N.A. Darwish (Jordan), R.A. Al-Mehaideb, and A.M. Break (UAE)
natural gas dehydration, BTEX emission, mixed solvents, Modelling, simulation.
In typical natural gas dehydration processes (where a solvent is used to absorb humidity) there is a severe air and water pollution problem resulting from the absorption of some hydrocarbons and other volatile organic compounds (VOC's), besides water vapor. Among these hydrocarbons, aromatics, like benzene, toluene, ethyl benzene, and xylenes (BTEX) represent a major threat. A process for natural gas dehydration using a mixed binary solvent of diethylene glycol (DEG) and triethylene glycol (TEG) as the dehydrating agent is simulated using a steady state flowsheeting simulator (Aspen Plus). The flowsheet included all major units in a typical dehydration facility, that is: absorption column, flash unit, heat exchangers, regenerator, stripper, and reboiler. The base case operating conditions are taken to resemble field data from one of the existing TEG-dehydration units operating in the United Arab Emirates (UAE). Effects of the mixed solvent composition and circulation rate on BTEX emission, the water content (dew point) of dehumidified natural gas, solvents losses, and the required heat duty for the process have been explored using the simulator. To strike a balance among solvents losses, BTEX emissions, and heat requirements for the regeneration process, a mixed solvent of both DEG and TEG with a certain optimum composition could be reached. The thermodynamic model adopted in the study is Peng Robinson with Modified-Huron-Vidal second approximation mixing rules (PR-MHV2).
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