Reaction zone model

The mechanism of many of the noncatalytic fluid-solid reactions can be described by a model in between unreacted core and homogeneous reactions models. Ishida and Wen (9) formulated such a model using the zone reaction concept of Ausman and Watson (10). In this model the reaction is not restricted to the surface of the core as in the unreacted core model but occurs homogeneously within a retreating core of reactant. Wen and Ishida (11) combined the grain concept with the zone reaction model and analyzed the reaction of SO2 with CaO particles. In the study conducted by Mantri, Gokarn and Doraiswamy (12) the concept of finite reaction zone model was further developed. 

Madsen et al. epplied the reaction zone model to the leaching of Butte ore for particles up to 6 in. in diameter. Columns 5 Ft in diameter, containing 5 tons of ore. were used. Tha principal copper mineral was CufS. Equation (9.4-13) in integrated form was used ... 

VII Deforming Reaction zone model for the CSTR. Chem. Eng. Sci. (1983), 911... 

Animations of the reaction zone models described in this chapter are on the CD-ROM in the directory /MOVIE/RXZONE.MVE and as a PowerPoint presentation in the /CLASS.PPT/CHAPTl directory. 

With respect to reaction-zone models, all types listed in Table 12.1 can be implemented. In the following, for sake of simplicity, only pseudo-homogeneous models are presented. IMR models can be one- or two-dimensional. Usually, axial mixing phenomena are neglected and therefore two model types can be implemented to describe IMR behaviour ... 

As reported above, the reaction-zone model can be two-fold an ideal model or a radial mixing model. 

If a ID reaction-zone model is implemented, the boundary conditions have to be imposed only in the inlet section. Boundary conditions for a ID IMR model are defined as follows ... 

If a 2D reaction-zone model is imposed, two boundary conditions on radius (r = 0 and r = 1) have to be defined as well ... 

To properly describe the reaction-zone model, a reaction-kinetics scheme is needed. There are many kinetics expressions reported in the literature, to which the Xu-Froment Equations [12.22], [12.23] and [12.24] are applied (XuandFroment,1989). 

The most notable theoretical analysis of the instability problem has been presented by McClure and Hart (M5). These investigators postulated a generalized combustion zone that includes a temperature-dependent and pressure-independent solid-phase reaction zone, and a temperature- and pressure-dependent gas-phase reaction zone. From this general model, Hart... 

Another reaction mechanism, which is conveniently mentioned under this heading, is due to Hill [479] who suggested that ions (atoms or molecules) frorh the product may move through the dislocation network of the reactant and activate potential nuclei, particularly in the vicinity of the reaction interface. Thus a reaction zone, within which potential nucleusforming sites are activated, is developed in front of an advancing interface. With appropriate assumptions, this reaction model provides an alternative explanation of the exponential rate law, eqn. (8), which in Sect. 3.2 was discussed with reference to chain reactions. 

---