Fuel monolith, conventional

Fixed bed reactors still predominate for fuel processing. However, fixed beds are susceptible to vibrational and mechanical attrition. Recently, monolithic reactors, either metallic or ceramic, have attracted interest for reforming processes since they offer higher available active surface areas and better thermal conductivity than conventional fixed beds. Low-pressure drop and robustness of the structure are major advantages of monolithic reactors. 

The techniques presented here allow to produce ultralight materials with anisotropic properties. Optical absorption and emission, hydrophobicity mechanical strength and index of refraction can be tuned within the same monolith. Conceivable applications of our technique include fabrication of photonic devices, membranes, radiation collimators, fuel cell electrodes as well as hierarchically structured materials that combine mechanical strength with the acoustic and thermal insulation properties of conventional aerogels. 

Monolithic catalysts (or honeycombs) have received much attention ever since they were first applied in automotive catalytic converters [1]. An increasing interest in the use of monolithic reactors for other applications has also been noticed during recent years [2]. One application which particularly profits from the opportunities offered by the honeycomb structure is catalytic combustion for use in advanced gas turbines [3]. In a catalytic combustor, a premixed lean fuel-air mixture is ignited by the catalyst which results in complete combustion at maximum temperatures far lower than possible in conventional gas-phase combustors. Hence, the thermal formation of nitrogen oxides can almost completely be circumvented. This fact has promoted large R D programs in catalytic combustion during recent years. 

A conventional system, as shown in Figure 5.60. It was composed of a monolithic autothermal reformer operated at a S/C ratio of 2.0 and 0/C ratio of about 0.8, high and low temperature water-gas shift reactors, a water-cooled three stage preferential oxidation reactor and a conventional low temperature PEM fuel cell cooled... 

A microstructured monolith for autothermal reforming of isooctane was fabricated by Kolb et cd. from stainless steel metal foils, which were sealed to a monohthic stack of plates by laser welding [73]. A rhodium catalyst developed for this specific application was coated by a sol-gel technique onto the metal foils prior to the sealing procedure. The reactor carried a perforated plate in the inlet section to ensure flow equi-partition. At a weight hourly space velocity of 316 L (h gcat). S/C 3.3 and O/C 0.52 ratios, more than 99% conversion of the fuel was achieved. The temperature profile in the reactor was relatively flat. It decreased from 730 °C at the inlet section to 680 °C at the outlet. This was attributed to the higher wall thickness of the plate monolith compared with conventional metallic monolith technology. The reactor was later incorporated into a breadboard fuel processor (see Section 9.5). 

The first catalytic converters were conventional fixed bed reactors. Today, the majority are monoliths that combine a low pressure drop with a small size and weight, and thus provide better fuel economy than fixed-bed reactors. The catalyst is mounted in a stainless-steel container with a packing wrapped around for resistance to vibration (Figure 6.18.3). 

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