Scenario presets
Switches and actions
Camera
Layers
Quality
High is the default on every device. Low or ?q=low lowers resolution and shadows.
Alarms
Numerical checks
The science
Two heat engines in series
A gas turbine burns fuel in compressed air (Brayton cycle) and exhausts at 600 C or more. Instead of wasting it, a heat-recovery steam generator (HRSG) boils water with that exhaust and a steam turbine (Rankine cycle) adds power. The bottoming cycle works on heat that the topping cycle has already rejected, so the efficiencies combine as ηcc = ηGT + (1 - ηGT) ηbot: for example 0.38 + 0.62 x 0.29 = 0.56.
Gas turbine
Compressor exit T2 = T1 [1 + (rp(γ-1)/γ - 1)/ηc], turbine exit T4 = T3 [1 - ηt (1 - rp-(γ-1)/γ)] (4 % pressure losses), with cp = 1.005 kJ/kg/K for air and 1.15 for hot gas. The fuel-air ratio follows from an enthalpy balance f = (cpgT3 - cpaT2)/(LHV ηb - cpgT3). Mass flow scales with load and with air density, so a hot day cuts output about 1 % per 2.5 K. Part load closes the inlet guide vanes, which raises compressor work and lowers efficiency.
HRSG, pinch point and the Q-T diagram
Water enters the economiser at the feedwater temperature, boils in the evaporator at the saturation temperature Tsat(P) (IAPWS-IF97 region 4) and is superheated. The hottest the exhaust gas can be at the evaporator inlet limit is Tsat + ΔTpp (the pinch). Heat above the pinch makes steam: ms = mg cpx(T4 - Tpinch)/(hsh - hf). The remainder warms the feedwater and leaves as stack gas, Tstack = Tpinch - ms(hf - hfw)/(mg cpx). A tighter pinch gives more steam but needs a bigger boiler. Stack gas below about 90 C risks sulphuric acid condensation, so the model also caps the steam flow by the feedwater temperature.
Steam turbine
Isentropic enthalpy drop Δhis = ceff T (1 - (Pc/P)(k-1)/k) with ceff = 2.1 kJ/kg/K and k = 1.3 (fitted to steam tables, 100 bar / 540 C to 0.05 bar gives about 1410 kJ/kg), then W = ηst ms Δhis minus feed-pump work vΔP/η. A higher steam pressure raises efficiency but makes the exhaust wetter; below about 0.82 dryness the model warns about blade erosion. Condenser heat goes to the cooling tower.
Honest simplifications
One pressure level, no reheat or deaerator extraction, constant gas properties per stream, hf and hg from cubic and quartic polynomial fits and a superheat cp that is a few per cent from the IAPWS tables (the checks quantify this), steam-turbine expansion by an ideal-gas-like formula, a duct burner modelled as a temperature rise of the exhaust, no start-up thermal stresses, no auxiliary power, first-order lags (25 s gas turbine, 140 s HRSG). It is a teaching model of a 440 MW class H-frame plant, not a design tool and not based on any manufacturer's data.