Experimental Investigation of the Adhesion Forces/Strengths of Cyclopentane Hydrate in a Gas Phase

Hydrate agglomeration in a bulk phase and hydrate deposition on pipe wall are the two processes that cause hydrate block in gas pipelines. Hydrate particle-particle/droplet adhesion forces and hydrate deposition-wall adhesion strengths are the essential reasons that determine agglomeration and deposition, respectively, which have been rarely studied in the gas phase. In the present work, the interaction behaviors of hydrate particle-particle/droplets and hydrate deposition-pipe wall in the cyclopentane (CyC5) vapor phase were investigated using custom-built micromechanical force (MMF) and shear strength measurement apparatuses, respectively. It was found that compared with the oil phase, hydrate formation from thawing ice particles in the CyC5 vapor phase is an outward growing process, and the formation rate is much higher. The particle surface is rougher and thus exhibits strong hydrophilic characteristics. The hydrate particle-particle adhesion forces slightly increase with the temperature, and the value is close to that in the oil phase. Due to the differences in the hydrophilic characteristics of hydrate particles in the oil and gas phase, the hydrate particle-droplet interaction behaviors are significantly different. With the gradual conversion of water in liquid bridges, the hydrate-droplet adhesion forces first increase, then decrease and finally level off. The early measured adhesion forces are approximately 2-3 times that in the oil phase. In the case of hydrate deposition, the adhesion strengths increase with the substrate roughness and the formation/annealing time, while they decrease with temperature. At a temperature of 1 °C, the measured adhesion strengths in the gas phase are close to those in the oil phase. While at a higher temperature of 4 °C, the strengths in the gas phase are significantly larger. This work can provide further understanding of hydrate plugging in the gas phase, which is important in advancing the management of hydrate formation in pipelines.