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Computing the diameter of a multicomponenant distillation column

Q: To design a multicomponenant distillation/fractionation column, I have studied the McCabe-Thiele method concerning the number of theoretical trays and feed trays and have looked to the Fenske equation for information on total reflux. I am still, however, facing difficulty in computing the required diameter and spacing between plates and trays. How do today's column designers compute the diameter of a multicomponenant distillation column?

A:

There are many parameters to consider when designing and sizing a tray. I suggest that you look into “Perry’s Chemical Engineering Handbook”, published by McGraw Hill, or “Distillation Design” by H.Z. Kister, published by McGraw Hill. A second book by Kister, “Distillation Operation” published by McGraw Hill, adds some useful information about tray design and installation. Tray sizing calculations usually require iterations to get to the final hydraulic and mechanical design and are now days done by computer. The Fair sieve tray entrainment and flood correlation (J.R. Fair, Petro/Chem Eng. 33 (10). P. 45. 1961) is quite useful and a similar correlation by Smith, Dresser and S. Ohlswager, Hydrocarbon Processing & Petroleum Refining( 40 (5) p, 183, 1963), would help you estimate the tray spacing for valve and sieve trays. The Smith correlation maybe less conservative than the Fair correlation.

I suggest that you contact tray vendors, some of whom may have preliminary sizing programs for their products that you can download from their website. Fractionation Research, Inc, FRI(SM) is a non-profit company that has programs for sizing tray and packed towers for use by its membership. Membership in FRI is open to all companies associated with distillation. FRI’s website, www.fri.org, gives information about FRI and a list of its member companies which include equipment suppliers and engineering companies that could help you with your design. 

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