Overall tower efficiency

The plate to plate type calculation is a fundamental procedure wherein the tower is assumed to be composed of theoretical equilibrium plates. The actual plates required are determined from the number of theoretical plates using a predicted overall tower efficiency. The starting point for a tower calculation is usually a specified feed composition, feed temperature, and tower operating pressure. The procedure involves defining the compositions and temperamres on each plate in the tower and subsequently the resultant compositions and temperatures of the product streams. The actual computations, which involve trial... 

The overall tower efficiency is defined as the ratio between the number of theoretical stages and the actual number of stages required for the... 

As an example for illustration, the McCabe-Thiele diagram (McCabe and Thiele, 1925) in Figure 12.2 indicates 12 actual stages required in comparison with 8 theoretical stages in the tower. Partial condensers and partial reboilers are counted in both the theoretical stages and actual stages. Thus, the overall tower efficiency is 67% (=8/12). 

The simplest approach is to use a correlation to determine overall tower efficiency. The O Connell (1946) correlation shown in Figure 12.3 is the standard of the industry for industrial tower efficiency (Kister, 1992). 

For a complex column, equation (13.5) cannot give the right answer as it is only applied to each section. Instead, fractionation correlation plots by O Connell (1946) (Figure 12.3) is widely used for overall tower efficiency, which is the standard for... 

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... 

Available-Energy Analysis. Using standard techniques (7-8) an available-energy analysis was performed on the system operating at a reflux ratio of 1.2, and shows the overall Second-Law efficiency to be 12.9% (9). The relevant equations for this analysis are given in Table II. The reboiler has a Second-Law efficiency equal to AAi/AAst or 74.2%. The tower efficiency, defined as AAfr>.p/(AA], + A ) is 55.7%. Note that it is of little use to... 

Distillation stage calculations are usually performed with ideal stages, The number of ideal stages required for the separation is divided by the overall column efficiency (Sec, 7,1,1) to obtain the required number of trays. In packed towers, the number of stages in the column is multiplied by the HETP (Height Equivalent of a Theoretical Plate, see Sec. 9.1,2) to obtain the packed height. 

Light-component analysis and the TBP and API gravity for the feed are given in Table 13-29. Representation of this feed by pseudocomponents is given in Table 13-30 based on 16.7°C (30°F) cuts from 82 to 366°C (180 to 690°F), followed by A1.1°C (TS T) and then 55.6°C (100°F) cuts. Actual tray numbers are shown in Fig. 13-114. Corresponding theoretical-stage numbers, which were determined by trial and error to obtain a reasonable match of computed- and measured-product TBP distillation curves, are shown in parentheses. Overall tray efficiency appears to be approximately 70 percent for the tower and 25 to 50 percent for the sidecut strippers. 

Rate of evaporation (cooling tower), gpm Overall column efficiency, %... 

Drickamer, H.G. Bradford, J.B. Overall plate efficiency of commercial hydrocarbon fractionating towers. Trans. AIChE 1943, 39, 319. 

The number of actual trays required in a tower to attain the perforomnce of a calculated number of theoretical stages is detemiined by the tray efficiency. Several types of tray efficiency have been proposed however, the two most widely used are the Murptuee vapor efficiency CMV, defined in Section 6.2 [Eq. (6.2-1)], which refers to individual trays, and the overall column efficiency Eq, which is defined simply as... 

Rgure 14.6 Overall tray efficiency, 4-foot-ID tower, at total reflux, illustrating drop of efficiency near the flood point (Reprinted with permission from T. Yanagi and M. Sakata, Ind. Eng. Chem. Proc. Des. Dev., vol. 21, p. 712, copyright (1982) American Chemical Society.)... 

EXAMPLE 10.6-J. Absorption of SO 2 in a Tray Tower A tray tower is to be designed to absorb SOj from an air stream by using pure water at 293 K (68°F). The entering gas contains 20 mol % SO and that leaving 2 mol % at a total pressure of 101.3 kPa. The inert air flow rate is 150 kg air/h m, and the entering water flow rate is 6000 kg water/h m. Assuming an overall tray efficiency of 25%, how many theoretical trays and actual trays are needed Assume that the tower operates at 293 K (20 C). 

Overall tray efficiency. The overall tray or plate efficiency Eq concerns the entire tower and is simple to use but is the least fundamental. It is defined as the ratio of the number of theoretical or ideal trays needed in an entire tower to the number of actual trays used. 

Two empirical correlations for absorption and distillation overall tray efficiencies in commercial towers are available for standard tray designs (OI). For hydrocarbon distillation these values range from about 50 to 85% and for hydrocarbon absorption from about 10 to 50%. These correlations should only be used for approximate estimates. 

Diameter of tower = 0.83 m Tray spacing = 0.61 m Overall tray efficiency = 60%... 

The overall tray efficiency is 60%, so that the present trays are providing 15 to 16 theoretical stages of separation. The vertical height from tray 1 to tray 26 is 51 ft 6 in. Can tower packing be installed to increase the column capacity by at least 50% without losing separating efficiency ... 

Overall tray efficiency Another method of describing the performance of a tray tower is through the overall tray efficiency,... 

Figure 6,25 Overall tray efficiencies of bubble-cap Uay distillation towers separating hydrocarbons and similar mixtures. For in centipoises, use as abscissa a Mi, O Connell [PO].)...

Muiphree gas-phase stage efficiency corrected for entrainment, fractional overall tray efficiency of a tower, fractional point gas-phase tray efficiency, fractional function... 

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