Hot-Slab Charging for Energy Conservation in Continuous Furnaces
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HOT-SLAB CHARGING FOR ENERGY CONSERVATION IN CONTINUOUS FURNACES S. V. Lukin,1 A. A. Zbrodov,2 and K. Yu. Levashev3
UDC 669.04
We considered the thermal operating balance of a continuous furnace being charged with 250 mm-thick cold steel slabs, and perform experimental measurements of the heat loss to the environment. The required heating time and peak productivity of a hot-charged furnace were determined under the assumption that the slabs were fed into the furnace at 700–1250°С. The calculations revealed that the amount of time required to heat the slabs is much shorter, productivity is higher, the amount of heat required per metric ton of metal is smaller, the amount of heat lost to the environment is lower, and the fuel (natural gas) consumption of the furnace per metric ton of metal is much lower. We also obtained a theoretical curve for fuel consumption as a function of charging temperature; according to this curve, as the charge temperature increases from 700 to 1000°C, the specific natural-gas consumption per metric ton of metal decreases from 27.7 m 3 /metric ton to 10.3 m 3 /metric ton, compared with 62 m 3 /metric ton for cold feedstock. We find that the energy savings in heating furnaces is maximized by feeding the slabs in immediately after they come out of the continuous billet casting machine. Keywords: Energy conservation; heating furnace; billet; slab; heating; hot charging; fuel consumption.
There is extensive scope for energy conservation using the physical heat from continuous-cast slabs in metal-rolling heating furnaces at large Russian metallurgical firms (Cherepovets Metallurgical Plant, Magnitogorsk Metallurgical Plant, and the Novolipetsk Metallurgical Plant) where continuous billet casting machines are used for pouring molten steel. This opportunity is unfortunately not currently being explored for a variety of reasons: Inadequate quality of cast billets, steel smelting shop far from the rolling shop, and inefficient logistics [1, 2]. At top-level metallurgical plants outside of Russia, continuous casting and rolling machines are combined into integrated casting and rolling modules in which the cast billets are immediately fed into the rolling units. Under Russian conditions, where the casting and rolling shops are in separate locations, insulated containers on railroad flatcars may be used for transportation of hot steel slabs, retention of physical heat, and equalization of temperature across the cross section. If the mean temperature at the outlet from the continuous-casting machine is 900– 1100°C and logistics are efficient, it may be possible to maintain a slab temperature of at least 700°C at the entrance to the furnace. One important condition is that the slabs used to charge the furnace have uniform temperature; only in this case will there be efficient heating of the billets, a substantial reduction in billet heating time, and a significant reduction in specific fuel consumption. Charging the furnace with billets at several different temperatures (from 0 to 300°C), as is done at
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