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A distillation unit is a set of machinery that is used to separate two or more mixed liquids by heating the mixture until each component reaches its boiling point. As each part of the mixture boils — turns to vapor — it can be segregated. A distillation unit consists of a boiler, a vertical space or column where the separation takes place, a condenser to turn the vapors back to liquid and storage vessels to store the separated liquids.
The process begins with a boiler heating the feed stock of mixed liquids. The boiler can be fueled by a variety of products, including fuel oil, natural gas, and coal. Some boilers are fueled by a byproduct of the mixed liquid that has already come through the process. Industrial distillation processes where there is steam available can also use steam to heat the feed stock.
As the component of the feed stock that has the lowest boiling point reaches that boiling point, it turns to vapor and rises in the column. The vapors are caught and piped toward a condenser. The condenser absorbs heat from the segregated vapor, turning it back into a liquid. The segregated liquid, or distillate, is transferred from the condenser to a storage vessel. To improve the purity of the distillate, the process might be repeated to further remove elements not identical to the distillate.
A fractional distillation unit separates mixed liquids where the boiling points are similar. A fractional distillation column has a series of levels using trays or packing where the feed stock is vaporized, condensed and vaporized again. The distillation process is repeated multiple times until the different components have been thoroughly separated. An example of fractional distillation is the separation of various grades of gasoline and oil from a crude oil stock.
A simple distillation unit is used when the feed stock is a single liquid with solid contaminants, such as the process of distilling plain water from seawater. When the seawater boils, the water molecules turn to vapor, and the salt is released from suspension in the water. The pure vaporized water, in the form of steam, is cooled to turn it back into liquid form.
A steam distillation unit forces steam up through a quantity of feed stock to vaporize liquid from within the feed stock. Steam distillation is suitable for stable materials that do not dissolve easily in water. The liquid vaporizes out of the mixture, often plant material, and mixes with the steam but separates readily after it is condensed and the steam turns back to water. Steam distillation is used to produce a large variety of essential plant oils, such as clary sage, peppermint and lemongrass.
A vacuum distillation unit places the feed stock under vacuum pressure by removing air from the distillation column to reduce the boiling point of the feed stock. This process is used in cases where the high boiling point might damage the quality of the feed stock or where the original boiling point is so high that the process becomes difficult or cost prohibitive. Vacuum distillation also can improve the efficiency of a distillation process by allowing it to operate with less heat.