Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 258

1400

F1 Mode F2 Mode

1200

1000

Heat input (including the sensible heat of air)
:930kW (800,000kcal/h) constant

800

Furnace temperature
(Normal temperature air)
Steel average
(Normal temperature air)

600

400

Furnace temperature
(High temperature air)
Steel average
(High temperature air)

200

197min. 238min.

0

0 50 100 150 200 250 300 350

Time, min.

FIGURE 5.18 Comparison of the rate of temperature rise under the constant heat input of
930 kW.

400

Ts3,max-Ts2,min (High temperature air)

Ts3,max-Ts2,min (Normal temperature air)

350

300

Ts3 Ts2 Ts1

250

200

Flame

150

100

50

0

0 50 100 150 200 250 300 350 400

Heating time, min.

FIGURE 5.19 Change of steel surface temperature with time.

1. Effect of flame locations
To change the locations where the flames were formed, combustion in the direction
of the furnace width (burners C, D, E, and F) was established so that the flames
were formed beneath the skids. As a result, the steel temperature near the skids rose
even under normal combustion, and the ion current that shows the existence of flames
also increased, but ∆ T was larger compared with that of the combustion with high
temperature air ( Figures 5.21 and 5.22 ). To enhance the dilution of air jet by the