Experimental investigation of the adhesion forces/strengths of cyclopentane hydrate in a gas phase

Abstract

Hydrate agglomeration in a bulk phase and hydrate deposition on pipe wall are 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 the hydrate agglomeration and deposition, respectively, which have been rarely studied in the gas phase. In the present work, the interaction behaviors of hydrate particle–particle/droplet and hydrate deposition-pipe wall in the cyclopentane (CyC5) vapor phase were experimentally investigated by using the custom-built micromechanical force (MMF) and shear strength measurement apparatuses, respectively. It has been found that hydrate formation from thawing ice particles in the CyC5 vapor phase is an outward growing process and the formation rate in the vapor phase is much higher than that in liquid CyC5. The particle surface is rougher and thus exhibits strong hydrophilic characteristics. The hydrate particle–particle adhesion forces in the CyC5 vapor phase slightly increase with the temperature, and the value is close to that in the liquid CyC5 phase. Due to the different hydrophilic characteristics of hydrate particles in the oil and gas phases, the corresponding 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 in vapor phase are approximately 2–3 times that in the liquid CyC5 phase. In the case of hydrate deposition, the adhesion strengths increase with the substrate roughness and the formation/annealing time and decrease with temperature. This work can provide a further understanding of hydrate plugging in the gas phase, which is important in advancing the management of hydrate formation in pipelines.