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Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilution of a dense vertical unconfined plunging jet to evaluate its performance as an outfall to dilute brine from desalination plants as well as a means to aerate water column. Experiments involved neutrally buoyant or dense plunging jets discharging in quiescent receiving water. The density difference between effluent and receiving water, the plunging jet length (height above water surface), and the receiving water salinity were varied in the experiments. Observed penetration depth for neutrally buoyant jets was somewhat greater than previously reported, and increased modestly with jet density. Increasing density also resulted in an increasing number of fine bubbles descending together with the dense plume. These observations can help guide the design of plunging jets to mitigate anoxic conditions in the water column when brine is introduced to a receiving water body, as with seawater desalination., Kuwait Foundation for the Advancement of Sciences (no. P31475EC01, PN1815EV07)

Brine discharges from desalination plants into low-flushing water bodies are challenging from the point of view of dilution, because of the possibility of background buildup effects that decrease the overall achievable dilution. To illustrate the background buildup effect, this paper uses the Arabian (Persian) Gulf, a shallow, reverse tidal estuary with only one outlet available for exchange flow. While desalination does not significantly affect the long-term average Gulf-wide salinity, due to the mitigating effect of the Indian Ocean Surface Water inflow, its resulting elevated salinities, as well as elevated concentrations of possible contaminants (such as heavy metals and organophosphates), can affect marine environments on a local and regional scale. To analyze the potential effect of background salinity buildup on dilutions achievable from discharge locations in the northern Gulf, a 3-dimensional hydrodynamic model (Delft3D) was used to simulate brine discharges from a single hypothetical source location along the Kuwaiti shoreline, about 900 km from the Strait of Hormuz. Using nested grids with a horizontal resolution, comparable to a local tidal excursion (250 m), far field dilutions of about 28 were computed for this discharge location. With this far field dilution, to achieve a total dilution of 20, the near field dilution (achievable using a submerged diffuser) would need to be increased to approximately 70. Conversely, the background build-up means that a near field dilution of 20 yields a total dilution of only about 12.

This paper presents strategies for producing negatively buoyant CO[subscript 2] hydrate composite particles for ocean carbon sequestration. Our study is based on recent field observations showing that a continuous-jet hydrate reactor located at an ocean depth of 1500 m produced curved negatively buoyant cylindrical particles with diameters ~2.5 cm and lengths up to ~1 m. Accordingly we performed new laboratory experiments to determine the drag coefficient of such particles and, based on the measured drag coefficient and the initial settling velocity observed in the field, have concluded that the reactor efficiency (percentage of liquid CO[subscript 2] converted to hydrate) in the field was ~16%. Using the dissolution rates observed in the field, we conclude that such particles would ultimately sink to depth below discharge of ~115 m. We have also predicted the sinking depth of particles potentially produced from various scaled-up reactors and have shown that, for example, a 10 cm diameter particle produced with a hydrate conversion of 50% could reach the ocean bottom before completely dissolving. In a real sequestration scenario, we are interested in following large groups of hydrate particles released continuously. We have previously shown that increasing particle size and hydrate conversion efficiency enhances the sinking of hydrate particle plumes produced by the continuous release of CO[subscript 2] in a quiescent ambient, but that a sufficiently strong current will cause the entrained particles to separate from the plume and settle discretely. In the latter case, particles of different sizes and hydrate conversions (hence different settling velocities) will follow different settling trajectories as they dissolve. This particle fractionation, if employed deliberately, spreads the discharged CO[subscript 2] in the down current and vertical directions, enhancing mixing, while turbulent diffusion helps spread the CO[subscript 2] in the third direction. A numerical, United States. Dept. of Energy. Office of Biological and Environmental Research. Ocean Carbon Sequestration Program (Grant DE-FG02-01ER63078), United States. Dept. of Energy. National Energy Technology Laboratory (Grant DE-FG26-98FT40334)

Plumes of negatively buoyant hydrate particles, formed by reacting liquid CO[subscript 2] with seawater at ocean depths of 1000–1500 m, have been suggested as a way to help sequester CO[subscript 2]. The vertical flux of CO[subscript 2] can be increased by constructing a shroud around the hydrate particle 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 will transport the dissolving particles to a depth of lower ambient disturbance. Laboratory PIV measurements are compared to an analysis of an idealized shroud that is long, frictionless and driven by a single phase source of buoyancy distributed uniformly over the shroud base. Results indicate that induced draft, and hence dilution of dissolved CO[subscript 2], increases with plume buoyancy, and shroud length and diameter, but efficiency decreases with increasing ratio of particle slip velocity divided by the characteristic induced draft velocity. While larger particles show reduced plume-like behavior and hence are less efficient in inducing draft, they still generated about half of the theoretically predicted flow., United States. Dept. of Energy (Ocean Carbon Sequestration Program, Biological and Environmental Research Grant DE-FG02-01ER63078), United States. Dept. of Energy (National Energy Technology Laboratory Grant DE-FG26-98FT40334), Martin Family Society of Fellows for Sustainability

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008., Includes bibliographical references (p. 203-211)., One strategy to remove anthropogenic CO₂ from the atmosphere to mitigate climate change is by direct ocean injection. Liquid CO₂ can react with seawater to form solid partially reacted CO₂ hydrate composite particles (pure hydrate plus unreacted CO₂ 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 CO₂ (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 CO₂. 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 CO₂. Second, we can release them from a stationary pipe to create a plume that generally sinks further than individual particles., (cont.) 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 distur-bance. 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., by Aaron C. Chow., Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004., Includes bibliographical references (p. 173-179)., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Experiments are performed where a dense multiphase plume is released vertically in a salinity stratified ambient. The constituent phase composition of the initial buoyancy flux can be dense brine, particles, or a mixture of the two in a prescribed ratio. The resulting trapping heights and peeling depths are recorded by visual acquisition and from dye fluorescence measurements. Also, the radial concentration distribution of the dispersed phase after the first peeling event is obtained by collecting the settled particles from the bottom of the tank. Analytical models assuming plug flow and well-mixed particle distributions within the intrusion layer are used to predict the spread of the particle distribution based on initial buoyancy flux, momentum flux, stratification parameter and particle fall velocity. The effects of initial momentum and volume flux on peel and trap depths were studied by comparing the predictions from these models. Finally the observed results are compared to a single-phase plume numerical prediction (CORMIX) and a multiphase numerical plume model. Observed peeling depths were not sensitive to buoyancy composition, while observed trap depths decreased slightly with high particle fractions, possibly from the 'lift-off' phenomenon where particle fallout decreases the bulk buoyancy of the intrusion layer. The observed radial distribution was Gaussian, consistent with particles being vertially well mixed in the intrusion layer, and the standard deviation agreed well with predictions., by Aaron C. Chow., S.M.