Construction underway on sCO2 Brayton cycle demo plant

3 January 2019

On 15 October, Southwest Research Institute (SwRI), Gas Technology Institute (GTI), GE, and the US Department of Energy/National Energy Technology Laboratory (DOE/NETL) celebrated groundbreaking at a 10 MW supercritical carbon dioxide (sCO2) Brayton cycle demonstration facility, called the Supercritical Transformational Electric Power (STEP) pilot plant.

The $119 million first-of-its-kind facility, being built at SwRI’s San Antonio site, in Texas, will “demonstrate the next generation of higher-efficiency, lower-cost electric power technology”, they say. According to DOE Assistant Secretary of Fossil Energy, Steven Winberg: “With this pilot plant, the technology is moving from the lab to the field. This project will provide important data on the potential challenges of operating the technology on a larger scale.”

The DOE is contributing about 70% of the costs and as part of its programme to commercialise supercritical CO2 for power generation applications. SwRI says it has conducted more than twenty DOE projects relating to supercritical CO2, including development of high-efficiency sCO2 power cycle concepts.

The STEP pilot plant is envisaged to operate over three years, with the aim of verifying the performance and integrity of components, demonstrating a pathway towards a thermodynamic cycle efficiency greater than 50% and showing the potential for cost savings in electricity generation applications.

The pilot plant will employ a natural gas fired heater and includes recuperators, heat exchanger, cooling tower, backup generators, emissions stack, plus balance of plant components, with the aim of demonstrating a fully integrated Brayton cycle power generation facility with supercritical carbon dioxide as the working fluid.

Supercritical CO2, held above a critical temperature and pressure, has the properties of a gas but the density of a liquid. Its use as a working fluid in a Brayton cycle has the potential to dramatically reduce the size of power generation equipment, while also providing significant efficiency gains.

Because of the efficiency of supercritical carbon dioxide as a thermal medium, sCO2 turbomachinery can be one tenth the size of conventional power plant components on a per MW basis, opening up the possibility of a “desk-sized sCO2 turbine” with an installed capacity of around 10 MW, its proponents say.

SwRI, GTI and GE have collaborated on the design of the STEP pilot plant, which is “specially designed to evolve over time to keep pace with industry advancements.” The facility features skid- mounted components that provide flexibility and a what is described as a “unique reconfigurable design.” Construction is scheduled to be completed in 2020. 

Doug Hofer of GE with a plastic model of a “desk-sized” sCO2 turbine could produce about 10 MW (image courtesy GE)
sCO2 turbomachinery can be one tenth the size of conventional equipment (image courtesy SwRI)
Visualisation of the STEP pilot plant (image courtesy SwRI)

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