Assessment of flow pattern and rheological properties of SF6 hydrate slurry

Abstract

Sulfur hexafluoride (SF6) has extremely high global warming potential and must be separated and recovered to avoid its emission into the atmosphere. Hydrate-based gas separation, which uses only water as the separation medium and has low environmental impact, is expected to become a new separation and recovery technology for SF6. However, this technique has the drawback that hydrate particles in the slurry can block equipment piping. Therefore, this study investigated the flow pattern and rheological properties of SF6 hydrate slurry using a loop-tube flow apparatus. SF6 hydrate slurry was observed to have three flow patterns as the flow velocity varied: homogeneous flow, heterogeneous flow, and moving-bed flow. We developed experimental relationships based on the Turian–Yuan equation to estimate the flow velocities at which the flow patterns change. These experimental equations were able to predict these velocities within an error of approximately 10%. The rheological properties of SF6 hydrate slurry were found to exhibit Newtonian tendency at low solid fractions and pseudoplastic tendency at high solid fractions. The relative viscosity of the slurry could be estimated within 25% error using the Krieger–Dougherty model.