Laboratory Studies

The Goal of our research is to investigate and reduce potential environmental consequences of direct injection

of CO₂ into the ocean. Current technologies for direct CO₂ injections at intermediate ocean depths produce

buoyant CO₂ droplets that can rise, gasify, and be released to the atmosphere (Figure 1). By using a novel

injection technique, we have produced a consolidate stream of CO₂ hydrate that sinks in water at conditions

corresponding to approximately 1200 m depth. Such hydrate streams are expected to disperse less than

CO₂ droplet plumes, and will consequently impact smaller zones in the ocean (Figure 2).

Figure 1. Positively buoyant CO₂ droplets produced by the injection of liquid CO_2.

Figure 2. Stream of CO₂ coming out of the injector.

Coflow Jet Reactor

The coflow jet reactor has been developed and used to extrude a composite paste of liquid CO₂/ water/ CO₂

hydrate in the laboratory. The reactor consists of an outer tube and a concentrically located inner capillary

tube. This design permits spraying of water droplets through the capillary tube into liquid CO₂ that is

continuously pumped in the reactor via the outer tube. The stainless steel capillary tube terminates

approximately 0.14 m from the end of the outer tube, creating a zone in which the liquid CO₂ and water 

vigorously mix, enhancing the production of CO₂ hydrate. The outer tube consists primarily of stainless

steel with a 0.125 m section of Teflon at the end; this construction prevents wetting of the wall by the

water phase in the mixing zone and keeps water finely dispersed in the CO₂ liquid phase. The

composite particles are produced in the mixing zone before being discharged into the ambient water. In

laboratory experiments using the SPS 72 L pressure vessel, water and liquid CO₂ were delivered through

the inner capillary and outer tubes via syringe pumps at predetermined flow rates of 15-25 and 2-10 mL/min,

respectively (West et al., 2003; Lee et al., 2003).

                                                           A.

                                                           B.

Figure 3. A.) Water and  liquid CO₂ are injected through the coflow jet reactor to mix. B.) The mixture forms a hydrate composite as it

is injected into the SPS.  

Field Studies 

The coflow jet reactor was field tested in ocean waters 1100 to1300 m in depth in Monterey Bay, CA in

collaboration with Peter Brewer's group at MBARI. In 2002 and 2004, the ROV Ventana was deployed by the RV

Point Lobos to perform the injections. The injector was mounted in a Plexiglass box (0.3 m wide, 0.25 m deep,

and 0.91 m high) that was open at the top and bottom and had an illuminated translucent rear panel. The box

allowed the injected composite particles to rise or fall freely based on their buoyancy but restricted lateral motion,

thus easing the vehicle piloting requirements. The illuminated rear wall of the box served to back light the particles

and also to screen out visual clutter from the ubiquitous midwater animals and marine snow. Carbon dioxide and

ambient seawater were pumped via a piston assembly. Volumetric flow meters were installed to measure the flow

rates of the fluids as they were introduced into the coflow jet reactor and were arranged so that they were

viewable with the primary HDTV camera system. In 2002, injections were performed using different volumetric

ratios of CO₂ to water and at different depths. The size and velocity of the resultant particles were determined

using the ROV, which traveled vertically to follow one randomly selected particle for each injection experiment

through the water column and recorded the particle using a HDTV camera as described previously. Selected video

frames in which the particle appeared to be oriented parallel to the frontPlexiglass plane were processed post

cruise, using image analysis software to determine the dimensions of the particle. The seawater depth,

temperature, density, and pressure were logged using the instrumentation suite installed on the ROV, and

recorded in time sequence throughout the experiment from the production of the composite particles through their

dissolution. These data were then used to estimate particle velocity, density, and dissolution rate. In the 2002

injections, particles were found to be floating to neutral. 

Figure 4. Schematics showing coflow jet reactor, syringe pumps, and flow meters used for ocean injections of composite particles performed

at 1000-1300m ocean depth on the ROV Ventana. The Plexiglass was  open at the top and bottom, allowing the composite to freely rise or

sink after injection.

In 2004, a larger injection was used along with higher CO₂and water flow rates to increase mixing. The experiments

were focused on the laser Raman spectroscopy of the composite, on scaling up the coflow injector, and producing

a rapidly sinking composite. Injections were conducted at intermediate depths using the remotely operated vehicle

(ROV) Ventana (Figure 5b). For the Raman experiments, the Deep-Ocean Raman In Situ Spectrometer (DORISS)

system was employed. The DORISS system allows for rapid determination of the composition and CO₂ phase of

the composite directly after formation at depth. Composite was produced at 1200--1600 meters using the coflow

injector and collected in a basket where it was excited by the Raman laser (Figure 5a). On the ship, the scans

were collected and are currently being analyzed at MBARI. (Note the sinking nature of the composite in the figure).

The scale-up sinking composite experiments were conducted using a larger injector than the one used in the

laboratory. It was expected that the larger injector would allow for higher flow rates of the two fluids, which would

result in better mixing and more hydrate formation. The resulting particles would be sink rapidly due to more

hydrate, and be larger in diameter to slow the CO₂ dissolution. The larger coflow injector was placed in a

plexiglass box that was open at the top and bottom (Figure 5c). After injection, the box allowed the particles to

float or sink freely in the water column, and the ROV was moved vertically to follow the particles. A 50% larger

water capillary was used and flow rates of CO₂ and water were roughly six times higher than in the laboratory

injections. The resulting composite produced sank at a rate of about 3 meters per minute, suggesting 20-30%

of the CO₂ was converted to hydrate. One particle was followed by the ROV for over 40 meters as it sank.   

A.) B.) C.)

Figure 5. A.) Raman Laser exciting hydrate at 1250m. B.) The ROV Ventana being lowered into Monterey Bay, CA. C.) Bubble Box used to

track the fate of injected particles attached to ROV arm.  

Joint Experiments with the National Energy Technology Laboratory (NETL)

One of the challenges of laboratory pressure vessel experiments is the need to measure the sinking and dissolution

rates of particles after injection. The high-pressure water tunnel facility (HWTF) developed by Robert Warzinski and

Ron Lynn at NETL (Figure 1) provides a system where sinking composite particles can be injected at high

pressure and their fate may be tracked over time using controlled counter-flow of water to keep them stationary. A

series of injections were conducted at pressures equivalent to ocean depths of 1200, 1500, and 1800 meters at

temperatures of 3-5 °C. At each depth, sinking particles of varying densities were produced by changing the CO₂

and water injection flow rates. Immediately after injection, the cylindrical particles were observed to break off of the

injector tip and aggregate into sinking clumps (Figure 2). The water flow in the tunnel was then adjusted to

suspend the particles, and images of the particles were continuously recorded for later analysis.

After several minutes, the clumps were observed to break up into discrete particles, and selected particles were

studied until they became too unstable to follow (Figure 3). In general, particles sank more rapidly just after

injection and then became progressively less dense and sank more slowly as they shrank in size. Analysis of

the sinking rate and particle volume change (to calculate the dissolution rate) of several particles is currently

being conducted. Future planned collaborations between ORNL and NETL ocean carbon sequestration

researchers using the HWFT will include injector scale-up studies.

.

Figure 1. The NETL high-pressure water tunnel facility. Figure 2. CO₂ hydrate particles produced in the NETL high-pressure water tunnel facility.   

Figure 3. A sinking CO₂ hydrate particle suspended by counter flow.

Ongoing Research in Ocean Sequestration

Future Research aims to take hydrate ocean sequestration technology aims to expand laboratory-scale CO2

hydrate injection to a technology useable for large-scale ocean carbon sequestration.  Larger injectors have been

designed and will be tested in the future.  These injectors will increase the amount of CO2 that can be sequestered.

A.) Dual Injector    B.) 2 inch Injector    C.) Water Dispersed    D.) CO₂ Dispersed    E.) Underwater Sequestration Device

Recent Publications

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