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New method for ocean disposal of CO2 by a submerged kenics-type static mixer



A new method for ocean disposal of anthropogenic CO2 is proposed. In this method, liquefied CO2 is transported through a pipeline to a Kenics-type static mixer, submerged at a depth between 500 and 1,000 m below the ocean surface and mixed with seawater in the mixer and then released into the ocean. Because the pressure and temperature for seawater at depths > 500 m satisfy those for hydrate formation, CO2 hydrate may form at the CO2–seawater interface. Thus, the release from the mixer is a mixture of liquid CO2, hydrate, and seawater. The apparent CO2 concentration of the release can be determined by the CO2–seawater mixing rate and distribution of the CO2 drops (with or without a hydrate layer) produced in the mixer. This proposed disposal method was simulated experimentally. The laboratory-scale simulation revealed that sizes of the dispersed CO2 drops and their distribution in the mixer were governed by the mixing rate and the Weber number on the basis of the continuous phase (seawater); larger Weber numbers led to smaller drop sizes and more uniform drop distribution. It was also observed that the drops with a hydrate layer were generally smaller than those without a hydrate layer under the same mixing rate and that a fairly uniform distribution for the dispersed CO2 drops was always obtained if the continuous-phase flow was fully turbulent. Results of the laboratory simulation suggest that the environmental impact induced by the CO2 released by a Kenics-type static mixer may be better predicted than from conventional injection methods. © 2004 American Institute of Chemical Engineers AIChE J, 50: 871–878, 2004