Columns agitated, multistage

Figure 7.1 Conventional equipment used for fluid-fluid reactions (columns (a) multistage agitated column, (b) packed column, (c) sieve tray column, (d) buss loop reactor, (e) tubular reactor, and (f) static mixer)...

The studies of Juvekar (1976) and Ramanarayanan and Sharma (1982) with a 0.2 m i.d. multistage contactor with d,/dx = 0.5 showed that both aL and kLaL are independent of superficial gas velocity above the critical speed of agitation, and they vary linearly with impeller speed. Both aL and kLaL were independent of the number of stages under otherwise identical conditions of dfdj, N, ug, and gas-liquid system. Thus, the results for a single stage are applicable to multistage systems. This conclusion needs to be verified for larger-diameter columns. 

The liquid-phase mixing in a multistage mechanically agitated reactor is best correlated by Eq. (2.31) in the absence of gas flow and by Eq. (2.32) in the presence of gas flow. The mixing time can be estimated from the study of Paca et al. (1976). Experimental work is needed to estimate gas-phase back-mixing. The use of Eq. (2.36) for the calculation of the gas-liquid volumetric mass transfer coefficient in a multistage mechanically agitated column is recommended. 

M.S. Takriff, Column Flooding, Gas Holtkip and Interstage Backmixing of an Aerated Multistage, Machanically Agitated, Compartmented Column, PhD Dissertation, University of Arkansas, 1996. 

M.S. Takriff, W.R. Penney, and J.B. Fasano, Interstage backmixing of an aerated multistage, mechanically-agitated compartinented columns, Can. J. Chem. Eng., 76, 365-369 (June 1998). 

Depending on the relative rates of mass transfer and the chemical reaction (as well as many process-specific conditions), the appropriate equipment for gas-liquid systems may conform to many different geometries. The conventional types include bubble columns, spray columns, multistage contactors (sieve or bubble plate, mechanically agitated etc.) and packed towers whose design aspects will be discusses in the two published volumes of this ASl. 

---