Models for three-phase slurry reactors

The standard models, such as the one described in Chap. 2 and the similar ones outlined by others,4,11,12,2° 22-4 9 analyze the steady-state behavior of the system and consider perfect mixing in the liquid and suspended phases and no change in the concentration of the gas phase within the reactor. Here we describe some other models for the flow systems which relax some of these assumptions. 

4-6-1 Model for Three-phase Slurry Reaction (i.e., No Liquid Flow) 

A large number of gas-liquid-suspended-solid operations are operated under no liquid flow (i.e., batch) conditions. A transient model for this type of isothermal reactor is given by Govindarao.10 Here, we briefly describe his model and the important results obtained from it. 

If the reaction is pseudo-first-order with respect to the gaseous reactant (i.e., if there is liquid reactant taking part in the reaction, its concentration is in excess and uniform) and if the reaction occurs only at the catalyst surface, the governing dimensionless material-balance equations for the reacting species in three phases are given as10 

In the above equations, AG, AL, and As are the gas-phase, liquid-phase and calalyst-surface concentrations of the reacting species, ACi is the average gas-phase concentration at the reactor inlet, Z is the axial distance from the reactor inlet, L is the total length of the reactor, m = H/RgT, where H is the Henry s law constant (cm3 atm g-mol ), Rg is the universal gas constant, and T is the temperature of the reactor. UG is the mean gas velocity, Us is the mean settling velocity of the particles, t is the time, k is the first-order rate constant, W is the catalyst loading, zc and ZP are the axial dispersion coefficients for the gas and solid phases, respectively. Following the studies of Imafuku et al.19 and Kato et al.,21 the axial dispersion coefficient for the liquid phase was assumed to be the same as that for the solid phase, w is the concentration of the particles and hG the fractional gas holdup. Other parameters have the same meaning as described earlier. 

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