Posted on Saturday September 28, 2019
Submarines: the new Naval Group AIP keeps its promises
Naval Group's development of an anaerobic propulsion system (Air Independent Propulsion - AIP) for submarines based on a new generation of fuel cells has taken a crucial step this year. The shore system of the French industrialist, installed on its Indret site, near Nantes, operated for 18 days under conditions representative of a real patrol. “It was a question of verifying the functioning of the system with an operational use profile, as well as the diving autonomy. For 18 days, the system, connected to batteries to be representative of actual use on a submarine, produced electricity from diesel, operating at high pressure, which means that it does not there is no limitation of immersion for its use ”, explains Anthony Covarrubias, former commander of one of the Chilean Scorpene who works today in the Marketing department of Naval Group.
Transits, very slow speeds, accelerations, rapid ascent to the surface, stopping of the AIP followed by restarting, management of a possible breakdown or damage… As on a real submarine, the system was confronted with situations concrete in order to validate its performance and reliability.
World first for reforming from diesel
With these successful tests, Naval Group has succeeded in a remarkable technical challenge for this device producing hydrogen from diesel. "18 days of electric production from the reforming of diesel, it is a world first, it went very well and we can reproduce it without problem", welcomes Marc Quémeneur, AIP product manager at Naval Group. The French industrialist offers this solution to increase the diving autonomy of conventional submarines and prevent them from returning to the surface to recharge their batteries, during which period the vessel is vulnerable.
Called AIP FC-2G (Second Generation Fuel Cell - FC-2G), this system required ten years of research. Technologically, it includes two main innovations. First, the hydrogen used to operate fuel cells is manufactured directly on board, via a chemical reforming process from the diesel used by the diesel-generators. This process allows increased safety by the absence of hydrogen storage on board. Exhaust gases are discreetly rejected, since they dissolve instantly in water. At the same time, Naval Group has designed a patented system allowing air to be produced by injecting nitrogen into the oxygen supply from the battery, this oxygen being stored in cryogenic form in a tank. Synthetic air reacts with the hydrogen in the fuel cell to generate electricity, which powers the submarine's batteries and the propulsion electric motor. The cell is confined in a closed and ventilated enclosure making it possible to control a possible leak of hydrogen or oxygen.
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Principle of the device (© NAVAL GROUP)
Photo source on the cover: The shore system on the Naval Group site in Nantes-Indret © NAVAL GROUP
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shema naval group publication on asafrance site
1: the reformer is used to produce hydrogen from diesel
2: the shift is used to increase the hydrogen yield and eliminate the carbon monoxide produced by the reformer
3: the purification membranes supply the fuel cells with ultra pure hydrogen
4: fuel cells produce electricity from hydrogen and oxygen
5: the oxygen storage tank in liquid form
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(© NAVAL GROUP)
Autonomous or tandem operation with batteries
Designed for a service life of 10 hours, the fuel cell has a capacity of 000 kW. It powers the electrical plant when the submarine is in AIP mode, thus making it possible to turn the electric propulsion motor and provide the onboard electrical consumption. The building can then evolve on this single system at a speed of up to approximately 250 knots, knowing that to obtain a diving autonomy of three weeks, the usage profile varies rather between 5 and 2 knots. To do this, the power required for the AIP FC-4G is between 2 and 130 kW. Beyond that, it is necessary to draw from the batteries, the passage from one energy source to the other being done without interruption. But one of the interests of the Naval Group's AIP is also to be able to supplement the energy supplied by the batteries. "In the event of acceleration, there is no interruption and, if we want to go faster than the maximum authorized by the AIP, we switch to the batteries but we can also continue to operate the AIP, which then comes to relieve the batteries and to avoid drawing from their reserves. In this way, if the submarine needs to sail for a few hours at high speed, the AIP is used, depending on the speed, to extend autonomy a little or appreciably underwater, ”underlines Anthony Covarrubias.
photo naval group fuel cells fc2g publication on asafrance site
FC-2G fuel cells (© NAVAL GROUP)
Many advantages over other systems
From an architectural point of view, Naval Group's AIP FC-2G constitutes a considerable advantage compared to existing systems, where hydrogen is stored in external tanks, posing weight problems (130 to 160 tonnes of hydrides, less of which 2% usable hydrogen) and refueling. The fuel cells currently in service use, moreover, pure oxygen, which generates a high wear, the filters and membranes having to be replaced very regularly. More efficient according to Naval Group, the AIP FC-2G offers, according to its designers, a time of use between each major maintenance about five times higher than that of its foreign competitors. “Our system really fits into the operational scheme of a submarine. It only requires a short interruption of three weeks each year, the only equipment to be changed during this maintenance period being the catalysts. In the meantime, there is nothing to do! Says Marc Quémeneur.
Finally, the choice of producing hydrogen from diesel facilitates refueling and storage (single fuel on the submarine) while improving safety compared to systems using for example methanol, more flammable and introducing toxic products in the event of a leak.
The device fully integrated in a stand-alone module
Like the MESMA, the first AIP developed by the French group and which equips the Pakistani Agosta 90B, the entire AIP FC-2G system is grouped in a single module, autonomous from the rest of the submarine. The system is housed in a section of hull approximately 8 meters long integrated into the boat from the start or added after redesign with a minimum of modifications compared to the existing one. Adaptable to buildings with a diameter of at least 6 meters, such as the Scorpene or the conventional propulsion version of the Barracuda, the AIP FC-2G module was obviously designed not to impact overall performance, starting with the capacity immersion and acoustic discretion.
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The AIP module (© NAVAL GROUP)
The shore system in service since 2011
The performances announced by Naval Group can therefore be guaranteed thanks to tests carried out in recent years on a full-size AIP FC-2G system located in Indret. After tests carried out on a demonstrator dedicated to hydrogen production from 2003 to 2010, the complete scale 1 device was built in 2010. It entered service the following year and now accumulates more than 6 hours of operation, the equivalent of six years of use. It is therefore, according to Naval Group, a system that is now reliable and proven before it has even been loaded onto a submarine. "000 hours of operation and production of hydrogen represent more than an operating cycle between two periods of major maintenance", underline Marc Quémeneur and Damien Lelandais, system architect of the FC-6000G program.
Ready to use with further improvement prospects
The system is therefore “ready to be marketed” and already offered by Naval Group to a certain number of navies. Pending initial orders, work will continue. "We will continue to conduct tests on operational profiles and focus on optimizing the system, its efficiency, its upkeep and its maintenance." For example, engineers will work on improving the system's efficiency by reducing oxygen consumption, in particular thanks to new technologies such as additive manufacturing. "We have very great prospects for the development of the system and we see a real potential for increasing performance in power as well as in autonomy which will allow us to go on large submarines while remaining in very interesting volumes".
While the device is today coupled with traditional lead batteries, Naval Group is also working on the integration on board of submarines of batteries using lithium-ion technology, which will make it possible to widen the operational performances offered.
Vincent Groizeleau
Sea and Marine
Replayed on the ASAF website: http://www.asafrance.fr
Photo source on the cover: The shore system on the Naval Group site in Nantes-Indret © NAVAL GROUP
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