Effects of non-hydrocarbons impurities on the typical natural gas mixture flows through a pipeline

Abstract

Natural gas mixture flowing in the transportation pipeline is impure owing to the presence of various impurities. The presence of non-hydrocarbons impurities in natural gas mixture impacts the natural gas properties at different extents. The effect of the existence of each impurity on the natural gas mixture has not been sufficiently studied and widely understood. In this study, various mixtures containing typical natural gas compositions and one impurity at maximum allowable concentration, flowing in the pipeline are evaluated to elaborate their effect on the pipeline performance. A pipeline string of Rodersdorf to Lostorf taken from the Trasitgas project with 55 km is simulated using Aspen Hysys and validated by Aspen plus. The molar flow rate is 30382.32 kgmole/h, the internal and external diameters specified to be 875.4 mm and 900 mm. 67.5 bar and 63.29 bar were deployed as input and minimum pressures with 55 °C as input temperature, to keep the fluid in the supercritical phase. The impact of each impurity is studied and the deviation from the typical natural gas mixture is determined. These deviations were classified to grade the impurities in order of degree of impact on each parameter. All the impurities came with at least one negative impact on the typical natural gas mixture fluid flow. 10% of nitrogen had the highest impact on the pressure drop, temperature drop, viscosity, and phase envelope. 5% of carbon dioxide had the highest impact on the density of the mixture while 5% of hydrogen sulfide had the highest impact on the critical temperature and the critical pressure of the mixture. 0.05% of argon, 0.01% of oxygen, 147 ppm water, and 0.5% helium had the lowest impact, hardly affecting the properties of the typical natural gas mixture.