Evaluation of the Two Phase Pressure Drop during the CO2-N2 Mixture Pipeline Transport

AbstractCaptured CO2 mixture for sequestration purpose can contain impurities such as N2, NOx, SOx, O2, H2O, H2, H2S, Ar. Such impurities affect the critical temperature and pressure, density, viscosity, saturation temperature-pressure line, etc. Among the impurities, N2 can affect the CO2 stream properties largely cause of the low boiling point and high specific volume, so a small ratio of N2 inflow might change the flow pattern of CO2 stream from single phase to two phase flow. To understand the flow behavior of two phase CO2 stream with N2 impurity, experimental investigations should be carried out and compared with existing correlation to figure out the accuracy of correlations. In this study we designed and installed an experimental facility to simulate the two phase flow behavior of CO2-N2 mixture during the pipeline transportation. The test section is composed of a single 6 meter STS304 tube with inner diameter of 3.8608mm with inlet absolute pressure transmitter and inlet-outlet differential pressure transmitter. Test condition was 21C and 85bar with varying N2 impurity ratio. In this study the two-phase flow pressure drop data of CO2-N2 mixture flow are compared with correlations of Lockhart-Martinelli, Zhang et al, and Misima & Hibiki. Among three candidate correlations Mishima & Hibiki correlation showed the best accuracy. All of three correlations showed rather low accuracy, but it might be from the reason that the correlations were originally designed to estimate water-vapor two-phase flow pressure drop. The result also shows the need to investigate further visualization and flow pattern identification