Fuel cell submarines offer underwater stealth
November 7, 2004 While fuel cell automobiles promise reduced emissions on land, the high seas have long enjoyed a virtual amnesty from air emission regulations. There is no effective way to regulate pollution emmissions from ships, yet the fuel cell has a bright future under the water as the best alternative to nuclear energy. The fuel cell has many advantages for submarines, the most compelling being that of completely silent running. A fuel cell submarine such as the new 212 and 214 from HDW can lurk beneath the waves invisibly for three weeks at a time. Unlike other non-nuclear submarine variants such as gas turbine and diesel engines, fuel cells can also be distributed throughout a ship for increased design flexibility, which in turn reduces shipbuilding costs. The company that makes this new monster also made the world's first wartime submarine, and is now offering retrofits.
Manufactured by German company Howaldtswerke-Deutsche Werft GmbH (HDW) in Kiel, this landmark modern-day U-boat can trace its lineage all the way back to the world's first operational submarine which saw service during the German-Danish war of 1851.
Then trading as Schweffel & Howaldt, the company was contracted to build the world's first submarine, the "Brandtaucher", only because the Danish troops had advanced too close to the shipyards of the first company contracted to create the submarine. A century and a half later, the HDW Group is a major force in the shipbuilding industry, and has been experimenting with fuel-cell technology for submarine propulsion since the late 70s.
The company's latest line of U212 and U214 Class non-nuclear submarines have been developed using a silent operating fuel cell plant that runs on nine 34-kilowatt Siemens polymer electrolyte membrane (PEM) hydrogen fuel cells. An air-independent fuel cell propulsion (AIP) system provides an extreme increase in underwater endurance, increased diving depth and overall efficiency.
Despite weighing over 1630 metric tons, the 212 can remain submerged for up to three weeks and stealthily discharge torpedoes with a water ram expulsion system to perform reconnaissance, interception and surveillance missions. Without needing to surface for such extended periods, the U212 can operate silently without emitting exhaust heat and thus reduce detection. Both models are also equipped with torpedo countermeasures including underwater effector jammers and offer minimised acoustic, thermal and magnetic signatures to provide a further degree of undetectability.
Fuel-cells are electro-chemical energy converters. The advantage of a fuel-cell system aboard submarines is their air independent operation. They use an energy carrier (e.g. hydrogen or methanol) and an oxidation agent (liquid oxygen/ LOx), all of which are stored on board. In the fuel cells hydrogen and oxygen are combined to water, thus giving off electricity (DC). Thanks to a very high efficiency, the amount of waste heat is very low. The electric energy produced is then fed to the submarine's main switchboard. The amount of stored reactants combined with the excellent efficiency of the energy converting fuel cells provide the submarine with a zero-emission, pollution free alternative power source.
The U212 combines a conventional diesel generator with a lead acid battery and an air-independent propulsion (AIP) system for silent slow cruising, and a fuel cell equipped with oxygen and hydrogen storage. The system consists of nine PEM (polymer electrolyte membrane) fuel cells, providing between 30 and 50kW each.
For higher speeds, connection is made to the high-performance lead acid battery. An MTU 16 V- 396 diesel engine powers the generator for charging the battery installed on the lower of the two decks at the forward section of the submarine. The diesel generator plant is mounted on a swinging deck platform with double elastic mounts for noise and vibration isolation. The propeller motor is directly coupled to the seven-bladed screwback propeller.
The U214 submarine, still in development, has a displacement of 1,700 tonnes, is 65 metres long and is manned by a crew of 27. The propulsion is again provided by a Siemens Permasyn engine which draws its power supply either from the fuel cells or from batteries which are fed by a diesel generator. Performance of the AIP system has been increased with two Siemens PEM fuel cells, which produce 120kW per module and will give the submarine an underwater endurance of two weeks.
The HDW fuel-cell plants are being incorporated into all newly designed boats such as the U212 and U214 Class, but a fuel-cell plug-in section can also be integrated into an existing non-nuclear submarine during modernisation upgrades.
The German Navy has ordered four of the U212 submarines, with another two being built by Fincantieri for the Italian Navy. HDW is also developing the U214 fuel-cell submarine for export markets. The Greek Navy - the first foreign navy to order fuel cell submarines from HDW, in February 2000 - has ordered four Class U214 submarines. It was also the first foreign navy to order Class 209 submarines for export from HDW in 1967 and now possesses eight of these vessels. Three of these are scheduled to be refitted at Hellenic Shipyards with a fuel cell propulsion system. South Korea has also ordered three U214 submarines to enter service in 2007, 2008 and 2009 and to be built by Hyundai Heavy Industries.
The American Office of Naval Research (ONR) is also developing innovative propulsion systems based on new fuel-cell technology for efficient generation of electrical power—and greater design flexibility—for future ships.
ONR program officer Anthony Nickens explains that "the Navy's shipboard gas-turbine engines typically operate at 16 to 18 percent efficiency because Navy ships usually sail at low to medium speeds that don't require peak use of the power plant. The fuel cell system that ONR is developing will be capable of between 37 to 52 percent efficiency."
ONR is testing a 500-kilowatt diesel fuel reformer, or "integrated fuel processor," that is compatible with a proton exchange membrane (PEM) fuel cell, at the Department of Energy Idaho National Engineering and Environmental Laboratory in Idaho Falls.
The ONR is also funding development of a method to extract hydrogen from diesel fuel. A diesel reforming system would take advantage of the relative low cost of the fuel and the Navy's established infrastructure for buying, storing, and transporting it.
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