Fluid dynamics of sinking carbon dioxide hydrate particle releases for direct ocean carbon sequestration

One strategy to remove anthropogenic CO 2 from the atmosphere to mitigate climate change is by direct ocean injection. Liquid CO 2 can react with seawater to form solid partially reacted CO 2 hydrate composite particles (pure hydrate plus unreacted CO 2 and water) with densities several percent above ambient seawater. The most recent field injections at depths of 1500 m in Monterey Canyon resulted in long curved cylinders with diameters 2.5 cm and lengths up to 1 m that were observed to sink at 4 cm/s. This thesis examines whether releasing the partially reacted hydrate particles into the ocean at 100 kg/s of CO 2 (roughly the output of one 500 MW coal power plant) is able to create sufficient dilution to minimize the impact on marine life. We developed a drag coefficient model for cylindrical particles in free fall. Applying the new drag coefficient model to recently observed field injections to predict their descent, the recently produced field particles were estimated to have had a ~ 16% reaction efficiency and to have sunk 100 m before completely dissolving. Ambient density stratification and currents will also affect particle descent, and in turn the dilution of dissolved CO 2. Three methods of injection of composite particles were evaluated, each with unique merits. Firstly, we can release hydrate particles (with a range of reaction efficiencies) continuously from a moving ship. This is shown to provide excellent dilution of the discharged CO 2. Second, we can release them from a stationary pipe to create a plume that generally sinks further than individual particles. However we show numerically that, while this method appears to be the most practical from an engineering standpoint, the dilutions and sequestration depths are highly dependent on ambient conditions. The third method involves constructing a shroud around a fixed source to shelter the plume from effects of ambient stratification and current. The shroud also serves as an inverted chimney, inducing a down draft that transports the dissolving particles to a depth of lower ambient disturbance. Laboratory measurements using particle image velocimetry (PIV) shows that the induced flow depends on the shroud length and diameter, as well as the particle buoyancy and size. Thesis Supervisor: E. Eric Adams Title: Senior Research Engineer of Civil and Environmental Engineering Acknowledgments This work was supported by the Ocean Carbon Sequestration Program, Biological and Environmental Research (BER), U.S. Dept. of Energy (grant number DE-FG0201ER63078), the National Energy Technology Laboratory, U.S. Dept. of Energy (grant number DE-FG26-98FT40334) and the Martin Family Fellows for Sustainability. I would first like to thank my thesis advisor, Dr. Eric Adams, for his valuable guidance throughout this journey. This thesis would not have been close to possible without his mentorship and insight. Committee members Profs. Heidi Nepf and Roman Stocker have been invaluable in providing comments during lab meetings, and their input has led to many interesting findings. From Oak Ridge National Laboratory (ORNL), I thank thesis committee member Costas Tsouris for his guidance and for hosting me at ESD, Scott McCallum for the painstaking experiments in the seafloor process simulator, and also David Riestenberg and Pete Szymcek. I also acknowledge Drs. Peter Brewer, Ed Peltzer, Peter Walz and members of the Monterey Bay Aquarium Rsearch Institute (MBARI) for sharing time, data, and ideas on the research vessel Western Flyer. Their field experiments with the (ROV) Tiburon at MBARI are what originally motivated the thesis. At MIT, Several Undergraduate Research Opportunities Program (UROP) members, Shannon O'Connell, Xiawa Wang, Emily Moberg and Henry Foote (a high school senior at the time; currently a Yale undergraduate) were also invaluable in their help with the experimental design and procedures with the shroud plumes and drag coefficient determination. Shannon in particular also taught me the value of logging my progress. I thank Prof. Dennis McLaughlin for recruiting Henry, and also for the time he supported me with a Teaching Assistantship, during which I learnt a lot about writing and presentation skills. At Parsons Lab, Peter Israelsson also contributed to the towed pipe scenario and furnished a global perspective to the problem of CO 2 sequestration. I also thank Peter and Janani for the many years of friendship and support. Parsons Lab students Anne Lightbody, Brian White, Yukie Tanino, David Gonzalez-Rodriguez, Charu Varadharajan and Marcos have provided me not only with friendship and good humor but they also, often unwittingly, provided insight to my thesis research. I wish to thank my friends at Parsons Lab, at MIT, in Boston and afar for their support. I thank Jeff Wingard for his unending support and also for helping me with manufacturing the particles and fishing them out of the Houdini tank during those crucial final days. Finally I thank my parents, my brother Jonathan, and my grandmother for their love, numerous phone calls and support.