Blastfurnaces

Foundry Coke This coke has different requirements from blastfurnace coke. The volatile matter should not exceed 2.0 percent, the sulfur should not exceed 0.7 percent, the ash should not exceed 12.0 percent, and the size should exceed 76 mm (3 in). 

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

Blastfurnace slag Iron smelting Nearly all used As roadstone, railway ballast, filter medium, aggregate for concrete, fertilizer and in manufacture of cement... 

Steel-making slag Steel making Some returned to blastfurnaces, remainder dumped or used as fill near steel works, or sold As roadstone... 

The first stage in the conversion of iron ore to steel is the blastfurnace (see Panel), which accounts for the largest tonnage of any metal produced by man. In it the iron ore is reduced by coke, while limestone removes any sand or clay as a slag. The molten iron is run off to be cast into moulds of the required shape or into ingots ( pigs ) for further processing — hence the names cast-iron or pig-iron . This is an... 

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. 

Iron is produced in a blastfurnace by reduction of ores its properties are modified by blending with other metals. 

Blastfurnace slag Iron smelting Nearly all used As roadstone, railway... 

Figure4.12 Iron blastfurnace, showing chemical reactions.

Carbon is so oxygen hungry that it can take O away from metal oxides, thereby reducing them to free metal. Free iron, for example, is obtained by the reduction of iron oxides in the presence of hot carbon, called coke, in blastfurnaces. In simplified form the nature of that reduction reaction can be represented C + 2FeO 2Fe + C02. Such furnaces are important to the world economy in the production of steel from iron. 

Various types of cement and pozzolanas (e.g., coal burning fly ash, lime, blastfurnace slag and similar materials) are mostly used as the stabilizing matrix. That stabilization technique is used for the immobilization of inorganic or organic waste. 

Due to the increasing cost of energy, the need to preserve the environment, and the non-existence or exhaustion of suitable natural raw materials in some areas, industrial and other waste materials are of interest as possible raw materials or supplementary fuels or both. Energy can be saved if even a part of the CaO can be provided by a material, such as blastfurnace slag, that does not require decarbonation. Supplementary fuels include such materials as used or reject tyres and pulverized household refuse, which can be introduced into the system in various ways. Some materials, such as pulverized fuel ash (pfa fly ash) can serve as raw materials that also possess some fuel content. Other wastes that have been used include calcium silicate residues from aluminium extraction, mining residues, and precipitated calcium carbonate from various industries. 

Table 9.1 Chemical compositions of some blastfurnace slags" (D35) ...

Table 9.2 Atom ratios in a typical ground granulated blastfurnace slag...

Fig. 9.6 Pore size distributions for pastes of Portland and composite cements (vv/s = 0.45. curing temperature 21 C), determined using mercury intrusion porosi-metry. CID. CIY Portland cement pastes cured for 1 day and 1 year. S2D. SIY Portland-blastfurnace slag cement (70% slag) pastes, cured for 2 days and I year. F.3D, FI Y pfa cement pastes (13% CaO in fly ash) cured for 3 days and 1 year.. After Feldman (F34).

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