Thursday, February 7, 2013

Separating water from natural gas

One of the substances that have to be removed from the natural gas stream is water. Although most of the free-standing water included in the gas is removed at the wellhead during extraction, water vapor still exists in some form inside the gas stream. The removal of water vapor is more complicated and involves either absorption, where water is taken out by an absorbent, or adsorption, where water is condensed and collected.

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There are two major dehydration processes that are used in natural gas processing: glycol dehydration and solid-desiccant dehydration.

Glycol dehydration makes use of the liquid desiccant dehydrators, the primary ingredient of which is glycol, which is strongly attracted to water. When glycol makes contact with the gas, it absorbs water out of the gas. As it does so, it becomes heavier than the gas and sinks, leaving the remaining gas free of water. It is an efficient process because the glycol solution has a higher boiling point than water and can just be heated to evaporate the water. It can then be reused over and over.

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Solid-desiccant dehydration is a dehydration process that involves two adsorption towers that are filled with solid desiccants. As the wet natural gas passes through these towers from top to bottom, the water from these gasses are adsorbed by the desiccants, leaving only dry gas exiting at the bottom.

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These processes may sound complicated, but in fact, they are not. Most of these processes are discussed in major textbooks about natural gas processing, such as Boyun Guo and Dr. Ali Ghalambor’s Natural Gas Engineering Handbook.

Visit Dr. Ali Ghalambor’s Facebook page for more information on natural gas processes and technologies.

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