Scaled-Up Ocean Injection of CO₂–Hydrate Composite Particles^†

Abstract

A pilot-scale, three-phase continuous-jet hydrate reactor, developed to produce CO 2 hydrate for ocean sequestration, was tested both in the laboratory and at sea. A 72-L pressure vessel was used for laboratory tests; field experiments were performed with a remotely operated vehicle at depths between 1200 and 2000 m off the coast of Monterey, CA. Rapid production of a consolidated sinking CO 2 –hydrate composite paste was achieved in both settings. The vertical and lateral movement of the extruded hydrate was monitored by the high-definition television camera mounted on the vehicle and with a 675-kHz scanning sonar, along with dissolution rates and associated temperature and pH changes during the injection operations. It was observed that globules of unconverted liquid CO 2 occluded in the structure of the hydrate composite largely determine the hydrate composite behavior in the ocean by providing sites for accelerated dissolution, thereby affecting the CO 2 –hydrate particle orientation, shape, lifetime, and sinking rate. Model calculations predict that large-scale releases of these particles (at a CO 2 injection rate of ∼100 kg/s) should show a descent depth of nearly 1000 m below their release point, as a result of plume dynamics and the increase in density caused by the CO 2 dissolution into the surrounding ocean water.