Modern civilization is inextricably linked with the development of production technology, which is impossible without improving the tools and materials used for their manufacture.

Among all materials of natural origin or created by man, the most significant place is occupied by ferrous metals - an alloy of iron and carbon with the presence of other elements.

Alloys containing 2–5% carbon are classified as cast iron; those containing less than 2% carbon are classified as steel. For melting metals, a special blast furnace technology is used.

ABC of production

Blast smelting is the process of producing cast iron from iron ore processed in blast furnaces or, as they are also called, blast furnaces.

The main materials needed in the process of such production are:

• fuel in the form of coke obtained from coal;
• iron ore, which is the direct raw material for production;
• flux – special additives made from limestone, sand, and other materials.

Iron ore enters blast furnaces in the form of pieces of small rock fused together - agglomerates or pellets, in the form of ore lumps. The feedstock is loaded into the blast furnace top layer-by-layer, alternating with layers of coke and layer-by-layer addition of flux.

Note: flux is necessary in order to make the waste rock and various impurities, which are called slag, float.

The slag that floats on the surface of the hot cast iron is drained before the metal hardens. The material loaded for cast iron smelting, consisting of iron ore, coke and flux, is called charge.

The blast furnace, which in profile resembles a tower with a wide base, is lined inside with fireproof material - fireclay.

The main design elements are:

• shoulders;
• steam;
• fire pit;
• mine
• horn

The steam chamber is the widest part of the blast furnace. It melts gangue ore and flux, resulting in slag. To prevent the impact of high temperatures on the masonry and furnace casing, refrigeration units with circulating water are used.

The blast furnace shaft is built in the shape of a cone that expands at the bottom - this design of the blast furnace allows the charge to fall freely during the smelting process.

The formation of cast iron, which goes down into the furnace during the smelting process, occurs in steam and shoulders. To hold the solid charge in the steam and shaft, the shoulders have the shape of a cone, with an expansion towards the top.

How does it work

The charge is poured into the blast furnace through the furnace in continuous portions.

To ensure continuity of work, a warehouse for pellets (sinter), flux and coke is installed near the blast furnace - a bunker designed for preparing the charge.

The supply of raw materials to the bunkers, as well as the supply of the charge to the filling devices at the top, is carried out in a continuous manner using conveyors.

Sinking under its mass, the charge enters the middle part of the furnace, where, under the influence of hot gases resulting from the combustion of coke, the iron ore material is heated, and the remaining gases exit through the top.

In the furnace, which is located at the bottom of the furnace, there are devices for supplying hot air flows under pressure - tuyeres. The tuyeres have windows with heat-resistant glass, allowing visual control of the process. Note:

To protect against high temperatures, the devices are cooled with water through the channels available inside.

The coke burned in the forge produces the temperature required for ore smelting, exceeding +2000 degrees.

During the combustion process, coke and oxygen combine to form carbon dioxide. The effect of high temperature on carbon dioxide converts the latter into carbon monoxide, which takes away the ore and reduces iron. The process of cast iron formation occurs after the iron passes through layers of hot coke.

As a result of this process, iron is saturated with carbon.

After the cast iron has accumulated in the forge, the liquid metal is released through the holes located below - tapholes. First of all, slag is released through the upper tap hole, and then cast iron is released through the lower tap hole. Through special channels, the cast iron is poured into ladles placed on railway platforms and transported for further processing.

Foundry cast iron, which will later be used for the production of castings, enters the casting machine and, when solidified, turns into bars - ingots.

Converting pig iron is transported to a steel foundry with converters, open-hearth furnaces or electric furnaces. In modern, huge blast furnaces, not only hot air flows are used to support combustion processes, but also pure oxygen, used together with natural gas.

This technology allows you to consume less coke, but is technologically more complex. Therefore, to control the production process and select optimal melting modes, computers are used that are capable of simultaneous analysis of the operation of all systems.

Watch an educational video that describes the operating principle and nuances of a blast furnace:

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§ 5. CONSTRUCTION OF A BLAST FURNACE

Various types of cast iron are produced from iron ores in a blast furnace. Blast furnaces that burn coke are called coke furnaces, and those that burn charcoal are called charcoal furnaces.

A blast furnace - a blast furnace (Fig. 13) is a continuous shaft furnace. It has the shape of two truncated cones, folded by wide bases, between which there is a cylindrical part called a raspar.

The upper (narrow) part of the furnace is called the top. The top has a charging apparatus for loading charge (ore, fuel, fluxes) and gas outlet pipes through which gases called blast furnace or top gases are removed from the blast furnace.

The part of the furnace between the top and the steam is called the shaft. The part of the furnace, facing upward with a truncated cone and supporting the charge in steam along with the charge and the top, is called shoulders. In this part of the furnace, there is a rather sharp reduction in the volume of loaded materials as a result of coke burnout and the formation of liquid smelting products.

The lower part of the furnace, which has the shape of a cylinder, in which the smelting products—liquid iron and slag—accumulate, is called the forge. The furnace has holes radially located at equal distances from each other (10-16, depending on the size of the blast furnace). Double-walled red copper, bronze or aluminum pipes are inserted into these holes. These holes are called tuyeres. Hot air heated in air heaters (coopers) is blown through the tuyeres by a fan or blowing machines. The tuyeres are cooled by water circulating in the space between the pipe walls. Rice. 13.

At the bottom of the hearth there are holes for releasing cast iron - a cast iron tap hole, and for releasing slag - a slag tap hole. The lower part, or bottom, of the forge is called the ridge. The ledge rests on the reinforced concrete foundation of the furnace. The walls of the blast furnace are lined with refractory fireclay bricks. The refractory masonry of the furnace is enclosed in a steel casing, which is made from sheets riveted or welded together. To increase the durability of the refractory masonry, it is cooled using metal refrigerators in which water circulates.

Currently, ferrous metallurgy is equipped mainly with large, high-performance blast furnaces. Modern blast furnaces are equipped with automatic control devices. These devices monitor, regulate and record the main parameters of the blast furnace process.

Nowadays, such main areas of blast furnace operation as ore supply, control of charge filling level, regulation of blast temperature, air humidity, gas pressure, and heating of air heaters are fully automated.

A number of instruments show the carbon dioxide content in the blast furnace gas, its temperature, etc.

In our country, the world's most powerful blast furnace is being built with a volume of more than 2000 m 3 and an annual productivity of more than 1 million tons. This furnace provides for comprehensive automation of unloading. Conventional scale cars are replaced by a plate conveyor system. Regulation of the quantity and stock of the charge, as well as loading modes, is carried out by a software device. Instead of opening the cast iron tap hole with an electric drill, remote control of this process will be used. Casting iron and slag is also mechanized.

A blast furnace is a shaft furnace for smelting pig iron from iron ore.

The diagram of a blast furnace is shown in Fig. 3.1. The furnace consists of the following elements in height: flue, shaft, steam, shoulders, hearth and flank. The level of filling of materials and the distribution of materials across the cross section of the shaft are formed at the top. The shaft is designed to heat the charge to the melting temperature. In addition, iron reduction processes also occur in the mine. The steam chamber is the widest part of the furnace, where the main melting processes take place. Below the furnace are shoulders that serve to overheat and transfer the melt and slag from the furnace to the furnace. The forge rests on a ledge - a masonry made of refractory bricks. The forge is needed to collect smelting products - cast iron and slag. At the border of the shoulders and the hearth there are tuyeres through which hot blast and sometimes fuel (natural gas) are supplied. The blast is air, usually enriched with oxygen.

The operating principle of a blast furnace is as follows. The charge is fed via a skip hoist into the receiving funnel at the top of the furnace. The charge includes fluxed sinter, coke, ore, limestone, and it is possible to load pellets. With the help of alternate operation of the small and large cones of the furnace, the charge is poured into the shaft.

During the operation of the furnace, the charge gradually falls down and is heated due to the heat of the upward moving gases formed in the furnace during the combustion of coke. The hearth gas has a temperature of 1900-2100 °C, consists of CO, H 2 and N 2 and, when moving in the charge layer, not only heats it, but also reduces iron oxides (FeO, Fe 2 O 3 and Fe 3 O 4) to Fe . The high temperature of the hearth gas is due, in particular, to the high temperature of air heating (1000-1200 °C) in blast furnace heaters. The gas leaving the furnace has a temperature of 250-300 °C and is called the top gas. After cleaning the blast furnace gas from dust, it will be called blast gas.

Blast furnace gas is a low-calorie fuel with a lower calorific value from 3.5 to 5.5 MJ/m 3 . The composition of blast furnace gas strongly depends on the enrichment of the blast with oxygen and on the supply of natural gas: 24-32% CO, 10-18% CO 2, 43-59% N 2, 0.2-0.6% CH 4, 1.0- 13.0% H 2 . Gas is mainly used to heat the nozzle of blast furnaces, as well as in a mixture with coke oven or natural gas - for heating heating, thermal and some other furnaces.

At the bottom of the blast furnace, the reduced iron melts and flows as pig iron into the furnace, where it gradually accumulates. Molten oxides of iron, manganese, silicon, etc., together with lime, form liquid slag. The slag is located (floats) above the cast iron due to the fact that the density of the slag is less than the density of cast iron. From the hearth, cast iron and slag are periodically released through a cast iron and slag tap hole, respectively. If relatively little slag is formed, then cast iron and slag are discharged together through one cast iron tap hole and separated from each other at the casting site. The temperature for releasing liquid cast iron is 1420-1520 °C.

For normal and high-performance operation of a blast furnace, powerful air heaters are required. Blast air heaters are regenerative heat exchangers. Blast-furnace air heaters are often called cowpers in honor of their English creator, E.A. Cowper. An idea of ​​the appearance of the cowper can be obtained from Fig. 3.1. A cowper is a vertical cylindrical casing, welded or riveted from sheet steel, with an enclosed nozzle, usually made of refractory brick. At the bottom of the cowper combustion chamber there is a burner and a hot blast air duct. The sub-nozzle space of the cowper is connected by valves to the cold blast air duct and to the outlet to the smoke hog.

A modern blast furnace has 4 cowpers that work alternately: the nozzle of two of them is heated by hot flue gases, and heated air (blast) is passed through one. The fourth cowper is usually in reserve. The blowing period lasts from 50 to 90 minutes. After this, the cooled cowper is switched to heating, and the blast is supplied through the next hottest cowper. In Fig. Figure 3.1 shows the case when air passes through the cowper to the right of the blast furnace, and the left one is heated (heated). During the heating period, the burner operates and the valve on the path of flue gases to the smoke hog is open, but the valves on the cold and hot blast air ducts are closed.

As a result, the combustion products formed during fuel combustion rise upward, successively pass through the combustion chamber, the under-dome space, and then fall down, pass through the nozzle, heating it, and only after that, at a temperature of 250-400 °C, go through the smoke valve to the chimney . During the blast period, it’s the other way around: the smoke valve is closed and the burner is turned off, but the valves on the cold and hot blast air ducts are open. In this case, cold blast under a pressure of 3.5-4 atm enters the sub-nozzle space, passes through the heated nozzle, where it heats up, and, descending in the combustion chamber, reaches the hot blast air duct. Through this air duct the blast is directed to the furnace.

Depending on the specific conditions, humidification of the blast relative to natural humidity, enrichment of the blast with oxygen or nitrogen can be used. In particular, enriching the blast with nitrogen makes it possible to save coke and regulate the intensity of blast furnace smelting. Enriching the blast with oxygen (up to 35-40%) together with the use of natural gas also makes it possible to reduce coke consumption. Increasing the blast humidity (up to 3-5%) allows you to increase the heating temperature of the blast in the cowper due to the intensification of radiant heat transfer in the nozzle and leads to a reduction in coke consumption.

The approximate height of the cowper is up to 30-35 meters, diameter – up to 9 meters. The upper part of the nozzle is laid out with high-alumina or silica bricks, the lower part with fireclay bricks. The thickness of the packed brick is 40 mm. Cells of 45×45, 130×45 and 110×110 mm are laid out from it. In addition to brick nozzles, nozzles made of hexagonal blocks with round cells and horizontal passages, as well as nozzles made of high-alumina balls, are used. The heating surface of a brick nozzle is about 22-25 m2 per 1 m3 of its volume. It can be approximately assumed that the packing volume of one cowper is 1-2 times less than the volume of a blast furnace. So, if the volume of the furnace is 2700 m3, then one cowper can have a volume of about 2700/1.5 = 1800 m3.

The most common cowpers are those with a built-in combustion chamber, as shown in Fig. 3.1. The main disadvantages of these cowpers: overheating of the roof and deformation of the combustion chamber towards the nozzle during long-term operation. There are cowpers with an external combustion chamber, as well as cowpers in which the burners are located under a dome. Cowpers with an external combustion chamber are easy to use and have high durability, but are more expensive than other cowpers. Cowpers with dome burners are inexpensive, but inconvenient to use, because... burners and valves are located at a considerable height.

During the blowing period, the air heating temperature gradually decreases from 1350-1400 °C to 1050-1200 °C. For a stationary blast furnace, such temperature changes in the blown blast are undesirable. Therefore, the temperature is controlled by adding cold air from the cold blast air duct. As the blast temperature decreases, the proportion of cold air in the mixture decreases in order to stabilize the blast temperature at 1000-1200 °C.

The approximate material balance of iron smelting is given in table. 3.1, and the corresponding heat balance of the blast furnace working space is in Table. 3.2.

When compiling balances, the following compositions of materials were adopted. Pellets: Fe 2 O 3 - 81%; FeO - 4; SiO 2 - 7; CaO - 5; Al 2 O 3 - 1; MgO - 1; MnO - 0.3; P 2 O 5 ~0.09; S ~0.03%. Agglomerate: Fe 2 O 3 - 63%; FeO - 16; SiO 2 - 7; CaO - 10; Al 2 O 3 - 2; MgO - 1; MnO - 1; P 2 O 5 ~0.25; S ~0.01%. Cast iron: Fe - 94.2%; C - 4.5; Si - 0.6; Mn - 0.7; S ~0.03%. Slag: FeO - 1%; SiO2 - 36; CaO - 43; Al 2 O 3 - 10; MgO - 7; MnO - 2; S - 1%. Top gas (blast furnace): CO 2 - 18.0% (vol.); CO - 25.2; H 2 - 12.5; CH 4 - 0.3; N 2 - 44%.

Let us analyze the fuel consumption in a blast furnace when using fluxed sinter.

Fuel consumption in a blast furnace consists of the consumption of coke and natural gas (510-560 kg s.e./t pig iron) plus the gas consumption for heating the blast furnace (90-100 kg s.e./t pig iron) and minus the output of blast furnace gas (170-210 kg s.e./t cast iron). Total total consumption: 535 + 95 – 190 = 440 kg s.e./t of cast iron.

If we take into account that fuel has already been spent on the production of coke (approximately 430-490 kg of coke per 1 ton of cast iron) and sinter (approximately 1200-1800 kg of sinter per 1 ton of cast iron), then the total consumption of primary fuel for the production of 1 ton of cast iron will be 440 + 40 + 170 = 650 kg s.e./t, where 40 and 170 kg s.e./t are fuel consumption for the production of coke and sinter, converted to 1 ton of cast iron.

The performance of the furnace is characterized by a specific indicator called KIPO (useful volume utilization rate). KIPO is equal to the ratio of the useful volume of the furnace to the daily smelting of pig iron and is therefore dimensional. For modern furnaces, KIPO ranges from 0.43 to 0.75 m 3 ⋅day/t. The lower this coefficient, the better the oven works. By its name, it would be more logical to consider KIPO as the ratio of productivity to a unit of volume. In this regard, it is more convenient to use such an indicator as the specific productivity of a blast furnace, equal to P y = 1 / KIPO and varying from 1.3 to 2.3 t/(m 3 ⋅day).

In order to save fuel on a blast furnace, the following can be recommended:

• transferring the furnace to work with increased (up to 1.5-2 ati) gas pressure at the top. At the same time, the volume of gases decreases, which makes it possible to increase the blast flow rate or reduce the removal of flue dust;
• increasing the air heating temperature in blast furnace heaters in order to save coke;
• use of physical heat of fiery liquid slags. This problem has not yet been solved due to the frequency of slag release from the furnace. A promising proposal is to air granulate slag and produce additional steam for local boiler houses;
• injection of hot reducing gases similar to what is done in a metallization furnace. This will help save up to 20% of coke;
• injection of pulverized coal fuel into the hearth in order to save approximately 0.8 kg of coke per 1 kg of pulverized coal fuel;
• using the heat of exhaust gases from blast furnace air heaters to heat blast furnace gas and air before feeding it into the burner.

A blast furnace, or blast furnace as it is often called, is designed to smelt iron from iron ore. This happens as a result of chemical reactions occurring at high temperatures. At the final stage of the process, the smelted iron is saturated with carbon and converted into cast iron (see Iron, steel, cast iron).

Blast furnace.

In a blast furnace, as a rule, it is not iron ore that is melted, but agglomerate (fine ore sintered into pieces) or pellets (spherical lumps obtained from fine ore or finely ground concentrate). They are loaded into the furnace in layers, interspersed with coke. Fluxes - lime, sand and some other substances - are also added to the blast furnace layer by layer. What are they needed for?

Together with the agglomerate and pellets, rock that does not contain iron enters the blast furnace. Metallurgists call it waste rock. It must be removed so that it does not get into the cast iron as it hardens. Fluxes cause waste rock and some other unnecessary substances (all this is called slag) to float to the surface of the liquid metal, from where the slag can easily be poured into a special ladle. So, agglomerate (or pellets), coke, and fluxes are included in a mixture of materials that is loaded into a blast furnace and is called a charge.

The blast furnace resembles a large round tower and consists of three main parts: the upper part is the furnace, the middle part is the shaft and the lower part is the forge. The inside of the blast furnace is lined (lined) with refractory masonry. To prevent the masonry from deteriorating and protect the furnace casing from high temperatures, refrigerators are used in which water circulates.

The charge is loaded into the blast furnace through the furnace in portions of several tons each. The download is continuous. To do this, a bunker is installed near the blast furnace - a warehouse where agglomerate (or pellets), coke and fluxes are delivered. In the bunker, they are used to form a charge using automated scale cars. Raw materials are fed continuously into the bunkers of large modern domains using conveyors. Also, conveyors in modern blast furnaces move the charge from the hopper to the top. In old blast furnaces, skip trailers are used for this, which run on inclined rails.

Under the influence of its own weight, the charge descends, passing through the entire blast furnace. In the middle part of the furnace - the shaft - it is washed by gases coming from the bottom up - the products of coke combustion. They heat the charge and then leave the blast furnace through the top. But the most important thing happens in the lower part of the blast furnace - the forge.

Here, in the casing of the blast furnace there are tuyeres - special devices for supplying compressed hot air to the furnace. The tuyeres have windows protected by glass, through which blast furnace workers can look inside the furnace and see how the process is going on. To prevent the tuyeres from burning, they are cooled with water flowing through the channels inside the tuyeres.

Hot air is needed to further heat the charge before melting. This reduces the consumption of expensive coke and increases the productivity of the blast furnace. In addition, to further reduce coke consumption, natural gas or fuel oil is introduced into the blast furnace as a heat source. Before being fed into the tuyeres, the air is heated in high towers filled with bricks inside - air heaters.

In the furnace of a blast furnace, coke (as well as natural gas or fuel oil) is burned, developing a very high temperature - over 2000 °C, under the influence of which the ore is completely melted. When burned, coke combines with oxygen in the air to form carbon dioxide. Under the influence of high temperature, carbon dioxide turns into carbon monoxide, which removes oxygen from the iron ore, reducing iron. Flowing down through a layer of hot coke, the iron is saturated with carbon and turns into cast iron. Liquid iron accumulates at the bottom of the hearth, and a layer of lighter slag accumulates on its surface.

When a sufficient amount of cast iron has accumulated in the forge, it is released through the holes in the lower part of the forge - the tap hole. First, the slag is released through the upper tap hole, then the cast iron through the lower tap hole. Next, the cast iron falls into ditches, from where it is poured into large cast iron ladles standing on railway platforms and sent for further processing.

If cast iron is intended for the production of castings - foundry cast iron - it goes into a casting machine, where it solidifies in the form of bars - pigs. If the cast iron is intended for conversion into steel (pig iron), it is transported to the steelmaking shop. There it enters open-hearth furnaces, converters or electric furnaces (see Electrometallurgy). Of the total amount of cast iron produced, approximately 80% is pig iron.

The first blast furnace of the Magnitogorsk Iron and Steel Works, which went into operation in 1932, had a volume of 900 m 3 . In 1986, the Severyanka blast furnace with a volume of 5500 m 3, one of the largest in the world, began operating at the Cherepovets Metallurgical Plant.

Previously, blast furnaces produced cast iron every 3–4 hours. With an increase in their volume, the production of cast iron accelerated - every 2 hours. Large blast furnaces - with a volume of 3000 m 3 or more - produce cast iron almost continuously.

In modern giant blast furnaces, not only heated air is used to maintain combustion, but also natural gas along with pure oxygen. This increases the productivity of the unit, reduces coke consumption, but at the same time makes it difficult to control the technological process. Therefore, electronic computers are now increasingly appearing in blast furnace shops. They analyze the readings of numerous instruments, monitor the progress of the process, and select the best melting modes.

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Our time has never been called: the age of the atom, space, plastics, electronics, composites, etc., etc. In fact, our age is still iron - its alloys still form the core of technology; the rest, although very powerful, is periphery. The path of iron into structures, products and structures begins with the smelting of cast iron from ore in a blast furnace.

Note: There are almost no rich iron ores left in the world immediately after extraction suitable for smelting. Current blast furnaces operate on enriched sinter and pellets. Further in the text, ore means just such a raw material for ferrous metallurgy.

A modern blast furnace (blast furnace) is a grandiose structure with a height of up to 40 m, a weight of up to 35,000 tons and a working volume of up to 5,500 cubic meters. m, producing up to 6000 tons of cast iron per melt. The blast furnace ensures the operation of a host of systems and units covering an area of ​​tens and hundreds of hectares. This whole facility looks impressive even when stopped with the blast furnace extinguished on a cloudy day, but in operation it is simply enchanting. The release of cast iron from a blast furnace is also an exciting spectacle, although in modern blast furnaces it no longer resembles a picture from Dante’s Inferno.

The basic principle

The operating principle of the blast furnace is the continuity of the metallurgical process for the entire life of the furnace until the next overhaul, which is carried out every 3-12 years; the total service life of a blast furnace can exceed 100 years. A shaft blast furnace: a charge of ore with limestone flux and coke is periodically immersed into it from above in portions (shanks), and molten cast iron is also periodically released from below and the molten slag is drained, i.e. the column of raw materials in the blast furnace shaft gradually settles, turning into cast iron and slag, and is built up on top. However, the path of the ferrous metallurgy to this seemingly simple scheme was long and difficult.

Story

The Iron Age gave way to the Bronze Age mainly due to the availability of raw materials. Raw iron was much inferior to bronze in everything else, including labor intensity and cost; the latter, however, during the time of slavery, few people worried. But bog ore, which is almost pure iron hydroxide, or high-grade iron ore, could be found everywhere in ancient times, in contrast to the deposits of copper and - especially - tin needed to obtain bronze.

The first iron from mineral raw materials was obtained, judging by archaeological data, by accident when the wrong ore was loaded into a copper smelter. When excavating ancient smelters, apparently discarded pieces of iron smelting are sometimes found near the furnaces (see below). The shortage of raw materials forced us to take a closer look at them, but the ancients, in general, thought no worse than us.

Initially, iron was obtained from ore so-called. using the cheese-blowing method in a blast furnace (not a blast furnace!). The reduction of Fe from oxides occurred due to the carbon of the fuel (charcoal). The temperature in the blast furnace did not reach the melting point of iron at 1535 degrees Celsius, and as a result of the reduction process, a mass of sponge iron supersaturated with carbon - kritsa - was established in the blast furnace. To extract the kritsa, the domnitsa had to be broken, and then the kritsa had to be compacted and the excess carbon literally knocked out of it, forging long, hard and persistently with a heavy hammer. From the point of view of that time, the advantages of the cheese-making process were the ability to produce kritsa in a very small furnace and the high quality of kritsa iron: it is stronger than cast iron and is less susceptible to rusting. How to obtain iron using the cheese-making method, see the video below.

Video: smelting iron using the cheese-blowing method

China was the first, much earlier than other countries, to move from slavery to feudalism. Slave labor ceased to be used in production there and commodity-money relations began to develop even when Ancient Rome was firmly in the West. The cheese-making process immediately became unprofitable, but it was no longer possible to return to bronze, there simply wouldn’t be enough of it. The role of flux in facilitating the smelting of metal from ore was known back in the Bronze Age; to smelt iron it was only necessary to increase the pressure, and the Chinese, through trial and error, by the 4th century. n. e. learned to build blast furnaces with supercharged bellows driven by a water wheel, on the left in Fig.

To an identical design in the second half of the 15th century. The Germans arrived, on the right in the figure. Quite independently: historians trace a continuous series of improvements from the blast furnace through the stukofen and blauofen to the blast furnace. The main thing that German metallurgists contributed to ferrous metallurgy was the combustion of high-quality coal into coke, which greatly reduced the cost of fuel for a blast furnace.

The terrible enemy of the original blast furnace process was the so-called. frosting, when, due to a violation of the blast regime or a lack of carbon in the charge, a “goat sat down” in the furnace, i.e. the charge was sintered into a solid mass. To remove the goat, the blast furnace had to be broken. This historical example is illustrative.

The Ural factory owners, the Demidovs, were known to be famous for their cruelty and inhumane treatment of workers, especially since there were many of them “unpatched,” runaway serfs and deserters. The “workers” were once completely fed up, and they presented their demands to the clerk, which, it must be said, were quite modest. According to Demidov’s custom, he literally sent them in Russian. Then the workers threatened: “Come on, come here yourself, otherwise we’ll put the goat in the oven!” The clerk stretched out, turned pale, mounted his horse and galloped away. Less than an hour passed (in the days of horse-drawn transport - instantly), the lathered “himself” galloped up on a lathered horse, and immediately said: “Brothers, what are you doing? What do you want me to do?” The workers repeated their demands. The owner, figuratively speaking, sat down and said “Koo!” and immediately ordered the clerk to do everything thoroughly.

Until the 19th century The blast furnaces were actually raw materials: unheated and not oxygen-enriched atmospheric air was blown into them. In 1829, the Englishman J.B. Neilson tried to heat the blown air to just 150 degrees (having previously patented his air heater in 1828). The consumption of expensive coke immediately dropped by 36%. In 1857, also an Englishman, E. A. Cowper, invented regenerative air heaters, later named Cowpers in his honor. In the cowpers, the air was heated to 1100-1200 degrees due to the afterburning of exhaust blast furnace gases. Coke consumption decreased by another 1.3-1.4 times and, what is also very important, the blast furnace with cowpers turned out to be not susceptible to fouling: when signs of fouling appeared, which happened extremely rarely with very serious violations of the technical process, there was always time to inflate the furnace. In addition, in cowpers, due to the partial disintegration of water vapor, the intake air was enriched with oxygen to 23-24% versus 21% in the atmosphere. With the introduction of the Cowper blast furnace, the processes in the blast furnace from the point of view of thermochemistry reached perfection.

Blast furnace gas immediately became a valuable secondary raw material; They didn’t think about ecology back then. In order not to waste it, the blast furnace was soon supplemented with a blast furnace apparatus (see below), which made it possible to load charge and coke without releasing blast furnace gas into the atmosphere. This is where the evolution of the blast furnace basically ended; its further development followed the path of important, but partial improvements, improvement of technical and economic, and then environmental indicators.

Domain process

The general diagram of a blast furnace with service systems is shown in Fig. The foundry yard is an accessory to small blast furnaces that produce mainly foundry pig iron. Large blast furnaces produce over 80% of converting pig iron, which the iron truck immediately takes from the casting site to the converter, open-hearth or electric smelting shops for conversion into steel. Foundry cast iron is cast into earthen molds, usually into ingots - ingots - which are sent to manufacturers of metal products, where they are melted down for casting into products and parts in cupola furnaces. Cast iron and slag are traditionally discharged through separate openings - tapholes, but new blast furnaces are increasingly equipped with a common taphole, divided into cast iron and slag by a heat-resistant plate.

Note: ingots of raw iron without excess carbon, obtained from cast iron and intended for processing into high-quality structural or special steel (second to fourth stages) are called slabs. In metallurgy, professional terminology is developed in no less detail and precision than in maritime affairs.

At present, it seems that there are no reserves of coal and coke ovens left at blast furnaces. A modern blast furnace runs on imported coke. Coke oven gas is a deadly poisonous environmental killer, but it is also a valuable chemical raw material that must be used immediately, while still hot. Therefore, coke production has long been separated into a separate industry, and coke is supplied to metallurgists by transport. Which, by the way, guarantees the stability of its quality.

How does a blast furnace work?

An indispensable condition for the successful operation of a blast furnace is an excess of carbon in it during the entire blast furnace process. For the thermochemical (highlighted in red) and technical and economic diagram of the blast furnace process, see Fig. Iron smelting in a blast furnace takes place as follows. way. A new blast furnace or one reconstructed after a 3rd category overhaul (see below) is filled with materials and ignited with gas; also heat one of the cowpers (see below). Then the air begins to blow. The combustion of coke immediately intensifies, increasing the temperature in the blast furnace, and the decomposition of the flux begins with the release of carbon dioxide. Its excess in the furnace atmosphere with sufficient blown air does not allow the coke to burn out completely, and carbon monoxide - carbon monoxide - is formed in large quantities. In this case, it is not a poison, but an energetic reducing agent, greedily taking oxygen away from the iron oxides that make up the ore. The reduction of iron with gaseous monoxide, instead of less active solid free carbon, is the fundamental difference between a blast furnace and a blast furnace.

As the coke burns and the flux breaks down, the column of materials in the blast furnace settles. In general, a blast furnace consists of two truncated cones formed by the bases, see below. The upper, high one is the blast furnace shaft, in which iron from various oxides and hydroxides is reduced to iron monoxide FeO. The widest part of the blast furnace (the place where the bases of the cones meet) is called raspar (raspar, raspar - incorrectly). In steam, the settling of the charge slows down, and iron is reduced from FeO to pure Fe, which is released in drops and flows into the blast furnace. The ore seems to be steaming, sweating molten iron, hence the name.

Note: The time it takes for the next batch of charge in a blast furnace to travel from the top of the shaft to the melt in the forge ranges from 3 to 20 or more days, depending on the size of the blast furnace.

The temperature in a blast furnace within the loading column increases from 200-250 degrees under the throat to 1850-2000 degrees in steam. Reduced iron, flowing down, comes into contact with free carbon and at such temperatures becomes highly saturated with it. The carbon content in cast iron exceeds 1.7%, but it is impossible to knock it out of cast iron. Therefore, the cast iron obtained from the blast furnace is immediately taken away liquid for the first processing into ordinary structural steel or slabs, so as not to waste money and resources on its remelting, and the blast furnace, as a rule (large and extra-large blast furnaces - exclusively), operates as part of a metallurgical plant .

Blast furnace design

The design of a blast furnace as a structure is shown in Fig:

The entire blast furnace is assembled in a steel case with a wall thickness of 40 mm. The bottom (under) of the cylindrical furnace is walled up in the heat-resistant stump of the blast furnace (base, head, top of the underground foundation). The lining of the hearth reaches a thickness of 1.3-1.8 m and is heterogeneous: the axial zone of the flange is lined with high-alumina brick, which conducts heat poorly, and the sides are lined with graphite materials, which have a fairly high thermal conductivity. This is necessary, since the thermochemistry of the melt in the furnace has not yet “calmed down” and some excess heat is released there against losses due to cooling. If it is not moved to the side, onto a heat-resistant stump, the structure of the blast furnace will require another repair of a higher level (see below).

The part of the blast furnace that expands upward - the shoulders - is lined with already graphite blocks with a thickness of approx. 800 mm; The fireclay lining of the shaft is of the same thickness. Fireclay, like the lining of a hearth with shoulders, is not wetted by molten slag, but is closer to the latter in chemical composition. That is, during operation, the blast furnace is minimally overgrown with soot and holds the internal profile better, which simplifies and reduces the cost of regular repairs.

The furnace and shoulders work in the most difficult conditions, excess weight loads are dangerous for them, so the blast furnace shaft rests with its shoulders (ring-shaped extension) on a strong steel ring - the marator - resting on steel columns, walled up in a stump. Thus, the weight loads of the hearth with shoulders and the shaft are transferred to the base of the blast furnace separately. Hot air from the cowpers is blown into the blast furnace from a ring-shaped tubular collector with thermal insulation through special devices - tuyeres, see below. There are from 4 to 36 tuyeres in a blast furnace (in giant blast furnaces for 8,000-10,000 tons of charge and 5-6 thousand tons of cast iron per day).

Repair ranks

The current state of the blast furnace is determined by the chemical composition of the cast iron and slag. If the content of impurities reaches the limit, repair of a 1st category blast furnace is prescribed. Melts are released from the forge, the cowpers are jammed (see below) and the blast furnace is left at low pressure, with a temperature inside the forge of 600-800 degrees. Level 1 repairs include visual inspection, mechanical inspection, furnace profile measurements, and lining sampling for chemical analysis. Once upon a time, a blast furnace was inspected at low breaths by people in special protective suits with self-contained breathing devices; now this is done remotely. After repairing the 1st category, the blast furnace can be restarted without ignition.

The result of the 1st category repair most often (unless bad ore, flux and/or defective coke was missed) is a 2nd category repair, during which the lining is corrected. Its partial or complete re-laying, straightening or replacement of the top apparatus is carried out in the order of repair of the 3rd category. As a rule, it is timed to coincide with the technical reconstruction of the enterprise, because requires a complete stop, cooling the oven, and then rebooting it, igniting it and restarting it.

Systems and equipment

The design of a modern blast furnace includes dozens of auxiliary systems controlled by powerful computers. Today's steelworkers still wear hard hats and sunglasses, but they sit in air-conditioned cubicles at consoles with displays. However, the operating principles of the basic systems and devices that ensure the operation of a blast furnace remain the same.

Cowpers

The Cowper air heater (see figure) is a cyclic device. First, the regenerator nozzle, made of heat-intensive, heat-resistant material, is heated by the burning blast furnace gases. When the nozzle temperature reaches approx. 1200 degrees, the cowper switches to blast: the outside air is driven through it into the blast furnace in a countercurrent manner. The nozzle has cooled down to 800-900 degrees - the cowper is switched again but warmed up.

Since the blast furnace must be blown continuously, there must be at least 2 cowpers, but at least 3 of them are built, with a reserve for accidents and repairs. For large, extra-large and giant blast furnaces, cowper batteries of 4-6 sections are built.

Top apparatus

This is the most critical part of the blast furnace, especially in light of current environmental requirements. The structure of the blast furnace blast furnace is shown in Fig. on right; it consists of 3 coordinated gas valves. Its work cycle is as follows:

1. initial state – the upper cone is raised, blocking the exit into the atmosphere. The windows at the bottom of the rotating funnel are located on a horizontal partition and are blocked. The lower cone is lowered, allowing blast furnace gases to escape to the smoke exhauster and then into the cyclone;
2. the skip (see below) tips over and dumps the flue of materials into the receiving funnel;
3. a rotating funnel with windows in the bottom turns and passes the load onto a small cone;
4. the rotating funnel returns to its original state (the windows are closed with a partition);
5. a large cone rises, cutting off blast furnace gases;
6. the small cone lowers, allowing the load to pass into the intercone space;
7. a small cone rises, further blocking the exit to the atmosphere;
8. a large cone lowers to its original state, releasing the charge into the blast furnace shaft.

Thus, the materials in the furnace shaft are laid out in layers, convex at the bottom and concave at the top. This is absolutely necessary for the normal operation of the blast furnace, so the lower (large) valve is always reverse-conical. The upper ones may be of a different design.

Skip

Skip, from English. - ladle, scoop, gaping mouth. Kolosha (from French) - a handful, a ladle, a ladle. By the way, this is where galoshes come from. Blast furnaces are supplied primarily with skip material lifts. The blast furnace skip (on the right in the figure) scoops up a bucket of material from the skip pit, is lifted by a special mechanism along an inclined trestle (on the left in the figure), overturns into the blast furnace apparatus and returns back.

Tuyeres and tapholes

The design of a blast furnace tuyere is shown on the left in the figure, with a cast iron taphole in the center and a slag taphole on the right:

The tuyere nozzle is aimed at the very heart of the blast furnace process; through it it is convenient to visually control its progress, for which purpose a peephole with heat-resistant glass is installed on the air duct of the tuyere. The air pressure at the tuyere nozzle exit is 2-2.5 ati (2.1-2.625 MPa above atmospheric pressure). After releasing the melt, the tapholes are sealed with a lump of heat-resistant clay. Previously, they were shot at with a plastic clay ball from a special cannon for this purpose. Nowadays, the tapholes are sealed with a remotely controlled electric gun (the name is a tribute to tradition), which approaches the taphole closely. This greatly reduced the accident rate, injury risk and environmental friendliness of the blast furnace process.

And with your own hands?

Ferrous metallurgy is a highly profitable business. Did you know that the “rise” from it is several times higher than from gold mining? Do you think there is little oil and gas left? No, at the current rate of consumption and complete disregard for the environment, they will last for another 120-150 years. But there is only about 30 years of iron ore left. So, is it possible to establish metallurgical production in your own backyard?

Commodity for profit - in no way. First, forget about permissions. Ferrous metallurgy is perhaps the main threat to the environment. Individual entrepreneurs and individuals are not licensed for it anywhere, in any way, and for any bribes, and the penalties for violations are severe.

The second is raw materials. There are only 2 deposits of rich ore that can be immediately loaded into a blast furnace in the world: in Australia and Brazil. Industrial reserves of bog ore were exhausted in ancient times, and it takes many thousands of years to restore them. Sinter and pellets are not and will not be widely sold.

In general, private ferrous metallurgy is absolutely unrealistic for the market now. Try printing better with a 3D printer. This is a promising business; over time, 3D printing, if it does not completely replace metallurgy, will certainly displace it into small niches where it is impossible to do without metal. For the environment, this will be equivalent to reducing hydrocarbon fuel consumption by at least 7-9 times.