Column Design for Fractionation and Purification

November 24, 2014

A distant observer can spot a skinny fractionation tower long before the rest of a petroleum facility comes within sight. The tall vertical structures dominate their finite industrial skylines, impressing their premium grade shells against a blue sky. Fabricated from 410S steel and chrome-blended alloys, the columns resist brittle effects introduced by high temperature changes. The mediums present in these columns vary. There's a flow of natural gas in some, a steam vaporized cloud of crude oil in others. Each tower has to be able to withstand pressure and temperature changes. After all, these are the key techniques used in the separation of vaporized liquids, the hydrocarbons trapped within oil and natural gas.

Fractionation columns are critical parts of the petroleum industry, but they're still subject to the laws that govern chemical reactions. Also, and this may aid the novice in understanding the process, fractionation can be regarded as a precise form of distillation, a process that is present in everything from alcohol production to air conditioning. The distillation technique uses the towers to separate gaseous petroleum products by evaporating and condensing oil and gas. The physical attributes of each tower can even identify the purpose of each tower if the engineer is sufficiently well trained and has sharp eyesight. Some fractionation towers are narrow on top and wide on the bottom, appearing like a two-tiered cylinder or a primitive metal bottle. Others reverse this design, looking, you guessed it, like an upside-down bottle. The reason behind these design changes relates to the precise function of the column. The distribution and separation characteristics of a particular gas are defined by pressure variations, by the diameter at a set height on the tower, and by the temperature at that point. It's really a case of basic chemistry and physics conducted on a massive scale.

To illustrate the above points, consider the inner workings of different fractionation towers. The different gases within natural gas are formed from heavy or light molecules where hydrogen and carbon have bonded. Begin the distillation process, and the heavy molecules will naturally split from the lighter molecules. The same dynamic applies to steam-vaporized crude oil. An intricate system of trays and beds within the hollow shell of the column are positioned at precisely calculated heights that match the boiling point or condensation point of a particular component of the input stream.

High-grade steel and multi-tiered designs define the typical fractionation column. Heat-treated to eliminate micro-flaws, the metal can resist high temperatures, 800F or more, without hardening or cracking. The chamber within the fractionation column purifies oil and natural gas, distilling core components that have narrow boiling points. To this end, the control and distribution of gas in these vertical columns has become an exacting science.

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1865 Frankston Flinders Road,
Hastings, VIC 3915

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