Treybal extractors

In order to permit sizing a tower, data must be available of the height of a transfer unit (HTU). This term often is used interchangeably with the height equivalent to a theoretical stage (HETS), but strictly they are equal only for dilute solutions when the ratio of the extract and raffinate flow rates, E/R, equals the distribution coefficient, K = xE/xR (Treybal, 1963, p. 350). Extractor performance also is expressible in terms of mass transfer coefficients, for instance, KEa, which is related to the number and height of transfer units by... 

Figure 14.12. Tower extractors without agitation, (a) Spray tower with both phases dispersed, (b) Two-section packed tower with light phase dispersed, (c) Sieve tray tower with light phase dispersed, (d) Sieve tray construction for light phase dispersed (left) and heavy phase dispersed (right), (e) Redistributor for packed tower with light phase dispersed (Treybal, 1963).

The most frequently used component separators are absorbers, strippers, fractona-tors, and extractors. According to Humphrey [74], fractionators are used in 90 to 95% of the separations in the US. The principles of conponent separators are covered extensively in several texts such as Treybal [29], King [30] and Henley and Seader [31, 65]. We will only consider short cut sizing methods. These methods are useful for preliminary design estimates and for first guesses for more exact calculations, requiring iterative calculation procedures. 

Figure 4.25 Vitro uranium extractor. From Treybal [T2], by permission.)...

Sieve-tray towers are very effective, both with respect to liquid-handling capacity and extraction efficiency, particularly for systems of low interfacial tension which do not require mechanical agitation for good dispersion. The general assembly of plates and downspouts is much the same as for gas-liquid contact except that a weir is not required. Towers packed with the same random packing used for gas-liquid contact have also been used for liquid extractors however, mass-transfer rates are poor. It is recommended instead that sieve-tray towers be used for systems of low interfacial tension and mechanically agitated extractors for those of high interfacial tension (Treybal, 1980). 

Liquid-liquid extractors can be classified as follows (adapted from Treybal, 1963 Warwick, 1973) ... 

There are two different analyses for mass transfer in a mixer-settler extractor available in the literature. The sinpler analysis (Seader and Henley, 2006 Treybal. 19801 assumes that the mixer is perfectly mixed. This means that the continuous phase is well mixed and the dispersed phase is well mixed. Thus, Xq, Xq, and Xq are all constant and equal to the values at the mixer outlet. Then Eq. fl6-81al sinplifies... 

---