Stirred reactors, with Rushton

In the example a gas-liquid reaction with particulate solids (e.g., a catalyst) operating in regime 11 in a stirred reactor with a Rushton turbine is to be scaled up. The primary process requirement is for the same degree of reaction conversion at each scale, which means the same number of moles of gas transferred per mole of liquid fed ... 

Fig. 45.4 Left Schematic diagram of a continuous stirred tank reactor with gas and liquid inlet and outlet. Right A Rushton-type turbine (adapted from [3]).

Double-impeller combinations Bouaifi et al. (2001) derived the following correlations for stirred gas-liquid reactors with various combinations of double impellers. The impellers used were the lightning axial flow impeller (A-310), the four 45° pitched blade turbine pumping down (PBTD) and the Rushton disk turbine (RDT). Furthermore, the tank was a dish-bottom cylindrical tank equipped with four baffles, while the gas was introduced by a ring sprager. The gas-flow rate ranged from 0.54 to 2.62 L/s, whereas the rotational speed was from 1.66 to 11.67 s. The gas holdup is... 

Correlations are available for mixing times in stirred-tank reactors with several types of stirrers. One of these, for the standard Rushton turbine with baffles [13], is shown in Figure 7.9, in which the product of the stirrer speed N (s ) and the mixing time t (s) is plotted against the Reynolds number on log-log coordinates. For (Re) above approximately 5000, the product N t (-) approaches a constant value of about 30. 

FIGURE 7A.3 Some commonly used impellers for two-/three-phase stirred reactors, (a) Standard six-blade Rushton turbine, (b) Six-blade 45° pitched turbine, (c) Lightnin A315 . (d) SC ABA 6SRGT. (Reproduced from Middleton 2000 with permission from Elsevier. 1992.)... 

The CSTR (continuously stirred tank reactor) with mechanical stirring, typically combining Rushton and marine impellers (see also Figure 1.15) is the standard design for practically all applications. The table gives an overview of all liquid-moving and mbcing options. 

A stirred-tank reactor equipped with a standard Rushton turbine of the following dimensions contains a hquid with density p = 1.0 g cm and viscosity... 

Schafer, M., Hofken, M. and Durst, F. (1997), Detailed LDV measurements for visualization of the flow field within a stirred tank reactor equipped with a Rushton turbine, Chem. Eng. Res. Des., 75, 729-736. 

A stirred-tank reactor equipped with a standard Rushton turbine of the following dimensions contains a liquid with density p = 1.000 gcm 3 and viscosity p = 0.013 gcm 1s 1. The tank diameter D = 2.4m, liquid depth HL = 2.4m, the impeller diameter d = 0.8m, and liquid volume = 10.85 m3. Estimate the stirrer power required and the mixing time, when the rotational stirrer speed N is 90r.p.m., that is, 1.5 s 1. 

Nocentini, M., Pinelli, D., and MageUi, F. (1998), Analysis of the gas behavior in sparged reactors stirred with multiple Rushton turbines Tentative model validation and scale-up, Industrial Engineering Chemistry Research, 37(4) 1528-1535. 

A critical analysis of the many publications concerning the simulation of liquid flow in baffied stirred tank reactors equipped with a Rushton turbine reveals several discrepancies. The most important differences between the simulations concern the dimensionality of the simulations (three-dimensional or axisym-metric), turbulence modeling, the modeling approaches for the Rushton turbine as well as the accuracy of the numerical predictions, which depends on the grid size. 

Street [8,9] has carried out detailed studies of temperature and flow patterns for highly viscous non-Newtonian flows in polymer stirred tank reactors, particularly with respect to the effect of vessel geometry on reactor performance. His work is extended in this example to the case of a Rushton... 

Figure 2.2 Characteristic times in a stirred-tank reactor (STR) at the 8m scale with a Rushton turbine. Mass transfer time (A) and (O) at a superficial gas velocity of 2 X 10 m s , ( ) without aeration. Short...

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