Minimum reflux calculation

For shortcut design of a distillation column, the minimum reflux calculation should be made first. 

Xit = mol fraction liquid at intersection of operating lines at minimum reflux. (Calculated or from graph.)... 

Levy SG, Van Dongen DB and Doherty MF (1985) Design and Synthesis of Homogeneous Azeotropic Distillation 2. Minimum Reflux Calculations for Non-ideal and Azeotropic Columns, Ind Eng Chem Fund, 24 463. 

Occasionally the minimum reflux calculated by this method comes out a negative number. That, of course, is a signal that some other method should be tried, or it may mean that the separation between feed and overhead can be accomplished in less than one equilibrium stage. 

Produce a shortlist of candidates by ranking the alternatives following the total vapor rate. A minimum reflux calculation design based on Fenske-Underwood-Gilliland method should be sufficiently accurate. 

Other shortcut methods. Other methods are also available for minimum reflux calculations. Van Winkle (28) surveyed them and recommended Underwood s and two others ... 

Oh = relative volatility of components heavier than heavy key at feed tray temperature ol = relative volatility of components lighter than light key at feed tray temperatures Xj, = mol fraction liquid at intersection of operating lines at minimum reflux. (Calculated or from graph.)... 

To find an explanation Table 7.30 present comparative results regarding the sequences 9 and 12. It can be observed that the sequence 9 handles the most difficult separation D/E as the last, while sequence 12 treated it as the first. We would expect the first solution to be more advantageous. The results shows practically the same duty, 16.15 versus 16.76, although we would expect much more energetic consumption when the four components ABCD are taken as overhead distillate instead just D. Actually, the presence of the other components has as effect a considerable reduction of the minimum reflux, 3 Instead 12 Thus, minimum reflux calculation based only on key components would give false predictions. This result reinforces the statement made before that the minimum vapour flow in sequencing should be determined by accurate methods. 

Levy, S.G., D.B.Van Dongen, and MJ. Doherty, Design and synthesis of homo geneous azeotropic distillations. 2. Minimum reflux calculations for nonideal and azeotropic columns. Industrial Engineering Chemistry, Fundamentals, 1985, 24(4) 463 474. 

Levy, S.G. and M.F. Doherty, Design and synthesis of homogeneous azeotropic distillations. 4. Minimum reflux calculations for multiple feed columns. Industrial and Engineering Chemistry Fundamentals, 2002, 25(2) 269 279. 

Abbas, R., S.T. Holland, and I.J. Halvorsen, Novel minimum reflux calculation using eigenvector maps, in Distillation and Absorption 2010, G.K. de Haan, editor. 2010, Eindhoven, The Netherlands Eindhoven University of Technology. 

Interestingly, since is always negative in the side rectifier, the feed quali is always pseudo superheated. Conversely, the feed to the thermally coupled junction in the side stripp is pseudo subcooled because is always positive. Everything in the pseudo column has been specified and we can proceed with the minimum reflux calculations in the same manner as shown previously for mple columns. For the same arbitrarily chosen product specifications as Hgure 6.34, the minimum reflux of the thermally coupled CSs can be represented using the TTs technique, as depicted in Figure 6.36. 

Barbosa, D. and M.F. Doherty, Design and minimum reflux calculations for single feed multicomponent reactive distillation columns. Chemical Engineering Science, 1988, 43 1523 1537. 

Kiva, V. N., Timofeev, V. S., Vizhesinghe, A. D. M. C., Chyue Vu Tam (1983). The Separation of Binary Azeotropic Mixtures with a Low-Boiling Entrainer. In The Theses of 5th Distillation Conference in USSR. Severodonezk (Rus.). Knapp, J. R, Doherty, M. F. (1994). Minimum Entrainer Flows for Extractive Distillation A Bifurcation Theoretic Approach. AlChE J., 40,243-68. Koehler, J., Aguirre, R, Blass, E. (1991). Minimum Reflux Calculations for Nonideal Mixtures Using the Reversible Distillation Model. Chem. Eng. Set, 46,3007-21. 

Conditions of Section Trajectories Joining and Methods of Minimum Reflux Calculating... 

Koehler, J., Aguirre, R, Blass, E. (1991). Minimum Reflux Calculations for Nonideal Mixtures Using the Reversible Distillation Model. Chem. Eng. Set, 46,3007-21. 

Levy, S. G., Van Dongen, D. B., Doherty, M. F. (1985). Design and Synthesis of Homogenous Azeotropic Distillation. 2. Minimum reflux Calculations for Nonideal and Azeotropic Columns. Ind. Eng. Chem. Fundam., 24, 463-74. 

Petlyuk, F. B., Danilov, R. Yu. (1999). Feasible Separation Variants and Minimum Reflux Calculations. Theor. Found. Chem. Eng., 33,571-83. 

Convert the atmospheric bubble point of the product liquid flowing to the stripper to this partial pressure. There will seldom be any discrepancy between this temperature and the value estimated from the minimum reflux calculations. 

Heat Effect Due to Minimum Reflux. Calculations can be made to determine the minimum reflux ratio required to affect the desired separation for a given thermal condition of the feed. This heat effect takes into account the heat removed by the condenser, QcM condensing the distillate plus the minimum amount of reflux required by the process and is expressed as... 

Minimum Reflux Double click on the minimum reflux button and perform minimum reflux calculation is checked, LK is benzene, HK is toluene, reflux ratio is 1.1. 

Products The molar flow rate of the product stream S2 is set to 4 kgmol/h. One needs to enable the minimum reflux calculations in the shortcut column to see the minimum number of tray and feed location. Once this option is selected then running the simulation, generates a text report. The required results are under the Summary of Underwood Calculations section in the report as shown in Figure 6.11. The stream property table is shown in Figure 6.12 where exit streams molar flow rate and conditions are obtained. 

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