UDT 2020 Latest Developments in Energy Systems Dipl.-Ing. Peter - - PDF document

UDT 2020 Latest Developments in Energy Systems

UDT 2020 – Latest Developments in Energy Systems

Dipl.-Ing. Peter Hauschildt Head of Technology and Innovation thyssenkrupp Marine Systems GmbH, Werftstrasse 112-114, 24143 Kiel, Germany peter.hauschildt@thyssenkrupp.com

Abstract — For SSKs energy storage is crucial; since the time being completely submerged – thus not having the need to snorkel – is essential to keep the operational advance of being stealthy. Air independent propulsion (AIP) systems today are state of the art while most submarine builders do not have mature systems operational; almost all are working on fuel cell systems. thyssenkrupp Marine Systems having supplied most AIP submarines that are operational based on fuel cells (FC) has developed a fourth generation of fuel cells. Compared to previous systems the new system features latest FC technology, thus improving operational availability, cost and independence of suppliers. T In addition, batteries are the traditional energy storage for SSKs. Having used lead-acid batteries for over 100 years, a technology change is under way. Lithium Ion batteries offer higher capacity, more power, faster charging and a longer

• lifetime. The paper will show the special requirements of the submarine application and the technical solutions, which

are now ready for use on board of submarines.

1 Introduction

Submarines are the ultimate stealth ships mainly due to one major feature – they can dive. In contrast to nuclear submarines, whose diving times are almost unlimited, non- nuclear submarines are always limited by the energy sup- ply. Because

• f

available technology, diesel electric submarines with lead acid batteries are limited to a few days of continuous dive, even if they just move slowly. When the batteries are exhausted, the submarine needs to recharge the batteries using the diesel generator sets while snorkelling. Snorkelling significantly increases the vulnerability of the submarine, because it loses a major part of its stealth feature: The snorkel and other hoistable masts have radar and infrared signatures, the diesel and the exhaust generate noise and the hull itself can be spotted either visually or by laser. Therefore, it is always a major goal for submarine yards to improve the energy system. This paper gives a status about the latest development in batteries and in air independent propulsion (AIP).

2 Submarine Batteries

Lead acid batteries have been standard for submarines since the early days. They are relatively cheap and can be manufactured in different sizes to ideally fit to the respective submarine design. However, lead acid batteries have some major drawbacks:

• In comparison to other battery types their energy

density is low

• They need maintenance: While not in use they

should be completely charged. They need to be “gas charged” on a regular basis: A procedure during which the battery produces dangerous hydrogen that enters the boats atmosphere. For this an external charging unit is required.

• The battery degrades during the mission until it

is maintained by “gas charging” which is normally done n port with no crew on board for safety reasons.

• On a regular basis water has to be refilled

manually to each of the cells

• At higher charging stages the charging current

has to be limited

• To avoid damaging by deep discharge, a lead

acid battery should not be used with the full specified capacity

UDT 2020 Latest Developments in Energy Systems

• When almost discharged the battery cannot give

it’s nominal current, limiting the flank speed of the submarine Modern batteries can overcome all these disadvantages. So why are almost all submarines still relying on lead acid batteries? Lead acid batteries have some advantages:

• They are relatively cheap
• They can be produced in adaptable sizes to be an

ideal fit to the respective submarine design. In the last years large format Lithium-Ion-Battery (LIB) cells have become commercially available. The e- mobility demand is a major driving factor for their development. But for a submarine LIB integration is not an easy task:

• Depending on the chemistry LIB are a

significant fire hazard.

• Fires could be cause by misuse (overcharge,
• verheat), internal failures or mechanical

damage.

• LIB can drive very high currents which are hard

to handle. thyssenkrupp Marine Systems has developed a LIB for submarines based on a safe chemistry with low to no fire hazard – the Iron Phosphate chemistry. Also the energy density of other Nickel or Cobalt based chemistries is higher, safety analysis has shown, that their integration into the closed manned atmosphere of a submarine would impose unacceptable hazards. Since available cells are significantly smaller than today’s Lead Acid batteries, many of the commercial cells are mounted in a common frame and form so called modules. Since deep discharge and overcharge as well as

• vercurrent or over temperature have to be securely

avoided, a monitoring electronic has to be part of the system, which fulfils highest standards in terms of reliability and safety. Each module has it’s own battery monitoring system. In addition, the battery monitoring system takes care, that all cells are equally charged. Modules are put in series until the desired voltage of the boats network is reached. This is called a string. Many strings are put parallel to have the desired capacity.

Fig 1: LIB module, inside view

Each string is connected to the network by a DC-DC converter that can limit the current in case of a short circuit in the network and can galvanically separate each string from the network, if necessary. In addition these CD-DC converters called string switch device are used to equalize and optimise use or charging of the strings. During development, many submarine requirements have to be considered:

• Shock
• Magnetic

(German Submarines are non magnetic)

• Electromagnetic compatibility
• Temperatures
• Charging and discharging rates
• Reliability
• Maintainability

UDT 2020 Latest Developments in Energy Systems

Fig 1: EMC testing of battery string

thyssenkrupp Marine Systems with it’s partners SAFT and ABB has developed under a contract of the German Procurement agency BAAINBw and tested the new system on prototype level and is in discussion with initial customers about submarine integration.

3 Air Independent Propulsion

Even with LIB submarines are limited to some days without snorkelling. To dive even longer air independent propulsion (AIP) Systems are needed which use a fuel and liquidly stored oxygen (LOx) to generate power. These AIP systems enable submarines to stay submerged for weeks at slow speed, while for fast transits the diesel gensets are still needed and only batteries give the power for flank speed. thyssenkrupp Marine Systems is working in the field of Fuel Cell based air independent propulsion (AIP) Systems for more than 30 years. We have chosen fuel cells over combustion systems since fuel cells have some

• utstanding advantages:
• Very high efficiency
• As a consequence low consumption of LOx
• As a consequence low heat transfer to the sea

water

• Absolute silence of the energy generating

process

• No exhaust gas to be dumped over board

As a consequence all relevant submarine builders claim today to have or develop fuel cell AIP, but so far only the systems of thyssenkrupp Marine Systems are operational in submarines. The first test fuel cell AIP system was realized on board of the submarine U1, which was in operation at the German navy, in 1988. The first series of fuel cell AIP is integrated in the HDW Class 212A, based on nine SIEMENS FC-Modules, with 30-40 kWel for each Module. This system is operated successfully by the German and the Italian navy on board

• f their submarines since then.

A third generation of fuel cells was developed together with SIEMENS for the HDW Class 214 submarines now having a power output of 120kW per FC module and 240kW in total.

Fig3: FC testing on “U1” in 1988

Based on our vast experience with prior generations of fuel cell systems, we have decided to develop a fourth generation of fuel cells based on latest technology. This so-called Advanced Submarine Fuel Cell (ASFC) unites advances in the development of the fuel cell industry

• ver the last 20 years. The configuration of ASFC is based
• n four independent systems with 80 kW each, namely the

ASFC line, resulting in 320 kW total FC power output. The ASFC system is operated on pure hydrogen and

• xygen. As single fuel cells always require gas in excess

to dispose of the reaction water, the system design includes gas recirculation for hydrogen and oxygen. Recirculation ensures that the fuel cells are always operated in optimal conditions, under full load as well as partial load.

Fig 4: ASFC module

UDT 2020 Latest Developments in Energy Systems An ASFC line comprises the following subsystems:

• Hydrogen and oxygen humidification
• Hydrogen and oxygen recirculation
• FC modules (shown in Figure 1)
• Encapsulation

The humidification systems ensure the correct gas humidity of the hydrogen and oxygen before they enter the fuel cell. The reaction water of the fuel cell is utilized for humidification. The FC modules are located at the front of the system. Inside the FC modules, a special electronic device monitors the status of the modules. Furthermore, the modules are coupled to the plant with clean-break

• couplings. This is an enormous advantage, because if a FC

module has to be dismantled, the gas systems and the cooling system remain closed. After coupling in another FC module, the system can be restarted automatically without time-consuming preparation work.

Fig 5: ASFC line with 80kW output

The encapsulation of the ASFC system is foreseen to ensure a detection barrier between the pipes, components and connections inside the ASFC system and the submarine’s atmosphere. It is part of the safety system for the ASFC, which ensures safe operation under all conditions as well as safe handling in case of malfunction inside the ASFC system. The related safety concept is reviewed and approved by DNVGL, and has been worked

• ut according to all up-to-date rules and regulations

relevant for submarines. The development implies the fulfilment of submarine specific requirements like shock loads, magnetic, EMC etc. The design can be implemented into the already known HDW Class submarines. The space requirement of the 320kW ASFC system, consisting of four ASFC lines, is identical to the FC battery with two FCM120. The peripheral systems of the FC plant can in principle stay identical to the existing, proven systems. The ASFC system works with metal hydride storage as well as with hydrogen provided by a methanol reformer system. Additionally, some peripheral systems can be simplified. For the electrical energy to be supplied to the ship’s propulsion system, a new FC DC / DC converter (FCDD) is required. The development of this FCDD is also part of the ASFC project. The new FCDD has already demonstrated very high efficiencies of more than 98%. During ASFC development, the functionality of all components has already been proven. For example, fuel cell stacks in the original design have been operated for more than 12,000 hrs. Accumulated, fuel cell stacks have been operated for more than 73,000 hrs now. Furthermore, all components have either been tested at component or already at system level.

4 Conclusion

With LIB and ASFC, thyssenkrupp Marine Systems has developed the most modern energy system for non-nuclear submarines. The system has more capacity and reliability than existing energy systems, thus enabling future submarines to have a higher operational availability, dive longer and, operate more flexible.

5 References

[1] S. Krummrich, Fuel Cell AIP – Maturity and Innovation for Today and Tomorrow, UDT 2017 [2] S. Krummrich, Advanced Submarine Fuel Cell (ASFC) - the FC System for the future, Naval Forces Special Edition SUBCON 2019

6 Author/Speaker Biographies

Peter Hauschildt Born 17.05.1969 1998-2002 Specialist on Research and Development, Project Manager R&D Ingenieurkontor Lübeck (IKL); 2002-2004 Head of Group Research and Development Naval Ships at Howaldtswerke-Deutsche Werft GmbH 2004-2015 Director Research and Development, Conceptual Design, Projects German Navy at Howaldtswerke-Deutsche Werft GmbH, later thyssenkrupp Marine Systems GmbH 2015-2018 Head of Product Management and R&D 2018- today Head of Technology, Innovation and Sustainability