Fractionator minimum reflux

Underwood minimum reflux constant XjF = Mol fraction of component i in the feed XjD = Mol fraction of component i in the distillate q = Thermal condition of the feed Bubble point liquid q =1.0 Dew point vapor q =0 General feed q = (Ls - Lr)/F... 

Gilliland" tells how his famous correlation was developed for relating actual and minimum reflux to actual and minimum theoretical stages for a fractionating column. Numerous plate-to-plate calculations were made and the results plotted using his well-known correlating parameters. The best curve was then drawn through points. 

Figure 8-23. Fractionation of binary mixture at minimum reflux condition.

R = piseudo minimum reflux 2 xpH = sum of all mol fractions heavier than heavy key in feed... 

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

Rg = sidestream component of minimum reflux S = flowrate of sidestream, mol/h Sk = flowrate of sidestream k, mol/h V = vapor flowrate, mol/h X = mole fraction of component i in liquid y = mole fraction of component i in vapor z F = mole fraction of component i in feed Zi Fj = mole fraction of component i in feed j z s = mole fraction of component i in sidestream Zj sk = mole fraction of component i in sidestream k a = relative volatility 0 = underwood parameter... 

Underwood AJV (1946) Fractional Distillation of Multicomponent Mixtures - Calculation of Minimum Reflux Ratio, 7 Inst Petrol, 32 614. 

A liquid containing four components, A, B, C and D, with 0.3 mole fraction each of A, B and C, is to be continuously fractionated to give a top product of 0.9 mole fraction A and 0.1 mole fraction B. The bottoms are to contain not more than 0.5 mole fraction A. Estimate the minimum reflux ratio required for this separation, if the relative volatility of A to B is 2.0. 

UNDERWOOD, A. J. V. J. Inst. Petroleum 32 (1946) 614. Fractional distillation of multi-component mixtures — calculation of minimum reflux ratio. 

The number of values of 8 and the number of Eqs. (13.121) is equal to 1 plus the number of components with relative volatilities between those of the light and heavy keys. When there is no distributed component, Eq. (13.121) may be used in terms of mol fractions and only a single form is needed for finding the minimum reflux,... 

Two important points need to be mentioned. First, as the mole fraction, y, approaches the equilibrium mole fraction, y g, the integrand approaches zero. Thus the point of minimum entropy production coincides with that of minimum reflux. Second, y > y guarantees that the argument of the logarithm cannot be less than unity, which means that Sp > 0. Finally Equation 24 is only applicable to cases wherein the diffusion processes represent the dominant mechanism for entropy production. 

Minimum reflux. The minimum reflux in a simple fractionator is calculated by drawing a straight line between the product composition on... 

The procedure for finding minimum raflux in each section of a complex fractionator is similar. First, the point of intersection of the component balance line with the 45° diagonal is found by using Eq. (2.38). Second, the point of intersection of the q-line for the feed or side product with the equilibrium curve is graphically determined. A straight line is then drawn between the two points. This line is the minimum reflux component balance line. The minimum reflux is found from the intercept of this line on they axis, using Eq. (2.40). 

As discussed in the problem statement, it is possible that the P recovered from the distillation could be sold, thus it is desirable to recover P in a state of reasonably high purity (say, 0.98 mole fraction). Therefore, drawing a line joining 0,98 distillate composition and the vapor composition in equilibrium with the feed in Fig. 5,5a produces ay intercept of 0.647, Therefore, minimum reflux ratio is, from Eq. (5.20)... 

Problem 16. Cost of Reboiler for Alkylation Unit Heat-Pump Fractionator if Fractionation Column Operation is Assumed to be at Minimum Reflux Ratiof... 

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. 

Short et al. [230] discuss minimum reflux for complex fractionators. 

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.)... 

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