Tray efficiency overall

The reboiler is considered 100% efficient, and likewise any partial condenser, if used. Therefore the value Nq represents the theoretical trays or stages in the column proper, excluding the reboiler and partial condenser. Eq represents the overall tray efficiency for the system based upon actual test data of the same or similar systems, or from the plot of Figure 8-29, giving operating information preference (if reliable). 

Mols of distillate or overhead product, lb mols/hr or batch distillation, mols Mols component, i, in distillate Vaporization efficiency of steam distillation Overall column efficiency Overall tray efficiency Eqg = Murphree point efficiency, fraction Murphree plate/tray efficiency, = E ... 

Calculate fraction absorbed for each component, assuming a fixed overall tray efficiency for an... 

Absorption Efficiency, or fraction absorbed Overall tray efficiency, fraction Stripping efficiency, or fraction stripped Fraction of v + li absorbed by the liquid Fraction of loi stripped out of the liquid Mols individual components stripped per hour Total heat of absorption of absorbed components, thousand Btu/day... 

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... 

As with distillation, the correlation for overall tray efficiency for absorbers, given in Equation 10.7, should only be used to derive a first estimate of the actual number of trays. More elaborate and reliable methods are available, but these require much more information on tray type and geometry and physical properties. If the column is to be packed, then the height of the packing is determined from Equation 9.64. As with distillation, the height equivalent of a theoretical plate (HETP) can vary... 

HETP is another quantity that is used to express the efficiency of a device for carrying out a separation, particularly in which mass is transferred by a stage-wise action rather than a differential contact. For example, in a tray column, the HETP value is the tray spacing divided by the fractional overall tray efficiency. 

As might be expected, the vapour phase may offer the controlling resistance to mass transfer in high pressure distillations. Values for tray efficiencies at elevated pressure are scarce [23, 24]. The prediction of tray efficiency may be approached in several ways. One way is to utilize field performance data taken for the same system in very similar equipment. Unfortunately such data are seldom available. When they are available, and can be judged as accurate and representative, they should be used as a basis for efficiency specification [25], Another way is to utilize laboratory-or pilot-plant efficiency data. For example a small laboratory-Oldershaw tray-column can be used with the same system. Of course, the results must be corrected for vapour-and liquid mixing effects to obtain overall tray efficiencies for large-scale design [26], Another approach is the use of empirical or fundamental mass-transfer models [27-30],... 

Tray Efficiencies in Tray Absorbers ana Strippers Computations of the theoretical trays N assume that the liquid on each tray is completely mixed and that the vapor leaving the tray is in equilibrium with the liquid. In practice, complete equilibrium cannot exist since interphase mass transfer requires a finite driving force. This leads to the definition of an overall tray efficiency... 

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. 

The intersection of the operating and equilibrium lines (X, Y ) represents the scrubber outlet gas and liquid conditions for a theoretical stage which represents 100% overall tray efficiency. The overall tray efficiency E is defined as ... 

Tray Efficiency The overall efficiencies of sieve trays typically are between 10 and 30 percent. One of the earliest models for predicting the overall tray efficiency was an empirical one reported by Treybal [Liquid Extraction, 2d ed. (McGraw-Hill, 1963)]. Krishna, Murty, and) Rao [Ind. Eng. Chem. Process Des. Dev., 7(2),... 

The overall tray efficiency may then be estimated by using... 

Two efficiency definitions are in common use for engineering design overall tray efficiency and Mur-phree tray efficiency. Murphree tray efficiency basis can be set on either the vapor phase or the liquid phase. Most literature reports data on a vapor phase... 

Overall tray efficiency is defined as the number of theoretical trays required for a service divided by the number of actual trays. 

For the separation problem described in Examples 12.1 and 12.4, estimate the number of trays required if the condenser can handle a maximum vapor rate of 150 kmol/h and the overall tray efficiency is 65%. 

Murphree tray efficiency with entrainment Murphree point efficiency in liquid terms Murphree tray efficiency in liquid terms Murphree tray efficiency in vapor terms Overall tray efficiency... 

Based on preliminary studies, it was determined that a 10-tray column is appropriate for an absorption operation. The overall tray efficiency is estimated at 60%. For the indicated feed gas and absorbent, determine the expected flow rates and compositions of the products using the Kremser method. 

The same separation would require a minimum reflux ratio of 0.6. Existing pumping facilities can deliver a reflux rate of 275 kmol/h. Determine the required number of theoretical stages. What minimum overall tray efficiency is needed to make the specified separation with the existing column ... 

An absorber column with 12 actual trays is used to lower the concentration of butane in a feed gas. The overall tray efficiency is estimated at 50%. The feed gas and absorbent are given below. 

A process is defined similar to Example 17.2, with the same components, initial charge and composition, the same constant distillate rate and required composition, and the same column pressure. In this case the reflux ratio is maintained at twice the minimum value. The column has six actual trays plus the reboiler, the equivalent of seven actual trays. The overall tray efficiency is 65%, and the relative volatility of butane to pentane is assumed constant at 2.315. 

The overall tray efficiency E fy (often called Murphree efficiency ) takes into account concentration gradients on the tray. It has an arbitrary definition based on the average total vapor composition leaving the froth and the specific liquid composition leaving the tray [not the average composition on the tray (see Figure 12.58)]. Because of this arbitrariness, the overall tray efficiency valne can exceed 1.0. When there are no composition gradients on the tray, = Ey,y... 

The point efficiency is a fundamental criterion of mass transfer, whereas the overall tray efficiency is the value that can be measured, especially for larger distillation columns. Large-column... 

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