Theoretical Maximum CO₂
Calculate the theoretical maximum CO₂ percentage in dry flue gas from complete combustion of a hydrocarbon C_xH_y, CO₂max = x ÷ (x + (x + y/4) × 3.762) × 100%, from the carbon x and hydrogen y atoms. The result, in %, is the CO₂ obtained with perfect stoichiometric combustion (no excess air) — the reference value of gas analyzers. Methane has CO₂max ≈ 11.7%; coal, ~18-20%. Comparing the measured CO₂ with the theoretical maximum indicates the excess air: the lower the measured CO₂ relative to the maximum, the more excess air diluting the gases. Enter x and y.
Resultado
—
CO₂ teórico máximo
Quando um hidrocarboneto C_xH_y queima completamente com a quantidade exata de ar (estequiométrica, sem excesso), os gases de combustão secos contêm o percentual máximo possível de CO₂. Esse CO₂ teórico máximo (CO₂max) é uma propriedade característica de cada combustível: CO₂max = x ÷ (x + (x + y/4) × 3,762) × 100%, onde x é o número de carbonos, (x + y/4) é o O₂ estequiométrico, e o 3,762 (= 79/21) converte O₂ no nitrogênio que o acompanha no ar. O denominador conta todas as moléculas dos gases secos: o CO₂ (x moléculas) mais o N₂ que veio com o ar. Valores típicos: metano (CH₄): CO₂max ≈ 11,7%; propano: ~13,8%; óleos: ~15-16%; carvão: ~18-20%; carbono puro: ~21%. Combustíveis com mais carbono e menos hidrogênio têm CO₂max maior (o hidrogênio vira água, que sai dos gases secos). O CO₂max é a referência dos analisadores de combustão. Como na prática sempre há excesso de ar, o CO₂ medido é sempre menor que o máximo teórico — o ar extra dilui os gases. Justamente essa diferença permite calcular o excesso de ar: comparando o CO₂ medido com o CO₂max (excesso de ar ≈ CO₂max/CO₂medido − 1, aproximadamente), ou medindo o O₂ residual. Por isso, ajustar a combustão para que o CO₂ medido se aproxime do máximo teórico (sem chegar a ponto de gerar CO por falta de ar) é o objetivo da otimização: maximiza o CO₂, minimiza o excesso de ar e a perda de chaminé. Informe x e y do combustível.
Related Tools
Excess Air (from Flue Gas)
Calculate the excess air of a combustion from the oxygen in dry flue gas, EA = O₂ ÷ (20.9 − O₂) × 100%, from the measured O₂ percentage in the stack. The result, in %, shows how much air was supplied beyond stoichiometric — measured by the leftover oxygen in the exhaust gases. Some excess air (10-30%) is needed to ensure complete combustion (avoid CO and soot), but too much wastes energy heating useless air that leaves hot through the stack. Gas analyzers measure O₂ and compute the excess air to optimize combustion efficiency. Enter the O₂ percentage in the gases.
CO₂ Volume Produced
Calculate the CO₂ volume produced in complete combustion of a hydrocarbon C_xH_y, V_CO₂ = x × 22.4 ÷ M, from the number of carbon atoms x and the fuel molar mass M (g/mol). The result, in Nm³ of CO₂ per kg of fuel, is the carbon dioxide generated by complete burning — information for emission inventories, exhaust system sizing and gas analysis. Each carbon atom in the fuel becomes one CO₂ molecule. Methane produces ~1.4 Nm³/kg. Fuels with more carbon per unit mass (coal, heavy oils) produce more CO₂. Enter x and the fuel molar mass.
Adiabatic Flame Temperature
Estimate the adiabatic flame temperature, T_ad = T_initial + LHV ÷ (m × cp), from the lower heating value LHV (kJ/kg fuel), the mass of combustion products per kg fuel m, the average specific heat of the gases cp (kJ/kg·K) and the initial temperature. The result, in °C, is the maximum theoretical temperature the gases would reach if all the combustion energy heated the products, with no heat loss. It is an upper bound: real flames are cooler (radiation losses, dissociation, excess air). It sets the thermal severity on materials and NOx formation. Enter the LHV, the gas mass, the cp and the initial temperature.
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.