Mechanically agitated contactor

Mechanically agitated contactors PM M 0.05-0.4 Can he varied over a wide range 0.3-1 1-800 0.3-800... 

Some examples of mechanically agitated contactors are the rotating-disk contactor (RDC), Karr, Oldshue-Rushton, Scheibel, and Kiihni columns shown in Figure 11. 

As mentioned earlier, the gas holdup in mechanically agitated contactors has been found to be, apart from geometric parameters, a function of liquid viscosity, surface tension, the electrolytic nature of the solutions, foaming character, etc. Hence, phenomenologically the reduction in power consumption should also depends on these characteristics of the system. Bruijn et al (1974) concluded that the surface tension does not affect the mechanism of cavity formation and its shape to an appreciable extent. However, liquid viscosity influences the stability of the cavity. Hughmark (1980) presented the... 

A more notable correlation for the heat-transfer coefficient at the wall of mechanically agitated contactors is given by Perry and Chilton (1973) as... 

Philadelphia Gear Co. has recently introduced a mechanically agitated contactor wherein the impeller is surrounded by a draft tube. The company claims higher values of the mass-transfer coefficient in this equipment, presumably as a result of increased gas holdup. The higher gas holdup is, however, expected to decrease the heat-transfer coefficient and the extent of mixing. 

Typical Values of Mixing and Mass-Transfer Parameters in Mechanically Agitated Contactors (Reprinted from Doraiswamy and Sharma. 1984, courtesy of Marcel Dekker, Inc.)... 

Surface aeration in the presence of gas sparging was studied by Calderbank (1958) for a six-bladed disk turbine in 0.3, 0.375, and 0.5 m i.d. mechanically agitated contactors. He suggested the correlation... 

The values of K for bubble columns can probably be calculated from the above correlation if the comparison between bubble columns and mechanically agitated contactors is based on the same value of average liquid circulation velocity, V. ... 

Figure 4. Comparison between experimental and predicted heat transfer coefficients in bubble columns (Equation 24) (analogy with mechanically agitated contactors) for symbol key, see Table II...

Mechanically agitated contactors 0.1-2 Mixed Mixed Unlimited 0.5-0.8 1-5 20-100 2-50... 

Panja, Phaneswara Rao D., Measurement of gas-liquid parameters in a mechanically agitated contactor, Chem. Engng. J. 52 (1993), p. 121-129... 

Figure CS11.2a shows a comparison of fractional gas holdup under sparging conditions, with and without the use of a gas-inducing impeller. In the absence of a gas-inducing impeller, such a system behaves like a conventional mechanically agitated contactor (MAC). The comparison is made in terms of gas holdup as a function of power consumption per unit volume for different superficial velocities of sparged gas (uq = 0, 6,18, and 29 mm/s). It can be seen that the fractional...

MAC=mechanically agitated contactor, BCR = Chapter 17 for a description of these reactors. 

As already noted, these reactions are characterized by hyperbolic rate forms. Empirical power law models can also be used, but their applicability is restricted to the ranges of parameter values used in their formulation. Note in the table that mechanically agitated contactors (MACs) and bubble-column reactors (BCRs) are the most commonly used reactors. The design of such reactors is considered in Chapter 16. 

A number of studies have been reported on solid-liquid mass transfer in different kinds of contactors, and they have been periodically reviewed, for example Miller (1971), Nienow (1975), Wen and Fan (1975), Briens et al. (1993). Of these, only the mechanically agitated contactor is used with or without a gas phase. It is the only truly two-phase solid-liquid contactor. The other types of contactors, such as the bubble-column contactor (usually), the trickle-bed reactor, and the three-phase fluidized-bed reactor, all involve three phases and are considered in Chapter 17 on multiphase reactions. 

Values of the mass transfer coefficients and interfacial areas for the more common contactors (packed columns, plate columns, bubble columns, mechanically agitated contactors, and static mixers) are usually known, or can be estimated from correlations published in the literature, or are supplied by the manufacturers. Typical values are given in Table 16.1. 

MF MF Steady-state Mechanically agitated contactor, packed column Hrjdj < 3), spray column... 

Mechanically agitated contactors are characterized by complete backmix-ing of both liquid and gas phases thus Equation 16.24 should be applicable to these contactors. Deviation from MF is possible at low stirrer speeds. If the reaction is in regime 2, accurate values of are needed. Because predictive correlations for this are unreliable, the values should be obtained by conducting experiments in a geometrically similar laboratory reactor 20 30 cm diameter. To obtain such similarity, it is recommended that the ratio of tip speed to tank diameter should be kept constant (Juvekar, 1976). 

It is proposed to oxidize a batch of 1000 liters of -butyraldehyde dissolved in n-bulyric acid in the presence of 0.1 % manganese acetate as a catalyst at essentially atmospheric pressure in a mechanically agitated contactor by passing air continuously through it. Given the following data, calculate the time required to obtain a conversion corresponding to a drop in the aldehyde concentration [.B]j from 6.0 to 0.85 x 10 niol/cm ... 

N 0.03 0.03-CJVcolumn Packed column Plate column Mechanically agitated contactor... 

The mechanically agitated contactor, referred to also as the stirred tank reactor (STR), is the most commonly used reactor for small and medium volume production in organic synthesis. Therefore, we shall summarize the important practical features of this reactor, which should also be applicable to CSTR. 

Gas-liquid mass transfer, (for A) [A], type of impeller and stirring speed (mechanically agitated contactor), gas velocity (sparged contactor) Temperature (flJb, dp, B ... 

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