Natural gas sweetening using low temperature distillation: simulation and configuration

Abstract

ABSTRACTHypothesis: Separation of CO2 from a stream of natural gas using low-temperature distillation process is complicated not only because of the existence of ethane (C2) and CO2 azeotrope but owing to the freezing of CO2. A modified process based on an existing Ryan–Holmes process in the form of a low-temperature distillation is presented here for the separation of sour gases. In addition, solvents were employed to prevent CO2 freezing and to avoid formation of the C2-CO2 azeotrope.Simulation: Simulation calculations were carried out using a natural gas stream containing CO2 and H2S. The process was designed and simulated using Aspen HYSYS 9.Findings: A low-temperature process for the separation of a feed stream containing up to 30 mole% CO2 and 2.5 mole% H2S was achieved, which lowered the levels of these gases to within 50 and 4 ppm, respectively. These values conform to liquefied natural gas specifications. The compositions of the product streams, the required solvent circulation flow rates, and the total energy requirements were estimated. The reported process successfully separated H2S and produced CO2 at a pressure of 25.0 bar and a temperature of −13°C, thereby ensuring its suitability for application in enhanced oil recovery. This described process also delivered the desired natural gas product at 35 bar and −90°C ready for liquefaction and further cooling.