Blast Furnace Smelting

a metallurgical process carried out in shaft furnaces, used mainly in nonferrous metallurgy for the smelting of lead bullion, copper, copper matte, and nickel matte. The charge is loaded from above and consists of lumped metal-bearing raw material, fluxes, and coke. As the coke is burned and the materials are smelted, the charge descends; the air or oxygen required for the combustion of the coke is blown through a tuyere, and the combustion products move toward the charge. An oxygen zone is created near the tuyeres, in which the coke is combusted primarily to CO₂, most of the heat is released, and the maximum temperature is reached. A reduction zone is formed beyond the oxygen zone, in which the hot gases react with the succeeding layers of coke in the reaction

CO₂ + C = 2CO

The gases become enriched with carbon dioxide as their temperature decreases since the reaction proceeds with the absorption of heat; the reaction virtually ceases at 800°C.

Reduction, sulfidizing, and oxidation variants of blast furnace smelting are used in nonferrous metallurgy. Reduction blast furnace smelting of lead produces lead bullion, slag, dust, and gases. Copper matte is also formed if the agglomerate has a high content of copper and sulfur. The exhaust gases pass through an electrical filter or bag filter that traps dusts with a high content of zinc and lead. Sulfidizing blast furnace smelting of nickel oxide ores with the addition of pyrites or gypsum is performed in a weakly reducing atmosphere and produces matte. Oxidation blast furnace smelting of copper sulfide ores is designed to produce copper matte and remove barren rock with the slag, as well as to oxidize a portion of the sulfur of the sulfides and remove it as sulfuric anhydride; two variants of the process are pyritic and semipyritic smelting. Copper-sulfur blast furnace smelting with the production of elemental sulfur is a combined oxidation-reduction process.

Blast furnace smelting is commonly characterized by various parameters. The unit smelting capacity may be defined as the weight of ore, agglomerate, or charge smelted in one day per square meter of cross-sectional area of the furnace in the plane of the tuyeres; it is 50–100 tons per sq m per day for lead sulfide and copper sulfide charges and 30–40 tons per sq m per day for nickel oxide ores. The unit coke consumption is the ratio of the weight of coke to the weight of loaded ore or charge. A third commonly used index is the degree of extraction of valuable metals. In comparison with reverberatory and fluidized-bed smelting, blast furnace smelting exhibits higher efficiency, lower temperature of the exhaust gases, and, consequently, higher thermal efficiency; in comparison with smelting in reverberatory and electric furnaces, it ensures greater desulfurization. The disadvantages of blast furnace smelting are the need for preliminary sintering of the raw material, the low concentration of sulfuric anhydride in the exhaust gases, and a high dust output.

Major trends in the effort to improve blast furnace smelting, in addition to further development of the design of shaft furnaces, include oxygen enrichment of the oxygen blast, heating of the blast, improvement of charge preparation, automation of control of the smelting process, and the combination of blast furnace smelting with processes for the subsequent extraction of valuable metals from slags and the improvement of gas and dust trapping.