(207d) Tray Capacity Limitations At Low Surface Tension

Tray vapor capacity correlations do not include a surface tension physical property parameter.  Low liquid surface tensions on a distillation tray can lead to tiny droplet sizes, high liquid entrainment and limited vapor capacity.  Several authors have examined surface tension in the past but today's leading vapor capacity correlations have omitted this important physical property parameter.  This paper will examine very low surface tension data as well as a wide range of surface tension capacity data and then present a new tray vapor capacity correlation that uses surface tension as one of the primary correlating parameters.  The intent of this paper is to show that tray designs of very high pressure trayed distillation towers, such as demethanizers and deethanizers, can be made without the need for "system factors" with this new correlation.  It is the author's opinion that the system factor should be used strictly for those tray applications that are limited in capacity due to foaming and not be used as a "fudge factor" to account for capacity correlation deficiencies.