Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 323

Overview of the tests

Objective: tests for the comparison of melting time and fuel consumption by
changing the distance between burners and material
Equipment: inner dimensions of the melting furnace (in mm):

length: 3200 × width: 1200 × variable height: ( H = 1750 to 1150)

Burner Type: one pair of regenerative burners using oil as fuel (alternative
20 s operation)
Combustion Capacity: 1255 MJ/h (flame length = 1400 mm)
Position: flame directly downward from the furnace ceiling

Test results
The comparisons of the test results of melting time and fuel consumption in per-
centage are shown in Table 5.26 .

Summary
Despite the fact that the temperature inside the furnace when the melting was
completed was 1020 to 1030˚C and the temperature during melting was almost the
same, the results were best for the case of “Middle” ( H = 1.45 m) regarding both
melting time and fuel consumption. The following reasons may account for this.

High: Emissive heat transfer from the internal gas layer inside the furnace was
the most effective but since the temperature inside the furnace was as low
as approximately 1000˚C, the expected efficiency might not have been
achieved.
Middle: The heat transfer effect by convection of flame collision was very
effective and the radiated heat from the ceiling and from the gas layer both
worked as expected. This probably explains why this produced the best
results overall.

TABLE 5.26
Test Results of Melting Time and Fuel Consumption a

Distance Between
Burners and Material

Melting Time,
%

Fuel Consumption,
%

High, H = 1.75m 96 98

Middle, H = 1.45m 86 89

Low, H = 1.15m 100 100

a With 100% for the case of short distance.