Multicomponent distillation minimum reflux

Unequal Molal Flow, 63 Ponchon-Savarit Method, 63 Example 8-21 Ponchon Unequal Molal Overflow, 65 Multicomponent Distillation, 68 Minimum Reflux Ratio — Infinite Plates, 68 Example 8-22 Multicomponent Distillation by Yaw s Method, 70 Algebraic Plate-to-Plate Method,... 

McCormick [97] presents a correlation for Gilliland s chart relating reflux, minimum reflux, number of stages, and minimum stages for multicomponent distillation. Selecting a multiplier for actual reflux over minimum reflux is important for any design. Depending on the com-... 

This, method for multicomponent distillation involving more than one feed and more than one side stream requires a reliable minimum reflux. 

The two most frequently used empirical methods for estimating the stage requirements for multicomponent distillations are the correlations published by Gilliland (1940) and by Erbar and Maddox (1961). These relate the number of ideal stages required for a given separation, at a given reflux ratio, to the number at total reflux (minimum possible) and the minimum reflux ratio (infinite number of stages). 

Colburn (1941) and Underwood (1948) have derived equations for estimating the minimum reflux ratio for multicomponent distillations. These equations are discussed in Volume 2, Chapter 11. As the Underwood equation is more widely used it is presented in this section. The equation can be stated in the form ... 

Just as with binary distillation, it is important to understand the operating limits for multicomponent distillation. The two extreme conditions of total and minimum reflux will... 

Glinos K, Malone MF. Minimum reflux, product distribution, and lumping rules for multicomponent distillation. Ind Eng Chem Process Des Dev 1984 23 764. 

Underwood,E.R., Fractional Distillation of Multicomponent Distillation -Calculation of Minimum Reflux Ratio, J. Inst Petrol., 32,274, 614, 1946. Van Winkle, M.C., Todd, W., Optimum Fractionation Design by Simple Graphics Methods, Chem. Eng., 78, 21,136,1971. 

Multicomponent distillation, 393 absorption factor method, 398 azeotropic, 420-426 bubblepoint (BP) method, 406-409 computer program references. 404 concentration profiles, 394 distribution of non-kevs. 395 Edmister method, 398,399 extractive, 412, 417-422 feed tray location, 397 free variables, number of 395 Lewis-Matheson method 404 MESH eauations. 405-407 molecular, 425-427 nomenclature, 405 number of theoretical trays, 397 packed towers, 433-439 petroleum, 411-415 reflux, minimum, 397 reflux, operating, 397 SC (simultaneous correction) method, 408-411... 

While Eq, (2) has been found satisfactory to employ for many cases of multicomponent distillation, use this equation with caution, as it may produce high values of the minimum reflux ratio when the composition of the light key in the distillate is not predominant. 

If one or more unit operations have been given infeasible specifications, then the flowsheet will never converge. This problem also occurs with multicomponent distillation columns, particularly when purity specifications or flow rate specifications are used, or when nonadjacent key components are chosen. A quick manual mass balance around the column can usually determine whether the specifications are feasible. Remember that all the components in the feed must exit the column somewhere. The use of recovery specifications is usually more robust, but care is still needed to make sure that the reflux ratio and number of trays are greater than the minimum required. A similar problem is encountered in recycle loops if a component accumulates because of the separation specifications that have been set. Adding a purge stream usually solves this problem. 

Underwood,E.R., Fractional Distillation of Multicomponent Distillation -Calculation of Minimum Reflux Ratio, J. Inst. Petrol., 32, 274, 614,1946. 

MINIMUM REFLUX RATIO. The minimum reflux ratio for a multicomponent distillation has the same significance as for binary distillation at this reflux ratio, the desired separation is just barely possible, but an infinite number of plates is required. The minimum reflux ratio is a guide in choosing a reasonable reflux ratio for an operating column and in estimating the number of plates needed for a given separation at certain values of the reflux ratio. 

NUMBER OF IDEAL PLATES AT OPERATING REFLUX. Although the precise calculation of the number of plates in multicomponent distillation is best accomplished by computer, a simple empirical method due to Gilliland is much used for preliminary estimates. The correlation requires knowledge only of the minimum number of plates at total reflux and the minimum reflux ratio. The correlation is given in Fig. 19,5 and is self-explanatory. An alternate method devised by Erbar and Maddox is especially useful when the feed temperature is between the bubble point and dew point. 

Use the Underwood equations to determine the minimum reflux ratio for multicomponent distillation. 

An exact method for calculating the minimum number of separating stages has been developed by Harbert [182], who refers the volatilities of the individual components to the vapour pressure of the most volatile constituent. An excellent article bj Bruijn [183] deals with the theory of multicomponent distillation at a minimum reflux ratio. The thermodynamic foundation of multicomponent rectifications has been treated systematically by Wagner in a series of publications [183a]. Starting from the physical properties of mixtures the various steps in distillation practice are described in an exemplary manner. The description is supplemented by a great number of references. 

In industry many of the distillation processes involve the separation of more than two components. The general principles of design of multicomponent distillation towers are the same in many respects as those described for binary systems. There is one mass balance for each component in the multicomponent mixture. Enthalpy or heat balances are made which are similar to those for the binary case. Equilibrium data are used to calculate boiling points and dew points. The concepts of minimum reflux and total reflux as limiting cases are also used. 

Minimum stages for total reflux. Just as in binary distillation, the minimum number of theoretical stages or steps, can be determined for multicomponent distillation for total reflux. The Fenske equation (11.4-23) also applies to any two components in a multicomponent system. When applied to the heavy key H and the light key L, it... 

In multicomponent distillation, it may be necessary to estimate the minimum reflux ratio using classical methods [1,2]. This estimate usually requires the solution of a polynomial in of degree n, such as the equation... 

Erbar, R. C., Maddox, R. N. (1962). Minimum Reflux Rate for Multicomponent Distillation Systems by Rigorous Plate Calculations. Can. J. Chem. Eng., 2,25-30. 

Franklin, N. L., Forsyth, J. S. (1953). The Interpretation of Minimum Reflux Conditions in Multicomponent Distillation. Trans Inst. Chem. Eng, 31, 363-88. 

Poellmann, R, Glanz, S., Blass, E. (1994). Calculating Minimum Reflux of Nonideal Multicomponent Distillation Using Eigenvalue Theory. Comput. Chem. Eng., 18,549-53. 

Sugie, H., Benjamin, C. Y. L. (1970). On the Determination of Minimum Reflux Ratio for a Multicomponent Distillation Column with Any Number of Side-Cut Streams. Chem. Eng. Set., 25,1837-46. 

Glinos, K., Malone, M. F. (1984). Minimum Reflux, Product Distribution and Lumping Rules for Multicomponent Distillation. Ind. Eng. Chem. Process Des. Dev., 23,764. 

The Underwood equations (Underwood, 1948) provide a shortcut method for determining the minimum reflux ratio, ilmin, in multicomponent distillation under the following assumptions constant relative volatilities and constant molal overflows in the stripping section as well as in the enriching section. The minimum reflux ratio, i min> is obtained from a solution of the following two equations for n components ... 

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