Sulfur steel making

General 1. Use cokeless iron- and steel-making processes, such as the direct reduction process, to eliminate the need to manufacture coke. 2. Use beneficiation (preferably at the coal mine) and blending processes that improve the quality of coal feed to produce coke of desired quality and reduce emissions of sulfur oxides and other pollutants. 

Steel making, broadly speaking, is an oxidation process in which impurities such as carbon, silicon, manganese, phosphorus and sulfur present in the pig iron are removed to specified levels. It can be anticipated from the Ellingham diagram that at about 1600 °C, the elements C, Si, and Mn would oxidize preferentially before iron undergoes excessive oxidation. The oxidation reactions may be represented by... 

Phosphorus and sulfur are present in pig iron and need to be removed in steel making because these elements, if present in any significant quantities in the steel, result in deterioration of its mechanical properties. The concentration normally tolerated is 0.04% for each of these elements, though in high-quality steels much lower levels are required. 

The carbon dioxide escapes from the steel-making furnace as a gas. The silicon dioxide (SiOi) forms slag. Slag is a crusty, metallic material that is scraped off after the steel is produced. Other impurities removed by a blast of oxygen are sulfur, phosphorus, manganese, and other metals. 

In the iron and steel making processes, sulfur in molten iron reacts with fi ee oxygen ion and is transferred into slag according to the following equation (32). 

Binder and/or lubricant selection depends on many considerations which are specific for the particular application. The additives must be compatible with the material to be agglomerated and the proposed uses of the product. For example, for pharmaceutical or food applications no toxic materials can be selected and for agglomeration of metal-bearing dusts intended for use in steel making sulfur-containing additives are normally prohibited. Many such limitations may be defined for specific materials and applications. 

Calcium carbide was initially used as the desulfurising agent. It was added, in a granular form, to the torpedo ladle (used to transfer the molten iron to the basic oxygen steel making process). It is now generally injected as a powdered mixture with lime (typically 60 to 80 % of calcium carbide) into the molten pig-iron in the transfer ladle. At an addition level of 7 kg/t of pig iron, such mixtures can reduce the level of sulfur to 20 % of the initial value. 

The use of tire-derived fuel as a cofiring feedstock in power generation has many advantages. Hrst, because of the high calorific value of TDF, particularly the wire-free TDF, the cost of TDF in GJ (ot /10 Btu) is lower than that of any fossil fuel - with the possible exception of Powder River Basin coal delivered locally or to a mine-mouth plant - and is competitive with even the lowest cost biomass fuels. This, combined with the lower ash content of TDF (without steel) makes it a viable blending fuel. In addition, the sulfur content of TDF is less than most eastern bituminous coals and conq>arable to medium-sulfur coals throughout the world. 

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry. 

Pure iron is a silvery white, relatively soft metal and is rarely used commercially. Typical properties are Hsted in Table 1. Electrolytic (99.9% pure) iron is used for magnetic cores (2) (see Magnetic materials, bulk). Native metallic iron is rarely found in nature because iron which commonly exhibits valences of +2 and +3 combines readily with oxygen and sulfur. Iron oxides are the most prevalent form of iron (see Iron compounds). Generally, these iron oxides (iron ores) are reduced to iron and melted in a blast furnace. The hot metal (pig iron) from the blast furnace is refined in steelmaking furnaces to make steel... 

Metallurgy. The strong affinity for oxygen and sulfur makes the rare-earth metals useflil in metallurgy (qv). Mischmetal acts as a trap for these Group 16 (VIA) elements, which are usually detrimental to the properties of steel (qv) or cast iron (qv). Resistance to high temperature oxidation and thermomechanical properties of several metals and alloys are thus significantly improved by the addition of small amounts of mischmetal or its siUcide (16,17). 

HydrometaHurgical Processes. The hydrometaHurgical treatments of oxide ores involve leaching with ammonia or with sulfuric acid. In the ammoniacal leaching process, the nickel oxide component of the ore first is reduced selectively. Then the ore is leached with ammonia which removes the nickel into solution, from which it is precipitated as nickel carbonate by heating. A nickel oxide product used in making steel is produced by roasting the carbonate. 

Coking coal is cleaned so that the coke ash content is not over 10%. An upper limit of 1—2 wt % sulfur is recommended for blast furnace coke. A high sulfur content causes steel (qv) to be brittle and difficult to roU. Some coal seams have coking properties suitable for metallurgical coke, but the high sulfur prevents that appHcation. Small amounts of phosphoms also make steel brittle, thus low phosphoms coals are needed for coke production, especially if the iron (qv) ore contains phosphoms. 

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