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Invited Article: A COMPARISON OF NATURAL GAS DEHYDRATION METHODS

Pages 1-16

Ebrahiem E. Ebrahiem, Ibrahim A. Ashour, M.M. Nassar, Abdel Aziz A.

Abstract

The allowable moisture content of transmission natural gas ranges from 4 to 7 pounds per MMSCF (64–112 mg/m3). Water content may leads to solid hydrate formation, corrosion of pipelines & process plants particularly in the presence of CO2 or H2S, slugging and erosion problems in the flowlines. Also, it leads to specific volume increasing, heating value decreasing and freezing in cryogenic and refrigerated absorption plants. Dehydration of natural gas is necessary in order to obtain a water dew point below operating temperature to avoid water condensation and subsequent free water on the system and hydrates formation. A comparison between different widely industry methods of natural gas dehydration is made in order to choose a method for achieving the required water dew point of export gas suitable for North Africa gas project. These methods are adsorption (using solid desiccants), absorption (using liquid desiccants), dehydration (by CaCl2, expansion refrigeration and membrane permeation). The comparison is made according to their energy demand and suitability for use in North African countries. At the central process facilities of North Africa project, flowline arrival pressure and temperature may be in the range 54 to 60 bar and 25°C to 50°C (in winter to summer) respectively. In North Africa Gas Project at south Tunisia, the required water dew-point specification of export gas in field is -12°C at any pressure. As a comparison result it was found that it is recommended to use a TEG (Triethylene Glycol) dehydration method due to many advantages.

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