Fluidized reactors conversion equation

We will now caleulate the fluidized CSTR catalyst weight necessary to achieve the same conversion as in the packed-bed reactor at the same operating conditions. The bulk density in the fluidized reactor is 0.4 g/cm. The design equation is... 

To summarize the model calculation, the concentrations of each species (reactant and products) in the bed are calculated using Eqs. (20) and (21). Equation (23) is used to calculate the concentration profiles of each species in the upper dilute region. The total gas flow rate can be calculated by addition of the molar flows of each species at any given axial location within the bed. The total flow rate can be converted to the volumetric gas flow rate, and the superficial gas velocity may be determined using Eqs. (24) and (25). The values for hydrodynamic parameters are then calculated for the obtained gas velocity and the set of equations is solved numerically. Figure 27 shows the axial profiles of butane and maleic anhydride concentrations calculated based on the model equations. The effects of fine particle (<7p < 45 pm) contents on butane conversion are also predicted as shown in Fig. 28. As surmised from the figure, the content of fine particles affects fluidization properties and reactor conversion. 

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Closure After completing this chapter, the reader should be able to derive differential equations describing diffusion and reaction, discuss the meaning of the effectiveness factor and its relationship to the Thiele modulus, and identify the regions of mass transfer control and reaction rate control. The reader should be able to apply the Weisz-Prater and Mears criteria to identify gradients and diffusion limitations. These principles should be able to be applied to catalyst particles as well as biomaierial tissue engineering. The reader should be able to apply the overall effectiveness factor to a packed bed reactor to calculate the conversion at the exit of the reactor. The reader should be able to describe the reaction and transport steps in slurry reactors, trickle bed reactors, fluidized-besd reactors, and CVD boat reactors and to make calculations for each reactor. 

Thus, for a nondeactivating catalyst, the nature of the solid presence (fixed or fluidized, or even moving as found by Sadana and Doraiswamy, 1971) is of no consequence, as long as the fluid flow patterns are the same, plug flow in this case. It is only when the catalyst is subject to decay that the performances of the reactors differ, and then the nature of the decay equation plays a significant role in determining the conversions achievable. 

The equation was applicable both to fixed-bed LTFT and to HTFT fluidized bed reactors. Note that when conversion is low, that is, the partial pressure of water... 

Equation (2) predicts that if the total pressure is increased and the gas feed rate is increased by the same factor, that is, the residence time in the catalyst bed remains the same, then the degree of conversion remains unchanged. This matched the actual experimental pilot plant findings. This means that the production rate should increase in proportion to the increase in pressure. On the basis of this prediction, new pilot plants were constructed at Sasol and tests up to 6.0 and 7.5 MPa both for the LTFT fixed-bed operations and for the HTFT fluidized bed operations, respectively, were carried out. These tests confirmed the kinetic predictions. A 4.5-MPa multitubular fixed-bed commercial reactor was... 

Although the Orcutt model is simple, it does allow us to explore the effects of operating conditions, reaction rate and degree of interphase mass transfer on performance of a fluidized bed as a gas-phase catalytic reactor. Figure 7.20 shows the variation of conversion with reaction rate (expressed as fcHmf(l — p/U)) with excess gas velocity (expressed as jS) calculated using Equation (7.65) for a first-order reaction. 

Iterative solution techniques are commonly required to match the conversion of the gas and solids, which must satisfy the stoichiometry of reactions like that described by Equation (42). While some fairly general models have been proposed for gas-solid reactions in fluidized beds (15,20,83), most models for reactions of this type are specific to a particular reaction or reactor. 

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