Solve the air supply problem for water gas combustion!
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The composition of water gas is as follows: CO: 28%, H2: 14%, CH4: 3%, N2: 48%, CO2: 6%, O2: 0–0.5%. The pressure of this water gas is 60 KPa. The gas is sent to a burner where it burns to provide heat for the system. How many cubic meters of air are required per 1 cubic meter of this gas?
My calculation method is as follows; please experts check if it’s correct, thank you! The composition of water gas is as follows: CO: 28%, H2: 14%, CH4: 3%, N2: 48%, CO2: 6%, O2: 0–0.5%. The molar mass is calculated as follows: M = 28×28% + 2×14% + 16×3% + 28×48% + 44×6% + 32×0.5% = 7.84 + 0.28 + 0.48 + 13.44 + 2.64 + 0.16 = 24.84. Therefore, the density of the mixture ρ = 24.84/22.4 = 1.109 kg/m3. According to the reaction equation: CO + H2 + O2 → CO2 + H2O, with the ratio 28+2 : 32 = 1109 : X, so X = 1182.9 grams. The mass of air required is 1182.9/21% = 5632.9 grams. The volume of air required is 5632.9/1.29 = 4366.6 liters, which is equivalent to 4366.6/1000 = 4.37 m3
In your calculations, the mass referred to is the mass of 1 cubic meter of gas, not the mass of the combustible gases CO and H2 present in that gas. Based on the mass you calculated, the mass fractions of CO and H2 in the gas are 0.3156 and 0.0113 respectively; therefore, the masses of CO and H2 are 0.35 kg and 0.013 kg respectively. Consequently, X equals 387.2 grams. Thus, the mass of air required is 387.2/21% = 1843.8 grams, and the volume of air required is 1843.8/1.29 = 1429.3 liters, which is equivalent to 1429.3/1000 = 1.43 m3. In other words, 1 cubic meter of this gas requires 1.43 m3 of air, and this is the theoretical value. In actual production, in order to ensure complete combustion of the gas, an appropriate coefficient must be used to increase the amount of air supplied. For example, the theoretical air volume ratio for the combustion of natural gas is 1:10; when selecting a fan, an air volume ratio of 1:12 is generally used.
Why is only one person answering? It seems much quieter here now; before, even a simple post would get several replies from people helping out. I asked the burner manufacturers about my question later, and they said that 2 would be a safer choice. I’m sharing this with everyone here too! Hope to help others! Thank you to the person on floor 4, but I still hope someone will calculate my problem as well, to see if there are any theoretical differences compared to what the person on floor 4 came up with!