Analysis of NOx formation at burning fuel oil and natural gas for a 80 MW steam generator

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

In this work has been developed a methodology to determine nitrogen oxides emissions (NOx) in steam generators that burn both fuel oil and natural gas. The methodology is based on four main parameters related to combustion process in the furnace active burning zone (ABZ). Such parameters are the following ones: air excess coefficient in ABZ, average temperature in ABZ, reflected heat in ABZ and the residence time of combustion products in ABZ. As a tool to apply this methodology, there was a specially designed software which was named “NOX AD”. It can calculate the four parameters above as well as the NOx concentration for different operational methods to get a maximized reduction of NOx. The methodology was applied in a 350-ton/h (80MW) steam generator manufactured by Combustion Engineering, which is equipped with tangential burners and is currently working in the thermoelectric plant Ing. Jorge Luque located in the State of Mexico. The fuel oil used has a mass percentage composition of C=84.9%, S=3.8%, N=0.4%, H=10.8%, O=0.0% and W=0.0%. The natural gas has a volume percentage composition of CH4 = 91.97%, C2H6 = 7.12% and C3H8 = 0.91%. Different methods of NOx decrease were applied by using “NOX AD” software: gases recirculation, entrance place of recirculation gases, water injection in the ABZ, combustion at two stages and combinations of methods. The determining of the four main parameters and the NOx concentration that corresponded to each diminishing method were made under the following loads: 45%, 67%, 87% and 100%. The recirculation and water injection percentages were: 0%, 5%, 10% and 15%. The “NOX AD” software displays graphics that show the NOx formation behavior for each diminishing method. The results shows the maximized NOx reduction when combinations of methods is applied.