Two Carbon-Trapping Plants Offer Hope of Cleaner Coal
Coal power plants in Saskatchewan and Mississippi will limit emissions, thanks to special circumstances.
Carbon emissions need to be reduced dramatically to avert major climate change.
Two of the world’s first coal-fired power plants with integrated carbon capture are nearing completion in Saskatchewan and Mississippi, providing a rare lift for a technology that has languished in recent years.
Carbon capture and sequestration (CCS) remains expensive, but the cost of stabilizing the climate could be much higher without it, according to the Intergovernmental Panel on Climate Change (see “The Cost of Limiting Climate Change Could Double without Carbon Capture Technology”). In a report last month, the IPCC noted that CCS is the only way to cut the carbon emissions of existing power plants, and that CCS-equipped power plants burning biomass could help remove carbon dioxide from the atmosphere. The IPCC says both strategies may be essential to limit global warming.
A 110-megawatt plant in Saskatchewan, a refurbished coal-fired generator, is set to restart in a matter of weeks with carbon capture added, according to Robert Watson, CEO for provincial power utility SaskPower.
Under Canadian regulations, the Boundary Dam power station can release no more than 420 tons of carbon dioxide per gigawatt-hour of power generation—the same as a state-of-the-art plant fired with natural gas. This is a tall order since the power station will burn lignite—the dirtiest form of coal. Yet SaskPower expects to release just 150 tons of carbon dioxide per day thanks to its new carbon dioxide scrubber, which will absorb and capture 90 percent of the carbon in the plant’s exhaust.
SaskPower could afford to build the $1.2 billion plant partly because lignite is so cheap, but also because Boundary Dam is adjacent to a lignite strip mine. Extra revenue will come from piping most of the 3,000 tons of carbon dioxide that the plant captures per day to Cenovus, a Calgary-based oil and gas firm. Leftover carbon dioxide will be stored in an aquifer 3.5 kilometers below the plant.
“If they couldn’t sell the CO2 for enhanced oil recovery, the project wouldn’t have been economic,” says Howard Herzog, an expert on carbon sequestration, and a senior research engineer with the MIT Energy Initiative.
SaskPower CEO Watson says that the cost of the power from Boundary Dam will be “comparable” to natural gas-fired generation providing the recent price increase in natural gas holds. He expects that natural gas prices will tend to rise over the next 30 years-plus that the Boundary Dam plant will operate.
The other coal plant with carbon capture, in Kemper, Mississippi, should start up later this year. Its owner, Mississippi Power, is counting on similar strategies to minimize operating costs. The plant is also adjacent to a lignite strip mine, and will boost revenues by selling its carbon dioxide to oilfield operators. The project also received $270 million from the U.S. Department of Energy.
However, at 565 megawatts, the Mississippi plant is five times bigger than the Saskatchewan plant, and it uses less conventional technology. It has also been far more controversial than the Boundary Dam project because it gasifies its coal, and because its price tag is now expected to be more than double Mississippi Power’s original projection of $2.4 billion.
The Mississippi plant uses a proprietary gasifier designed by Southern Company and Houston-based engineering firm KBR to turn lignite into a mix of carbon dioxide and hydrogen. The firms have also licensed the design for use in China (see “Cleaning Up on Dirty Coal”). Another novel component is the plant’s carbon dioxide capture system, which will remove 65 percent of the carbon dioxide from its gas mix before firing the turbines. The carbon dioxide will be captured at the same time that the plant captures its sulfur dioxide, using the same solvent scrubber that conventional coal plants use to remove sulfur dioxide.
Despite the controversy, experts are not greatly concerned by the cost overruns. “The costs of a first-of-a-kind plant are always going to be higher than the cost of your nth plant,” says Sarah Forbes, a senior associate at the World Resources Institute in Washington, D.C.
Herzog agrees: “Kemper was a real first of a kind. You’ve got a lot of first-mover costs in there, and people tend to underestimate first mover costs drastically. By the time you do it half a dozen times, you’re knocking out a lot of cost.”
Watson says a second project of the same type as Boundary Dam would cost 20 to 30 percent less. But whether SaskPower and other utilities get a chance to build more plants with carbon capture may be a matter of policy, according to Herzog. CCS is going to lose out in most cases, he says, if fossil fuels can be burned with impunity. “If you’re allowed to put the CO2 in the atmosphere, as we are today, it’s not going to be applied,” he says.
The original version of this article stated that regulations limit carbon dioxide emissions to 420 tons per megawatt-hour of power generation. It was corrected to say gigawatt-hour.
Hear more about carbon capture at EmTech MIT 2017.Register now