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Show enough accuracy so the results can be used for design purposes. Although great progress has been made on the development of these models, researchers appear to be several years away from useful implementation in industryl. This paper will show how straightforward equilibrium chemistry modeling can be used to predict trends, until better models are available that can predict NOx quantitatively. MODEL AND EXPERIMENTAL SETUP The equilibrium calculations were done using the well-known program developed by NASA that minimizes the Gibbs Free Energy of a gaseous system2. The simplified chemical balance for the stoichiometric combustion of methane with pure oxygen is as follows: (1) - One important parameter to consider is the stoichiometry, defined here as the volumetric ratio of oxygen to methane. Theoretically, complete combustion would have a stoichiometry of two, while fuel rich and fuel lean combustion would have stoichiometries less than two and greater than two, respectively. A more generalized chemical balance can be written as: Based on equation (2), stoichiometry and oxygen purity can be defined as follows: qJ - stoich iometry = x x - 02 purity = x / (x + y) (2) (3) (4) For the modeling, \}J and X were varied from 0.5 to 4.0 and 0.75 to 1.0, respectively. It is interesting to note that no nitrogen oxides are formed in equation (1) due to the complete elimination of nitrogen, while variable amounts will be formed in Equation (2) depending on the stoichiometry and oxidizer composition. The experimental data was collected from a KT -3 burner firing in a large pilot scale furnace (see Fig. 1). Details of the burner and furnace are given elsewhere3• Positive pressure was maintained in the furnace to exclude the effects of air infiltration. The furnace temperature was about 2200 degF. The oxidizer was produced by blending high purity oxygen (99.5+ %) with high purity ni trogen (99.98 + %). Typically, the main impurity in these gases is water vapor. The fuel was natural gas, consisting of 95 .5 % CH4, 1.0% C02, 0.4 % N2 and 3.1 % higher hydrocarbons. Therefore, the only significant source of N2 available to form NOx when high purity 02 was used as the oxidizer was that contained in the natural gas. The amount of N2 in natural gas can vary dramatically by geographical location and can be as high as 15 % which is common in Europe. 2 |