Process simulation of triethylene glycol based dehydration processes
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Natural gas contains impurities when produced from a reservoir among these impurities is water. In order to meet downstream transport-, process- and appliance specifications the natural gas need to be dehydrated. One of the most used techniques for removing water from natural gas is absorption dehydration using tri ethylene glycol (TEG) as the absorbent. In this report the natural gas processing is reviewed, with emphasis on TEG- dehydration. The collective components constituting a TEG- dehydration unit is thoroughly described together with giving an insight into the design methods used for designing a TEG- dehydration process. During the course of this work the simulation software Hysys (v.8.6) and Pro II (v.9.3) were used. In Hysys the Glycol Package (GP), Peng- Robinson (PR) and Cubic-Plus-Association (CPA) models were tested, in Pro II the Glycol Package was tested. The CPA model was linked to Hysys using the NeqSim software. Statoil provided field data from the Åsgard B dehydration unit. The field data was used as reference material for the results from the simulation models. The field data originates from three different tests: the June 2012- test, the 1st May 2014- test (log 1) and the 2nd May 2014- test (log 2). Experimental data was also gathered for comparison. The Hysys- CPA model was found to most accurately predict the real life dehydration unit at Åsgard B. The Hysys- CPA model provided results that where in correlation with the Pro II model, with the exception of Pro II calculating a low reboiler duty, a higher TEG loss and a slightly too high lean TEG purity. The Hysys- PR calculated a high water content in the dry gas, accompanied by a high water dew point temperature. The Hysys- GP calculated a low water content in the wet gas and an abnormal influence of water on the solubility of LHC and CO2 in TEG. Hence the Hysys- PR and -GP models, compared to Hysys- CPA and Pro II, are regarded to make the least accurate prediction of the real life dehydration unit at Åsgard B.