Correlating the additional amine sweetening cost to acid gases load in natural gas using Aspen Hysys

Natural gas with high acid gas contents represents a challenge in process engineering and energy industry. Exploring the alternative solutions requires correlating additional costs accompanying the process scale-up to treat high acid-gas contents. This work estimates this relation and validates it against various conditions in amine sweetening plants. An amine sweetening process was simulated using Aspen Hysys to treat a natural gas (25 MMSCFD, 1.7 mol% H2S and 4.13 mol% CO2). Amine circulation rate, lean amine temperature, re-boiler temperature and amine concentration were chosen as the main input variables to optimize the process total cost using the central composite experimental design model. The process was scaled-up to handle a sour gas up to (25 mol% CO2 and 3 mol% H2S) by scaling up the amine circulation rate. The capital and operating costs showed a linear relationship with the increase of CO2 percentage in natural gas. Moreover the utility requirements, regenerator column diameter and the surface area of the re-boiler, the lean-rich amine heat exchanger and the lean amine cooler showed a strong linear increase correlation. There was no statistical difference using either Li–Mather or Kent–Eisenberg thermodynamic models. Low feed gas pressure yielded a similar linear relationship irrespective of the costs for purchasing and operating the inlet compressor and air cooler. No statistical difference found between cost regressions lines of different tray efficiency of the distillation tower. For various partial pressures of CO2 and H2S, assuming no other sulphur compounds, the economics scaled up as a second order polynomial.