Low-emission energy supplies at truck stops · Projektinfo 02/2013 Low-emission energy supplies at truck stops Engine off: Diesel-operated fuel cell system supplies electricity to

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Projektinfo 02/2013

Low-emission energy supplies at truck stops Engine off: Diesel-operated fuel cell system supplies electricity to parked commercial vehicles

Long-distance trucks also require electrical power when they are not moving or parked in truck stops – for air conditioning, communications technology, lighting, kettles and refrigerators. However, if the driver lets his 400-PS engine idle, he will use too much diesel – and noise, exhaust fumes and soot pollute the environment. As an environmentally friendly alternative, engineers are developing an engine-independent onboard power supply with a high-temperature fuel cell system that uses diesel as the fuel.

For truck drivers, the driver’s cabin is both their workplace and home when they are underway. This means that there is also a considerable requirement for a low-emission and energy-efficient onboard power supply during resting periods. This is being exacerbated by stricter environmental requirements that, for example, prohibit American truck drivers from running their truck engines while at standstill in order to operate their heating and air conditioning systems. These so-called anti-idling laws make it necessary to install an independent onboard power supply in long-distance trucks. In order to achieve this task, developers are working on a new onboard power system with high-temperature fuel cells. The solid-oxide fuel cells (SOFCs) can supply the loads in the driver’s cabin more efficiently, quietly and with fewer emissions than the diesel generators already on the market. With a targeted efficiency of 30%, a fuel cell-operated auxiliary power unit (APU) is much more economical than an engine-operated APU, which achieves around 25%.Fuel cell devices produce electrical power with five times the efficiency of an idling truck engine and, compared with diesel-operated APUs, achieve greater efficiency and thus 20% fuel savings. The pollutant emissions of nitrogen oxide, carbon monoxide and soot particles are close to the detection limit. The new system is quieter than auxiliary heating systems.

This research project is funded by the

Federal Ministry of Economics and Technology (BMWi)

Development of a compact and economical high-temperature fuel cell for trucksAt the same time, mobile high-temperature fuel cells for providing auxiliary air conditioning and electricity in truck cabins need to be light, compact and very robust. They are subject to shaking and vibrations and their components, in particular the stack seals, must be capable of with-standing large thermomechanical loads caused by heat-ing and high operating temperatures. The combustion gas for operating fuel cells is reformed from “onboard” diesel fuel. The sulphur content of this widespread fuel causes critical interactions between the system compo-nents in all operating phases. This presents the developers with the challenge of reducing the degradation of the overall system to a minimum. In order that the highly promising new technology can establish itself on the market, its performance capability, stability and production tech-nology needs to be improved.The new fuel cell device is based on a lightweight SOFC stack. The device combines all the system components within a highly compact space and at extreme tempera-tures (Fig. 1).As part of a joint research project, the companies in-volved are developing a system that achieves maximum power density, works reliably in the long term and is cost-effective. They are improving the function and sta-bility of the reformer, fuel cell, burner and heat ex changer, and are developing electronic components as well as a fuel and air supply system suitable for vehicles that has exhaust gas recirculation. The first steps towards achieving a pre-production series have also been taken. Until now, the developers have been worked on secur-ing the basic function of the overall system across sev-eral cycles.In a follow-up project called “Development of SOFC-APUs for commercial vehicles”, which was started in 2012 and will run until 2015, they are concentrating on service life tests and serial production development. The fuel cell system is scheduled to reach market maturity in three years time with a sales potential in the mid-five-figure area.The progress already made by the companies involved in improving the efficiency and function stability is out-lined in the following section.

Many small steps to series productionThe main aims of the stack development are to ensure the cycle stability and short start-up times. The developers have been able to achieve this by using a consistently light-weight structure made of thin sheeting and by simulta-neously minimising the cell thickness. For the SOFC seal-ing they have developed a metal-ceramic joint concept in which the ceramic layer provides the electrical insulation and the metal solder guarantees the cycle stability. Further improvements in cleaning the reformer gas are intended to prevent sulphur from rapidly degrading the catalyst. The components and parts must be optimised so that they can withstand the high operating temperatures of around 800 °C as well as the high temperature fluctua-tions when starting up and shutting down the system. Using new material combinations the developers are working on reducing damage caused by material failure. New joint techniques and stack designs are improving the thermomechanical properties and thus the durabil-ity. Changes in the cathode material, electrolyte thick-ness, stack assembly and contacting are designed to increase the combustion gas utilisation and the power

density. In addition, a semi-automated stack assembly has created the pre-requisites for series-ready production.

Sulphur tolerance: Although the higher operating temperature means that SOFCs place less demand on the fuel purity than other fuel cell types, the sulphur content in the diesel fuel (in Germany approx. 10 ppm; in the USA approx 15 ppm) already creates an unacceptable loss of power after just a few operating hours. For this reason the developers are working on making the system more tol-erant to sulphur, either by desulphurising the hot reformate or by modifying the stack. Although power losses have already been considerably reduced by altering the stack and using a sulphur-compatible catalyst, further progress is still required.

Redox resistance: If air-based oxygen reaches the anode side of the stack when starting up or shutting down the system, the anode oxidises to nickel oxide and is reduced to nickel again during the subsequent operation. These so-called redox cycles can irreversibly damage the fuel cells. A satis-factory solution for securing a “redox -resistant” APU unit is still being worked on.

Interaction between the reformate and anode: During cold starts the anode can be irreversibly damaged by carbon deposits. In order to prevent the build up of soot in the stack, the start concept and the reformate quality have been improved.

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Periphery insulation box

Stack insulation box

Start burner heat exchanger

Heat exchanger

Stack

insulation boxx

Stack

+ electrical air conditioner

Stack module

Air blower

Air distribution

Fuel supply650 mm

Reformer

Fig. 2 Depiction of the complete, ready-to-install fuel cell-based APU with its main components. Source: Eberspächer

Fig. 1 Depiction of the SOFC system with the fuel cell stack and insulation box, reformer, residual gas burner and exhaust gas heat exchanger, start burner and start burner heat exchanger, air compressor, hot gas compressor, electronic control system, valves and flaps, fuel supply and exhaust gas system. Source: Eberspächer

Thermomechanics: Many cold starts with short heating times ranging from the room temperature to an operating temperature of around 750 °C place a considerable strain on the components. Tests have shown that thermally induced mechanical loads can cause the stack seals to fail. As a result, the stack itself fails before the target of 250 cold starts has been reached. To improve the thermomechanical resistance, the developers are optimising the design and are developing materials, joint connections and operating strategies.

Heat exchangers: Because the heat exchangers used in high-temperature process engineering do not meet the special requirements of SOFC systems in terms of the power density, rapid start-up capability and operating tem-peratures up to 900 °C, they have developed a start burner heat exchanger that heats up the system and an exhaust gas heat exchanger that heats up the cathode air for the fuel cell using the exhaust gas from the residual gas burner.Considerable research was required in regard to the corrosion of the high-temperature resistant steels and chromium volatilisation from the materi-als. Materials that form a protective Al2O3 layer provide the best results. SiO2 coatings also lengthen the time until oxide spalling occurs.Which materials and production processes will ultimately be used will be determined during the further development to production readiness in ac-cordance with, for example, the specified number of cycles, temperature level, costs and development progress (with the chromium volatilisation).

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Insulation box: High-temperature fuel cell systems re-quire thermal insulation. This reduces the heat losses during the heating up and secures thermally self- sustaining operation even with partial loads. This also slows down the cooling of the system once it has been switched off, which reduces the thermomechanical loading and shortens the start-up time in the event that the system is restarted while still warm.

Demonstrator system and follow-up projectThe current demonstrator system achieves a gross elec-trical capacity of approximately 2.9 kW with a reformer capacity and diesel input of 10 kW. The companies are continuing to work on reducing the impact of perfor-mance inhibiting factors and on improving its current efficiency of around 22%. In the already started follow-up project, the SOFC-APU will be integrated within a future onboard power system for testing and demonstrating its continuous function in trucks. In order to secure its commercial application, the aim is to achieve an operating duration of seven hours based on daily use across a period of around five years. The system is intended to be started from cold only once a week, i.e. only after the weekends, and must be able to cope with more than 250 cold cycles and more than 1,500 warm cycles in this period.With an efficiency of 30%, the fuel cell-based onboard power supply is intended to achieve a net electrical ca-pacity of 3 kW. This would consume one litre of diesel per operating hour. In addition, the new system aims to be better than diesel engine-operated systems in terms of the price, service life and dimensions.

Fig. 3 This is how it will look like: Diesel-operated fuel cell system on the truck. Source: Eberspächer

Fig. 4 a) The functioning prototype of the system: The ENSA II demonstrator. Source: Eberspächer b) The fuel is converted into synthetic gas in the reformer. Source: Eberspächer

Fig. 5 Schematic diagram of the SOFC-APU. Source: Eberspächer

System concept

By means of catalytic partial oxidation, diesel fuel and ambient air are converted into a hydrogen- and carbon monoxide-rich synthetic gas in the reformer. The electro-chemical reaction of combustion gas and air-based oxygen creates an electric current in the SOFC (Fig. 5). This process runs with a theoretical efficiency of more than 35 per cent with temperatures of more than 800 °C. A start burner module comprising a start burner and start burner heat exchanger (not included in the schematic diagram) ensures that the fuel cell is heated up gently.Because the fuel cell does not convert all the combustion gas, a residual gas burner combusts the remaining hy-drogen- and carbon monoxide-containing components in the fuel cell exhaust gas. The resulting exhaust heat heats the cathode air for the fuel cell. This can be used for providing auxiliary heating in the truck cabin. In a similar way to the exhaust gas recirculation in com-bustion engines, part of the fuel cell exhaust gas that is not converted is circulated back into the reformer for cooling and improving the process.

Current

SOFC Heat exchanger

Residual gas burner

H2

CO

H2CO2

Diesel

Reformer

Air

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Versatile fuel cells With their development work, the companies involved are optimising the fuel cell system for long-distance trucks. With the development of more stable, efficient and cost-effective components, they are paving the way for further application areas for mobile fuel cell systems. These can supply modes of transport with increased electrical requirements such as mobile homes, yachts and coaches. More powerful fuel cell systems can also be used for cooling payloads. Stationary systems can be used as CHP units for supplying electricity and heat in residential buildings and in remote areas, for example in mountain huts. Various automotive manufacturers are bundling their research and development work internationally in order to be able to offer fuel cell-operated vehicles by the end of the decade. Because the new fuel cell system uses sulphur-containing diesel as the fuel, the gas processing is very complex. It needs to be able to compete on the market with devices that use methanol or camping gas. Compared with idling truck engines, fuel cell systems enable a considerable reduction in the consumption, noise and emissions. The CO2 emissions are reduced by 20% compared with standard competitive systems. Experts from the manufacturing companies forecast that around 9,000 US dollars in fuel costs can be saved per truck and year in the USA.The experience gained in the previous projects is now being incorporated in various follow-up projects. The European support project entitled “Demonstration of 1st European SOFC Truck APU (DESTA)” is comparing SOFC systems from the AVL and Eberspächer production companies, which are both equipped with fuel cells from the Danish manufacturer TopsoeFuelCell. Using an additional component it is possible to utilise the exhaust heat from the system to heat cabins. Given the high operating and standby temperatures, it would be worthwhile developing concepts for them in follow-up projects.

Project participants >> Project management, development of the reformer and the overall system:

Eberspächer Climate Control Systems GmbH & Co. KG, Esslingen, Germany, Andreas Kaupert, [email protected]

>> SOFC stack development and production: ElringKlinger AG, Dettingen, Germany, Dr. Thomas Kiefer, [email protected]

>> Manufacture of high-performance heat exchangers: BEHR GmbH & Co. KG, Stuttgart, Germany, Martin Brenner, [email protected]

>> Basic development of the reformer/ residual gas burner, development of operating strategies, lifetime determination tests: Oel-Waerme-Institut (OWI), Aachen, Germany, Jörg vom Schloß, [email protected]

>> Heat exchanger and stack tests, development of operating strategies: Research Centre Jülich, Germany, Professor Ludger Blum, [email protected]

Links and literature>> www.eberspaecher.com | www.elringklinger.de | www.behrgroup.com

www.owi-aachen.de | www.fz-juelich.de | www.now-gmbh.de | www.desta-project.eu>> ENSA II joint project: “Entwicklung Nebenaggregate SOFC-APU II”, project number 0327823A-C>> ENSA III joint project: “Entwicklung SOFC-APU” (2012 – 2015), project number 03ET2048A-C>> ZeuS III joint project: “Entwicklung eines industriell herstellbaren Leichtbau-SOFC-Stacks”,

project number 0327766A-D>> FIZ Karlsruhe GmbH. BINE Informationsdienst, Bonn (Hrsg.): On-board power supply with fuel cells.

2011. Projektinfo 10/2011>> FIZ Karlsruhe GmbH. BINE Informationsdienst, Bonn (Hrsg.): New approaches to supplying

domestic energy – Generating electricity and heat more efficiently using fuel cell heating units. 2012. Projektinfo 05/2012

More from BINE Information Serviceb This Projektinfo brochure is available as an online document at www.bine.info

under Publications/Projektinfos.

b BINE Information Service reports on energy research projects in its brochure series and newsletter. You can subscribe to these free of charge at www.bine.info/abo. Co

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Project organisationFederal Ministry of Economics and Technology (BMWi) 11019 Berlin Germany

Project Management Organisation Jülich Research Centre Jülich Dr. Peter Malinowski 52425 Jülich Germany

Project number 0327823A-C, 0327703A-C

ImprintISSN0937 - 8367

Publisher FIZ Karlsruhe · Leibniz Institute for Information InfrastructureHermann-von-Helmholtz-Platz 1 76344 Eggenstein-LeopoldshafenGermany

AuthorGerhard Hirn

Cover imageSuper Road Train. Herd Integrated Vehicle Protection, Winnipeg, Canada, www.herd.com

CopyrightText and illustrations from this publication can only be used if permission has been granted by the BINE editorial team. We would be delighted to hear from you.

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