Clean Coal Test: Power Plants Prepare to Capture Carbon

Can coal be cleaned up? Power plants in Mississippi and Canada will soon find out.

A 210-foot-tall carbon dioxide absorber is moved to Southern Company's Kemper, Mississippi, power plant site.

In Juliette, Georgia, Southern Company operates a coal-fired power plant that is the single largest source of planet-warming carbon dioxide emissions in the United States.

In Kemper County, Mississippi, the same company is pioneering a technology that many experts believe will be crucial to preventing a climate disaster: It's building the world's first new power plant designed to capture and store most of its carbon.

Carbon capture and storage, or CCS, has been hailed for decades by some as an essential solution to the climate problem, and pilloried by others as unworkable and a dangerous distraction. This year, at last, it will be tested at full commercial scale. (See related, "Can Coal Ever Be Clean?" and photo gallery, "The Visible Impacts.")

The test ground won't be only a new power plant in Mississippi. It also will be about 1,600 miles north of here, in Saskatchewan, Canada, where a public utility is attempting to show that an old coal-fired power plant can be cleaned up. SaskPower has almost finished retrofitting one 110-megawatt unit of its Boundary Dam Power Station to capture 90 percent of the CO2 before it flies out the smokestack. In Saskatchewan as in Mississippi, the CO2 will be pumped underground into a partially depleted oil field and—after it has helped squeeze valuable oil to the surface—stored there indefinitely.

The battle to forestall climate change, President Barack Obama said in a speech last summer, requires us "to put an end to the limitless dumping of carbon pollution from our power plants." But because coal is one of the cheapest ways to fuel electricity, with abundant stores all around the world, global carbon pollution is growing. (See related "Quiz: What You Don't Know About Electricity.") Over the next two decades, when science says aggressive steps must be taken to curb greenhouse gas emissions, several hundred million people in the world will be getting electricity for the first time—and a lot of it will be fueled by coal. Many believe the world won't be able to stop drastic climate change without a technology for curbing emissions from the cheapest, most-carbon intensive fuel. (See related "Quiz: What You Don't Know About Climate Change Science.")

In February, construction was nearing completion at Kemper. The facility expects to go on line by the end of this year.

In the vanguard of the effort is a company that has always fought mandated government limits on CO2.

In 2009, Southern Company lobbied hard against the climate bill passed by the House of Representatives—which died the following year in the Senate—on the grounds that it would have raised energy prices too much. It is now opposing regulations, promised by Obama and proposed in January by the Environmental Protection Agency, that would require new power plants to capture roughly half their CO2. (See related story: "As U.S. Cleans Its Energy Mix, It Ships Coal Problems Abroad.")

But in Mississippi, Southern is building a plant designed to capture 65 percent of its CO2—a coal plant that would be as clean as the cleanest natural-gas-fired one. After delays and cost overruns that have doubled its price tag to more than $5 billion, the 582-megawatt Kemper plant is scheduled to go online late this year. That would put it among the larger U.S. coal plants. When fully operational, it is designed to provide power for 165,000 Mississippi homes and businesses. Ratepayers will shoulder much of the cost, and the U.S. Department of Energy (DOE) has contributed $270 million. But Southern's shareholders have already absorbed a loss of more than $1.1 billion on the project.

"Southern has definitely been one of the more resistant" companies to federal carbon restrictions, said Sally Benson, a Stanford University researcher and expert on carbon storage. "Yet look what they're doing [at Kemper]. They've really gone out on a limb. It's a fantastic thing."

"A Lot of Pots and Pans"

Twenty miles north of Meridian on highway 493, the thing itself rises like a fantastic industrial castle from the pinewoods and cow pastures of eastern Mississippi. "If you were driving here a few years ago, you were either hunting or lost," said Jeff Shepard, a spokesman for Mississippi Power, a Southern subsidiary. Now you're almost certainly headed to the Kemper County Energy Facility. A sea of parked cars separates it from the highway; more than 5,000 construction workers are mostly hidden inside, putting the finishing touches on a bewildering mass of pipes, silos, tanks, and domes.

"We're taking coal and converting it into gas to burn in a gas turbine," said Randall Rush, a chemical engineer from Southern's research facility in Wilsonville, Alabama. "That takes a lot of pots and pans."

As one tours the site with Rush and his colleagues, the maze of piping gradually becomes penetrable—as do Southern's reasons for building it in this corner of Mississippi. Mississippi Power owns 42 square miles (109 square kilometers) of land around the Kemper plant. Under that land, at a depth of 25 feet to 125 feet (8 to 38 meters), lies a 9-foot (2.7-meter) thick seam of lignite—part of an enormous formation that arcs out of Mexico through Texas and Louisiana.

Lignite and other low-rank coals make up half the world's coal reserves, but not many American power plants use them. Lignite has high ash and water and low heat content. (See related, "Germany Plans to Raze Towns for Brown Coal and Cheap Energy.") But at the Wilsonville lab, with support from the DOE, Southern has spent nearly two decades perfecting a system for gasifying and burning lignite efficiently. Kemper is its commercial debut.

On the south side of the power plant, at the Liberty Mine, a giant dragline is already taking 86-cubic-yard (65.7-cubic-meter) bites out of the countryside. From the edge of the pit, trucks must drive only a few hundred yards to dump their loads of coal onto a conveyor belt that carries it up and into the power plant. There the coal will be crushed, dried—the Kemper lignite is 45 percent water—and pulverized to a consistency "between beach sand and face powder," Rush said.

The coal grains will be blown at high pressure into the gasifier—essentially a tall pipe. Swirling in steam and air, the coal is heated to 1,800°F (982°C), but without enough oxygen to burn it completely. That converts most of the coal into "syngas," which is mostly hydrogen and carbon compounds, and the rest into ash.

The hydrogen will get burned in two gas turbines-essentially jet engines strapped to the ground. "The thrust that would make an airplane fly is used to turn a shaft and make electricity," Rush explained. "The gases that come out of that jet engine are hot, and you recover that heat in a steam generator, and you use it to turn a shaft in a steam turbine. So you're making electricity in two places."

A crane lifts one of Kemper's six CO2 absorbers into place.

Cleaning Up

That system, called an IGCC (for "integrated gasification combined cycle"), makes burning syngas more efficient than burning coal directly. But syngas is also easier to clean up. At Kemper, the "gas cleanup unit" stands between the gasifier and the power block and a little to the north. It will strip out most of the dust, 90 percent of the toxic mercury, and 99 percent of the hydrogen sulfide—all of which is required by existing Clean Air Act regulations. It will also remove 65 percent of the CO2, even more than would be required by regulations proposed by the EPA in January. (See related, "Poland Hosts Climate Talks, While Boosting Coal Industry.")

CO2 capture was not part of the original plan for Kemper. The plan was to remedy Mississippi Power's problem—an aging fleet of power plants concentrated on the Gulf Coast, where one was damaged by Hurricane Katrina—by tapping into the lignite at Kemper. "The CO2 was added later," said Rush. That was in 2009, when it seemed likely that Congress might pass a climate bill.

As it turns out, though, CO2 can be removed from syngas with the same liquid solvent, Selexol, that strips out the sulfur; it just takes more pots and pans. The basic principle is simple. You fill a tall tank with packing material, said Rush, to increase the surface area where gas and solvent meet. You pour Selexol in at the top and pump syngas into the bottom at 600 pounds per square inch—about 20 times the pressure in car tires. Under high pressure, the CO2 dissolves in the Selexol as it does in Coke. When you release the pressure, it's like popping the cap on a Coke bottle—the CO2 comes bubbling out in pure form.

The Kemper plant will capture 3.5 million metric tons of CO2 a year and compress it to a liquid-like state. The energy required to do that will use up the efficiency gained by the IGCC process. But there's a bright side: Mississippi Power will actually sell the CO2, delivering it by pipeline to Denbury Onshore and another independent oil company. Those companies already use CO2 for "enhanced oil recovery" at aging fields along the Gulf Coast. Right now they mine their CO2 from a natural deposit near Jackson, a hundred miles west of Kemper.

The Kemper plant will also sell 150,000 tons a year of sulfuric acid to the Gulf Coast chemical industry, which is flourishing these days because of cheap natural gas. The fracking boom has transformed the electric power industry too; coal-fired plants all over the country have been switching to natural gas. Since 2008, Southern has cut its reliance on coal in half, from 69 percent to 36 percent of its generating capacity. Mississippi Power already generates 75 percent of its power from gas.

The Sierra Club, which strongly opposes the Kemper project—"It's dirty, it's expensive, and it's unnecessary," said Louie Miller, the Club's state director—argues that the state as a whole has excess generating capacity and that Mississippi Power, which serves southern Mississippi, could have bought an existing natural gas plant at a fraction of the cost of building Kemper. To help pay for the plant, in the poorest state in the nation, the utility has already raised rates 18 percent—about $270 a year for its average customer. It expects to ask for another hike of 4 to 6 percent next year. Miller predicts more rate hikes will follow.

Southern says it doesn't want to rely too much on natural gas, which has a history of volatile prices. At Kemper, Southern owns the lignite and has a long-term contract with North American Coal to extract it. The price is stable and cheap. In fact, said Southern start-up manager David Hardin, with revenues of at least $50 million a year expected from the sale of CO2 and other byproducts, "it's almost like the fuel is free."

There are 600 million tons of lignite at Kemper, more than three times as much as the plant will burn in its 40-year lifetime. "Maybe somewhere down the road we'll want to put in another facility that burns lignite," Hardin said.

The conveyer belt will carry lignite from the adjacent mine into the Kemper plant. The dome on the right protects a few days' supply of coal from Mississippi rains.

Boundary Dam

The view from southern Saskatchewan is similar. "We sit on top of a 300-year supply of coal," said SaskPower CEO Robert Watson. But the regulatory outlook is clearer.

Under Canadian regulations that will take effect in July 2015, any new coal-fired plant, and any existing one that's at least 50 years old, can emit no more than about 925 pounds of CO2 per megawatt-hour. (EPA's proposed limit is 1,100 pounds per megawatt-hour for new plants; Kemper will emit around 800 pounds.) When a Canadian power plant turns 50, it must either be shut down or start capturing carbon.

The Boundary Dam station consists of six separate units that burn pulverized lignite. SaskPower shut down the oldest unit last year and plans to close a second one. Unit 3 will turn 50 in 2017. "We had to do a major reno or shut it down," Watson said. "We determined it would be the perfect unit to try out new technology."

Gasifying the coal and capturing the CO2 before combustion was not an option; that would have required an entirely new plant like Kemper. SaskPower will do its cleanup after the coal is burned. Because CO2 is less concentrated and at much lower pressure in smokestack gases than it is in syngas, it won't spontaneously dissolve into a liquid solvent. SaskPower will use a solvent called an amine that reacts with CO2 chemically and grabs it out of the air.

That process had been considered more costly, but the technology has been improving. SaskPower claims it will actually spend less energy capturing CO2 than Kemper will—with a technology that can be applied to existing coal plants, not just fancy new IGCCs. And SaskPower aims to capture 90 percent of the CO2, from that one unit at least, to bring its emissions downs to about 330 pounds per megawatt hour. That's "far better than any other fossil fuel unit around," Watson said.

Mississippi Power owns 42 square miles of land and 600 million tons of lignite around the Kemper plant.

The CO2 will be sold to Canadian oil company Cenovus Energy and injected into the Weyburn oil field in Saskatchewan. That field has been the site of a long-running experiment in carbon storage monitored by the Paris-based International Energy Agency. So far no major leaks or other problems have been reported.

The renovation of Boundary Dam Unit 3 is costing about $1.2 billion, of which the Canadian government is paying close to 20 percent. Like Southern, SaskPower hopes to sell its technology overseas, especially in China. "We think we will show a model to the world," Watson said, "to allow companies to keep burning coal, but do it cleaner. Everybody agrees we've got to clean it up." (See related, "Harbin Smog Crisis Highlights China's Coal Problem," and "Coal Burning Shortens Lives in China, New Study Shows.")

Adequately Demonstrated?

The amine process that SaskPower is relying on is not new; it has been widely used in other industries. It has also been successfully tested at a Southern Company plant near Mobile, Alabama. As of last fall, Southern had stored 100,000 metric tons of CO2 underground. Like other companies in the industry, though, Southern opposes EPA's efforts to require carbon capture and storage on the grounds that the technology has not been "adequately demonstrated," as the Clean Air Act requires.

There is much debate about what that term means. "'Adequately demonstrated' doesn't mean it has to have been run at commercial scale," said Howard Herzog, senior research engineer and carbon capture specialist at Massachusetts Institute of Technology. "If it's been shown to work at pilot plants, it's adequately demonstrated. As far as the capture goes, there's no doubt that the technology is here today. It's demonstrated that it will work."

What's still uncertain is the long-term cost of CCS—and that's why the two plants that are coming online this year are so important. The new Boundary Dam unit will be switched on this summer, Watson said. Mississippi Power expects to start making syngas at Kemper in June, and to connect to the grid by the end of the year. A half-million-ton pile of coal is already mined and waiting.

"Psychologically it's very important for Kemper to work," said Herzog. "But the Boundary Dam is probably a truer test of how carbon capture can be adapted to the marketplace."

"You've got to give Southern credit though—they really are trying to push the technology. From an engineering viewpoint, Boundary Dam was a much simpler project. This is a very ambitious project Southern is doing. I'm hoping they're going to pull it off." (See related interactive map: "Four Ways to Look at Global Carbon Footprints.")