Fuel Tech: The Propulsion Revolution
January 1, 2020
The International Maritime Organization (IMO) regulations limiting the sulfur content of bunker fuel to 0.5 percent, a reduction of over 80 percent from previous levels, took effect at the start of this month. They are part of the organization's commitment to reduce greenhouse gas emissions, particularly CO2, from the world's merchant fleet by at least 50 percent over the next three decades compared to 2008 base levels. This will require tremendous changes within the maritime sector.
To date, ship operators have been following three basic paths to comply with the new IMO mandate: switching to low-sulphur fuel but at a higher cost; continuing to use high-sulphur fuel but installing "scrubbers" to clean the exhaust, or using a cleaner alternative fuel, such as liquefied natural gas (LNG) which requires engine modifications and the installation of large cryogenic fuel tanks. In addition, a number of auxiliary propulsion and fuel-saving devices, such as rotors, fuel cells, solar cells, batteries, kites and sails are being experimented with to improve vessel efficiency and reduce overall pollution.
Some of these devices are limited to wind-prevalent routes or short runs where electrical charging can be accomplished from shore. Nevertheless, the shift to new technologies, including the use of such fuels as hydrogen, alcohol, biomethane and ammonia, is being accelerated and it is changing how ships are being propelled as well as how they are designed.
According to the United Kingdom-based Exhaust Gas Cleaning Systems Association between 2,000 and 2,500 scrubber installations have been completed to date with another 1,000 of the units on order for installation this year. The retrofitting of these units, which takes up a considerable amount of space, usually sees them fit in a ship's funnel by enlarging it or by the construction of a completely new housing. In addition, as seawater is used in the cleaning process, a large amount of new piping is required along with pumps and electrical control cables.
Two types of scrubber systems have been developed, closed-loop and open-loop, with the latter returning the seawater with its contaminants to the ocean while the former requires retention of the water and treatment with caustic soda. Although the use of scrubbers cleans exhaust gases the contaminants remain and some ports have already forbidden entry of ships using open-loop systems. Currently, the purchase and installation of a scrubber can cost shipowners between $2 million and $10 million, depending upon ship type and yard used, and can take as little as two days to as many as five weeks if combined with other work. The scrubber payoff is the ability to continue using relatively cheap heavy fuel oil.
Beyond the use of scrubbers or expensive low-sulphur fuel a number of vessels are being built or retrofit to burn alternative fuels, the leader in this category being liquid natural gas (LNG). Dual-fuel engines capable of running on both regular fuel and LNG were introduced to the maritime sector over 30 years ago and several hundred ships now operate on gas. However, because the energy density of LNG is much lower than traditional marine fuels, its storage tank must be considerably larger if it is to support the vessel's required operational range.
Not wanting to lose potential revenue-generating space internally, most cargo ship owners have opted for cylindrical tanks installed horizontally on the weather deck.
Ferries, which only require small tanks for short runs, are also taking advantage of deck installations but most cruise ship owners, not wanting large tanks in public view, are having them fit internally. A case in point is the world's largest cruise ship operating on LNG, AIDA Cruises' 183,858-gt AIDAnova, which incorporates three type C tanks housed in an internal module measuring 120-meters by 42-meters and standing four decks high. With a total capacity of 3,550 m3 this gives the ship a 14-day cruising range before refueling is required. As a safety precaution, and also to be in compliance with "safe return to port" requirements, AIDAnova has additional storage capacity for marine gas oil (MGO) in case LNG is not available at a particular port.
Although most cargo ship owners have opted for deck-mounted LNG storage tanks there is a growing movement to have the tanks installed internally, especially on container vessels where the weather decks and hatch covers are used for container securing. This is especially true now that French engineering company GTT has developed membrane tanks that can be better shaped to fit a ship's internal hull configuration.
Such tanks have been chosen for a series of 23,000-TEU capacity container carriers being built in China for French operator CMA CGM. The tanks on these vessels, which will provide fuel for 12-cylinder X92DF main engines of 63,840 kW (85,610hp) output, have a total capacity of 18,000 m3. This will allow a complete round trip between Asia and Europe before refueling is required. Bunkering will be accomplished in Europe using a 18,600 m3 capacity tanker being completed in China that will deliver over 300,000 tons of LNG to CMA CGM ships annually.
Internally fitted membrane type tanks have also been chosen for installation in the first large container ship to be retro-fit to burn LNG, Hapag-Lloyd's 2014-built Sajir, which will undergo the $27 million process later this year at China's Shanghai Huaran Dadong Dockyard. The tanks will have a capacity of 6,700 m3 which means the vessel will have to bunker twice on a round trip between Asia and Europe. In addition, the ship's MAN B&W 9S90MEC10 main engine is to be converted to a high-pressure, dual-fuel powerplant that will be fitted with MAN's Pump Vaporizer Unit (PVU) which pressurizes and vaporizes fuel to the specific pressure and temperature required for LNG use. As with the AIDA cruise ship, low-sulphur fuel oil will be carried as a back-up and safety precaution.
LNG-Fueled Ore Carriers
Internal LNG tanks are also being considered for a series of large ore carriers being developed by Japan's Kawasaki Kisen Kaisha (K-Line) in partnership with compatriot shipbuilder Namura Shipbuilding for the carriage of ore between Australia and China. Because of the high density of the cargo being carried ore ships traditionally have a large amount of void space in their hulls, portions of which can be used for tank placement.
The 250,000-dwt ships envisioned will have their cylindrical LNG tanks arranged in the center section of the hull. Although not previously considered for LNG conversion, the demand for dual-fuel ore carriers has increased since mining giant BHP announced it will be tendering for enough LNG-fueled vessels to transport more than 27 million tons of ore per year from its mines to consumers. This represents about ten percent of its annual ore output.
Banking on Batteries
The use of LNG as a fuel is also being put to use in conjunction with batteries in several applications, including Hurtigruten's new cruise ship Roald Amundsen (see Pacific Maritime Magazine, Nov/Dec 2019) while battery power alone is propelling a growing number of smaller vessels. In the latter sector Norwegian fjords are now being crossed daily by all-electric ferries while Japan is developing an all-electric bunkering tanker for employment on Tokyo Bay.
The use of all-battery propulsion is also moving into the tugboat sector following a decision by New Zealand's Port of Auckland to order an all-electric ship-handling tug from Holland's Damen Group.
Although to be equipped with two 1,000-kW generator sets for emergency purposes, the tug will not be considered a hybrid because its battery system has been designed to meet all normal operational requirements without working in conjunction with diesels. This will allow it to handle three to four large ship moves before its 2,800 kWh battery bank will need to be recharged, which will be accomplished in two hours using a 1.5MW shore-based installation.
In one of the largest hybrid battery applications to date AIDA Cruises' 2017-built AIDAperla is to be refitted with a battery bank from British Columbia's Corvus Energy this year that will produce 10 MWh, the largest battery storage system ever installed on a passenger ship. Corvus, now a leading supplier of lithium-ion battery storage systems, has reduced the volume of its batteries per kWh supplied by 50 percent over previous batteries and their weight per kWh by 30 percent. This is important as the battery pack installed in Denmark's all-electric ferry Ellen (see Pacific Maritime Magazine, September 2019) and supplied by Switzerland's Leclanché, has a weight of more than 55 tons. As the size and weight of batteries is reduced their use is expected to increase but lithium-ion systems can also be hazardous. This was demonstrated in October when the Norwegian hybrid ferry Ytterøyningen suffered a fire and gas explosion in its battery room during regular operations, an incident that has required more vigilance of the storage systems by their operators.
The use of wind to assist in propulsion by employing fixed and flexible sails as well as kites and rotors is being examined by several shipowners but few ships are yet taking advantage of it. This may change as continuing development leads to better products. Flettner rotating cylinders, operated by low power motors that use the Magnus effect to generate forward thrust, have shown they can cut fuel consumption when wind conditions are right and at an installed cost of between $1.1 and $2.5 million. To date about a half dozen ships have been fitted with the devices and the results have been positive. One of the first installations, two 18-meter high, 3-meter diameter rotors installed on the 18,205-gt ro/ro ship Estraden in 2014, produced verified fuel savings of 5 percent. Another pioneering rotor ship, Enercon's E-ship 1, has been operating with four rotors since 2010 and normally obtains fuel savings of 10 to 20 percent.
In October, Maersk Tankers announced that twin Norsepower rotors installed on its tanker Maersk Pelican had demonstrated fuel savings of more than 8 percent during a year-long testing period. The next ship to be retrofitted with a rotor will be Scandlines' 1,300-passenger hybrid ferry Copenhagen which already uses a combination of diesel and battery power while operating between Gedser, Denmark and Rostock, Germany.
With the European Union now forecasting that there could be up to 10,700 wind propulsion installations on ships by 2030 Finland's Wärtsilä has signed an agreement with Norsepower under which the Norwegian company can order service work from Wärtsilä on its installed units while Wärtsilä will be able to sell Norsepower rotors with technical support from Norsepower. This is expected to see further applications of Flettner rotors worldwide with Lloyd's Register recently presenting South Korea's Hyundai Heavy Industries with an Approval in Principle (AiP) for a Very Large Crude Carrier (VLCC) that would be fitted with four Norsepower rotors.
The ship would be primarily propelled by an engine capable of using a combination of volatile organic compounds produced from naturally occurring vapors within its cargo tanks mixed with LNG stored in deck-mounted tanks as fuel while the rotors would offer auxiliary power.
Beyond rotor sails, a non-rotating wind assist product, Conowind's Ventifoil system, is to be installed on the 3,600-dwt general cargo ship Ankie, operated by Holland's van Dam Shipping. The 10-meter tall Ventifoil units, which have taken three years to develop using financial assistance from the European Union, are modular and shaped as a non-rotating wing element with vents and an internal fan. They are similar to the TurboSail developed by Jacques Cousteau in the 1980s but with several refinements to take advantage of boundary layer suction created by their egg-shaped cross-section.
Two will be installed on the forecastle of Ankie and the resulting fuel savings are expected to give a payback period for both the product and installation of about three years. Although various wind-assist schemes have been tried in the past, including rotors, sails and kites, one advantage today's products have is very accurate weather forecasting which can provide the best possible route for use of the devices.
The use of hydrogen, both in fuel cells and as a vessel's fuel, is in its infancy but there are expectations that hydrogen will play a much greater role in the future. Governments view the cells, which combine hydrogen and oxygen in a chemical reaction to produce electricity while leaving only water as an exhaust, as a way of eliminating pollution and are financially supporting their development. Several very small excursion craft are already employing hydrogen fuel cells for power in Europe and larger vessels using the gas are now being built. These include the 20-meter by 8.2-meter tug Elektra, being constructed by the Hermann Barthel Shipyard in Derben, Germany for logistics specialist Behala, and the 84-passenger ferry Water-Go-Round, nearing completion in California.
A larger and faster ferry using fuel cells is being developed in Norway by Hyon AS in a government-sponsored project that is also developing a fuel cell-powered coastal container ship. As the technology is refined there are estimates that, within five years, vessels using hydrogen fuel cells combined with battery storage systems will make up a significant segment of northern Europe's coastal fleet.
Hydrogen is also being considered as a fuel in itself and the Port of Antwerp has ordered the world's first hydrogen dual-fuel tug from Compagnie Maritime Belge that will be powered by combustion engines burning hydrogen in combination with diesel fuel. The ultra-low-emission "Hydrotug" will be equipped with a particulate filter and catalyzer to complement its dual-fuel system, allowing it to fully comply with the EU's Stage V emission standards when it enters operation in 2021.