Carbon capture and storage (CCS) is often promoted as a way for coal power to be made “clean”: Projects such as the in-progress Kemper power plant in Mississippi and the recently announced Petra Nova project in Texas aim to trap the carbon dioxide from burning coal and then store it into underground storage or into previously depleted wells to extract more oil. (See related story: “Clean Coal Test: Power Plants Prepare to Capture Carbon.”)
CCS is being applied to natural gas-fired electricity as well (just today a new effort in Scotland was announced), and a new project in the U.S. aims to produce fossil power with zero emissions and greater efficiency than other facilities have been able to achieve. A group of companies, including Chicago-based energy producer Exelon and Durham, N.C.-based technology purveyor NET Power, this week announced plans for the project, a $140 million carbon-capture natural gas-fired plant in Texas.
The “first of its kind” demonstration plant is different because, instead of using steam as a component of electricity generation the way a typical plant would, it instead produces a pure stream of carbon dioxide from natural gas combustion and uses that to produce additional electricity more efficiently. The carbon dioxide that emerges from that high-pressure, oxygen-only combustion process needs no further processing to be injected underground, according to John Thompson, director of the Fossil Transition Project for Clean Air Task Force, which monitors and promotes new clean energy technology.
The energy saved by not having to process the carbon dioxide further would address one of the pitfalls of CCS: the process of capturing and storing the carbon is typically so energy-intensive that taking a bite out of how much energy a plant can produce per unit of fuel. But Thompson said that the NET Power project, which is targeted for completion in 2017, would convert natural gas with the same or higher efficiency compared to a traditional gas plant, even when you factor in the carbon capture.
The NET Power project is “really focused on coming up with a much cheaper way of capturing carbon dioxide from natural gas emissions,” Thompson said. The plant will have a modest 50-megawatt capacity and lower capital costs than a conventional plant; the project release said the cost of power from its CCS gas plant will be “highly competitive” with that of conventional plants. The project’s backers are also looking at ways to transfer the technology to coal plants, but it can only be applied at plants that gasify coal rather than burning it conventionally, Thompson said.
The U.S. Environmental Protection Agency has encouraged a transition to natural gas from coal as way for states to meet emissions reduction targets associated with its proposed Clean Power Plan. Gas emits about half as much as coal when burned, but the emphasis on natural gas for reducing emissions has been questioned by some who point out that it might hinder the scaling up of renewable energy, and that natural gas production sites are likely emitting much more methane than the government initially estimated. (See related stories: “Switch to Natural Gas Won’t Reduce Carbon Emissions Much, Study Finds” and “Methane Emissions Far Worse Than U.S. Estimates, But Study Concludes Natural Gas Still Better Than Coal.”)
Thompson said that CCS is needed for gas so that it can support renewable energy, serving as backup power without undercutting greenhouse gas emissions reduction efforts. “Intermittent energy sources like wind and solar power work best when they have a low carbon backbone to work with,” Thompson said. With the transition from coal to natural gas currently under way, that backbone is getting clean in the United States, he said, but “has to get a lot cleaner.” (Vote and comment: Can Natural Gas Be a Bridge to Clean Energy?)