Nitrogen Oxides, Sulfur Dioxide, and Oxygen Emissions from Stationary Gas Turbines – USEPA Method 20

USEPA Method 20 is used to determine nitrogen oxides (NOx), sulfur dioxide (SO₂), and oxygen (O₂) emissions from stationary gas turbines.  For the NOx and O₂ determinations, this method includes:

• measurement system design criteria;
• analyzer performance specifications and performance test procedures;
• procedures for emission testing.

A gas sample is continuously extracted from the exhaust stream of a stationary gas turbine; a portion of the sample stream is conveyed to instrumental analyzers for determination of NOx and O₂ content.  During each NOx and O₂ determination, a separate measurement of SO₂ emissions may be made, using Method 6C, or its equivalent.  The O₂ determination is used to adjust the NOx and SO₂ concentrations to a reference condition.
 
A preliminary O₂ or CO₂ traverse is made for the purpose of selecting sampling points of low O₂ values or high CO₂ concentrations as appropriate for the measurement system.  This determination is conducted at the turbine operating condition that is the lowest percentage of peak load operation included in the program.  Eight sampling points at which the lowest O₂ concentrations or highest CO₂ concentrations were obtained are then used for sampling during each run at the different load conditions.