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Chapter 6: Capturing and Sequestering Carbon Dioxide
Energy supply technologies incorporating carbon capture and storage were found capable of contributing significantly to future near-zero or very low emissions energy supply. When combined with other sequestration technologies capable of capturing CO2from the atmosphere, reduced, avoided, or sequestered global carbon emissions, compared to a reference case, and depending upon assumptions, ranged from low amounts up to nearly 300 gigatons of carbon (GtC) over the course of the 21st century. Although bracketed by a number of uncertainties, this range suggests both the potential role for advanced technology and a long-term goal for contributions from this area in the future global economy. The three main focus areas for R&D related to carbon cycle management include: (1) the capture of CO2emissions from large point sources, such as coal-based power plants, oil refineries, and industrial processes, coupled with storage in geologic formations or other storage media; (2) enhanced carbon uptake and storage by terrestrial biotic systems�terrestrial sequestration; and (3) improved understanding of the potential for ocean storage and sequestration methodologies. [1] If current world energy production and consumption patterns persist into the foreseeable future, fossil fuels will remain the mainstay of global energy production well into the 21st century. The Energy Information Administration (EIA) projects that by 2025, about 88 percent of global energy demand will be met by fossil fuels, because fossil fuels will likely continue to yield competitive advantages relative to other alternatives (EIA 2004a). In the United States, the use of fossil fuels in the electric power industry accounted for 39 percent of total energy-related CO2emissions in 2003, and this share is expected to slightly increase to 41 percent in 2025. In 2025, coal is projected to account for 50 percent of U.S. electricity generation and for an estimated 81 percent of electricity-generated CO2emissions. Natural gas is projected to account for 24 percent of electricity generation and about 15 percent of electricity-related CO2emissions in 2025 (EIA 2005). Many scenarios of the future suggest that world coal markets will continue to grow steadily over the course of the 21st century, in the absence of CO2emissions restrictions. While increased energy efficiency, and use of renewable and nuclear energy afford good opportunities for reducing CO2emissions, fossil fuel reserves are abundant and economical, making their continued use an attractive option. In various advanced technology scenarios where CO2capture and storage technology were assumed to become a cost-competitive technology strategy, fossil-based energy continued to supply a large portion of total electricity consumed into the future (e.g., various studies estimated a 55-70 percent share), even under high carbon management requirements. Human activities related to land conversion and agricultural practices have also contributed to the buildup of carbon dioxide to the atmosphere. During the past 150 years, land use and land-use changes were responsible for one-third of all human emissions of CO2(IPCC 2000). Over the next 100 years, global land-use change and deforestation are likely to account for at least 10 percent of overall human-caused CO2emissions. The dominant drivers of current and past land-use-related emissions of CO2are the conversion of forest and grassland to crop and pastureland and the depletion of soil carbon through agricultural and other land-management practices (IPCC 2000). Past CO2emissions from land-use activities are potentially reversible, and improved land-management practices can actually restore depleted carbon stocks. Therefore, there are potentially large opportunities to increase terrestrial carbon sequestration. The potential storage and sequestration capacity for CO2in various "sinks" is large. Some estimates indicate that about 83 to 131 gigatons of carbon (GtC) could be sequestered in forests and agricultural soils by 2050 (IPCC 2001b), while others estimate geologic storage capacities within a broad range of 300 to 3,200 GtC (IEA 1994a, 1994b, 2000). The ocean represents the largest potential sink for anthropogenic CO2. Analysis indicates that the ocean is currently absorbing passively some 7.3 Gt of excess atmospheric CO2per year (Sabine et al. 2004), partially offsetting the impact on atmospheric concentrations of CO2from annual anthropogenic emissions of CO2of about 25 Gt per year. The potential storage capacity of the ocean is largely unknown, although some researchers estimate that it might hold thousands of GtC or greater (Herzog 2001, Smith and Sandwell 1997, Hoffert et al. 2002). There are potential ancillary benefits associated with carbon capture, storage, and sequestration. Many land-management practices that sequester carbon can improve water quality, reduce soil erosion, and benefit wildlife. The injection of CO2into geologic structures can be beneficially used to enhance recovery of oil from depleted oil reservoirs and the recovery of methane from unmineable coal seams. Carbon capture, storage, and sequestration technologies have become a high-priority R&D focus under CCTP because they hold the potential to reduce CO2emissions from point sources, as well as from the atmosphere, and to enable continued use of coal and other fossil fuels well into the future. Near-term R&D opportunities include optimizing carbon sequestration and management technologies and practices in terrestrial systems, and accelerating the development of technologies for capturing and geologically storing CO2for enhanced oil recovery (EOR). Longer-term R&D opportunities include further development of other types of geologic storage and terrestrial sequestration options, as well as furthering the understanding of both the role oceans might play in storing carbon and the potential consequences of using the oceans for carbon sequestration. In 2005, the Intergovernmental Panel on Climate Change (IPCC) released its Special Report on Carbon Dioxide Capture and Storage (IPCC 2005). While this report is not focused on future R&D options, it serves as an authoritative reference on the state-of-the-art methods in CO2capture and storage. The remaining sections in this chapter summarize the current and potential future research activities and challenges associated with developing carbon sequestration technology. In each section, the description of the current R&D activities includes a hyperlink to the CCTP report, Technology Options in the Near and Long Term (CCTP 2005). 6.1 Carbon CapturePoint source CO2emissions from power plants vary depending on the combustion fuel, technology, and operational use. Concentrating and capturing CO2from flue gas is a technological challenge. Flue gas from conventional coal-fired power plants contains 10 to 12 percent of CO2by volume, and flue gas from integrated gasification combined cycle (IGCC) plants contains between 5 and 15 percent CO2. For a combined cycle gas turbine system, the CO2concentration is about 3 percent. The CO2in flue gases must be concentrated to greater than 90 percent for most storage, conversion, or reuse applications. Thus, R&D programs are targeted at capture systems that can produce a concentrated and pressurized stream of CO2at relatively low cost.Potential Role of TechnologyLarge CO2point sources, such as power plants, oil refineries, cement plants, and other industrial facilities are considered the most viable sites for CO2capture. The current technology for CO2capture uses a class of chemical absorbents called amines that remove CO2from the gas stream and produce byproduct food-grade CO2often used in carbonated soft drinks and other foods. However, the current absorbent process is costly and energy intensive, increasing the cost of a coal-fired plant by 50 to 80 percent (Davison et al. 2001) and energy reductions on the order of 30 percent of the net power generation rate (DOE 1999). Thus, several R&D opportunities are being pursued to reduce CO2capture costs and lessen the energy reductions in power generation, or the "net energy penalty."Technology StrategyRealizing the possibilities for point source CO2capture employs a research portfolio that covers a wide range of technology areas, including post-combustion capture, oxy-fuel combustion, and pre-combustion decarbonization. R&D investments in technologies that use pure oxygen during combustion, pre-combustion de-carbonization technologies, regenerable sorbents, advanced membranes, and hydrate formation can potentially reduce costs, as well as the net energy penalty. After component performance evaluations are completed, the next short-term step would be to conduct pilot scale and slip stream (i.e., diversion of a small stream from the total emissions of an existing plant) level testing of the most promising capture technologies. Larger or full-scale tests might be appropriate within the next few decades to demonstrate and have a suite of capture technologies available for deployment. Fully integrated capture and storage system demonstration (i.e., FutureGen) helps to enable commercial deployment to mitigate the financial and technical performance risks associated with any new technology that must maintain a high availability, such as required by the power generation sector.Current PortfolioThe metrics and goals for CO2capture research are focused on reducing the cost and energy penalty, because analysis shows that CO2capture drives the cost of sequestration systems. Similarly, the goals and metrics for carbon storage, measurement, and monitoring are focused on ensuring permanence and safety. All three research areas work toward the overarching program goal of 90 percent CO2capture, with 99 percent storage permanence at less than 20 percent increase in the cost of energy services by 2007, and less than 10 percent by 2012. A large-scale demonstration (i.e., FutureGen) would still be necessary.Across the current Federal portfolio, agency activities are focused on a wide range of technical issues. [2]
Future Research DirectionsThe current portfolio supports the main components of the technology development strategy and addresses the highest priority current investment opportunities in this technology area. For the future, CCTP seeks to consider a full array of promising technology options. From diverse sources, suggestions for future research have come to CCTP's attention. Some of these, and others, are currently being explored and under consideration for the future R&D portfolio. These include:
6.2 Geologic StorageDifferent types of geologic formations can store CO2, including depleted oil reservoirs, depleted gas reservoirs, unmineable coal seams, saline formations, shale formations with high organic content, and others. Such formations have provided natural storage for crude oil, natural gas, brine, and CO2over millions of years. Each type of formation has its own mechanism for storing CO2and a resultant set of research priorities and opportunities. Many power plants and other large point sources of CO2emissions are located near geologic formations that are amenable to CO2storage. For example, DOE, along with private and public sector partners, is conducting research on the suitability of geologic formations at the Mountaineer Plant in West Virginia.Potential Role of TechnologyGeologic formations offer an attractive option for carbon storage. The formations are found throughout the United States, and there is extensive knowledge about many of them from the experience of exploration and operation of oil and gas production (Box 6-4). Opportunities exist in the near-term to combine CO2storage with EOR and enhanced coal-bed methane (ECBM) recovery using injected CO2. In 2000, 34 million tons of CO2, roughly equivalent to annual emissions from 6 million cars, were injected as part of EOR activities in the United States.Coal-bed methane has been one of the fastest growing sources of domestic natural gas supply. Pilot projects have demonstrated the value of CO2ECBM recovery as a way to increase production of this resource. In the long-term, CO2storage in saline and depleted gas formations is being explored. One project is currently in commercial operation, where one million tons of CO2per year are being injected in a saline formation at the Sleipner natural gas production field in the North Sea. The Frio Brine Pilot experiment near Houston, Texas, is the first U.S. field test to investigate the ability of saline formations to store greenhouse gases (GHGs). In October 2004, 1,600 tons of CO2were injected into a mile-deep well. Extensive methods were used to characterize the formation and monitor the movement of the CO2. The site is representative of a very large volume of the subsurface from coastal Alabama to Mexico and will provide experience useful in planning CO2storage in high-permeability sediments worldwide. The overall estimated capacity of geologic formations appears to be large enough to store decades to centuries worth of CO2emissions, although the CO2storage potential of geologic reservoirs depends on many factors that are, as yet, poorly understood. For example, characteristics of reservoir integrity, volume, porosity, permeability, and pressure vary widely even within the same reservoir, making it difficult to establish a reservoir's storage potential with certainty. Assessments of storage capacity could help to better understand the potential of geologic formations for CO2storage.
Technology StrategyPotential CO2sources and sinks vary widely across the United States, and the challenge is to understand the economic, health, safety, and environmental implications of potential large-scale geologic storage projects. The geologic storage program was initiated in 1997 and initially focused on smaller projects. However, field testing is the next step to verify the results of smaller-scale R&D, and the program is taking on larger projects, as knowledge grows and opportunities become available.In the near-term, activities will focus on addressing important carbon storage-related issues consistent with the Carbon Sequestration Technology Roadmap and Program Plan (DOE 2005). Among these activities are developing an understanding of the behavior of CO2when stored in geologic formations. Long-term activities could include understanding and reducing potential health, safety, environmental, and economic risks associated with geologic sequestration. Regional domestic partnerships and international cooperation are viewed as key to deploying carbon storage technologies. Field validation activities test the large-scale viability of point-source capture and storage systems and demonstrate to interested parties the potential of these systems. Current PortfolioThe goal of geologic storage R&D portfolio is to advance technologies that would enable development of domestic CO2underground storage repositories capable of accepting around one billion tons of CO2per year. Toward this goal, there is a need to demonstrate that CO2storage underground is safe and environmentally acceptable, and an acceptable GHG mitigation approach. Another need is to demonstrate an effective business model for CO2EOR and ECBM, where significantly more CO2is stored for the long-term than under current practices.The Federal portfolio for geologic storage activities includes several major thrusts designed to move technologies from early R&D to deployment. [3] Core RD&D focuses on understanding the behavior of CO2when stored in geologic formations. For example, studies are being conducted to determine the extent to which CO2moves within the geologic formation, and what physical and chemical changes occur to the formation when CO2is injected. This information is needed to ensure that CO2storage will not impair the geologic integrity of an underground formation and that CO2storage is secure and environmentally acceptable. There are three major research thrusts:
Two activities cited in Section cited in Section 6.1.3 will continue to play an important role in encouraging the deployment of technologies developed under the core RD&D program. The Regional Partnerships Program [5] is building a nationwide network of Federal, State, and private sector partnerships to determine the most suitable technologies, regulations, and infrastructure for future point source carbon capture, storage, and geologic sequestration in different areas of the country. The Carbon Sequestration Leadership Forum is facilitating the development and worldwide deployment of technologies for separation, capture, transportation, and long-term storage of CO2. In addition, the FutureGen project (Box 6-5) is expected to be the world's first coal-fueled prototype power plant that will incorporate geological storage. It will provide a way to demonstrate some of the key technologies developed with Federal support, and demonstrate to the public and regulators the viability of large-scale carbon storage. Future Research DirectionsThe current portfolio supports the main components of the technology development strategy and addresses the highest priority current investment opportunities in this technology area. For the future, CCTP seeks to consider a full array of promising technology options. From diverse sources, suggestions for future research have come to CCTP's attention. Some of these, and others, are currently being explored and under consideration for the future R&D portfolio. These include:
In the long-term, CO2capture can be integrated with geologic storage and/or conversion. Many CO2conversion reactions are attractive, but too slow for economic chemical processes. Use of impurities in captured CO2(e.g., SOX and NOX) or additives could possibly enhance geologic storage and provide an opportunity to combine CO2emissions reduction with criteria pollutant emissions reduction. Field tests are the next step to verify R&D results. It is possible that additional tests will eventually be carried out through the Regional Partnerships Program based on analysis of CO2sources and sinks by participants to determine the highest benefit projects. 6.3 Terrestrial SequestrationTerrestrial sequestration can play a significant role in addressing the increase of CO2in the atmosphere. A wide range of technologies and practices, including tree planting, forest management, and conservation tillage practices are available to increase the sequestration of carbon in plants and soils. Terrestrial sequestration activities can provide a positive force for improving landscape-level land management and provide significant additional benefits to society, such as improvements in wildlife and fisheries habitat, enhanced soil productivity, reduction in soil erosion, and improved water quality. Terrestrial sequestration represents a set of technically and commercially viable technologies that have the capability to reduce the rate of CO2increase in the atmosphere. Given the size and productivity of the U.S. land base, terrestrial sequestration has distinct economic and environmental advantages. Globally, the potential for terrestrial sequestration is also significant, due in part to low-cost opportunities to reduce ongoing emissions from current land-use practices and land conversion and to enhance carbon stocks via afforestation, forest restoration, and improved forest and agricultural management.Terrestrial sequestration technologies refer broadly to equipment, processes, decision tools, management systems and practices, and techniques that can enhance carbon stocks in soils, biomass, and wood products, while reducing CO2concentrations in the atmosphere. Extensions of terrestrial sequestration can use sustainably generated biomass to displace fossil fuels. Examples of terrestrial sequestration technologies include conservation tillage, conservation set-asides, cover crops, buffer strips, biomass energy crops, active forest management, active wildlife habitat management, low-impact harvesting, precision use of advanced information technologies, genetically improved stock, wood products life-cycle management, and advanced bioproducts. Potential Role of TechnologyIncreasing terrestrial carbon stocks is attractive because it can potentially offset a major fraction of emissions and serve as a bridge over an interim period, allowing for development of other low-CO2or CO2-free technologies. Carbon stock management technologies and practices that enhance soil and forest carbon sinks need to be maintained once the carbon stock reaches higher levels. Although the benefits can be temporarily reversed by fire, plowing of cropland soils, and other disturbances, the potential improvements in carbon stocks are of such magnitude that they can play a significant overall role in addressing the increase in atmospheric CO2emissions from the United States and globally throughout the 21st century.Other opportunities described in this section can provide benefits essentially indefinitely. For example, changes in crop management practices can reduce annual emissions of trace GHGs; sustainable biomass energy systems can displace fossil fuels and provide indefinite net CO2emissions reductions; and enhanced forest management and conversion to durable wood products provide a mechanism to allow forests to continually sequester carbon. Estimates of the global potential for terrestrial sequestration activities remain uncertain. Such estimates are generally of the technical potential (i.e., the biophysical potential of managed ecosystems to sequester carbon), and disregard market and policy considerations. The IPCC (IPCC 2001c) estimates such technical potential of biological mitigation options (i.e., forest, agricultural, and other land-management activities) to be on the order of 100 GtC cumulative by 2050, at costs ranging from about $0.10 to about $20/t carbon in tropical countries, and from $20/t carbon to $100/t in non-tropical countries. Technical potential estimates for the United States range widely, depending on assumptions about biophysical sequestration rates per hectare, the land area available for different activities, and other factors. Widely cited estimates of U.S. technical potential for carbon sequestration include about 55�164 teragrams of carbon (TgC) per year for potential sequestration on croplands (Lal et al. 1998); 29�110 TgC per year on grazing lands (Follett et al. 2001); 210 TgC per year on forest land (Joyce and Birdsey 2000); and 91�152 TgC per year on dedicated bioenergy croplands (Tuskan and Walsh 2001). In addition, dedicated bioenergy crops would substitute for fossil fuels, leading to an estimated 450 TgC reduction of CO2emissions (Tuskan and Walsh 2001). These estimates generally represent technical potential that does not reflect barriers to implementation, competition across land uses and sectors, or landowner response to public policies and economic incentives. A recent study of cropland (Eve et al. 2002) indicates a potential of about 66 TgC per year on croplands, toward the lower end of the Lal et al. (1998) range. With regard to bioenergy, a recent DOE/USDA analysis estimates that U.S. forest and agricultural lands could sustainably supply up to 1,300 Tg of biomass/year for bioenergy, similar to the findings of Tuskan and Walsh, but without major shifts in land use or food or fiber production (Perlack et al. 2005). Such a quantity of biomass could displace over 30 percent of current U.S. petroleum consumption. Technology StrategyRealizing the opportunities to sequester carbon in terrestrial systems will require managing resources in new ways that integrate crosscutting technologies and practices. A balanced portfolio is needed that supports basic science, technological development, emerging technology demonstrations, innovative partnerships with the private sector, and techniques and metrics for measuring success.An array of actual and potential technologies can be found in the short-, mid-, and long-terms. In the short-term, some technologies and practices being routinely used can be expanded to increase carbon sequestration. In addition, improvements to many current systems are needed to enable them to enhance above- and below-ground carbon stocks, and manage wood products pools. In the mid to long-term, research can focus on options that take advantage of entirely new technologies and practices. In the near- and long-term, the R&D portfolio is based on the following:
Current PortfolioMuch of the research currently underway that could have applications for increasing terrestrial carbon sequestration is being undertaken for multiple reasons, often unrelated to climate change. Significant investments are being made in developing sustainable natural resource management systems that provide economic and environmental benefits. In particular, advances have been made in increasing forest productivity, developing effective and environmentally sound uses of crop fertilizers, enhancing soil quality, and in producing biomass feedstocks (Figure 6-1).Across the current Federal portfolio of terrestrial sequestration-related RD&D, multi-agency activities are focused on a wide range of issues, including the following:
Future Research DirectionsThe current portfolio supports the main components of the technology development strategy and addresses the highest priority current investment opportunities in this technology area. For the future, CCTP seeks to consider a full array of promising technology options. From diverse sources, suggestions for future research have come to CCTP's attention. Some of these, and others, are currently being explored and under consideration for the future R&D portfolio. These iclude:
6.4 Ocean SequestrationBecause of the large CO2storage capacity of the ocean, increasing the carbon uptake and storage of carbon in the oceans cannot be ignored (Figure 6-2). Indeed, the ocean is currently playing an important role in consuming significant amounts of anthropogenic CO2via passive air-sea exchange, biological uptake, and ocean mixing (e.g., Sabine et al. 2004). This natural rate of CO2uptake (about 7.3Gt CO2/yr), however, is not keeping pace with the rate of current anthropogenic emissions. Also, there are consequences. Ocean acidification that is accompanying the air-sea flux, for example, could have undesirable environmental consequences, if allowed to continue (e.g., Caldeira and Wickett 2003, Feely et al. 2004, Orr et al. 2005).To understand the additional role the ocean could play in mitigating the effects CO2emissions on atmospheric concentrations, several issues must be addressed, including the capacity of the ocean to sequester CO2, its effectiveness at reducing atmospheric CO2concentration levels, the depth and form (e.g., molecular or chemically bound, gas, liquid, or solid) for introduction of the carbon, and the potential for adverse environmental consequences. Ocean storage has not yet been deployed or thoroughly tested, but there have been small-scale field experiments and 25 years of theoretical, laboratory, and modeling studies of intentional ocean storage of CO2. Nevertheless, there is still much that is unknown and more needs to be learned about the potential environmental consequences to ocean ecosystems and natural biogeochemical cycles. Although there are a variety of potential ocean carbon sequestration options (see Future Research Directions), two strategies have received the most attention: (1) direct injection of a relatively pure stream of CO2into the ocean's deep interior, and (2) iron fertilization to stimulate the growth of nutrient-constrained biota and enhance the ocean's natural biological pump. It is generally thought that direct injection of CO2may be technically feasible and effectively isolate CO2from the atmosphere for at least several centuries. The primary concerns relate to possible adverse environmental effects. In contrast, the technical feasibility and effectiveness of ocean fertilization remain open to question. Further, whereas direct injection approaches seek to minimize ecosystem impacts, ocean fertilization depends upon the manipulation of ecosystem function over large areas of the ocean's surface. Over the period of centuries, it is estimated, the oceans will passively take up about 70 percent of global fossil carbon emissions, as CO2diffuses into the ocean, is transported across the ocean thermocline, and mixed into deep ocean waters (IPCC 2001a). Direct injection of captured CO2would seek to augment to this natural CO2flux to the deep sea and, thus, more rapidly slow or reverse the increase in atmospheric CO2concentrations. The potential for the ocean to absorb CO2over the long-term is large relative to that which would be generated by fossil-fuel resources. But several factors may affect the capacity and desirability of direct injection. Unless consumed by biological or chemical processes, excess CO2placed in the deep sea will eventually, via diffusion and ocean circulation, interact with the atmosphere, adding some part of the injected CO2to the atmospheric burden. For example, injection of about 8,000 Gt CO2to the deep ocean will eventually produce atmospheric CO2concentrations of about 750 ppm, even in the absence of additional CO2release to the atmosphere. Experiments and models have shown that high concentrations of CO2depress ocean pH (i.e., acidification), and thus may harm marine organisms and biogeochemical processes (e.g., Portner et al. 2004, TRS 2005). The true scope and magnitude of such effects could be the subject of further study. Alternatives to direct injection and fertilization have been proposed for CO2mitigation strategies. While they may avoid the preceding concerns, they may have environmental, capacity, and cost limitations of their own (see Future Research Directions). Potential Role of TechnologyOcean sequestration offers the potential to significantly reduce the level of CO2concentrations in the atmosphere. There are many technological options envisioned for accomplishing this. Under the direct injection approach, for example, CO2could be captured from large point sources, (e.g., fossil-fired power plants, industrial processes, etc.), and then pressurized to liquid form (a supercritical liquid) and injected at depths of 2,000 to 3,000 meters below the surface. Once there, because its density as a liquid is greater than that of sea water, it would be expected to remain for centuries. However, this option has yet to be tested or deployed in a continuous mode at industrial concentrations.Technology StrategyThe key to any successful technology strategy in this area is to assess adequately (a) the potential of ocean-based options as mitigation strategies; (b) the potential adverse impacts on the ocean biosphere; and the (c) potential effectiveness as evaluated against specific R&D criteria. This includes a research portfolio that seeks to determine, via experimentation and computer simulations, the potential for storing anthropogenic CO2in the world's oceans while minimizing negative environmental consequences.Various studies based on models and ocean observations indicate that the isolation of CO2from the atmosphere generally increases with the depth of injection. In the near-term, the key research questions that are related to direct injection involve evaluating the impact of added CO2and/or nutrients on marine ecosystems and the biogeochemical cycles to which they contribute. This is being investigated through both observations and modeling of marine organisms and ecosystems, as is now being funded by DOE and the National Science Foundation (NSF), among others. In the long-term, R&D activities could focus on improving an understanding of the effects of elevated concentrations of CO2on marine organisms and ecosystems. Another potential area of study is the effectiveness and environmental and ecological consequences of iron fertilization. Alternative ocean CO2mitigation strategies (see "Future Research Directions") pose a different set of environmental and efficacy concerns that need to be evaluated should the effects of direct injection prove to be unacceptable. Current PortfolioOngoing research activities target ocean carbon sequestration using direct injection and iron fertilization. These activities are summarized below:
Future Research DirectionsThe current portfolio supports the main components of the technology development strategy and addresses the highest priority current investment opportunities in this technology area. For the future, CCTP seeks to consider a full array of promising technology options. From diverse sources, suggestions for future research have come to CCTP's attention. Some of these, and others, are currently being explored and under consideration for the future R&D portfolio. These include:In summary, the ocean is currently playing an important role in mitigating significant amounts of anthropogenic CO2via passive air-to-sea transfer. The chemical impacts accompanying this flux, including ocean acidification, may have serious environmental consequences. Any scheme that introduces additional molecular CO2(unreacted or uncombined) to the ocean will contribute to these impacts. There are alternative, potentially promising ways for ocean carbon addition that lessen or avoid these impacts. However, such approaches are likely to be attended by other unresolved issues of their own, and the economic and environment mental costs and benefits of such schemes could be the subject of further research. All options for safely using the ocean's potential for carbon uptake need to be seriously and carefully considered. 6.5 SummaryThe development of the technical, economic, and environmental feasibility and acceptability of CO2sequestration strategies has important implications for meeting the needs for food, fiber, and energy while minimizing GHG emissions. As the current energy infrastructure evolves around fossil fuels, the viability of sequestration could provide many options for a future of near-net-zero GHG emissions. Carbon sequestration has the potential to reduce the cost of stabilizing GHG concentrations in the atmosphere, conceivably at lower costs than other alternatives, if successful, and further support domestic and global economic growth. If carbon sequestration were to prove technically and economically viable, fossil fuels could continue to play an important role as a primary energy supply.This chapter reviews various forms of advanced technology, their potential for reducing emissions by capturing, storing, and sequestering carbon dioxide, and the R&D strategies intended to accelerate the development of these technologies. Although uncertainties exist about both the level at which GHG concentrations might need to be stabilized and the nature of the technologies that may come to the fore, the long-term potential of advanced technologies to capture, store, and sequester carbon dioxide is estimated to be significant, both in reducing emissions (as shown in the figure at the beginning of this chapter) and in reducing the costs for achieving those reductions, as suggested by Figure 3-14. Further, the advances in technology development needed to realize this potential, as modeled in the associated analyses, animate the R&D goals for each carbon dioxide capture and sequestration technology area. As one illustration among the many hypothetical cases analyzed,16 GHG emissions were constrained to a high level over the course of the 21st century in such a way that a stabilized GHG concentration levels could ultimately be attained. The lowest-cost arrays of advanced technology in capturing, storing, and sequestering carbon dioxide, when compared to a reference case, resulted in reduced or avoided emissions of between 10 and 110 GtC over 100 years. The breadth of this range is due to a large degree of uncertainty at this point in time in the cost and viability of some sequestration technologies. For perspective, these quantities amounted to, roughly, between 2 and 20 percent of all GHG emissions reduced, avoided, captured and stored, or otherwise withdrawn and sequestered needed to attain this level over the same period. Similarly, the costs for achieving such emissions reductions, when compared to the reference case, were reduced by roughly a factor of 3. See Chapter 3 for other cases and other scenarios. As described in this chapter, CCTP's technology development strategy supports achievements in this range. The overall strategy is summarized schematically in Figure 6-3. Advanced technologies are seen entering the marketplace in the near-, mid-, and long-terms, where the long-term is sustained indefinitely. Such a progression, if successfully realized worldwide, would be consistent with attaining the potential for carbon dioxide capture and sequestration portrayed at the beginning of this chapter. The timing and pace of technology adoption are uncertain and must be guided by science and supported by appropriate policies (see Approach 7, Chapters 2 and 10). In the case of the illustration above, the first GtC per year (1GtC/year) of reduced or avoided emissions, as compared to an unconstrained reference case, would need to be in place and operating, roughly, as early as 2040. For this to happen, a number of new or advanced technologies to capture, store, and sequester carbon dioxide would need to penetrate the market at significant scale before this date. Other cases would suggest faster or slower rates of deployment. See Chapter 3 for other cases and other scenarios. Throughout Chapter 6, the discussions of the current activities in each area support the main components of this approach to technology development. The activities outlined in the current portfolio sections address the highest-priority investment opportunities for this point in time. Beyond these activities, the chapter identifies promising directions for future research, identified in part by the technical working group and assessments and inputs from non-Federal experts. CCTP remains open to a full array of promising technology options as current work is completed and changes in the overall portfolio are considered. ReferencesBoyd, P.W., A.J. Watson, C.S. Law, E.R. Abraham, T. Trull, R. Murdoch, D.C.E. Bakker, A.R. Bowie, K.O. Buessler, H. Chang, M.A. Charette, P. Croot, K. Downing, R.D. Frew, M. Gall, M. Hadfield, J.A. Hall, M. Harvey, G. Jameson, J. La Roche, M.I. Liddicoat, R. Ling, M. Maldonado, R.M. McKay, S.D. Nodder, S. 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Footnotes1 In this Plan, the three approaches are collectively referred to as "capturing and sequestering carbon dioxide" or "capturing and sequestering carbon."2 See Section 3.1.1 (CCTP 2005) 3 See Section 3.1.2 (CCTP 2005). 4 See Section 3.1.2 (CCTP 2005). 5 For more information on the Regional Partnerships Program. 6 See Section 3.2.1.1 (CCTP 2005). 7 See Section 3.2.1.2 (CCTP 2005). 8 See Section 3.2.1.3 (CCTP 2005). 9 See Section 3.2.1.4 (CCTP 2005). 10 See Section 3.2.1.5 (CCTP 2005). 11 See Section 3.2.1.6 (CCTP 2005). 12 See Section 3.2.2.1 (CCTP 2005). 13 See Section 3.2.3.1 (CCTP 2005). 14 See Section 3.2.3.2 (CCTP 2005). 15 See Section 3.3.1 (CCTP 2005). 16 In Chapter 3, various advanced technology scenarios were analyzed for cases where global emissions of GHGs were hypothetically constrained. Over the course of the 21st century, growth in emissions was assumed to slow, then stop, and eventually reverse in order to ultimately stabilize GHG concentrations in the Earth's atmosphere at levels ranging from 450 to 750 ppm. In each case, technologies competed within the emissions-constrained market, and the results were compared in terms of energy (or other metric), emissions, and costs.
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