Single-fluid-phase reactors, modeling

The reactor models developed for fixed-bed reactors have been exploited for use in other situations, for example, CVD reactors (see Vignette 6.4.2) for microelectronics fabrication. These models are applicable to reaction systems involving single fluid phases and nonmoving solids. There are numerous reaction systems that involve more than one fluid phase. Figure 10.4.3 illustrates various types of reactors... 

In moving catalyst basket reactors, the flow regime is ill-defined and the contact between catalyst and gas can be poor even if well-mixed conditions for the fluid phase are achieved. Perhaps the most successful representative of this category is the Carberry reactor (1964, 1966). Even in this model only a single layer of catalyst can be charged in the cruciform catalyst basket because the fluid flows in a radial direction outward and... 

Computational fluid dynamics based flow models were then developed to simulate flow and mixing in the loop reactor. Even here, instead of developing a single CFD model to simulate complex flows in the loop reactor (gas dispersed in liquid phase in the heater section and liquid dispersed in gas phase in the vapor space of the vapor-liquid separator), four separate flow models were developed. In the first, the bottom portion of the reactor, in which liquid is a continuous phase, was modeled using a Eulerian-Eulerian approach. Instead of actually simulating reactions in the CFD model, results obtained from the simplified reactor model were used to specify vapor generation rate along the heater. Initially some preliminary simulations were carried out for the whole reactor. However, it was noticed that the presence of the gas-liquid interface within the solution domain and inversion of the continuous phase. 

In the next section various reaction models are considered. Then global rate equations are developed in Sec. 14-3 for one model (shrinking core). In Sec. 14-4 integrated conversion-vs-time relationships (for single particles) are presented. Such relationships are suitable for use in design of reactors in which the fluid phase is completely mixed. In Secs. 14-5 and 14-6 all these results will be applied to reactor design. 

The overall reactor model comprises, as the heart of it, the single catalyst pellet model which is formulated in an overall framework that includes the changes in the bulk fluid phase. The equations for the catalyst pellet coupled with the equations for the bulk fluid phase represent what we may call in certain cases, the overall reactor model or in a more restricted sense, the catalyst bed module. This catalyst bed module may represent the overall reactor model in certain cases such as the single adiabatic catalytic packed bed reactor. In other cases, this module may represent only the essential part of the overall reactor model such as in non-adiabatic and multi-bed reactors. 

Van Welsenaere and Froment [R.J. Van Welsenaere and G.F. Froment, Chem. Eng. Sci., 25, 1503 (1970)] propose the following model for a one-dimensional tubular reactor with constant wall temperature, a single reaction, and a fluid phase of constant density. 

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