Coke smelting

Darby, Abraham I (1678-1717) was born in Staffordshire he patented sand casting in 1708 and invented coke smelting in 1709. 

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as ... 

Ferromanganese is produced iu blast fiimaces and electric smelting fiimaces. Economics usually determine which smelting process is chosen for ferromanganese. Both methods require about the same amount of coke for reduction to metal, but iu the case of the blast fiimace, the thermal energy required for the smelting process is suppHed by the combustion of additional coke, which iu most countries is a more expensive form of energy than electricity. 

Pitch. The principal outlet for coal-tar pitch is as the binder for the electrodes used in aluminum smelting. These are of two types. Older plants employ Sn derberg furnaces, which incorporate paste electrodes consisting of a mixture of about 70% graded petroleum coke or pitch coke and 30% of a medium-hard coke-oven pitch. This paste is added periodically to the top of the monolithic electrode as it is consumed. The more modem smelters employ prebaked electrodes requiring less binder, about 18%. 

The demand for electrode binder pitch has grown as aluminium output has expanded and the requirement for aluminium smelting is now between 1.5 and 2 x 10 t /yr. In Japan pitch is used for mixing with coal for carbonization in coke ovens to make metallurgical coke. 

Raw Materials. The basic raw materials limestone and coke or coal (qv) should be high quaHty. Limestone should contain a minimum of 95—97% CaCO and a maximum of 1.5% MgCO, 1—1.5% Si02, 1% Fe202 plus AI2O2, and 0.006% phosphoms (see Lime and limestone). The limestone is first converted to lime in a rotary or vertical shaft kiln. The lime is screened to eliminate fines that interfere with the evolution of carbon monoxide in the smelting process. 

Carbon monoxide Chlorinated hydrocarbons G Coke ovens Incomplete combustion generally Smelting Vehicle exhausts Metal extraction and refining... 

Cokers produce no liquid residue but yield up to 30% coke. Much of the low-sulfur product is used for electrolytic electrodes for smelting of aluminum. Lower-quality coke is burned as fuel im.xcd with coal. 

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

A variety of smelting processes have been employed to effect the reduction of ZnO by coke ... 

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. 

The CuS is then smelted, a process in which metal ions are reduced by heating the ore with a reducing agent such as carbon (in the form of coke). At the same time, the sulfur is oxidized to S02 by blowing compressed air through the mixture of ore, limestone, and sand ... 

Zinc, Zn, is found mainly as its sulfide, ZnS, in sphalerite, often in association with lead ores (see Fig. 15.11). The ore is concentrated by froth flotation, and the metal is extracted by roasting and then smelting with coke ... 

It is to be noted that in the above reaction it is assumed that the reduction of Fe203 is performed by CO, not by C, this being supplied by combustion of C of the coke in the tuyere zone. Some of the carbon of the coke is consumed in reduction of silicon, manganese, and phosphorus in the smelting zone, and some by contact with iron oxides farther up in the furnace, for example ... 

The oxygen in the blast penetrates but a short distance above the tuyere level. It is all consumed in burning the carbon of the coke to CO. Most of the carbon in the coke descends through the shaft of the furnace until it reaches the tuyere zone, where it is met by the blast and burned to carbon monoxide. The high temperature precludes the formation of carbon dioxide. Some of the carbon, however, through actual contact with iron oxide, is oxidized (either to CO or C02) in the upper part of the furnace. This oxidation, of course, liberates heat above, instead of in, the smelting zone where it is most needed and likewise tends to decrease the proportion of carbon fully oxidized to C02 in the furnace and thereby the quantity of heat developed in the furnace. 

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