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A pilot-scale, three-phase continuous-jet hydrate reactor, developed to produce CO2 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 CO2–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 CO2 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 CO2–hydrate particle orientation, shape, lifetime, and sinking rate. Model calculations predict that large-scale releases of these particles (at a CO2 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 CO2 dissolution into the surrounding ocean water.

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A continuous-jet hydrate reactor originally developed to generate a CO2 hydrate stream has been modified to continuously produce CH4 hydrate. The reactor has been tested in the Seafloor Process Simulator (SPS), a 72-L pressure vessel available at Oak Ridge National Laboratory. During experiments, the reactor was submerged in water inside the SPS and received water from the surrounding through a submersible pump and CH4 externally through a gas booster pump. Thermodynamic conditions in the hydrate stability regime were employed in the experiments. The reactor produced a continuous stream of CH4 hydrate, and based on pressure values and amount of gas injected, the conversion of gas to hydrate was estimated. A conversion of up to 70% was achieved using this reactor.