Energy Saving Devices for Hydrogen Fuel Cell Ships

Version	Summary	Created by	Modification	Content Size	Created at	Operation
1		Callum Stark	+ 1704 word(s)	1704	2022-03-15 07:28:52	\|
2	corrected the format	Dean Liu	-1 word(s)	1703	2022-03-28 04:39:19	\|

This entry is adapted from the peer-reviewed paper 10.3390/jmse10030388

Energy saving devices (ESDs) for ships are more important than ever, as implementation of rules and regulations restrict the use of fossil fuels while promoting zero-emission technology. Researchers aims to bridge that gap by firstly identifying the new challenges that a hydrogen-powered propulsion system brings forth and then reviewing the quantitative energy saving capability and qualitive additional benefits of individual existing and emerging ESDs in standalone and combination, with recommendations for the most applicable ESD combinations with hydrogen-powered waterborne transport presented to maximise energy saving and minimise the negative impact on the propulsion system components

energy-saving devices hydrogen propulsion

1. Introduction

The decarbonisation of waterborne transport is arguably the biggest challenge faced by the maritime industry presently. By 2050, the International Maritime Organization (IMO) aims to reduce greenhouse gas emissions from the shipping industry by 50% compared to 2008, with a vision to phase out fossil fuels by the end of the century ^[1]. To meet such targets, action must be taken immediately to address the barriers to adopt the various clean shipping options currently at different technological maturity levels. Green hydrogen as an alternative fuel presents an attractive solution to meet future targets from international bodies and is seen as a viable contributor within a future clean shipping vision ^[2]. The cost of hydrogen fuel—in the short-term at least—is higher compared to conventional fuel; therefore, energy-saving devices (ESDs) for ships are more important than ever as implementation of rules and regulations restrict the use of fossil fuels while promoting zero-emission technology. However, existing and emerging ESDs in standalone/combination for traditional fossil fuel driven vessels have not been researched to assess their applicability for hydrogen-powered ships, which present new challenges and considerations within their design and operation.

2. Key Components of a Hydrogen Fuel Cell-Powered Propulsion System

It is envisaged that future shipping will run solely on sustainable means with no reliance on fossil fuels; therefore, the hydrogen-powered propulsion system discussed will be as such, although within the transition phase there will likely be some percentage of craft using hydrogen–diesel hybrid solutions until a global commercially viable green hydrogen supply chain and bunkering infrastructure can be established.

A potential future hydrogen-powered propulsion system are shown in Figure 1. The hydrogen could be stored as either compressed gas, liquid or metal hydrides—all with their own challenges. Compared to typical diesel fuel, the volumetric energy density for all forms of hydrogen is considerably less, meaning that, generally, to complete the same route with the same amount of fuel when compared to conventional fuel, the storage required will increase by several times, which will reduce cargo space.

Figure 1. Hybrid (fuel cell/battery) hydrogen-powered propulsion system.

Within the fuel cell, the hydrogen reacts with oxygen supplied by the air intake to produce electricity, which can be supplied to the electric motor to power the vessel. Compared to internal combustion engines, fuel cell technology can achieve a higher efficiency of 65% when compared to roughly 40% ^[3], although low-speed two-stroke diesel engines commonly used on larger ships can achieve efficiencies of up to 50% with a waste heat recovery system ^[4]. More recently, the use of fuel cell technology for maritime applications has been reviewed, suggesting that for journeys below 12 h, a liquified hydrogen low-temperature polymer electrolyte (also known as proton exchange) membrane fuel cell (LT-PEMFC) provides a power-dense solution for ships; however, for journeys above 100 h, the limited hydrogen storage density is expected to result in 1.5–5 times larger total system volumes compared to alternative systems ^[5]. Mekhilef et al. ^[3] suggested that PEM fuel cell technology was particularly suited for transportation applications such as automotive and buses. DNV GL., Shu et al. ^[6] conducted a dedicated risk assessment of fuel cells for shipping applications and concluded that the most attractive fuel cell system was the PEM fuel cell followed by the high-temperature PEMFC. The PEM fuel cell is a mature technology being successfully used in maritime applications when compared to its high-temperature counterpart which is still at a demonstrator phase. The major disadvantage of the PEMFC is sensitive to impurities in the hydrogen, a complex water management system (both gas and liquid) and a moderate lifetime. However, they are lightweight and more compact when compared to other fuel cell technologies, which makes them well suited to shipping applications, and they operate at relatively low temperatures, which makes it easier to contain and reduce thermal losses. Xing et al., 2021 ^[7] conducted a review of fuel-cell power systems for maritime applications and concluded that although fuel cells have significant advantages such as reduced emissions, improved efficiency and low noise operations, drawbacks such as power capacity, durability and economic costs are the main barriers to adoption for the technology. It was also suggested that development in strict rules and regulations, investment in infrastructure in fuel bunkering systems and development of design rules and operational guidelines were necessary as the technology develops.

On the other hand, quick spikes in power demand from the vessel can cause a high voltage drop in the fuel cell in a short time, known as starvation, which can reduce performance and lifetime of the fuel cell ^[3]. The consensus is that fuel cells can be combined with batteries which can supply the quick spikes in power demand, therefore reducing the negative impact on the fuel cell and improving the responsiveness of the hybrid (battery/fuel cell)-powered propulsion system in such conditions, while overcoming the drawbacks of a battery-only system such as very low distance range and extensive recharging time ^[8]^[9]. When the vessel is operated at a low power, such as while loading/unloading, the fuel cell can recharge the battery, while the fuel cell is expected to supply the power demand at cruise speed and maximum power demand supplied by both fuel cell and battery. The fuel cell could also be used to supply auxiliary power for the hotel load of a ship ^[10]. However, the hybridisation of fuel cells and batteries requires further research to understand their capability to deliver the load demands; thus, an appropriate power management system is critical to create an effective power delivery system ^[5]^[11].

3. Impact of Transient Power Fluctuations on Hydrogen Fuel Cell-Powered Propulsion

Transient loads can have a negative impact on the fuel cell performance and lifetime, and such time-varying loads can occur when marine vessels are in operation. Transient loads can occur due to: blade passing fluctuations behind non-uniform wake, propeller operating under cavitation and/or ventilation, ship manoeuvring/dynamic positioning, and ship in waves/strong wind ^[12]. However, in terms of severity, operating in head waves is the most challenging in terms of dynamic loads ^[13].

However, the limit of time-varying load fluctuations for fuel cell applications for the vast range of waterborne transport in operation still needs to be further investigated and uncovered; this will likely depend on aspects of the propulsion system such as fuel cell stack/battery combination, power management system and power demand of the vessel. Boekhout ^[11] investigated the implementation of fuel cell battery systems on hydrogen-powered ship propulsion for high-speed craft, suggesting that load changes of above 10% of its maximum power per second should be avoided for PEMFC. It was also deduced that the fuel cell could follow load variations with a low-frequency; however, the fuel cells reach their dynamic limit with high-frequency load fluctuations. For one fuel cell stack, the encounter frequency limit was 1 rad/s, while for a combination of two fuel cell stacks it was 1.2 rad/s. It was recommended, from a power management point of view, for the battery to supply the desired power in high-frequency load fluctuations due to its high responsiveness, protecting the fuel cell. As this may be case-specific, it is reasonable to assume in the current state of developments that any form of reduction in transient load mitigation from the different aspects of ship operation mentioned would be an additional benefit to the vessel, improving performance and prolonging the life of the hydrogen-hybrid propulsion system.

Although energy-saving devices (ESDs) have been continually developed to meet the IMO guidelines over the last few decades, they have not been designed with a scope to be applied within hydrogen-fuelled propulsion systems, which the IMO now sees as a potential future shipping fuel to meet their current ambitious targets. As regulations to achieve decarbonisation tighten, the use of more costly (in the projected short-term at least), alternative fuels will increase, and this will make ESDs more important than ever. Therefore, it is now crucial to identify the challenges of adopting hydrogen-fuelled propulsion for maritime vessels in comparison to the traditional propulsion system, review the emerging and existing ESDs and, finally, how they can be combined in harmony with the hydrogen propulsion system to contribute to solving the technical and economic barriers for the adoption of hydrogen fuel, maximise energy efficiency and meet the IMO’s targets for the shipping industry.

4. Energy-Saving Devices (ESDs) and Their Suitability for Hydrogen Fuel Cell-Powered Propulsion

Energy savings can be achieved through numerous methods, for example, technical measures such as hull optimisation, waste and heat recovery systems installed on the main propulsion plant, and operational measures such as route optimisation, slow steaming and maintenance optimisation ^[14]. However, this entry of focused on energy-saving devices that can be retrofitted or incorporated into new builds on the exterior of the ship.

Energy-saving devices can be categorised into five areas: hull resistance reduction measures, propeller flow conditioning devices, propeller/hub modifications, manoeuvring energy-saving devices and renewable energy-assisted propulsion (see in Figure 2). They vary in general location with respect to the vessel as are shown in Figure 3. Quantitative energy saving or propulsive efficiency savings are reviewed, the method in which the saving was achieved such as model-scale tests, CFD and full-scale demonstrations as well as the vessel types best suited for each ESD. Focus is also given to additional qualitive benefits that could improve the suitability of the ESD for hydrogen-powered propulsion by mitigating aspects of ship operation that can negative impact on the hydrogen propulsion system. Finally, research conducted on combination ESDs are reviewed while combination ESDs that would be most compatible with hydrogen-powered ships based on the available literature are suggested by the researcher’s as well as a conservative estimated energy saving.

Figure 2. Categorisation of existing and emerging energy-saving devices (ESDs).

Figure 3. General application of energy-saving devices (ESDs) from a location point of view.

References

International Maritime Organization (IMO). IMO Action to Reduce GHG Emissions From International Shipping; International Maritime Organization: London, UK, 2019.
McKinlay, C.J.; Turnock, S.R.; Hudson, D.A. Route to zero emission shipping: Hydrogen, ammonia or methanol? Int. J. Hydrog. Energy 2021, 46, 28282–28297.
Tronstad, T.; Atrand, H.; Haugom, G.; Langfeldt, L. Study on the Use of Fuel Cells in Shipping; EMSA European Maritime Safety Agency: Lisbon, Portugal, 2017.
Shu, G.; Liang, Y.; Wei, H.; Tian, H.; Zhao, J.; Liu, L. A review of waste heat recovery on two-stroke IC engine aboard ships. Renew. Sustain. Energy Rev. 2013, 19, 385–401.
van Biert, L.; Godjevac, M.; Visser, K.; Aravind, P.V. A review of fuel cell systems for maritime applications. J. Power Sources 2016, 327, 345–364.
Thounthong, P.; Raël, S.; Davat, B. Energy management of fuel cell/battery/supercapacitor hybrid power source for vehicle applications. J. Power Sources 2009, 193, 376–385.
Xing, H.; Stuart, C.; Spence, S.; Chen, H. Fuel cell power systems for maritime applications: Progress and perspectives. Sustainability 2021, 13, 1213.
Corbo, P.; Migliardini, F.; Veneri, O. Dynamic behaviour of hydrogen fuel cells for automotive application. Renew. Energy 2009, 34, 1955–1961.
Markowski, J.; Pielecha, I. The potential of fuel cells as a drive source of maritime transport. IOP Conf. Ser. Earth Environ. Sci. 2019, 214, 012019.
Ballard Power Systems Inc. Fuel Cell Applications for Marine Vessels; Ballard Power Systems Inc.: Burnaby, BC, Canada, 2019.
Boekhout, M. Hydrogen Powered Ship Propulsion for High-Speed Craft the Implementation of Fuel Cell Battery Propulsion Systems. Master’s Thesis, Delft University of Technology, Delft, The Netherlands, 2020. Available online: http://repository.tudelft.nl/ (accessed on 5 January 2022).
Taskar, B.; Yum, K.K.; Steen, S.; Pedersen, E. The effect of waves on engine-propeller dynamics and propulsion performance of ships. Ocean Eng. 2016, 122, 262–277.
Foteinos, M.I.; Christofilis, G.I.; Kyrtatos, N.P. Response of a direct-drive large marine two-stroke engine coupled to a selective catalytic reduction exhaust aftertreatment system when operating in waves. Proc. Inst. Mech. Eng. Part M J. Eng. Marit. Environ. 2020, 234, 651–667.
Xing, H.; Spence, S.; Chen, H. A comprehensive review on countermeasures for CO2 emissions from ships. Renew. Sustain. Energy Rev. 2020, 134, 110222.

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