Zaccheaus M. Mokua
To: Mr. Paul Zajac
ENGLISH 202 C
2/25/2013
HOW A DISTILLATION COLUMN WORKS FOR A CONTINOUS CHEMICAL
PROCESSES
Much of the chemical processes performed in onsite drilling locations are centered on the
separation of components. Separation of components is achieved with the use of distillation
columns. These columns are large cylindrical shaped towers approximately .6 meters in diameter
and .6 meters in height as well. Distillation columns have complex interior that allows the
accomplishment of the distillation of the liquids via chemical characteristics such as temperature
and pressure. Separation of components is the key step in many refinery sites and is defined as
the process that the contents, usually liquid, inside the distillation column are separated based on
chemical characteristics such as volatilities. Physical aspects of the fluid such as the flow rates
and boiling points bear huge significance in operations.
Continuous Steady State characteristics operating via a distillation column
One process that the distillation column is largely used for in onsite refineries is the
continuous steady state process. A continuous process is a chemical progression based on the
principles of conservation of mass. Continuous processes run via a distillation column are
procedures that feed is supplied into the column and experiences constant separation while also
constantly exiting via a column’s bottom streams. Consequently, the conservation of mass under
a continuous steady state process is described as an in and out balance. This is derived from the
general conservation of mass equation that states that accumulation must equate amount in
subtracted by amount added while taking reactions in consideration as well. Steady state
indicates that the properties inside the column, namely temperature, pressure, volume, remain
constant and thus create a scenario where no reactions occur inside the column. Continuous
steady state process is the most practical operation per scale, which explains why chemical
engineering companies prefer it to other processes such as Batch and Semi-Batch processes.
In order to fully comprehend the distillation column and its procedures around a
continuous steady state operation, one must first be familiar with the column’s key components.
These components do not necessarily each bare similar importance and are not all addressed
equally.







Pre-Heater
Bottoms Liquid
Feed stream
Reboiler
Condenser
Sieve Trays
Reflux Drum
Pre-Heater:
A Pre-Heater is a mechanical device connected to the
feed stream that heats the liquid under pressure to a
temperature very close but below the liquid’s boiling point.
The liquid is then sent into the column at the set temperature.
The column is unique in that it operates under a set pressure.
The pressure of the column is lower than that of the preheater. Due to exposure to the new pressure, the liquid
reaches its boiling point.
Bottoms Liquid:
The evaporation of the liquid is used as a purification
method as well as separation. The heavy components of the
mixture flow down the column and exit as bottoms fluid.
This bottoms liquid is then maneuvered into two routes. The
first route is a bottoms product which exits the process while
the other is to the Reboiler. The Reboiler is a heat exchanger
that also utilizes pressure to heat its components. The
Reboiler vaporizes the contents from the bottoms liquid and
pumps them back to the column as vapor.
Condenser:
The condenser is located at the summit of the tower.
The condenser receives vapor from the tower. It then
condenses this vapor back to liquid and pumps it into the
reflux drum or the rest of the plant as overhead produce. The
reflux drum simply infuses the liquid back into the
distillation column. This infused liquid is known as external
reflux. External reflux is crucial as it is used to increase
component purity inside the column.
1. A Diagram showing the
distillation column and how it
facilitates in a continuous
process flow operation
Sieve Trays:
The sieve trays in the column are crucial to operations. The sieve trays are stacks of metal
sheets fitted with gaps in between them throughout the column, vertically. These trays are
essential in the distillation process. The trays are formulated such that they can hold water on
each side as depicted by the diagram above and hence create streams that travel down the
column. Meanwhile, the gaps in between the trays allow vapor from the bottom to travel all the
way up. Consequently, contact between the vaporized product with lighter components and water
product with heavier components is present. Thus, the contact leads to both vaporization and
condensation. Overall, more vaporization occurs which leads to an increase in the desired
overhead product from the distillation column.
1. http://en.wikipedia.org/wiki/File:Continuous_Binary_Fractional_Distillation.PNG
The distillation column is separated into sections
named as a result of the processes described previously.
The middle section that receives the original stream is
noted as the flash zone, while the bottom section that
bares the Bottoms liquid is noted as the stripping zone.
This is because this is the area where the reflux from the
reheater strips the bottoms liquid of the lighter, desired
components, causing them to evaporate and aid in
distillation as well as become part of the overhead
product.
Conclusion:
The continuous and steady state process flow
operation is achieved in large chemical plants primarily
by use of a distillation column. Distillation columns are
designed to achieve the separation of components to
produce a desired product via utilizing pressures,
temperature and other physical chemical components of a
liquid. The column operates via its own internal
components, mainly the sieve trays, but also through the
external connections of the pre-heater, condenser,
reboiler, and reflux drums.
2. A more detailed interior,
detailing the trays and different
components of the column
2. http://en.wikipedia.org/wiki/File:Tray_Distillation_Tower.PNG