Wrap-up of industrial power generation, Turbines I GEOS 24705 ...
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Wrap-up of industrial power generation, Turbines I GEOS 24705/ ENST 24705 Copyright E. Moyer 2011
Transcript of Wrap-up of industrial power generation, Turbines I GEOS 24705 ...
Wrap-up of industrial power generation, Turbines I
GEOS 24705/ ENST 24705
Copyright E. Moyer 2011
Tesla’s AC is “three-phase”
3-phase generation animation
http://www.launc.tased.edu.au/online/sciences/physics/3phase/threeph.htm
Generators are virtually unchanged in 100 yrs
Stator, 3-phase generator, Brakpan, South Africa, 1897. Photo: Siemens
Stator, 3-phase generator, Wellluck Co., China, 12.5 MW, 2010
Industrial generation design specs
• Generator should be large for heat dissipa3on • Voltage much higher than 110 V to minimize resis3ve hea3ng
• Many loops to increase voltage and power output • No sliding mechanisms that carry big current: current carried in stator
• Magnet in stator, use electromagnet for bigger B-‐field
• Mul3ple poles if needed for higher frequencies
Rotor carries electromagnet
Small Hydro Generator rotor - Rotor Assembly Area - Alstom Hydro
Manufacturing site in Galindo (Spain) copyright © 2010 M. Monteaux for Alstom
Old mill rotor (source unknown)
Turbo-generator power grew very quickly (though seems to be leveling off)
From Vaclav Smil, “Energy at the Crossroads”
* Requires growth not just in generators but in prime movers that power them * exponential growth in several stages * topping-out of steam P and T ca. 1960
First major hydropower station, Niagara Falls, 1895
Adams power station, 10 5MW AC generators. Photo: Tesla Society
Hoover Dam hydropower station, upgraded 1961
17 generators, average 120 MW. Photo: source unknown
The prime movers driving the world’s electricity supply
Invented by Parsons, 1884. 80% of world’s electricity today (all external combus3on). Power growth rapid: first turbine 75 kW (1890), by 1912 turbo-‐generator system installed in Chicago (at Fisk!) was 25 MW, -‐> 50 MW in Parson’s life3me, > 1 GW now Efficiency gain rapid: More efficient than reciproca3ng engines, also simpler – fewer moving parts. By 1916 best demonstrated ε ~ 37%. Modern turbines average ~ 33%. Mari:me use: demonstra3on of turbine-‐propelled ship, the Turbinia, 1897 Chief drawback: high rota3on rates
1. STEAM TURBINE
The prime movers driving the world’s electricity supply
Conceived of in 1791. But no means of prac3cal building 3l 1903 (Elling). Power growth slow: no commercializa3on 3l 1918, no rou3ne use 3l 1930s. Lowest-‐cost new fossil genera3on choice today.
2. GAS TURBINE
Turbine diversity: all kine3c -‐> kine3c, and yet look different. Why? All designed to use flowing fluid to rotate something – yet diversity of designs.
Features that may matter to turbine design
• Fluid velocity • Fluid density • Pressure drops -‐ whether turbine works by changing fluid pressure (“reac3on turbine”) or just allowing molecules to push on blades (“impulse turbine”), or something in between (“impulse-‐reac3on”)
Features that may matter to turbine design
Wind: Water wheel or run-‐of-‐river hydro: Dam hydro: Gas or steam turbine:
Features that may matter to turbine design
Wind: low velocity, low density, no pressure drop Water wheel, run-‐of-‐river hydro: low velocity, high density, no pressure drop Dam hydro: low velocity, high density, large p drop Gas or steam turbine: high velocity, low density, large pressure drop
Steam and gas turbine similarities & differences
Steam and gas turbine similarities & differences
Both • Work by lefng high-‐pressure gas expand • Blades of turbine are turned by the “wind” of steam • Combina3on impulse-‐reac3on turbines • To make high-‐pressure gas, heat the gas • Both are heat engines
Steam and gas turbine similarities & differences
Steam – Rankine cycle • external combus3on • condensible species (so can’t raise temperature
adiaba4cally – must put heat in for latent heat) • Tmax lower than combus3on temperature (limited by what boiler can withstand)
• slow to dispatch (hours -‐ must heat water to make steam) • expensive to build & install (needs firebox, boiler) Gas – Brayton cycle • internal combus3on • non-‐condensible species • Tmax is gas is combus3on temperature – more efficient • fast to dispatch (ca. 10 minutes) • cheap to build & install (compact, single unit) What’s not to like about gas? …only that coal is cheaper!
Gas turbine – internal combustion Why are blades so different on the sides of the turbine?
Image: from LidyaSavitri.wordpress.com; Copyright unknown.
Brayton cycle patented 1791 (John Barber), first use in piston engine 1872 (George Brayton)
First successful turbine build: 1903 (Aegidius Elling)
… by 1918 General Electric has a gas turbine division.
Now generator of choice for fast installa3on.
Gas turbine – internal combustion
Where does air/gas enter? What is compression ratio?
Image: from dieselduck.net Copyright: Martin Leduc?
Gas turbine – internal combustion
Air-fuel mixture enters from left into compressor, which compresses air 5-20x. Air/fuel ignites in combustor, and expands to right, turning rotor. The rotor powers both a generator and drives the compressor itself
(which can take up ½ the power output of the turbine). Combustion temperatures typically > 1000 C (1300 K) as opposed to ~600 C (900K) for steam. Note that the walls of the turbines must be kept cooler than the gases inside else their metal would degrade, and even so, special steel is required to withstand the high Ts.
Image: from dieselduck.net Copyright: Martin Leduc?
Gas turbine thermodynamic cycle: Brayton cycle Two adiabats and two isobars (constant pressure)
Compression and expansion are still nearly adiabatic, as in Carnot cycle. But gas combustion means that heat is input at constant pressure instead of constant temperature, and cooling also takes place at constant pressure.
Intrinsically less efficient than the Carnot cycle since heat isn’t added at hottest temperature and removed at coolest. But temperatures are hot! (> 1300 K). Efficiency depends on compressor P too.
Carnot efficiency would be ~75%. Ideal Brayton cycle ~ 60%. Commercial units actually ~ 40-50%.
Diagram: Wikimedia Commons
Steam turbine – external combustion
Image: from LidyaSavitri.wordpress.com; Copyright unknown.
Steam turbine thermodynamic cycle: Rankine cycle Trying to be adiabats and isotherms, but limited by Clausius-Clapeyron
The Clausius-Clapeyron relationship of liquid and vapor prevents raising T at constant entropy, so cannot make the same rectangular T-S diagram as the Carnot cycle. Stages: In stage 1-2 the liquid is compressed by a pump. 2-3 has two segments: heating of liquid, then evaporation to make steam. If you then try to expand adiabatically, water would condense. Superheating the steam (3-3’) both prevents condensation on expansion and also produces more work. Superheat also makes the cycle more Carnot-like and more efficient: think of making the cycle on a T-S plot more rectangular. After expansion the steam is brought into contact with cooling water and condensed (4-1 or 4’-1) at constant temperature. Diagram: Wikimedia Commons
Steam turbine thermodynamic cycle: Rankine cycle Adding more reheat cycles improves efficiency
Most modern steam systems use two separate expansion stages (3-4) and (5-6), with the steam re-heated in between. The steam is never allowed to condense. In the second reheat stage some cooling is needed to drop temperature so that steam can condense (the segment by the “6”).
Ideal Rankine-‐with-‐reheat efficiency for 1000 F (550 C or 800 K) is ~40%.
Carnot would be ~60%.
Actual turbines get a bit over 30%
Rankine not worse than Brayton – ε would be about the same if a steam turbine could be run as hot as a gas turbine. Diagram: Wikimedia Commons
Steam turbine efficiency is achieved with multiple stages Original idea: Parsons, 1910s
Steam enters at left. Blades increase in size as P drops. Steam is removed and reheated (and superheated) before being reintroduced at the low-pressure stage.
Diagram: Govt. of Australia
Steam turbines no longer increasing in efficiency
From Vaclav Smil, “Energy at the Crossroads”
• As seen before.. steam P and
T topped out ca. 1960
• Efficiency stalled as well
• A bit below ideal Rankine limit
• Note that average is below best possible – best is closer to ideal Rankine
unnecessary waste heat in condensation stage? turbine design?
Steam turbines are virtually unchanged in 100 yrs
Low-pressure turbine rotor, 50 MW turbine, ca. 1929
Photo: “The Steam Turbine and Other Inventions of Sir Charles Parsons, O.M.” R.H. Parsons, 1942.
Copyright, The British Council
Low-pressure turbine rotor, for installation in a nuclear power plant (Siemens SST5 9000)
Photo: Siemens Power Generation
Where is steam injected? How do you know?
Turbo-generators are virtually unchanged in 100 yrs
Turbine hall with steam turbine & generators, ca 20 MW each,1929 Photo: “The Steam Turbine and Other Inventions of Sir Charles Parsons, O.M.” R.H. Parsons, 1942. Copyright, The British Council
Turbo-generators are virtually unchanged in 100 yrs
The turbine hall of Bruce Power's Bruce A nuclear power plant in Ontario, Canada. Photo: Bruce Powell
Steam and gas turbine similarities & differences
Steam – Rankine cycle • external combus3on • condensible species (so can’t raise temperature
adiaba4cally – must put heat in for latent heat) • Tmax lower than combus3on temperature (limited by what boiler can withstand)
• slow to dispatch (hours -‐ must heat water to make steam) • expensive to build & install (needs firebox, boiler) Gas – Brayton cycle • internal combus3on • non-‐condensible species • Tmax is gas is combus3on temperature – more efficient • fast to dispatch (ca. 10 minutes) • cheap to build & install (compact, single unit) What’s not to like about gas? …only that coal is cheaper!
Selected power plant options
Coal-‐fired power (steam turbine) cheap fuel, lowest efficiency (30-‐35%)
Natural gas power plant (gas turbine)
expensive fuel, bener efficiency (40-‐50%) Combined-‐cycle power (gas + steam)
expensive fuel, high efficiency (55-‐60%) IGCC (coal-‐fired gas + steam)
cheap fuel, high efficiency (55-‐60% -‐ cost of making syngas) Cogenera:on (generally gas, re-‐use waste heat)
expensive fuel, can be highest “efficiency” (> 80%) since waste heat is no longer wasted
Coal-fired power always involves steam
Fuel burns to make heat; heat boils water to make steam; steam drives steam turbine; turbine spins generator; generator make electricity. Items to note: 1) Compressor (not labeled here) compresses liquid water to high pressure. 2) Steam is recirculated, to permit use of purified water and a final drop in P below atmospheric, as in Newcomen engine. Operating conditions: Firebox T ~ 2200 C, Steam T ~ 550 C (800 K), P up to 200 atmospheres.
Diagram: Tennessee Valley Authority
Combined cycle = combining gas and steam Exhaust from gas turbine still high enough T to be hot side of steam turbine
Get ~ 40% from gas turbine, 60% waste. But then get 30% of that waste back. 0.3*0.6 ~ 0.2. Total efficiency rises to 60%!
Note: combined cycle is not the same as cogeneration (also called “combined heat and power” or CHP). It means you literally have combined two different turbines. Image: Copyright unknown.
Gas supply
IGCC = gasification of coal, then combining gas and steam
This is “integrated gasification – combined cycle”, or IGCC. Image: copyright unknown.
Cogeneration borrow waste heat for industry or buildings Usually done with gas
Image: Cangen Energy
Why gas?
Because cogeneration is usually done in the home or business, where you couldn’t burn coal…
