Question

The partial dry basis flue gas composition in mol fractions for a combuster burning n-hexane with excess air is 0.090 CO2, 0.090/3 CO, 0.00265 n-hexane. The remaining dry gas is oxygen and nitrogen. If the flue gas is at a pressure of 760 mmHg (absolute), what is its dew point temperature in degrees Celsius.

Answer 1

since the mol fraction is 0.090 CO2, 0.090/3 = 0.03 CO, 0.00265 n-hexane

The equation for n-hexane combustion is

C6H14 + 7.75O2 ----> 6CO2 + 7H2O

SInce there is partial burning as CO is present

Actually ratio of CO2 to H2O will be 6 mol to 7 mol but since CO is present then carbon content is 0.09 + 0.03 = 0.12 mol so H2O will be (0.12/6 x 14 )/2 = 0.14 mol H2O

So the partial pressure of water is 0.14 x 760 = 106.4

So relative humidity is 106.4/23.76 = 4.478 at 25^oC

TD: =243.04*(ln(RH/100)+((17.625*T)/(243.04+T)))/(17.625-ln(RH/100)-((17.625*T)/(243.04+T)))

Substituting we get Td or dew point temperature is -18.6 ^oC