Development of a throttling venting model for CO2 pipelines and study of venting characteristics

CO2 pipeline venting is essential to mitigate overpressure risks. The design of the venting structure must account for the risk of dry ice blockage caused by CO2 throttling and its effectiveness in alleviating overpressure in the main pipeline. A comprehensive assessment of the impact of different venting structures on temperature and mass flow rate is necessary. This study uses a one-dimensional throttling model to investigate the effects of various venting structures on pressure, temperature, and mass flow rate. An orthogonal experimental design is applied to quantitatively analyze and compare their impact on low temperature and mass flow rate. The results indicate that flow rate is the fundamental reason for the temperature drop before and after changing the throttle valve. Increasing the number of vent valves, reducing the opening of the final stage valve, and decreasing the diameter of the vent pipe will all raise the temperature of CO2 within the venting structure. However, the cost of improving low-temperature conditions is to reduce the mass flow rate. Through orthogonal experiments, it has been determined that the diameter of the vent pipe has the most significant impact on the mass flow rate and the extent of temperature reduction, followed by the valve opening, and finally the length of the vent riser. Therefore, in practical operation, the diameter of the ventilation pipe should be carefully selected to balance the risks of low temperature and overpressure.