Fractioning Column

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Fractioning columns are devices used heavily in distillation processes and primarily associated with chemical plants. Distillation is the method in which essential components of a mixture are separated or purified through boiling, evaporation, and condensing of the mixture. A fractioning column is essential to these processes. In this article you will learn about the operating principle of fractioning columns, industrial applications, and maintenance and repair processes.

Fractional distillation - Wikiwand
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Operating Principles

Fractioning columns separate various compounds from a base or crude chemical through a series of separation chambers. Manipulating the condensation of the different compounds to be extracted, fractioning columns utilize heat to separate out the desired components of the mixture at the bottom of the fractioning column. Initially, a crude or unprocessed mixture is placed at the bottom-most point of a fractioning column. The bottom of the column is then heated until it begins to boil and evaporate. Via principles of conduction and convection, temperature decreases as column height increases. As the temperature drops, the mixture separates and condenses, allowing for the separation into individual compounds by their condensing points. Upon condensing in the fractioning column, the compounds are pulled out.

What are the functions of the fractionating column? - Quora
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The mixture being separated by the column must have compounds with similar boiling points to each other for the separation column to operate properly. The construction of a distillation column is crucial for proper mixture separation. Inside a column, there are a series of plates stacked onto one another. At the bottom of the column, the mixture enters the column from a boiler where the liquid is heated to a vapor and separated by the plates of the column. As the separate compounds reach their respective condensation temperatures they stop at certain levels in the column. Any vapors that make it to the top are condensed and placed back in the column.

distillation column block diagram
Courtesy: SRS

Typically, in between the plates are small holes or bubble caps which slow down the rising vapors in the column and allow for them to condense should they be at their associated level in the column. All other vapors are allowed to continue onto the next level while the condensed vapors are collected at the level of the column they condensed at.

oil refinery tower distilling tower vs cracking tower
Courtesy: Bismarck State College National Energy Center

Industrial Applications

Fractioning columns play a major role in fractioning crude oil into the different chemicals crucial in many industries and is by far the largest industrial application it is used for. Crude oil is a mixture of a variety of different hydrocarbons from which fractioning columns are able to separate out the different oils and chemicals such as gasoline, petroleum, diesel, plane fuel, and naphtha. In terms of engineering, the fractioning and distillation of crude oil plays the largest role in fractioning column utilization.

fractional distillation crude oil
Courtesy: VectorStock

Other applications for fractioning columns include water purification and chemical plant distilleries for the separation of many organic compounds. Fractioning columns are also used heavily in the alcoholic beverage industry allowing for the distillation of drinks such as whiskey. Fractioning columns may also be used in the production of distilled vinegar and a variety of other chemicals at refineries.

Maintenance and Repair

Proper maintenance of fractioning columns are crucial in getting the proper output from the distillation process. The columns are crucial in determining the quality of the product being put out by a plant making maintenance and repair even more necessary.

Richmond Refinery, Fluid Catalytic Cracking Distillation Column. | Chemical  engineering, Chemical suppliers, Distillation
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Most fractioning columns are monitored as to prevent liquid entrainment. When the levels of a column hold more liquid than they should, they flood and cause an excess accumulation of the liquid. To prevent this, it is important to ensure the correct placement of each tray as vapor velocity may cause for the movement of some droplets to levels higher than they should be at or even the other way in a phenomenon called weeping.

Weeping in a Distillation Column | AIChE
Courtesy: AICHE

Similarly, corrosion is another major consideration when it comes to the maintenance of fractioning columns. Any corrosive by-products may interfere with the distillation process and must be monitored for in the columns and treated to prevent especially between levels.

Inspecting Distillation Towers Part 1: Turnarounds | AIChE
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Overheating of a column may lead to structural failure and must be monitored and maintained as well at the proper operating temperatures. Any excess heat may lead to structural failures leading to massive collapse and danger to anyone at the plant.