Activity factors reforming

The first step is to Pull data from the simulation. When Aspen HYSYS pulls data, current operating conditions, feed stock information and process parameters enter the reforming environment. A Calibration refers to the set of the activity factors that produce a given product yield and reactor performance (which we provide to the calibration environment) based on the current model state. We pull data by click on the Pull Data from Simulation button (Figure 5.78). 

The selectivity of the reforming process depends on various factors such as the nature of the catalytically active metal, support, solution pH, feed and reaction conditions, as shown in Figure 6.4. By manipulating the process conditions, it is possible to control the product distribution. 

A kinetic reforming model must properly represent these catalyst effects. Thus, catalyst composition and state factors such as metal type and activity, acid activity through chloride control and alumina type, and the role of the second metal must be built in to the kinetics. 

If methane is considered for reaction (3.13), a first order reaction rate is usually assumed, i.e. the coefficient n of expression (3.22) is equal to 1. According to Achenbach [22], the activation energy of methane steam reforming is 82 kJ mol-1 and the pre-exponential factor is 4274 mol m-2 bar-1 s-1. More recent experimental studies report an activation energy of 112 15 kJ mol-1 [23],... 

The characterization technique of CO Temperature-Programmed Desorption has been studied with Pt reforming catalysts. Critical factors in the experimental procedure and the catalyst pretreatment conditions were examined. The CO desorption spectrum consists mainly of two peaks which are probably combinations of other peaks and the result of various binding energy states of CO to Pt. These in turn could be due either to the interaction between Pt and the alumina support or the results of high and low coordination sites on the Pt crystallites. No significant relationship between the character of the CO desorption profile and the activity of commercial catalysts was observed. 

An overall review of the world activity of existing units shows that they operate on the average with a high stream factor, which is around 310 days/year, and which tends to improve with increasing size. The main cause of incidents is still the synthesis compressor. but also the primary reforming step. 

In the extrinsic reaction rate, mass transfer plays a dominant role. The combined effect of the molecular diflusion of the reactants from the bulk gas through the gas film around a catalyst particle to the geometrical surface of the particle, and to some extent the Knudsen diflusion within the catalyst pores, are the limiting factors. As the intrinsic reaction is fast, the reactants will have reacted before they travel down the lenght of the pore. The effectivity of a steam reforming catalyst, that is, how much of the catalyst particle is utilized, varies with the reaction conditions and is only about 1 % at the exit. Because of this, the apparent activity increases with decreasing particle size, and the geometrical shape of the catalyst particle also has a distinct influence (Section 4.1.1.3). 

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