Kenji Yamane

Solubility of CO2 and density of CO2 hydrate at 30 MPa

Data needed for evaluation of ocean CO2-sequestering technologies include the solubility of CO2 and density of CO2 hydrate at 30 MPa. Theses were measured using a high-pressure facility suitable for simulating pressure and temperature conditions 3000 m beneath the ocean surface. The solubility decreases linearly with decreasing water temperature, which is opposite to the temperature dependence in the non-hydrate region. The measured solubility agrees with the published value for the non-hydrate region at an equilibrium temperature of 12 °C. The hydrate density was estimated from pressure drop, temperature increase, and concentration changes, followed by precipitation of CO2 hydrate. The estimated CO2 hydrate density varies from 1.11 to 1.09, depending on the fraction of CO2 in hydrate form.

A field study of the effects of CO2 ocean disposal on mobile deep-sea animals

Before the feasibility of ocean sequestration of anthropogenic carbon dioxide can be evaluated completely, there is a clear need to better understand the potential biological impacts of CO2-enriched (low pH and high pCO2) seawater in regions of proposed disposal. We describe here the first empirical study directly examining animal responses to dissolving CO2 hydrates on the deep-sea floor. Using a remotely operated vehicle (ROV) to conduct experiments within Monterey Canyon, CA, we found that several species (both invertebrate and vertebrate) did not avoid rapidly dissolving flocculent hydrates when attracted by the scent of food. Furthermore, while there were no apparent short-term effects of decreased pH, mobile animals appeared to suffer from respiratory distress due to increased pCO2 when in close proximity to hydrates. Losses of higher organisms as a result of CO2 disposal in the deep-sea may therefore be more extensive than previously predicted from toxicological models. However, the extent of changes to surrounding seawater chemistry, and thus biological impact, is largely dependent on CO2 release method or the type of hydrate formed.

Experiments on the ocean sequestration of fossil fuel CO2: pH measurements and hydrate formation

Abstract We have carried out a series of in situ experiments to investigate the formation of a CO 2 hydrate (CO 2 :5.75 H 2 O) for the purpose of evaluating scenarios for ocean fossil fuel CO 2 disposal with a solid hydrate as the sequestered form. The experiments were carried out with a remotely operated vehicle in Monterey Bay at a depth of 619 m. pH measurements made in close proximity to the hydrate–seawater interface showed a wide range of values, depending upon the method of injection and the surface area of the hydrate formed. Rapid injection of liquid CO 2 into an inverted beaker to form a flocculant mass of hydrate resulted in pH initially as low as 4.5 within a few centimeters of the interface, decaying slowly over 1–2 h towards normal seawater values as dense CO 2 rich brine drained from the hydrate mass. In a second experiment, slower injection of the liquid CO 2 to produce a simple two-layer system with a near planar interface of liquid CO 2 with a thin hydrate film yielded pH values indistinguishable from the in situ ocean background level of 7.6. Both field and laboratory results now show that the dissolution rate of a mass of CO 2 hydrate in seawater is slow but finite.

Deep ocean experiments with fossil fuel carbon dioxide: Creation and sensing of a controlled plume at 4 km depth

The rapidly rising levels of atmospheric and oceanic CO2 from the burning of fossil fuels has lead to well-established international concerns over dangerous anthropogenic interference with climate. Disposal of captured fossil fuel CO2 either underground, or in the deep ocean, has been suggested as one means of ameliorating this problem. While the basic thermodynamic properties of both CO2 and seawater are well known, the problem of interaction of the two fluids in motion to create a plume of high CO2/low pH seawater has been modeled, but not tested. We describe here a novel experiment designed to initiate study of this problem. We constructed a small flume, which was deployed on the sea floor at 4 km depth by a remotely operated vehicle, and filled with liquid CO2. Seawater flow was forced across the surface by means of a controllable thruster. Obtaining quantitative data on the plume created proved to be challenging. We observed and sensed the interface and boundary layers, the formation of a solid hydrate, and the low pH/high CO2 plume created, with both pH and conductivity sensors placed downstream. Local disequilibrium in the CO2 system components was observed due to the finite hydration reaction rate, so that the pH sensors closest to the source only detected a fraction of the CO2 emitted. The free CO2 molecules were detected through the decrease in conductivity observed, and the disequilibrium was confirmed through trapping a sample in a flow cell and observing an unusually rapid drop in pH to an equilibrium value.

Ocean abyssal carbon experiments at 0.7 and 4 KM depth

Publisher Summary The chapter reviews and compares observations from the two experiments performed in 2003. The main focus is on the way in which CO 2 behaves and is transported away from the site in realistic deep-sea conditions where hydrates form and where CO 2 is exposed to sediments. The synthesis of observations is then used as a basis for discussing and presenting best estimates of the fate of larger quantities of CO 2 placed on the seafloor. The chapter also discusses observations from small-scale CO 2 experiments conducted off the coast of California at 684 m depth and at 3942 m depth. In both experiments, when the seawater velocity was sufficiently strong, parcels of liquid CO 2 were torn off and transported away as discrete units by the turbulent water current. In the deep experiment, newly formed frazil hydrate was observed at the interface, occasionally including sediment particles. Hydrate furthermore collected and created a floating consolidated solid in the downstream end of the trough, dissolving slowly from one day to the next. These observations have important implications for understanding and modeling of larger scale disposal at the seafloor. When CO 2 is released by the interfacial instability mechanism driven by strong currents, the seawater density increase due to dissolution of CO 2 may not have time to act and stabilize the water column before the discrete parcels of liquid phase CO 2 are advected away from the disposal site. The floating solid that formed at the interface is hypothesized to consist of hydrate and additional trapped seawater. Its appearance was not expected in advance and its role in delaying dissolution cannot be determined from the present experimental set-up. A capability for long-term seafloor perturbation experiments is deemed to be crucial both for direct ocean-storage research and for studying effects of invasion of anthropogenic CO 2 from the atmosphere.

Simulating experiments of CO2 ocean storage with a large high-pressure tank

Publisher Summary This chapter discusses the simulating experiments of CO2 ocean storage with a large high-pressure tank to investigate dissolution of CO2 drops with CO2 hydrate films, and compares the experimental results with those predicted with Ranz–Marshalls equation. In the experiments, the CO2 drops were stored in fresh water pressurized at 30MPa in two temperature regions for two days to observe change of drop diameter and to measure pH change in ambient water around the drops. The diameter change in the experiments, where there was no artificial flow, was larger than that predicted under no-flow condition, which implies that the dissolution could be enhanced by slight disturbance around the drops. On the other hand, the pH measurement showed the lowering of pH during the experimental period, and the pH change was depressed at lower temperatures, which agrees with temperature dependency in the dissolution rate predicted.

Progress of COSMOS (CO2 Sending Method for Ocean Storage) and OACE (Ocean Abyssal Carbon Experiment)

The storage of liquid CO2 at an ocean floor, one of promising measures to mitigate the global warming, requires 3500 m depth for the gravitationally stable storage, a breakthrough technology and a reasonable cost to realize, although it has large advantages such as the sequestration term longer than 2000 years. However CO2 can be sent to the ocean floor by shallow release, if we can use the nature that the cold CO2 to be shipped by a CO2 carrier is much denser than the ambient seawater even at shallow depths. The National Maritime Research Institute (NMRI) conducted several joint field CO2 release experiments with the Monterey Bay Aquarium Research Institute (MBARI, USA) since 1999 under the auspices of the NEDO, and proposed the improved COSMOS, CO2 Sending Method for Ocean Storage, in which CO2 is released into 200 m depth as slurry masses (mixture of dry ice and cold liquid CO2 ). Since 2002, under the NEDO Grant, the NMRI started a new international joint research, OACE, Ocean Abyssal Carbon Experiment with the MBARI and the University of Bergen (UoB, Norway), in order to accumulate the basic data on the long-term stability of stored CO2 and its environmental effects around storage site.Copyright

F202 Effect of CO_2 Hydrate on Flow Behavior of Liquid CO_2 in Porous Media

In the sea around Japan, there is the region of sufficient environment of CO2 hydrate generation. When liquid CO2 is injected in those regions, choking of liquid CO2 flow is expected to occur due to CO2 hydrate generation in pipe arrangement or seabed. The purpose of the present study is to evaluate the influence of CO2 hydrate on the flow of liquid CO2 when liquid CO2 injected in a porous media as simulating seabed. In order to reveal the influence of CO2 hydrate, differential pressure is measured under both condition of CO2 hydrate generated and not generated. As the results, in the case of the hydrate generation environment, it is identified that differential pressure became large compared with the case of no-hydrate generation. In the upstream part, the differential pressure became large compared with the downstream region. It is suggested that flow resistance occurred due to choking of CO2 hydrate membrane on the porous media. Friction factor is also compared with the Ergun’s equation which is proposed for single-phase flow in a porous media. The measured friction factor is larger than the value from Ergun’s equation.

Development of Ballast Water Treatment with Anthracite Filtering

To minimize the risk to the environment and to human health and arising from the transfer of harmful aquatic organisms and pathogens through the discharge of ships ballast water, an international treaty has been adopted, February 2004. The installation of a ballast water processing system, which complies with the standard of the treaty, is required for ships constructed after 2009. Via various methods; such as electrolytic, ozone and specialized pipes have been developed. However, the practical application has yet to be achieved. Mud precipitating in the ballast tank, and microorganisms in the mud were observed. The processing burden of the ballast water was examined. By developing a test plant to demonstrate of ballast water processing, and using anthracite filtrating, we have obtained basic data of characteristics of marine organism filtration. The unit showed an effective removal of the microorganisms, excepting pathogens, from the natural seawater. This was achieved with low operational costs and avoided impact to environment.

STUDY ON CO2 RELEASING NOZZLE FOR CO2 OCEAN STORAGE

Ocean storage of CO2 is one of greenhouse gas control technologies, where CO2 captured from flue gas of fossil fuels is injected into deep sea below 3500m depth to be sequestered from the atmosphere. A CO2 sending method, COSMOS, was proposed as a method of ocean storage, which enables CO2 drops released in mid-depth water to descend to deep sea floor below the depth of 3500m. Then, the authors have worked for development and evaluation of COSMOS. In the first phase of the COSMOS project, the concept of COSMOS was demonstrated by in situ experiments of small-scale CO2 releasing at mid-depth water in Monterey Bay, U.S.A. Three models of CO2 releasing nozzle unit were developed for the experiments. The first model of nozzle unit released liquid CO2 as one mass; however, it was immediately broken into small droplets and soon turned to ascend. The second and third models were designed to have thermal insulator enough to keep low temperature so that both models successfully released liquid CO2 with dry ice, which continued descending for a few minutes. Based on these results, COSMOS was improved, where injection of a mixture of liquid CO2 and dry ice, CO2 slurry, is expected to enable small CO2 drops to descend to deep sea floor below 3500m depth. Then, in the second phase of the COSMOS project, the authors started an investigation on the effect of the aspects of releasing nozzle on the behavior of released slurry drops, and obtained a few results from lab experiment of CO2 slurry releasing from two types of nozzle head.Copyright