Modeling of Fluidized Bed Reactors

It can be generalized somewhat more by introducing the Prandtl number. The correlation is based on a pseudo-single-phase model. It follows from the correlation that the gas approaches the temperature of the solid in the very first centimeters of the bed already. This is confirmed by a correlation of Balakrishnan and Pei [1975]  

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On the basis of different assumptions about the nature of the fluid and solid flow within each phase and between phases as well as about the extent of mixing within each phase, it is possible to develop many different mathematical models of the two phase type. Pyle (119), Rowe (120), and Grace (121) have critically reviewed models of these types. Treatment of these models is clearly beyond the scope of this text. In many cases insufficient data exist to provide critical tests of model validity. This situation is especially true of large scale reactors that are the systems of greatest interest from industry s point of view. The student should understand, however, that there is an ongoing effort to develop mathematical models of fluidized bed reactors that will be useful for design purposes. Our current... 

Among the many mathematical models of fluidized bed reactors found in the literature the model of Werther (J ) has the advantage that the scale-dependent influence of the bed hydrodynamics on the reaction behaviour is taken into account. This model has been tested with industrial type gas distributors by means of RTD-measurements (3)and conversion measurements (4), respectively. In the latter investigation (4) a simple heterogeneous catalytic reaction i.e. the catalytic decomposition of ozone has been used. In the present paper the same modelling approach is applied to complex reaction systems. The reaction system chosen as an example of a complex fluid bed reaction is the synthesis of maleic anhydride (Figure 1). 

Flow Distribution between Phases. One of the principal assumptions underlying many of the models of fluidized bed reactors is the two-phase theory of fluidization. This theory, really no more than a postulate, holds that the flow beyond that required for minimum fluidization passes through the bed as translating void units. Although not included in what the originators of this postulate (38) appeared to have in mind, the two phase theory is often held to imply, in addition, that the dense phase voidage remains constant and equal to e - for all U > U. ... 

Some aspects of fluidized-bed reactor performance are examined using the Kunii-Levenspiel model of fluidized-bed reactor behavior. An ammonia-oxidation system is modeled, and the conversion predicted is shown to approximate that observed experimentally. The model is used to predict the changes in conversion with parameter variation under the limiting conditions of reaction control and transport control, and the ammonia-oxidation system is seen to be an example of reaction control. Finally, it is shown that significant differences in the averaging techniques occur for height to diameter ratios in the range of 2 to 20. 

Werther J (1978) Mathematical Modeling of Fluidized-Bed Reactors. Chem Ing Techn 50(ll) 850-860... 

Select the most suitable model for a spedlic reaction system among various models of fluidized-bed reactors. 

Bubbling bed model of fluidized-bed reactors Bubbling bed Bubble rise velocity Main features... 

Fryer C, Potter OE. Bubble size variation in two-phase models of fluidized bed reactors. Powder Technology 6 317-322, 1972. 

Modeling of fluidized bed reactors is difficult, and thus problems arise during scale-up. 

Some Features of the Fluidization and Transport of Solids Heat Transfer in Fluidized Beds Modeling of Fluidized Bed Reactors... 

Fryer, C. and O.E. Potter. Bubble Size Variation in Two-Phase Models of Fluidized Bed Reactors. Powder Technol. 6 (1972) 317-322. 

Potter (1 ) has recently reviewed the modelling of fluidized bed reactors. 

Gascon J, Tellez C, Herguido J, Jakobsen HA, Men6ndez M,(2006) Modeling of fluidized bed reactors with two reaction zones. AlChE J 52(11) 3911-3923... 

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