FEATURE

Fuel Cells Bulletin September 201412

Driven by regulationIn 2009, the European Parliament and the Council of Europe passed a regulation to reduce CO2 emissions of passenger cars, giving manufacturers the order to reduce their average CO2 emissions of their product line down to 95 g CO2/km by 2021.[1] This target reflects the need to drastically reduce greenhouse gas emissions.

Although ambitious, the objective is realistic, and one industry answer is the electric vehicle. Depending on the source of primary energy and also the energy/fuel distribution system, electric vehicles such as fuel cell electric vehicles (FCEVs), battery electric vehicles (BEVs), or plug-in hybrid electric vehicles (PHEVs) in electric drive mode do not emit CO2 on a well-to-wheel basis.

FCEVs can be instrumental in helping Europe to meet its environmental goals. As the most abundant element in nature, hydrogen as a fueling source makes sense. However, getting an infrastructure in place to assist in fueling the number of FCEVs that regulators hope to see on the roads will take innovative developments in technology [Figure 1]. As new hydrogen compression technology is developed and adapted, the industry is paving the way for an advanced hydrogen infrastructure worldwide.

The Linde Group has been at the forefront of this advancement, and many of the world’s hydrogen fueling stations (HFS) are equipped with Linde technology. The company has actively shaped this area for the last 25 years with its compression technology, including its cryogenic hydrogen pump and ionic compressor, the latter being a key feature at the world’s first small-series production facility unveiled in July in the Austrian capital, Vienna.

Infrastructure to refuel hydrogen FCEVsFCEVs face the same problems as the BEV, since vehicle and infrastructure manufacturers are confronted with the ‘chicken or the egg’ causality issue. Earlier infrastructure projects which conquered the same challenges (i.e. mobile communications networks or railway networks)[2] show that public hydrogen fueling stations are one of the steps from prototype market to real rollout.

In July of this year, the first small-scale serial production of HFS worldwide was launched at a plant in Vienna.[3] The production capacity has increased to around 50 HFS per shift per annum in 2014 [Figure 2]. The responsible department developed and has

tested an HFS type over more than three years in a wear test. It fulfills the specification of the H2 Mobility consortium and the SAE requirements.[4] This type of HFS also includes the ionic compressor technology, and has been optimised with respect to initial costs, operating costs, energy consumption, and footprint.

The development of this small-series production capability is a key milestone to powering the hydrogen infrastructure, as the facility will allow Linde to deliver its proven technology worldwide. Many ground-breaking hydrogen fueling innovations have originated from the company’s research and development hubs in Munich and Vienna, including the company’s cryogenic pump and its compact ionic compressor, the IC 90.

Main types of HFSIn this relatively small market for hydrogen refueling, stations for gaseous refueling of 350 or 700 bar (35 or 70 MPa, 5000 or 10 000 psi) tanks are the most common

Linde pioneers hydrogen compression techniques for fuel cell electric vehiclesInnovative hydrogen compression technology is needed to help roll out the required hydrogen infrastructure to refuel the growing number of fuel cell electric vehicles (FCEVs) that are expected to hit the road in the next few years. The Linde Group has been at the forefront of these advances, and many of the world’s hydrogen fueling stations (HFS) are equipped with Linde technology. The company has developed a cryogenic hydrogen pump and ionic compressor, the latter being a key feature at the world’s first small-series production facility unveiled in July in Vienna.

Figure 1. Linde is responsible for the overall hydrogen handling process at Total’s new ‘Green Hydrogen Hub’ (H2BER) hydrogen fueling station at the Berlin Brandenburg Airport under construction in Germany.

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technology. There are three pressurisation methods for gaseous refueling:

Indirect refueling: The pressurising unit delivers hydrogen from any supply into high-pressure buffer storage. For 700 bar refueling the high-pressure buffer storage usually consists of vessels with an operat-ing pressure between 850 and 1000 bar (12 330 and 14 500 psi). The pressure difference between the high-pressure buffer storage and the vehicle tank is used to stream hydrogen into the vehicle tank. Therefore, a relatively large number of high-pressure vessels are needed, but the required capacity of a pressurising unit is much lower than for direct refu-eling.Direct refueling: The pressurising unit directly delivers hydrogen from any supply into the vehicle tank. To fulfill the required refueling specifications of three minutes for a passenger car,[4] the capacity of the pressurising unit has to be multiple times higher than for indirect refueling. Only a small or no high-pressure buffer storage is required.Booster refueling: This is a combination of indirect and direct refueling. In the first step, the pressurising unit delivers hydrogen from the supply into medium-pressure buffer storage. For 700 bar refueling the medium-pressure storage usually consists of vessels with an operat-ing pressure between 300 and 550 bar (4350 and 7980 psi). The second step is to use the pressure level of the medium-pressure buffer storage at the inlet of the pressurising unit. This leads to an enor-mous delivery rate, which makes direct refueling possible.

Layout and function of typical 700 bar HFS for indirect fillLike common compressed natural gas (CNG) fueling stations, an HFS consists of three main parts [Figure 3]. First in line is the supply, which could be any source of hydrogen (i.e. tank for gaseous hydrogen, electrolyser, liquid hydrogen tank, hydrogen pipeline). The second part is the compressor station, including the hydrogen compressor, control valves, high-pressure buffer storage, and gas conditioning unit. The last is the dispenser, which includes the user interface, temperature compensation unit, and the fueling equipment.

The hydrogen compressor supplies the required hydrogen for fueling from hydrogen supply storage into the high-pressure buffer storage of the system. This process ends as soon as the target pressure of the high-

pressure buffer storage is reached. If refueling equipment is connected to the nozzle of an FCEV and the ‘start’ button is pressed on the dispenser, the system starts the pressure leak test with hydrogen supplied over the dispenser line. Using the measured values from the leak test, the control unit calculates the amount of hydrogen which is to be filled.

If the leak test is completed successfully, the refueling will start and take a maximum of three minutes.[4] For 700 bar, three minutes of indirect refueling of hydrogen has to be cooled down to –40°C to prevent the vehicle tank from overheating. Therefore the gas conditioning unit cools the hydrogen down, and the temperature compensation unit compensates for the heat entering the dispenser line. Cooled dispenser lines are available, but it leads to higher initial and operating costs.

The refueling itself works over the pressure equalisation from the high-pressure buffer storage to the vehicle tank. If the pressure in the high-pressure buffer storage drops beyond a specific limit, the compressor starts operation and fills the high-pressure buffer storage to the maximum again.

Main equipment for hydrogen pressurisation

To fill 700 bar vehicle tanks, the pressurisation units need to reach outlet pressures of up to 1200 bar (17 400 psi).

Since standard compressors and pumps are not suitable for adequate delivery rates at such high pressures, companies such as Linde have adapted existing technologies, or have developed new ones to satisfy the requirements of the car manufacturers [Figure 4].

Fuel Cells Bulletin

Figure 2. Assembled IC 90 ionic compressor stations lined up for dispatch at the Vienna Application Centre small-series manufacturing facility.

Figure 3. Flow chart of Linde’s hydrogen fueling station (HFS) for 700 bar refueling (indirect fill).

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Liquid hydrogen pump

The liquid hydrogen pump is an optimal choice to serve larger amounts of hydrogen. As the energy to increase the density of the hydrogen is spent during the liquefying stage, less energy is consumed while pressurising the hydrogen to the required pressure level. The handling of cryogenic hydrogen requires in-depth expertise to preserve the liquid state during the pumping process. The low temperature of –252.8°C (depending on pressure) is maintained by the use of specifically designed materials such as vessels, seals, and gaskets.

This type of technology includes the cryogenic hydrogen pump. During the pressurisation process, liquid hydrogen from a vacuum-insulated hydrogen tank or an equal supply is pumped from around 2.5 bar (36 psi) up to

900 bar (13 050 psi). After pressurisation and conditioning, the hydrogen is used for indirect refueling via high-pressure buffer storage or directly for refueling the FCEV.

Cryogenic pumps can reach very high delivery rates using less energy than common compressors. Normally they perform direct refueling, and this technology requires a liquid hydrogen supply. Liquid hydrogen supply is the preferred option when it comes to larger and continuous demand for hydrogen. If the extraction of the liquid hydrogen tank reaches a certain level, zero boil-off operation is possible. In this early market phase, this technology is mainly used at HFS for buses, forklift trucks and boats, because such stations usually require larger amounts of hydrogen.

Linde has made great strides in the development of cryogenic pumps, and its

cryogenic hydrogen piston pump has set new standards for the next generation of hydrogen refueling stations, with operation in several demonstration projects, for example at a Shell service station in Berlin, Germany within the Clean Energy Partnership (CEP).

Reciprocating compressors

For the early market phase and lower daily demand for hydrogen, non-cryogenic compressors are used for pressurisation. These are also suitable for liquid hydrogen sources, but gaseous hydrogen at similar temperatures could also be used at the inlet, so there are no boil-off losses. Direct refueling is also possible, but it leads to huge compressors with a high connected load. Therefore this technology is used for indirect refueling over high-pressure buffer storage or booster refueling. The advantage is a reduced compressor capacity, which also leads to smaller connected loads.

The ionic compressor is a shining example of this technology. In 2002, Linde developed the ionic compressor as a replacement for the conventional metal piston that can be used for indirect or booster refueling. Specially designed to create a nearly incompressible ionic liquid, the system has several advantages, including virtually eliminating mechanical wear, low energy consumption, a small number of moving parts, close to 100% energy conversion efficiency, low maintenance and material costs, and low noise emissions. The ionic compressor uses ionic liquid for compressing, lubrication and cooling. Ionic liquid is a liquid salt which has no vapour pressure, so it is possible to

FEATURE

Figure 4. Specification of Linde’s 700 bar European hydrogen fueling station (HFS), featuring the IC 90 ionic compressor now in series production.

Figure 5. The Linde compressor station, featuring the IC 90 ionic compressor (shown in close-up on the right).

separate it from hydrogen at the end of the compression process.

Linde’s IC 90 compact ionic compressor uses a five-stage compression concept which meets the latest fueling standards to allow for quick and safe refueling of hydrogen vehicles [Figure 5]. The ionic compressor is applied for 350 bar and 700 bar hydrogen fueling stations. It has very low energy consumption, and higher durability than normal dry-running piston compressors. The market share of this technology for 700 bar hydrogen fueling stations is >50%, so it can be labelled as state-of-the-art.

The ionic compressor is ideal for 700 bar hydrogen fueling, and has already received orders from around the world, including a deal for 28 hydrogen fueling stations with ionic compressors from Iwatani Corporation in Japan, the first of which has gone on-stream in Amagasaki, near Osaka.

‘The successful commercialisation of fuel cell cars hinges on a sufficiently widespread hydrogen infrastructure,’ says Professor Dr Aldo Belloni, member of the Executive Board of Linde AG. ‘It gives us the flexibility we need to meet rising demand in different markets. Our standard agreement with Iwatani shows that we are on the right path, along with our partners.’

ConclusionsExisting well known technologies like diaphragm or dry-running piston compressors have fulfilled the requirements of the market in the early stage

of demonstration. The big advantage was to have them available with only a few modifications, to meet the requirements of the car manufacturers. Their disadvantage is that these technologies were developed for other applications, with lower pressures and other requirements referring to initial and operating costs.

New technologies like the ionic compressor or cryogenic pump have been specially developed for 700 bar hydrogen refueling. They have the potential to (or already) meet the requirements with respect to energy consumption, performance, footprint, service and maintenance, and cost reduction. It is analogous to the gasoline-powered combustion engine and the hydrogen-powered fuel cell electric motor system. The old technology is maxed out and the new one is in the early stage of product lifecycle, which could lead to teething troubles.

The first steps in the direction of small serial production of the new technologies lead to potential cost savings of up to 30% compared to single-unit production. Further cost reduction is realistic, but it depends on the overall market uptake and hence the increasing demand for hydrogen fueling stations.

AcknowledgmentThis article has been adapted from Michael Stefan’s paper, From prototype to serial production – manufacturing hydrogen fuelling stations, presented at the 20th World Hydrogen Energy Conference, WHEC 2014 in Gwangju, South Korea in June.

References1. European Union Regulation (EC)

443/2009 of the European Parliament and Council, 23 April 2009: Setting emission performance standards for new passenger cars as part of the Community’s integrated approach to reduce CO2 emissions from light-duty vehicles. Available online: http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32009R0443

2. Marius Brand and Alexander Schmidt: Herausforderung Elektromobilität: Lehren aus den Entwicklungen des Strom-, Bahn- und Mobilfunkmarktes. et – Energiewirtschaftliche Tagesfragen, 3/2014 (March 2014) 105–107. Abstract online: http://tinyurl.com/et-brand-schmidt [in German].

3. Linde starts hydrogen station series produc-tion. Fuel Cells Bulletin (July 2014) 1.

4. Fueling protocols for light duty gase-ous hydrogen surface vehicles. SAE International Technical Information Report, SAE TIR J2601, March 2010. Available online: http://standards.sae.org/j2601_201003 [now superseded by 2014 revision].

For more information, contact: Stefan Metz, Manager of Clean Technology Communications, Linde AG, Linde Gases Division, Seitnerstrasse 70, D-82049 Pullach, Germany. Tel: +49 89 35757 1322, Email: stefan.metz@linde.com, Web: www.linde-gas.com or www.the-linde-group.com/en/clean_technology/clean_technology_portfolio/hydrogen_as_fuel/index.html

September 2014 Fuel Cells Bulletin15

FEATURE

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Heat transfer structure for DMFC stack, with heat pipe(s) to uniformly provide heat to cellsAssignee: Samsung SDI Co, KoreaInventor: M.-J. OhPatent number: US 8703357Published: 22 Apr. 2014 (Filed: 12 Oct. 2007)

Fuel feed systems to provide steady fuel flow to vapour feed

DMFC, tolerate varying reservoir pressuresAssignee: MTI MicroFuel Cells, USAInventors: J. Meschter et al.Patent number: US 8703358Published: 22 Apr. 2014 (Filed: 20 Nov. 2008)

Thin planar DMFC with integrated fuel supply and vaporisation sections, for use in mobile devicesAssignee: Sony, JapanInventors: K. Fukushima et al.Patent number: US 8703359Published: 22 Apr. 2014 (Filed: 27 June 2008)

PEMFC MEA fabrication prevents electrolyte membrane breaking or deformation, without need for high precision in die-mouldingAssignee: Panasonic, JapanInventors: Y. Tsuji et al.Patent number: US 8703360Published: 22 Apr. 2014 (Filed: 4 Dec. 2008)

Low-cost PEMFC MEA fabrication using release paper and incision part, without separate sub-gasketAssignee: Hyundai Motor Company, KoreaInventor: K.S. LeePatent number: US 8703361Published: 22 Apr. 2014 (Filed: 30 July 2010)

Laser micromachining of flexible electrolyte sheets, and electrolyte-supported multi-cell SOFC devicesAssignee: Corning, USAInventors: W.C. Blanchard et al.Patent number: US 8703362Published: 22 Apr. 2014 (Filed: 20 Apr. 2012)

Porous dendritic Pt tubes as PEMFC electrocatalysts with improved activity and durabilityAssignees: General Motors USA and University of Western Ontario, CanadaInventors: M. Cai et al.Patent number: US 8709127Published: 29 Apr. 2014 (Filed: 14 Sep. 2011)