Ocean Disposal of CO₂: Conditions for Producing Sinking CO₂ Hydrate

Abstract

Carbon dioxide sequestration at intermediate ocean depths in the form of a sinking CO₂ stream has been shown to be technically feasible. Buoyancy characteristics of CO₂ hydrate particles obtained from a coflow reactor operating under conditions that produce negatively buoyant CO₂ hydrate composite particles were studied. Using a simplified process model, the limiting ratios of CO₂ to water to produce sinking hydrate composite streams were established for pressure and temperature conditions of intermediate ocean depths. A kinetic model involving a mass transfer step and a reaction step was proposed to explain experimental data using a seafloor process simulator. Results suggest that the reactor operates under mass‐transfer controlled conditions. Although the density of freshwater is only a few percentage units less than that of seawater, operating conditions derived from freshwater‐based studies are significantly different for ambient seawater. Owing to the higher density of seawater, greater conversion of CO₂ to hydrate is needed to obtain a sinking CO₂ composite stream than at the same depth of freshwater.

Keywords:

• Ocean carbon sequestration
• CO₂ hydrate
• Mass transfer