Document Type


Date of Award


Degree Name

Master of Science in Chemical Engineering - (M.S.)


Chemical Engineering and Chemistry

First Advisor

Ralph Ceccheti

Second Advisor

Edward Charles Roche, Jr.

Third Advisor

John E. McCormick


Multipass fractionating trays are vapor-liquid contacting devices with high liquid handling capabilities which can be economically used in large fractionating towers. However, process design engineers in the chemical and petroleum industries seem to have an aversion to specifying multipass trays for their tower designs. This thesis presents the case for using multipass trays as well as methods for their design.

Because multipass trays are not symmetrical, as one and two pass trays are, the liquid and vapor need not split equally between the three or four passes. Equations are developed which enable the vapor and liquid flowrate for each pass to be determined. A computer program is presented which is capable of either rating existing multipass trays or designing multipass trays for new services. Also, techniques for the optimum design of multipass trays are suggested.

The present energy shortage has provided strong incentive to build larger refineries, which means larger capacity fractionation towers are required. This thesis demonstrates how the use of multipass trays can reduce investment costs for these large towers.

The use of the tools presented in this thesis enable process engineers to design multipass trays without relying on the proprietary techniques and programs of others, not readily available to them. It is hoped that this will enable multipass trays to be specified whenever they are economically justified.



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