Model Fryer-Potter

The concentration profiles in the bubbles, cloud and emulsion phases are plotted in Figure 1 for a set of parameter values. For the sake of comparison, the profiles for the same values of parameters obtained using the Fryer-Potter model are shown in Figure 2. Figures 3-6 show the influence of parameters such as... 

The formulation of the model as above has the advantage that mathematically it picturizes the bed as an initial value problem in contrast to the more complicated boundary value representation of the Fryer-Potter model. The implications of this reduced complexity become more evident (and considerably more important) when the reactions involved are nonlinear. 

The behavioural features of the fluidized bed have been modeled based on a modified representation of the Fryer-Potter model. The restrictive assumption of plug flow of the emulsion gas has been removed, and model equations developed based on complete mixing of the emulsion gas. This simplification, in addition to bringing the model closer to reality, has led to the conversion of a boundary value problem (Fryer-Potter model) to a simpler initial value problem. Except at very low bubble diameters, the predictions of the two models (based on terminal conversion) agree closely with each other. On the other hand, agreement between the average concentration profiles in the bed predicted by the two models is less satisfactory. While therefore the modified model proposed in this work has the advantage of simplicity and is perhaps closer to reality, further experimental work on industrial size equipment is necessary for a firmer opinion on the latter (nature of gas flow in the emulsion phase). 

The Fryer-Potter model assnmes ping flow in all the phases, inclnding the emulsion phase. Experimental evidence indicates that the emulsion phase gas is more nearly mixed than in plug flow. If... 

FIGURE CS5.1 Schematics of several fluidized-bed reactor models (a) Davidson model, (b) Kunii-Levenspiel model, (c) Miyauchi model, (d), (e) Fryer-Potter and Jayaraman-Kulkami-Doraiswamy models. 

The counter-current backmixing model of Fryer and Potter has been modified by assuming mixed flow in the emulsion phase. The terminal conversions obtained with the present model are compared with those of the original model and found to agree well except at very low values of bubble diameter. The assumption of complete mixing in the emulsion phase converts the original two-point boundary value problem into a simpler initial value problem, thereby considerably reducing the mathematical complexity. 

Fryer and Potter (1972), using the model of Davidson and Harrison, reported that a bubble size found at about 0.4h could be used as the single bubble size in that model. Earlier in this paper, the bubble size found at 0.5h was used arbitrarily in calculating the conversion in an ammonia oxida tion system using the K-L model. 

Here, we note that the influence of particle motion on an impulse response has been treated by van Deemter (V2), Yoshida and Kunii (Y15), Fryer and Potter (FIO, Fll), and Nguyen and Fryer (N2), but their models are all different from the one treated above. 

Fryer, C. Potter, O.E. Experimental investigation of models for fluidized bed catalytic reactors. AIChE J. 1976, 22, 38-47. 

In the models considered so far, no distinction was made between the velocities of the gas in the bnbble, clond/wake, and emulsion phases. In a model of Fryer and Potter (1972a, b), the following featnres are postnlated ... 

The bubbling bed model proposed by Kunii and Levenspiel (1969) can be considered a modified version of the two-phase model where, in addition to the bubble and the emulsion phases, a cloud-wake phase is also considered. The model represents a group of models often referred to as backmixing or dense phase flow reversal models (see also Van Deem ter, 1961 Latham et al., 1968 Fryer and Potter, 1972). A key difference between this model and the rest of the two-phase models is that the interphase mass transfer considers two distinct resistances, one from the bubble phase to the cloud-wake phase, and the other from the cloud-wake phase to the emulsion phase. 

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

Fryer, C. and O.E. Potter. Countercurrent Backmixing Model for Fluidized Bed Catalytic Reactors. Indust. Engng. Chem. Fundam. 11 (1972) 338-344. 

A comparison between cell model predictions and the experimental data of Fryer and Potter (1975) is shown in Figure 11.12 (Peters et al. 1982). The basic parameters used to calculate the model parameters for the prediction in Figure 11.12 are given in Table 11.1. These parameters are the inlet conditions, the condi-... 

To test different models for their suitability, one has to formulate the objectives that are aimed for in the application of the model because there does not exist an "ideal" fluid bed model. Most models have been tested in rather small scale units on their overall conversion prediction, sometimes inserting emperical relations for pareuneters measured under similar conditions. Chavarie and Grace (4 ) Fryer and Potter (47) also tested profiles. In this work we shall consider the usefulness of different models in process development / scaling-up activities. A model is considered to be useful if it can reduce the numbers and the complexity of the experiments necessary for a safe scaling-up or design procedure, and if it adequately describes the operation performemce of the full scale reactor. 

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