Distillation program

A wide array of general-purpose distillation packages are available to the engineer. Some of the distillation software is stand-alone, whereas other packages are a part of a general-purpose flow sheet or process-simulation system. Because distillation is so universal, all process simulators have one or more distillation program modules for this unit operation. Often the nature of the distillation modules determines the suitabiUty of or the preference for the use of a specific simulator for an appHcation. 

Distillation appHcations can be characterized by the type of materials separated, such as petroleum appHcations, gas separations, electrolyte separations, etc. These appHcations have specific characteristics in terms of the way or the correlations by which the physical properties are deterrnined or estimated the special configurations of the process equipment such as having side strippers, multiple product withdrawals, and internal pump arounds the presence of reactions or two Hquid phases etc. Various distillation programs can model these special characteristics of the appHcations to varying degrees and with more or less accuracy and efficiency. 

Many industrial separations require a series of columns that are connected in specific ways. Some distillation programs can model such a system as a hypothetical single column with arbitrary cross-flows and connections and then carry out the distillation calculations for the modeled hypothetical column. Alternatively, such a system can be modeled as a process flow sheet using a process simulator. 

There are several valuable references to developing and applying a multicomponent distillation program, including Holland [26, 27,169], Prausnitz [52, 53], Wang and Henke [76], Thurston [167], Boston and Sullivan [6], Maddox and Erbar [115], and the pseudo-K method of Maddox and Fling [116]. Convergence of the iterative trials to reach a criterion requires careful evaluation [114]. There are sever-... 

The linearisation method of Naphtali and Sandholm has been used by Fredenslund et al. (1977) for the multicomponent distillation program given in their book. Included in then-book, and coupled to the distillation program, are methods for estimation of the liquid-vapour relationships (activity coefficients) using the UNIFAC method (see Chapter 8, Section 16.3). This makes the program particularly useful for the design of columns for... 

The support and cooperation of the Office of Saline Water, U. S. Department of the Interior, in a solar distillation program, a portion of which is the subject of this paper, are gratefully acknowledged. 

The methods used here to give the phase equilibria are reviewed, and the Azeotropic Distillation Program ADP/ADPLLE is described. Application of the program to calculate an azeotropic distillation problem is shown and discussed, and a sample computer output is given and is briefly discussed. Finally, calculated azeotropic distillation results are compared for dehydrating aqueous ethanol for the three entrainers, n-pentane, benzene, and diethyl ether. 

This ternary azeotropic distillation program uses a special system of utility subroutines with programmed initialization. Eight main controls, KNTRL, are used with various options on each. Four parameter options are built into the program, but the values are changed by the user by using PRMTR cards. Twenty-one DATA cards allow the user to give the pertinent conditions and specifications for the separation to be calculated. 

Table I. Ternary Azeotropic Distillation Program (ADP/ADPLLE)...

To examine the performance of this recipe, it is helpful to use a batch distillation program is a process simulator, such as BATCHFRAC by Aspen Technology, Inc. (Boston et al., 1981). Then, a... 

In some ways, the most difficult part of writing a multicomponent distillation program has not been discussed. This is the development of a physical properties package that will accurately predict equilibrium and enthalpy relationships IBarnicki. 2002 Carlson. 1996 Sadeq eta1 1997 Schad. 19981. Sadaq et al. (1997) compared three process simulators and found that relatively small differences in the parameters and in the VLE correlation can cause major errors in the results. Fortunately, a considerable amount of research has been done (see Table 2-2 and Fredenslund etal.. 1977 and Walas. 19851 to develop accurate physical property correlations. Very detailed physical properties packages can be purchased commercially and are included in the commercial process simulators. 

Most distillation and equilibrium parts of process-design computer programs (e.g.. Aspen, ChemCad, ProMax) report A, values for each species in the VLE data for mixtures, and some distillation programs report a. It must be clear from their definitions that they are made up from values of the y, and Xi. The computer programs mostly first compute the y and Xi, by the methods shown in the rest of this chapter and the next, and then compute and report the A, and a values for the convenience of users who prefer that formulation the, x, and y are the basic values. The common hand-calculation methods of estimating VLE are presented in terms of the A values in Section 8.9. 

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