Investigation of CO₂ hydrate growth kinetics in gas-dominated systems

Objective CO₂ is prone to form hydrates when in contact with liquid water under low-temperature, high-pressure conditions, impacting the safe operation of pipelines. Thus, it is essential to enhance the understanding of CO₂ hydrate growth characteristics in gas-dominated systems within pipelines, elucidate the growth kinetics of these hydrates, and establish a theoretical framework for predicting and preventing hydrate formation in CO₂ transmission pipelines.

Methods A high-pressure, low-temperature multiphase flow loop test device was employed to conduct 16 groups of tests on CO₂ hydrate growth and decomposition under conditions of 4.00–4.50 MPa pressure, 1.0–3.0 °C ambient temperature, 2.20 m/s flow rate, and 4％ water content. The growth and decomposition kinetics of hydrates in gas-dominated systems at low flow rates and low water content were analyzed, along with the adhesion mechanism during formation and factors influencing the growth rate of CO₂ hydrates. Additionally, a correlation equation for the proportionality factor u, related to system temperature and pressure, was proposed based on the Turner kinetic model to enhance the understanding of mass transfer and supercooling effects on CO₂ hydrate growth rates, thereby refining the basic Turner kinetic model.

Results The kinetics of CO₂ hydrate growth and decomposition were observed in four distinct stages: induction, rapid growth, slow growth, and decomposition. The induction time decreased with increasing initial pressure and increased with higher ambient temperatures. Low temperatures and liquid accumulation on the pipe wall were essential for hydrate growth under low flow rate conditions, with mass transfer identified as a primary control mechanism. The growth rate was influenced by system temperature and pressure; higher pressures and lower temperatures resulted in faster growth rates.

Conclusion The average relative error of the modified model in predicting hydrate growth rates decreased from 82.55％ to 10.74％, significantly enhancing the accuracy of predictions in gas-dominated systems under low flow rates.