Height equivalent to theoretical stage

Efficiencies of several kinds of small-scale extractors are shown in Fig. 19-28. Larger-diameter equipment may have less than one-half these efficiencies. Spray columns are inefficient and are used only when other kinds of equipment may become clogged. Packed columns as liquid-liquid reactors are operated at 20 percent of flooding. Their height equivalent to theoretical stage (HETS) range is from... 

Fractionation efficiency, 6,11,195-196, 209, 365 fractionator problems, 195-196, 209 Fractionator problems (FCCU product fractionation), 18f3-200 flooding, 188-189 load observation, 189-191 liquid loading sensitivity, 189 capacity comparison, 189,192-193 heattransfer coefficients, 193-194 structured packing heat transfer, 193 height equivalent to theoretical stage,... 

Height equivalent to theoretical stage (HETS) for vapor-liquid contacting is 0.4-0.56 m (1.3-1.8... 

Design data for separation of the particular or similar mixture in a packea column are not available. Design procedures are better estabhshed for tray-type columns than for packed columns. This is particularly so with respect to separation efficiency since tray efficiency can be estimated more accurately than packed height equivalent to a theoretical stage (HETP). 

The height equivalent to a theoretical stage (HETS) in an extraction tower is simply the height of the tower Zt divided by the number of theoretical stages achieved [Eq. (15-29)]. 

HETP = Height equivalent to a theoretical plate/tray/stage, in. or ft, or possibly mm... 

The HETP (Height Equivalent to a Theoretical Plate (stage or plate)) is the tray spacing divided by the fractional overall tray efficiency [82]. The transfer unit concept has been useful for generalized correlations [89]. Because packed towers operate with continuously changing compositions through the packed height, the concept... 

Figure 11.59. Height equivalent to a theoretical stage for common packings...

An additional expression of performance used for countercurrent cascades, particularly for those in the design of towers (see below), is HETS, the height equivalent to a theoretical stage. 

Prediction of the height equivalent to a theoretical stage presents a difficult problem. A lack of fundamental data necessitates an empirical approach, and at the present time... 

Plate height is the constant of proportionality between the variance, cr2, of the band and the distance it has traveled, x. The name came from the theory of distillation in which separation could be performed in discrete stages called plates. Plate height is also called the height equivalent to a theoretical plate. Plate height is approximately the length of column required for one equilibration of solute between mobile and stationary phases. We explore this concept further in Box 23-2. The smaller the plate height, the narrower the bandwidth. 

HETP Height equivalent to a theoretical plate (or tray). Also called an equilibrium separation stage. 

These terms sometimes are used interchangeably with height equivalent to a theoretical stage (HETS), but they are nearly the same only when the ratio kjka is a large number in the case of HTUa. Example 13.12 studies this difference. 

The most useful measure of the separating power of packed towers is the HETP, the height equivalent to a theoretical plate or stage. It is evaluated simply as the ratio of packed height used for a certain degree of separation to the theoretical number of stages. Its relation to the fundamental quantity, HTU, or the height of a transfer unit, is... 

Although the most useful extraction process is with countercurrent flow in a multistage battery, other modes have some application. Calculations may be performed analytically or graphically. On flowsketches like those of Example 14.1 and elsewhere, a single box represents an extraction stage that may be made up of an individual mixer and separator. The performance of differential contactors such as packed or spray towers is commonly described as the height equivalent to a theoretical stage (HETS) in ft or m. 

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... 

HETS, relative height equivalent to a theoretical stage. source R.F. Strigle, Jr., Random Packings and Packed Towers, Gulf Publishing, Houston, TX, 1987. Reprinted with permission. 

Eckert [9] showed that a relative height equivalent to a theoretical stage (HETS) vs. the dispersed-phase velocity revealed the packed-column efficiency, or simply the required height, to make one theoretical stage. (See Fig. 7.10). Eckert and others [6, 8] have shown that normally the theoretical packed-column stage requires 2.5 ft of column packed height. All this of course refers strictly to liquid-liquid extraction processing. Also, the continuous-phase velocity Vc (ft/h) and the dispersed-phase velocity VD (ft/h) are referenced to the liquid-phase... 

An analytical solution is also available for theoretical stages as opposed to transfer units, and the height equivalent to a theoretical plate (HETP). The number of theoretical stages or plates Np can be determined by counting the steps between the operating line and the equilibrium line as is done with distillation problems (see Example 8.1 in Section 8, Distillation), but a more convenient analytical solution is as follows ... 

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