Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 321

waste heat, metal heat exchangers are used in most cases, but recently regenerative
burners using balls or honeycombs have become available, making it possible to
build higher performance aluminum-melting furnaces.
Table 5.24 shows the comparison of the energy efficiency of a conventional
aluminum-melting furnace and a high performance furnace of 40 t/ch (tonnage per
charge) each.
On reduction of NO x (converted to 12%O 2 ), oil burning regenerative burners
used for aluminum-melting furnaces must comply with NO x values regulated not
only internationally (180 ppm, converted to 12%O 2 ) but also domestically (around
130 ppm). Two types of burners can satisfy these regulations. One is a concentrated
collision flame oil burner (F1). This type of burner reduces NO x by lowering the
flame temperature. It does this by jetting fuel from the burner center and by expelling
in the furnace atmosphere from around the combustion air. This type of burner has
good combustion efficiency, but the NO x value is slightly higher. The second is the
distributed collision flame oil burners (F2). Combustion air is jetted out of the burner
center and fuel is jetted from around the center, which results in distributed flames,
thereby lowering both the flame temperature and the NO x . With this type of burner,
the NO x value is lower but the combustion efficiency in the low furnace temperature
zone is somewhat inferior. The test results of a kerosene oil burner burning 2093
MJ/h are shown in Table 5.25 .
On reduction of CO 2 , the application of regenerative burners to an aluminum-
melting furnace will lead to a reduction of energy by 30%. The heating source of
an aluminum-melting furnace is primarily fossil fuel, and the following is the trial
calculation assuming a reduction of CO 2 made feasible by this reduction of fuel
consumption in Japan.
Assumptions for the calculation:

M Al =3 million t/year

1. Aluminum demand in Japan:

2. Fuel unit consumption of a conventional furnace: Q fuel = 2930 MJ/t

3. Ratio of melting furnaces in Japan with regenerative burners: r = assumed

as 50%

Combustion heat of fuel oil: H f = 42.2 MJ/kg

4.

TABLE 5.24
Comparison of Energy Efficiency

Heat
Exchanger

AverageTemperature
of Combustion Air

Furnace
Efficiency

Waste Heat
Recovery Rate

Energy
Saving Rate

Conventional
furnace

Metallic
recuperator

200˚C 40% 17% 30%

High performance
furnace

Regenerative
burner

720˚C 60% 63%

Both capacities are the same, 40 ton/ch (tons per a charge).