Fuel micro structured

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

For the chemical reactor, the researchers used a nanoparticle catalyst deposited on metallic micro-structured foils. They tested Cu/ZnO and Pd/ZnO catalysts deposited on the microstructured foils. The Cu/ZnO catalyst was more active than the Pd/ZnO catalyst and had a lower selectivity to undesired carbon monoxide. However, because the Pd/ZnO catalyst was more stable, it was selected for use in their fuel processor. The Pd/ZnO carbon monoxide selectivity of the powder catalyst pressed into a pellet was lower than that of the nanoparticle catalyst deposited on the microstructured foils. This effect was attributed to contact phases between the catalyst and the metal foils. ... 

First of all, the physical structure of the packed bed in the conversion system is defined. The fuel bed structure can be divided into three phases, namely the interstitial gas phase, the intraparticle solid phase, and the intraparticle gas phase. By means of this terminology it is easier to address certain mass and heat transport phenomena taking place on macro and micro scale inside the packed bed during the thermochemical conversion, see Figure 8. 

The long-term goal in the science of thermochemical conversion of a solid fuel is to develop comprehensive computer codes, herein referred to as a bed model or CFSD (computational fluid-solid dynamics). Firstly, this CFSD code must be able to simulate basic conversion concepts, with respect to the mode, movement, composition and configuration of the fuel bed. The conversion concept has a great effect on the behaviour of the thermochemical conversion process variables, such as the molecular composition and mass flow of conversion gas. Secondly, the bed model must also consider the fuel-bed structure on both micro- and macro-scale. This classification refers to three structures, namely interstitial gas phase, intraparticle gas phase, and intraparticle solid phase. Commonly, a packed bed is referred to as a two-phase system. 

Micro Structured Fuel Processors for Energy Generation... 

This chapter deals with development work in the field of micro structured fuel processors, which convert various fuels to hydrogen for fuel cells and other power generation modules. 

So far, micro structured fuel processor systems seem to be limited to the first two technologies. Figure 2.1 shows a general flow scheme of a fuel processor with heterogeneously catalyzed reactors for gas purification. Devices shown in dashed lines are not mandatory for the system. 

This section will provide information about micro structured reformer reactors, gas purification devices and catalytic burners, the last also in combination with an evaporator, for fuel processors. However, the specific problems related to the peripheral equipment will not be discussed in depth. 

Cheap fabrication techniques feasible for mass production need to be applied for fuel processors. The various techniques available for micro structured fuel processors will be discussed in Section 2.9. 

Catalyst cost may play a significant role in the overall fuel processor cost and may reach values as high as 38% [4]. Here micro structured devices offer significant possibilities for cost reduction owing to the improved mass transfer in small channel systems, which allow for a higher efficiency of the catalyst. 

After the start-up heating procedure, stable operation of the fuel processor needs to be achieved. Micro structured devices allow for rapid system stabilization due to the fast dynamic response at the low residence times applied. 

Generally, load changes from 5 to 100% should be tolerated by a fuel processor [11]. However, this is of course a more crucial issue for drive train applications than for APUs. Micro structured devices offer benefits concerning the load-change behavior of fuel processors owing to the small fluid volumes applied [12, 13]. 

Design Concepts of Micro Structured Reactors for Fuel Processing Applications... 

Integrated reactors One type of integrated reactor is micro structured heat exchanger/reactor concepts, which may work as cross- or counter-flow reactors. Another type couples endothermic and exothermic reactions in two separate flow paths normally operated in the co-current mode. Both reactor types are designed as prototype components of future fuel processors for mobile applications. 

In Sections 2.4-2.6 micro structured testing reactors for reforming, combustion and gas purification purposes and chip-like devices are presented Section 2.7 is dedicated to integrated reactors and micro structured fuel processor concepts and... 

Micro Structured Test Reactors lor Fuel Processing... 

Micro Structured Test Reactors for Fuel Processing I 289... 

However, most fuel cell systems can tolerate methane concentrations up to at least 1% in the reformate, no special purification reactions are required. In contrast, hence, removing small residual amounts of carbon monoxide from pre-purifled reformate applying the methanation reaction may be considered as an alternative to the preferential oxidation of carbon monoxide, provided that the CO concentration is low enough to have no significant impact on the hydrogen yield. However, no applications of methanation for CO clean-up in micro structured devices appear to have been reported, hence the issue is not discussed in depth. Finally, during hydrocarbon reforming all hydrocarbon species (saturated and unsaturated) smaller than the feed molecule may be formed. 

This section will focus on published work dealing with reactor development, catalyst development and investigations elucidating the mechanisms and kinetics of reforming in micro structured channel systems. Integrated concepts of fuel processors will be presented in Section 2.7. 

Chin et al. [31] studied Pd/ZnO catalysts for methanol steam reforming, heading for a 10-50 W micro structured fuel processor. The catalysts under investigation contained 4.8, 9.0 and 16.7 wt.% Pd deposited on ZnO powder by impregnation. The catalysts were thoroughly characterized by thermogravimetry (TG), TPR, XRD and TEM. 

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