Impact of Nonhydrocarbon Impurities on the Performance of Natural Gas Pipelines in Dense and Supercritical Phases

Abstract

Transmission of natural gas through pipelines in dense and supercritical phases is an appropriate method due to the reduction in pressure drop. Natural gas can contain various nonhydrocarbon impurities (nitrogen, carbon dioxide, hydrogen sulfide, hydrogen, and argon). The presence of these impurities significantly affects the performance (critical properties, physical properties, and operational conditions) of the natural gas pipeline. Sufficient studies have not been conducted to assess the impact of these impurities on the performance of natural gas pipelines in dense and supercritical phases. This research investigates the influence of the maximum presence of these impurities in typical natural gas on the performance of the pipeline in the dense and supercritical phases. Furthermore, the pipeline performance in the dense and supercritical phases was compared with the vapor phase. The specifications of the American Gas Association (AGA) for pipelines were utilized for this purpose, and Aspen Plus software was employed for simulation. Literature results were used for validation. The results indicated that the presence of 10% nitrogen in natural gas had the highest significant impact, while the presence of 0.02% hydrogen and 0.05% argon had the least impact on the pipeline’s performance in the dense and supercritical phases. The presence of all impurities, except hydrogen, led to an increase in density, viscosity, temperature drop, and a decrease in pressure drop, heat capacity, velocity, erosional velocity, and volume flow rate in the dense and supercritical phases. The results also indicated that natural gas transmission is more efficient in the dense phase, compared to the supercritical and vapor phases, due to fewer variations in key factors in the presence of all impurities.