Blast furnace operation

The principal U.S. lead producers, ASARCO Inc. and The Doe Run Co., account for 75% of domestic mine production and 100% of primary lead production. Both companies employ sintering/blast furnace operations at their smelters and pyrometaHurgical methods in their refineries. Domestic mine production in 1992 accounted for over 90% of the U.S. primary lead production the balance originated from the smelting of imported ores and concentrates. 

Ore Size. The particle size of manganese ores is an important consideration for the smelting furnace. In general, the ore size for the furnace charge is —75 mm with a limit to the amount of fines (—6 mm) allowed. Neither electric furnaces nor blast furnaces operate satisfactorily when excessive amounts of fines are in the charge. 

The lead blast furnace operates at a lower temperature than the iron blast furnace, die temperature at the tuyeres being around 1600K as opposed to 1900K in the ironmaking furnace (see p. 333) and this produces a gas in which die incoming air is not completely reduced to CO and N2, as much as one per cent oxygen being found in the hearth gas. 

Figure 10. Shows air emissions from blast furnace operations.

Hochofen, m. blast furnace, -anlage, /. blastfurnace plant, -betrieb, m. blast-furnace operation. gas, n. blast-furnace gas. -guss, m. blastfurnace cast iron, -koks, m. blastfurnace coke, metallurgical coke, -schlacke, /, blast-furnace slag, -schmelze, /, blastfurnace smelting, -verfahren, n. blastfurnace process. 

In the blast furnace, the reaction of the nitrogen in the blast with coke leads to the formation of poisonous chemicals such as hydrogen cyanide and cyanogens, and each cubic meter of the blast furnace gas contains from 200 to 2000 mg of these compounds. The blast furnace gas is scrubbed with water in the dust collection system the cyanide compounds dissolve in the water, which is then discharged after the compounds have been destroyed. Another poisonous emission in blast furnace operations is hydrogen sulfide. The sulfur present in the coke is converted into calcium sulfide in the slag, the water-quenching of... 

Iron making. Molten iron is produced for steel making in blast furnaces using coke, iron ore, and limestone. Blast furnace operations use water for noncontact cooling of the furnace, stoves, and ancillary facilities and to clean and cool the furnace top gases. Other water, such as floor drains and drip legs, contribute a lesser portion of the process wastewaters. 

EXAMPLE 2.1 MODELING AND OPTIMIZING BLAST FURNACE OPERATION... 

The blast furnace operates continuously although the individual particles see a batch mode of reaction. The actual reaction conditions must be based on the batch reactor sequence for the particles since complete conversion is desired. This requires control of the mass throughput in the furnace, but primarily it requires accurate temperature control. Control of the solids is maintained at the bottom discharge port. Gas flow rate is controlled by blowers or by a stack discharge fan. 

We will be managing the 20 MW MHD combustor competitive prototype projects that are currently under way. One of these three contractors will be selected to develop and produce the combustor for a 50 MW MHD component development and integration facility scheduled for operation in Montana in FY 82. We will also be managing two coal/oil mixture demonstration projects. One will involve a utility steam generator and one is a blast-furnace operation. 

TABLE 14.3 Approximate Composition Ranges of the Products of Blast Furnace Operation"... 

The ability to vary oxygen enrichment levels instantaneously also provides the cupola or blast furnace operator with an extremely flexible device to control furnace operations better in spite of unavoidable changes in coke and metallic charge quality, blast humidity and temperature, and cast house demand pattern. Today, hundreds of cupola foundries worldwide use oxygen to increase cupola capacity and/or reduce unit operating cost, and most modem blast furnaces are equipped with oxygen injection. 

Carbonization. When coal is heated to temperatures 900 to 1200°C in the absence of air, most of the volatile matter is driven off, leaving a char, or, in the case of metallurgical bituminous coal, a coke. The atmosphere in a coke oven consists principally of hydrogen and methane. Consequently, pyrite is reduced to a mixture of iron sulfide (troilite and pyrrhotite) and iron metal [ ]. The amount of iron metal formed depends on both the temperature and the composition of the coke-oven gas. The reduction of iron sulfide to iron metal is desirable since blast furnace operation is more efficient with low sulfur coke. Calcite reacts with the liberated sulfur to form calcium sulfate, thus retaining sulfur in the coke. Calcium XANES spectra of coke produced from Pittsburgh seam coal in which all calcium is initially present as calcite indicate that approximately 70 percent of the calcite is converted to calcium sulfate during coking. 

Coke is used in blast-furnace operations, foundries and in the manufacture of water-gas, producer gas, domestic heating, and industrial purposes. 

The amount of SO2 produced in the blast furnace operation depends on the sulphur content in the treated raw material and in the fuel. The emissions escape into the air, particularly due to the furnace not being gas-tight. The blast furnace is also a source of other gaseous pollutants, particularly nitrogen oxides and hydrocarbons. 

The roast-reduction process using Dwight-Lloyd sinter machine and blast furnace operation is still the basis for the majority of the lead produced in primary smelters. Since the last survey (1), however, the total number of smelters based on this conventional technology has been remarkably reduced. 

A blast furnace can typically treat up to 1000 tons of sinter per day, producing approximately 450 tons of lead bullion, and 350 tons of slag. The blast furnaces operate 24 hours per day, 7 days per week, 11 A months per year and maintenance is accomplished on an as needed basis. A typical analysis of the slag is contained in Table II. 

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