A blast furnace, or blast furnace, is a complex complex technological equipment, used in the metallurgical industry to produce ferrous metal. In fact, this large building, which includes not only the oven, but also auxiliary components.
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What is a blast furnace for? It has one goal - to obtain cast iron, which will be used in metallurgy for the manufacture of machines, equipment and other metal-containing products.
Operating principle
The operating principle of a blast furnace is as follows: ore charge with coke and limestone flux is loaded into the receiving chamber. In the lower part, periodic release of cast iron/ferroalloys and separately molten slag is carried out. Since the level of material in the blast furnace decreases during release, simultaneous loading of new batches of charge is required.
The operating process is constant, combustion is maintained with a controlled supply of oxygen, which ensures greater efficiency.
The design of the blast furnace ensures a continuous process of ore processing, the service life of the blast furnace is 100 years, major repairs are carried out every 3-12 years.
Photo of a blast furnace
Who invented it?
The modern blast furnace was invented by J.B. Neilson, who was the first to heat the air supplied to the blast furnace, which happened in 1829, and in 1857 E.A. Cowper introduced special regenerative air heaters into use.
This made it possible to significantly reduce coke consumption by more than a third and increase the efficiency of the furnace. Before this, the first blast furnaces were actually cheese-blowing furnaces, that is, unenriched and unheated air was blown into them.
The use of cowpers, that is, regenerative air heaters, made it possible not only to increase the efficiency of the blast furnace, but also to reduce or completely eliminate contamination, which was observed in case of technology violations. We can safely say that this invention made it possible to bring the process to perfection. Modern blast furnaces operate precisely on this principle, although their control today is automated and provides greater safety.
Domain process
Modern furnaces for melting cast iron provide approximately 80% of the total amount of cast iron; from the casting sites it is immediately supplied to electric smelting or open-hearth shops, where ferrous metal is converted into steel with the required qualities.
Pig iron is produced from cast iron, which is then sent to manufacturers for casting in cupola furnaces. To drain slag and cast iron, special holes called tapholes are used. However, in modern furnaces, not separate, but one common tap hole is used, divided by a special heat-resistant plate into channels for supplying cast iron and slag.
How does a blast furnace work?
The blast furnace process is entirely dependent on the excess carbon in the furnace cavity; it consists of thermochemical reactions occurring inside when all components are loaded and heated.
The temperature in a blast furnace can be 200-250°C directly under the top and up to 1850-2000°C in the active zone - steam.
When hot air is supplied to the furnace and coke is ignited, the temperature in the blast furnace rises, the process of decomposition of the flux begins, as a result of which the carbon dioxide content increases.
When the column of material in the charge decreases, iron monoxide is reduced; in the lower part of the column, pure iron is reduced from FeO, flowing into the furnace.
As the iron drains, it actively contacts carbon dioxide, saturating the metal and giving it the required properties. General content carbon in iron can range from 1.7%.
Blast furnace diagrams
Sectional diagrams of a blast furnace (different options):
Blast furnace device
The design of a blast furnace is very complex; it is a large complex that includes the following elements: 
- hot blast zone;
- melting zone (this includes the hearth and shoulders);
- steam, that is, the zone where FeO reduction occurs;
- a mine where Fe2O3 reduction occurs;
- fire pit with pre-heating of the material;
- blast furnace gas;
- the area where the material column is located;
- outlets for slag and liquid iron;
- collection for waste gases.
The height of a blast furnace can reach 40 m, weight – up to 35,000 tons, the capacity of the working area depends on the parameters of the complex.
The exact values depend on the load of the enterprise and its purpose, requirements for the volume of metal produced and other parameters.
A more detailed version of the device:
Blast furnace repair grades
To maintain the working condition of the blast furnace, major repairs are carried out regularly (every 3-15 years). It is divided into three types:
- The first category includes work on the production of melting products and inspection of equipment involved in the technological process.
- The second category is a complete replacement of equipment elements subject to medium repair work.
- The third category requires a complete replacement of the device, after which a new filling of raw materials is carried out with straightening of the tops.
Systems and equipment
A blast furnace is not only an installation for producing cast iron, but also numerous auxiliary components. This is a charge and coke supply system, removal of slag, molten iron and gases, an automatic control system, cowpers and much more.
The operating principles of the furnace remain the same as centuries ago, but modern computer systems and production automation have made the blast furnace more efficient and safer.
Cowpers
The modern design of a blast furnace involves the use of cowper to heat the supplied air. This is a cyclic installation made of heat-resistant material, which heats the nozzle up to 1200°C.
The cowper switches on the nozzle to 800-900°C when cooling, which ensures continuity of the process, reduces coke consumption and increases the overall efficiency of the design.
Previously, such a device was not used, but starting from the 19th century. it is necessarily part of the blast furnace.
The number of cowper batteries depends on the size of the complex, but usually there are at least three, which is done with the expectation of a possible accident and maintaining operability.
Top apparatus
The blast furnace apparatus - this part is the most responsible and important, including three gas seals operating according to an agreed scheme. 
The operating cycle of this node looks like this:
- in the initial position the cone is raised, it blocks the exit, the lower cone is lowered;
- the skip loads the mixture into the furnace;
- the rotating funnel turns and passes the raw material through the windows onto a small cone;
- the funnel returns to its original position, closing the windows;
- the small cone is lowered, the load passes into the intercone space, after which the cone rises;
- the large cone takes its original position, releasing the charge into the cavity of the blast furnace for processing.
Skip
Skips are special charge lifters. With the help of such galosh lifts, raw materials are captured from the skip pit and conveyed upward along an inclined trestle.
Then the galoshes are tipped over, feeding the charge into the loading area, and returned down for a new portion. Today this process is carried out automatically; special computerized units are used for control.
Tuyeres and tapholes
The nozzle of the furnace lance is directed into its cavity, through which you can observe the progress of the smelting process. To do this, peepers with heat-resistant glass are mounted through special air ducts. At the cut, the pressure can reach 2.1-2.625 MPa.
Tapholes are used to drain cast iron and slag; immediately after release, they are tightly sealed with special clay. Previously, guns were used that were built with a plastic clay core; today, remote-controlled guns are used that can approach the structure closely. This solution made it possible to reduce the trauma and accident rate of the process and make it more reliable.
How to make a blast furnace with your own hands?
Nuances
Cast iron production is a highly profitable business, but it is impossible to establish the production of ferrous metal without serious financial investments. Do-it-yourself blast furnace in “makeshift conditions” is simply not feasible, which is associated with many features:
- the extremely high cost of a blast furnace (only large plants can afford such expenses);
- the complexity of the design, despite the fact that a drawing of a blast furnace can be found in the public domain (above the diagram), it will not be possible to assemble a full-fledged unit for the production of cast iron;
- individuals and individual entrepreneurs cannot engage in the production of cast iron, simply no one will issue a license for this;
- deposits of raw materials for ferrous metallurgy are almost exhausted; there are no pellets or sinter on free sale.
But at home, you can assemble an imitation furnace (mini-blast furnace), with which you can melt metal.
But these works require maximum attention and are highly not recommended in the absence of experience. Why might it be necessary to make such a structure? Most often, this is heating for a greenhouse or cottage with the most efficiently used fuel.
Tools and materials
To make a structure at home, you need to prepare:
- metal barrel (can be replaced with a pipe with a larger diameter);
- two pieces of round pipe with a smaller diameter;
- channel section;
- sheet steel;
- level, hacksaw, tape measure, hammer;
- inverter, set of electrodes;
- bricks, clay mortar (necessary for the foundation of the structure).
All work should be carried out only outside, since the process is quite dirty and requires free space.
Step by step instructions
- The top of the prepared barrel-shaped workpiece is cut off (it should be left, as it will be needed later).
- A circle with a diameter smaller than the diameter of the barrel is cut out of steel, and a hole is made in it for the pipe.
- The pipe is carefully welded to the circle, and sections of channel are welded at the bottom, which will press down the fuel during operation of the furnace.
- The furnace lid is made from the previously cut bottom of the barrel, in which a hole is made for a hatch with a door. It is also necessary to make a door through which the remaining ash will be removed.
- The stove must be installed on a foundation, as it gets very hot during operation. To do this, first a concrete slab is installed, then several rows of brick are laid out, forming a recess in the center.
- To remove combustion products, a chimney pipe is installed; the diameter of the straight part will be larger than the diameter of the stove body (required for better gas removal).
- The reflector is not a mandatory design element, but its use can increase the efficiency of the furnace.
Design Features
The features of such a self-made stove are:
- efficiency level is good;
- it is possible to work offline for up to 20 hours;
- In the furnace, there is not active combustion, but smoldering with constant heat release.
The main difference between a “household” blast furnace will be the restriction of air access to the combustion chamber, that is, smoldering of wood or coal will occur at a low oxygen level. An industrial blast furnace works on a similar principle, but a household blast furnace is used only for heating; metal cannot be melted in it, although the temperature inside the chamber will be sufficient.
Cost using the example of efficiency factor No. 7
Manufacturing blast furnaces is a resource-intensive and expensive process that cannot be put into production. Since blast furnaces are used exclusively in industry, their design and assembly are carried out for a specific metallurgical complex, which includes many objects and components of the internal infrastructure. This situation is observed not only in the Russian Federation, but also in other countries of the world that have their own metallurgy facilities.
The cost of manufacturing and installing a blast furnace is quite high, which is due to the complexity of the work. An example is the large domain complex No. 7 called “Rossiyanka”, installed in 2011. Its cost was 43 billion rubles; the best engineers from Russia and foreign countries were involved in production. 
The complex includes the following units:
- ore receiving device;
- inlet stations of the bunker overpass and the central hub;
- bunker overpass;
- compressor station (installed at the foundry yard);
- installation for injection of pulverized coal fuel;
- utilization thermal power plant;
- control center and administrative building;
- foundry yard;
- blast furnace;
- air heating blocks;
- pumping station.
Complex performance:
The new complex ensures the production of more than 9,450 tons of cast iron per day, the useful volume of the furnace is 490 cubic meters, and the working volume is 3,650 cubic meters. The design of the blast furnace ensures waste-free and environmentally friendly production of cast iron; blast furnace gas for thermal power plants and slag used in road construction are obtained as by-products.
Conclusion
A blast furnace is a metallurgical equipment that makes it possible to obtain cast iron by processing iron ore on an industrial scale.
The peculiarity of the technology ensures not only high quality of the resulting products, but also economical coke consumption. During the production process, it is possible to control the melting conditions using computerized systems and obtain a product with strictly specified properties.
←Previous article Next article →Topic 1. General scheme of blast furnace process 1
1.1. Goals and objectives of domain process 1
1.2. Blast furnace 2 design
1.3. General operating diagram of a blast furnace 5
1.3.1. Charge materials 5
1.3.1.1. Iron ore materials 6
1.3.1.2. Fluxes 6
1.3.1.3. Solid fuel 8
1.3.2. Combined blast 9
1.3.3. Blast furnace products 10
1.3.3.1. Cast iron 10
1.3.3.2. Slag 10
1.3.3.3. Top gas 11
1.3.4. Conclusions 12
1.4. Blast furnace performance indicators 13
1.5. Blast furnace cast iron 14
1.5.1. Classification of cast iron by purpose. 14
1.5.2. Chemical composition pig iron, foundry and special cast iron. 15
1.5.2.1. Pig iron 15
1.5.2.2. Cast irons 17
1.5.2.3. Special cast irons. 19
General diagram of the blast furnace process
Goals and objectives of the domain process
In order to have a complete understanding of the blast furnace process and blast furnace production in general, it is necessary to first become familiar with the general scheme. This will then allow us to consider individual elements, having an idea of their place in the overall complex of various processes occurring in a blast furnace, and the overall technological scheme iron production.
The goal of blast furnace production is to produce high-quality cast iron (of a given composition with a low content of impurities) with the lowest fuel and energy costs and maximum (specified) productivity. The requirement for minimum fuel and energy reserves will become more obvious when considering the general scheme of blast furnace production, production volumes, raw material costs for the production of 1 ton of products and prices for raw materials.
The main product of blast furnace smelting is pig iron. It should be noted that there are also blast furnace smelting technologies, the main product of which is slag. For example, the product of bauxite smelting, slag, is used to produce high-quality concrete.
Blast furnace design
The main unit for extracting iron from iron ores is the blast furnace.
According to the principle of operation, a blast furnace belongs to shaft-type smelting furnaces, furnaces whose working space is elongated vertically, and the horizontal section is a circle. The flow of processes in shaft furnaces is based on the counterflow of materials and hot gases.
The outline of the furnace working space in a vertical axial section is called a profile. The furnace profile, depending on their geometric shape and technological purpose, is divided into five parts (Fig. 1.1 -1).
The upper part of the furnace, which has a cylindrical shape, is called the top (K). The blast furnace top is equipped with a top device. The top device is a complex of metal structures for various purposes and includes devices for feeding and loading materials into the furnace, gas outlets for uniform removal of gases from the furnace (at least 4), devices for the production of repair and installation work. The charging apparatus of the blast furnace loading device is used to load and distribute materials in the blast furnace. At the same time, it hermetically closes the oven and isolates its interior from the atmosphere.
ABOUT
Rice. 1.1‑1. Blast furnace
The lower part of the furnace, which is shaped like a cylinder, is called the forge (G). The hearth, in turn, is divided into an upper and lower hearth or a tuyere zone and a metal receiver, respectively. In the upper part of the hearth there is a large number (30...40) of tuyere holes (F) evenly distributed around the circumference, through which blast is supplied from the ring air duct 5 to the furnace through special devices - tuyeres. The bottom of the metal receiver is called the flange . The part of the metal receiver below the cast iron tap hole is called the sump or “dead” layer. This zone, filled with liquid metal, protects the bream from high-temperature processes occurring in the forge. The lower hearth is equipped with cast iron and slag tapholes - devices for releasing cast iron and slag. Tapholes for tapping iron are made in the wall of the hearth above the sump in the form of rectangular channels of dimensions 250...300 x 450...500 mm, in which holes are drilled in the carbon lining of the metal receiver with a diameter of 50...60 mm. A hole for processing the upper slag - a slag tap hole - is made in the furnace at a mark determined when calculating the furnace profile. The diameter of the slag taphole is usually 50...65 mm, depending on the diameter of the furnace hearth.
This configuration of the working space has developed in the process of improving the technological unit, and creates the most favorable conditions for the occurrence of aerodynamic and physical-chemical processes.
The outside of the blast furnace is enclosed in a metal casing consisting of a number of cylindrical and conical belts. The metal structures of the furnace rest on a foundation, which serves to uniformly transfer the pressure of the furnace with raw materials loaded into it to the ground.
The interior of the furnace is lined with refractory bricks, the safety of which is ensured by a cooling system for several years of operation. Refractory masonry serves to reduce heat losses and protect the furnace casing from various influences: temperature stress, gas pressure, charge and liquid smelting products, chemical exposure, abrasive effects of descending charge materials and rising gas flow carrying large number dust, etc.
The dimensions of the components of a blast furnace determine its working space, its so-called useful volume. The useful volume is equal to the volume of the furnace from the axis of the cast iron tap hole to the filling device in its extreme lowered position. The distance from this level to the axis of the cast iron tap hole is called the usable height of the furnace. These furnace profile parameters: usable furnace volume and usable height furnace, as well as the ratio of the diameters of the flue, steam and hearth determine the configuration of the furnace profile and are its characteristics.
Dimensions of an average blast furnace with a volume of 2002 m 3.
The blast furnace is installed on a foundation (reinforced concrete mass, designed for enormous loads, heat-resistant concrete) up to 10 m high. Considering the dimensions of the top device - up to 15...18 m, one can imagine that the blast furnace is a very serious structure with a height of about 60 m.
The largest blast furnace is blast furnace No. 5 of CherMK. Its volume is 5580 m 3 , useful height is 33.5 m, steam diameter is 16 m.
A modern blast furnace is a complex technological complex that includes the blast furnace itself, as well as main and auxiliary equipment, the purpose of which is determined by the technological tasks of blast furnace production.
A blast furnace is a shaft furnace for smelting pig iron from iron ore.
The performance of the furnace depends on its size. The most powerful blast furnaces have a volume of 2000-5000 m 3. Their height is 32-37 meters, diameter - 11-16 meters.
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 rasp are shoulders that serve to overheat and transfer the melt and slag from the rasp 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 the blast furnace gas strongly depends on the enrichment of the blast with oxygen and on the supply natural gas: 24-32% CO, 10-18% CO2, 43-59% N2, 0.2-0.6% CH4, 1.0-13.0% H2. 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. Introduction to appearance Cowper can be obtained from rice. 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, 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, exit through the smoke valve to 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 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 productivity 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.
Despite the large number of synthetic and polymer materials that have become widespread in modern industry and everyday life, the use of iron alloys is not inferior to the palm. The most critical parts, mechanisms, tools and other components are made of various grades and types of metal that have the necessary properties to solve the assigned tasks. Active searches for a complete replacement for metal alloys have not yet been successful, since the difference in the properties of the materials is too great. The development of metallurgy does not stop; new technologies and methods for producing high-strength and hard materials are emerging. At the same time, the old, traditional methods of metal smelting, worked out over centuries and studied in detail by many generations of metallurgists, have not been forgotten. Let's consider the design of a blast furnace - one of the oldest designs for the production of foundry cast iron, which is actively used to this day.
Story
The need to improve iron smelting technology arose a long time ago. Low-melting ores, located almost on the surface of the earth, did not have large volumes and were quickly consumed. The existing smelting technique was untenable and did not allow working with refractory ores. There was a need to improve existing equipment and technology. First of all, it was necessary to increase the size of the furnaces and significantly strengthen the pressurization mode.
The first mentions of structures similar to blast furnaces were found in China. They date back to the 4th century. In Europe, the appearance of blast furnaces dates back to the 15th century; before that, so-called cheese-blowing furnaces were used. The immediate predecessor of the blast furnace was the Catalan forge, which used technological techniques close to the blast furnace production method. His distinctive features were:
- Continuous charge supply process;
- Use of powerful hydraulically driven air supply units.
14th century blast furnace
The volume of the Catalan forge was only 1 m³, which did not allow obtaining large volumes of products. In the 13th century, the Stutofen, an enlarged and improved version of the Catalan bugle, was created in the European principality of Styria. It was about 3.5 m in height and had two technological openings - the lower one for air supply, the upper one for extracting kritsa (raw iron). Stukofen produced three types of semi-finished iron products:
- Steel;
- Malleable iron;
- Cast iron.
The difference between them was in the carbon content - most of it was in cast iron (more than 1.7%), in steel it was less than 1.7%, and in malleable iron the content was 0.04%. High level carbon content was assessed negatively, since cast iron cannot be forged, welded, and it is difficult to make weapons from it.
This is important! Initially, cast iron was classified as industrial waste because it could not be forged. Attitudes towards it changed only after the start of secondary smelting, which began to be done due to a shortage of fusible ores. Convertible iron obtained from cast iron was of higher quality, which served as an incentive to expand the conversion process.
Further expansion of capacity and improvement of technology gave rise to the emergence of the blaufen, which was already about 5–6 m high, capable of smelting cast iron and iron simultaneously. It was already practically a blast furnace, albeit a somewhat smaller, simplified design. A two-stage process was established, when the first stage was the production of cast iron, and the second was the smelting of iron from it under increased pressure.
The appearance of the first blast furnaces in Europe dates back to the end of the 15th century. Almost immediately, similar designs appeared in England, and in the USA the first blast furnaces were created much later - in 1619. The first blast furnace in Russia was built by A. A. Vinius at his manufactory in Tula. The process consisted of the following steps:
Iron was removed from the bottom of the forge and forged, removing liquid slag and compacting the pigs. With this method, the yield of finished iron was about 92% of the original weight of cast iron, and its quality significantly exceeded that of a critical product.
The fuel crisis became a serious problem. Charcoal was used to smelt the ore, which led to the destruction of forests. The problem grew to such proportions that metal was imported into England from Europe, and later from Russia, for 2 centuries. It turned out that the forest grows slower than it burns. Attempts to use coal have shown that it contains a large amount of sulfur, which significantly reduces the quality of the metal. Many experiments were carried out that were not successful.
This is interesting! The solution was found only in 1735 by the English metallurgist A. Derby II, who found a way to convert coal into coke. Since that time, the fuel problem was overcome, and the process received a new impetus for development.
The next revolutionary discovery was the heating of the air used for supercharging. It made it possible to significantly reduce coal consumption by up to 36%. There are special requirements for the grade and quality of metal in terms of manganese, silicon, and phosphorus content. The technology and design of furnaces were improved and supplemented, little by little coming to a modern look.
Design and principle of operation
The blast furnace is a vertical shaft-type structure, resembling a cone, expanding downwards. The height of the furnace can reach 70 m, the working volume is 2700 m³. The daily productivity of a blast furnace of this size reaches 5000 tons of cast iron. The main feature of the operation of blast furnaces is the continuity of the process. Work is carried out around the clock and does not stop until the moment overhaul or dismantling the furnace, which can take a period of 3 to 15 years. If work is stopped and the stove is left without fuel, the so-called “contamination” will occur, the solidification of the materials inside. It is impossible to restart a furnace that has been stopped in an abnormal way. This specificity forces specialists to constantly worry about maintaining the operating mode of the installation, but also allows them to obtain maximum productivity.
Materials required to implement the blast furnace process:
- Coal coke (fuel);
- Iron ore (sinter, pellets);
- Flux (sand, limestone and others necessary materials, organizing the rise of slag upwards).
There are very few deposits of iron ore, the quality of which allows it to be used in the smelting process without pre-treatment, in the world. Therefore, in most cases, specially prepared raw materials are used - agglomerate or pellets, which are lumps of enriched ore material. They have the form of round granules (pellets) or irregularly shaped particles (agglomerate) 2–5 cm in size.
Blast furnace design diagram
The design of the furnace is a massive vertical tower, lined with fireclay (refractory) bricks on the inside. It is installed on a solid foundation, raised above the zero level to a certain height. The upper, heat-resistant part of the base is called a stump. The top of the foundation has a horizontal platform - a platform, which takes on all dynamic and temperature loads, and therefore is water-cooled. The oven is protected from the outside by a durable metal casing, the thickness of which is 4–6 cm.
The interior of the furnace is a cone-shaped tower consisting of several sections:
- Mine (or ottoman). The cone-shaped part of the tower, gradually expanding downwards.
- Rasp. The widest (middle) part of the tower, in which the processes of slag formation and melting of raw materials begin. The temperature in this area ranges from 1400°.
- Shoulders. A relatively short section in the form of a cone, tapering at the bottom. This is where the final melting of the metal occurs. The temperature in this area is 1600–1900°.
- Horn. The lower part of the tower where the air supply holes (tuyeres) are located. The cast iron and slag tapholes (holes for releasing cast iron and slag) are also located there. The bottom of the forge is upper part foundation (flake).
Using a filling apparatus, the mixture and flux are fed into the furnace. As the cast iron and slag melt and are removed, the materials fall down, and new portions take their place. Gases formed during chemical processes are removed through pipelines located in the top part of the tower. They have a high temperature and are used to heat the fresh stream entering the blast furnace for pressurization. Heating is carried out in cowpers - installations that take in fresh air, heat in heat exchange devices and supply hot air to the furnace.
Blast furnace diagrams
The design of blast furnaces and the smelting process are practically the same in all countries and have no fundamental differences. But there are different schemes load-bearing structures with own characteristics and specificity.
Features of schemes of different furnace designs
- Scottish scheme (a). The fire pit is mounted on special supporting structures called main columns. As a rule, their number corresponds to the number of tuyeres. This is done for ease of operation and maintenance of the air supply holes. If you use other placement options, the tuyeres will have to be placed unevenly, which will affect the pressurization mode and the overall quality of the metal. The disadvantage of this scheme is the possibility of transmitting vibration from the loading devices to the furnace structure. In addition, there are difficulties in carrying out urgent repairs or reconstruction. At the same time, such a stove is cheaper and has less weight, which reduces construction time.
- German (b). The fire pit is installed on its own supports (columns). This improves the quality of forge service, but creates the possibility of excessive stress in the shoulder area due to loads from the weight of the tower. Strengthening the structure creates problems with access to the shoulders, which affects the mode and quality of work.
- Combined (c). In this version, the stress on the shoulders is reduced, but this is done at the expense of more complex maintenance of the hearth section. At the same time, this scheme ensures high strength of the casing, which continues to function effectively even in the presence of noticeable cracks. This feature of the circuit is appreciated by specialists working on raw materials with a high percentage of zinc. It creates excessive pressure on the tower walls, increasing the frequency of major repairs.
- Japanese (g). Load-bearing structures are 6 columns equipped with brackets. Despite the increased load-bearing capacity, there are noticeable disadvantages - load imbalance increases the weight of the supports, the diameter of the air duct is increased compared to other design options, which contributes to an increase in loads on the tuyere equipment. An additional disadvantage is the difficulty of organizing floor transport in the forge area.
- American (d). The scheme is distinguished by the presence of 4 load-bearing columns. The advantages are reduced vibration that occurs during operation of the loading mechanisms, as well as significantly improved access to the taphole and tuyere area.
These schemes were developed and improved under different conditions, which was the reason for the appearance of some differences in the design. However, all of them are quite successfully operated and produce high quality products.
DIY blast furnace
Making a blast furnace yourself at first glance seems like a ridiculous idea. It is unlikely that it would occur to anyone to organize a miniature metallurgical workshop on their site. There are several reasons for this:
- Lack of raw materials. There are only 2 deposits with rich ore left in the world - in Brazil and in Australia. It is almost impossible to buy pellets or agglomerate - they are not available for free sale, all supplies go through commodity exchanges and amount to thousands of tons.
- It is impossible to obtain permission to build a miniature metallurgical production facility. Ferrous metallurgy is a source of significant environmental problems, so no official would dare to give permission for such an undertaking.
- Neighbors will flood all authorities with complaints, since the constant smoke and fumes will make their life unbearable.
Only the most basic reasons are indicated; in reality there are many more. The use of a blast furnace for metal production in a private home is excluded.
However, if you take into account the specifics of the blast furnace, in particular the continuous combustion mode, then you can use it to heat rooms. This effective solution for supplying heat to both residential and office premises- garage, greenhouses, auxiliary buildings, etc. Unlike a conventional solid fuel furnace, where it is necessary to frequently load fuel and the efficiency is quite low, a blast furnace ensures even smoldering of the material for 15–20 hours. This is achieved due to the limited supply of air, which does not allow the fuel to actively burn and extends the process over a long period.
You can make a blast furnace yourself
The oven is usually made from a metal barrel. Carefully cut out the bottom (it will be needed later), install the barrel on a pre-made foundation. The cut circle is reinforced with channel sections to add more weight - it will press down on the fuel, promoting compact placement and efficient smoldering. They cut a hole for the chimney, usually a pipe with a diameter of 10 cm is enough. Then you need to cut out a lid for the barrel from a sheet of metal, since the bottom is already used as a pressure for fuel. A circle of appropriate size is cut out and carefully welded to the barrel. It also makes a hole for the pipe. A hole is cut in the bottom of the barrel for the door through which fuel will be added. You can make an additional door underneath to remove ash.
The chimney is welded on top, the length of its straight part (up to the first elbow) should exceed the diameter of the barrel (ideally much larger). During operation, the stove gets very hot, so many people line it with bricks or create a heat-reflecting screen. The optimal operating mode is found experimentally. Measures must be followed fire safety, ideally, for such a stove it is necessary to allocate a separate room without flammable objects.
Video: the birth of steel
The blast furnace is one of the oldest and most proven designs. Its effectiveness has been tested by time, technological methods and techniques have been carefully studied and tested. The capabilities of the blast furnace are such that the operation of such devices will last for a very long time, designs and technologies will be improved.