Flue Gases Average Dew Point Typical Fuels

Overview

Engineering reference data for Flue Gases Average Dew Point Typical Fuels in air psychrometrics.

Key Formulas

Humidity Ratio

$\omega = 0.622 \frac{P_v}{P_a}$

Mass of water vapor per mass of dry air.

Relative Humidity

$\phi = \frac{P_v}{P_{vs}} \times 100\%$

Ratio of actual to saturation vapor pressure.

Wet Bulb Temperature

$T_{wb} = T_{db} - \frac{P_{vs} - P_v}{\gamma}$

Temperature measured by wet-bulb thermometer.

Enthalpy of Moist Air

$h = c_p T + \omega h_g$

Sensible + latent heat per unit mass of dry air.

Variables

Symbol	Description	Unit
$\omega$	Humidity ratio	kg/kg
$\phi$	Relative humidity	%
$P_v$	Vapor pressure	Pa
$P_{vs}$	Saturation vapor pressure	Pa
$T_{db}$	Dry bulb temperature	°C
$T_{wb}$	Wet bulb temperature	°C

Fuel Dew Points

The following table provides typical dew point temperatures for flue gases from common fuel types, based on standard combustion conditions.

Practical Insights

The dew point temperature is critical for designing heat recovery systems and preventing corrosion. A key factor influencing the dew point is the excess air ratio. Operating with lower excess air generally lowers the dew point slightly, but the dominant factor is the fuel's sulfur and hydrogen content. Fuels with higher sulfur content (e.g., Fuel Oil) produce sulfur oxides (SO₂/SO₃), which combine with water vapor to form sulfuric acid, significantly raising the acid dew point.

Note: The values above are approximate. For precise design, the acid dew point must be calculated considering the specific fuel's composition (especially sulfur content) and the actual flue gas composition.

References

• Original Source