Reforming reactions reaction composition profile

Fig. 1. Reaction composition profile. Reforming at 794 K, 2620 kPa. Zone A dehydrogenation zone zone B isomerization zone zone C hydrogenation and cracking zone. [Charge stock A, hexane (HEX) , benzene (BENZ) V, cyclohexane (CH) O, methylcyclopentane (MCP).]...

The differences in reactions at different reactor positions was studied by Springmann et al. who reported product compositions for ATR of model compounds as a function of reactor length in a metal monolith coated with a proprietary noble metal containing Rh. As expected, the oxidation reactions take place at the reactor inlet, followed by the SR, shift, and methanation reactions. Figure 32 shows the product concentration profiles for a 1-hexene feed, which are typical results for all the fuels tested. These results show that steam, formed from the oxidation reactions, reaches a maximum shortly after the reactor inlet, after which it is consumed in the shift and reforming reactions. H2, CO and CO2 concentrations increase with reactor length and temperature. In this reactor, shift equilibrium is not reached, and the increase in CO with distance from the inlet is the net result of the shift and SR reactions. Methane is... 

The significance of this small effectiveness factor is the following The chemical reaction rate occurring inside the catalyst pores is much faster than the rate at which the reaction components can enter and then leave the catalyst pores. This means that the composition inside the pores can be at equilibrium the bulk gas composition is quite far from equilibrium. Therefore, when checking to see whether a reforming mixture has a tendency to form carbon, it is necessary to check the bulk composition of the gas as well as the equilibrium composition of the gas. As mentioned earlier, steam reformers can be said to be heat flux-limited, which means that the reactor is usually limited by heat transfer considerations and not by reaction kinetics. In other words, once the reformer has been configured in terms of the number of tubes and their dimensions to achieve the desired heat flux profile, there should be enough catalyst volume in the tubes to achieve the desired level of conversion. 

To evaluate the potential of carbon formation in a steam reformer, it is therefore essential to have a rigorous computer model, which contains kinetic models for the process side (reactor), as well as heat transfer models for the combustion side (furnace). The process and combustion models must be coupled together to accurately calculate the process composition, pressure, and temperature profiles, which result from the complex interaction between reaction kinetics and heat transfer. There may also be a temperature difference between bulk fluid, catalyst surface, and catalyst interior. Lee and Luss (7) have derived formulas for this temperature difference in terms of directly observable quantities The Weisz modulus and the effective Sherwood and Nusselt numbers based on external values (8). 

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