Zero-emissions power cycle achieves first fire

8 June 2018

A significant milestone has been achieved at NET Power’s ‘supercritical carbon dioxide’ (sCO2) power plant. This is a test facility in La Porte, Texas, built to demonstrate the potentially revolutionary natural gas–fuelled Allam Cycle.. The project is designed to produce low-cost electricity from natural gas while generating near-zero atmospheric emissions, including full CO2 capture.

NET Power, which is based in Durham, North Carolina, said on May 30 that the project achieved firing of a commercial-scale 50 MWt combustor made by Toshiba. The demonstration project partners are Exelon Generation, engineering and construction firm McDermott, and 8 Rivers Capital, the firm that invented the Allam Cycle.

First fire of the combustor is a remarkable milestone for the project, which broke ground in March 2016, because it validates the fundamental operability and technical foundation the power system. Successful operation of the project could allow the company to develop larger 300 MWe commercial-scale plants as early as 2021, it believes.

The Allam Cycle, named for its lead inventor, Rodney Allam, burns natural gas (or synthetic gas from coal gasification) with pure oxygen and uses high-pressure sCO2 as a working fluid in a semi-closed loop to drive a combustion turbine. Its byproducts are liquid water, pipeline-ready CO2, and argon and nitrogen, which could also be sold as commodities.

The company says its technology is potentially game-changing because it efficiently tackles CO2 emissions from natural gas–fired power plants. “Existing natural gas plants burn natural gas with air, which is a mix of oxygen and nitrogen” it says. “These technologies emit CO2, which is difficult and expensive to separate from the nitrogen and residual oxygen. Unfortunately, this has made carbon capture uneconomic for traditional power plants. NET Power addresses the cost hurdles of older technologies with a novel process – an oxy-fuel, supercritical CO2 power cycle – that produces electricity efficiently while inherently eliminating all air emissions.” With a small reduction in efficiency, the technology can also operate without water, it added.

The USA has one of only a few state-led efforts to develop sCO2 cycles. Others include South Korea, which is exploring a sCO2 Brayton cycle for a small modular reactor, and China, which has funded research into a cascaded sCO2 system integrated with solar and biomass. The technology has strong backing from the US Department of Energy, partly at least because of its potential to be applied to a large variety of heat sources. Its applications could be expanded to power generation from nuclear, coal, gas, oil, concentrating solar, waste heat recovery, and geothermal, says DoE.

A handful of projects is underway across the USA to explore sCO2 Brayton cycles. Developers say sCO2 power cycles have the potential to exceed 40% efficiency, compared with Rankine’s efficiency of 33%. Benefits include reduced fuel consumption and emissions, low cooling water consumption, and a compact design that should lower capital cost, if the technical challenges can be overcome.

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