3 ms·

> Closed Brayton cycles for power generation have a commercial history dating to the late 1930’s when the first of a series of power generation plants using the

by twic 5y ago

> Closed Brayton cycles for power generation have a commercial history dating to the late 1930’s when the first of a series of power generation plants using the closed Brayton cycle made use of air as a working fluid. These closed air Brayton units operated from the late 1930’s through the 1970’s using a variety of energy sources including coal, gas, and waste heat. These recuperated Brayton cycle installations achieved good reliability and relatively high efficiencies as compared to other power generation technologies of the era. So why did we stop using them?

namibj 5y ago
My guess: expensive. Gas turbine power plants are not cheap, but fuel wasn't that expensive back then. I'd expect the replacement to either use hydrogen with hydrogen-resistant steel, or, more likely, helium. I think carbon-carbon composite can handle extreme temperatures in a helium atmosphere, beyond what you can reasonably reach with a fuel flame. However, the temperatures should be feasible for fusion power plants, which could use helium or another noble gas (in case helium diffuses too fast) to cool the chamber-facing tiles. The light gas would be for power density by way of having a high speed-of-sound. Also, we mostly switched to Rankine cycle for external combustion power plants. Steam turbines are quite good at what they're doing.
- pfdietz 5y ago
  Gas turbine power plants (specifically, combustion turbines) are actually very cheap. The reason is they avoid heat exchangers. Simple open cycle combustion turbines don't need heat exchangers at all, neither before the turbine nor after it (to condense/cool a working fluid). A simple cycle gas turbine power plant might be as little as $400/kW, vs $10,000/kW for a nuclear power plant.
WJW 5y ago
> to other power generation technologies of the era. Emphasis added. These days we can design significantly better steam turbines due to advancements in computational fluid dynamics and air as a working fluid is just not as nice (thermodynamically speaking) as steam. The Brayton cycle is still used in jet engines and CCGT power plants though.

by twic 5y ago

namibj 5y ago

My guess: expensive. Gas turbine power plants are not cheap, but fuel wasn't that expensive back then. I'd expect the replacement to either use hydrogen with hydrogen-resistant steel, or, more likely, helium. I think carbon-carbon composite can handle extreme temperatures in a helium atmosphere, beyond what you can reasonably reach with a fuel flame. However, the temperatures should be feasible for fusion power plants, which could use helium or another noble gas (in case helium diffuses too fast) to cool the chamber-facing tiles. The light gas would be for power density by way of having a high speed-of-sound. Also, we mostly switched to Rankine cycle for external combustion power plants. Steam turbines are quite good at what they're doing.

pfdietz 5y ago
Gas turbine power plants (specifically, combustion turbines) are actually very cheap. The reason is they avoid heat exchangers. Simple open cycle combustion turbines don't need heat exchangers at all, neither before the turbine nor after it (to condense/cool a working fluid). A simple cycle gas turbine power plant might be as little as $400/kW, vs $10,000/kW for a nuclear power plant.

WJW 5y ago

> to other power generation technologies of the era. Emphasis added. These days we can design significantly better steam turbines due to advancements in computational fluid dynamics and air as a working fluid is just not as nice (thermodynamically speaking) as steam. The Brayton cycle is still used in jet engines and CCGT power plants though.