Determination of Dissolved BTEX in Glycol Dehydrators by Developing an In-House Technique

Tri-Ethylene Glycol (TEG) is the most widely used solvents for natural gas dehydration process in the Oil & Gas industry. However, TEG also has a capacity to absorb other species such as benzene, toluene, ethylbenzene, and xylenes (BTEX) that may be present in the processed gas at the dehydrator contactor conditions and then desorbed at regeneration conditions giving rise to atmosphere as off-gas in atmosphere regeneration system. BTEX and other volatile compounds and light components are released in the regeneration process together with water vapor as Off-gas. In an open regeneration system, the off-gas stream is vented to atmosphere where it becomes a source of emission of various constituents including BTEX. In this paper we will elaborate the study which was conducted to establish test method to quantify BTEX at one of the gas gathering facilities handling sweet associated gas. At initial stage, there was no a well-known methodology to enable determination of BTEX from the Rich and Lean TEG. Two novel test methods were developed to find the proper and accurate quantification technique to determine BTEX concentration in Rich and Lean Glycol samples using Gas Chromatography Mass spectroscopy (GC-EA) and unique sample extraction techniques, a) by using Purge and Trap technique for Mixed diluted sample with aid of methanol 1:1 ratio. B) by Direct injection after Liquid/Liquid extraction with ultra-pure n-Hexane solvent. Both techniques were applied using Gas Chromatography Mass Spectroscopy technique using DB-5MS capillary column (30 m in length, 0.32mm inner Diameter and 0.25 µm stationary phase film thickness). The obtained results of Toluene, Ethyl-Benzene and Xylene were matched by both sample injection techniques; however, Benzene recovered concentration was 25 % lower at the direct injection mode with liquid/liquid extraction, which is due to its high volatility and low boiling point. The data has been derived through comprehensive study for the BTEX concentration inlet and Outlet of the feed gas stream of the TEG Absorber and was matched with the mass balance and flow assurance analysis. The data analysis shows high values of emitted BTEX to atmosphere by 20-35% more than the accepted limits for all components, therefore a modification has been conducted to reconnect the off-gas with the production stream which will enhance the recovery of the gas and eliminate release of BTEX to atmosphere.