Refrigeration – Storage of solidified or liquified gas – Underground or underwater storage
Reexamination Certificate
2001-10-16
2003-07-29
Capossela, Ronald (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Underground or underwater storage
C588S250000
Reexamination Certificate
active
06598407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods for direct injection of CO
2
into the ocean for carbon sequestration. More particularly, it relates to the production of a negatively buoyant CO
2
hydrate in the form of a consolidated CO
2
-hydrate/CO
2
-liquid/water stream that sinks upon release at intermediate ocean depths of about 1000 m.
2. Background Information
The concentration of carbon dioxide (CO
2
) in the atmosphere is steadily increasing as a result of both land use changes and the combustion of fossil fuels for energy production. Due to the enhanced greenhouse effect caused by increasing concentrations of CO
2
and other greenhouse gases in the atmosphere (e.g., methane), it is predicted that greater amounts of heat will be retained within the atmosphere leading to a gradual increase in the surface temperature of the earth. Reducing the potential risks of human-induced global climate change will require that means be found to slow the rate of increase in atmospheric CO
2
levels. One of the strategies is to capture and sequester CO
2
by enhancing the natural capacity of the terrestrial biosphere and the oceans to take up and store carbon.
Direct injection of CO
2
into the ocean has been proposed as a means for carbon sequestration because it offers a large storage capacity for carbon (Herzog 1998). Depending on the depth of injection as well as the subsequent interaction of CO
2
with seawater, the residence time of CO
2
in the ocean can be on the order of several hundred years, leading to significantly reduced rates of atmospheric CO
2
increase as well as lower peak levels. The thermodynamic properties of CO
2
and seawater, in combination with ambient pressure and emplacement methodology, will strongly influence the form and subsequent fate of CO
2
that is injected into the ocean. For example, at depths less than ~500 m, CO
2
will be a gas and will therefore be more likely to partition back into the atmosphere within decades to centuries. At depths between ~500 and ~2600 m, the density of liquid CO
2
is lower than that of seawater. At greater depths, liquid CO
2
is denser than the surrounding seawater. Thus, CO
2
injected at depths between 500 and 2600 m will be in liquid form and will tend to rise (i.e., be positively buoyant), while CO
2
released at depths >2600 m will sink (i.e., be negatively buoyant).
Direct ocean CO
2
injection will be considered successful if the following conditions are met: the residence time of CO
2
released in the ocean is on the order of several centuries or more; negligible environmental impacts are associated with the release; the energy requirement for the ocean emplacement is small relative to that obtained from CO
2
generation; and the process is cost-effective.
Several methods for direct CO
2
injection have been suggested. These include: (1) injection at moderate depths of 1000-2000 m through a fixed or towed pipe resulting in a rising liquid CO
2
droplet plume; (2) injections into ocean floor depressions at depths >2600 m forming a CO
2
lake; (3) disposal as dry ice; and (4) shallow discharge as a dense solution of seawater with dissolved CO
2
forming a dense sinking liquid plume. These and other methods are reviewed in the recent papers of Caulfield (1997) and Herzog (1998).
Because emplacement costs increase significantly with injection depth, the lowest cost is anticipated for the dense-plume approach (alternative 4), which requires injection depths between 500 and 1000 m. However, the low cost of implementation for this approach may be offset by the negative environmental impact on the marine ecosystem that would result from a highly concentrated CO
2
composition and low pH in the vicinity of the sinking dense plume. Injection at depths >1000 m is therefore believed to have lesser environmental impacts and lower rates of release to the atmosphere. A high cost is associated with the CO
2
-lake disposal (alternative 2) because of the need for special pipelines that can withstand hydrostatic pressures at the required injection depth (>2600 m) where CO
2
becomes denser than seawater. Dry ice (alternative 3) can be discharged at shallow depths, however, its production and handling cost can be very high.
When compared to the other disposal alternatives, droplet plume disposal at injection depths of 1000-2000 m (Alternative 1) appears to be the most favorable when factors such as development cost, difficulty and environmental impacts are considered. As CO
2
is only slightly miscible with seawater, the CO
2
-seawater system is hydrodynamically unstable, and liquid CO
2
discharged into seawater will break up into droplets due to interfacial instability. The droplets will rise because injection depths are shallower than the ~2600-m required for CO
2
to be negatively buoyant in seawater. To ensure that the rising CO
2
droplets completely dissolve into the seawater before it reaches depths where CO
2
becomes gaseous (~500 m), sufficient injection depth (>1500 m) is required.
The preceding review of current research shows that the positive buoyancy of CO
2
droplets has a negative impact on the long-term environmental success of liquid CO
2
injections at intermediate depths. In addition, although CO
2
is in liquid state at depths >500 m, injections must be performed at depths greater than 1500 m to ensure that rising CO
2
drops dissolve completely before reaching the critical 500-m depth threshold.
Our invention is a CO
2
injection method based on the production of a new CO
2
injection form, comprising of a consolidated CO
2
-liquid/CO
2
-hydrate/water paste-like stream, that sinks at shallower depths than other CO
2
forms. To date, no studies discussing generation of a negatively buoyant CO
2
-liquid/CO
2
-hydrate/water consolidated stream for ocean sequestration have been reported. The result is the achievement of cost savings without the negative environmental impact of other shallow depth injection methods.
REFERENCES
1. J. A. Caulfield, D. I. Auerbach, E. E. Adams and H. J. Herzog, “Near Field Impacts of reduced pH from Ocean CO
2
Disposal”,
Energy Convers. Mgmt
. Vol. 38, pp. S343-348 (1997).
2. H. J. Herzog, “Ocean Sequestration of CO
2
— An Overview”, Fourth International Conference on Greenhouse Gas Control Technologies, Interlaken, Switzerland, pp. 1-7, Aug. 30-Sep. 2, 1998.
3. J. J. Morgan, V. R. Blackwell, D. E. Johnson, D. F. Spencer and W. J. North, “Hydrate Formation from Gaseous CO
2
and Water”,
Environ. Sci. Technol
. Vol. 33, pp. 1448-1452 (1999).
4. S. Hirai, Y. Tabe, G. Tanaka and K. Okazaki, “Advanced CO
2
Ocean Dissolution Technology for Longer Term Sequestration with Minimum Biological Impacts”,
Greenhouse Gas Control Technologies
, P. Riemer, B. Eliasson and A. Wokaun, editors, Elsevier Science, Ltd., pp. 317-322 (1999).
5. A. Yamasaki, M. Wakatsuki, H. Teng, Y. Yanagisawa and K. Yamada, “A New Ocean Disposal Scenario for Anthropogenic CO
2
: CO
2
Hydrate Formation in a Submerged Crystallizer and its Disposal”, Energy Vol. 25, pp. 86-96 (2000).
6. T. J. Phelps, D. J. Peters, S. L. Marshall, O. R. West, L. Liang, J. G. Blencoe, V. Alexiades, G. K. Jacobs, M. T. Naney and J. L. Heck, Jr., “A New Experimental Facility for Investigating the formation and Properties of Gas Hydrates under Simulated Seafloor Conditions”,
Rev. Sci. Instrum
. Vol. 72, No. 2, pp. 1514-1521 (2001).
OBJECTS OF THE INVENTION
It is a first object of the invention to provide a consolidated CO
2
-hydrate/CO
2
-liquid/water stream that sinks upon release at intermediate ocean depths of about 1000 m.
Another object of the invention is to reduce pressurization of CO
2
liquid for ocean injection by providing a negatively buoyant CO
2
stream for injection at shallower depths.
Another object of the invention is to provide a CO
2
injection form having a longer residence time in the ocean.
A further object of the invention is to dissolve CO
2
slowly, imposing minimal environmental impact.
A still further object of the invention is to provide efficient
Liang Liyuan
Tsouris Constantinos
West Olivia R.
Capossela Ronald
Spicer James M.
UT-Battelle LLC
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