Closed-cycle gas turbine
A closed-cycle gas turbine is a turbine that uses a gas (e.g. air, nitrogen, helium, argon, etc.) for the working fluid as part of a closed thermodynamic system. Heat is supplied from an external source. Such recirculating turbines follow the Brayton cycle.
The initial patent for a closed-cycle gas turbine (CCGT) was issued in 1935 and they were first used commercially in 1939. Seven CCGT units were built in Switzerland and Germany by 1978. Historically, CCGTs found most use as external combustion engines "with fuels such as bituminous coal, brown coal and blast furnace gas" but were superseded by open cycle gas turbines using clean-burning fuels (e.g. "gas or light oil"), especially in highly efficient combined cycle systems. Air-based CCGT systems have demonstrated very high availability and reliability. The most notable helium-based system thus far was Oberhausen 2, a 50 megawatt cogeneration plant that operated from 1975 to 1987 in Germany. Compared to Europe where the technology was originally developed, CCGT is not well known in the US.
Gas-cooled reactors powering helium-based closed-cycle gas turbines were suggested in 1945. The experimental ML-1 nuclear reactor in the early-1960s used a nitrogen-based CCGT operating at 0.9 MPa. The cancelled pebble bed modular reactor was intended to be coupled with a helium CCGT. Future nuclear (Generation IV reactors) may employ CCGT for power generation, e.g. Flibe Energy intends to produce a liquid fluoride thorium reactor coupled with a CCGT.
Supercritical carbon dioxide closed-cycle gas turbines are under development; "The main advantage of the supercritical CO2 cycle is comparable efficiency with the helium Brayton cycle at significantly lower temperature" (550°C vs. 850°C), but with the disadvantage of higher pressure (20 MPa vs. 8 MPa).
- Nitrogen or Air Versus Helium for Nuclear Closed Cycle Gas Turbines | Atomic Insights
- AN ASSESSMENT OF THE BRAYTON CYCLE FOR HIGH PERFORMANCE POWER PLANTS
- Frutschi, Hans Ulrich (2005). Closed-Cycle Gas Turbines. ASME Press. ISBN 0-7918-0226-4. Retrieved 7 December 2011. Note: front matter (including preface and introduction; PDF link) is open access.
- Thermodynamics and Propulsion: Brayton Cycle
- A REVIEW OF HELIUM GAS TURBINE TECHNOLOGY FOR HIGH-TEMPERATURE GAS-COOLED REACTORS
- Keller, C. (1978). "Forty years of experience on closed-cycle gas turbines". Annals of Nuclear Energy. 5 (8–10): 405–201. doi:10.1016/0306-4549(78)90021-X.
- "Nuclear Power: Small modular reactors". Power Engineering (magazine). 7 June 2012. Retrieved 7 June 2012.
- McDonald, C. F. (2012). "Helium turbomachinery operating experience from gas turbine power plants and test facilities". Applied Thermal Engineering. 44: 108–181. doi:10.1016/j.applthermaleng.2012.02.041.
- ML-1 Mobile Power System: Reactor in a Box | Atomic Insights
- IAEA Technical Committee Meeting on "Gas Turbine Power Conversion Systems for Modular HTGRs", held from 14-16 November 2000 in Palo Alto, California. International Atomic Energy Agency, Vienna (Austria). Technical Working Group on Gas-Cooled Reactors. IAEA-TECDOC--1238, pp:102-113
- Introduction to Flibe Energy: YouTube Video (~20 min) and PDF of slides used
- Introduction to Gas Turbines for Non-Engineers (see page 5)
- V. Dostal, M.J. Driscoll, P. Hejzlar, A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors at the Wayback Machine (archived 27 December 2010) MIT-ANP-Series, MIT-ANP-TR-100 (2004)
- US Patent 5309492 "Control for a closed cycle gas turbine system"
- Industrial Closed-cycle Gas Turbines for Conventional and Nuclear Fuel (1967)
- on YouTube (at Sandia National Laboratories, 2014)
-  "Aviation Jet Oils"