The NOx emission, produced by gas turbines varies with ambient conditions and with fuel gas composition. Often, legislation requires that the NOx emissions of gas turbines has to be corrected to standard conditions. The EPA formula may be used for the correction for ambient temperature and humidity. In the Netherlands, the correction for fuel-gas composition is based on the observation that for natural gases, NOx emission varies linearly with the Lower Calorific Value (LCV).

It is concluded that both the EPA and LCV correction formulas are equivalent to the following relation between flame temperature and NOx emission:  
NOxa=NOxb*(1.0065)TaTb
where Ta and Tb represent characteristic flame temperatures under conditions a and b. In the paper, the utility of the EPA and the LCV correction formulas for gas turbines equipped with modem lean-premixed combustors is discussed.
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