A new technology to sink and store carbon dioxide deep in the ocean is being developed by the National Maritime Research Institute (NMRI; Tokyo; edlinks.chemengonline.com/6896-536), in cooperation with the National Institute of Advanced Industrial Science & Technology (AIST; Tsukuba), and IHI Marine United Inc. (Tokyo, all in Japan). The Cosmos project (COâ‚‚ sending technology for ocean storage) is being supported by the Japanese Railway, Construction, Transport and Technology Agency (Yokohama).
The project’s concept (diagram) is to first liquefy captured COâ‚‚ at its triple point (0.52 MPa and 216.6K) and transport the liquefied COâ‚‚ to an offshore platform. There, a slurry of liquid COâ‚‚ and dry ice is formed by pressurized crystallization of the liquid along the solid-liquid line of COâ‚‚’s phase diagram. The slurry (liquid/solid = 50/50) is then injected through nozzles at a depth of about 500 m, and the mixture then sinks to a depth of up to 3,500 m.
Preliminary simulations by the researchers show that injecting the COâ‚‚ slurry (as 48-cm-dia. balls) to a depth of 200 m is sufficient for the material to sink below the critical depth of 2,700 m, where the density of liquid COâ‚‚ equals that of seawater. Because of the high pressure and the low temperature at such depths, a membrane of COâ‚‚ hydrate forms at the interface between the liquid COâ‚‚ and the seawater, which is expected to prevent the COâ‚‚ from being dispersed. A 1-to-80-scale model of the platform and injection system has been constructed, and the group plans to test the entire concept in the future.