2. CGE Extraction Steam Turbine Model
• CGE : a COGENERATION plant
– Simultaneous production of power and heat (50# and 400# steam)
– Max Efficiency when steam flows to condensers are minimized
Higher extraction loads → Higher Plant Efficiency
Best Efficiency when 50# loads are highest
– 400# and 50# Steam extracted from TG1 and TG2 to maintain 400# and 50#
header pressures
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3. • A demand-driven model:
– User inputs are :
400# & 50# extraction flows
Power
– Splits the real turbine in 2 imaginary turbines
An extraction-only turbine with no flow to condenser
A straight-to-condenser turbine with no extraction
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CGE Extraction Steam Turbine Model
4. • Extraction-Only Turbine Model:
– Mass Balance :
(i) f800 to extrac = f400 + f50
– Energy Balance :
Q800 to extrac = Q400 + Q50 + MWextrac
MWextrac = Q800 to extrac - Q400 - Q50
(ii) MWextrac = 0.9 x (H800 x f800 to extrac - H400 x f400 - H50 x f50)
“TG1 Ideal Load Equation” with 90% alternator efficiency to convert
mechanical energy to electricity.
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CGE Extraction Steam Turbine Model
f800 to extrac, Q800 to extrac
f400 , Q400
f50 , Q50
MWextrac
5. • Straight-to-condenser Turbine Model:
– Energy Balance :
accounts for Power production in excess of “Ideal Load” produced by extraction-
only turbine
MWextra Dmnd = MWTotal Dmnd – MWextrac
MWextra Dmnd = Q800 to cond - Qcond
(iii) MWextra Dmnd = 0.9 x f800 to cond x (H800 - Hcond)
– Mass Balance :
(iv) f800 to cond = fcond
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CGE Extraction Steam Turbine Model
f800 to cond, Q800 to cond
fcond, Qcond
MWextra Dmnd
6. • Recombined Turbine Model:
– Mass Balance :
f800 total = f800 to extrac + f800 to cond
f800 total = f400 + f50 + f800 to cond
– Energy Balance :
Q800 = Q800 to extrac + Q800 to cond
Q800 = Q400 + Q50 + MWextrac + MWextra Dmnd + Qcond
Q800 = H400 x f400 + H50 x f50 + MWtot + Hcond x fcond
Result :
a sensible and easy-to-implement set of formulas satisfying Mass, Energy Balances
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CGE Extraction Steam Turbine Model
f800 totaL, Q800
f400 , Q400
f50 , Q50
MWtot
fcond, Qcond
7. • CGE : extraction loads and their impact on plant efficiency
– Impact on TG1’s thermal and electrical efficiency
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75.00
80.00
85.00
90.00
95.00
100.00
0.75 0.77 0.79 0.81 0.83 0.85 0.87 0.89 0.91 0.93 0.95
Efficiency [%]
[(50# + 400#) Extraction / 800# Inlet] Ratio
TG1 - Efficiency vs [Extraction/Inlet] Ratio
Reality vs Model
CGE Extraction Steam Turbine Model
