Shrinking-particle model system

Ruether (29) examined the case of oxydesulfurization for completely backmixed stirred tanks in series assuming the diffusion-controlled mechanism. The reaction in the particles was described by the shrinking core model. The results obtained on the conversion as a function of residence time were shown for various number of reactors in series. The procedure to calculate the conversion for a system having a distributed particle size... 

With these we enlist the two fundamental approaches to the noncatalytic gas-solid reaction systems The shrinking core model and volume reaction model. In the volnme reaction model, the solid is porous, the fluid easily diffuses in or ont of the solid, such that the reaction can take place homogeneously everywhere in the solid. On the other hand, with the shrinking core model (SCM), also called the sharp interface model (SIM), there is a sharp interface between the unreacted core and reacted shell of the particles. 

We can model the FCC catalyst system as a combination of a shrinking core of sites not yet deactivated by coke and a progressing shell of large hydrocarbon molecules and metal contaminants, penetrating into the catalyst particle.The relative velocities of these fronts will be of great importance and will be strongly determined by the accessibility of the various functional sites of the catalyst [40]. 

By allowing one of the spheres to shrink to a point and assuming its motion to be similar to a gas molecule s, the coagulation problem is rendered slightly more tractable. In the case of only surface interaction, the problem reduces to that of condensation or sorption. Conversely, if longer range potentials, which are not necessarily monotonic such as the electrostatic interaction with a polarizable aerosol particle are considered, the system can be taken to model one of two important aspects of realistic two-particle interactions. This aspect is the role of particle size relative to gas density in the determination of an interactant s collision or repulsion. The other aspect which cannot yet be addressed, is that of attraction due to mutual shielding discussed above. 

The reaction system studied includes reactions R1 and R2 only. Gaseous reduction of a single iron ore particle proceeds following the shrink unreacted core model. Gas film resistance on mass transfer around the particle could be ignored since ore fines are under bubbling state. The shrink unreacted core model is used for expressing the reaction rates of R1 and R2 and they are expressed as Eqs.( 3-4). 

The most common models are derived isothermally and are associated with the shrinking core of a globular particle, which maintains a sharp reaction boundary [3,413,414]. Using a simple geometrical representation, the reacting system can be classified as a set of spheres where each reaction interface is... 

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