Methanol Fuel Processors

Fuel Processing for Fuel Cells. Gunther Kolb 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31581-9 

The development of a methanol fuel processor prototype was described by Hdhlein et al. [556]. The methanol burner dedicated to this system has been described in Section 7.5. Later, a complete methanol reformer was developed by Wiese et al. [154]. It was operated at a S/C ratio of 1.5 and a pressure of 3.8 bar. The feed was evaporated and superheated to 280 °C. The reformer itself consisted of four pairs of concentric stainless steel tubes. In the annular gap between the tubes, steam was condensed at 65 bar and 280 °C for the heat supply, while the inner tube carried the copper/zinc oxide catalyst for steam reforming. The reformer response time to a load change from 40 to 100% was about 25 s, which was mainly attributed to the slow dynamics of the dosing pump. Because the dynamic behaviour of the reformer was too slow for an automotive drive system, which had been the target appUcation of the work, an additional gas storage system was considered. To improve the system dynamics, Peters et al. considered the application of microreactor technology for a subsequent improved fuel processor [569]. 

Johnson Matthqr developed the HotSpot fuel processor, a modular autother-mal reformer. The basic idea of the HotSpot was that hydrogen back-diffusion to the reaction front, where it would be consumed by the oxygen feed, was prevented by the spot wise feed injection into the centre of the reactor. The heat of the exothermic reaction was also distributed from the centre of the reactor to its periphery, where it was required to supply the endothermic reactions with energy 

The unit was then improved for onboard methanol processing dedicated for the automotive drive train [573] but also for residential combined heat and power systems [575]. The catalyst bed was uniform and filled with a combined precious metal/base metal multi-component catalyst. The reaction produced 2.4 mol hydrogen per mole methanol [573], which corresponds to a S/C ratio of about 0.4 and an O/C ratio of about 0.6 in the feed. These conditions resulted in 58 vol.% dry hydrogen content of the reformate. The maximum temperature in the fixed bed was reduced to 400 °C 

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All fuel cells for use in vehicles are based on proton-exchange-membrane fuel cell (PEMFC) technology. The methanol fuel-processor fuel cell (FPFC) vehicle comprises an on-board fuel processor with downstream PEMFC. On-board methanol reforming was a development focus of industry for a number of years until around 2002. Direct-methanol fuel cells (DMFC) are no longer considered for the propulsion of commercial vehicles in the industry (see also Chapter 13). 

Pfiefer et al. are developing a methanol fuel processor system using steam reforming for a 200 Wg fuel cell based power supply. The researchers are currently working on the methanol reformer reactors, heat exchangers, combustors, and preferential oxidation reactors (Figure 23) for the system. The reactor bodies are either stainless steel or copper. 

Integrated Autothermal Methanol Fuel Processor (Ballard)... 

Schuessler et al. [85] of XCELLSiS (later BALLARD) presented an integrated methanol fuel processor system based on autothermal reforming, which coupled fuel/water evaporation with exothermic preferential oxidation (PrOx) of carbon monoxide. The reactor technology was based, in contrast to most other approaches, on a sintering technique. 

Integrated Methanol Fuel Processor for 100 W Power Output... 

Schouten et al. [113] presented the design of a methanol fuel processor for an electrical power output of 100 W, which was done in the scope of a project funded by the European Union (MiRTH-e). In contrast to [ISMol 3], the processor was composed of three separate devices. 

Figure 2.75 Methanol fuel processor concept for 15 W electrical power output [18] (by courtesy of Springer-Verlag).

A 200 mW methanol fuel processor was presented by Hu et al. [32], A 9% efficiency was determined for the device running at 1 vol.% carbon monoxide in the reformate stream. 

The aim of the work was to develop a methanol fuel processor for a 50 kW automobile engine. An integrated heat exchanger/reactor was fabricated and results were presented by Hermann et al. [120] of GM/OPEL. The specifications for the system were ambitious, amongst others ... 

Sintering as a micro structuring (see the section above) and bonding technique was applied by Schuessler et al. [85] of Ballard for their compact methanol fuel processor (see Figure 2.94). The stack of plates and the endplate are connected in a single bonding step. 

Palo, D. R., Holladay, ). D., Rozmiarek, R. T., Guzman-leong, C. E., Wang, Y., Hu,)., Chin, Y.-H., Dagle, R. A., Baker E. G., Development of a soldier-portable fuel cell power system. Part I a breadboard methanol fuel processor, J. Power Sources 2002, 108, 28-34. 

Men, Y., Kolb, G., Zapf, R. et al. (2008) A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications. International Journal of Hydrogen Energy, 33, 1374-1382. 

For different applications, the power needed from the fuel cells varies from less than 1W for small applications such as sensors and mobile phones to over 100 kW for automobiles and stationary applications. With microreactors, hydrogen flows capable of producing power in the range from 0.01 W to 50 kW have been achieved [3]. Numerous applications of fuel conversion in microstructured devices have dealt with the combination with fuel cells to yield a power supply for microelectric devices and microsensors and as an alternative to a conventional battery. Thus, the resulting power output of the fuel cell has been in the low watts area, from 0.01 Wto a few watts, as in the integrated methanol fuel processors built by companies such as Casio and Motorola [4]. PNNL has developed various low-power portable fuel processor systems, from lower than 1W [5-7] to systems that could provide 15 W, such as a portable and lightweight system for a soldier portable fuel cell [8,9]. In the range of... 

Figure 24.4 2.5 W methanol fuel processor-fuel cell system developed by Casio [53].

Men et al. reported the operation of a small-scale bread-board methanol fuel processor composed of electrically heated reactors [15]. A methanol steam reformer, two-stage preferential oxidation reactors and a catalytic afterburner were switched in series. A fuel cell equipped with a reformate-tolerant membrane, which had a 20 W nominal power output, was connected to the fuel processor and operated for about 100 h. 

A complete methanol fuel processor for the electrical power equivalent range 60-170 W was reported by Holladay et td. [63]. The device, which is shown in Figure 24.7, had a volume of less than 30 cm, a mass lower than 200 g and a... 

Figure 24.7 Integrated methanol fuel processor with lOOW power equivalent [63],...

An integrated heat exchanger-reactor for methanol steam reforming was developed by Hermann et al. [65] at GM/OPEL for a 50 kW methanol fuel processor. The system specifications included a volumetric power density of more than 5 kW dm, a gravimetric power density of more than 2.5 kWkg and a transient response to load changes from 10 to 90% in milliseconds. 

Shah and Besser presented results from their development work targeted at a 20 Wei methanol fuel processor-fuel cell system [66]. The layout of the system consisted of a methanol steam reformer, preferential oxidation, a catalytic afterburner and an evaporator. Vacuum packaging was the insulation strategy for the device, which is in line with other small-scale systems described above. A micro fixed-bed steam reformer coupled to a preferential oxidation reactor was then developed by the same group with a theoretical power output of 0.65 W. 

M. Wichert, V. Hessel, H. Lowe, A complete miniaturized microstructured methanol fuel processor/fud cell... 

K Shah, R. S. Besser, Key issues in the microchemical systems-based methanol fuel processor energy density, thermal integration and heat loss mechanisms,... 

Yoshida et al. [173] designed an integrated methanol fuel processor from silicon and Pyrex glass substrates for a power equivalent of 10 W. It contained functional layers for steam reforming, evaporation, and combustion. Commercial Cu/ ZnO catalyst served for reforming and the Pt/TiOa combustion catalyst was prepared by a sol-gel method. A power density of 2.1 W/cm was determined for the device. 

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