By: Steve Blankinship, Associate Editor
No topic so dominates coal plant construction today as carbon emissions, specifically the production of CO2, the largest single anthropomorphic (man-made) greenhouse gas associated with global warming. Coal plants account for about 37 percent of the 26 billion metric tons of anthropogenic CO2 produced in the world each year. And it appears all but certain that carbon emissions from coal plants will eventually be regulated just as particulate matter, sulfur dioxide, sulfur trioxide and nitrogen oxide already are, and as mercury will be within a few years.
 Tests like this one gauge how well geologic formations can sequester carbon. Photo courtesy Seay Nance, U. of Texas |
But the ability to capture CO2 produced when using coal to make electricity won’t help address growing concerns about climate change unless it can be prevented from being released into the atmosphere. It will have to be stored - that is to say “sequestered” - in the ground.
There are two major ways to do that. One is to first capture the CO2 from large sources such as coal-fired power plants and then place it into the ground by injecting it into deep geologic formations, which are selected as safe and secure permanent storage repositories. This process is called CO2 capture and geologic storage or CCS.
A second way is to remove CO2 from the atmosphere by photosynthesis and then absorbing it into soils and vegetation. This process is called terrestrial sequestration, which includes both removing CO2 from the atmosphere and limiting CO2 emissions from terrestrial ecosystems into the atmosphere.
The existence of several commercial markets, such as enhanced oil recovery (EOR) and enhanced coal bed methane (ECBM), can accommodate a small percentage of all the CO2 produced by coal plants. Such commercial markets can make sequestration more cost effective, thus offsetting the costs of storage while putting some captured carbon dioxide to useful purposes.
Since any CO2 capture strategy must inevitably include sequestration, the latter has become one of the most critical research and development elements associated with coal-based power production. Dozens of sequestration research projects are underway throughout the world.
In the U.S., the single largest coordinated effort is being carried out under the U.S. Department of Energy’s (DOE’s) Regional Carbon Sequestration Partnership Program. Together, the seven regional partnerships, in coordination with DOE’s National Energy Technology Laboratory (DOE/NETL), are conducting research aimed at developing sequestration technology and strategies.
One of the largest of the seven regional groups - in terms of power generated by coal and CO2 produced - is the Midwest Regional Carbon Sequestration Partnership (MRCSP) led by Columbus, Ohio-based research firm Battelle. Large fossil-fired plants in the region account for 84 percent of the annual CO2 emissions from MRCSP’s large stationary CO2 point sources. MRCSP’s 30-plus partners include major power producers, universities, state geological surveys, non-governmental organizations, state and federal government agencies and private companies.
In the first phase of its research, the partnerships assessed the technical, economic and social feasibility of carbon sequestration in their respective regions. In the second phase, the partnerships will conduct small-scale field tests of sequestration opportunities. Also in Phase II, MRCSP plans to focus on demonstrating soil carbon sequestration in cropland, reclaimed marshland and reclaimed mining areas.
Because MRCSP is one of the most strategic of the large-scale sequestration efforts in North America, Power Engineering magazine talked with the two men at the epicenter of the research being conducted - David Ball, the partnership’s project manager, and Neeraj Gupta, who heads up the geological demonstration program for the MRCSP and other sequestration projects at Battelle.
Power Engineering: This question is for Neeraj. How did you come to be one of the lead researchers for geologic sequestration at Battelle?
Gupta:My initial entry into this subject resulted from my doctoral research Ohio State University that included modeling of brine flow in the deep geologic sediments across the Midwest and its implications for underground liquid injection. During the mid 1990s the relevance of this research to DOE’s emerging geologic storage program led to initial funding of Battelle projects by NETL. During the last 10 years as the DOE program has grown, our team has also progressed from initial paper and modeling assessments, laboratory experiments, geologic mapping and site characterization, to the current field demonstrations stage with increasing industrial participation.
PE: And to Dave, how did you find yourself managing the MRCSP?
 David Ball, Battelle program manager. |
Ball: I became involved with the MRCSP project in 2004. Before that I had managed and conducted research in a variety of energy and environmental areas at Battelle. I worked with utility industry clients and, in fact, started my career as an engineer working in a large coal-fired power plant here in Ohio. In addition to having a technical background in mechanical and environmental engineering, I was drawn to this project because of the potential impact of sequestration on the technologies used on power generation.
PE:Due to the very high concentration of coal-fired power plants in the region should we expect some of the most significant results to emerge from the work you are doing?
Ball: We refer to the MRCSP as the nation’s engine room. It is one-sixth of the U.S. economy and accounts for one-fifth of the nation’s power generation, more than 80 percent of which is generated with coal. As such, all of our partners recognize the importance of needing to develop sequestration technologies and to understand the implications of their implementation. Three of our partners, all major power companies, have volunteered and invested in being host sites for our Phase II geologic sequestration field tests. Their interest and participation make these tests unique learning experiences. We think the findings of the current and future work in this area will be a significant factor in determining the carbon management strategies, not just for the region but for the entire country.
PE: Summarize the work so far.
 Neeraj Gupta, research leader, Battelle. |
Gupta: In Phase I, the MRCSP and in particular our team carried out a first-ever coherent mapping of the geological resources in the region. We demonstrated conclusively that this region has a vast geological potential, especially in deep saline formations. This resource theoretically has the capacity to contain all the emissions produced by our 300 large CO2 point sources for literally hundreds of years. Nearly all these sources are coal-fired power plants that collectively produce nearly a billion tons of CO2 annually. Our team also found that our deep saline formations are relatively close to many of our large point sources. That yields the potential for a large amount of the CO2 produced in the region to be sequestered with minimal need for long distance pipelines.
In addition, there also appears to be significant storage potential in oil and gas fields, deep coal seams and perhaps in the organic shale layers. Our team of six universities mapped five selected land-use types across the region for terrestrial sequestration potential. We found that by implementing land management practices conducive to sequestration, the region’s croplands, forests, minelands, marginal lands and wetlands could increase sequestration equivalent to about 15 percent of the emissions from our large point sources.
PE:What about Phase II?
Ball: In phase II the MRCSP is conducting six field tests-three geological in deep saline formations and three terrestrial. The three geologic tests, two at operating power plants and one in the only active enhanced oil recovery field in the northeast U.S., involve three different geologic provinces that underlie a large fraction of the region. These three tests also involve working with three different regulatory agencies that oversee injection permitting to evaluate what it will mean to use CCS on a commercial scale. The three terrestrial tests (one each involving croplands, minelands and wetlands) are providing valuable knowledge of how to validate and enhance the sequestration potential of these important land types. Phase II also includes continued geologic mapping and characterization of the region to help evaluate the sequestration resource.
PE: The entire DOE sequestration study project encompasses seven regional organizations. How will the various regional efforts differ?
Ball: The differences in the regional partnerships stem primarily from the fact that each region has a different set of characteristics with respect to the types of emissions, economic drivers, types and availability of terrestrial and geologic storage sinks and future infrastructural needs. With the support of the over 300 non-federal entities that collectively make up the regional partnerships, each is developing an understanding of what it takes to implement sequestration technologies in their respective regions. For example, our region is more heavily dependent on coal-based power compared to some of the western states. The differences in the geologic structures and the resulting impact of storage potential are perhaps the most important differentiating factors.
PE: There are currently about 1,000 coal-fired units in the U.S. and many more will have to be built to keep pace with power demand. How much CO2 are we talking about being produced, both now and in the foreseeable future?
Gupta: It is estimated that humans around the globe currently emit about 26 billion tons of CO2 annually. About 15 billion tons are emitted by the world’s large point sources. The U.S. emits about 7.1 billion tons of CO2, of which about 3.8 billion tons are emitted by about 4,400 large point sources. In the next 100 years it is estimated that humans around the globe will cumulatively emit anywhere between 4,000 and 8,000 billion tons of CO2, unless explicit actions are taken to address climate change.
PE: Does that mean that somewhere in the not-too-distant future, we would be expected to capture and sequester nearly all of that CO2?
Ball: How much sequestration we implement depends on the nature of future climate policy, the degree to which other advanced energy technologies-such as nuclear-can continue to improve their cost and performance as much as it does on geologic storage potential in a given region or the policy and regulatory environment that will guide the commercial deployment of CCS technologies. The IPCC estimates that CCS technologies could potentially account for as much as 40 percent of all of the needed emissions mitigation over the course of this century, and therefore CCS is clearly a key technology for addressing climate change. However, it is equally clear that sequestration is one of the several carbon mitigation options that will need to be used for meaningful reductions in CO2 emissions and no single option by itself will be sufficient.
PE: Does North America have the underground capacity to store all the carbon produced by the nation’s coal-fired power plants?
Gupta: Researchers at Battelle estimate that North America has an estimated geologic storage capacity of about 4,000 billion tons of CO2. So, theoretically, we have the potential to store centuries’ worth of CO2 from large anthropogenic CO2 point sources such as coal fired power plants combined with CCS. That is very good news as it means we should be able to continue using a diverse and balanced portfolio of energy sources while simultaneously making progress on climate change.
The real challenge will be in finding geologic capacity near large point sources so that it can be used economically. Thus the accessible storage capacity may be less than total theoretical capacity. For example, in the regions such as MRCSP, the concentration of point sources along the Ohio River could lead to competition for storage space between adjacent point sources. This may be resolved through regional infrastructure planning including pipeline networks that distribute CO2 away from point source clusters, but there is also clearly an early mover advantage for companies that are able to secure storage rights.
PE: Texas has gone so far as to indemnify all CO2 captured by FutureGen by agreeing to take possession of it, and Illinois is taking similar action. What exactly are some of the potential risks associated with CO2 capture and storage?
Gupta: For CCS technologies to be accepted and widely deployed, the real or perceived risks and related liability aspects must be addressed in a comprehensive nature and for the entire nation. The actions in Texas and Illinois are important first steps. In the end it will be important to develop a uniform standard for dealing with long-term liability aspects across the country and even internationally. Federal and state governments will need to play a key role in providing a framework for this. For a properly defined and permitted facility that operates within the safety margin, the risk of leakage should be minimal, if any. In this context, any investment made in a careful upfront characterization will help mitigate future risks. The long-term risk at most facilities would generally decrease as the pressure subsides to background levels after injection stops. It is also hoped that the current and planned demonstration tests will help ease public concerns about risks.
PE: Right now, commercial markets exist for only a small fraction of the immense quantities of carbon produced by burning coal. What are the prospects for those markets to rise significantly?
Ball: Most assessments of future CO2 supply and demand conclude that the commercial CO2 market is likely to be very small compared to CO2 emission reduction requirements. Furthermore, many of the proposed processes for commercial use of CO2 result in the CO2 eventually being released back into the atmosphere rather than removing it permanently.
PE: EOR represents by far the largest single commercial market for CO2, but at the present demand would still only require a small percentage of the carbon that could be captured by all the nation’s coal plants. Can the EOR market be increased dramatically?
Gupta: With a few exceptions, most of the present CO2 demand for EOR (approximately 30 million tons a year) is being supported through low-cost natural CO2 sources and it is primarily focused in the West Texas. Even if all of the natural CO2 sources could be switched to anthropogenic sources, it would only use CO2 from a very small number of point sources. CO2-driven EOR probably delivers its greatest value-added as means for boosting domestic energy production, which is important in and of itself. In terms of addressing climate change, our work (as well as that of many other research groups) indicates that for a variety of reasons deep saline formation will likely be the storage reservoir of choice for most commercial applications of CCS in the future.
PE: What about the potential for other commercial markets?
Ball: In terms of the potential to prevent the release of billions of tons of CO2 to the atmosphere on a year-in/year-out basis, we are not aware of any other commercial markets that could make a significant impact and remove CO2 permanently.
PE: Most sequestration talk and apparent potential seems to be about putting CO2 into the ground. Your research is addressing terrestrial sequestration as well. Would terrestrial sequestration increase the “footprint” needed for coal-fired generation by requiring additional lands be set aside for vegetation?
Ball: Terrestrial sequestration provides an important and possibly lower-cost option for carbon mitigation. The footprint requirement will depend on the type of sequestration strategies and intensity of deployment. It is likely that a large fraction of terrestrial sequestration can be deployed through changes in land use management.
PE: Do potential sites for geologic sequestration exist reasonably close to most coal plants or would some - or many - face the prospect to having to sequester far from the point of combustion?
Gupta: As we said earlier, proximity of point sources to storage sites varies greatly. In general, however, many parts of the U.S. have a reasonable probability of finding storage capacity close to the source. In research published last year by Battelle, we showed that 95 percent of the 500 largest CO2 point sources in the U.S. lie within 50 miles of at least one candidate geologic storage reservoir. That suggests that CCS could make a significant contribution to reducing CO2 emissions in the U.S. without an extensive CO2 pipeline system at least for the next few decades.
PE:What about parasitic load associated with sequestration? Would not captured CO2 have to be pressurized at the point where it enters the pipeline? What about additional pressurization at the other end, where it might be used commercially or merely placed in the ground for permanent storage?
Ball: Most studies would say that the parasitic energy costs for applying CCS would be 10 percent to 40 percent depending upon the type of power plant the CCS technology is applied to. Most of this is related to capture and initial compression at the power plant. If additional compression was needed once the CO2 left the plant, it would likely be a small incremental cost.
PE: How long must we expect captured carbon to remain in the ground? And will it be possible for large amounts to escape at one time, say in the event of an earthquake? What would be the environmental effect of such a “burp?”
Gupta: In geologic sequestration the attempt and the expectation is that the CO2 will be sequestrated permanently in the deep geologic formations. This certainly means thousands or even millions of years. While there is always a probability of some leakage over a long time, this can be avoided though careful site selection and injection within safe limits. The probability of a large-scale release due to an earthquake is not a plausible scenario because the storage sites are unlikely to be permitted along active seismic fault zones. Even if there was an earthquake in the storage area, we are not aware of any risk studies that point to the chances of the entire amount of stored CO2 being released within a short period.
PE: Doesn’t sequestration end up making coal-fired power generation very expensive? Are there any projections on how much it would be expected to add to the cost of making electricity with coal?
Gupta: As we said, the additional cost could be 10 percent to 40 percent with the majority of those costs relating to the energy needed to capture CO2 and compress it to pipeline pressures. However, comparing the cost of electricity generated with CCS to what today’s electricity costs misses a key point. The reason to employ CCS technologies is to reduce CO2 emissions while simultaneously producing affordable power. In comparison to other low carbon means of generating base-load electricity, CCS-enabled fossil-fired power plants still look very cost-effective. Battelle’s research shows the large-scale deployment of CCS technologies around the world could reduce the cost of addressing climate change by 30 percent or more. That’s a cumulative savings of trillions of dollars over the course of this century.
PE: Does anyone have any idea how long it would take - or how much carbon would have to be captured and stored - to start making a difference in terms of lessening the impact greenhouse gas emissions are thought to be having on climate change?
Ball: The main reason to employ CCS technologies is to help cost effectively reduce CO2 emissions while still providing the energy services that the economy runs on. It is also important to emphasize that CCS technologies are a part of a broader portfolio of technologies and policies that would be needed to address climate change. All of our work - as well as that from many other research groups around the world - suggests that CCS technologies truly are a key to cost effectively reducing climate change.
PE:Skeptics question the validity of tying global warming to anthropogenic carbon production. What if decades from now, we discover that carbon storage was not only unnecessary but in some ways harmful?
Ball: If one looks at the recent IPCC reports that have been released this winter and spring and the enormous body of literature that those reports are based upon, I think there is substantial scientific agreement that climate change is happening and actions need to begin to avoid the problem from getting worse. CCS is a part of the solution to addressing climate change. Other parts of the solution include increasing energy efficiency and the continued expansion of renewable energy. Those are things that society will likely want to pursue in any event.