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The Global Energy Prize annually honors outstanding achievements in energy research and technology from around the world that are helping address the world’s various and pressing energy challenges.

Breaking ground for a groundbreaker: the first Allam Cycle power plant

May 15, 2017
Modern Power Systems

On 9 March, NET Power – a collaboration between Exelon Generation, CB&I, and 8 Rivers Capital – announced it had broken ground on a first-of-a-kind power plant that will demonstrate the Allam Cycle. This novel concept (described by its inventor, Rodney Allam, in Modern Power Systems, May 2013 issue) employs oxyfuel combustion of gaseous fuel and supercritical high pressure carbon dioxide as the working fluid to drive a turbine, with the inherent elimination of all atmospheric emissions without requiring expensive, efficiency-reducing “add-on” carbon capture equipment.

The 50 MWt demonstration plant is being built in La Porte, Texas.

NET Power is the first technology that allows policy and economics to work together, instead of against each other, to ensure the world meets our climate targets," said NET Power's CEO, Bill Brown. The groundbreaking "marks a significant step for our world-class team, including Exelon, CB&I, 8 Rivers and Toshiba, towards delivering a technology that will be the cornerstone of a modern global energy infrastructure that is clean, affordable and flexible."

Executives from each of the companies gathered on the site to mark the start of construction of the demonstration plant. The $140 million programme - which not only includes demonstration plant design and construction, but also ongoing technology advancement, a full testing and operations programme, and commercial product development - is funded by a combination of cash and in-kind contributions from Exelon and CB&I. Toshiba has developed and is now manufacturing a new supercritical carbon dioxide turbine and combustor fortheproject.CB&Iisperformingthe engineering, procurement, and construction of the plant. Exelon is providing operations, maintenance, and development services. 8 Rivers, in which Rodney Allam is a partner, owns the technology and continues to develop it. Hideo Nomoto, formerly with Toshiba and largely responsible for the Japanese company's involvement, saying he became "quickly fascinated" by the Allam Cycle when it was first introduced to him, has also recently joined 8 Rivers.

The Allam Cycle based plant produces only electricity, liquid water and pipeline- ready carbon dioxide, while at the same time operating as efficiently as the best natural gas power plants available today, says NET Power, capable of a net efficiency of 58.9%.

(LHVbasis) ongas (withfullcarboncapture), 51.4%(LHVbasis) oncoal (employingan integrated gasifier), again with full carbon capture.

In addition, for a small reduction in efficiency, the technology "can operate without water, actually becoming a net water producer."

NET Power's 50MWt demo plant will be a "fully operational unit that will generate power to the grid while demonstrating all key aspects of the Allam Cycle", with commissioning expected to begin in late 2016 and be completed in 2017.

The facility will also provide the validation to begin constructing the first 295 MWe, commercial-scale plants says NET Power, which "is already engaged with customers across several industries on the design and development of these projects", including in the USA and UK.

As well as the new turbine, combining elements of both gas and steam technology, and the new combustor (which has been successfully tested on a test rig in California), key to implementation of the Allam Cycle is the recuperative heat exchange system downstream of the turbine (see item 7 of the flow diagram, right), which must be highly efficient while coping with onerous conditions, including high temperatures and pressures. The outlet temperature of the carbon dioxide stream leaving the turbine is about 750°C. This is cooled to around 50°C and the heat transferred to the 300 bar carbon dioxide stream entering the combustor, which is heated to about 720°C prior to entering the combustor.

A key feature of the Allam Cycle is that heat goes in at two temperature levels, high, via fuel combustion, and low, less than 400°C. The low temperature heat is vital in attaining high efficiency and can be derived from, eg waste heat from the air separation unit, waste heat from a gasifier quench, LNG regasification, solar power, existing power station. This means the cycle can be seen as "a platform with diverse applications", its developers say.

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