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Maritime Transport in an Energy Constrained Future
Submitted by Dan Sweeney on Fri, 2008-07-25 18:40.
Most discussions of future transportation systems focus more or less exclusively on automobiles, and, for good reason. More fossil fuel is consumed by personal transportation than by any form of public or commercial transport. Still, in aggregate, air and sea transport as well as heavy wheeled traffic involving trucks or trains account for almost half of the total petroleum consumption within the transportation sector, which itself accounts for the bulk of total petroleum consumption worldwide. So, obviously, nonautomotive transport matters in terms of its sheer impact on resource consumption, leaving aside its vital importance to commerce and to the maintenance of an industrial civilization.
Obviously, heavy transport is profoundly effected by rising crude oil prices, and, if we assume that a decline in fossil fuel recovery is imminent or already underway, then we are compelled to ask the question, what sort of coping strategies can we expect in these other transportation segments? Will they be going to hydrogen and fuel cells as will the auto industry—if the major manufacturers are to be believed?
Let’s start with maritime traffic because collectively ships and boats are the biggest users of petroleum after automobiles.
You won’t find very many ship builders or naval architects talking about fuel cells or the hydrogen economy. True, the HDW ship works in Germany has built a handful of naval submarines utilizing PEM fuel cells, but that’s scarcely a large market. In the areas of merchant shipping, fishing vessels, or surface naval vessels no one is seriously considering hydrogen or fuel cells at this time nor is anyone doing any prototyping. A few U.S. Coast Guard vessels have molten carbonate fuel cells on board for supplying auxiliary power, but the power output of even the largest of such devices is far too meager to drive a ship’s propulsion system, and the cost is highly disadvantageous compared to existing diesel power plants. And, in any event, shipboard molten carbonate fuel cells run on diesel and are scarcely pollution free.
Interestingly, there is movement among designers of both naval vessels and cruise ships to utilize hybrid electric drives where a diesel generator provides electrical energy for both propulsion and the operation of various other electrical systems on the ship. Such hybrid systems are in fact somewhat more energy efficient than parallel plants where diesel engines drive the propellers directly and diesel auxiliary power units run the ship’s generator. Incidentally, such hybrid drives are scarcely new. During the World War II era and for some time after, the majority of large naval vessels used hybrid electric drive, although steam turbines rather than diesel piston engines provided the heat engine component in such systems.
Could fuel cells or other novel propulsion systems gain at least a foothold in the future?
I am doubtful. The large two stroke diesels used in the biggest ships are approximately
50% efficient today, on a par with fuel cells, in fact, and they are very much a known quantity. Replacing them with an unknown quantity requiring bulky hydrogen storage that will occupy valuable cargo space seems an unlikely eventuality.
Still, diesel prices are likely to continue to rise and so shippers will face a dilemma. That 50% efficiency figure is unlikely to be significantly improved upon, and the only other marine power plant in use today, namely the gas turbine, is much less efficient unless it is combined with recuperation.
So what happens?
More diesel will likely be produced from natural gas in the future, but with natural gas prices rising almost in tandem with petroleum prices, that’s scarcely a solution. Biodiesel is a possibility, and it may be utilized on a much larger scale in the future than at present, but because it is mostly produced by energy intensive agriculture involving oil seed crops, I’m not sure that it will ever be inexpensive.
I see a remote possibility in a new technology developed by a Sacramento based company calling itself Clean Energy Systems. Clean Energy is a company that was literally founded by rocket scientists, refugees from the moribund U.S. space program. The Clean Energy team has devised a combustor that works equally well with low or high grade coal or various kinds of biomass and produces a combination of high pressure steam and carbon dioxide. The company claims 60% energy utilization without recuperation, which, if true, is quite remarkable. Clean Energy is aiming at stationary power utilities, not the shipping industry, but I see no reason that the technology could not be employed in maritime applications. Up until the mid twentieth century the majority of merchant ships used steam turbines for propulsion, and they’re still used in liquid natural gas tanker ships today. The infrastructure exists for building them and if they can be made to outperform diesel piston engines and to utilize cheaper fuel while producing less air pollution, then why not? How ironic if the age of steam recommenced on the high seas?
Another possible future power plant is the Jirnov turbine, also known as the vortex turbine. Jirnovs were developed in the old Soviet Union by an inventor of the same name emigrated to the United States fifteen years ago and founded a company named General Vortex Energy aimed at promoting his invention. The Jirnov differs from conventional gas turbines in utilizing a special fuel injection system that generates a vortical movement in the fuel and is said to promote more complete combustion and better than 60% efficiency. The U.S. Navy has provided the company with a grant to further the development of the design for ship propulsion, and if the project is successful we may eventually see such designs in merchant ships and even recreational watercraft. In the past, navies have tended to embrace advanced propulsion concepts before civilian shippers, and a design win in the U.S. Navy could prove highly significant.
In any case, we don’t see heat engines being displaced by fuel cells or other power sources any time in the foreseeable future. We would expect that various attempts to introduce modernized sailing vessels would have a better chance of success than new forms of chemical propulsion.
In fact a number of ships have been constructed using wing sails in lieu of traditional fabric sails in recent years, the best known of which was the Cousteau family’s famous Calypso II. These designs have considerably more lift than conventional sails and produce less heeling, that is, the tendency of the sail to push the vessel over on its side when sailing into the wind. A company calling itself SkySails, GmbH. and headquartered in Germany has taken another approach, utilizing a gigantic computer controlled kite for motive power. Many kite sails for boats have been built over the years on an experimental basis, and they provide for both superior performance and greater safety than either old fashioned fabric sails or more modern wing sails. Such sails are favored by some wind surfers as well, and have long been commercially available in that market. Kite sails are somewhat difficult to launch and recover, however, and no one has previously attempted to construct such a device for a full sized ship.
SkySails is introducing the system now and claims to have presold a number of the kites to manufacturers of super-yachts. So far the company has garnered no sails involving merchant vessels.
The company claims to be able to retrofit the sails on most ships and boats and so the design doesn’t necessarily have to attract ship builders in order to succeed. SkySails also claims that the sails can generate close to two horsepower of traction per square meter of surface, an amazing feat if true. Their largest sails are said to produce speeds in excess of thirteen knots in ships of thousands of tons of displacement and to offer performance equivalent to that of large two stroke diesels rated at tens of thousands of horsepower. Because of the variability of the wind, the SkySail would provide auxiliary power. The company expects that the kite could reduce fuel consumption by 50%.
We do not predict any widespread use of wind power in merchant shipping any time soon, however. Schemes for the re-introduction of wind have been rife for decades, and while some governments, notably Denmark and Japan, have sponsored extensive research in this area, ship builders have demurred. Wind was used as an auxiliary power source in ships fairly extensively right up into the nineteen twenties and there are men still alive who can remember the problems with such vessels. Sure, the sails saved fuel, but separate crews were often required for sail handling and engine maintenance and labor costs could nullify any savings in coal or diesel.
To be sure, a SkySail differs considerably from traditional sailing rigs. Launch, recovery, and management of the device are largely automated, and, if promotional videos are to be believed, do not require large skilled crews. And the SkySail is powerful. We saw a heavy steel tender being dragged along at a good twelve knots. If fuel prices keep inching up, who knows?