โก Combined Cycle Power Plant
Model gas turbine (Brayton) topping and steam (Rankine) bottoming cycles with HRSG pinch point analysis.
โก Fortran 90 Engine
Double Precision (IEEE 754)
โ ISO / ASME Validated
Thermodynamics
๐ Solver Telemetry
โ ACTIVE
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๐ฆ Fortran Code
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Released
Jun 2026
โฑ๏ธ Latency
< 1 ms
๐ Configuration
Key Equations:
ฮทcombined โ 1โ(1โฮทB)(1โฮทRยทQHRSG/Qin)
HRSG: แนgcp(TexhโTstack) = แนs(hโโhfw)
Pinch: TgasโTsat โฅ ฮTpinch
ฮทcombined โ 1โ(1โฮทB)(1โฮทRยทQHRSG/Qin)
HRSG: แนgcp(TexhโTstack) = แนs(hโโhfw)
Pinch: TgasโTsat โฅ ฮTpinch
๐ Results
Configure inputs and click Analyze to view results.
๐ Methodology
Combined Cycle
A gas turbine (Brayton) topping cycle exhausts hot gas into a Heat Recovery Steam Generator (HRSG), which drives a steam turbine (Rankine) bottoming cycle. Overall efficiency exceeds either cycle alone.
HRSG & Pinch
The pinch point โ minimum temperature difference between hot gas and boiling water โ constrains steam production. Lower pinch = more heat recovery but larger HRSG.
Assumptions
- Air-standard Brayton with constant cp and ฮณ.
- Simplified water saturation curve fits.
- Single-pressure HRSG (no reheat).
- No pressure losses in HRSG.
๐ Calculation Methodology: Combined Cycle Gas Turbine (CCGT) Thermal Efficiency
Mathematical Model & Theory
CCGT power plants recover the high-temperature exhaust heat from a topping Brayton gas turbine cycle to generate steam for a bottoming Rankine steam turbine cycle:
$$\eta_{cc} = \eta_{GT} + \eta_{ST}(1 - \eta_{GT}) = 1 - (1 - \eta_{GT})(1 - \eta_{ST})$$
$$\dot{W}_{net,cc} = \dot{W}_{GT} + \dot{W}_{ST} = \dot{Q}_{in} \cdot \eta_{cc}$$
Assumptions
- Complete heat recovery in Heat Recovery Steam Generator (HRSG).
- Independent thermodynamic cycle efficiencies.
Academic References
- Kehlhofer, R. et al.: Combined-Cycle Gas & Steam Turbine Power Plants, PennWell.
- Saravanamuttoo, H. I. H. et al.: Gas Turbine Theory, Pearson.
Worked Engineering Example
Problem Statement:
A gas turbine with $\eta_{GT} = 40\%$ exhausts into an HRSG driving a steam turbine with $\eta_{ST} = 34\%$. Calculate overall plant efficiency.
Step-by-step Solution:
1. $\eta_{cc} = 0.40 + 0.34 \times (1 - 0.40) = 0.40 + 0.34 \times 0.60 = 0.40 + 0.204 = 0.604 = 60.4\%$.
Final Result:
Combined cycle thermal efficiency is $\mathbf{60.4\%}$.
A gas turbine with $\eta_{GT} = 40\%$ exhausts into an HRSG driving a steam turbine with $\eta_{ST} = 34\%$. Calculate overall plant efficiency.
Step-by-step Solution:
1. $\eta_{cc} = 0.40 + 0.34 \times (1 - 0.40) = 0.40 + 0.34 \times 0.60 = 0.40 + 0.204 = 0.604 = 60.4\%$.
Final Result:
Combined cycle thermal efficiency is $\mathbf{60.4\%}$.