Prediction of Hydrate Formation in Long-Distance Transportation Pipeline for Supercritical-Dense Phase CO₂ Containing Impurities

Supercritical-dense phase CO₂ pipeline transportation has been proven to have excellent economic and safety benefits for long-distance CO₂ transportation in large-scale. Hydrates are easily generated in the high-pressure and low-temperature sections, resulting in blockage, so it is necessary to build the prediction model for hydrate formation in the long-distance CO₂ pipeline transportation. In the prediction model of hydrate formation of our work, the phase equilibrium was determined by the Chen-Guo model, and the lateral growth of hydrate was calculated by the comprehensive growth model, and the hydrate growth was estimated by analogy with the condensation process. Subsequently, the prediction model for hydrate volume in the CO₂ pipeline was established considering the process of hydrate growth and water droplet distribution. The effects of thermodynamic conditions, impurities, and operating conditions on the hydrate formation were analyzed. The impurities can expand the temperature and pressure ranges for hydrate generation. The increase in the moisture content, the increase in the pressure, the decrease in the temperature, or the increase in the fluid velocity could increase the volume of hydrates in the pipeline. After running for 10 h, the hydrates volume in the pipeline with the moisture molar fraction of 0.05% is over 10 times that with the moisture molar fraction of 0.005%. In addition, by using the proposed hydrate formation prediction model, the hydrate formation in a supercritical-dense phase CO₂ long-distance pipeline was predicted, and a suggested cleaning cycle was achieved. This study can guide the operation of CO₂ long-distance transportation pipelines.