Distillation
columns are made up of several components, each of which is used
either to tranfer heat energy or enhance materail transfer. A
typical distillation contains several major components:
a
vertical shell where the separation
of liquid components is carried out
column
internals such as trays/plates and/or packings
which are used to enhance component separations
a
reboiler to provide the necessary
vaporisation for the distillation process
a
condenser to cool and condense the
vapour leaving the top of the column
a
reflux drum to hold the condensed
vapour from the top of the column so that liquid (reflux)
can be recycled back to the column
The
vertical shell houses the column internals and together with the
condenser and reboiler, constitute a distillation column. A schematic
of a typical distillation unit with a single feed and two product
streams is shown below:
Basic
Operation and Terminology
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
vapour 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 prod
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
vapour 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.
