Phase diagram of water

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Combined Cycle Gas Turbine (CCGT) Stations v) h 4 = (1−x)h f4 + xh g4 h 4 = (1−x)126 + 2566 x x = 0.769 h 4 = 2002 kJ/kg In recent years gas turbines and steam turbines have been combined to increase the efficiency to around 50-60% (upper temperature ~1200 C) Gas Turbine air 34 isentropic so W 34 = h 3 – h 4 = 3564 – 2002 = 1562 kJ/kg vi) η = useful work/heat in = (W 34 – W 12 )/Q 23 = (1562 – 17)/3421 = 0.452 = 45.2% vii) cf Carnot Cycle η c = (T 3 − T 4 )/T 3 = (873 − 303)/873 = 0.653 = 65.3% T W 12 Q 3 23 2 W 34 1 4 Q 41 S T T max Compressor Combustion Compressor Gaseous fuel p compressed air Combustion Chamber p atmos Turbine Brayton Cycle S Turbine Exhaust gas a) Heat generated by internal combustion rather than via a high temperature heat exchanger (boiler) b) No cooler required since exhaust gases vented to atmosphere Plant much smaller. Work done by compressor is significant, though this is compensated by very high temperature ~ 1200 C (Turbine blades ceramic coated and water cooled) ω CCGT Station 660 MW Power Plant air Compressor Gaseous fuel compressed air Combustion Chamber Turbine Exhaust gas Water Pump Heat in Boiler Turbine Exhaust gas Condenser ω combustion Cooling water Heat out T Rankine Cycle compressor S turbine boiler Brayton Cycle Heat of exhaust gases used to raise steam for steam turbine Many CCGTs have been built in the UK in the 90s due to availability of cheap gas and relaxation of governmental controls Stator for a 660 MW generator being assembled Low pressure turbine, part of a 660 MW assembly Power density ~ 1000 MW e per sq km
Types of Fossil Fuel Power Stations CCS Type T o C bar Efficiency Subcritical 538 167 up to 39% Supercritical 540-566 250 up to 46% Ultra-supercritical 580-620 270-285 50-55% IGCC: Integrated gasification combined cycle Coal + O 2 + H 2 O → H 2 + CO (syngas) mainly Power Plant Today Future Syngas used in combined cycle gas turbine (CCGT) power station Efficiency ~ 45% Shift reaction : CO + H 2 O → H 2 + CO 2 Pre-combustion Carbon Capture and Storage (CCS) Conventional Coal 24-40% 15-20% Natural Gas 11-24% 8-11% Advanced Coal 14-25% 9-12% Typical Energy Penalty(increase fuel use per KWh produced due to CO 2 capture) Potential by 2050 ~1000 GW e with CCS Power density ~ 1000 MW e per sq km CCS CCS Technical Solutions to Disposing of CO 2 • Underground storage In aquifiers, used gas/oil fields - huge storage potential, but possibility of spontaneous gas eruptions (1750 people killed by CO 2 eruption from volcanic lake in 1986) •Deep ocean disposal Large hydrostatic pressure CO 2 liquifies - long-term viability uncertain - effect on ocean deep-sea creatures uncertain (affects food chain of surface creatures Air Capture Electrocatalytic CO 2 Conversion to Oxalate by a Copper Complex. SCIENCE VOL 327 15 JAN. 2010 • Pump CO 2 into lakes/breed algae Algae dried biomass alternative to fossil fuel Or Algae biodiesel alternative to petrol or diesel from oil (CO 2 –neutral if re-used; sequestered if buried)
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Phase diagram of water

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