Is the flue gas aleady at the dew point?

Is condensation occurring because the DGI is at a lower temperature than the flue?

If the DGI is at a lower temperature than the flue, raise the DGI temperature.

If the gas stream is saturated then try a diffusion dryer upstream of the DGI.

Sample conditioning (dilution) requires proper mixing and temperature control. If you have a dew point measuring device, the best method of dilution control is by measuring dew point. The calculation may not be simple because of other constituents in the flue gas.

Dekati has sample dilution equipment that may be less expensive than designing your own.

Thank you for your answer.

The dew point of flue gas with 20 % of water is 60 degrees of C. The flue gas itself is above 80 degrees of C. Upstream the DGI and before the dilution system (PRD +ED) we have a heater, which preheats the flue gas till 105 degrees of C. I am interested, how the dilution will affect the flue gas temperature (it will decrease) and its dew point...We do not have a dew point measuring device. By approximate calculations the DR factor should be 10. However, would be nice to have a calculation for that and by the DR control the dew point.

You state:

The dew point of flue gas with 20 % of water is 60 degrees of C.

I assume you know the water content of the the flue gas, 20%.

Knowing the water content you should be able to find the water vapor pressure by pV=nRT. T is degrees C + 273.3. Let V be 1 m3.

The saturation pressure of water, ps, at T is

ps = 6.11exp(17.269T/(273.3 +T)).

From the saturation temperature you can find the dew point temperature Td by

Td =273.3 ln(ps/6.11)/(17.269 - ln(ps/6.11)).

For dilution return to pV=nRT. The n will reduce by dilution and T will change with dilution.

Thank you for such a detailed explanation!