Wrap-Up of Industrial Power Generation, Turbines I GEOS 24705/ ENST 24705

Wrap-up of industrial power generation, Turbines I GEOS 24705/ ENST 24705

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, Wellluck Co., Stator, 3-phase generator, Brakpan, South China, 12.5 MW, 2010 Africa, 1897. Photo: Siemens Industrial generation design specs

• Generator should be large for heat dissipaon

• Voltage much higher than 110 V to minimize resisve heang

• 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

• Mulple poles if needed for higher frequencies Rotor carries electromagnet

Old mill rotor (source unknown)

(though seems to be leveling of)

* 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

From Vaclav Smil, “Energy at the Crossroads” 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 combuson).

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 lifeme, > 1 GW now

Eﬃciency gain rapid: More eﬃcient than reciprocang engines, also simpler – fewer moving parts. By 1916 best demonstrated ε ~ 37%. Modern turbines average ~ 33%.

1. STEAM TURBINE Marime use: demonstraon of turbine- propelled ship, the Turbinia, 1897 Chief drawback: high rotaon rates The prime movers driving the world’s electricity supply

Conceived of in 1791. But no means of praccal building l 1903 (Elling).

Power growth slow: no commercializaon l 1918, no roune use l 1930s. Lowest-cost new fossil generaon choice today.

2. GAS TURBINE Turbine diversity: all kinec -> kinec, 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 (“reacon turbine”) or just allowing molecules to push on blades (“impulse turbine”), or something in between (“impulse-reacon”) 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 leng high-pressure gas expand • Blades of turbine are turned by the “wind” of steam • Combinaon impulse-reacon turbines • To make high-pressure gas, heat the gas • Both are heat engines

Steam and gas turbine similarities & differences

Steam – Rankine cycle • external combuson • condensible species (so can’t raise temperature adiabacally – must put heat in for latent heat)

• Tmax lower than combuson 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 combuson • non-condensible species

• Tmax is gas is combuson 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?

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 installaon. Image: from LidyaSavitri.wordpress.com; Copyright unknown. Gas turbine – internal combustion

Image: from dieselduck.net Copyright: Martin Leduc?

Where does air/gas enter? What is compression ratio? Gas turbine – internal combustion

Image: from dieselduck.net Copyright: Martin Leduc?

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. Gas turbine thermodynamic cycle: Brayton cycle Two adiabats and two isobars (constant pressure) Diagram: Wikimedia Commons

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%. 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 Diagram: Wikimedia Commons or 4’-1) at constant temperature. 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 Diagram: Wikimedia Commons as hot as a gas turbine. Steam turbine efficiency is achieved with multiple stages

Original idea: Parsons, 1910s Diagram: Govt. of Australia

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. Steam turbines no longer increasing in efficiency

• As seen before.. steam P and T topped out ca. 1960

• Efciency 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?

From Vaclav Smil, “Energy at the Crossroads” Steam turbines are virtually unchanged in 100 yrs

Low-pressure turbine rotor, for installation in a nuclear power plant (Siemens SST5 9000) Photo: Siemens Power Generation

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

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 combuson • condensible species (so can’t raise temperature adiabacally – must put heat in for latent heat)

• Tmax lower than combuson 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 combuson • non-condensible species

• Tmax is gas is combuson 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, beer 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)

Cogeneraon (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

Diagram: Tennessee Valley Authority

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. Combined cycle = combining gas and steam Exhaust from gas turbine still high enough T to be hot side of steam turbine

Gas supply

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. 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

Why gas?

Because cogeneration is usually done in the home or business, where you couldn’t burn coal… Image: Cangen Energy