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.
