FEATURE
The Pros and Cons of
Carbon Dioxide Dumping Global warming concerns have stimulated a search for carbon sequestration technologies. CAROLA H A N I S C H
2 0 A • JAN. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
ast month, at the international climate change conference in Kyoto, Japan, progress toward establishing uniform targets and timetables for curbing C0 2 emissions was frustratingly slow. However, with the reality of increasing fossil fuel use, most attendees agreed that research aimed at developing and deploying promising technologies that can prevent release of C0 2 to the atmosphere must be aggressively pursued. Capture and disposal of C0 2 are actively being sought as a means to avoid release of the greenhouse gas to the atmosphere. At the Sleipner West gas field in the North Sea, Norway's state-owned oil company, Statoil, is conducting the world's first carbon sequestration project that has as its main objective protection of the atmosphere (i). C02, a natural gas contaminant, is being recovered and pumped into a huge aquifer beneath the sea floor. Another project is planned off Hawaii's Kona coast, where a multinational research team will soon perform field trials, testing options for direct ocean disposal of CO,. At the Natuna gas field, north of Borneo, another project is planned that will annually sequester millions of tons of C0 in aquifers under the sea floor Land-based options for capture and disposal of CO such as reuse for enhanced oil recovery operations and capture of fossil-fueled power plant emissions are at commercial stages of development Intrigued by research possibilities for C0 2 capture and disposal, Henry C. Kelly of die White House Office of Science and Technology Policy said, "There are only a limited number of options we have to reduce carbon dioxide emissions, and this is definitely worth looking into." Critics of C22 disposal, however, question the safety, cost, and even the need for such an approach. Although Michael Oppenheimer, chief scientist of the Environmental Defense Fund, agrees with Kelly, stating, "We should continue to support research on C0 2 capture and disposal," he is uncertain whether such technologies are environmentally and economically sound. "I don't see a large-scale application of these techniques in the short term," he said. Darren Goetze, a biophysicist at the Union of Concerned Scientists in Washington, D.C., said, "It is very expensive and completely unnecessary. There are much more readily available options like renewable energies ^That we need to be focusing on is the reduction of the use of fossil fuels" Ocean storage is a more disputed option than underground disposal into deep aquifers. Dan Lashof of the Natural Resources Defense Council is concerned about potential impacts on marine organisms that may result from changes in the pH of ocean
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water in the presence of increased levels of C0 2 . Reacting to various schemes for sequestering carbon in the oceans, George Woodwell, director of the Woods Hole Research Center in Massachusetts, said, "We should stop putting carbon dioxide in the air instead of fiddling around with trying to make the oceans absorb more." Many researchers are convinced that with the impetus of increasingly stringent carbon restrictions, C0 2 capture and disposal technology will play an important role in the future. They also believe that the technology can be improved to control costs. "Offthe-shelf techniques are far from being optimized," said Amit Chakma, dean of engineering at the University of Regina in Saskatchewan, Canada. C0 2 disposal has been performed for reasons not related to global warming concerns. For example, natural underground C0 2 fields in the United States have been tapped to aid oil companies in oil recovery operations. The gas is piped to on-shore oil fields, where it is injected into underground reservoirs and replaces recovered oil. Sam Holloway, a geologist at the British Geological Survey in Nottingham, observed, "This has been an everyday operation for years. These operations are not considered to involve any undue risks to man or the natural environment." However, he agrees with Lashof that more research needs to be done on CO migration paths in geologic formations. According to Chakma, C0 2 disposal into underground formations, such as depleted oil and gas reservoirs, is not unproven technology. Several commercially viable projects for enhanced oil recovery have been operating throughout the United States for many years. Chakma estimates that the storage capacity of oil and gas reservoirs already depleted in the United States is sufficient to store up to 2870 million metric tons of C0 2 . Techniques available for capture and disposal of C0 2 are expensive to use, however. According to Howard Herzog, principal research engineer at the Massachusetts Institute of Technology (MIT) Energy Laboratory, costs can range from $30 to $90 to avoid the release of 1 ton of C0 2 to the atmosphere (2).
Seabed disposal in the North Sea The largest C 0 2 seabed disposal project, initiated in September 1996 (i), is Statoil. It has been pumping IAJ 2 mto a 32,uuu-square-Kuometer (.km ) aquifer. inis porous, salt water-filled sandstone formation lies 800 m below the floor of the North Sea. The amount of C0 2 injected into the aquifer—1 million tons per year—represents about 3% of Norway's total emissions. Natural gas extracted from the field reservoir contains 9.5% C0 2 , which must be reduced to about 2.5%, the specified C 0 2 content limit for commercial natural gas. Waste C0 2 would normally be released into the atmosphere, but because the contaminant already has to be removed from collected natural gas to meet commercial fuel specifications, additional costs for pumping C0 2 into the aquifer are relatively small. Total commercial gas production costs are raised by about 1%, a small price to pay compared with carbon taxes that would be levied on any uncontrolled C0 emissions. 2 2 A • JAN. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Off the coast of Norway, C0 2 is being separated from natural gas and pumped into a huge aquifer 800 meters below the ocean floor. Other companies are considering this type of disposal to prevent climate damage. (Courtesy Statoil)
In Norway, a carbon tax has been in effect since 1991. According to Olav Falk-Pedersen of Kvaerner Water Systems in Sandefjord, Norway, this carbon tax "motivated the Norwegian oil and gas companies to study new methods and technologies for reduction of the total C 0 2 emissions." The carbon tax internalizes estimated costs of climate damages associated with atmospheric release of CO, and is equivalent to $55/ ton of emissions. In Alberta, Canada, 20 land-based, acidgas (consisting of CO, and H2S) reinjection projects, the first started in 1989, are in operation. However, according to Chakma, "No one is contemplating reinjection of CO -only gases in Alberta because it is not required by law." Erik Lindeberg, senior scientist of the Continental Shelf Institute Petroleum Research group in Trondheim, Norway, considers off-shore underground disposal of C0 2 from gas fields a permanent and safe solution. In a 1993-95 study that he carried out for the European Union, Lindeberg estimated the capacity of North Sea aquifers alone would be large enough to take up all C0 2 emissions produced at European Union power plants for the next several hundred years (3). Lindeberg said his model calculations show that it will take more than 10,000 years before "even minor amounts of C0 2 " escape from the aquifer and make their way up to the sea floor-ocean interface. In the event of an undetected fracture 8000 m from the injection well, lindeberg estimates that it will take approximately 500 years before stored C 0 2 reaches the fracture. In a worst-case scenario, 20% of the sequestered C0 2 might then escape during the following 1500 years. Thomas Palm, an employee of the Bellona Foundation, a Norwegian environmental organization, agreed and said, "If you accept that natural gas is produced and used, then disposing of C02 is the best way to control emissions." Statoil plans to expand the use of disposal technologies as part of its program to curtail emissions of C0 2 . In September, Statoil announced a new program for
cutting C0 2 emissions by 30% over a 10-year period. In part, this will be accomplished by capture and disposal of C0 2 emissions from land-based plants used for natural gas processing and compression. C0 2 disposal is also being considered by a consortium, including Exxon and the Indonesian state-run oil company, Pertamina, at the Natuna off-shore gas field. C0 2 will be injected into an aquifer located deep beneath the South China Sea. The Natuna gas field, 375 miles east of Singapore, is one of the largest in the world. If the project is implemented, 100 million tons of C0 2 would be disposed of annually. Expensive power plant C0 2 removal In addition to imposing carbon taxes, Norway is the first country to require C0 2 capture and disposal from land-based, gas-fired power plants. Naturkraft, which wants to build Norway's first two gas plants, recentiy announced plans to develop a C0 2 capture technology. However, unlike the situation at Statoil, where project economics favor injecting separated C0 2 into deep, off-shore aquifers, emissions capture from power plants can be expensive. When oil prices were high in the late 1970s and early 1980s, C0 2 was routinely captured from U.S. power plants for use in enhanced oil recovery operations. Most of these operations were shut down when prices dropped in the mid-1980s. Some C0 2 is still recovered from power plant emissions for use in food industry market applications and for sodaash production. Recovery involves the use of chemical absorption processes that consume significant amounts of energy. "In the power sector, carbon dioxide removal may increase electricity production costs by 30-100%," estimated Wim C. Turkenburg of the Department of Science, Technology, and Society at Utrecht University in The Netherlands. Other C0 2 recovery processes have been considered, including membrane separation, cryogenic fractionation, and adsorption using molecular sieves; but all are even less energy efficient and more expensive than chemical absorption. As a result, power companies tend not to be enthusiastic about C0 2 disposal techniques. James Smithson, an employee of the Illinois Power Company, said, "None of the different strategies seems to be cost-effective." Robert Kane, the program manager of the Office of Planning and Environmental Analysis Global Climate Change program at the U.S. Department of Energy (DOE), is more optimistic. "While costs and energy requirements for current capture processes are high, the opportunities for significant reductions exist, since researchers have only begun to address these needs" he said Current DOE funding for research in this area is $1 6 million annually According to Perry Bergman, an engineer with the DOE Power and Engineering Systems Division, the storage potential of deep aquifers in the United States is between 5 billion tons and 500 billion tons of C02. Annual U.S. power plant C0 2 emission is about 1.7 billion tons. Bergman believes that 65% of C02 captured from U.S. power plants could possibly be injected directly into deep aquifers without any need for transport through long pipelines.
FIGURE 1
Options for direct ocean disposal of CO2 Disposal scenarios that are the focus of current research include droplet plume and dense plume dissolution, dry ice and towed pipe dispersion, and isolation as a dense lake of C02 on the sea floor. Towed pipe and droplet plume scenarios may offer the best approach in the near future.
TABLE 1
Costs of different capture and disposal options Storage potential in the ocean and in geological formations is largest, but these options are also the most expensive. Further research may narrow down cost-range estimates. Reduction potential (million metric tons C02)
CO, mitigation option 3
Capture with utilization Capture with enhanced oil recovery Capture (industrial sources) w i t h storage Capture with geological storage*3 Capture with ocean storage 0
Net cost (in 1990 dollars; S/metric ton C02 emissions avoided) High
Low
20 50
5 45
0 10
80
76
24
900
91
31
600
91
31
* Capture options refer to power plants, except as noted. Utilization refers to food industry use and soda ash production. Includes storage under the ocean. c Direct injection into the ocean. Source: Reference 4.
Safety issues need to be considered, say critics who cite the natural disaster that occurred in 1986 at the volcanic crater lake, Nyos, in Cameroon. A large-scale release of C02 killed more than 1500 people and all animal life up to 14 km from the crater site. Although the release of C02 from Lake Nyos bears little relation to scenarios involving injection of C02 into an aquifer— the mechanisms completely differ—the illustration serves to flag dangers of potential large-scale C02 releases and the need to anticipate possible flow rates in plausible scenarios. Liability questions would have to JAN. 1, 1998/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 3 A
C0 2 emissions produced at fossil-fueled power plants can be captured using commercially available absorption technology such as this C0 2 recovery plant in Shady Point Okla. Widespread near-term use is uncertain because this technology can be expensive. (Courtesy ABB Lummus Global/AES)
be solved before power companies would embark on large-scale disposal, said Herzog.
Direct ocean disposal scrutinized Direct ocean disposal presents a possibly safer alternative, at least to humans. Large and natural potential C0 2 reservoirs, oceans are considered as sites for direct disposal, but only theoretical studies of ocean disposal have been performed. "The amount of carbon in the oceans is 60 times greater than in the atmosphere. That means even if you inject flue gases from the world's power plants, die overall concentration in the oceans would barely change," explained Herzog. Model calculations show that most C 0 2 emitted today will eventually end up in the oceans anyway. However, the ocean's absorption of gas occurs very slowly. "It takes about 1000 years, too long to even out the quick increase of carbon dioxide in the air," explained Eric Adams, a senior research engineer at the MIT Energy Laboratory. However, by pumping the gas directly into the sea the natural process could be accelerated mitigating the rise of CO in the atmosphere. Several different disposal techniques have been studied, including injection of C0 2 by pipeline and releasing it from a ship, either as dry ice blocks or as a liquid poured from a towed pipe (see Figure 1) (4). The most significant anticipated environmental impact is lowering the pH in surrounding waters. Although skeptical of the approach in general, Woodwell is not particularly concerned about possible pH changes. "The oceans are pretty well buffered," he said. At the Energy Laboratory, David Auerbach and Jennifer Caulfield simulated C 0 2 injection and estimated possible marine-life impacts. They showed that die ocean's natural pH of 8 can be lowered to as much as pH 4 near the injection point. Alternative designs of injection devices, which disperse C0 2 as it dissolves, can be tested to ensure that biological impacts resulting from changes in ocean pH are minimized. 2 4 A • JAN. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
The first direct ocean disposal field experiment is scheduled to take place in 2000, possibly at a site along the Kona coast of Hawaii. The project will be conducted in collaboration with MIT, the Japanese Research Institute of Innovative Technology for the Earth, and the Norwegian Institute for Water Research. Dumping C0 2 into the ocean also faces international and national legal and regulatory hurdles. Judith Kildow, a professor for ocean policy at MIT, believes that the London Dumping Convention most likely would have to be amended if C0 2 were placed in the oceans, even though it does not explicitly deal with C0 2 . She added that in 1972, the United States passed the Ocean Dumping Act, part of the Marine Protection, Research and Sanctuaries Act. This legislation forbids off-shore disposal of any kind without special permits. Bill Eng of EPA indicated that a section of Title 40 of the U.S. Code of Federal Regulations requires parties considering ocean dumping of C0 2 "to determine whether the discharge causes unreasonable degradation of the marine environment." Yet to define "unreasonable degradation," further studies of the effect of pH change on the marine environment must be undertaken. Many scientists and environmentalists remain skeptical about ocean disposal. "How do we know that the ocean really is a permanent sink for COz?" asked Kelly Sims, science policy director of Ozone Action in Washington, D.C. Voicing related concerns, Ronald Prinn, director of the Center for Global Change Sciences at MIT, said, "I would like to see more study on the stability of ocean currents." Mick Follows, an MIT ocean modeler, agreed. "I am skeptical about C0 2 disposal. I am not convinced that a rapid injection would be safe for the ocean environment. How soon the injected CO, comes back into contact with the atmosphere depends on where you put it. That requires a good understanding of ocean circulation and mixing processes. Yet many aspects of this are not known especially the [timedependent] variability of ocean currents" he said Herzog believes that within the next 10 years, capture and sequestration will be viable only in niche applications, such as oil and gas operations at the Sleipner West field, or for fulfilling a commercial need for C0 2 , such as in enhanced oil recovery operations. However, over the next 30 years, he believes, "We may see most new power plants include C 0 2 control technology, just as today's power plants control S0 2 , NO , and particulate."
References (1) Hileman, B. Chem. Eng. News s197, 75(33), ,4. (2) Herzog, H. C02 Capture, Reuse and Storage gechnologies for Mitigating Global Climate Change; DE-AF2296PC01257; Massachusetts Institute of Technology Energy Laboratory: Cambridge, MA, 1996. (3) Lindeberg, E. The Underground Disposal ofC02; Joule II Project No. CT92-0031; British Geological Survey: Keyworth, Nottingham, U.K., 1996; Chapter 3. (4) Herzog, H.; Drake, E.; Adams, E. C02 Capture, Reuse, and Storage Technologies for Mitigating Global Climate Change; DE-AF22-96PC01257; Energy Laboratory, MIT: Cambridge, MA, lanuary 1997. Carola Hanisch is a freelance writer based in Nashville, Tenn.
