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The liquid
mixture that is to be processed is known as the
feed and this is introduced usually somewhere near the middle of
the column to a tray known as the
feed tray. The feed tray divides the column
into a top (enriching or
rectification) section and a bottom (stripping)
section. The feed flows down the column where it is collected at the
bottom in the reboiler.
Heat is
supplied to the reboiler to generate vapour. The source of heat input
can be any suitable fluid, although in most chemical plants this is
normally steam. In refineries, the heating source may be the output
streams of other columns. The vapour raised in the reboiler is
re-introduced into the unit at the bottom of the column. The liquid
removed from the reboiler is known as the bottoms
product or simply, bottoms.
The
Basic Operation and Terminologyvapour moves up the column, and as it exits the top of the unit, it is
cooled by a condenser. The condensed liquid
is stored in a holding vessel known as the reflux
drum. Some of this liquid is recycled back to the top of the
column and this is called the reflux. The
condensed liquid that is removed from the system is known as the
distillate or top
product.
Thus,
there are internal flows of vapour and
liquid within the column as well as external flows
of feeds and product streams, into and out of the column.
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