A bench-scale flow loop study on hydrate deposition under multiphase flow conditions

Abstract

Gas hydrates are crystalline compounds containing water and small guest molecules. Hydrates, if not properly managed, can cause capital losses and raise safety concerns. In recent years, hydrate control strategies have changed from complete prevention to proper management. Hydrate management requires satisfactory understanding in all hydrate challenges, including agglomeration, deposition, and bedding. The importance of deposition motivates the investigation of its mechanisms. This work aims to provide further insights into hydrate deposition under multiphase flow conditions using a bench-scale single-pass flow loop. The flow loop was equipped with a horizontal test section, transparent windows, temperature sensors, and differential pressure transducers. The experiments were performed with a methane/ethane gas mixture at constant 38.7 bara. The mutual effects between the flow pattern and the deposit growth were observed. Most experiments in this study started with stratified flow. Non-uniform hydrate deposition was observed with relatively slow growth of the top deposit exposed to the gas phase and relatively fast growth of the bottom deposit with direct contact to the liquid phase. The hydrate buildup gradually changed the flow pattern from stratified flow to stratified wavy flow and eventually to slug/bubble flow. The deposit growth and the flow pattern change were reflected on the pressure drop measurement across the test section. The wall temperature showed a big effect on the growth rate and the steady-state thickness. The hydrate slurry presence and the water cut did not noticeably affect the steady-state deposit thickness, while the MEG addition seemed to reduce the thickness.