Numerical simulation of high-pressure CO₂ pipeline venting and safe release

Abstract

[Objective] Carbon capture, utilization and storage(CCUS) is an indispensable technology for achieving carbon neutrality,and CO2 pipeline transmission is a significant component of this technology. In the process of supercritical CO2 pipeline transmission,unintentional pipeline leakage or venting operations may cause localized low temperatures in the trunk pipelines and vent piping due to the strong throttling effect caused by CO2, resulting in dry ice that blocks the pipeline and makes it brittle. [Methods] In the study, the OLGA software was utilized to develop a high-pressure CO2 pipeline relief model. The simulation results obtained from the model were then compared against foreign experimental data. The comparative analysis indicated that the OLGA software provided relatively accurate calculations for pressure drop and tended to be more conservative in calculating temperature drop. These findings supported the software's suitability for performing calculations related to the design of CO2 pipelines. Building upon this foundation, a long-distance high-pressure CO2 pipeline venting model was established to simulate and analyze the effects of different valve openings, initial temperatures, and initial pressures on temperature decrease, phase state changes, and venting duration during the CO2 pipeline venting process. [Results] It was revealed that reducing the vent valve opening effectively prevented excessively low temperatures within the pipeline during venting. Under the venting simulation conditions selected for this study, 13.5% valve opening effectively prevented dry ice formation, and the valve opening below 4.5% could maintain the pipeline temperature at higher than-30 ℃. The venting process of the high-pressure CO2 pipeline exhibited low convective heat transfer intensity and significant temperature drops, predominantly observed away from the relief port. The initial temperature had a substantial impact on the temperature in the pipeline during venting. More specifically, a lower initial temperature resulted in a decrease in the temperature in the pipeline during venting, increasing the likelihood of dry ice formation. [Conclusion] Therefore, in engineering practice, it is crucial to focus on fuid temperature in sections far from the relief port along the trunk pipelines and automatically reduce the vent valve opening in response to temperature drops, aiming to slow down the temperature drop rate during the venting process. Special attention should be paid to protecting CO2 pipelines, especially when operating under low-temperature dense phase conditions.

Keywords

• co₂ pipeline
• ccus
• venting simulation
• safety relief