Slurry reactor power consumption

If we compare the sparged (BSCR) and mechanically stirred (MSSR) reactors, we can stress that the slurry bubble column may be operated in a semi-batch mode, does not use any moving parts, and requires minimal maintenance, smaller floor space and has lower power consumption. 

Power or energy dissipated in the aerated suspension has to be large enough (a) to suspend all solid particles and (b) to disperse the gas phase into small enough bubbles. It is essential to determine the power consumption of the stirrer in agitated slurry reactors, as this quantity is required in the prediction of parameters such as gas holdup, gas-liquid interfacial area, and mass- and heat-transfer coefficients. In the absence of gas bubbling, the power number Po, is defined as... 

Gas holdup is an important hydrodynamic parameter in stirred reactors, because it determines the gas-liquid interfacial area and hence the mass transfer rate. Several studies on gas holdup in agitated gas-liquid systems have been reported, and a number of correlations have been proposed. These are summarized in Table VIII. For a slurry system, only a few studies have been reported (Kurten and Zehner, 1979 Wiedmann et al, 1980). In general, the gas holdup depends on superficial gas velocity, power consumption, surface tension and viscosity of liquids, and the solid concentration. The dependence of gas holdup on gas velocity, power consumption, and surface tension of the liquid can be described as... 

The power in aerated slurry reactors in regime c can be calculated using Equation (3.3). In general, relations summarized by Baldi (1986) can be used for the calculation of power consumption. The most widely used correlation for the minimum rotational speed of agitation required for complete suspension of solids is that of Zweitering (Equation (3.6)). The most versatile... 

The gas holdup in a slurry reactor depends upon superficial gas velocity, power consumption, the surface tension and viscosity of the liquids, and the solids concentration. For the first three parameters, the relationship cg oc yO.36-o.75pO.26-o.470.o.36-o.65 holds. For low solids concentration and waterlike liquids, the relationship eg = f(P/V, ug) is useful, although the nature of such a relationship depends upon the foaming characteristics of the liquids. An increase in solids concentration decreases gas holdup, whereas an increase in viscosity first increases and then decreases the gas holdup. A decrease in surface tension and an increase in stirrer speed increases the gas holdup. 

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