Domna is a furnace for smelting pig iron

Blast furnace is used for smelting pig iron in the modern metallurgical industry. This furnace is a mine type, which is not a very complicated structure, which, however, looks impressive. To bring the production of cast iron to perfection, mankind had to accumulate centuries of experience.

Partly explains what a blast furnace, the Old Slavic root of its name. "To blame" means to blow.

Ancestors of blast furnaces - tuukofen

In the Middle Ages, people needed different metals. The weapons and tools were made of steel, flexible and solid, and ordinary iron was used for items of household utensils. Sour-hearth furnaces have been used to produce the right metal for a very long time, for millennia, and they fully satisfied the needs until the stocks of low-melting ores were exhausted. High temperatures were achieved by increasing the height (so increased traction), the air was shaken and hand-operated furs. However, over time, Europeans had to switch to less quality raw materials, which served as an incentive for progress. Stukofen became the invention, after which the first blast furnace appeared. It was a closed-type furnace that operated on a specific cycle. It needed to load ore, coal, then there was heating with blowing (there was not enough manual effort, so the drive was used from water wheels), after which it was necessary to wait for cooling and extract the metal, separating it from scale and other unsuitable byproducts called kritzey. The main advantage of the guns was the better concentration of thermal energy due to the closed volume during the working cycle, due to the reduction of its leakage into the atmosphere.

Cast-iron civilization

The main problem of medieval metallurgists in the thirteenth century was the refractoriness of iron. When in shtukofene got cast iron (i.e., iron-carbon alloy with a carbon concentration of 1.7% and higher), it was surprised at its low melting point, but it did not come as a surprise. Obtained metal was easier to get than steel and especially iron, but its mechanical quality from the point of view of the then consumers left much to be desired: too fragile and not strong enough. However, in just two centuries the attitude towards pig iron has changed. First, it was a simple matter to extract it from the furnace, it could simply be drained in a molten form. Secondly, this metal has found its application, and very diverse. And thirdly, it was a raw material for further purification from excess carbon, and it was much easier to get steel from it than from ore. So, after centuries of experiments, the most productive metallurgical technology was found, and a blast furnace was invented. The furnace in the Westphalian town of Siegerland (second half of the 15th century) could work with an uninterrupted cycle for several years, producing over one and a half tons of cast iron daily. Then it was very much.

The structure of a blast furnace

Just after visiting this giant furnace, you can understand how great the modern blast furnace is. Photos give an idea of its cyclopean dimensions only when they depict a man who appears small, like an ant. However, despite the impressive appearance, the principle of action remained the same, medieval. The design includes five main nodes. The upper one, the top, is designed to load raw materials and evenly distribute it inside the furnace. Below it is located part of the conical shape, in which the heating and recovery process takes place (about it later). The third is the top unit, called steam, where iron melts. Then another conical part, this time tapering downwards, is the shoulder in which carbon monoxide (reducing gas) is released from the coke. And at the very bottom - the furnace, from which the finished product and production waste are extracted .

Chemistry of the process

Chemical processes are oxidative and reducing. The first means a connection with oxygen, the second, on the contrary, rejection of it. Ore is an oxide, and in order to get iron, a reagent is required that can "take away" excess atoms. The most important role in this process is played by coke, which, during combustion, releases a large amount of heat and carbon dioxide, which decomposes at high temperatures into a monoxide, a chemically active and an unstable substance. CO tends to again become a dioxide, and, when encountered with ore molecules (Fe ₂ O ₃ ), "takes away" all the oxygen from them, leaving only iron. There are, of course, other substances in the raw materials, unnecessary, which form waste, called slag. That's how the blast furnace works. This, from the point of view of chemistry, is a fairly simple recovery reaction, accompanied by heat consumption.

What is it, a modern blast furnace?

The service life of the blast furnace is relatively small for facilities of this scale - about a decade. During this time, the structure is subjected to heavy loads, weighed down by thermal heating, then a major repair or demolition is required. The production of cast iron can not be called harmless, it is associated with emissions of phosphorus, sulfur and other not very useful substances into the atmosphere. Together, these circumstances prompt many countries to curtail or modernize metallurgical production (especially if the industry is the basic and budget-forming industry). The modern blast furnace is quite simple in its principle, a system that requires, however, a complex control scheme with numerous control loops that ensure the most efficient use of raw materials and energy resources.