Capturing carbon dioxide from the atmosphere ("air capture") in an industrial process has been proposed as an option for stabilizing global CO2 concentrations. Published analyses suggest these air ...capture systems may cost a few hundred dollars per tonne of CO2, making it cost competitive with mainstream CO2 mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO2 emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO2, requiring it to be powered by CO2-neutral power sources in order to be CO2 negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of CO2, based on experience with as-built large-scale trace gas removal systems.
Capturing carbon dioxide from the atmosphere ("air capture") in an industrial process has been proposed as an option for stabilizing global CO2 concentrations. Published analyses suggest these air ...capture systems may cost a few hundred dollars per tonne of CO2, making it cost competitive with mainstream CO2 mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO2 emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO2, requiring it to be powered by CO2-neutral power sources in order to be CO2 negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of CO2, based on experience with as-built large-scale trace gas removal systems.
Permanent Carbon Dioxide Storage in Deep-Sea Sediments House, Kurt Zenz; Schrag, Daniel P.; Harvey, Charles F. ...
Proceedings of the National Academy of Sciences - PNAS,
08/2006, Letnik:
103, Številka:
33
Journal Article
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Stabilizing the concentration of atmospheric CO₂ may require storing enormous quantities of captured anthropogenic CO₂ in near-permanent geologic reservoirs. Because of the subsurface temperature ...profile of terrestrial storage sites, CO₂ stored in these reservoirs is buoyant. As a result, a portion of the injected CO₂ can escape if the reservoir is not appropriately sealed. We show that injecting CO₂ into deep-sea sediments >3,000-m water depth and a few hundred meters of sediment provides permanent geologic storage even with large geomechanical perturbations. At the high pressures and low temperatures common in deep-sea sediments, CO₂ resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO₂ to be gravitationally stable. Additionally, CO₂ hydrate formation will impede the flow of CO₂(l) and serve as a second cap on the system. The evolution of the CO₂ plume is described qualitatively from the injection to the formation of CO₂ hydrates and finally to the dilution of the CO₂(aq) solution by diffusion. If calcareous sediments are chosen, then the dissolution of carbonate host rock by the CO₂(aq) solution will slightly increase porosity, which may cause large increases in permeability. Karst formation, however, is unlikely because total dissolution is limited to only a few percent of the rock volume. The total CO₂ storage capacity within the 200-mile economic zone of the U.S. coastline is enormous, capable of storing thousands of years of current U.S. CO₂ emissions.
We describe an approach to CO2 capture and storage from the atmosphere that involves enhancing the solubility of CO2 in the ocean by a process equivalent to the natural silicate weathering reaction. ...HCl is electrochemically removed from the ocean and neutralized through reaction with silicate rocks. The increase in ocean alkalinity resulting from the removal of HCl causes atmospheric CO2 to dissolve into the ocean where it will be stored primarily as HCO3 − without further acidifying the ocean. On timescales of hundreds of years or longer, some of the additional alkalinity will likely lead to precipitation or enhanced preservation of CaCO3, resulting in the permanent storage of the associated carbon, and the return of an equal amount of carbon to the atmosphere. Whereas the natural silicate weathering process is effected primarily by carbonic acid, the engineered process accelerates the weathering kinetics to industrial rates by replacing this weak acid with HCl. In the thermodynamic limit—and with the appropriate silicate rocks—the overall reaction is spontaneous. A range of efficiency scenarios indicates that the process should require 100–400 kJ of work per mol of CO2 captured and stored for relevant timescales. The process can be powered from stranded energy sources too remote to be useful for the direct needs of population centers. It may also be useful on a regional scale for protection of coral reefs from further ocean acidification. Application of this technology may involve neutralizing the alkaline solution that is coproduced with HCl with CO2 from a point source or from the atmosphere prior to being returned to the ocean.
Injecting liquid CO2 into deep‐sea sediments below ca. 3 km of seawater has been suggested for the permanent storage of anthropogenic CO2. At the pressures and temperature found below 3 km of ...seawater, CO2 becomes denser than seawater and so is likely to remain permanently sequestered in the sediment. Deepwater engineering, however, is expensive and seawater depths of greater than 3 km are often only reached far from shore. Here, we consider the less expensive alternative of injecting CO2 into marine sediments at depths shallower than required for denser‐than‐seawater CO2 storage. We compare the mobility of liquid CO2 that has been injected into deep‐sea reservoirs with the mobility of supercritical CO2 that has been injected into geologically equivalent (i.e., identical porosity, permeability, and effective stress) reservoirs with terrestrial pressure and temperature conditions. We demonstrate that buoyant liquid CO2 with a density of about 90 % that of seawater is sufficiently immobile that it can be considered trapped by gravity and capillarity. In contrast, supercritical CO2 under typical terrestrial conditions is highly mobile and only trapped by the appropriate confining layer in either a structural or stratigraphic trap. As a result of its very high mobility under terrestrial conditions, CO2 injected in an unconfined formation would spread beneath the confining layer to produce a large flat cylindrical‐shaped plume of pure‐phase CO2. In contrast, the less mobile CO2 in a typical deep‐sea reservoir produces a spherical‐shaped plume, resulting in a pure‐phase‐CO2 footprint that is much smaller than the pure‐phase‐CO2 footprint formed in the confined‐terrestrial reservoir.
Injecting liquid CO2 into deep‐sea sediments below ca. 3 km of seawater has been suggested for the permanent storage of anthropogenic CO2. It is demonstrated that buoyant liquid CO2 with a density of about 90 % that of seawater is sufficiently immobile that it can be considered trapped by gravity and capillarity.
A review of the literature has found a factor of 4 spread in the estimated values of the energy penalty for post-combustion capture and storage of CO from pulverized-coal (PC) fired power plants. We ...elucidate the cause of that spread by deriving an analytic relationship for the energy penalty from thermodynamic principles and by identifying which variables are most difficult to constrain. We define the energy penalty for CCS to be the fraction of fuel that must be dedicated to CCS for a fixed quantity of work output. That penalty can manifest itself as either the additional fuel required to maintain a power plant's output or the loss of output for a constant fuel input. Of the 17 parameters that constitute the energy penalty, only the fraction of available waste heat that is recovered for use and the 2nd-law separation efficiency are poorly constrained. We provide an absolute lower bound for the energy penalty of similar11%, and we demonstrate to what degree increasing the fraction of available-waste-heat recovery can reduce the energy penalty from the higher values reported. It is further argued that an energy penalty of similar40% will be easily achieved while one of similar29% represents a decent target value. Furthermore, we analyze the distribution of PC plants in the U.S. and calculate a distribution for the additional fuel required to operate all these plants with CO capture and storage (CCS).
Capturing carbon dioxide from the atmosphere ("air capture") in an industrial process has been proposed as an option for stabilizing global ... concentrations. Published analyses suggest these air ...capture systems may cost a few hundred dollars per tonne of ..., making it cost competitive with mainstream ... mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large ... emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing ... from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of ..., requiring it to be powered by ...-neutral power sources in order to be ... negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of ..., based on experience with as-built large-scale trace gas removal systems. (ProQuest: ... denotes formulae/symbols omitted.)
Capturing carbon dioxide from the atmosphere (“air capture”) in an industrial process has been proposed as an option for stabilizing global CO
2
concentrations. Published analyses suggest these air ...capture systems may cost a few hundred dollars per tonne of CO
2
, making it cost competitive with mainstream CO
2
mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO
2
emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO
2
from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO
2
, requiring it to be powered by CO
2
-neutral power sources in order to be CO
2
negative. We estimate that total system costs of an air capture system will be on the order of $1,000 per tonne of CO
2
, based on experience with as-built large-scale trace gas removal systems.
Abstract
Injecting liquid CO
2
into deep‐sea sediments below ca. 3 km of seawater has been suggested for the permanent storage of anthropogenic CO
2
. At the pressures and temperature found below 3 ...km of seawater, CO
2
becomes denser than seawater and so is likely to remain permanently sequestered in the sediment. Deepwater engineering, however, is expensive and seawater depths of greater than 3 km are often only reached far from shore. Here, we consider the less expensive alternative of injecting CO
2
into marine sediments at depths shallower than required for denser‐than‐seawater CO
2
storage. We compare the mobility of liquid CO
2
that has been injected into deep‐sea reservoirs with the mobility of supercritical CO
2
that has been injected into geologically equivalent (i.e., identical porosity, permeability, and effective stress) reservoirs with terrestrial pressure and temperature conditions. We demonstrate that buoyant liquid CO
2
with a density of about 90 % that of seawater is sufficiently immobile that it can be considered trapped by gravity and capillarity. In contrast, supercritical CO
2
under typical terrestrial conditions is highly mobile and only trapped by the appropriate confining layer in either a structural or stratigraphic trap. As a result of its very high mobility under terrestrial conditions, CO
2
injected in an unconfined formation would spread beneath the confining layer to produce a large flat cylindrical‐shaped plume of pure‐phase CO
2
. In contrast, the less mobile CO
2
in a typical deep‐sea reservoir produces a spherical‐shaped plume, resulting in a pure‐phase‐CO
2
footprint that is much smaller than the pure‐phase‐CO
2
footprint formed in the confined‐terrestrial reservoir.
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