Introduction
Congressional interest in carbon capture and sequestration (or carbon capture and storage, CCS) has been renewed since the U.S. Environmental Protection Agency (EPA) re-proposed standards for carbon dioxide (CO2) from new fossil-fueled power plants on September 20, 2013. As re-proposed, the standards would limit emissions of CO2 to no more than 1,100 pounds per megawatt-hour of production from new coal-fired power plants and between 1,000 and 1,100 (depending on size of the plant) for new natural gas-fired plants. The standards would not apply to existing facilities. EPA proposed the standard under Section 111 of the Clean Air Act.1 According to EPA, new natural gas-fired stationary power plants should be able to meet the proposed standards without additional cost or the need for add-on control technology. However, new coal-fired plants only would be able to meet the standards by installing carbon capture and sequestration (CCS) technology. The proposed standard would allow an option of up to seven years for a new coal-fired plant to comply. But that option would require a more stringent standard for those plants and limit CO2 emissions to an average of 1,000-1,050 pounds per megawatt-hour over the seven-year period.
The promise of CCS lies in the potential for technology to capture CO2 emitted from large, industrial sources, thus significantly decreasing CO2 emissions without drastically changing U.S. dependence on fossil fuels, particularly coal, for electricity generation. The future use of coal—a significant component of the U.S. energy portfolio—in the United States will likely depend on whether and how CCS is deployed if legislative or regulatory actions curtail future CO2 emissions. The September 20, 2013, proposed rule for limiting CO2 emissions from new fossil-fueled power plants is one such action. In addition, Section 111 of the Clean Air Act requires that EPA develop guidelines for pollutants—which has been interpreted to include greenhouse gas emissions—for existing plants whenever it promulgates standards for new power plants. In a June 25, 2013, memorandum, President Obama directed the EPA to issue proposed guidelines for existing plants by June 1, 2014, and to issue final guidelines a year later.2 These proposed actions will likely draw additional congressional scrutiny of the viability of large-scale CCS as the primary technology for mitigating CO2 emissions from coal-fired power plants.
Unlike the other two components of CCS, transportation and geologic storage, the first component of CCS—CO2 capture—is almost entirely technology-dependent. For CCS to succeed at reducing CO2 emissions from a significant fraction of large sources in the United States, CO2 capture technology would need to be deployed widely. Widespread commercial deployment would likely depend on the cost of capturing CO2, although other factors, such as incentives for reducing greenhouse gas emissions, would also influence deployment.
The transportation and storage components of CCS are not nearly as technology-dependent as the capture component. Nonetheless, transportation and sequestration costs, while generally much smaller than capture costs, could be very high in some cases. They would depend, in part, on how long it would take to reach an agreement on a regulatory framework to guide long-term CO2 injection and storage, and on what those regulations would require. CCS deployment would also depend on the degree of public acceptance of a large-scale CCS enterprise. Several CRS reports (see below) address these policy issues of CO2 transportation and storage.
Structure of this Report
This report is a brief summary of a longer study—CRS Report R41325, Carbon Capture: A Technology Assessment—that provides a "snapshot" of technological development current through mid-2010. The technology assessment is both prospective and retrospective in that it examines emerging or advanced technologies that may affect future CCS deployment, and looks at lessons from past experience with large-scale technological development and deployment as guidelines that could be used to shape energy policy. The longer report consists of 10 chapters, together with figures and tables.
This report and the longer CRS report focus on the first component of a CCS system, namely, the CO2 capture process. The goal of these reports is to provide a realistic assessment of prospects for improved, lower-cost technologies for each of the three current approaches to CO2 capture.
The technology assessment was undertaken by Carnegie Mellon University, Department of Engineering and Public Policy, under the leadership of Edward S. Rubin, together with Aaron Marks, Hari Mantripragada, Peter Versteeg, and John Kitchin. The work was performed under contract to CRS, and is part of a multiyear CRS project to examine different aspects of U.S. energy policy. [author name scrubbed], CRS Specialist in Energy and Natural Resources Policy, served as the CRS project coordinator.
CRS Report R41325, Carbon Capture: A Technology Assessment, was funded, in part, by a grant from the Joyce Foundation.
Other CRS Reports on CCS
CRS has written a suite of products on different aspects of CCS that complement this assessment of carbon capture technologies. These include:
- CRS Report R42532, Carbon Capture and Sequestration (CCS): A Primer, by [author name scrubbed].
- CRS Report R42496, Carbon Capture and Sequestration: Research, Development, and Demonstration at the U.S. Department of Energy, by [author name scrubbed].
- CRS Report R43028, FutureGen: A Brief History and Issues for Congress, by [author name scrubbed].
- CRS Report R42950, Prospects for Coal in Electric Power and Industry, by [author name scrubbed], [author name scrubbed], and [author name scrubbed].
- CRS Report RL33971, Carbon Dioxide (CO2) Pipelines for Carbon Sequestration: Emerging Policy Issues, by [author name scrubbed], [author name scrubbed], and [author name scrubbed].
- CRS Report R40103, Carbon Control in the U.S. Electricity Sector: Key Implementation Uncertainties, by [author name scrubbed].
- CRS Report RL34316, Pipelines for Carbon Dioxide (CO2) Control: Network Needs and Cost Uncertainties, by [author name scrubbed] and [author name scrubbed].
- CRS Report RL34307, Legal Issues Associated with the Development of Carbon Dioxide Sequestration Technology, by [author name scrubbed] and [author name scrubbed].
- CRS Report RL34601, Community Acceptance of Carbon Capture and Sequestration Infrastructure: Siting Challenges, by [author name scrubbed].
- CRS Report R43127, EPA Standards for Greenhouse Gas Emissions from Power Plants: Many Questions, Some Answers, by [author name scrubbed].
Background
Global climate change is an issue of major international concern and the focus of proposed mitigation policy measures in the United States and elsewhere. In this context, CCS technology has received increasing attention over the past decade as a potential method of limiting atmospheric emissions of CO2—the principal "greenhouse gas" linked to climate change.
Worldwide interest in CCS stems principally from three factors. First is a growing consensus that large reductions in global CO2 emissions are needed to avoid serious climate change impacts.3 Because electric power plants are a major source of CO2, curtailing their emissions has become a focus.
Second is the growing realization that large emission reductions cannot be achieved easily or quickly simply by using less energy or by replacing fossil fuels with alternative energy sources that emit little or no CO2. The reality is that the world (and the United States itself) today relies on fossil fuels for over 85% of its energy use (including fuel for transportation, not just electricity generation). Changing that picture dramatically would take time. CCS thus offers a way to get large CO2 reductions from power plants and other industrial sources until cleaner, sustainable energy technologies can be widely deployed.
Finally, energy-economic models show that adding CCS to the suite of other GHG reduction measures significantly lowers the cost of mitigating climate change. Studies also have affirmed that by 2030 and beyond, CCS is a major component of a cost-effective portfolio of emission reduction strategies.4
Figure 1 depicts the overall CCS process applied to a power plant or other industrial process. The CO2 produced from carbon in the fossil fuels or biomass feedstock is first captured, then compressed to a dense liquid to facilitate its transport and storage. The main storage option is underground injection into a suitable geological formation.
At the present time, CCS is not commercially proven in the primary large-scale application for which it is envisioned—electric power plants fueled by coal or natural gas. Furthermore, the cost of CCS today is relatively high, due mainly to the high cost of CO2 capture (which includes the cost of CO2 compression needed for transport and storage). This has prompted a variety of government and private-sector research programs in the United States and elsewhere to develop more cost-effective methods of CO2 capture.
Overview
The following is an assessment of prospects for CCS capture technologies; namely, post-combustion capture from power plant flue gases using amine-based solvents such as monoethanolamine (MEA) and ammonia; pre-combustion capture (also via chemical solvents) from the synthesis gas produced in an integrated coal gasification combined cycle (IGCC) power plant; and oxy-combustion capture, in which high-purity oxygen rather than air is used for combustion in a pulverized coal (PC) power plant to produce a flue gas with a high concentration of CO2 amenable to capture without a post-combustion chemical process.
Currently, post-combustion and pre-combustion capture technologies are commercial and widely used for gas stream purification in a variety of industrial processes. Several small-scale installations also capture CO2 from power plant flue gases to produce CO2 for sale as an industrial commodity. Oxy-combustion capture, however, is still under development and is not currently commercial.
The advantages and limitations of each of these three methods are discussed in CRS Report R41325, Carbon Capture: A Technology Assessment, along with plans for their continued development. While all three approaches are capable of high CO2 capture efficiencies (typically about 90%), the major drawbacks of current processes are their high cost and the large energy requirement for operation (which significantly reduces the net plant capacity and contributes to the high cost of capture). Another drawback in terms of their availability for greenhouse gas mitigation is that at present, there are still no applications of CO2 capture on a coal-fired or gas-fired power plant at full scale (i.e., a scale of several hundred megawatts of plant capacity).
Current Research and Development (R&D) Activities
To address the current lack of demonstrated capabilities for full-scale CO2 capture at power plants, a number of large-scale demonstration projects at both coal combustion and gasification-based power plants are planned or underway in the United States and elsewhere. These projects and the technologies they plan to employ are summarized in CRS Report R41325, Carbon Capture: A Technology Assessment. Many of these demonstrations are expected to begin operation in 2014 or 2015. Planned projects for other types of industrial facilities also are discussed.
Also elaborated in the longer report are the substantial R&D activities underway in the United States and elsewhere to develop and commercialize lower-cost capture systems with smaller energy penalties. To characterize the status of capture technologies and the prospects for their commercial availability, five stages of development are defined: conceptual designs; laboratory or bench scale; pilot plant scale; full-scale demonstration plants; and commercial processes. The CRS report reviews current activities at each of these stages for each of the three major capture routes.
Current R&D activities include development and testing of new or improved solvents that can lower the cost of current post-combustion and pre-combustion capture, as well as research on a variety of potential "breakthrough technologies" such as novel solvents, sorbents, membranes, and oxyfuel systems that hold promise for even lower-cost capture systems. Most of the latter processes, however, are still in the early stages of research and development (i.e., conceptual designs and laboratory- or bench-scale processes), so that credible estimates of their performance and (especially) cost are lacking at this time. Table 1 lists the major approaches being pursued for post-combustion capture, although many of these approaches apply to pre-combustion and oxy-combustion capture as well.
|
Liquid Solvents |
Solid Adsorbents |
Membranes |
|
Advanced amines |
Supported amines |
Polymeric |
|
Potassium carbonate |
Carbon-based |
Amine-doped |
|
Advanced mixtures |
Sodium carbonate |
Integrated with absorption |
|
Ionic liquids |
Crystalline materials |
Biomimetic-based |
Source: Edward S. Rubin, Aaron Marks, Hari Mantripragada, Peter Versteeg, and John Kitchin, Carnegie Mellon University, Department of Engineering and Public Policy.
Processes under development at the more advanced pilot plant scale are, for the most part, new or improved solvent formulations (such as ammonia and advanced amines) that are undergoing testing and evaluation. These advanced solvents could be available for commercial use within several years if subsequent full-scale testing confirms their overall benefit. Pilot-scale oxy-combustion processes also are currently being tested and evaluated for planned scale-up, while two IGCC power plants in Europe are installing pilot plants to evaluate pre-combustion capture options.
In general, the focus of most current R&D activities is on cost reduction rather than additional gains in the efficiency of CO2 capture (which can result in cost increases rather than decreases). A number of R&D programs emphasize the need for lower-cost retrofit technologies suitable for existing power plants. As a practical matter, however, most technologies being pursued to reduce capture costs for new plants also apply to existing plants. As the fleet of existing coal-fired power plants continues to age, the size of the potential U.S. retrofit market for CO2 capture will continue to shrink, as older plants may not be economic to retrofit (although the situation in other countries, especially China, may be quite different).
Future Outlook
Whether for new power plants or existing ones, the key questions are the same: When would advanced CO2 capture systems be available for commercial rollout, and how much cheaper would they be compared to current technology?
To address the first question, CRS Report R41325, Carbon Capture: A Technology Assessment, reviews a variety of "technology roadmaps" developed by governmental and private-sector organizations in the United States and elsewhere. All of these roadmaps anticipate that CO2 capture will be available for commercial deployment at power plants by 2020. Current commercial technologies like post-combustion amine systems could be available sooner. A number of roadmaps also project that novel, lower-cost technologies like solid sorbent systems for post-combustion capture will be commercial in the 2020 time frame. Such projections acknowledge, however, that this will require aggressive and sustained efforts to advance promising concepts to commercial reality.
That caveat is strongly supported by a review of experience from other recent R&D programs to develop lower-cost technologies for post-combustion SO2 and NOx capture at coal-fired power plants. Those efforts typically took two decades or more to bring new concepts (like combined SO2 and NOx capture processes) to commercial availability. By then, however, the cost advantages initially foreseen for these novel systems had largely evaporated in most cases: the advanced technologies tended to get more expensive as their development progressed (consistent with "textbook" descriptions of the innovation process), while the cost of formerly "high-cost" commercial technologies gradually declined over time. The absence of a significant market for the novel technologies put them at a further disadvantage. This may be similar to the situation for CO2 capture systems today. Thus, the development of advanced CO2 capture technologies is not without financial risks.
With regard to future cost reductions, based on past experience, the costs of environmental technologies that succeed in the marketplace tend to fall over time. For example, after an initial rise during the early commercialization period, the cost of post-combustion SO2 and NOx capture systems declined by 50% or more after about two decades of deployment at coal-fired power plants. This trend is consistent with the "learning curve" behavior seen for many other classes of technology. It thus appears reasonable to expect a similar trend for future CO2 capture costs once these technologies become widely deployed. Note, too, that the cost of CO2 capture also depends on other aspects of power plant design, financing, and operation—not solely on the cost of the CO2 capture unit. Future improvements in net power plant efficiency, for example, would tend to lower the unit cost of CO2 capture.
Other cost estimates for advanced CO2 capture systems are based on engineering-economic analysis of proposed system designs. For example, recent studies by the U.S. Department of Energy (DOE) foresee the cost of advanced PC and IGCC power plants with CO2 capture falling by 27% and 31%, respectively, relative to current costs as a result of successful R&D programs. No estimates are provided, however, as to when the various improvements described are expected to be commercially available. In general, the farther away a technology is from commercial reality, the lower its estimated cost tends to be. Thus, there is considerable uncertainty in cost estimates for technologies that are not yet commercial, especially those that exist only as conceptual designs.
More reliable estimates of future technology costs typically are linked to projections of their expected level of commercial deployment in a given time frame (i.e., a measure of their market size). For power plant technologies like CO2 capture systems, this is commonly expressed as total installed capacity. However, as with other technologies whose sole purpose is to reduce environmental emissions, there is no significant market for power plant CO2 capture systems absent government actions or policies that effectively create such markets—either through regulations that limit CO2 emissions, or through voluntary incentives such as tax credits or direct financial subsidies. The technical literature and historical evidence examined in CRS Report R41325, Carbon Capture: A Technology Assessment, strongly link future cost reductions for CO2 capture systems to their level of commercial deployment. In widely used models based on empirical "experience curves," the latter measure serves as a surrogate for the many factors that influence future technology costs, including the level of R&D expenditures and the new knowledge gained through learning-by-doing (related to manufacturing) and learning-by-using (related to technology use).
Based on such models, published estimates project the future cost of electricity from power plants with CO2 capture to fall by as much as 30% below current values after roughly 100,000 megawatts (MW) of capture plant capacity is installed and operated worldwide. That estimate is in line with the DOE projects noted above. If achieved, it would represent a significant decrease from current costs—one that would bring the cost and efficiency of future power plants with CO2 capture close to that of current plants without capture. For reference, it took approximately 20 years following passage of the 1970 Clean Air Act Amendments to achieve a comparable level of technology deployment for SO2 capture systems at coal-fired power plants.
Uncertainty estimates for these projections, however, indicate that future cost reductions for CO2 capture also could be much smaller than indicated above. Thus, whether future cost reductions would meet, exceed, or fall short of current estimates will only be known with hindsight.
In the context of this report and CRS Report R41325, Carbon Capture: A Technology Assessment, the key insight governing prospects for improved carbon capture technology is that achieving significant cost reductions would require not only a vigorous and sustained level of R&D, but also a substantial level of commercial deployment. That would necessitate a significant market for CO2 capture technologies. At present such a market does not exist. While various types of incentive programs can accelerate the development and deployment of CO2 capture technology, actions that significantly limit emissions of CO2 to the atmosphere ultimately would be needed to realize substantial and sustained reductions in the future cost of CO2 capture.