An experimental study on the choked flow characteristics of CO2 pipelines in various phases

High pressure pipeline transportation has been an established technology for economically transporting large amounts of CO2. However, there are still issues and associated risks that have to be effectively addressed and adequately understood. It is well known that a strong Joule-Thomson Cooling effect can occur when pressurized CO2 flows through a choke valve. Thus, to investigate the choking characteristics especially the temperature drop of high pressure CO2, a new laboratory scale experimental setup (total length of 14.85 m and the inner diameter of 15 mm) was constructed. Steady choked flow and transient choked flow tests were carried out respectively for pressurized CO2 in various initial phases. The phase transitions and temperature drop characteristics were then studied following the choked flow and the results show that the phase transitions in steady choked flow differs significantly from that in transient choked flow. For transient choked flow of various initial phases, all the flows downstream would transfer from single phase to gas–liquid two-phase flow. Furthermore, the effect of water on transient choked flow of supercritical CO2 pipeline was investigated, and the phenomena of solid particles deposition was captured which was paramount importance of ensuring the safety operation of CO2 pipelines when throttling by the choke valves.