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Conversion of Air Pollution Results i.e. mg/m3 to mg/Nm3

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  • Conversion of Air Pollution Results i.e. mg/m3 to mg/Nm3

    Hi kindly help me to convert to normal conditions for SO2. I measured from the boiler stack and I collected the following data: 48.78mg/m3, ambient temperature 25 degrees (298k), flue temperature 428k, measured pressure 0.54mBar (0.4050mmHg), stack diameter 0.42m, stack section area 0.1386m2, flue velocity 7.075m/s, sampling time 58 minutes (1 hour)

  • #2
    Originally posted by Chrispine Matongo Mweemba View Post
    Hi kindly help me to convert to normal conditions for SO2. I measured from the boiler stack and I collected the following data: 48.78mg/m3, ambient temperature 25 degrees (298k), flue temperature 428k, measured pressure 0.54mBar (0.4050mmHg), stack diameter 0.42m, stack section area 0.1386m2, flue velocity 7.075m/s, sampling time 58 minutes (1 hour)
    Please do not use the following for compliance. Local pollution laws usually detail exactly how the calculations must be done and may include additional corrections. Excess combustion air can "dilute" most pollutants so calculation usually requires measurement of O2 in the stack gas and correction to a standard excess air value. If limits are stated in terms of dry stack gas, a water vapor correction is also required. We do not have the info to do those, and they may depend on local law.

    Consider a 1 m control volume of stack gas. Imagine it in a "magic balloon" that does not affect pressure or temperature, but does not allow any molecules to enter or leave the control volume. Like any gas, it will change volume with temperature and pressure. The 48.78 mg of SO2 will remain inside, but the volume will be different at "normal conditions, 1013.25 mbar and 273.15 K. You need local atmospheric pressure at your elevation, not reduced to sea level. As you didn't give it, we'll call it P and add the stack gauge over pressure to it. Assuming the ideal gas law, the 1 m control volume will change to

    1 m x 273.15 K/428 K x (P + 0.54 mbar)/1013.25 mbar

    at normal conditions. Divide the 48.78 mg SO2 by this reduced "normal" volume

    If you were at sea level, the pressure term would be very close to unity, you would have 0.6385 Nm and 76.4 mg/Nm

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    • #3
      Thank you very much sir thank you I will post to show you how I have been calculating it

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