Coal may be a four-letter word for former Vice President Al Gore and many environmentalists. But some researchers believe technology may yet salvage the concept of “clean coal” — or at least cleaner coal — as an alternative to foreign oil while the drive for longer-term alternative energy picks up steam.
Among the latest scientists to weigh in, researchers at the University of Padova in Italy have led detailed simulations concluding that a new process for transforming coal into gas could improve on the efficiency of conventional coal-to-gas, or gasification, techniques by 28 percent and release 22 percent less carbon dioxide — the main gas linked to global warming. Coupling the scheme to a coal-to-liquid process, the authors conclude, could yield 40 percent more synthetic fuel, release 32 percent less carbon dioxide and contribute to a 70 percent rise in overall energy efficiency.
The study, being published in the Nov. 19 issue of the journal Energy & Fuels, carries several big caveats, including an estimated price tag that may be hard for power companies to swallow. And many environmental organizations have dismissed the notion that coal could ever be extracted and burned in an earth-friendly way as little more than “greenwashing.”
But as part of his campaign platform, President-elect Barack Obama has pledged to enter into public-private partnerships to develop five “first-of-a-kind” commercial scale coal-fired plants with clean carbon capture and sequestration technology.
Coal-producing states such as Pennsylvania and Montana also have proposed building coal-to-liquid plants, in part to relieve dependence on foreign oil.
And with some studies suggesting the U.S. boasts an abundant (though non-renewable) supply, a host of new modifications are being proposed for cleaning up the pollution-spewing source of nearly half of all electricity produced in the country.
With its assertion that coal is “the only reasonable large-scale conventional source left in the medium term,” the new Italian study argues that “the urgent need of exploiting coal to produce both electric power and liquid fuels is a strong motivation to study how to improve the related production processes.”
Alberto Bertucco, a professor of chemical engineering at the University of Padova and a study co-author, said the big question is whether the concept will be economically feasible for a full-size plant producing syngas, a mixture of hydrogen and carbon monoxide gas.
“If the idea is good technically, probably it’s worthwhile to see if it could be applied at this scale. You get rid of the need for Saudi Arabia,” he said. “But this process must be sustained to get plants which are viable in the sense that they don’t cost too much.”
Traditional coal combustion produces steam capable of turning electricity-generating turbines. As coal’s carbon content oxidizes, however, the process also yields the potent pollutants sulfur dioxide and nitrogen oxide, as well as the greenhouse gas carbon dioxide.
A somewhat less polluting alternative, a process known as integrated gasification combined cycle (IGCC), produces syngas to power a turbine generator. Another possibility is to use that syngas mix to produce heavier hydrocarbons in the form of liquid synthetic fuels.
For the gasification reactions, burning coal typically requires pure oxygen, Bertucco said. “So there is a part of the plant that is to get pure oxygen to be fed to the gasifier. This part is expensive and energy-demanding.”
In collaboration with the global engineering and construction contractor Foster Wheeler and an independent consultant, Bertucco and post-doctoral fellow Maria Sudiro proposed burning the needed coal with cheaper air instead of oxygen.
Last month, Foster Wheeler won the right to perform a feasibility study for a coal-to-liquid (CTL) plant in China spearheaded by South Africa’s Sasol Synfuels International, owner of the only currently operational CTL plant.
The new study, akin to a how-to guide, explains how the necessary separation of the combustion and gasification processes could be safely achieved. “In the combustor, we burn roughly one-fourth of the coal, and we do this with air,” Bertucco said.
But the process needs something to transport the generated heat to the gasifier. The solution, he said, is heat-conducting sand.
“Coal plus steam makes carbon monoxide plus hydrogen, but a lot of energy is needed and this is relieved by the sand,” he said. “This is circulated continuously from one reaction to another, back and forth.”
The process requires abundant caution to avoid the risk of an explosion, though Bertucco said the danger can be overcome by properly controlling the pressure in different parts of the plant to prevent air from coming into contact with the gasifier.
Weaning U.S. from fossil fuels
Although the idea of using sand to aid coal gasification isn’t necessarily revolutionary, Bertucco said the engineering study was the first to attach reliable efficiency and emission numbers to the process of separating combustion from gasification.
As for the economics of outfitting new plants to use air and sand, he conceded the upfront costs would be “quite high” until the first facilities come online. As a rough estimate, he said the CTL process, including capital and operational costs, would require between $30 and $50 to produce the equivalent of one barrel of oil.
Coal-to-liquid processing has been around since German chemists invented the Fischer-Tropsch technique to convert coal-based syngas into liquid fuel in the 1920s to supply the coal-rich but petroleum-poor nation with fuel for its military.
But in the last half-century, only South Africa’s Sasol petrochemical company has used the chemical process for full-scale synthetic fuel production. Only a handful of plants in the U.S. even use the initial reaction in that process, the coal-to-gas IGCC technique, though more are expected to come online in the next few years.
The same general principles also could be used for transforming biomass to syngas, though Bertucco said the process is more complicated than coal gasification.
Many environmentalists still consider the notion of “clean coal” — no matter what the technological advances — anathema to weaning the U.S. from fossil fuels.
In a Nov. 9 New York Times editorial, Gore argued that “those who spend hundreds of millions promoting ‘clean coal’ technology consistently omit the fact that there is little investment and not a single large-scale demonstration project in the United States for capturing and safely burying all of this pollution. If the coal industry can make good on this promise, then I’m all for it. But until that day comes, we simply cannot any longer base the strategy for human survival on a cynical and self-interested illusion.”
Vaclav Smil, an energy policy expert at Canada's University of Manitoba , dismissed the Italian study’s premise outright, writing in an e-mail, “There are literally hundreds of such ‘breakthroughs’ every month in energy conversion literature, theoretical or tiny pilot plant studies that eventually amount to nothing or to marginal gains not worth pursuing compared to the real root of the problem,” which he characterized as excessive energy consumption by the U.S.
At a Nov. 10 Seattle screening of the new pro-biodiesel documentary “FUEL,” however, Rep. Jay Inslee (D-Wash.) said he believed “clean coal” intended for electricity production could be viable if paired with carbon capture and sequestration.
Federal money for research and development could be directed toward improving the carbon sequestration technology, he said, as long as it was made clear to coal companies that the funding wouldn’t come at the expense of a push toward alternative energy. As for coal-to-liquid technology, Inslee said, “I think that is highly unlikely to be successful.”
Need for government support
Nevertheless, Los Angeles-based Rentech Inc. has developed its own version of the Fischer-Tropsch process to convert coal to liquid fuel.
Earlier this year, the company’s demonstration facility in Commerce City, Colo., became the only operational synthetic transportation fuels facility in the country, producing about 10 barrels per day of transportation fuels such as jet fuel and diesel.
Harold Wright, chief technology officer for Rentech, said the method of improving the efficiency of synthetic gas and fuel production outlined by Bertucco’s group seems reasonable. Anything that can be done to lower the considerable expense associated with separating oxygen from air for coal combustion, he said, would be “very positive.” But a full-scale facility operating under those principles, Wright said, would likely require government support.
Large coal-based research projects in the U.S., such as a 275-megawatt IGCC plant in Illinois that would have demonstrated advanced coal gasification and carbon capture and sequestration, already have foundered over budgetary concerns.
Officials at the Department of Energy’s FutureGen Program dramatically scaled back plans for the plant earlier this year when the cost was revised dramatically upward, from $950 million to $1.6 billion, due largely to an increase in the cost of construction.
A scaled-back FutureGen project, according to Office of Fossil Energy spokesman John Grasser, will consist of a commercial coal plant venture paired with a carbon capture demonstration.
Under the cooperative agreement with the coal industry, the commercial sector would build a power plant while the project would contribute money toward carbon capture technology.
In the meantime, smaller companies are charging ahead with their own technology. Bismarck, N.D.-based Basin Electric Power Cooperative operates a coal-gasification plant near Beulah, N.D., that captures more carbon dioxide than any other site in the world, sending 9,000 tons of the gas by pipeline to Saskatchewan, Canada, to be used for enhancing underground oil recovery.
The geological question of whether sequestration can be a permanent solution remains unanswered, though Rep. Inslee pointed to companies such as Bellevue, Wash.-based Ramgen Power Systems, which is using supersonic air and gas compressors more commonly associated with aircraft technology to compress, capture and sequester carbon dioxide.
“No utility is going to sequester carbon dioxide if it’s significantly more expensive than current technology,” Grasser said. “The goal is to produce the electricity coming from a coal gasification facility with carbon capture and to get the cost down so that it’s no more than 10 percent above a similar process where you don’t capture the carbon dioxide.”
In the end, the question of whether “clean coal” technology can begin to approach viability as a greener energy solution is likely to boil down to a fundamental matter of economics.