Combined Cycle Efficiency
Calculate the efficiency of a gas-steam combined cycle, η_cc = η_gas + η_steam − (η_gas × η_steam ÷ 100), combining the gas turbine efficiency (Brayton, topping) with the steam cycle (Rankine, bottoming) that recovers heat from the exhaust gases. The result, in %, exceeds either cycle alone because the heat rejected by the gas turbine, instead of being wasted, raises steam for a second turbine. This is why modern combined-cycle plants top 60% efficiency, the highest in thermal generation. Enter the gas-cycle and steam-cycle efficiencies (in %).
Resultado
—
Eficiência de ciclo combinado
A central de ciclo combinado é a campeã de eficiência da geração térmica, e o motivo é elegante: ela empilha dois ciclos. Primeiro, uma turbina a gás (ciclo Brayton, dito topping) queima o combustível e gera potência — mas rejeita gases de exaustão ainda muito quentes (500–600 °C). Em vez de jogar esse calor fora, uma caldeira de recuperação o usa para gerar vapor que aciona uma segunda turbina a vapor (ciclo Rankine, dito bottoming). A eficiência global combina as duas: η_cc = η_gás + η_vapor − (η_gás × η_vapor ÷ 100). O termo subtraído evita contar duas vezes a energia — o ciclo a vapor só processa o que o ciclo a gás rejeitou, não a energia original. O resultado é sempre maior que qualquer um dos ciclos isolados: 40% (gás) somados a 30% (vapor sobre o rejeito) dão 58%, não 70%. É por isso que as plantas de ciclo combinado a gás natural ultrapassam 60%, frente aos ~40% de uma termelétrica a vapor simples. Informe as eficiências do ciclo a gás e do ciclo a vapor.
Related Tools
Rankine Cycle Efficiency
Calculate the thermal efficiency of a Rankine cycle, η = (w_turbine − w_pump) ÷ q_boiler × 100%, dividing the net work (turbine work minus pump work) by the heat added in the boiler, all in kJ/kg. The Rankine cycle is the basis of steam power plants: water is pumped, heated and vaporized in the boiler, expands through the turbine producing work, then condenses. The result, in %, measures how much boiler heat becomes useful work; real cycles run 30–45%. Enter the turbine work, the pump work and the boiler heat.
Back Work Ratio (BWR)
Calculate the back work ratio (BWR) of a power cycle, BWR = w_compressor ÷ w_turbine, dividing the work consumed by the compressor (or pump) by the gross work produced by the turbine. The dimensionless result shows what fraction of turbine work is reinvested to compress the fluid. In gas turbines (Brayton cycle) the BWR is high (0.4–0.6), since compressing gas is costly; in steam Rankine cycles it is tiny (~0.01), since pumping liquid is cheap. A high BWR makes the cycle sensitive to component efficiencies. Enter the compressor work and the turbine work.
Boiler Efficiency
Calculate the thermal efficiency of a boiler by the direct method, η = (m_steam × Δh) ÷ (m_fuel × LHV) × 100%, comparing the useful heat absorbed by the water/steam (steam flow × enthalpy gain) with the energy released by burning the fuel (fuel flow × lower heating value). The result, in %, shows how much fuel energy actually reached the steam; the rest is lost in flue gases, blowdown, radiation and unburnt fuel. Well-run industrial boilers reach 80–90%. Enter the steam flow, enthalpy gain, fuel flow and LHV.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.