OCR Text |
Show 10 -= 1900 o o 1300 NoJ Heating Zone No.2 Heating Zone Before Installation t- T- CO •" in O) Fis .18 Change of fuel consumption rate before and after installation of regen erative combustion system 4. Development of N2 iet heater 4.1 Background At No.4 Slab Caster, Kawasaki Steel's Mizushima Works, for the purpose of reducing the tundish refractory consumption, as shown in Fig. 19, two hot tundishes are alternately and cyclically used without returning to the maintenance yard.6) In such an operational condition, while one tundish served the casting operation, the other had to be kept hot with preheater by gas burner during its long waiting time for the next casting campaign. (Termed burner-heated method) The preheating, however, causes the reoxidation of remains in the cyclically used tundish as referred in equation (1). The oxidized remains react with Al in molten steel and generate the alumina inclusions in the following casting operation as referred in equation (2), needless to say, resulting in the deterioration of slab qualities especially in the first casting heat. Waiting : 2 F e + 0 2 => 2FeO (1) Casting : 3FeO+2Al => 3Fe+Al203 (2) No preheating stand-by operation was tested with supplying inert gas into the tundish.(Termed non-heated method) 7) The flow rate of sealing gas should have been regulated to secure the minimum tundish temperature for the smooth cast start. Subsequently, as shown in Fig.20, the oxygen content in tundish could not be steadily controlled to suppress the reoxidation of remains. Thus, the new heating method with non-oxidizing atmosphere was required. No.2 tundish (Waiting) Tundish tilting car Ladle Gas burner No.1 tundish (Casting) No No .1 tundish .2 tundish mm\ 4 I W///A mm 4 SLZ 4 W///M H H Casting I | Slag off and Waiting Fig.19 Hot-cycle operation with two tundishes at No. 4 C C |