Reforming kinetics predictions with

Steam reformers are used industrially to produce syngas, i.e., synthetic gas formed of CO, CO2, 11-2, and/or hydrogen. In this section we present models for both top-fired and side-fired industrial steam reformers by using three different diffusion-reaction models for the catalyst pellet. The dusty gas model gives the simplest effective method to describe the intermediate region of diffusion and reaction in the reformer, where all modes of transport are significant. This model can predict the behavior of the catalyst pellet in difficult circumstances. Two simplified models (A) and (B) can also be used, as well as a kinetic model for both steam reforming and methanation. The results obtained for these models are compared with industrial results near the thermodynamic equilibrium as well as far from it. 

The model derived from the above procedure compares quite favorably with experiment, see Fig. 10. We are now ready to combine the model with the coking kinetic model to predict the observed changes in the reforming rate constants during the lifetime of the catalyst. 

Although not shown here, with Eq. (8), and Eq.(12) we have been able to correctly predict the reactor coke profile based on model-predicted C5N concentration profile. This is detailed elsewhere [15]. We thus complete the circle by providing an overall kinetics package that can predict not only the time evolution of the reforming products but also the coke profile along the catalyst bed. 

To reveal the complete reaction mechanism, the reaction was investigated at lower temperatures. The product ion mass spectrum recorded at 100 K with O2 and CO in the ion trap (Fig. 1.63b) shows the appearance of the coadsorption complex Au2(C0)02 discussed above. This complex represents a key intermediate in the reaction mechanism of the catalytic oxidation of CO to CO2 as has been predicted in the earlier theoretical study [382]. The experimental evidence obtained so far demonstrates that O2 adsorption is likely to be the first step in the observed reaction mechanism. Subsequent CO coadsorption yields the observed intermediate (Fig. 1.63b) and finally the bare gold dimer ion must be reformed. The further strategy to reveal the full reaction mechanism consists in varying the available experimental parameters, i.e., reaction temperature and reactant partial pressures. This procedure leads to a series of kinetic traces similar to the one shown in Fig. 1.64b and c [33]. The goal then is to find one reaction mechanism that is able to fit all experimental kinetic data obtained under the various reaction conditions. This kinetic... 

For reforming of methane, kinetics allow methane to decompose into carbon instead of reacting with steam even if thermodynamics predict no carbon formation. However, with proper reformer design, industrial operation at HgO/CH =... 

The reformer reactions (reforming and water gas shift) are modeled using the best available heterogeneous kinetic relationships from the literature, " and have been validated with industrial data and literature data over a wide range of conditions. Equilibrium relationships are appropriately incorporated into the rate relationships, but the model does not use the empirical approach to equilibrium temperature as the basis for predicting outlet compositions. Nor does the model use pseudo-homogeneous rate relationships. 

Figure 5.54 shows the Feed Data tab from the Reformer sub-model. The Feed Type is a basic set of relationships and initial values for the all kinetic lumps in the reactor model. Aspen HYSYS uses bulk property information such as density, distillation curves and total PNA content in conjunction with the feed type to predict the composition of feed lumps to the model. The Default type is sufficient for hght-to-heavy naphtha. However, there is no guarantee that a particular feed type represents the actual feed accurately. Aspen HYSYS will attempt to manipulate the feed composition to satisfy bulk property measures given. In general, we advise users to develop a few sets of compositional analysis to verify the kinetics lumps calculated by Aspen HYSYS. We discuss a process to verify these lumps later. 

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