Experimental Investigation of the Characteristics of Supercritical CO2 during the Venting Process

Abstract

Carbon capture utilization and storage (CCUS) is the technology with the greatest potential to decrease the content of CO2 in the atmosphere, which is the main contributor to global warming and can result in a significant number of environmental problems. The transportation of CO2 is the most important node in the CCUS chain and a pipeline is an economical and efficient means of transportation. In the process of CO2 pipeline building, a certain amount of venting devices should be installed to prevent overpressure of the main pipeline and allow for overhaul of the main pipeline. Hence it is necessary to obtain the characteristics of CO2 inside the venting pipe during the venting process in order to maintain the safety of both the venting pipe and the main pipeline during release. In this study, two 2 m long venting pipes were connected by valves and installed on an industrial-scale pipeline. Two group venting experiments were carried out with two different openings of the valve. Industrial-scale experiment apparatus was used to obtain crucial data and get results closer to an actual industrial setting. During the experiments the evolution of the temperature and the pressure of the CO2 were measured. Based on the pressure and temperature data, the differences of the phase transition of the CO2 in the two experiments were compared. No dry ice was generated inside the pipe during the experiments. A throttling effect was generated in one group experiment but not in the other. In addition, the evolution trend of the Joule–Thomson coefficient was discussed. During the whole venting process, the wall temperature was obtained and the Nusselt number was selected as a parameter to discuss the process of heat transfer between the CO2 and the pipeline wall.