Gas Analysis for the Determination of Emission Rate Correction Factor or Excess Air – USEPA Method 3B

USEPA Method 3B is used to determine oxygen (O₂), carbon dioxide (CO₂), and carbon monoxide (CO) concentrations in the effluent from fossil-fuel combustion processes for use in excess air or emission rate correction factor calculations.  Where compounds other than O₂, CO₂, CO, and nitrogen (N₂) are present in concentrations sufficient to affect the results, the calculation procedures presented in this method must be modified, subject to the approval of the Administrator.
 
A gas sample is extracted from a stack by one of the following methods:

• single-point, grab sampling;
• single-point, integrated sampling;
• multi-point, integrated sampling.

The gas sample is analyzed for percent CO₂, percent O₂, and, if necessary, percent CO using an Orsat combustion gas analyzer.
 
Several compounds can interfere, to varying degrees, with the results of Orsat analyses.  Compounds that interfere with CO₂ concentration measurement include acid gases (e.g., sulfur dioxide, hydrogen chloride); compounds that interfere with O₂ concentration measurement include unsaturated hydrocarbons (e.g., acetone, acetylene), nitrous oxide, and ammonia.  Ammonia reacts chemically with the O₂ absorbing solution, and when present in the effluent gas stream must be removed before analysis.