Smelting Reduction Process with a Thick Layer of Slag for Producing Ferroalloys and Iron

Abstract

A flexible manufacturing system for the production of iron and steel is required. One of the potential technologies for this purpose is the smelting reduction process with a thick layer of slag. A feature of the process is that an oxygen jet is separated from the metal bath by a thick layer of slag. This is realized by the coexistence of carbonaceous materials for controlling slag foaming, and it allows high post combustion operation without disturbing the reducing reaction.
Experiments using furnaces of 100 kg, 600 kg, 3 t and 100 t for the production of Cr–Fe–C (Cr≤58%), Mn–Fe–C (Mn≤65%) and Fe–C by smelting reduction were done successfully. The procedure of experiments is reviewed and the phenomena of slag foaming and its control by the coexistence of carbonaceous materials, the physical properties of the slag layer, the reducing reaction, the method for supplying fine ore from the top without agglomeration, the limit of post combustion, the mechanism of heat transfer particularly by the circulation of carbonaceous materials in the slag layer, and the behavior of impurities during smelting reduction are discussed. There would be no problems in enlarging except that post combustion decreases when carbonaceous materials of high volatile matter are used, and coal consumption does not decrease as much as expected from the decrease of heat loss by enlarging.
This process can also be applied for scrap melting. An interesting phenomenon found in scrap melting with a thick layer of slag is the accelaration of Sn removal as SnS.
In the production of ferroalloys and hot metal, features of this process are (1) heating without electricity, (2) high post combustion, (3) decrease of dust formation which is a common problem in the use of oxygen gas, and (4) effective removal of some impurities.
Though there are some problems particularly on how to use high volatile matter coal effectively, this process shows a new direction for future iron and ferroalloy production, particularly for increasing the flexibility.