Nippon Steel Corporation constructed two rotary hearth furnace (RHF) plants at Kimitsu Works from 2000 to 2002. These plants have processed dusts and sludge emitted in the steel works. The conventional palletizing mothod is applied for processing dusts, and a new wet processing method was developed for sludge processing. Thus almost all the dusts and sludge are recycled with the RHF plants. Total capacity of the plants is 300,000 t/y. We established technologies of operation and methods of producing DRI from the oxide waste. Functions of the RHF are reducing iron oxide and extracting zinc of the dusts and sludge. High metallization of iron (70%) and de-zinc ratio (80-90%) are obtained.
Another new technology is making very high stength DRI pellets by the RHF. Controled factors are chemical compositions of raw materials, temperature and atmosphere profiles in the furnace, and so on. The DRI pellets produced by the two RHF plants are strength enough for being charged in the blast furnaces (BF). The DRI charging to the blast furnace results in reduction in coke consumption and increase in production of hot metal. About 26,000tons of mixture of waste oxide and carbon is processed and 14,000 tons of DRI is fed in the BF plants at Kimitsu Works every month. As a result, 3,000 to 4,000 tons of coke is saved evry month.
We evaluated the combination of the RHF and the BF for ironmaking mainly by the viewpoint of productivity. The combination of the RHF and the BF is more efficient in terms of productivity and energy efficiency than that of sintering plant and BF. It is also more productive for making hot metal with a same volume of a blast furnace. The conbination of the RHF and the BF is one of proposals of new ironmaking practice. |
