Gilliland correlation, trays

Gilliland correlation, trays, 397 Molokhanov equation, 397 Globulation, 351 Glossary... 

The Gilliland correlation appears to be conservative for feeds with low values of q (the thermal condition of the feed), and can be in error when there is a large difference in tray requirements above and below the feed. The principal value of the correlation appears to be for preliminary exploration of design variables which can be refined by computer calculations. Although it is often used for final design, that should be done with caution. Other possibly superior but more difficult to use correlations have been proposed and are described in standard textbooks for example, Hines and Maddox (1985). 

The flnal compositions and relative volatilities are then used to calculate the minimum reflux, R, using the Underwood method (Equations 12.29 and 12.30). The calculated values of and are next applied in the Gilliland correlation to determine a suitable combination of trays and reflux, N and R, consistent with economic and design considerations. The column can then be approximately sized based on the internal liquid and vapor flows as calculated from the reflux ratio and product rates. 

The Gilliland correlation is used to determine the ratio corresponding to r. This determines the number of trays N, which is held constant in subsequent time steps in which the reflux ratio becomes the calculated variable. 

A mixture of xylenes plus other aromatics is separated in a large fractionating column operating at atmospheric pressure. Calculate the minimum number of plates and the minimum reflux ratio for the conditions in Table 19.4. Use the Gilliland correlation to estimate the reflux ratio that will permit the separation to occur in 100 ideal stages. The relative volatilities are calculated for 18 psia and 150°C, the estimated conditions near the feed tray. 

Common operating practice usually involves setting the reflux at about 1.25Hn,in. Once the values of Nmin and are known, the Gilliland correlation between reflux ratio and number of theoretical stages allows the reflux ratio to be worked out for a column with a known number of trays (N) ... 

The last step in the Hdist program is the calculation of actual trays with a given actual reflux input. Gilliland s [10] correlation of stages and reflux does this step. Gilliland s equation follows ... 

The maximum deviation using Gilliland s correlation in terms of tray number is within the7% range [39]. 

Compute (a) The minimtim reflux ratio and (h) the minimum number of trays. At a reflux ratio 2.0, estimate (c) the product analyses and (d) the number of theoretical trays by the correlations of Gilliland (17], Erbar and Maddox [12], Brown and Martin [5], and Strangio and Trcybal [59]. 

From Gilliland s correlation and an appropriate efficiency, estimate the actual tray requirements. 

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