Pioneering Zero-EmissionNatural Gas Power Cycle Achieves First-Fire

First-fire has been achieved at NET Power's supercritical carbon dioxide (sCOa) power plant-a test facility in La Porte, Texas, to demonstrate the potentially revolutionary natural gas-fueled Allam Cycle. The project is designed to produce low-cost electricity from natural gas while generating near-zero atmospheric emissions, including full COa capture.

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

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" of NET Power's power system. Successful operation of the project could allow the company to develop larger 300-MWe commercial-scale plants as early as 2021.

A Revolutionary Technology

NET Power's 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 sCOa as a working fluid in a semi-closed loop to drive a combustion turbine. Its byproducts are liquid water, pipeline-ready COa, and argon and nitrogen, which could also be sold as commodities.

The company says its technology is potentially game-changing because it efficiently tackles COa emissions from natural gas-fired power plants. "Existing natural gas plants burn natural gas with air, which is a mix of oxygen and nitrogen. These technologies emit COa, 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 COa 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 Allam Cycle. Courtesy: NET Power

A Critical Milestone

The U.S. has one of only a few state-led efforts to develop sCOa cycles. Others include South Korea, which is exploring a sCOa Brayton cycle for a small modular reactor, and China, which has funded research into a cascaded sCOa system integrated with solar and biomass. The technology has strong backing from the U.S. Department of Energy (DOE), which touts the technology's economic and environmental benefits. These include a "broad applicability to [a] variety of heat sources." Its applications can be expanded to power generation from nuclear, coal, gas, oil, concentrating solar, waste heat recovery, and geothermal, it says.

A handful of projects are underway across the U.S. to explore sCOa Brayton cycles. Developers say sCO₂ power cycles have the potential to surpass 40% efficiency, compared with Rankine's efficiency of 33%. That translates into reduced fuel consumption and emissions, low cooling water consumption, and a compact design that should lower capital cost. However, before they can be used for commercial applications-including for waste heat recovery, concentrating solar power, nuclear, and fossil energy-several technical challenges must be overcome.

For now, at least, NET Power's 50-MWth (25-MWe) demonstration plant is the world's only industrial-scale supercritical carbon dioxide-based power plant and COa cycle test facility.

NET Power's 50 MWth Demonstration Plant in La Porte, Texas (PRNewsfoto/NET Power, LLC)

Fired-Up Potential

According to the company, firing of the combustor involves the integrated operation of the full NET Power process. "Following rigorous testing, the combustor will be integrated with the turbine and power will be generated," it said.

Successful operation of the 50-MWth combustor will allow NET Power to use several together in commercial facilities, each of which is envisioned to be 300 MWe. To boost the development of these commercial-scale 300-MWe natural gas plants, the company said it is "working on projects with power generation, oil and gas, and industrial companies in the U.S. and globally, as well as a number of governmental agencies abroad."

The company is banking on passage of 45Q carbon capture tax credit reform in the U.S., and demand for low-cost COa in industrial processes that use and sequester COa to fuel demand for NET Power plants and Toshiba turbines. It anticipates interest "in the very near term," it said.

"This is the exciting culmination of a process that required the hard work and dedication of our investors," said Charlie Bowser, NET Power's president. "We were also very fortunate to bring together an extraordinary group of key contractors and equipment suppliers. Because of the collaborative effort of the extended team, our achievements have fully met our expectations."

NET Power is targeting the global deployment of 300MWe-class commercial-scale plants beginning as early as 2021.

-Sonal Patel is a POWER associate editor (@sonalcpatel, @POWERmagazine)

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