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Electric Power & Utilities/Jet engines vs electrical gas turbine power plants


What is the difference between a gas turbine jet engine that produces thrust and an electrical gas turbine engine that turns a generator and produces electricity.  In other words why doesn't the gas turbine engine at a simple cycle power plant fly off into space.

Hi Jeff -
Good question.

In any gas turbine (GT) engine, stationary or aviation, atmospheric air flows in, is compressed to high pressure, and is mixed with burning fuel that heats it to a high temperature-high pressure-high energy gas. This high energy gas then gives up some of its energy as it partially expands through a power turbine that turns the shaft that drives the compressor (and fan blades, in the aviation fan-jet).

In a stationary GT the partially expanded high energy gas continues to fully expand back to atmospheric pressure through additional stages of the power turbine, thus doing additional work to turn the shaft that drives the electric generator. Fully expanded exhaust gas exits the final stage of the power turbine at essentially atmospheric pressure, thus there is little or no further pressure drop available to accelerate the exhaust gas and create thrust. Any small unbalanced thrust created within the stationary GT is taken by a thrust bearing, and is resisted by anchor bolts that hold the engine in place on its foundation.

But in an aviation GT, the partially expanded high energy gas that has driven the compressor (and fan blades) is still at considerable pressure/temperature levels and has considerable energy. It completes its full expansion to atmospheric pressure by accelerating to high speed flow through a nozzle (it becomes a high speed "jet" of exhaust gas) at the jet engine exhaust. The high speed jet of exhaust creates a reaction force (thrust) that pushes back on (does work on) the engine and the airplane in the same way that air escaping from an inflated rubber balloon pushes back on the balloon. If the pilot does not stand on the brakes the plane will accelerate until the drag force of air flowing over the surface of the plane equals the thrust force from the jet exhaust. Ideally, that would not not happen until well after liftoff.  ;-)

Good luck!

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W.A. (Bill) Stevens


I can explain the technical and economic tradeoffs of making electricity from natural gas, coal, nuclear, wind, solar, and biomass energy sources. I'm familiar with air pollution control technologies, including CO2 capture and sequestration. I have a good understanding of the science on global warming and can explain how energy use inefficiencies and various fuels and technologies contribute to that process. I can tell you why we have to build more new gas, nuclear, wind, and solar power plants, but will still have to keep using coal for a few decades to make elctricity. I can explain energy conversion efficiency and power plant operations. However ... I'm not an electrician, so probably cannot help with questions on motors or wiring. ;-)


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