How A Column still Works

Column stills (also called continuous stills) are a more advanced type of still that have been around for about two centuries, with former Irish tax collector Aeneas Coffey inventing his Coffey still in the 1830s. While his invention was not the first continuous distillation system, it certainly had the greatest impact. Today, his designs have gone through countless iterations, producing everything from vodka to whiskey and everything in between. Compared with pot stills, column stills can continue to distill, have higher production efficiency, and produce higher alcohol concentrations, generally up to 95%. They are generally composed of two columns, one for the analyzer and one for the distillation. There are distillation plates or trays placed at certain intervals in the tower. After preheating, the original wine slurry is introduced into the top of the analyzer. After the alcohol is separated through the thin plates, it flows into the bottom of the rectifier.

There are distillation plates or trays placed at certain intervals in the tower still. The preheated material to be distilled (often called "feedstock" in industry jargon) is pumped onto a feed plate somewhere in the middle of the column. Fresh steam enters the tower from the bottom and travels upward, eventually coming into contact with the feedstock. The steam volatilizes (evaporates) components of the feedstock, such as flavor compounds and the all-important ethanol, which continue to move up the column in the form of vapor. The heavier components of the feed continue downward, leaving the still as the "bottom".

As the vapors move up through the tower, they come into contact with each successive plate. In a way, each tray behaves like a miniature cycle, with the more volatile compounds continuing upward while the heavier, less volatile compounds flow back and fall out of the column. To assist this reflux system, there is usually some form of precondenser at the top of the column through which the coolant flows. This helps establish a temperature gradient throughout the column, with the plates near the precondenser being slightly cooler than the plates below. Therefore, the more trays there are in a distillation column, the greater the temperature gradient and therefore more reflux, forcing more compounds to break off and be removed from the final spirit. The lightest compounds, such as the toxic methanol found in the overhead fraction of a pot still, are removed through the highest plate in the column, while the product or alcohol plate allows the distillate to flow out through a condenser several plates below.

In short, there are 5 steps in total.

1.Heating and Evaporation:

 The mixture is initially heated, causing the liquid components to evaporate. This occurs in the reboiler at the bottom of the column. 

2. Rising Process:

 Vapor ascends through the column, which may contain packing material like ceramic or metal to increase surface area, promoting more condensation and evaporation.

3.Condensation and Liquefaction:

 As vapor ascends, the top of the column is cooler, causing the vapor to condense back into liquid. These liquid components then descend along the height of the column. 

4. Separation: 

Due to the different rates of descent and ascent in the column, the liquid mixture gradually stratifies. Lighter components may condense at the top, while heavier ones liquefy at the bottom.

5.Product Collection: 

Ultimately, different purity components can be collected from various heights in the column. This is the process, for instance, in alcohol distillation to obtain high-purity ethanol.

This intricate process of heating, vaporizing, condensing, and separating enables the column still to effectively isolate and collect distinct components from the original mixture.