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GENERATION TECHNOLOGIES

-- Bhanu Bhushan --

(April, 2011)

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• Thermal -- Coal / Lignite

• Gas turbine / Combined cycle

• Hydro -- Storage / R-o-R / Pumped

• Nuclear

• Wind and other Renewable

• Captive and Co-generation

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• Process

• Conversion efficiency

• Variable cost

• Peaking capability

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• MCR, under different conditions

• Reactive capability

• Over-loading capability

• Loading restrictions

• Ramp-up / ramp-down rates

• Start-up times -- cold / hot

• Impact of voltage and frequency

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Main parameters to be controlled in a thermal generating unit

1) Turbine speed / MW

2) Steam pressure

3) Steam temperature

4) Drum level

5) Furnace draft

6) Air - fuel ratio

7) Condenser level

8) De-aerator level

9) Voltage / MVAR

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Abnormal situations / contingencies

• Tripping of an auxiliary -- Stand-by should take-over, or run-back / interlocked trip.

• Parameters deviate from normal -- safety valves open, HP / LP bypass, operator intervention on alarms.

• Tripping of a Unit causes thermal shocks and reduces plant life; should be avoided / prevented as long as possible.

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• Coal to electricity efficiency : 30 – 35 %.

• Variable cost : 114 p/kWh, if coal cost (landed) is Rs 1500 / ton, consumption = 0.7 kg / kWh, aux = 8%.

• MCR goes up (down) when circulating water temperature goes down (up).

• Over-load capability: design margins, VWO, short-time over-stressing.

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• Oil support required below about 60% MCR, depending on which mills are operating.

• Turbine blades overheat if load < 20% MCR.

• Start-ups and controlled shut-offs require a few hours each, considerable operator effort & alertness, extra cost and reduce life.

• Daily shut-off not recommended, but Units with high fuel cost can be boxed up by turn.

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Combined cycle power plants

• Gas to electricity efficiency : 45 – 50 %.

• Critical parameter : Firing temp. of GT; direct effect on MW, efficiency, life, cost.

• MCR goes up (down) considerably when ambient temperature goes down (up).

• O/L capability only at the expense of life.

• GT operation at part - load is not desirable; one GT in a module should be switched off.

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• All CCPPs should be preparing for 2 - shift operation; may be Module-wise by turn.

• Gas supply system must have adequate “line - pack”.

• Frequency response only at the expense of life or efficiency. Operated in constant firing temperature mode. No FGMO.

• Full-load trip causes high thermal stresses and reduces GT life by 500 hours.

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Nuclear power plants

• No bulk mining; no bulk transport.

• No ash; no CO2 emission.

• Reactor power controlled by inserting / withdrawing the control rods.

• The critical parameter for stable reactor control : temperature differential of coolant across the reactor.

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Impact of frequency variations on generating stations

• When frequency falls, output capability of plants of all type goes down, due to slowing down of auxiliaries (for thermal & nuclear), and due to slowing down of compressors (for gas turbines).

• Frequency fluctuations have serious implications for Nuclear, but can be safely withstood by plants of other types.

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Safe shut down in emergency

• Turbine speed• Bearing lubrication; H2 sealing• Even cooling of turbine casing & rotor• Steam temperature & pressure• Furnace draft• Condenser vacuum• Reactor cooling• Plant lighting• Controls, alarms, fire-fighing.

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Idukki Generation 10th November’06

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100

200

300

400

500

600

700

0 2 4 6 8 10 12 14 16 18 20 22 0HRs

MW

48.5

49

49.5

50

50.5

51

51.5

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Generation/Pumping at Kadamparai

10th November’06

-600

-400

-200

0

200

400

600

0 2 4 6 8 10 12 14 16 18 20 22 0

HRs

MW

48.5

49

49.5

50

50.5

51

51.5

FREQ