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A casual conversation in Copenhagen in June led me to attend a session on supercritical CO2 (S-CO2) at the last International Gas Turbine Institute conference. That sparked my interest, and for the last few months I’ve been conducting a long series of interviews on the subject.
It turns out that S-CO2 could well be the next great frontier in turbine engineering. While there are clearly further gains in efficiency to be eked out of steam and gas turbines, this is likely to be attained via small incremental improvements.
Supercritical CO2, on the other hand, demands a whole new type of turbine, one that is designed for lower temperatures and much higher pressures. The thermodynamic details are outlined in this issue’s cover story, and the potential is immense: The turbomachinery footprint reduced by two orders of magnitude; the ability to recycle CO2 and turn it into a power source; perhaps even the potential to augment combined cycle power plant efficiency and push it towards the 70% mark (with simple cycle efficiency exceeding 50%); and a turbine that does not emit NOx.
Understandably, the U.S. Department of Energy is investing plenty of R&D dollars in this technology. Research bodies from Sandia National Labs to Southwest Research Institute are all over it, too. Sandia (in conjunction with Barber-Nichols) has already erected a small-scale test loop which includes a prototype CO2 turbine. It started up in July and is running successfully.
Meantime, Echogen and Dresser-Rand have produced a working 7.5 MW system (shown on the cover), which is currently undergoing factory testing. It should be commercially available next year. Not to be outdone, Argonne National Labs has been working with Pratt & Whitney Rocketdyne to develop the specifications for a 1 GW nuclear plant which would include CO2 turbines.
The applications for supercritical CO2 extend as far as geothermal, solar and even coal. Harassed by regulators and burdened with the development of expensive carbon capture systems, the coal industry could come to look upon S-CO2 as the economic shot in the armthat carbon capture and storage technology needs to make it more than a sideline science project for electric utilities. Could it open the door to an affordable clean coal industry? That would certainly upset the energy applecart.
Of course, it is still early days and barriers remain. Each and every component and system will likely come under a supercritical microscope as engineers seek to scale SCO2 up commercially.
Heat exchangers, for example, play a key role in capturing exhaustCO2 and turning it into useable energy. Companies like Brayton Energy,Heatric andThar Energy are involved in a hotly contested battle to design and manufacture a new generation of heat exchangers that are up to the task of supporting large-scale CO2 machines.And then there are the turbines themselves. Echogen/Dresser-Rand and Barber- Nichols are early entrants. GE is taking notice courtesy of GE Global Research.
It’s not often you find mechanical engineers giddywith excitement about a newfield.Yet the folks at Sandia Labs are likening S-CO2 R&D to theApollo Space Program during the sixties. Give it another couple of years and S-CO2 products could perhaps be making headlines well beyond the energy sector.