Discussion on “Beyond Brayton Cycle: It is Time to Change the Paradigm” (S. Can Gülen, ASME J. Eng. Gas Turbine Power, 140(11), p. 111703)

Abstract

The author is to be commended for his excellent paper showing potential efficiency and value advantage for alternative system architectures over today's highly evolved state of the art (SOA) gas turbine combined cycle (GTCC) offerings. Dr. Gülen has deftly outlined the second law constraints facing the engineers immersed in the difficult task of configuring next generation equipment and plant solutions. There are many technology options to be considered, each of which is uniquely positioned across the full complement of customer value parameters by thermodynamic entitlement, the maturity of core technologies, and the development and projected mature system costs. On top of these technical constraints are complex and rapidly changing market dynamics. Today's markets support a broad range of gas fired plants including simple cycle peakers (all sizes), small industrial size systems (often in CHP configurations), and large midrange or base-loaded plants of the H/J class. How will these markets change as low cost but intermittent renewables displace large base loaded fossil plants, including GTCC? What role(s) will gas fired plants play as renewables gain market share and storage goes mainstream? Which market niche will be large enough (and long enough lasting) to recoup the investments necessary to advance GTCC SOA? How scalable does the architecture need to be? How advantaged would a new architecture need to be for market acceptance? How much would it cost to validate it?GE is perhaps in a unique position to provide historical context on questions of GTCC system architecture [1]. In the early 1990s, both ABB and GE elected to invest in new engine architectures based on a belief that the conventional air-cooled Brayton cycle GTCC was nearing performance entitlement. Reheat combustion addresses combustion exergy losses. Closed circuit steam cooling relieves hot gas path cooling limitations. We learned how to make these products successful for our customers, but in the meantime entitlement for the air-cooled Brayton GTCC kept increasing as TBC coatings, 3D aero, manufacturing technology, design software, and DLN combustion progressed. Today we have additive manufacturing and CMC materials to further open up performance headroom, and digital solutions to help our customers extract maximum value. Introducing a new system architecture represents a large technical and financial risk. Pushing the SOA along the more traveled road also requires strong commitment and deep pockets. Thank you to Dr. Gülen for helping the industry navigate the complex and challenging path forward.