Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 338

high performance industrial furnaces to lower NO x emission levels (as to how low
the level can be reduced). However, it must be noted that the NO x emission level
was reduced by application of these newly developed high performance industrial
furnaces to the same extent or more than that reached with conventional technology.
With the conventional furnaces, the NO x level increased to a level of several hundred
ppm when the combustion air was heated to a high temperature (800˚C or higher),
so that heating the combustion air to a high temperature could not be used in
industrial technology ( Figure 5.88 ) . The main achievement of this field test was that
the emission level was below 50 ppm (converted to 11% O 2 ) in the range higher
than 1000˚C.

200

Modified furnaces: Comparison between NO x value
and processing temperature

150

Conversion O 2 11%

100

50

0

0 200 400 600 800 1000 1200 1400 1600

Furnace temperature, ° C

100

Modified furnaces: NO x values/Legal
restriction values

80

60

40

20

0

0 200 400 600 800 1000 1200 1400 1600

Furnace temperature ° C

Continuous heating furnace Batch type heating furnace

Ladle Continuous heat treatment furnace

Batch type heat treatment furnace Gas treatment furnace

Melting furnace

FIGURE 5.88 Relationship between atmosphere temperature in furnace and NO x emission.