Natural gas power plant promises to capture carbon at no cost
Net Power, a new power station in La Porte, Texas, aims to capture the CO2 it produces at no extra cost. The $140m plant uses the so-called Allam Cycle, which instead of heating water to create steam and power the turbines, feeds pure oxygen, carbon dioxide, and natural gas into a combustor, which ignites the gas. The supercritical CO2 created in the process drives the adjacent turbine then goes through a series of compressors, pumps and heat exchangers to recuperate as much of the heat as possible and return the carbon dioxide to the beginning of the cycle. Net Power, due to start operation by December is a collaboration between North Carolina-based technology investor 8 Rivers Capital, plant operator Exelon Generation and energy construction firm CB&I.
Eight Rivers was cofounded by a pair of MIT alumni: Bill Brown, who was previously a managing director at Morgan Stanley, and Miles Palmer, who worked in aerospace technology at SAIC, a massive defense contractor. As Wall Street banks stood on the verge of collapse in 2008, Brown pitched Palmer on setting up 8 Rivers, saying by his recollection: "Why don't we get together and do good for a change?"

They initially focused on developing clean coal technologies, hoping to tap into some of the energy funds in the 2009 federal stimulus package. But they found companies simply wouldn't buy anything that added costs to the process. They were eventually introduced to Allam, who had been thinking about the potential of using supercritical CO₂ to integrate carbon capture into a power plant. He was eventually hired by 8 Rivers and, with other members of its team, he set to work developing the technology necessary to make the process compete with standard, combined cycle natural gas plants.

To truly do so, the company will have to get pretty close to the capital expenditure construction costs of such plants, which stood at $1,056 per kilowatt of capacity in 2014, according to the National Renewable Energy Laboratory. The company expects its first commercial plant to cost around $1,600 per kilowatt, in part due to higher capital expenses, warranties, and other costs associated with a first project of its kind. But they believe they can get costs down to around $1,000 by the time they’ve built five to seven full-scale plants.

Eventually, Net Power expects to produce electricity for around $42 per megawatt-hour, on par with combined cycle natural gas without carbon capture. But on top of all that, the company can also sell several by-products to the market, including carbon dioxide. Taken together, those could effectively push energy production costs down to around $20 per megawatt-hour (theoretically even as low as $9 per megawatt-hour).

Local, state, or federal clean-energy policies—such as carbon taxes, cap and trade systems, and emissions standards—could all improve the economics even further.

Net Power initially intends to act as a licensing company, rather than a developer or operator, selling the technology to utilities, oil and gas companies, and others. The company has already begun conversations and explored potential sites for its first commercial plant, which it hopes will come online as early as 2021.

“There’s always gremlins and you figure them out as you move along,” says Brock Forrest, senior research and development engineer at 8 Rivers. “But from an engineering and technical perspective, we are confident we will be able to show that supercritical CO₂ will be able to generate electricity.”

There are a few additional caveats to consider: the main market for the captured carbon dioxide would be for use in enhanced oil recovery, where energy companies inject it into aging wells to help free up remaining oil. That suggests the captured gas would continue to contribute at least indirectly to the collection and burning of fossil fuels. Crucially, the extraction of natural gas itself carries environmental consequences as well, including leakage of greenhouse gases, contamination of water tables, and earthquakes triggered by subsequent wastewater disposal.

But to the degree that Net Power technology could reduce the use of coal, and prevent the release of untold tons of carbon dioxide from natural gas, it very likely adds up to a net environmental benefit — at least compared to other fossil-fuel power plants.

This story was updated to correct estimated construction costs.