Changeover to triethylene glycol on a gas-drying unit at the West Tarko-Sale gas deposit

Abstract

Diethylene glycol (DEG) is presently used in the gas industry on domestic units for the preparation of gas by the absorption method. The use of DEG is due mainly to its availability from Russian manufacturers and its lower cost compared to triethylene glycol (TEG). At the same time, TEG is used on gas-lift units by the petroleum industry to dry casing-head gas, mainly due to the more exacting standards for the initial parameters of this drying operation. The leading foreign companies also used teeming almost exclusively for gas-drying. Among the principal advantages of teeming compared to DEG is the more thorough drying achieved with gases, the smaller loss of the drying agent with the dried gas, and better regenerability. For example, at a mass concentration of 99.5% "lEG, the dew point depression of the gas is roughly 7 ~ more than for DEG at the same concentration. The amount of TEG lost in droplet form with the dried gas is 2-3 times lower than the analogous loss of DEG. Here, it must be considered that such losses account for 70-75% of the total loss of glycol on the process unit. Triethylene glycol also begins to break down at a higher temperature (206~ than DEG (164~ making it possible to regenerate a TEG solution without the use of a vacuum up to concentrations of 98.7% (97% for DEG).The feasibility of using TEG was shown by an analysis of the cost-efficiency of changing over to operation with TEG on large gas-preparation units at West Siberian deposits, as well as by test calculations performed for equipment designed for operation on DEG. Triethylene glycol meeting the specifications of the standard TU 6-01-5-88 is currently produced at four plants in the Russian Federation (in Kazan, Dzerzhinsk, Nizhnekamsk, and Salavat).The above considerations were the basis for recommendations made to change over to TEG on gas-drying units at the West Tarko-Sale deposit. Figure 1 presents the flow diagram of the gas-processing unit (GPU). Gas from the wells enters the separator S-1 for separation of the liquid in drop form -water and condensed hydrocarbons. The separated gas is then sent to absorber A-1 for drying. The dried gas, now in commercial condition with respect to dew point, subsequently enters a commercial measurement unit before being sent through the main for distribution. Regenerated triethylene glycol (RTEG) fed into the top part of the absorber absorbs water vapor from the gas. The resulting saturated solution is sent to degasifier D-l, where the aerating gas is separated from the glycol. The saturated triethylene glycol (STEG) then enters three-phase fractionating column C-1 to remove the hydrocarbon condensate. The main product subsequently proceeds in succession through a coal filter F-I, a f-me-cleaning filter F-2, and a magnetic treatment unit M-1. Filter F-1 uses activated carbon to remove heavy hydrocarbons and decomposition products from the STEG. Filter F-2 captures particles of mechanical impurities larger than 20/am. Permanent magnets in the M-1 unit convert hard salts present in the STEG to...