Numerical Simulation of an Industrial Absorber for Dehydration of Natural Gas Using Triethylene Glycol

Models of an absorber for dehydration of natural gas using triethylene glycol are presented. The models were developed by applying the law of conservation of mass and energy to predict the variation of water content of gas and the temperature of the gas and liquid with time along the packing height. The models were integrated numerically using the finite divided difference scheme and incorporated into the MATLAB code. The results obtained agreed reasonably well with industrial plant data obtained from an SPDC TEG unit in Niger-Delta, Nigeria. Model prediction showed a percentage deviation of 8.65% for gas water content and 3.41% and 9.18% for exit temperature of gas and liquid, respectively. 1. Introduction Natural gas needs to be dried before pipeline transport, because the water molecules present in the gas in both vapour and liquid state form hydrates which cause flow restrictions and pressure drops and lower the heating value of gas and corrode pipelines and other equipment. Other problems associated with the presence of water molecules are foaming, degradation, puking, corrosion, low pH, oxidation, thermal decomposition, inadequate absorber design for flow conditions, and salt contamination. Extensive literature is available on common gas dehydration systems including solid and liquid desiccant and refrigeration-based systems [1, 2]. There are several methods of dehydrating natural gas. The most common of these are liquid desiccant (glycol) dehydration and solid desiccant dehydration [3, 4]. Among these gas dehydration processes, absorption is the most common technique, where the water vapor in the gas stream becomes absorbed in a liquid solvent stream. Glycols are the most widely used absorption liquids as they approximate the properties that meet commercial application criteria [5, 6]. Several glycols have been found suitable for commercial application. Triethylene glycol (TEG) is by far the most common liquid desiccant used in natural gas dehydration as it exhibits most of the desirable criteria of commercial suitability [2]. The glycol absorber (contactor) contains trays that provide an adequate intimate contact area between the gas and the glycol. One other option to the tray TEG contactor is the use of structured packing. Structured packing was developed as an alternative to random packing to improve mass transfer control by use of a fixed orientation of the transfer surface. The combination of high gas capacity and reduced height of an equilibrium stage, compared with tray contactors, makes the application of structured packing desirable for