Processes of combustion of natural gas in industrial burner devices have been considered. It has been shown that complex model of formation of nitric oxides cannot be developed. In connection with this, simple mathematical model of the processes has been developed with the use of differential equations. Method offered by Ya.B. Zel'dovich has been applied in this case. Calculation of emissions of nitric oxides is performed with the use of GRI-Mech program package. Index of emission of nitric oxides is function of chemical composition and temperature. Methods of acceleration of calculation have been offered.