Effects of Impurities on CO2 Pipeline Performance

Abstract

Carbon dioxide (CO2) is a chief constituent of greenhouse gases and should be captured, transported and stored in saline aquifers or used for enhanced oil recovery. This study is focused on pipeline transportation of impure CO2. The major impurities in captured CO2 from power plant stations and gas processing facilities are mainly nitrogen, methane, hydrogen sulphide, and water. Impurities affect the density and viscosity of the CO2 stream thereby impacting on the fluid phase, pressure and temperature of the stream. CO2 pipeline models, however, rarely consider the effects of impurities in the determination of design parameters. Aspen HYSYS (ver.9) is used to model the effect of impurities on the pressure drop, phase envelope and critical pressure and temperature of captured CO2 fluids flowing in pipelines. Cortez, Canyon Reef and Choctaw pipelines in the USA and Weyburn pipeline in Canada were selected as the case studies. The results show that the pressure drop increased in these pipelines due to the impurities with the highest pressure drop occurring in the Canyon Reef pipeline. The impurities increased the pressure drop by about 0.09 bar/km, 0.2 bar/km, 0.10 bar/km and 0.04 bar/km for Cortez, Canyon Reef, Choctaw and Weyburn pipelines respectively. The lower molecular weight gases were found to decrease the mixture density and increase the pressure drop. The results also reveal that the bubble point pressure was increased by impurities in three pipelines but slightly reduced in the Weyburn pipeline and the critical temperature was reduced in all pipelines.