Figure 2.19 summarizes the system and nomenclature to be considered. Liquid and vapor rates in the section above the feed ("rectifying" section) are called Lr and VR in mols/minute. Liquid and vapor rates below the feed in the stripping section are called Ls and Vs. These are assumed to be constant
Simple distillation column
Simple distillation column on all trays throughout each individual section. This constancy of molar flow rates is what we call "equimolal overflow." Primarily it assumes that the molar heats of vaporization of the components are about equal. In many systems this is a pretty good assumption.
A total condenser is used to produce liquid reflux and distillate product. The reboiler is a "partial reboiler" (vapor is boiled off a liquid pool). The composition of this liquid pool is the same as the bottom product composition. Thermosyphon, kettle, internal, and forced-circulation reboilers are all usually partial reboilers.
The parameter q will be used to describe the thermal condition of the feed. The ratio of the internal reflux flow rate LR to the distillate flow rate D is called the reflux ratio R.
Reflux ratio is widely used as an indication of the energy consumption.
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