Chapter 6 - Dehydration of Natural Gas

Abstract

This chapter reviews several methods used for dehydrating natural gas. Dehydration is the process by which water is removed from natural gas. This is a common method used for preventing hydrate formation. There are other reasons for dehydrating natural gas. Removing water vapor reduces the risk of corrosion in transmission lines. Furthermore, dehydration improves the efficiency of pipelines by reducing the amount of liquid accumulating in the lines—or even eliminates it completely. There are several methods of dehydrating natural gas. The most common of these are: glycol dehydration (liquid desiccant), molecular sieves (solid adsorbent), and refrigeration. The most common method for dehydration in the natural gas industry is the use of a liquid desiccant contactor-regeneration process. In this process, the wet gas is contacted with a lean solvent. The lean solvent, producing a rich solvent stream and a dry gas, absorbs the water in the gas. Unlike glycol dehydration, which is an absorption process, dehydration with molecular sieves is an adsorption process. Water in the gas adheres to the solid phase (the solid being the mole sieve), and thus is removed from the natural gas. Molecular sieves are usually used when very dry gas is required. The usual purpose of a refrigeration plant is to remove heavy hydrocarbons from a natural gas stream—to make hydrocarbon dewpoint specification—but this process also removes water.