This paper describes the low NOx combustion technology for a compact boiler.
In the bench-scale experiment, the NOx emission from the flame stabilized by a bluff body was lower than the 1/3 of that from the flame stabilized by a pilot flame while the volumetric heat release was nearly twice as much as the conventional combustion method.
The NOx emission at the air ratio above 1.1 was reduced less and less as the fuel and air mixture became more and more homogeneous. The NOx emission at the air ratio of about 1.1 was reduced as the ratio of the diameter of a bluff body (D1) to that of a premixed gas nozzle (D2) increased, because the maximum temperatures of the flames were lower with increasing values of D1/D2.
In the case of full-scale burners, when the fuel was injected from a fuel nozzle perpendicularly to the flow of air, the fuel made the most homogeneous mixture.
In the combustion test of the full-scale boiler, the NOx emission from single burner was equal to that of the bench-scale experiment. But in the case of the multiple burners, the flames influenced each other, and the NOx emission was higher than that of the single burner. When the multiple burners were separated each other as far apart as possible, the NOx emission was reduced as much as one burner.
From the results of above experiments, the NOx emission could be reduced to below 60ppm (O20%) at 10%-100% load of the 10t/h compact boiler.
