Utilization of Static Mixer on the Injection of Liquid CO₂ Into Water for the Ocean Disposal

Authors:

Hideo Tajima

Akihiro Yamasaki

Fumio Kiyono 

This research explores a novel method for sequestering carbon dioxide by using a static mixer to inject liquid CO₂ into the ocean at depths of approximately 500 m. The study demonstrates that the static mixer effectively controls CO₂ droplet size and prevents nozzle blockage through the formation of a surface hydrate film, ensuring the droplets dissolve completely before reaching the sea surface. Ultimately, the findings suggest that this approach is an energy-efficient solution for long-term CO₂ disposal with significantly lower power requirements than traditional stirring methods.

Key Learnings

• Effective Droplet Control: The static mixer allows for precise control over the size of liquid CO₂ droplets, ensuring they stay below the critical 4.0 mm diameter required to prevent vaporization and ensure complete dissolution before reaching the sea surface.
• Hydrate Film Benefit: At depths below 500 m, the formation of a CO₂ hydrate film on the droplet surfaces prevents them from merging into larger masses, which maintains a uniform size distribution and aids the sequestration process.
• Operational Stability: Using a static mixer helps prevent the common problem of nozzle blockage caused by the agglomeration of solid hydrates, allowing for a continuous and stable injection process.
• Energy Efficiency: The process is highly energy-efficient, with an estimated energy consumption of only 0.35 MJ/t-CO₂, which is negligible compared to the energy required for CO₂ separation or liquefaction.
• Flow Rate Correlation: The final droplet size is significantly influenced by the flow conditions; higher water flow rates (represented by higher Reynolds numbers) lead to smaller, more uniform droplets.