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GENERATION TECHNOLOGIES. -- Bhanu Bhushan -- (April, 2011). Thermal -- Coal / Lignite Gas turbine / Combined cycle Hydro -- Storage / R-o-R / Pumped Nuclear Wind and other Renewable Captive and Co-generation. Process Conversion efficiency Variable cost
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GENERATION TECHNOLOGIES -- Bhanu Bhushan -- (April, 2011)
Thermal -- Coal / Lignite • Gas turbine / Combined cycle • Hydro -- Storage / R-o-R / Pumped • Nuclear • Wind and other Renewable • Captive and Co-generation
Process • Conversion efficiency • Variable cost • Peaking capability
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
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 • De-aerator level 9) Voltage / MVAR
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.
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.
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.
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.
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.
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.
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.
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.
