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Fuel cells for ships

Research and Innovation, Position Paper 13 - 2012

Contact details:Kristine Bruun Ludvigsen - Kristine.Bruun.Ludvigsen@dnv.com

Eirik Ovrum - Eirik.Ovrum@dnv.com

Research and Innovation in

DNV

This isDNV

The objective of strategic research is through new knowledge and services to enable long term innovation and business growth in support of the overall strategy of DNV. Such research is carried out in selected areas that are believed to be of particular signifi cance for DNV in the future. A Position Paper from DNV Research and Innovation is intended to highlight fi ndings from our research programmes.

DNV is a global provider of services for managing risk. Established in 1864, DNV is an independent foundation with the purpose of safeguarding life, property, and the environment. DNV comprises 300 offi ces in 100 countries with 9,000 employees. Our vision is to create a global impact towards ensuring a safe and sustainable future.

Fuel cell technology has recently been proven successful in large maritime demonstration projects. Although fuel cell technology is not new, this success means that it has become relevant to discuss the potential for fuel cell technology in on-board applications and the current status of the technology, as done in the present paper. This paper also discusses certain safety aspects, and highlights the development of mathematical models for assessing performance and operational aspects of shipboard fuel cell systems via simulation.

The main drivers for developing maritime fuel cell technology are reduction in fuel consumption and less local and global impacts of emissions to air from ships. Additional benefits include insignificant noise and vibration levels, and lower maintenance requirements compared with traditional combustion engines. Key challenges include the demand for clean, low carbon fuel and the need to decrease investment costs, improve service lifetime, and reduce the current size and weight of fuel cell installations.

DNV Research and Innovation has taken a leading role in facilitating the demonstration of safe and reliable fuel cell applications for ships. In the FellowSHIP project, a 330 kW fuel cell was successfully installed, and demonstrated smooth operation for more than 7000 hours on board the offshore supply vessel Viking Lady. This is the first fuel cell unit to operate on a merchant ship, and proves that fuel cells can be adapted for stable, high-efficiency, low-emission on-board operation. When internal consumption was taken into account, the electric efficiency was estimated to be 44.5 %, and no NOX, SOX and PM emissions were detectable. When heat recovery was enabled, the overall fuel efficiency was increased to 55 %. Nevertheless, there remains potential for further increasing these performance levels.

Although operational experiences have shown that fuel cell technology performs well in a maritime environment, further R&D is necessary before fuel cells can be used to complement existing powering technologies for ships.

Summary

4

Rising fuel pRices and impending environmental regulations have created a pressure for ships to operate more efficiently and in an environmentally friendly manner. Fuel cell power production is a technology that can eliminate NOX, SOX and particle (PM) emissions, and reduce CO2 emissions compared with emissions from diesel engines. Fuel cells powered by low carbon fuels (e.g. natural gas) will have local and regional benefits as both emissions and noise are reduced. In the longer term, hydrogen fuel generated from renewables could lead to ships with zero carbon emissions.

The use of the fuel cell as an electricity generator was invented by William Grove in 1842 (Vielstich et al., 2001). Due to the success and efficiency of combustion engines, fuel cells have not been widely considered for general use, and, until recently, fuel cells have been applied only for special purposes, such as space exploration and submarines. However, rising fuel prices and a strong focus on reduction of global and local emissions have led to an increasing focus on the development of fuel cells for application in other areas as well. Recent market studies (Fuel Cell Today, 2011) have revealed that fuel cells should no longer be considered as a technology for the future; they are already commercially available today for a diverse range of applications (e.g. portable electronics, power plants for residential use, and uninterruptible power supply).

The FellowSHIP1 project designed, developed, built, and tested a 330 kW marine fuel cell power pack installed on board the Norwegian supply vessel Viking Lady (owner: Eidesvik Offshore ASA). With this first large-scale fuel cell

1 www.vikinglady.no

pilot in operation, Viking Lady docked in Copenhagen during the COP-15 international climate conference in December 2009, (Biello, 2009), (Figure 1). This not only demonstrated that fuel cells can operate successfully in a marine environment, but also confirmed the long-term efforts of DNV and our project partners towards developing and facilitating the introduction of new greener technologies (Eide and Endresen, 2010).

DNV recognized the potential of fuel cells in ships at an early stage, and has taken a leading role in research, development, and demonstration in order to facilitate safe and reliable introduction of this technology on board (Tronstad and Endresen, 2005; Mangset et al., 2008; DNV, 2008; Ovrum and Dimopoulos, 2011; Ludvigsen, 2012). Early efforts to evaluate fuel cells for marine applications include feasibility studies in the projects FCSHIP (FCSHIP, 2004) and FellowSHIP (Sandaker et al., 2005).

Large-scale marine concepts have been tested onshore in the US Ship Service Fuel Cell (SSFC) project (Hoffman, 2011) and in two EU projects, FELICITAS (2006) and MC-WAP2. While the FellowSHIP installation on Viking Lady adapted land-based technology for on-board testing, the METHAPU3 project developed solid oxide fuel cell technology that was tailored for use in marine applications. METHAPU resulted in a 20 kW installation on a car-carrier. The currently on-going PaXell4 project aims towards developing and building fuel cell units for power supply on board cruise vessels. A summary of fuel cells installed on ships and boats until 2009 is provided in McConnell (2010) where also a number of small-scale

2 www.mc-wap.cetena.it3 www.methapu.eu4 www.e4ships.de/e4ships-home.html

Introduction

5

applications such as pleasure boats, sailboats, ferries, and water taxis are listed.

DNV has supported a number of the R&D projects mentioned above (e.g., FCSHIP, FellowSHIP, METHAPU and PaXell), conducting feasibility studies, safety and risk assessments, and rule development. Through these projects, significant competence has been built, enabling us to facilitate future introduction of fuel cells on DNV classed vessels. DNV also initiated the development of a modelling platform for analysing and optimising the new increasingly complex energy systems launched for ships (Kakalis and Dimopoulos 2012).

The first part of this paper introduces fuel cell technology and highlights its advantages and challenges for marine applications. Operational experience gained through the FellowSHIP project is presented in the following section, and the FellowSHIP installation is used as a case study illustrating how advanced modelling and simulations can facilitate safe and optimal installation of future fuel cell power packs in a ship environment. Finally, the paper focuses on the safety of fuel cell installations.

Figure 1: Viking Lady in Copenhagen during COP-15, 15-17 December 2009 (Photo: Sten Donsby).

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A fuel cell poweR pAck consists of a fuel and gas processing system (the balance of plant), and a stack of fuel cells that convert the chemical energy of the fuel to electric power through electrochemical reactions. The process can be described similar to that of a battery, with electrochemical reactions occuring at the interface between the anode or cathode and the electrolyte membrane, but with continuous fuel and air supplies, see Figure 2. Different fuel cell types are available, and can be characterized by the materials used in the membrane. The most relevant types of fuel cells for ship applications are introduced in the next section. For further information on fuel cell technology see e.g. Larimine (2003).

The main advantages and challenges related to introducing fuel cell technology onto ships are presented below.

Figure 2: Basic principles of fuel cells (courtesy of FuelCellToday)

AdvAntAges:Improved efficiencyFigure 3 shows how the direct electrochemical conversion of fuel energy to electricity in fuel cells provides fewer sources of loss than in combustion engines. At optimal load, the best fuel cell stacks have an electric efficiency of 50-55 %, giving a fuel to electric efficiency of 45-50 % when internal consumption is included. These values are slightly higher than the typical values of fuel to electric efficiency for state-of-the-art marine diesel generators, which are just above 40 %. New gas engines claim to achieve efficiencies greater than 45 %. For part load operation, where combustion engines have lower efficiencies and emissions of local pollutants are higher, fuel cell power packs generally maintain or even increase their efficiency.

Figure 3: Electricity from electrochemical vs. combustion process

(illustration from www.vikinglady.no)

Losses in the electrochemical conversion process generate heat that is recoverable. Depending on the type of fuel cell technology, the amount and quality of exhaust from fuel cell stacks are high compared with combustion engines. Thermal integration with steam turbines or some form of

Fuel cells - advantages and challenges

7

a Rankine cycle (i.e., converting heat into work) can thus increase the electric efficiency significantly, as discussed in the next section.

Reduced emissions to airCO2 emissions lead to global warming. By using fuels such as liquid natural gas (LNG) or methanol that have less carbon content than conventional ship fuels, these emissions can be reduced. CO and CH4 emissions can occur from fuel cells depending on the choice of fuel, but are significantly lower than for combustion engines running on LNG. When hydrogen is used as fuel, no carbon compounds are emitted.

PM, NOX, and SOX emissions from ships can result in severe consequences to human health and the environment (e.g. Corbett et al. 2007; Eide et al. 2012). In the long-term, the potential uptake of fuel cells on board could contribute to reducing these consequences. NOX is formed by combustion at high temperatures, a process that does not occur in fuel cells, and thus NOX emissions from fuel cells are negligible. As sulphur must be removed from the fuel before it is supplied to the fuel cell, SOX emissions are eliminated. PM is not emitted from fuel cells, as the fuel cannot contain heavy hydrocarbons.

Other advantagesDue to fewer moving parts, use of a fuel cell power plant instead of a combustion engine will reduce noise and vibrations, improving comfort for crew and passengers. Fewer moving parts also lead to a reduction in maintenance requirements during operation compared with combustion engines. Fuel cell technologies that have a small balance of plant, i.e. when limited space is required for fuel and gas processing, can easily be installed in independent modules. This makes the total installation

less vulnerable to single failures and, in principle, the modules could be placed in several different locations around the ship. Together with lower vibrations and noise, modularity makes the engine room location less critical. Given that safety issues are handled appropriately, this provides a high degree of design flexibility.

chAllenges:New fuelsAll fuel cell types require either pure hydrogen or fuels that can be reformed to hydrogen and CO, either before entering the fuel cell or inside the fuel cell. The gas entering the cells must be sulphur-free, and low temperature fuel cells have restrictions on the amount of CO that can be tolerated. Some projects have aimed towards reforming marine diesel oil (MDO) to hydrogen for use with fuel cells. These projects have not yet been successful and it seems that fuel cells have greater potential when alternative fuels to MDO or heavy fuel oil (HFO) can be applied on board. Thus, the relevant short-term options are fuels such as methanol or LNG. However, the distribution network for such fuels is currently limited. Should hydrogen become more readily available in the future, this will also be a relevant option.

Investment costsThe current cost of fuel cells is high. This is due to limited market penetration and because only a few large-scale installations are in operation. For fuel cells to be relevant for ships, fuel cell manufacturing costs must be reduced. The investment costs are not expected to compete directly with combustion engines at 3-400 $/kW, and thus the lifetime costs of the installation must be compared (investments and operation). Fuel cell prices vary significantly between different fuel cell technologies. For MCFC modules, prices have been reported to be as low as 3000 $/kW, but also significantly higher. A target of 1500 $/kW has frequently

8

been used as a development goal for commercialisation of fuel cells (Escombe, 2008). Fuel cell producers claim that this target will be achieved between 2020 and 2025.

LifetimeDaily maintenance requirements for fuel cells are low, but stack replacement is necessary. Fuel cell stacks have not yet reached the goal of 40000 operating hours without suffering from significant performance degradation. Due to continuous R&D efforts, fuel cell lifetime is increasing. System design must therefore allow for replacement of the fuel cell stacks approximately every 5 years, while the remaining balance of plant typically has a 20-year lifetime.

Operational costsThe costs of stack replacement can be partly offset by reduced maintenance costs compared with a combustion engine. Due to the higher investment outlay, fuel costs need to be lower than that of a comparable combustion engine over the lifetime of the installation. As indicated by Mangset et al. (2008), reduced fuel costs due to increased efficiency and a shift to cheaper alternative fuels (e.g., LNG) may favour fuel cells in terms of life cycle costs. A possible introduction of carbon taxes may also mean that alternatives to MDO become more profitable. In general, economics of installation are significantly dependent on the assumptions made about an individual ship’s operating profile and fuel consumption, and each ship must be considered on a case-by-case basis.

Life Cycle AssessmentsLife Cycle Assessments for marine fuel cell applications have been carried out, for example by Reenaas (2005) and Alkaner and Zhou (2006). These assessments concluded that the environmental footprint favours fuel cells over conventional power generator sets (diesel engines), mainly

because higher fuel efficiency is assumed for the fuel cells. In comparison with diesel engines, the production phase has significantly higher impact on a fuel cell unit’s life cycle performance. If fuel consumption is not decreased when replacing combustion engines with fuel cell technology, then the environmental footprint will generally increase. However, there is a considerable potential for lowering energy consumption under the production phase as the technology matures (Alkaner and Zhou, 2006).

SizeThe size of fuel cell installations varies with the type of technology chosen. However, in terms of volume and weight per kW installed, it will be hard to compete with combustion engines, especially for fuel cell types that require a complex balance of plant. Estimated electric efficiency based on lower heating value of the relevant fuel, specific power, and power density are compared for two types of fuel cells power packs (cf. next section) and two types of internal combustion engines (4-stroke diesel and lean burn gas) in Table 1.

Electric power generator

Electricefficiency

(%)

Specific power

(kW/m3)

Power density(W/kg)

Fuel cell (MCFC) 45-50 3 15

Fuel cell (HTPEM) ~45 30 60

Marine diesel (4-stroke) 40 80 90

Marine gas (4-stroke) 45 80 90

Table 1: Characteristic properties of two fuel cell types and two types of combustion engines. Numbers are roughly estimated based on available product documentation for the fuel cells and DNV internal Report No 2010-0605 for the combustion engines.

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seveRAl fuel cell types exist, and their names reflect the materials used in the electrolyte. The properties of the electrolyte membrane affect the allowable operating temperatures and the nature of electrochemical reactions and fuel requirements (Larminie, 2003; U.S. DOE, 2011). During the last decades several different fuel cell technologies have been proposed and developed, and their levels of maturity, realistic efficiency potential, and future prospects vary significantly. Table 2 shows operating temperatures, and average reported fuel to electric efficiencies (when internal consumption is included), for the fuel cell types considered to be of most relevance for marine applications.

Fuel cell typeTemperature

(°C)

Electric efficiency

(%)

Proton Exchange Membrane (PEM)

30-100 35-40

High Temperature PEM (HT-PEM)

160-200 ~45

Molten Carbonate (MCFC)

~650 45-50

Solid Oxide (SOFC) 500-1100 45-50

Table 2: Fuel cell properties, (Escombe, 2008; McConnell, 2009).

Proton Exchange Membrane Fuel Cell (PEMFC) fuelled by hydrogen is the most widespread and developed fuel cell technology. It operates on hydrogen, and this needs to be of high quality as impurities will damage the membranes. High temperature PEM (HTPEM) is a modified version of PEMFC with a novel membrane that can withstand temperatures up to 200°C.

Higher temperature of operation enable a simpler balance of plant, because the needs for cooling, water management, and purification are reduced compared with PEMFC. HTPEM fuels cells also have a higher tolerance for CO, and are therefore more suitable for use with reformed fuels (methanol, natural gas, and ethanol). The PEM technologies have excellent dynamic capabilities, and electric efficiencies of around 40 % have been demonstrated. Higher efficiencies (45-50 %) have been claimed for HTPEM due to less internal energy consumption, but data derived from operating experience are limited (McConnell, 2009).

PEMFC are produced in smaller units, up to 100 kW, and are thus suited for distributed power supply. Typical applications are cars, stationary power generation, small-scale power sources, and combined heat and power systems. HTPEM fuel cell units consist of independent modules, typically 5-15 kW, with small built-in reformer units. The modules can easily be assembled into larger power packs, and up to 1 MW has been suggested. These technologies are significantly more compact than the high temperature technologies presented in the following section.

Submarines, yachts, ferries and recreational boats have been fitted with PEM fuel cells running on hydrogen. Examples are the 2 x 50 kW units on the ferry FCS Alsterwasser in Hamburg5 and the 60-70 kW installation on the ferry Nemo H2 in Amsterdam6. A 12 kW HTPEM has also been installed on the harbour ferry MF Vågen in Bergen, Norway7. A larger installation of HTPEM on a cruise vessel will be demonstrated through the PaXell project.

5 www.zemships.eu/en/index.php6 www.lovers.nl/co2zero/factsheet/7 www.tu.no/industri/article263210.ece (in Norwegian)

Fuel cell types

10

Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC) technologies are high-temperature fuel cells that are flexible regarding choice of fuel: methanol, ethanol, natural gas, biogas, and hydrogen are most commonly used. MCFC is the more mature of these two technologies, while SOFC is considered to have the greatest potential in terms of efficiency and power density. As an example, Figure 4 shows the electrochemical reactions inside a MCFC, in which both carbonate and hydrogen ions are involved in electricity production.

An electric stack efficiency of 50-55 % has been obtained from both MCFC and SOFC installations, and when internal consumption is included this is lowered to 45-50 %. High operating temperatures lead to high exhaust temperatures (400-800 °C) that, together with a large volume flux of exhaust, yield a significant potential for heat recovery. The fuel to electric efficiency can be increased to 55-60 % for MCFC plants and to above 60 % for SOFC plants when heat recovery is included (Escombe, 2008).

A complex balance of plant to handle fuel and air treatment is required for both technologies and larger units are therefore preferred. MCFC units generally have one fuel cell stack of about 200–500 kW, while an SOFC unit is built from several smaller stacks of 1-20 kW each. The SOFC units can be built to be significantly more compact than MCFC units, but the complete power packs remain large in volume compared with diesel generators. High-temperature fuel cells must operate at stable temperatures, and therefore have low tolerance to rapid load changes. In general, these fuel cell types can only be justified in applications where power and heat demands are high and stable.

High-temperature fuel cells are currently used for uninterruptable power supplies in hospitals and server parks, as well as for power generation from landfill or industrial biogas. The lack of dynamic capabilities means that these fuel cells are best suited for providing base-load electric power on ships. A methanol-fuelled marine SOFC plant of 20 kW was tested on board the car carrier Undine in 20108. The largest marine fuel cell installation to date is the 330 kW MCFC installed on board Viking Lady 9.

The uptake of these technologies is hard to project due to high market uncertainty and current investment costs. The most promising avenues, to date, are the following:

• Harbour-mode solutions, with the possibility of decreasing the detrimental health effects of chemical emissions and noise from ship traffic in urban areas, are currently of considerable interest. Fuel cells can be used as an alternative to cold ironing for all ship types that have space available for fuel cells as an auxiliary unit. The preferred fuel cell alternatives would then be HTPEM, or a hybrid combination of batteries and MCFC or SOFC, all running on low carbon fuels. If hydrogen is available, PEM or HTPEM would be the preferred choices.

• Ferries operating on short routes are suitable candidates for the first ships powered only by fuel cells due to their relatively low power requirements and frequent refuelling possibilities. The same is true for ships operating on inland waterways. Hybrid installations, with PEM fuel cells and batteries, already exist as pilot installations, and would provide a zero

8 www.methapu.eu 9 www.vikinglady.no

11

emission alternative if hydrogen can be produced from renewable sources.

• Cruise ships will benefit from the reduction of noise and vibrations, as well as from reduced local emissions while in port and cruising in environmentally sensitive areas. Most cruise ships today are diesel-electric, and a fuel cell installation could easily be integrated into the designs. The public perspective of a soot-free cruise will be a huge advantage for the first fuel cell powered cruise ships. HTPEM units are the most realistic alternatives due to their high specific power, see Table 1.

Figure 4: Chemical processes inside an MCFC (courtesy of MTU Onsite Energy)

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the supply vessel Viking Lady is the first merchant ship to have a large-scale fuel cell installation operating on board. It is also the first vessel to use high-temperature fuel cell technology. The choice of fuel cell technology was based on fuel availability and the maturity of the available technologies. The MCFC power unit, developed by MTU in Germany, had been successfully demonstrated for several land-based installations, and was modified for operation in a marine environment. The FellowSHIP project (phase II)10 was responsible for the modification, installation, testing, and operation of the power pack. When the project closed in July 2010, the system had operated for 7000 hours, demonstrating unequivocally that existing fuel cell technology can be integrated into a ship environment.

LNG is the main fuel in the gas-electric propulsion system of Viking Lady, and the vessel therefore provided a good test-bed for MCFCs, since no additional fuel system was needed. In the current installation, the MCFC delivers power to a direct current (DC) link that is connected to the ship’s alternating current (AC) bus through power converters. The ship’s electric propulsion system therefore consume fuel cell power equivalently to power provided by the main generators.

The fuel cell stack, together with the required balance of plant, is located in a large, purpose-built container (13 x 5 x 4.4 m). Project-specific electrical components (transformers, converters and DC bus) designed to protect the fuel cell from potentially harmful disturbances on the

10 Partners of the FellowSHIP project, phase II, were the ship-owner Eidesvik Offshore ASA, Wärtsilä Ship Design AS, Wärtsilä Norway AS, MTU Onsite Energy, and DNV Research & Innovation, financially supported through the Research Council of Norway, Innovation Norway, and the German Federal Ministry of Economics and Technology.

power grid, are situated in a standard 20-ft container; see Figure 5. The total weight of the containers is 110 tons, but both weight and volume could be significantly reduced in future fully integrated systems. Since the FellowSHIP installation was retrofitted, the current design allows for temporary installation on deck, as well as an onshore test period for the whole power pack, and therefore the size and weight were not optimised.

An onshore test period ensured proper functionality of all power and control interfaces between the two containers and the overall safety systems, and minimised the time needed for hook-up and modifications on board. Viking Lady was delivered for operation on the North Sea in April 2009, and, in September of the same year, the 330 kW MCFC power pack was installed. The fuel cell was connected to the main switchboard for the first time in December 2009. After initial testing, Viking Lady became the first vessel to obtain the class notation FC-Safety, as described in the DNV Rules (DNV, 2008).

During its first year in operation, the fuel cell stack showed no signs of degradation, indicating that the measures taken to protect the fuel cells were appropriate. The stack was protected against electric disturbances. In addition, ship movements, hull vibrations, and air salinity were also taken into consideration when designing the fuel cell stack and its container and support systems. In January 2012, the fuel cell was cooled down and conserved for future demonstration projects. A total of 18 500 operating hours were logged without signs of severe performance degradation. Approximately half of the time logged was in idling mode.

Fully loaded, the fuel cells produced electricity at a measured electric efficiency of 52.1 % based on the lower

Fuel cell testing on-board Viking Lady

13

Figure 5: Stord, Norway, September 2009: Installing containers on Viking Lady, the white for fuel cells and the blue for power electronics.

heating value of the LNG. Although exact measurements of gas to grid efficiency were not possible for the current system setup, this was estimated to be 48.5 % including internal consumption, and 44.5 % when DC/AC conversion was also accounted for. A heat exchanger that produced warm water from the fuel cell exhaust was tested, with about 80 kW heat recovered. This increased

the overall fuel efficiency to slightly above 55 %. With optimal system integration, there is the potential for increasing the electrical efficiency to close to 50 %, and the fuel efficiency up to 60 %.

The FellowSHIP installation is not classed as main or auxiliary power, but is considered as supplementary power.

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Viking Lady’s main engines must always be on-line. In some operating conditions, e.g., in calm weather and while docked in harbour, a load reduction is required for the fuel cell in order to avoid the main engines operating at unfavourable load conditions. Load changes on an MCFC must be slow, but when load changes are performed in a controlled manner, operating at low-load conditions is not dangerous for these fuel cells and may even prolong the lifetime of the stack. Nevertheless, the aim is for continuous operation at close to full load in order to allow full exploration of the environmental benefits and fuel-saving potential of this technology.

Although the cost, weight, and volume of the test installation were high, the feasibility of installing and operating a fuel cell power pack in a marine environment was successfully demonstrated on board Viking Lady. In future marine MCFC designs, more focus should be directed towards thermal integration, utilizing the high quality exhaust heat, and on including some form of energy storage to allow for stable load conditions for the fuel cell.

In order to explore the potential benefits of combining fuel cells and engines with energy storage, Viking Lady will host another large-scale technology demonstrator. The FellowSHIP project is to be continued, and a battery pack for hybrid operation with the combustion engines and the fuel cell will be installed within 2013 (Eason, 2012). The project will also make modifications to allow the ship to be powered only by the combined fuel cell and battery power pack during certain test runs and in harbour mode.

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in the fellowship pRoJect, DNV developed a detailed mathematical model describing the thermodynamic behaviour and transport phenomena inside the marine MCFC installed on Viking Lady. The main focus of the model development was to analyse operation and performance of the fuel cells under steady and dynamic conditions. The model was calibrated by measurements on board Viking Lady, and details of the implemented model and results have been published in Ovrum and Dimopoulos (2011). A similar modelling approach will be followed for the HTPEM fuel cells in the on-going PaXell project.

Modelling and simulation have been used extensively to analyse fuel cells and their potential in marine power systems (Bruun, 2009; Bensaid et al., 2009; San et al., 2010). Our modelling work follows the key concepts and approach developed in the DNV COSSMOS (acronym for Complex Ship Systems Modelling & Simulation) framework (Dimopoulos and Kakalis, 2010). Within this framework, DNV develops model-based methods

and a computer tool for the synthesis, design, and optimisation of integrated marine machinery systems (Kakalis and Dimopoulos, 2012). The fuel cell models enable investigation of thermal and electrical integration of the fuel cell for design and optimisation of ship power production systems for different modes of operation.

Figure 6 shows that the model predictions agreed well with the actual MCFC unit on board Viking Lady. The model was calibrated against a range of data from on-board measurements, and fi nally validated against a different set of test data. The model shows an average error of about 4 %, as seen in the fi gure below, where all the values are relative to a reference value and therefore dimensionless. The following examples show the model in use:

Dynamic modelling of fuel cells

Figure 6: Calibration and validation of the MCFC (Ovrum and Dimopoulos, 2011).

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Reliability of power production is of paramount importance in the marine setting, as a ship should always have the power to return to port. Studies of temperature distribution, shown in Figure 7, can provide valuable information on how the use of the fuel cell affects its lifetime, since hot spots and large temperature variations in time degrade the cell performance. By simulating the dynamics of the system, the loads and fuel utilization that the fuel cell must endure on ships with different operating profiles can also be investigated. Thus, modelling can manage, and potentially improve, the lifetime and reliability of a fuel cell system.

Capability of representing transients is essential in order to estimate how a novel system responds to critical events. As an example, loss of fuel flow can be simulated as shown in Figure 8. The fuel flow is reduced by 1 % of its original flow every second, increasing the fuel utilization, until after 40 seconds the system regains control. Another critical event is overheating of a fuel cell system due to loss of gas flow. With such high values of fuel utilization or temperatures, the MCFC might be degraded, reducing its performance and lifetime. These are examples of using modelling to supplement potentially destructive experiments for design studies of novel marine machinery systems.

Figure 7: Temperature distribution in fuel cell membrane at 100 % load (Ovrum and Dimopoulos, 2011).

Figure 8: Loss of fuel flow and the consequences for current density (Ovrum and Dimopoulos, 2011).

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Preliminary studies of marine fuel cells (FCSHIP, 2004) focused on gaining a common understanding of basic safety requirements. The studies concluded that safe fuel cell systems are technically possible, but that there was a lack of standard guidelines and rules to facilitate the design and approval process. The first rules for fuel cells were published by DNV in 2008 (DNV, 2008), and class guidelines were issued by GL in 2003 (GL, 2003). In the DNV rules, there are two different class notations for fuel cells; FC-SAFETY is mandatory for all fuel cell installations, and, if the fuel cell unit is used for main or auxiliary power, the class notation FC-POWER is also mandatory (Table 3). An important part of the FellowSHIP project was to develop and implement these rules to allow for safe installation on Viking Lady.

The main safety hazard to be handled with on-board fuel cells is the introduction of new fuels with low flammability limits such as LNG, methanol, or hydrogen. This sets requirements for sufficient ventilation, alarm systems, and fire protection, as well as introducing other measures to limit the likelihood and consequences of a gas leakage. LNG as a fuel is well-covered by rules, and there is significant experience with such installations.

However, there is far less experience with ship-borne hydrogen or methanol installations. The use of methanol on board was demonstrated in the METHAPU project. In the FellowSHIP project, in which LNG was used as main fuel and hydrogen as auxiliary gas, safety measures were implemented that resulted in a FC-SAFETY notation for Viking Lady.

Reliability and redundancy are very important issues if fuel cells provide propulsion or auxiliary power, according to the FC-POWER notation. This also sets requirements to the control systems and the interface with the ship’s overall power distribution.

In order to stay ahead of the technological development, DNV is positioned at the forefront of development of rules for new technologies. In this context, a continuation of the FellowSHIP project was kicked-off in 2011. This project, named HybridShip, is concerned with introducing batteries for on-board energy storage, integrated with fuel cells and gas engines.

A 200 Class notation 201 Ships where the fuel cell power is used for essential, important or emergency services shall satisfy the requirements in this rule chapter and will be given class notation FC-POWER.

202 Ships where the fuel cell power is not used for essential, important or emergency users shall satisfy the safety and environmental requirements. Installations complying with the requirements in this chapter, except Section 2 will be given class notation FC-SAFETY.

Table 3: Extract from DNV Rules for classification of Ships, Pt.6 Ch.23: “Fuel cell installations”

Safe operation

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The FellowSHIP demonstration project, led by DNV, developed and installed a 330 kW fuel cell power pack on board the offshore supply vessel Viking Lady. This was the first large-scale fuel cell unit to be installed on a commercial ship. The system delivered power to the ship grid for over 7000 hours, demonstrating unequivocally the applicability of fuel cells for ships. The fuel cell unit on board Viking Lady had an overall efficiency of above 55 % when heat recovery was included. DNV rules for introducing fuel cells were developed, and the DNV class notation FC-SAFETY was obtained by Viking Lady. This ensured safe integration of new fuels (LNG and hydrogen), as well as safe integration of fuel cells into the ship’s power system.

High fuel efficiency over a wide range of loads and elimination of emissions of SOX, NOX, and PM, thereby avoiding local consequences of air pollution from ships on human health and the environment, are, together with reductions in noise and vibrations, the main benefits from introducing fuel cells to ships. CO2 emissions are also reduced, or even completely eliminated if hydrogen from renewables becomes available, thus lowering the contribution from shipping to global warming.

The electrical efficiency of fuel cell stacks depends upon the fuel cell technology, with values ranging from 35-50 %. This efficiency is only slightly higher than the values claimed from generating electricity using state-of-the-art combustion engines. Therefore, optimal system integration, resulting in additional electric and thermal power, is essential. Significant reduction in costs is also required if the fuel cell technologies discussed in this paper are to become competitive for ships. With the recent commercialisation of certain land-based fuel cell applications, there is reason to believe that costs will fall.

For ship applications, reductions in size and weight are also of immense importance.

DNV recognizes that fuel cells can become a part of the future power production on ships. By leading and participating in large R&D and pilot projects, we have built competence and developed rules, thereby paving the way for safe and smooth introduction of fuel cells for ships. Methods to enable assessments of new fuel cell designs and their system integration through modelling and simulation have also been developed, in support of DNV’s class and advisory services. We recognize that it will take time before fuel cells can become a realistic on-board alternative; this is mostly because of price, but also because of limited product development tailored to the maritime market. National and regional incentive schemes for environmentally friendly technologies could also play a central role regarding when fuel cells can become cost-competitive. Increased availability of alternative fuels, such as LNG and hydrogen, may also accelerate introduction. The FellowSHIP project has taken some important first steps towards a possible future for fuel cells on ships.

It is concluded that fuel cells for shipping require further R&D before this technology can complement existing powering technologies. However, in the near future we might expect to see successful niche applications for some specialised ships, particularly with hybrid systems.

Conclusions

19

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