SPECIAL REPORT: Energy industry examining CO2 sequestration options

May 14, 2007
Global climate change presents challenges associated with balancing potential environmental impacts with a wide variety of economic, technical, and lifestyle changes that may be necessary to address the issue.

Global climate change presents challenges associated with balancing potential environmental impacts with a wide variety of economic, technical, and lifestyle changes that may be necessary to address the issue. Carbon dioxide emissions from the use of fossil fuels such as coal, oil, and natural gas are the largest anthropogenic contributor to greenhouse gases, which are believed to contribute to climate change. The overall objective of carbon management is to develop a strategy and portfolio of technologies for stabilizing CO2 concentrations in the atmosphere and, thus, slow climate change.

Carbon sequestration is one class of carbon management technologies. It involves permanently sequestering and storing CO2 in the earth. There are two broad classes of sequestration: terrestrial and geologic.

Terrestrial sequestration involves absorbing CO2 from the air using biologic materials such as crops, trees, and grasses. Ultimately, the carbon is transferred to the soil in which the biologic materials grow. By optimizing the way we manage our land, we can do much to optimize the effectiveness of terrestrial sequestration around the globe. In geologic sequestration, the primary focus of this article, CO2 is captured, compressed, transported by pipeline, and injected into deep reservoirs, such as saline formations, oil and gas reservoirs, and coal seams. This option is amenable to reduction of CO2 emissions from point sources such as power plants and refineries. Such point sources contribute about half of the CO2 emissions.

Before the CO2 can be injected into a deep geologic reservoir, it first must be captured in a concentrated form from a fossil fuel-fired process such as those used for power generation or petroleum refining. Capturing CO2 in a nearly pure form is necessary to minimize the volume needed for storage and so that the CO2 can be compressed to a supercritical state. A number of pathways are currently available or under development for CO2 capture. For example, in post-combustion capture, CO2 can be scrubbed or otherwise removed from the flue gas after combustion of fossil fuels. However, this flue gas stream is relatively dilute, usually less than 15% by volume, making capture difficult and expensive. Commercial processes exist today for doing this based on absorption of CO2 from the flue gas with monoethanolamine (MEA). However, the cost of capture due to the steam and energy requirements for the process makes it too expensive to be feasible for retrofit to existing plants in an efficient manner. A number of improved processes are under development, including advanced MEA processes and more recently the ammonia-based capture, but these will require time to develop and commercialize.

Another option is to separate the CO2 before combustion, precombustion capture. By first using a process called gasification, such as in integrated gasification combined cycle (IGCC) processes for power generation, fossil fuels such as coal and biomass can be converted into hydrogen and other components that can be used directly as a fuel or converted into other fuels such as those used for transportation today. Gasification can facilitate CO2 capture by creating a relatively pure and concentrated CO2 stream. The FutureGen project, funded jointly by government and industry, will utilize IGCC technology with the goal to build a near zero-emission coal-based power plant, including geologic sequestration of CO2.The site for FutureGen has been narrowed to either Illinois or Texas. Final site selection is expected to be announced this year.

Through the Midwest Regional Carbon Sequestration Partnership, Battelle scientists drilled an 8,000 ft test well at First Energy’s R.E. Burger Plant near Shadyside, Ohio, to evaluate CO2 storage potential in Appalachian basin. Drilling was completed in February. Photo from Battelle.
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Another combustion type is oxy-combustion, which uses oxygen instead of air for combustion of fossil fuels in boilers, furnaces, and other processes and produces flue gas with a high concentration of CO2 with the intent of facilitating its capture.

With the ongoing research and development, it is anticipated that there will be continuing improvements in the costs, integration of capture with power plant operations, and reduction in energy penalties for the capture technologies. In addition, there is a need to evaluate the CO2 composition from various capture processes for permitting and injection purposes.

Geologic storage

Sequestration in geologic formations builds on strong experience in the oil and gas industry. The primary types of geologic reservoirs for storing CO2 underground are depleted oil and gas reservoirs, unmineable coal seams, and deep saline formations. The target reservoirs are typically, but not always, over 2,500 ft deep and consist of layers of sandstone or other porous rocks where CO2 can be stored. The target reservoirs would also be capped by layers of nonporous rocks that act as seals to prevent the CO2 from leaking out. Deep reservoirs are targeted because they are well away from drinking water supplies and because they are naturally at a pressure above about 1,100 psi. At this pressure or above, the CO2 is in a supercritical state where its density is near that of a liquid, thus greatly reducing its volume compared to a gas. Also at these pressures, the CO2 is less mobile than as a gas and, thus, more easily contained in deep geologic reservoirs for long periods. Recently the US Department of Energy (DOE) completed the first edition of a National Atlas describing these reservoirs and their capacities as estimated by DOE’s Regional Carbon Sequestration Partnership Program. The atlas discusses the partnerships’ estimated storage potential and implementation aspects in various reservoir types, such as:

  • Depleted oil and gas reservoirs. Oil and gas fields are considered a natural choice for storing CO2 for several reasons. They make attractive CO2 sequestration targets since they have already proven their ability to contain oil, gas, and water for millions of years and their geologic character is well defined by previous exploration efforts. According to the atlas, these types of reservoirs in the US are estimated to contain about 90 gigatons of storage capacity. Currently, CO2 is injected in depleted oil fields to enhance oil recovery because under suitable reservoir conditions CO2 mobilizes the oil trapped in fine pore spaces through miscible or immiscible displacement processes. The US is a world leader in enhanced oil recovery (EOR) technology, using about 30 million tonnes/year of CO2 for this purpose, mostly from natural CO2 sources. However, these are primarily operated as EOR projects with an effort to maximize economic returns through CO2 recycling rather than maximizing CO2 storage in the reservoirs. CO2 injection also may be used to maintain reservoir pressure in depleted oil and gas zones. Enhanced oil and gas recovery offers a near-term potential for geologically storing CO2, as well as an opportunity to sequester carbon at low cost, due to the revenues from recovered oil or gas. Of course, for anthropogenic CO2 to be useable, an appropriate match between sources and sinks is needed, and that might not be possible in many locations.
  • Unmineable coalbeds. CO2 can be injected onto coal seams that are considered unmineable-the seam is too thin, too deep, or otherwise does not allow for the coal to be economically recovered. There is much debate about how to define what coal seams fall into this category since technology for recovering coal continues to evolve making coal that is unmineable today potentially is mineable tomorrow. It is estimated that in the US unmineable coal seams represent a potential storage target of over 170 gigatons of CO2. The primary economic benefit of this option is that it can be used for enhanced coalbed methane production (ECBM), because the coal seams have a greater affinity for CO2 adsorption than for methane. Typically, the amount of CO2 adsorbed or sequestered on the coal surface is much greater than the amount of carbon produced as methane. Because the CO2 for ECBM can be injected in gas phase, this technology can be deployed at shallower depth compared to other options. A key limitation is the potential environmental issues and cost associated with an increase in produced water from the gas production.
  • Deep saline reservoirs. Deep saline reservoirs are sedimentary formations such as sandstones and carbonate rocks that have pore spaces filled with saline water or brine. In the shallower sedimentary layers, the pore spaces have fresh water, but with increasing depth the water salinity increases to high levels such that it is no longer useable for drinking or industrial uses. The presence of highly saline brine in these formations also indicates that these have been isolated from leakage from freshwater zones for a very long time. Further, these layers must be overlain by low-permeability and unfaulted caprock such as shale or dense limestone so that the injected fluids do not leak into the freshwater zones or the atmosphere. Typically, depths greater than 2,500 ft are suitable because at these depth the injected CO2 is likely to remain in a dense and less mobile supercritical phase. They have two important benefits as CO2 storage targets. First, the estimated carbon storage capacity of saline formations in the US is very large, estimated to be several thousand gigatons, making them a viable long-term target for storage of CO2 from large point sources. And second, many existing large CO2 point sources in the US are within relatively close proximity to a potential future saline reservoir injection point, making it feasible to consider transporting CO2 from the source to the reservoir or even injecting CO2 onto a reservoir at the source site itself.

Theoretically, geologic reservoirs have the capacity to store all the CO2 produced by the large point sources of CO2 in the US and globally for hundreds of years. However, in practical terms, each major CO2 source has to be evaluated individually relative to its proximity to potentially suitable reservoirs, the economics of implementing CO2 capture, and the feasibility of transporting the CO2 to the injection site. The large volumes of CO2 involved, over 5 million tonnes/year from a single major US coal-fired power plant, make pipeline delivery of supercritical CO2 the only practical means of transport.

Sequestration projects

Geological sequestration of CO2 has been seen as a prominent option only during the last 10 years or so. However, in this time, significant progress has been made in evaluating this option through paper studies, computer and laboratory tests, pilot demonstrations, and commercial projects. Examples of large-scale projects include the Weyburn project in Canada, where EnCana Corp. uses CO2 that comes via a 200-mile pipeline from a coal gasification plant near Beulah, ND. Similarly, large-scale injection of about 1 million tonnes/year of CO2 from gas purification into deep saline reservoirs is under way at Sliepner field in North Sea and at the In Salah project in central Algeria. Another large-scale project under planning is the FutureGen project, which will use coal gasification to produce power and hydrogen in a near-zero emission plant with CO2 sequestration.

While a small number of current large-scale projects provide valuable experience, there is a strong need to build a foundation for the technology through evaluating storage potential in various regions of the US and the world-a purpose served in the US by the regional carbon sequestration partnerships. As part of an effort to further develop carbon sequestration technologies and develop ways to reduce CO2 emissions while protecting the industrial economy of the Midwest, Battelle is leading the Midwest Regional Carbon Sequestration Partnership (MRCSP) for the DOE and 30 other partners. The MRCSP covers eight states (Indiana, Kentucky, Maryland, Michigan, New York, Ohio, Pennsylvania, and West Virginia). The MRCSP is one of seven partnerships in the DOE Regional Carbon Sequestration Partnership Program.

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In Phase I, the MRCSP focused on defining the region’s existing sources of CO2, geological and terrestrial reservoirs, potential options for transporting CO2, regulatory framework, and economics of implementing sequestration opportunities in the region, as well as reaching out to public stakeholders to educate them about sequestration and receive their feedback on key issues.

In Phase II, which began in 2005 and is scheduled to end in 2009, the MRCSP’s research is building on the Phase I results by using a series of field validation tests to determine how the region’s large, well-distributed, and competitively priced sequestration potential can be used to simultaneously advance economic growth and environmental protection. Three of the field tests involve implementation of geologic sequestration by injecting CO2 into deep saline formations in Ohio, Michigan, and Kentucky. A noteworthy feature of these tests is that they are hosted or sponsored by major regional utilities, which increases the probability of commercial implementation in the future. Similar tests are being implemented by other partnerships, and DOE recently announced plans for larger-scale demonstrations.

Another noteworthy project has been under way at American Electric Power’s Mountaineer Plant in New Haven, W.Va., to evaluate geologic storage potential in the Appalachian basin, a key area for coal-fired power generation. This project funded by DOE, AEP, and others and operated by Battelle has completed a detailed site characterization through seismic survey, test well drilling, and modeling. AEP recently announced plans to proceed with an extensive injection and monitoring phase with CO2 to be provided from an experimental capture technology demonstration. It will be the first use of carbon capture technology on a commercial scale at a coal-fired power plant and will provide a test case for retrofitting of existing plants. These projects represent an example of an expedited pace in development and deployment of carbon sequestration technologies.

Accounting framework

The US currently has no national regulations governing CO2 emissions. There are a number of voluntary trading markets, including the Chicago Climate Exchange.

There are state initiatives such as that implemented by California and a number of northeastern states through the Regional Greenhouse Gas Initiative. It is possible that, at some point in the not-too-distant future, national regulations will be implemented that will regulate emissions of CO2 from various sources.

The imposition of such regulations creates a range of uncertainties for those affected. While companies know the amount of emission reductions they need, figuring out the most cost-effective way to achieve these reductions is not an easy task. Companies may change their operations to reduce their emissions, or they may acquire emission allowances from other companies that do not need them. They also may acquire approved emission-reduction credits created under two project-based mechanisms under the Kyoto Protocol: the Joint Implementation (JI) or Clean Development Mechanism (CDM) programs.

JI allows industrialized countries to fulfill part of their required greenhouse-gas emission reductions by paying for emission-reducing projects in other industrialized countries. CDM allows industrialized countries to invest in emission-reducing projects in developing countries.

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In addition to the voluntary or state initiatives in the US, experiences in carbon control and trading in other countries provide valuable lessons. Major capital investments that may reduce greenhouse-gas emissions will often have lifetimes that extend far past 2012, when the Kyoto Protocol and the first phase of the European Emissions Trading Scheme expire. The exact mechanism, scope, and participation levels that will emerge after 2012 remain uncertain. During the first year, the market price of European Union emission allowances has been volatile, reaching over $30/tonne of CO2 equivalent in the summer of 2005 but decreasing substantially after that. JI and CDM emission reduction credits can be acquired for a fifth of this amount. However, until these credits are actually created and approved, uncertainty exists as to whether they will be delivered and useable in the EU program.

Businesses-faced with uncertainties in mechanisms combined with an anticipation of US carbon controls-find themselves taking a more comprehensive stock of their climate control-related risks and options. Battelle has quantified the emission reductions and cost-effectiveness of greenhouse-gas emission-reduction technologies and has assisted international companies (steel, petroleum, utilities) with understanding their emissions and options for reducing them. Specific projects include working with the International Petroleum Industry Environmental Conservation Association, International Association of Oil & Gas Producers, and the American Petroleum Institute to develop guidelines for reporting emissions and supporting individual companies in conducting corporate emission inventories using the Battelle-developed SANGEA Emissions Estimation Software.

Building experience

A number of modeling studies and forecasts demonstrate that no single measure will stabilize atmospheric concentrations of CO2 at a safe level-there is no silver bullet.

These studies, including those done as part of the Global Technology Strategy Program by the Joint Global Change Research Institute, show that a suite of technologies will be required and that sequestration of CO2 from fossil fuel processes will be an important factor if we are to continue taking advantage of economical fossil fuels.

If carbon sequestration is not undertaken, the use of fossil fuels may have to be severely diminished, with significant consequences for the world’s economy. The current pilot-scale field projects funded by the government and industry provide a unique opportunity to build expertise and experience in this technology so that a broader deployment can be undertaken in the future with greater public confidence and in compliance with national and international greenhouse gas mitigation regulations.

The authors

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David A. Ball ([email protected]) is a program manager in the applied energy systems product line for Battelle’s energy, transportation, and environment division. Since March 2004, Ball has served as project manager for the Midwest Regional Carbon Sequestration Partnership. During over 30 years at Battelle, he has served in various management and research roles in the energy and environment areas.

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Neeraj Gupta ([email protected]) is research leader, environmental restoration, for Battelle’s energy, transportation, and environment division. With Battelle since 1993, he participates in various multidisciplinary projects given his technical background in hydrogeology, geology, and geochemistry. Gupta leads Battelle’s efforts in evaluating and deploying greenhouse-gas control technologies, particularly CO2 capture and geologic storage technologies. These include management of the Mountaineer project, the geologic storage demonstrations component for MRCSP, participation in FutureGen technical team, and many commercial projects.

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Bernhard Metzger ([email protected]) is vice-president and product line manager of environmental management international for Battelle’s energy, transportation, and environmental division. He manages the organization’s environmental management practice. His 20 years of professional consulting experience includes various upstream and downstream projects. Metzger participated in a Gas Research Institute study assessing the impact of climate-change regulations on businesses. He has worked for industry, government, and as a research scientist and has lectured at universities.