Distillation columns, integral in chemical engineering and particularly vital in the oil and gas industry, are sophisticated pieces of equipment designed for separating liquid mixtures into their individual components.
These columns, also known as fractionating or fractional columns, leverage the differing volatilities of substances to achieve separation.
The working principle of a distillation column is rooted in the process of heating a mixture to a temperature between the boiling points of its components.
Take a water and ethanol mix, for instance. Water boils at 212ºF and ethanol at about 176ºF.
By heating the mixture to around 195ºF, ethanol vaporizes while water remains liquid. This principle forms the foundation of distillation.
In a fractionating distillation column, this separation is made more efficient.
The column consists of a series of stacked plates, and the mixture is fed into the column at specific points.
As the liquid flows over these plates, vapor bubbles up through holes in the plates, interacting with the liquid multiple times – a crucial aspect of the distillation process.
This interaction facilitates the exchange of energy, allowing molecules of higher boiling substances to condense and lower boiling substances to vaporize.
At the column’s base, there’s a substantial volume of liquid, mostly comprising the higher boiling point component.
Part of this liquid is drawn off, heated in a reboiler, and returned to the column, a process known as ‘boil up.’
Meanwhile, vapor escaping the column’s top is condensed back into liquid in the condenser. A portion of this liquid is reintroduced into the column as reflux, and the rest is collected as the top product or distillate.
The distillation column functions akin to a heat exchanger.
It cools the rising vapors, causing some to condense and fall back down the column.
The temperature decreases progressively higher up the column, allowing different hydrocarbon groups to condense at various levels – the heaviest at the bottom and the lightest at the top. The outcome is a refined product, restored to its original state.
