Numerical Analysis of the Natural Gas Combustion Products

Abstract

The combustion products of fuels containing the elements C, H, O, N and S are calculated. The methodology is based on the equations obtained in the stoichiometric balance of atoms. The adiabatic flame temperature is determined considering that the pressure of the boiler furnace remains constant. The scope of this work is limited to the analysis of natural gas (methane) with molecular formula CH 4 . The methodology can, however, be employed for the calculation of combustion products of a great variety of hydrocarbons under the established restrictions.In the development of the methodology two cases are contemplated: Φ ≤ 1 (lean and stoichiometric mixture) and Φ > 1 (rich mixture). In the first case it is considered that when the combustion is complete, the combustion products are O 2 , H 2 O, CO 2 , N 2 , SO 2 , and the solution follows directly. When the combustion is incomplete, however, the products H, O, N, H 2 , OH, CO, NO, O 2 , H 2 O, CO 2 , N 2 and SO 2 can be generated, according to Stephen R. Turns, (2000). When bal-ances of atoms are performed, four conservation equations are obtained, one for each of the C, O, H and N elements. An additional restriction requires that the sum of the molar fractions of the products equals one mol. Finally, seven equilibrium constants, corresponding to the seven chemical reactions of combustion, are introduced. All this provides a system of four nonlinear equations which is solved with the Newton-Raphson method.