Supercritical carbon dioxide |


Mechanical completion celebrated


Mechanical completion of STEP Demo was marked by a celebration on 26 October 2023 attended by project members, partners, industry leaders, government officials, and the press.


Some quotes from the day:


“We are excited to collaborate with our partners through the STEP pilot project to showcase the benefits of supercritical carbon dioxide technology for power


production” Dr Paula Gant (President and CEO, GTI Energy)


“This technology is incredibly versatile, whether it be in zero-emission waste heat


recovery, or coupled with concentrating solar, nuclear, biomass, geothermal, coal, or for long-duration thermal storage, the


applications are many” Don Stevenson (VP GTI Energy)


“STEP will undoubtedly change the way we think about power generation” Dr Adam Hamilton (President and CEO SwRI)


“With GE Vernova providing the equipment that generates one-third of


with wide applicability across different modalities and has the potential to be a


the world’s power and one-half of US power, decarbonising the power and industrial sector is at the forefront our mind. sCO2


is an emerging technology


key part of the decarbonisation roadmap” Jason Mortzheim (sCO2


Platform Leader, GE Vernova Advanced Research)


“The STEP Demo facility was built with flexibility and modularity in mind, so


it can serve as a test bed for future development and validation of system


components or alternate supercritical CO2 cycle configurations. I’d like to thank GTI Energy, Southwest Research Institute, GE Research, DOE’s National Energy Technology Laboratory, and all of the vendors involved who made this first-of- a-kind power plant based on sCO2


as the


working fluid a reality” Robert Schrecengost (Division Director at DOE’s


Office of Fossil Energy and Carbon Management)


analysis extensively performed by the vendor, Heatric, SwRI, and GTI Energy to arrive at an acceptable design for the header, including the header nozzle locations and manifold design. This analysis resulted in significant schedule delays, but fabrication was successfully completed, and the HTR was delivered to site and installed in January 2023.


The turbine stop and control valve controls the flow of CO2


to the turbine and shuts off in an


emergency situation. For the STEP Demo plant, this valve is adapted from GE’s commercial steam turbine product line by casting the valve body from Haynes 282 nickel alloy to accommodate sCO2


and has been received and installed. The turbine is 16 MW (gross) and is an advancement on the predecessor US DOE funded SunShot project sCO2


Above: Rotor of sCO2 turbine (16 MW gross)


turbine, which SwRI


and GE fabricated and successfully tested to 715°C and 27 000 rpm.


Ribbon cutting for the STEP Demo facility, 26 October 2023. Pictured left to right: Jason Mortzheim, GE Vernova; Don Stevenson, GTI Energy; Texas State Senator José Menéndez; Robert Schrecengost, US Department of Energy; Adam Hamilton and Walter Downing, SwRI


fluid and the high operating temperatures. Significant challenges have been experienced with the production casting of this ~5 ton valve resulting in surface inclusions requiring removal by grinding and weld repair followed by machining. Applying this traditional procedure to HA282 material is slower than normal as the inclusion removal and weld repair needs to be controlled and slow to avoid excessive heating that could cause new cracks to form. The valve body is currently still in production. Because of the manufacturing challenges and delays encountered with the 715°C turbine stop and control valve, an action was taken to additionally procure a lower temperature valve to meet the project plans for simple cycle configuration testing. This second valve was fabricated with 316 stainless steel for <550°C and 275 bar service


16 | November/December 2023| www.modernpowersystems.com


The compact 10 MWe STEP Demo design, with its small internal diameter relative to its length, created manufacturing challenges not experienced with larger power equipment of similar power output. It proved difficult for machine tools to reach within the case to meet required tolerances. 5-axis EDM was successfully applied to the rotor and stators, each from monolithic blocks of Nimonic 105 material.


Above: sCO2


turbine, cross-sectional isometric view (16 MW gross)


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