Figure 2.1 summarizes the nomenclature conventions that will be used throughout this book. At this point we will consider only a simple single-feed, two-product column separating a binary (two-component) mixture.
Feed rate is F mois per minute. Feed composition is zF mol fraction of the more volatile component. The column trays are numbered from the base upward, with feed introduced on the NF tray. The total number of trays in the column is Nt.
Products removed from the top and bottom of the column are called "distillate" or "top product," and "bottoms" or "bottom product," respectively, with flow overhead vapor overhead vapor
Nomenclature and conventions for typical distillation column
Nomenclature and conventions for typical distillation column rates D and B mois/min and compositions xD and xB mol fraction light component.
Heat is transferred into the process in the "reboiler" (typically a tube-and-shell heat exchanger) to vaporize some of the liquid from the base of the column. The heat-transfer rate is qR energy units/time (e.g., Btu/hr, pcu/hr, joules/minute, etc.).
The vapor coming from the top of the column is liquified in another tube-and-shell heat exchanger called a condenser. Heat is transferred out of the condenser at a rate qc, pcu/hr.
Liquid from the condenser drops into the reflux drum. Distillate product is removed from this drum. In addition, some liquid, called "reflux" (Lc, mols/min), is fed back to the top tray of the column. This liquid reflux and the vapor boilup in the base of the column are necessary to achieve the separation or "fractionation" of chemical components. The energy required to make the separation is approximately the heat added to the reboiler.
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