Progress of COSMOS (CO

Proceedings of OMAE2003 The 22nd International Conference on Offshore Mechanics & Arctic Engineering 8-13, June, 2003, Cancun, Mexico

OMAE2003-37211 PROGRESS OF COSMOS (CO2 SENDING METHOD FOR OCEAN STORAGE) AND OACE (OCEAN ABYSSAL CARBON EXPERIMENT) Izuo Aya, Sadahiro Namie, Kenji Yamane, Ryuji Kojima, Yasuharu Nakajima and Hideyuki Shirota National Maritime Research Institute 3-5-10 Amanogahara, Katano, Osaka 576-0034, Japan Email: [email protected]

Peter G. Brewer and Edward T. Peltzer, III Monterey Bay Aquarium Research Institute 7700 Sandholdt Road, Moss Landing, CA 95039, USA

Peter M. Haugan, Truls Johannessen, Bjorn Kvamme , Richard G.J. Bellerby University of Bergen Allegaten 70, N-5007 Bergen, Norway

ABSTRACT 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 CO 2 ). 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. Figure 1: Concept of Original COSMOS proposed in 1998. INTRODUCTION One advantage of the concept of storage of CO2 on the ocean floor, at depths >3500m where liquid CO2 is gravitationally stable, is that the sequestration time until atmospheric exposure

is far longer than from injection at shallower depths. This depth, however, poses greater challenges of cost and technical difficulty than the dissolution of a rising plume, in which CO2 is

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released between 2000 to several 100 meters depth as small droplets or bubbles. In order to get over this disadvantage, the authors [1] proposed the idea of COSMOS (CO2 Sending Method for the Ocean Storage), utilizing the increased density of cold CO2 as shipped by a CO2 carrier, to achieve efficient transport to depth from a shallower injection point. Figure 1 shows the original concept. Here the CO2 is cooled down close to its triple point (-56.6 ºC) in order to reduce the tank pressure of a CO2 carrier as much as possible. Such cold CO2 is much denser than the ambient seawater at mid -depth (~500 meters). Thus a cold CO2 droplet released at mid-depth will sink until heat transfer from ambient seawater increases its buoyancy above the local value. A numerical analysis [1] showed that if a cold CO2 mass was larger than 1 meter, it could sink to the ocean floor beyond 2750 meters depth where, at thermal equilibrium, CO2 has the same density as the seawater. In order to explore this concept a team from the National Maritime Research Institute (NMRI), and the Monterey Bay Aquarium Research Institute (MBARI), conducted four joint in situ experiments in Monterey Bay, CA from October 1999 to February 2002. These experiments were specifically designed for testing of cold CO2 release techniques developed under the COSMOS project. These field tests were supported by a continuing set of laboratory high-pressure tank experiments. The environmental effect around the storage site is a remaining unsolved problem to realize the CO2 ocean storage. Then in 2002, under the auspices of the New Energy and Industrial Technology Development Organization (NEDO), the NMRI started another international joint research, OACE (Ocean Abyssal Carbon Experiment) project, with the MBARI and the UoB, to accumulate the scientific data on the fate of stored CO2 through in situ and laboratory experiments as well as numerical simulations. 2. COSMOS PROJECT 2.1 Joint In Situ Experiments Table 1 summarizes the purposes and results of all four joint in situ ocean experiments conducted so far. Experimental

planning began in September 1997 during an informal visit to MBARI. Beginning in November 1998, field experiments were carried out once a year until February 2002. The experiments progressed from initial release of CO2 at ambient temperature, to final release of a slurry (dry ice + cold liquid CO2 ) as techniques improved. ROV Ventana and R/V Point Lobos of the MBARI were used for these one-day cru ise field experiments. The 1st in situ experiment was conducted on November 17-18, 1998. The purposes of this experiment were to examine the formation and dissolution process of CO 2 hydrate at relatively shallow depths (350 – 600m) in the real sea [2] and to observe the behavior of deep-sea animals such as Hagfish (Eptatretus stouti) to the CO2 enriched seawater [3]. The first dive revealed that rapid release of CO2 resulted in snow-like hydrate and slow release results in flat membrane-like hydrate on the interface between CO2 and seawater. This behavior was anticipated from land-based experiments carried out at NMRI. The snow-like hydrate dissolved rather fast, which resulted in low pH around it. The flat hydrate membrane, however, dissolves very slowly as earlier land experiments showed [4], and the observed pH change was negligibly small. The purpose of 2nd, 3rd and 4th in situ experiments was to acquire basic data for the development of the COSMOS concept. The data for cold CO2 release techniques is of special importance since this is considered essential breakthrough technology. The important requirements for development of a cold CO2 release nozzle for an in situ experiment are simplicity and effectiveness. The initiation of CO2 release must be simple so that the ROV arm can effect the required manipulation. The thermal insulation must be sufficient to keep CO2 cold for about one hour during ROV transit to 500m depth, and also sufficient to keep the mechanism for CO2 release free from sea ice formation. The pressure in the chamber must be automatically balanced with the ambient pressure for smooth opening, and so on. The third release nozzle made of blue nylon chamber, however, was free from this balancing system to make the system much simpler. Figure 2 shows the three CO2 release nozzles used for each in situ experiment.

Table 1 Summary of Joint In Situ Experiments No.

Date

1

1998.11.17-18

2

1999.10.13

3

2000.10.5-6

4

2002.2.19-20

Purpose and Result Initial testing of CO2 release techniques at ambient temperature. The formation and dissolution for two types of CO2 hydrates were observed. The pH change was large for disseminated snow-like hydrate, but small for flat hydrate membranes at the liquid interface. Functioning of the 1st CO2 release nozzle was tested. CO2 was warmed to ambient value due to insufficient thermal insulation; the CO2 mass released was quickly broken up into small droplets by Taylor type interface instabilities. (Two dives) Cold CO2 release was achieved for the first time. The movement of a CO2 slurry (liquid + solid phases) mass of 8 cm diameter was precisely observed for 50 m of sinking. A thick ice layer covering the CO2 prevented it from breaking up until melted by seawater. (Two dives) Cold CO2 release was again achieved using a simpler (without a complicated pressure balancing system) nozzle. Similar sinking behavior of the CO2 slurry mass was observed. The results suggest effective deep disposal from release CO2 as slurry masses at 200-500- m depth. (Two dives)

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Figure 2: Three CO2 release nozzles used for 2nd (left), 3rd (center) and 4th (right) in situ experiments, respectively. The 2nd in situ experiment, the 1st COSMOS field test, was conducted on October 13, 1999. The apparatus shown in Figure 2 was used. In this design the thermal insulation was insufficient to keep the CO2 temperature as low as required. During ROV transit to the release depth (around 500 meters) CO2 in the chamber was heated almost to the ambient seawater level before release. As shown in Figure 3, the liquid CO2 , released as one mass as shown in (a), was quickly broken up into small droplets of a few cm size , and probably covered with hydrate film (b). Taylor type interface instabilities seemed to cause this rapid break-up. The numerical simulations [5] suggested that the heat capacity stored in a cold CO 2 mass of this size was large enough to grow a thick ice layer, which may prevent or greatly delay the break up. The simulations also showed that the CO2 hydrate, which requires CO2 and water molecules, forms as a very thin film at the interface between cold CO2 and ice layer. A land-based experiment made clear, however, that a large cold CO2 droplet was apt to break up due to the aforementioned instability before a thick ice layer covered the droplet. Considering the result of 2nd in situ experiment, the thermal insulation of the apparatus was greatly improved.

(a) Just released CO2 mass

The 3rd in situ experiment was conducted on Oct. 5-6, 2000, in which a CO2 slurry mass (mixture of dry ice and liquid CO2 ) instead of cold liquid CO2 was successfully released at 500 meters depth for the first time. In contrast to the liquid release mentioned above, the outer ice layer grew so fast that the CO2 mass was initially prevented from breaking up. Figure 4 shows an image of a CO2 slurry mass of 8 cm diameter, covered with thick layer of ice, captured as it sank at 530 meters depth. Supporting laboratory experiments at University of Bergen showed that the rapidly formed sea ice has unusual properties

(b) A few seconds after release Figure 3: Heated CO2 mass released into 450 m depth.

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including low heat conductivity [6], which should be taken into account in future modeling. Figure 5 shows the trajectory of the CO2 slurry mass released at 500 meters depth. Figure 5 shows the trajectory of the CO2 slurry mass released at 500 meters depth. It shows that the CO2 slurry mass reached 548 meters depth, where it had then absorbed sufficient heat from the surrounding ocean that it slowed and began to ascend When it reached 535 meters depth during ascent, the ice layer melted and CO2 mass broke up into small droplets in a similar way as the pure liquid release, although not before showing curious movements due to imbalance of surface tension. This result suggests that the COSMOS slurry release of CO2 is rather promising not only to realize deep disposal, but also to minimize the local pH change during dissolution. The 4th In Situ Experiment was carried out on February 19-20, 2002 in order to confirm the promise of a CO2 slurry release. In the 4th in situ experiment, a very simplified release nozzle, without the sophisticated pressure balancing system, was tested. A slurry of CO2 /dry ice about 8 cm size was carefully released in two experiments at 500m depth, and sinking and dynamic behavior similar to that observed in the 3rd experiment was observed.

Figure 4: A CO2 slurry mass sinking at 0.3 m/s.

2.2 Numerical Simulation After verifying that the numerical analysis that the authors developed for the original COSMOS [1] design could correctly simulate the processes shown in Figure 5, the sinking and ascending motions of a larger CO2 slurry mass, applicable to a real system, were examined using the same program. Changes of depth, ice layer thickness, temperature and normalized mass after release of a slurry mass at 100 meters depth were calculated for various conditions (The release depth can drastically be reduced from the original COSMOS). As a result, in case of slurry size 0.38 meter with dry ice content α = 0.5, the slurry reaches 1900 meters depth and then u-turns, and moves upwards. However, in case of 0.40 meter with the same α, it sinks to the ocean floor. This means that the minimum size that can reach the storage site is between 0.38 and 0.40 meters diameter for α = 0.5. Figure 6 provides a summary of the numerical simulations, and it suggests that release at 100 meters is possible, because the heat capacity of the cold CO2 slurry mass is large enough to provide transport of coherent units to depth. The existence of a u-turn depth for smaller diameters means that the slurry release technique can also be applied to the dissolution method in the water column if, for instance, this is found to be more environmentally acceptable. 2.3 Proposal of Improved COSMOS Based on the above-mentioned promise of release of a slurry mass of CO2 /dry ice, the authors propose a new technique [7] as shown in Figure 7. In this new technique, CO2 is transported as a slurry in order to keep the pressure of the CO2 tanks as low as possible. The dry ice content (α) at release is adjusted by using the residual power of the main engine of the transport ship that is almost idle while releasing CO2 at sea above the storage site. This new technique, improved COSMOS, in which a release depth of 200 meters is assumed for safety, has the following advantages: (1) CO2 temperature can be kept constant at the triple point (56.6 Celsius) and the tank pressure of carrier can be

Depth (m)

Descending Rate (m/s)

D. Rate

depth

Time (s)

Figure 5: Trajectory of a sinking slurry mass. 0

α=0. 5 -50 0 D=0 .36m

D ep th (m )

-1000 -1500

D= 0.38m

-2000 -2500

D= 0.40m

-3000 D=0 .42m -3500 D=0 .44m -4000 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5

0

5 10 15

T em pe rat ure ( ℃ )

Figure 6: Summary of CO2 slurry trajectory. minimized (0.52 MPa) by transporting CO 2 in the slurry state. (2) The dry ice content, α, can be adjusted to the best value for ocean sequestration by using the residual power of the main engine during CO2 release as shown in Figure 7. (3) The minimumsize of the CO2 slurry to reach the ocean floor below 3500 m depth (0.4 m) is less than half of the original

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CO 2 Carrier Sea Condenser water

COLiquid 2 SlurryCO 2  (-55℃） (-55℃ )

Dry ice Refrigerator content adjuster

Main engine & Compressor Thermal insulator

∼  2 0 0m ー Suspension of Solid and Liquid CO2

Figure 7: Concept of improved COSMOS. COSMOS design. (4) The discharge depth can be reduced to 200 meters, which is shorter than the typical CO2 carrier length, and this results in no complex pipe connections and manipulations at sea. (5) The U-turn depth can be selected arbitrarily by changing α and slurry size (nozzle diameter). Thus this improvement on the original COSMOS design can also be applied to the dissolution method, in which the full depth from ocean floor to the phase change depth (about 400 m) can be utilized for the dissolution pro cess. By this way, the CO2 concentration and pH change around a release site can be significantly minimized. 3. OACE PROJECT 3.1 Background of the Project Nations are committed to finding ways to achieve "stabilization of (atmospheric) greenhouse gas concentrations ... at a level that would prevent dangerous anthropogenic interference with the climate system." Direct deep-ocean disposal of fossil fuel CO 2 is

one of the strategies being considered for realizing this goal. Approximately 30% of the fossil fuel CO2 now released into the atmosphere, or about 20-25 million tons CO 2 per day, is quickly transferred by gas exchange from the atmosphere to the surface ocean. And in the long term some 85% of all CO2 emissions will be transferred to the ocean waters. Thus by-passing the atmospheric release step, with its attendant global warming, and transferring some fraction of CO 2 directly to ocean depths may be regarded simply as a logical extension of current practice. However before any large scale program can be considered serious ocean and environmental science and technology issues must be resolved. Our research project is designed to answer some of these questions as they relate to the physical sciences by using precise observation of small releases; biological issues are dealt with in a parallel project. A sketch of a possible lake of liquid CO 2 , stored on the deep ocean floor, is shown in Figure 8, with critical fluxes to the open ocean and processes of hydrate formation schematically identified.

Figure 8: Image of CO 2 storage at a dented ocean floor.

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Figure 10: RV Western Flyer for Tiburon.

Figure 9: ROV Tiburon for 4000 m depth. 3.2 Outline of the Project Over the last few years NMRI and MBARI have developed the skills to transport several liters CO2 to deeper than 3500m ocean depth, using advanced remotely operated vehicles (ROV) and research vessels (RV) as shown in Figures 9 and 10, respectively , and to release this material in precise amounts for observation and measurement of fundamental properties. We intend to carry out team experiments to measure the lifetime of CO2 , the reaction with seawater and sediments, and properties and distribution of the CO2 enriched plume as the material slowly dissolves. Field experiments, although critical for success, still have limited observing power and can not independently control important variables, such as water flow and temperature. For this we will use a 40 MPa loop facility (Figure 11) and a 60 MPa high pressure large tank (Figure 12) with a controlled flow capability. This will permit careful observation of critical smallscale effects, particularly those involving the reaction of CO2 with seawater to form a solid ice-like hydrate. Numerical modeling of the observed and predicted effects is critical for correct application of theory, and for prediction of patterns beyond the experimental control area. We will combine knowledge of ocean physics with the experimental results to provide important analyses and predictions of the processes at work, and of the resulting plume [8].

Figure 11: 40 MPa loop facility high-pressure at Osaka of NMRI.

Monitoring Monitoring Camera Camera

3.3 Future Directions New instruments and tools will be created to carry out these experiments , including the further development of an in situ spectrophotometric pH sensor [9] to monitor CO2 dissolution from the stored CO2 . The first field experime nt is planed on February 2003 at Monterey Bay. Figure 13 shows the lay out of CO2 dissolution experiment and Figure 14 shows the advanced experiment to clarify the memory effect of hydrate. In Figure 15, we show a fragment from the pH record obtained close to an experimental site at 3600m depth. The tidal signature with 12.4 hour period is clearly seen, with strongly varying pH. We will

3.0 m

Liquid Liquid CO CO22 Injection Injection Tube Tube

Horizontal Horizontal Flow Flow Generator Generator Liquid LiquidCO CO22 With With Hydrate Hydrate on on sediments sediments

Figure 12: 60 MPa large tank at Mitaka of NMRI.

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５００ｍ

Hole Fresh water or Surface seawater (without Hydrate cluster)

Transparent pail (glass, acrylic etc.) 0.35m

Mirror for observation ROV Ventana

０．６ｍ

Metal wire

Transparent holder

Liquid CO2

Plume pH sensors

Seawater (with Hydrate cluster)

(PET bottle, D=0.075)

Check valve

CO2 droplet

ROV-Arm

Seawater holes

Liquid CO2 Line from ROV

0.3m

Buoy Double valve

flow

Aluminum frame 0.2m

Pail

Weight : about 5Kg

Anchor

Figure 13: CO2 dissolution experiment at shallow depth.

Figure 14: Experiment for hydrate memory effect.

create novel sensors based on optical absorption, and Raman spectroscopy, techniques, operating accurately at great ocean depths, to capture this information. The rapid dilution of the signal away from the small experimental source will require very sensitive and rapid response techniques. The interaction of CO 2 with seawater and sediments can be complex. The tidal flows along the ocean floor can create waves on the surface of a liquid CO2 lake, greatly affecting the dissolution rate, and thus the fluid dynamics must be known. The liquid CO2 can convert to a solid hydrate if a critical fluid dynamic instability is initiated. And penetration of liquid CO2 into the sediments will greatly change the experimental outcome. All of these effects are now candidates for study. 4. REQUIRED SIZE OF STORAGE SITE Table 2 shows the comparison of dissolution method and storage method for CO2 ocean sequestration, in the items of sequestration term, reversibility if necessary and difficultness in the evaluation of environmental effects. It is obvious that the storage method is superior in all of these factors. This is the reason why we chose the storage method for our research target. When we consider the realization of storage method, it is a great matter of concern how large site is required. Any type of CO2 ocean sequestration has non-zero effect on the ocean environment. Therefore the ocean seques tration has to be applied to the CO2 that cannot be reduced by the conventional measures such as the energy savings, the utilization of natural energies and the forestation. In case of Japan, the amount of unreduced CO2 by conventional measures is 5 % of the total emission at the most, that is, about 100,000 tons per day. This

Figure 15: An example of field pH records. Authors thank Jim Barry and Chris Lovera of MBARI for preparation of the data. amount requires us the ocean space of 0.0365 km3 every year, considering the specific weight of liquid CO 2 is nearly the same as water. For 50 years, 1.825 km3 of ocean space is required. This space is almost equivalent to the water stored at the Lake Mashuu in Hokkaido of Japan. If the all of CO2 becomes hydrate, this volume increases more than 3.35 times, depending on the hydrate number. The experimental evidence obtained so far suggests that this situation is very unlikely, because the hydrate glows very slowly [10].

Table 2 Comparison of Dissolution Method and Storage Method

Method Dissolution Method Storage Method

Sequestration Term

Reversibility

50 ∼ 300 years

No

> 2000 years

Yes

Evaluation of Ecological Effect 0×∞ Difficult Δ×Δ Possible

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5. CONCLUSIONS The NMRI and MBARI team have conducted four joint in situ CO2 release experiments in Monterey Bay from 1998 to 2002 in order to obtain basic data for the development of a cold CO2 release nozzle, the breakthrough technology required to realize effective disposal of tanker transported liquid CO2 . Both land-based and in situ experiments suggested that simple cold liquid CO2 release, the requirement of the original COSMOS, is theoretically possible but technically not easy, because of Taylor type interface instabilities causing liquid break up. Two in situ experiments confirmed, however, that a slurry release technique was very promising to prevent the breaking up of CO2 into small droplets. This is due to its large heat capacity, which enables a thick ice layer to grow rapidly , thus protecting against boundary instabilities. Based on these experimental results a new technique to release CO2 as a slurry of liquid and solid phases is proposed. The new technique has several advantages , such as reducing the size of the CO2 nozzle diameter to less than one half of the original design. In addition, a shallower release depth of about 200 meters is permitted, which eliminates difficult pipe connections and manipulations at sea, and application to the mid-water dissolution method by controlling the u-turn depth at which the released CO2 will ascend. The remained major concern on the CO 2 ocean storage is the fate of stored CO2 and the ecological effects around the site. Then the new international joint research team OACE was formed and started preparing the field experiments at Monterey Bay from February 2003. In these planned experiments, the scientific data concerning the dissolution rate of CO2, pH distribution around stored CO2 and the interaction between CO2 and sediments on the ocean floor. The effect on the ecosystem is to be evaluated putting together our data and the results obtained from the environmental research group of the MBARI. ACKNOWLEDGEMENT The activities of NMRI and UoB in COSMOS and OACE projects were supported by the International Research Grants from the NEDO (New Energy and Industrial Technology Development Organization). The MBARI support was provided by the David and Lucile Packard Foundation, and by the U.S. Dept. of Energy Ocean Carbon Sequestration Program. The authors wish to express heir sincere gratitude to the all members who have supported above two international joint research programs .

REFERENCES [1] I. Aya, K. Yamane and K. Shiozaki, “ Proposal of Self Sinking CO 2 Sending System: COSMOS,” Greenhouse Gas Control Technologies, Pergamon, Oxford, pp.269-274, 1999. [2] P.G. Brewer, E.D. Peltzer, G. Friederich, I. Aya and K. Yamane, “ Experiments on Ocean Sequestration of Fossil Fuel CO2 : pH Measurements and Hydrate Formation,” Marine Chemistry 72, pp.83-93. 2000. [3] M.N. Tamburri, E.D. Peltzer, G. Friederich, I. Aya, K. Yamane and P.G. Brewer, “A Field Study of the Effect of CO2 Ocean Disposal on Marine Deep-sea Animals,” ibid. 72, pp.95-101, 2000. [4] I. Aya, K. Yamane and H. Nariai, “Solubility of CO2 and Density of CO2 Hydrate at 30 MPa,” Energy 22, 2/3, pp.263271, 1997. [5] B. Kvamme , “Droplets of Dry Ice and Cold Liquid CO2 for Self Transport to Large Depth,” International Journal of Offshore and Polar Engineering, 13(1), pp.1-8, 2003. [6] L.H. Smedsrud, T.M. Saloranta, P.M. Haugan and T. Kangas, “Sea Ice Formation on a Very Cold Surface,” Geophysical Research Letter, pp.1-4, 2002. [7] I. Aya, K. Yamane, K. Shiozaki, P.G. Brewer and E.T. Peltzer, “Proposal of Slurry Type CO2 Sending System to the Ocean Floor, New COSMOS,” In: Proc. Fuel Chemistry Division Reprint 2002, 47(1). 223rd ACS Meeting. 2002. [8] I. Far and P.M. Haugan, “Dissolution from a liquid CO2 lake disposed in the deep ocean,” Limnology and Oceanography 48(2), 2003. [9] R.G.J. Bellerby and T. Johannessen. "Development of a deep water pH sensor for the COSMOS," Proc. Deep sea and CO2 2000, 3.1.1-3.1.3. 2000. [10] R. Kojima, K. Yamane and I. Aya, “Dual Nature of CO2 Solubility in Hydrate Forming Region,” Proc. 6th Int. Conf. on Greenhouse Gas Control Technologies, Kyoto, Japan, 2002.

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