Simulation of Natural Gas Transmission in the Pipeline in Two-Phase and Supercritical Conditions

The pipeline transportation of natural gas serves as a conventional and economical method for transmitting natural gas, making it crucial to investigate for reducing pressure drop and preventing the occurrence of two-phase fluid formation. To address these concerns, this study delves with the transport of natural gas under supercritical conditions. Under such supercritical conditions, the gas temperature must be between the critical temperature and the maximum temperature within the two-phase region, while the gas pressure must exceed the maximum pressure within this region. The main objective of this study is to simulate natural gas pipeline behavior under supercritical and two-phase conditions utilizing Aspen Plus software version 12.1. The Peng-Robinson equation was employed to compute thermodynamic properties for pipeline simulation. Validation of pipeline simulations indicate a maximum relative error of 4.5% between simulated and actual pipeline data, demonstrating satisfactory agreement between simulation and pipeline data. After validation, pressure drop, temperature variations, density variations, and associated costs under supercritical and two-phase conditions were investigated. Findings reveal that under supercritical conditions, the pressure drop is three times less compared to two-phase conditions. Additionally, temperature reduction under supercritical conditions amounts to 21%, contrasting with a 53% reduction in two-phase conditions. Density variations in supercritical and two-phase states were approximately 5% and 36%, respectively. Finally, it was found that the cost of the total energy consumption required per year in supercritical and two-phase mode is almost similar and is equal to 1,860,000 and 1,831,000 dollars per year, respectively.