Bed-scale apparent reaction rate

Figure 4. Bed scale apparent reaction rate against the liquid superficial velocity at different temperatures (— model +, o, s experiments).

In order to fit the proposed model of the bed scale apparent reaction rate on the experimental results, we considered two parameters. The first one is the surface energy E, as... 

The results of the fitting are presented in Figures 4 and 5 in terms of the bed scale apparent reaction rate r a9ainst the liquid superficial velocity. L... 

The variations of the bed scale apparent reaction rate may be interpreted in terms of a contacting efficiency u c and an external efficiency rig (representing the external mass transfer limitaitons). nc is given by... 

Obviously, the bed scale apparent reaction rate is proportional to the product ric U Typical variations of these... 

Bed scale apparent reaction rate against the liquid superficial... 

The particle scale apparent reaction rate has been determined in a discontinuous Carberry type reactor and in a continuous micro-trickle bed reactor in which catalyst particles... 

The following developments will be restricted to laminar liquid flow with very low gas-liquid interactions that is the flow regime prevailing with the operating conditions adopted in the experimental work. Application of Eq.8, with some simplifications, will be presented for the modelling of the different processes controlling the apparent reaction rate at the bed scale. 

In summary, the stagnancy/catalyst effectiveness model predicts that liquid and/or gas velocity effects on the apparent reaction rate will be observed for catalysts vfliich are at least marginally diffusion limited and run in a trickle bed reactor under low velocity conditions. The model predicts that for scale-up of reactions which are diffusion limited or at least marginally so, the pilot plant should be designed to run at elevated velocities which do not show sensitivity to liquid velocity. Conversely, if a pilot reactor is used for providing data for scaleup showing velocity effects, there is a good likelihood that the catalyst suffers from diffusion limitations. 

The holdups can play an important role in the reactor performance. For example, in a pilot-scale trickle-bed reactor, the liquid holdup can play an important role in changing the nature of the apparent kinetics of the reaction. When homogeneous and catalytic reactions occur simultaneously, the liquid holdup plays an important role in determining the relative rates of homogeneous and catalytic reactions. In a three-phase fluidized-bed reactor, the holdup of the solid phase plays an important role in the reaction rate, particularly when the solid phase is a reactant. The gas holdup, of course, always plays an important role in reactor performance when a gaseous reactant takes part in the reaction. 

P-particles. The reaction appears to take place at the solid surface and is so rapid, that its rate is completely determine by the rate of mass transfer of A to the particles (B is used in excess). TTie mean particle size is 0.1 mm, the solid has an apparent density of 900 kg/m. The minimum fluidization velocity is 0.007 m/s. In a bench scale fluid bed reactor, equippped with a porous distributor plate, and with a bed height of 0.25 m, the conversion of reactant A is measured for various gas flow rates. When these are 0.01, 0.02 and 0.04 the degrees of conversion are, respectively, 0.91, 0.89 and 0.80. For the interpretation of these results we may use Van Swaaij s "simple model", that is shown in the Appendix to section 4.5.1. We find with eq. (4A.1) that the experimental results can be fitted as follows ... 

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