegetable oils can be derived from corn, soy beans, rapeseed, sugar, blue-green algae, jatropha (a kudzu-like plant from South America that thrives in poor soil otherwise unsuitable for farming), many grasses, woodchips, straw, etc. (Save-the-tropical-forests advocates do not seem to have yet realized that biofuel derived from palm tree oil often means that tropical jungles were cut down in order to plant orderly rows of easily harvested palm trees!) Shell will soon start creating synthetic diesel fuel (biodiesel) in Europe from waste plant material such as woodchips and straw. Animal oils are classed as yellow grease and can be used deep-fat-frying oils or fat from livestock and poultry-processing plants.

On the West Coast, Brusco’s Wynema Spirit and Lulapin at Port Hueneme, California, Campbell Maritime‘s several small tugs in the Seattle area, and Pacific Tugboat Services’ tugs are among tugs using biodiesel.

What about natural gas? Natural gas is basically methane but usually includes varying amounts of ethane, propane, butane, and pentane. Widely used on land for many years in internal-combustion engines in place of gasoline or diesel fuel, natural gas is lean-burning, clean-burning, and provides long engine life (up to 100,000 hours before overhaul). The gas is usually transported in two forms. Liquified natural gas (LNG) is stored and carried in the liquid state at extremely low temperatures and converted back to its gaseous state at the destination. Compressed natural gas (CNG) remains in the gaseous state but is compressed at high pressures for carriage and storage. CNG is widely used for land-side operations such as propelling buses. At sea, the boil-off from tanker cargoes of LNG is often used to fire boilers producing steam to drive turbines and some of newer LNG tankers have dual-fuel diesel engines. On smaller vessels, natural gas has propelled the Norwegian ferry Glutra since 2000, two supply boats since 2003, and is appearing on other supply boats. In BHP Billington’s application for a floating offshore LNG-unloading facility off Southern California, it promised that all escort tugs, crew boats, and associated land vehicles would be powered by natural gas. (The application was denied.)

Hydrogen? Nice stuff. Highly energetic (ask your local Space Shuttle for a reference here). Clean-burning but note that if you ever have to fight an onboard hydrogen-leak fire, it burns with an invisible flame. But hydrogen is not yet available at your local marina or refueling point. Hydrogen can be made from methane, petroleum, and coal via various chemical reactions, and from biomass (landfill waste, wastewater sludge, and livestock waste). It can also be made from water by electrolysis but is currently made primarily from natural gas (methane). Although hydrogen is used in the Space Shuttle rocket engines, hydrogen is more likely to power fuel cells on vessels like tugboats. Honda has just revealed a zero-emissions car that is powered by electricity generated by a hydrogen fuel cell. Two hundred examples of this Honda FCX Clarity model will be leasable in California next year.

And coal? Coal is perhaps the most-common fuel in the world and the US has tremendous reserves. So why not use it as it comes from the earth, perhaps ground into a flour-like powder and burned in something like a fluidized-bed boiler? There are those who believe that coal is the fuel of the future. Bob Hill at Ocean Tug & Barge Engineering (OT&BE) was recently approached by a European who wanted OT&BE to design a tug using the latest coal-burning technology to generating steam for an improved version of the Skinner Uniflow steam engine.

But liquid fuels can be synthesized from coal using the Fischer-Tropsch process. Never heard of it? Have you ever wondered how Nazi Germany fueled those tanks and fighter plane during World War II when Germany was denied access to crude oil? Or how did South Africa kept functioning when sanctioned for its apartheid policies? The answer lay in coal-derived synthetic fuels and they created by the Fischer-Tropsch process, invented in the Thirties and since improved with better catalysts. Maybe we’ll see marine diesel fuel derived from coal.

And even trash? An Italian engineer presented a paper at the recent World Maritime Technology Conference stating that Rome’s Worldwide Ecological Shipping & Transport had developed a patented process for driving ships with steam from a rubbish-fired boiler. He figured that a 4,800-teu container ship would consume 176,000 tons of waste in 275 days of annual navigation. Air emissions would be cut by up to 98% and there would be freedom from oil’s price fluctuations. But trash does seem an unlikely fuel for tugboats and the like.

That completes the fuel story. Hybrids are now being used in seemingly everything including automobiles, locomotives, container gantry vehicles, and even Formula 1 racecars—BMW will have one next year. Electricity generated by the racecar’s braking will be stored in a battery or super-capacitor, and released in a burst of eighty additional horsepower for up to six seconds.

Let’s look at some proposed and planned tugs, most of which (but not all) are hybrids. Hybrids are nothing new; they have been afloat for many decades. For example, World War II submarines used hybrid drives; diesel engines, electric motors and generators, and a massive storage battery system. (Sounds vaguely reminiscent of a Toyoto Prius, doesn’t it?) A submarine in the pre-nuclear power days, was propelled by either its engines or its motors, which used electricity stored in the batteries, and the engine/generator sets recharged the batteries. Post-war, many new harbor tugs were built using war-surplus main engines turning surplus generators that powered surplus electric propulsion motors, and the diesels revved up and down in response to load variations. Today’s hybrid tugs will require clean-burning gensets operating at constant rpm, modern control electronics, and the development of new and radically advanced types of batteries.

Interestingly, the US Navy’s new warships will be propelled by down-sized electric motors using superconducting magnets and sophisticated electronic control systems. Little of this technology seems apparent in what is being developed for commercial applications.

The all-electric, non-battery, non-hybrid tug. Why not a pure diesel-electric tug? Later, a Dutch tug is described that closely approximates the following setup but with the addition of an unusual component or two.

A little background: Generating electrical power for vessel propulsion is possible via several routes. Historically, a diesel engine spun the rotor of a generator and the engine revved up or down in accordance with the load imposed on the system’s electric propulsion motor. Nowadays a constant-speed diesel turns a constant-speed generator, whose output to the motor and other loads is controlled either by varying the generator’s field strength or by using a chopper arrangement to control output from a DC generator set or a variable-frequency drive on an AC set.

On a tug, such a set-up on a tug might copy many cruise ships that are powered by father-son combinations of diesel-powered generators, each placed online in accordance with the load demand—one “son” for “hotel” service while docked, maybe a “father” while transiting to a job, then everything online during a big push on a container ship during, say, hurricane winds. And note that Schottel already offers electrically driven azimuthing drives.

RailPower. Perhaps the first company to commercially produce technology that realizes the benefits gained by using clean-burning diesel engines with generators and motors coupled to large battery packs was the Canadian company RailPower Technologies. It originally set out to create a “clean-power” switching engine but model-train buff Bob Hill recognized that ship-assist tugs and other workboats have remarkably similar duty cycles and so his OT&BE obtained a license of RailPower’s technology for marine applications. The basis is one or more electric drive motors supplied from massive battery packs (think 2,000 hp or so each) continuously recharged by one or more small gensets. (The gensets might even be used to power a tug at light loads, such as while under way to a job.) OT&BE’s subsidiary company EcoMarine Propulsion LLC is designing such systems in association with Railpower Technologies for a group of six new 5,000-hp tugs propelling articulated tug/barges (AT/B).

The Foss hybrid tug. This tug will probably be the first hybrid tug to see service. It is based on Foss’s series-built Dolphin-class tug but the 5,080 hp of the standard tug will be approximated by a combination of propulsion units. When idling or transiting, up to 2,012 hp will be taken from two 671-hp battery packs battery packs supplemented by and maintained by two 396-hp generator sets. Two main engines output 3,400 hp total and are used only when maximum efforts are needed.

Originally, the Foss hybrid tug was going to be hull 9 in the Dolphin series but now it will be hull 10. The reason illustrates the state of progress in battery design and construction. Nickel-metal-hydride batteries were to be used but the selected brand is longer made. Gel-based lead acid batteries will be substituted, at a lower cost and a considerable increase in weight.

GE and C-MAR’s tug. General Electric and Texas-based maritime engineering and management firm C-MAR plan to provide cleaner power for nautical applications. They will start with a hybrid tug. It will use either the GE V228 (formerly the 7FDM engine, with powers ranging from 1,753-3,506 hp at the 900 rpm continuous rating) or the new Tier 2-compliant V250 engine (2,725-3,626 hp under the same conditions) to drive a generator that will keep a battery pack charged. That will supply power to an electric motor. Neither the type of battery or motor has been identified but it may of significance that GE Financial Services recently invested more than $20 million into A123 Systems, a developer and maker of lithium-ion batteries. Look for the tug in about two years.

OT&BE’s natural-gas fueled tugs. OT&BE is also designing three tugs powered by diesel engines fueled by natural gas. One tug would be the prime-mover of an AT/B. The boil-off from its cargo of LNG would power the tug’s engines. When the barge is empty, the tug would use stored CNG, as would the two other tugs. The method of CNG storage is to be determined; it may be tanks or cylinders or tight coils of piping. No other details are available.

A Dutch fuel cell-powered tug: Inquiries were made abroad as to what was happening outside the US and only three projects were identified. The pedigree of the first is impeccable: a highly knowledgeable member of a great Dutch tugboating family who has a smart design group at his beck and call and partners in the form of two smart tugboat companies, both Dutch and one a world-leader in the business. Michiel Wisjmuller owns Worldwise Marine and it is a part of the Offshore Ships Designers group. The companies are Rotterdam’s Smit Towage and Jmuiden’s Iskes Towing and Salvage.

Worldwise is designing an electrically-driven, azimuthing stern-drive harbor tug that will use hydrogen fuel cells and batteries to provide zero emissions while on standby and mobilizing/demobilizing. “[It] will save up to 98% of SOx, NOx, and particulate matter and 30% of CO2 emissions in total compared to a conventional harbor tug over the whole employment cycle. This is a major step forward for tug operators who have tugs operating in densely populated areas," said Wijsmuller, managing director of Offshore Ship Designers.

Hydrogen will be stored at 430 bar (over 6,000 psi) and the proton-exchange-membrane fuel cells will use the NedStack Fuel Cell Technology. Two main electric propulsion units deliver 1,733 hp (1300 kW) each while four 650-kW Caterpillar C32 generator sets provide additional power as needed to deliver the full 50-tonne bollard pull. Power will also be created thru regeneration from winch feed-outs or propeller rotation while the tug is in a braking or escort mode. Interestingly, the tug is fitted with a bow-mounted retractable Voith bow propulsion unit that is used when the tug is operating on electric/hydrogen power. When the tug switches to the berthing/assisting mode and is running on one or more of the four diesel generators, the Voith unit is retracted, to cut hull drag.

As far as is known here, this project has yet to get past the planning stage but, because of the partners involved, one should expect tugs to be built.

A Finnish hybrid tug. Anchor-handling tugs/supply boats (AHTS) need flexible power systems and diesel-electric systems are becoming more popular. Finland’s Aker Yards has orders for two big (308 feet overall) AHTS and they are said to be “equipped with a hybrid propulsion solution” for a bollard pull in excess of 350 tonnes (about 385 tons). Sparse specifications provide few clues except that there are two main engines of 8,000 kW (10,728 hp) each and an “auxiliary“ engine” of 11,000 kW (14,750 hp). One might guess that the auxiliary engine is actually a single electric motor connected to one shaft.

Finally, a multi-national hybrid tug. One truly hybrid project is already in series production. Norwegian design group VIK-Sandvik and Indonesian shipyard PT Batamec have been cooperating on creating a large, high-powered, “clean” AHTS and twenty of the resulting VS491 CD vessels are on order for deliveries in 2008-2011. This hybrid vessel uses a mix of diesel engines, generators, and electric motors. Fuel cells could replace the diesels in powering the motors.

In a scheme somewhat reminiscent of a World War II submarine, each of two controllable pitch propellers can be driven by a diesel engine and/or a variable-speed electric motor. Each 10,730-hp main engine has a power take-off in the front end that drives a 3,000-kW shaft generator. With this arrangement, the main engine can be used as the propulsion engine at variable speeds (but not below the idle speed of the engines), can be the propulsion engine at a constant generator speed, or can be a generator-driving engine disconnected from the propeller. The variable-speed electric motors have two nominal ratings and speeds. When operating in parallel with the diesel engine, they turn 1370 rpm in order to match the nominal propeller speed of 144 rpm. When operating as the only propulsion device, the nominal speed is 800 rpm, equal to a propeller speed of 84 rpm. This hybrid system minimizes the total installed engine power (electrical and diesel) and provides a propulsion system that is efficient over a mission profile that includes extensive high-load and low-load operations including anchor-handling and rig-towing, a transit speed of 15 knots, and precise dynamic positioning.

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