Dilution Strategies for Direct Ocean Carbon Sequestration

摘要

Ocean carbon sequestration is being mentioned as one approach to help reduce the build-up of greenhouse gases in the atmosphere. Among the issues requiring consideration is the need to obtain high initial dilution, in order to minimize the excess concentrations of dissolved inorganic carbon, and hence associated increases in pCO_2 and decreases in pH, to which aquatic life would be exposed. Here we examine three dilution strategies that promote mixing in the longitudinal, lateral and vertical directions. A point release of negatively buoyant solid CO_2 hydrate particles from a moving ship would get acceptable dilution near the source, while subsequent concentrations would be very low due to longitudinal mixing afford by the ship's speed. A long bottom-mounted diffuser discharging buoyant liquid CO_2 droplets can be designed for high lateral mixing, resulting in arbitrarily small near source concentrations, but because the resulting near field plume would be very wide, subsequent dilution would be slow. A stationary point release of hydrate particles achieves good vertical mixing, due to the negatively buoyant plume effect, resulting in intermediate local and subsequent concentrations. While directly applicable to ocean carbon sequestration, results presented here also provide guidance for the effective three-dimensional dispersal of other substances, such as nutrients for open water aquaculture, or flocculants or algaecides for improving water clarity in reservoirs or town ponds.