Temperature, effect steam reforming

Pumomo, A., Gallardo, S., AbeUa, L., Salim, C., Hinode, H. (2008). Effect of ceria loading on the carbon formation during low temperature methane steam reforming over a Ni/Ce02/ Zr02 catalyst. Reaction Kinetics and Catalysis Letters, 95, 213—220. 

It is important to note that the selectivity of sulfur-passivated catalysts towards steam reforming is greatly enhanced because carbon formation is effectively suppressed. The decrease in activity can to largely be compensated for by selecting inherently more active catalysts and by operating at higher temperatures. Unfortun-... 

Tube wall temperature is an important parameter in the design and operation of steam reformers. The tubes are exposed to an extreme thermal environment. Creep of the tube material is inevitable, leading to failure of the tubes, which is exacerbated if the tube temperature is not adequately controlled. The effects of tube temperature on the strength of a tube are considered by use of the Larson-Miller parameter, P (Ridler and Twigg, 1996) ... 

This study was carried out to simulate the 3D temperature field in and around the large steam reforming catalyst particles at the wall of a reformer tube, under various conditions (Dixon et al., 2003). We wanted to use this study with spherical catalyst particles to find an approach to incorporate thermal effects into the pellets, within reasonable constraints of computational effort and realism. This was our first look at the problem of bringing together CFD and heterogeneously catalyzed reactions. To have included species transport in the particles would have required a 3D diffusion-reaction model for each particle to be included in the flow simulation. The computational burden of this approach would have been very large. For the purposes of this first study, therefore, species transport was not incorporated in the model, and diffusion and mass transfer limitations were not directly represented. 

Our initial work on reaction thermal effects involved CFD simulations of fluid flow and heat transfer with temperature-dependent heat sinks inside spherical particles. These mimicked the heat effects caused by the endothermic steam reforming reaction. The steep activity profiles in the catalyst particles were approximated by a step change from full to zero activity at a point 5% of the sphere radius into the pellet. 

Halides in fuels such as naphtha have deleterious effects on steam reforming and low temperature shift, thus halogen guards need to be included in the fuel processing. 

Logistic fuels, such as jet and diesel fuels, are readily available, but a compact and effective way to remove sulfur from these fuels is needed for portable hydrogen production. Consequently, for most portable applications, it is likely that sulfur-free fuels, such as methanol, will be used. An additional advantage of methanol is that it is easier to activate at low temperatures than other hydrocarbons. Therefore, a portable hydrogen production unit based on methanol steam reforming would be simpler and less costly than other alternatives. Methanol can also be considered an energy carrier as an alternative to liquefied natural gas... 

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