Ultra-long-distance transport of supercritical natural gas (SNG) at very-high mass flow rates via pipelines through land, underground, water bodies, and ocean

Abstract

A detailed study of SNG transport using a computational model that accounts for compressibility and Joule-Thomson effects is presented, for the first time. It shows that the transport distance and mass flow rate of supercritical natural gas (SNG) - above the cricondenbar and cricondentherm, and beyond the anomalous state - can exceed far beyond that achieved or proposed under high pressure, dense phase conditions, thus far. As an example, SNG (average composition of USA/Canada gas), at 800 kg/s can travel, without recompression, to 4801 km. It is revealed that the pressure-drop and pumping power per unit length decrease asymptotically as the inlet pressure increases beyond 20 MPa; orders-of-magnitude lower than that at low pressures. The increase in inlet pressure, pipe diameter, and/or heat conductance of the pipe wall increases the distance travelled by SNG whereas the increase in mass flow rate and surrounding temperature has a negative effect, including the strengthening of Joule-Thomson cooling near the exit. SNG pipelines at ocean bottom offer many advantages, including shorter distances, isothermal flows (∼4 °C), and balance between the outer and inner pressures. Also, SNG delivery at 6 MPa can allow regional distribution without immediate recompression. SNG pipelines therefore offer enormous possibilities of energy-efficient transport of natural gas to far-distant intra- and inter-continental destinations, not feasible thus far, which is urgently needed for uninterrupted supply of natural gas and worldwide energy security.