Blast furnace / Industry - Economy-point.org

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A blast furnace is a plant in shaft furnace building method, in the iron by reduction of ferric oxide is won.

The blast furnace is fed with two substantial raw materials from above: the in such a way specified as carriers of the raw materials, and the blast furnace coke as sources of energy and reducing agents. When designated (of the old-German mixture) thereby the iron ore (usually in the form of nature ores or as burn-ups of roasting sulfidischer or carbonatischer iron ores), that with aggregates (e.g. lime, gravel and dolomite) (for the decrease of the melting point of the ores and better liquefaction of the mixture) one shifts.

The raw materials are carried above, emptied with promotion excavator buckets (Hunte) over an inclined elevator to the charging hole (the furnace-top bell) at the blast furnace, and brought over a double bell air-lock system in the inside. With modern blast furnaces here meanwhile conveyors are used, which two alternating with ores, aggregates and coke to fill.

At the foot of the blast furnace oxidizes the carbon mono oxide formed from coke and oxygen from the air to carbon dioxide, which extracted in addition necessary oxygen the ferric oxide, which is reduced thereby to iron. Liquefied blast furnace contents are inferred down at the furnace by an opening; this opening is normally locked with a ceramic mass and periodically with the tap so mentioned is drilled. Effluent contents led in to the furnace the bordering tap-resounds over a gutter system in the soil, and separated from the cinder swimming due to their smaller density on the pig iron. The separating device is called also fox, since it is "smart" like that to differentiate between the iron and the cinder. Most blast furnaces possess however two tap devices. One for the cinder and a something lower-lying for the molten metal. Also here the density variation is used for the separation.

The cinder developing during the blast furnace process is a valuable raw material. It can be used after oversize awls in a cinder crushing mill as variously.

The process in the blast furnace is held by means of down hot air injected at the blast furnace (the wind in such a way specified) on. This wind important for the enterprise is brought in air heaters (Cowper) on temperature. Apart from the function of the oxygen supply the wind provides also for the turbulence of the caused raw materials, which would bond together otherwise only at the furnace reason and no more to be heated up would be. If it comes once to a baking, to dissolve with the procedure of tossing (short interruption of the wind) tries these again. Tossing corresponds to stirring up a furnace fire, with which the draft of air threatens to succumb by too much ash on the lattice. The blast furnace is a counter current reactor: While the filled in material runs from top to bottom by the reactor, the developing reaction gases (the blast furnace gases) flow from bottom to top. They are taken above at the charge, cleaned by smoke particles and supplied to further use in the chemical industry and/or burned for wind production in the Cowpern.

The external wall of the blast furnace is permanently cooled over a water cooling. In former times the cooling system was openly implemented, i.e.: Water was led coldly into the furnace wall and cooled down then in a cooling tower again. That brought large a loss of energy and water with itself. The new blast furnaces are equipped with closed cooling circuits. "The white giant "in Duisburg has for example five different cooling circuits, which are separately self-contained all. Water, which is lost through variations in temperature or loss, is replaced by special, lime-free water with 0,1 "°dH.

The actual blast furnace is usually 25-30 m highly, the entire plant up to 60 M. "the black giant "in Duisburg has a furnace height of 42 m and a rack diameter of approximately 14 M.

Middle blast furnaces reach 6,000 t, large blast furnaces reach daily performances of up to 13.000 t pig irons.

Blast furnaces are approximately 10 years continuous in enterprise. After the end of this Ofenreise in such a way specified the actual blast furnace must be revised extensively; mostly the complete lining from fireproof stones is renewed and various structural steel members is replaced. The opportunity for the preparation of a new Ofenreise is then used often also for process improvements and the installation of new mechanisms for the energy conservation and quality improvement.

Important fundamental chemical reaction equations are the following:

(1) C + O_2 \ Longrightarrow CO_2 (energy supplying burn coke)
(2) CO_2 + C \ Longleftrightarrow 2 CO (production of the gaseous reducing agent carbon mono oxide)
(3) Fe_2O_3 + 3 CO \ Longrightarrow 3 CO_2 + 2 Fe (reduction of the ferric oxide to elementary iron)

Reaction (1) supplies on the one hand the energy for the entire process. There the oxygen in form of injected, preheated air is supplied, runs the reaction so violently that temperatures are reached until over 2000 "°C. One can make oneself this effect at a grill fire, whose coal glows clear violently white, if one blows with a warm foehn on it. On the other hand the reaction supplies the carbon dioxide CO2, which is needed for reaction (2).

Reaction (2) supplies the poisonous carbon monoxide CO, which works as actual reducing agent in the blast furnace. Contrary to firm carbon the gaseous CO can all surfaces of the ferric oxides easily reach and react there. This reaction is a typical Gleichgewichtsreaktion (Boudouard equilibrium). At high temperatures the equilibrium is right, with low left.

Reaction (3) shows the reduction typical iron (III) - of the oxide (red iron stone, rust) in summarized form. It actually runs over several intermediate stages, which run off in different zones of the blast furnace: