|December 18, 2006|
Can Coal Come Clean?
|How to survive the return of the world's dirtiest fossil fuel.|
On a steamy, torpid summer morning in Florida, the Polk power plant is performing a small feat of modern alchemy. Every hour it converts 100 tons of the dirtiest fuel on the planet---coal---into 250 million watts of power for about 56,000 homes and businesses around Tampa. The alchemy part? Vernon Shorter, a tall, bluff consultant for the Tampa Electric Company (TECO), points to a looming smokestack. "Look at the top of that stack," he shouts over the cacophony of generators and coal-grinding machines. "That is the main emissions source. You can't see anything. You don't even see a heat plume."
He's right. No smoke mars the lazy blue Florida sky. The Polk plant captures all its fly ash, 98 percent of its sulfur---which causes acid rain---and nearly all its nitrogen oxides, the main component of the brown haze that hangs over many cities. Built to demonstrate the feasibility of a new way to wring economical power from coal without belching assorted toxins into the air, the $600 million plant has been running steadily since 1996. "It makes the lowest-cost electricity on TECO's grid," Shorter says. "It also has very, very low emissions. Particulate matter is almost undetectable."
What is both distressing and remarkable about the Polk plant is that it could do much more. "There's no requirement for mercury capture, but 95 percent of it could be captured very easily," Shorter adds. More important, the plant could also capture nearly all of coal's most elusive and potentially disastrous emissions: carbon dioxide, the main gas that drives global warming.
That capability could prove vital. With oil and natural gas prices rising rapidly and nuclear power stuck in political limbo, the world's appetite for coal is soaring. In the United States, the Department of Energy estimates that 153 new coal-fired power plants will be built by 2025. Meanwhile, China and India, the world's second and third largest coal producers, are embarking on a coal power plant building spree. China alone is expected to construct 562 new coal-fired plants over the next eight years. Since the life span of a typical coal-fired plant is 50 years, coal's share of the world's energy production will rival oil's for most of the century.
The 4,300-acre Polk Power Station, 40 miles southeast of Tampa, burns coal using a state of the art low-emissions gasification process. Even so, it emits far more sulfur and nitrogen oxide than an equivalent natural gas-fired plant.
Industry advocates brag that the United States, which has 27 percent of all known coal reserves, is "the Saudi Arabia of coal," with enough to burn for the next 180 years at the current rate of use. Unfortunately, coal is as filthy as it is cheap and abundant. When burned it releases three pounds of sulfur dioxide and four pounds of nitrogen oxide for every megawatt-hour of operation. The nation's plants produce a total of about 48 tons of mercury annually. "If all the coal-burning power plants that are scheduled to be built over the next 25 years are built, the lifetime carbon dioxide emissions from those power plants will equal all the emissions from coal burning in all of human history to date," says John Holdren, a professor of environmental policy at Harvard University's Kennedy School of Government.
Holdren and many others are especially concerned about the carbon dioxide, which unlike coal's other emissions is completely unregulated in the United States. By 2012, the new coal plants in the United States, China, and India will send 2.7 billion tons of carbon dioxide into the atmosphere each year. According to leading climate models, all the added CO2 could trigger an average global temperature rise of up to 10 degrees Fahrenheit by 2100. That much warming could raise sea levels several feet, flooding the world's coastlines and shifting global weather patterns in ways that could cause massive recurring crop failures.
The smoke-free skies above the Polk plant hint at a way out. We now have the technology to capture and store most of the carbon dioxide generated by burning coal. "It's very important what we do with the next 25 years of coal plants," says Holdren. "If all those coal plants are built without carbon control, the amount of carbon dioxide added to the atmosphere would make it virtually impossible to stabilize atmospheric carbon dioxide concentrations at a moderate level." Right now the Polk power plant is one of just four of its kind in the world. If we are going to survive our coal-fueled future, we will probably need a whole lot more like it.
The technology behind the Polk plant is called an integrated gasification combined cycle---a mouthful usually shortened to IGCC. Unlike conventional coal-fired generators, IGCC plants don't actually burn the coal itself; they convert it into gas and burn the gas. This highly efficient process makes it possible to selectively pull out the resulting emissions, including carbon dioxide, which could then be collected and buried rather than released into the air.
Vernon Shorter walks through the maze of pipes and towers that is the Polk power plant, giving me a tour of how IGCC works. He points out a conveyor belt that carries a steady stream of coal from a 5,000-ton storage silo to a grinding mill, where the coal is mixed with water. The resulting mudlike slurry is then pumped under 400 pounds per square inch of pressure to the plant's most novel feature, the 300-foot-tall gasification tower.
The tower looks like an unfinished skyscraper, a boxy skeleton of steel. At its top sits a 30-foot-tall vessel filled with 96 percent pure oxygen heated to 2500ºF. When the slurry is injected into the chamber, it doesn't ignite. Instead, the coal reacts with the oxygen and immediately starts to break down into its component gases, mostly hydrogen and carbon monoxide. Those gases are cooled and pumped through a series of filters that remove sulfur, particulate matter, and other pollutants; only then is remaining synthetic gas, or syngas, burned for power.
Shorter then points out the progress of the syngas through a set of pipes descending from the gasifier to a building that houses a combustion turbine---essentially a jet engine mounted on the floor. The syngas ignites inside the turbine, spinning the turbine blades that generate about half the plant's electricity. Torrid exhaust gases from the turbine are captured and used to heat water, which is fed to a separate steam turbine to yield another 125 megawatts. This two-turbine scheme makes an IGCC plant about 15 percent more energy efficient than a conventional coal plant.
IGCC technology also gives engineers unprecedented control over what happens to the different components of coal after they go into the power plant. In normal coal-fired plants, nearly all the pollutants go up the smokestack, where some of them are captured from the exhaust by scrubbers. Here they never even hit the flame. Conventional plants burn pulverized coal in the air, which contains about 78 percent nitrogen. Since the burning takes place at low pressure, the carbon dioxide is diffuse; isolating it is difficult and expensive. Burning gasified coal in pure oxygen at high pressure concentrates the carbon dioxide, making it far easier to capture.
Although Polk does not capture carbon dioxide (it still goes up the exhaust stack, at a rate of 5,000 tons a day), it could easily be retrofitted to do so; new IGCC plants could have the capacity built in. Shorter reports that TECO is planning to replace this plant with a much larger, 600-megawatt IGCC facility. "The rumor I've heard is that it will be online by 2013. I'm sure the new plant will be CO2-capture ready. It wouldn't make sense not to. Anyone that's going to build one today has got to be thinking that carbon-emissions permits are going to be required in the future. What do you do when that day comes and you're not ready for it?"
An IGCC plant in Sicily (above) shows the environmentally friendly face of coal, but mountaintop removal in Appalachia tells a darker story (below, right).a conventional one. "The biggest obstacle is simple economics," says Holdren. "There is no incentive for capturing carbon in the United States, India, or China. The most important thing that could happen to drive IGCC forward would be putting a price on CO2 emissions in the form of a mandatory economy-wide 'cap and trade' approach, which is what a Senate resolution passed last summer recommended."
Although the Senate resolution went nowhere, David Hawkins, the director of the Climate Center at the Natural Resources Defense Council in Washington, D.C., is convinced that the political landscape will change as the effects of global warming become impossible to ignore. Signs of that change are already evident in several states---most notably California, where Governor Arnold Schwarzenegger has introduced legislation that will require a 25-percent reduction in greenhouse gases by 2020. When policies shift, the economics will follow. "We're talking to Wall Street investors and telling them that if someone wants to borrow a billion dollars to build a coal plant and you don't ask them what their strategy is to control carbon dioxide, you're making a very bad investment," Hawkins says.
The Polk plant, on the other hand, has been a very good investment. Tampa Electric actually makes money from the pollutants that the IGCC process removes from the coal. The utility sells sulfur captured from the syngas to the fertilizer industry. Slag left from the coal is sold to the cement industry. All the slurry water is recycled to the gasifier; there is no waste water and very little solid waste. "Almost nothing goes to a landfill," Shorter says.
That squeaky-clean image starts to fall apart, however, as I'm leaving Polk and encounter a dump truck loaded with 54 tons of that black rock. Another truck rolls along every 15 minutes or so, 24/7, feeding the plant's 2,400-tons-per-day habit. Some of that coal, no doubt, once lay beneath a mountain in West Virginia. And that chapter of the coal story is anything but tidy.
On a rainy early summer afternoon in the ancient mountains of West Virginia, Larry Gibson is showing me the other face of coal. We're on top of Kayford Mountain, in the heart of Appalachia, walking through 50 acres of hardwood forest where Gibson's family has lived for more than 200 years. Many generations of coal miners are buried in a family cemetery on this mountain. As we walk, a low steady rumble filters through the dense stands of spruce, maple, and hemlock. It is the sound of a mountain dying, and it's coming from just ahead, where the forest ends in a sheer 500-foot drop.
Coal mining has effaced a million acres of forest and polluted rivers in the Appalachian mountains, tarnishing the squeaky-clean image of IGCC power plants.
Below us and extending to the misty horizon lies a desolate pit of gray-black rock and rubble where, 14 months ago, a heavily forested mountain once stood. The grating rumble we hear is made by the biggest bulldozer I've ever seen. Its blade is 12 feet high and 18 feet wide. Several hundred vertical feet of mountain have been blasted to smithereens to expose a rich vein of coal; the bulldozers are moving in to harvest the bounty. This is mountaintop-removal mining, where a handful of men working some of the largest vehicles ever built can level an entire mountain in a matter of months.
"I can count 9 men on this site now, 15 at most," says Gibson, a white-haired 60-year-old mountain gnome of a man. "They've been working here for 14 months. Get a lot done in 14 months---took millions of years to form the mountains and a blink of an eye to drop them. This is the most insane thing I've ever seen in my life."
Like thousands of others throughout the region who have seen their communities ravaged by the effects of mining, Gibson laughs at the notion of coal being clean or green. More than 7 percent of Appalachian forest---the most diverse temperate forest in the world---has been obliterated by mountaintop-removal mining. "Some people like to talk about the cheap cost of coal," he says. "How the hell can you call that cheap?"
Lax enforcement of environmental regulations has let mining companies destroy communities and taint groundwater throughout Appalachia. I visit one family whose home was filled with sulfur fumes from their tap water. Arsenic, benzene, and other mining wastes contaminate the drinking water in many areas, which may be why Appalachia's cancer rates are abnormally high. And the death rate in coal mining is 60 percent higher than it is in oil and gas extraction. When I mention clean-coal technology to Judy Bonds, a local activist and coal miner's daughter in Whitesville, West Virginia, she scoffs: "Even if you could get marshmallows to come out of a power plant's smokestacks, you can't wash the blood off coal."
Even if IGCC offers no solution to the dangers of pulling coal from the earth, it at least provides a way to control some of the most hazardous by-products of burning (or gasifying) the coal. For some of the captured contaminants, like fly ash, this is a straightforward matter of burying the waste in a landfill. Carbon dioxide is a much trickier proposition. The research of how and where to store it safely for essentially forever is just starting.
In September 2005, the Intergovernmental Panel on Climate Change, a United Nations organization that includes scientists from nearly every country in the world, released a report estimating that 2 trillion tons of carbon dioxide could be stored in old coal mines, abandoned oil and gas fields, and in various other geologic formations around the world. That's a huge reservoir, even compared to the rate at which humans are now burning fossil fuels. "The estimated storage capacity equals about 80 times the total rate at which we make carbon dioxide from everything per year," Robert Socolow, a Princeton University physicist who coheads its Carbon Mitigation Initiative. Coal-power plants account for about 25 percent of that carbon dioxide, so it's 320 years of coal-power emissions."
Three large-scale carbon storage, or sequestration, projects are testing ways to bury carbon dioxide effectively. The world's oldest carbon-sequestration experiment began in the North Sea oil fields in 1996. Statoil, the Norwegian national oil company, extracts carbon dioxide from natural gas and pumps 2,800 tons of it every day 3,000 feet below the North Sea floor, trapping it in sandstone. A 250-foot-thick layer of shale covers the entire sandstone formation, and it seems to be leakproof. Statoil estimates that all the carbon dioxide emissions from every power plant in Europe for the next 600 years could be stored in the formation.
by Tim Folger