Gas Concentration of CO from ppm to mg/Nm3.
To convert gas concentrations for environmental reporting at a cement plant, you must account for the gas's molecular weight, standard temperature/pressure conditions, and dilution from false air (oxygen correction).
Converting ppm to mg/Nm3 (Dry Basis)
Under standard-normal conditions (0°C and 101.3 kPa), the conversion depends on the molecular weight of the specific pollutant.
The standard formula is: mg/Nm3=ppmxMolecular Weight/22.41
For CO, the formula becomes;
CO[mg/Nm3]=CO[ppm]x1.25
Correcting for Oxygen (False Air Adulteration)
Environmental regulations require emissions to be reported at a specific reference oxygen level (typically 10% in Europe or 7% in the US) to prevent plants from "fixing" high emission numbers by diluting them with ambient "false air".
The Correction Formula: Multiply the Correction Factor to account for the O2 reference
Cref=Cmeas×[(21−O2,ref)/(21−O2,meas)]
- Cref: Concentration at the reference O2 level (e.g., 10%).
- Cmeas: Actual concentration measured by the analyzer.
- O2,meas: Actual oxygen percentage measured at the same time.
- 21: The percentage of oxygen in ambient air.
Important Definitions for Reports
- Nm3 (Normal Cubic Meter): Gas volume at 0∘C and 1 atm (760 mm Hg).
CO:
- Allowable Limits...
- Reported Ranges...
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