Equilibrium Ratios of Water in the Water-Triethylene Glycol-Natural Gas System

Abstract

Abstract Equilibrium data which should be useful in the design and/or evaluation of glycol dehydration units were prepared from an analysis of various published data and the correlation of these data by the use of the thermodynamic equilibrium ratio. The equilibrium ratios of water are used to solve the glycol absorber problem; such solutions are necessary to define the number of trays and the glycol circulation rate needed to meet drying requirements. Activity coefficients were obtained which relate directly to the equilibrium ratios of water in the water-TEG-natural gas system. These activity coefficients have been used to calculate the equilibrium dew points for aqueous TEG concentrations of 60 to 99.9 weight per cent for the temperature range of 40 to 120F. They also provide a means of calculating equilibrium ratios for water in the water-TEG-natural gas system; this applies to any desired TEG concentration and to the temperature range from 40 to 120F. Introduction During the last several years, the drying of natural gas with aqueous triethylene-glycol (TEG) solutions has become very prominent. Most users of TEG as a drying agent have been satisfied with the performance of TEG solutions at the conditions used; however, there always has been some discussion of the drying ability of TEG solutions at conditions not commonly encountered such as temperatures below 50 or 60F, but more particularly temperatures above 100F, and pressures above 1,000 psia. Today, when higher wellhead temperatures such as 120F are more commonly encountered many are skeptical of TEG's ability to dry sufficiently well to provide dew points around 32F, which is generally the maximum tolerable when attempting to dry a gas to contract specifications of 7 lb/MMscf. These views probably have evolved to some extent from the days when suppliers would not guarantee dewpoint depressions in excess of 65 to 75F. Also, the feelings about TEG drying may have arisen from the lack of information about the equilibrium relation of water in the drying operations.