Blast furnace process for producing cast iron
The blast furnace process is a countercurrent type. A column of charge materials is lowered towards the rising flow of hot gases formed during the combustion of coke at the tuyeres.
A gas stream containing CO, CO2, H2, N2, etc. is formed as a result of the combustion of coke carbon. In this case, a temperature of more than 2000 °C develops in the furnace slightly above the level of the tuyeres. Hot gases, rising, give off heat to the charge materials, cool to a temperature of 200 - 300 ° C and exit the furnace through the top. Hence the name of the gas - top gas.
The useful volume of the blast furnace is constantly filled with charge materials. The lowering of the charge occurs under the influence of its weight, and the condition for its movement is the release of space in the lower part of the blast furnace as a result of the combustion of coke and the melting of ore material and flux.
After loading into the furnace, the charge begins to heat up and as it is continuously lowered, the following processes sequentially develop:
- evaporation of charge moisture;
- reduction of iron oxides and some other elements;
- dissociation of carbonates.
Evaporation of charge moisture
The charge loaded into a blast furnace contains hygroscopic and sometimes hydrate moisture. Hygroscopic moisture easily evaporates and is removed at the top, since the temperature of the top gases is higher than the temperature of moisture evaporation.
H2Ozh → H2Sap.
Hydrate moisture is removed at temperatures above 400 °C, and the released water vapor interacts with carbon monoxide or carbon, enriching the gas stream with hydrogen.
H2Opar + CO = CO2 + H2,
H2Opar + C = CO + H2.
Reduction of iron oxides and some other elements
As a result of the interaction of iron oxides with carbon monoxide and solid carbon from coke, as well as hydrogen, iron is reduced. Reduction by gases is called indirect, and reduction by solid carbon is called direct. Indirect reduction reactions are accompanied by the release of heat and occur in the upper horizons of the furnace. Direct reduction reactions are accompanied by heat absorption and occur in the lower part of the blast furnace, where the temperature is higher.
The reduction of iron from ore occurs as the charge moves down in several stages, from the highest oxide to the lowest:
Fe2O3 → Fe3O4 → FeO → Fe
Up to temperatures of 700 – 900 °C, reduction is carried out with a gas reducing agent (CO) according to the reactions:
3Fe2O3 + CO = 2Fe3O4 + CO2,
Fe3O4 + CO = 2FeO + CO2,
FeO + CO = Fe + CO2.
As the charge descends to horizons with a temperature of 900–1200 °C, carbon dioxide (CO2) released during reduction begins to interact with fuel carbon according to the reaction:
CO2 + C = 2CO.
The recovery process changes significantly and follows the reaction:
FeO + C = Fe + CO.
Thus, the material loaded into the blast furnace begins to be reduced indirectly. As the charge sinks, the CO2 released as a result of reduction begins to interact with the carbon of solid fuel and the process of indirect or indirect reduction turns into direct reduction.
Part of the iron oxides of the ore is reduced by hydrogen formed in the blast furnace as a result of the decomposition reaction of water vapor:
H2O + C = H2 + CO
The reduction of iron oxides with hydrogen occurs in the same way as with carbon monoxide (CO), in stages from higher to lower
3Fe2O3 + H2 = 2Fe3O4 + H2O;
Fe3O4 + H2 = 3FeO + H2O;
FeO + H2 = Fe + H2O.
Hydrogen, as a reducing reagent, is characterized by a higher degree of utilization. Due to the smaller size of the molecule compared to the CO molecule, hydrogen penetrates into small pores and cracks of the reduced piece of ore material, into which CO molecules cannot penetrate. Therefore, despite the relatively low hydrogen content in the blast furnace gas, it produces significant reduction work.
In addition to iron, other elements included in the charge are also reduced in the blast furnace.
Manganese
Manganese is found in all iron ores in greater or lesser quantities. In accordance with the principle of sequential transformations, manganese oxides are reduced sequentially from higher to lower:
MnO2 → Mn2O3 → Mn3O4 → MnO → Mn.
Higher manganese oxides in a blast furnace are completely reduced to MnO indirectly by interacting with CO. MnO oxide is reduced only directly, and then partially by the reaction:
MnO + C = Mn + CO.
By interacting with solid carbon, MnO forms carbide Mn3C, which dissolves in iron, increasing the manganese and carbon content in cast iron. The other part of MnO goes into slag.
Silicon
Silicon enters the blast furnace with a charge in the form of SiO2. Its reduction, like that of manganese, is carried out partially at high temperatures with solid carbon:
Source: https://MetalSpace.ru/education-career/osnovy-metallurgii/domennaya-pech/394-domennyj-protsess-polucheniya-chuguna.html
Blast furnace
The blast furnace, after numerous transformations and modernizations, at the present stage is a design for producing cast iron as the main ingredient of the steel industry.
The design of the blast furnace allows for continuous smelting until major repairs, which are carried out once every 3-12 years. Stopping the process leads to the formation of a continuous mass due to sintering of the components (sintering). To remove it, partial disassembly of the unit is necessary.
Blast furnace
The working volume of a modern blast furnace reaches 5500 m3 at a height of 40 m. It is capable of producing about 6000 tons of cast iron per melt. And the special equipment servicing the systems located around it occupies several tens of hectares of land.
The blast furnace is used to produce cast iron, which is subsequently smelted to produce various grades of cast iron or sent for recovery to produce structural steels.
Modern blast furnaceMedieval blast furnace
The great need for metal coincided with the stage of electrification and mechanization of production. In this regard, the successes of ferrous metallurgy are associated with the beginning of the use of electric drives and electrical automatic control systems at all stages of the production process.
Blast furnace design
At the dawn of ferrous metallurgy, the smelting of bog ore was carried out in a blast furnace - this is a mini blast furnace, into which air came from bellows. And the enrichment of iron with carbon came from charcoal. The volumes of metal smelted in this way were small and varied in frequency.
Blast furnace design
The structure of a blast furnace resembles a mine. Its diameter is three times less than its height. The high-rise structure is installed on a concrete foundation 4 m thick. The need for such a massive foundation arises due to the mass of the blast furnace, which is more than 30,000 tons.
Columns and a solid (monolithic) cylinder, which are made of heat-resistant concrete, are fixed to the foundation slab. The internal space of the structure is lined with fireproof materials, and the upper part is lined with fireclay. In the area of the shoulders, where the temperature reaches 2000°C, graphite materials are used, and under the cast iron bath there is an alumina lining. A furnace furnace is also mounted on the foundation.
The lower part of the blast furnace, where the temperature is maximum, is equipped with water-cooled refrigerators. To hold the assembled refractory structure, the outside of the blast furnace is enclosed in a metal jacket 40 mm thick.
The process of reducing iron occurs from ore in a limestone flux environment at high temperature. The melting point is reached by burning coke. To maintain combustion, air is needed, so the blast furnace has 4 - 36 tuyeres or tapholes.
The large internal volume requires large volumes of air, which are supplied by turbine blowers. In order not to reduce the temperature, the air is heated before supply.
Schematically, a blast furnace looks like this.
Layout of equipment for blast furnace production
Casting production design composition:
- charge (ore and limestone);
- coking coal;
- loading lift;
- a fire pit that prevents gases from entering the blast furnace into the atmosphere;
- layer of loaded coke;
- charge layer;
- air blowers;
- discharged slag;
- cast iron;
- container for receiving slag;
- receiving ladle for melt;
- a Cyclone type installation that cleans blast furnace gas from dust;
- cowpers, gas regenerators;
- smoke exhaust pipe;
- air supply to cowpers;
- coal powder;
- coke sintering furnace;
- coke storage tank;
- removal of high temperature blast furnace gas.
The blast furnace is served by auxiliary systems.
The flue is the shutter of the blast furnace. The environmental situation around production depends on its proper operation.
Fire pit device
Furnace structure:
- receiving funnel;
- small cone funnel, rotating;
- small cone;
- interconal space;
- large cone;
- skip.
The operating principle of the fire pit is as follows:
- The large cone is lowered and the small one is raised. The windows in the rotating funnel are blocked.
- The skip loads the charge.
- Turning, the funnel opens the windows, and the charge falls onto a small cone 3. Then it returns to its place.
- The cone rises, thereby preventing the blast furnace gases from escaping.
- The cone is lowered to transfer the charge into the intercone space, then raised to its original position.
- The cone is lowered, and with it the charge is loaded into the blast furnace shaft.
This dosed feed ensures layer-by-layer distribution of materials.
Skip is a scoop with which it is carried out. It is performed using conveyor technology. Air blowers - tapholes and tuyeres supply air into the blast furnace at a pressure of 2-2.5 MPa.
Lance and cast iron tap hole
Cowpers serve to heat the supplied air. In regenerators, it is heated by blast furnace gases, thereby reducing the energy load on the unit. The air is heated to 1200°C and supplied to the shaft. When the temperature drops to 850°C, the supply stops and the heating cycle resumes. For uninterrupted supply of hot air, several regenerators are installed.
Operating principle of a blast furnace
To produce cast iron, the following ingredients are required: charge (ore, flux, coke), high temperature, constant air supply to ensure continuous combustion.
Thermochemical reactions
Reduction of iron from oxides by a stepwise chemical reaction:
3Fe2O3+CO→2Fe3O4+CO2,
Fe3O4+CO→3FeO+CO2,
FeO+CO→Fe+CO2.
General formula:
Fe2O3 + 3CO → 2Fe + 3CO2.
Obtaining the required amount of carbon dioxide and carbon monoxide ensures the combustion of coke:
C + O2 → CO2,
CO2 + C → 2СО.
Limestone flux is used to separate iron from impurities. Chemical reactions that form slag:
CaCO3 → CaO + CO2,
CaO + SiO2→CaSiO3.
The operating principle of a blast furnace is as follows. After loading, the blast furnace begins to be ignited with gas. As the temperature rises, the cowper is connected and air blowing begins. Coke, the fuel for the blast furnace, begins to burn more intensely, and the temperature in the mine increases significantly. When the flux decomposes, a large amount of carbon dioxide is formed. Carbon monoxide acts as a reducing agent in chemical reactions.
Cast iron production scheme
After the coke burns and the flux decomposes, the charge column is lowered, and another portion is added on top. From below, in the widest part of the shaft, complete reduction of iron occurs at temperatures of 1850°C - 2000°C. Then it flows into the forge. Here the enrichment of iron with carbon occurs.
The temperature in the blast furnace increases as the charge is lowered. The reduction process takes place at 280 °C, and melting occurs after 1500 °C.
The melt is poured in two stages. At the first stage, slag is drained through tapholes. At the second stage, cast iron is drained through cast iron tapholes. More than 80% of the cast iron produced goes into steel production. The remaining cast iron is cast into molds into blanks.
The blast furnace operates continuously. From loading the charge to obtaining the alloy, 3-20 days pass - it all depends on the volume of the furnace.
Blast furnace maintenance and repair
Any equipment that operates 24/7 requires constant maintenance. Regulations are included in the technical passport of the equipment. Failure to comply with the maintenance schedule will result in a reduction in service life.
Maintenance work on blast furnaces is divided into periodic and major repairs. Periodic work is carried out without stopping the work process.
Major repairs are divided into three categories based on the volume of work performed. During the first discharge, all equipment is inspected, and melts are removed from the shaft. During the second discharge, the lining is repaired and failed equipment elements are replaced. With the third category, the unit is completely replaced. Typically, such repairs are combined with modernization or reconstruction of the blast furnace.
Source: https://stankiexpert.ru/spravochnik/litejjnoe-proizvodstvo/domennaya-pech.html
Design of a blast furnace, operating principle of a blast furnace
Smelting cast iron on an industrial scale is impossible without large, complex and powerful furnaces. A blast furnace is a vertical shaft-type structure in which iron ore is smelted into useful metal. The design of a blast furnace implies continuous operation of the structure for 3-12 years, until major repairs.
Figure 1. Blast furnace
Blast furnace device
A modern furnace is a huge structure weighing up to 35,000 tons and a height of up to 40 m. In order for long-term smelting without downtime to be possible, the furnace must be durable and reliable. The outside of the device is covered with a steel casing - the base is lined with thick sheets (up to 4 cm).
There is a fire-resistant lining on the inside. It needs constant cooling, so metal containers are installed below in which water circulates. Since a lot of liquid is needed, evaporative cooling is sometimes used. The essence of the method is the evaporation of boiling water, which actively absorbs thermal energy.
Figure 2. Blast furnace design
A furnace is a structure consisting of many elements. The main ones are presented:
- Kolosnik (grid-iron);
- steamed;
- mine;
- mountain;
- shoulders.
Koloshnik
This is the upper element, which serves to load raw materials (charge) and remove exhaust gases. part of the top is the filling unit. In most cases, the devices for filling the charge are double-cone. Both cones are covered between the fillings. After the raw material is supplied, the smaller element is lowered and the iron ore falls into the larger one. As soon as the required portion is collected, the small cone closes and the ore from the large one enters the furnace. After this, the large device is also sealed.
More advanced blast furnaces have an improved top design. The role of a large cone is played by a rotating chute with an adjustable angle of inclination. Thanks to this, it is possible to fill the raw materials from any side.
The flue also serves as a gas outlet. The smelting process produces a huge amount of gas. Along with it, iron-containing dust is also removed, which is captured by gas purifiers.
Figure 3. Scheme of blast furnace production
Mine
The shaft occupies most of the furnace space. The structure, expanding downward, is a truncated cone. Thanks to this, the charge is fed evenly. The blast furnace is a vertical structure and quite high. This is necessary to ensure chemical and thermal treatment of raw materials with heated gases.
Raspar
The cylinder-shaped element is located in the middle part of the working domain zone. Raspar is characterized by the largest diameter. The purpose of the design is to increase the furnace space and eliminate unnecessary raw materials. This is where waste rock is formed.
Shoulders
A shortened cone-shaped version of the raspar - the truncated component faces the wide part upward. With the help of shoulders, the volume of melted charge in the production of cast iron is reduced.
Horn
The main part in which metal smelting takes place. Here coke burns and gas is formed, slag and cast iron accumulate and liquid metal is regularly released from the structure. The forge consists of a tuyere zone and a metal receiver. Through the tuyeres, through an air heater and a ring air duct, hot air enters the furnace. It is necessary for fuel combustion. The bottom of the metal receiver is called the flange.
At the bottom of the hearth there are slag and cast iron tapholes - holes through which molten metal passes. After the cast iron is released, the hole is closed using a piston mechanism with a fire-resistant mass.
The slag holes are located 1.5-2 m above the cast iron tapholes. They are closed using steel corkscrews with tips. The slag is separated from the cast iron using a unit located on the furnace chute. Both components are fed into special ladles.
This whole gigantic structure has a huge mass. This weight must be transferred evenly to the ground. Therefore, the blast furnace is installed on a massive concrete foundation, the thickness of the base of which can reach 4 m. The base serves as a support for the columns, which, in turn, support the metal structures. The upper foundation part is made of heat-resistant concrete in the format of a monolithic cylinder.
The pressure of a huge mass on the ground is compensated by the construction of a powerful foundation
The table shows the relationship between the sizes of some modern stoves.
| Dimensions, mm | Useful volume of blast furnace, m3 | ||
| 2000 | 3000 | 5000 | |
| Diameter: | |||
| fire pit | 7300 | 8200 | 11200 |
| raspara | 10900 | 12900 | 16300 |
| forge | 9750 | 11700 | 14900 |
| Height: | |||
| mines | 18200 | 20100 | 19500 |
| forge | 3600 | 3900 | 4500 |
| useful | 29200 | 32200 | 32200 |
| full | 32350 | 34650 | 36900 |
Additional furnace elements
The operation of the oven requires the operation of auxiliary devices. Among them:
- air heaters; large tower-type elements are located next to the furnace; blast furnace gas enters them, which then burns; due to this, even hotter gas is formed, heating the air through a complex system; the latter - heated to a temperature of at least 1000 degrees - is used for smelting cast iron;
- blowers; compressed air is necessary for fuel combustion; air enters the furnace thanks to devices that generate a pressure of about 25 MPa;
- devices for lifting and filling the charge;
- gas purifiers for cleaning blast furnace gases;
- other auxiliary devices - for example, overhead cranes with which foundry yards are equipped.
Figure 4. Example of a modern blast furnace
Modern furnaces are equipped with automation systems. Computerization makes it possible to control and regulate the basic parameters associated with the functioning of the blast furnace. The level of raw material filling, gas pressure, blast temperature, etc. are under control.
Modern blast furnaces are left to automation. The computer controls the main production processes
The operating principle of a blast furnace is based on complex physical and chemical processes. The following operations are distinguished:
- fuel combustion;
- iron recovery;
- decomposition of limestone into calcium oxide and carbonic anhydride;
- saturation of iron with carbon;
- metal smelting;
- slag melting, etc.
Figure 5. Iron production from a chemical point of view
In the most general sense, blast furnace smelting is the production of pig iron from iron ore raw materials. The main materials with which cast iron can be smelted are:
- fuel - coke;
- iron ore is the raw material from which cast iron is smelted;
- flux – special additives made from sand, limestone and some other materials.
The charge enters the furnace in the form of small fused pieces - pellets or agglomerates. The ore substance can be manganese ore or various variations of iron ore. The raw materials are poured into the furnace in layers, alternating with layers of flux and coke.
The purpose of the flux is to separate cast iron from impurities and waste rock (slag)
Slag floats to the surface of hot cast iron. Impurities are drained off before the liquid metal hardens.
The supply of raw materials, like the operation of the furnace, must be continuous. The consistency of the process is ensured by special conveyors. Getting into the furnace through the described elements, the charge goes through a number of technological processes.
Figure 6. Blast furnace diagram
Burning coke gives the required temperature, which should not fall below 2000 degrees. Combustion promotes the combination of oxygen and coal. At the same time, carbon dioxide is formed. Under the influence of high temperature, the latter becomes carbon monoxide. Thanks to this, iron is restored.
Iron recovery is one of the most important production steps. Without this process, it is impossible for the metal to acquire the necessary strength.
Cast iron becomes cast iron after the iron passes through molten coke. For the result to become possible, the iron must be saturated with carbon. Cast irons include alloys containing 2-5% carbon.
After the finished metal has accumulated in the forge, it is released through tapholes. The slag is first released through the upper hole, and then the cast iron is released through the lower hole. The latter is drained through channels into buckets and sent for subsequent processing.
Conclusion
The blast furnace is one of the most important components of ferrous metallurgy. In modern realities, blast furnaces are usually “built-in” into metallurgical plants. An average furnace is capable of producing about 12,000 tons of pig iron daily, while consuming approximately 20,000 tons of feedstock.
Source: https://ZnatokTepla.ru/pechi/domennaya-pech.html
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Blast furnace process
Steels are considered to be alloys of iron and carbon with a carbon content of up to 2.14%. Anything that has a higher carbon content is cast iron. Steel is produced on the basis of two processes - blast furnace (the result is pig iron) and the actual production of steel, when steel and alloys of the desired grade and composition are obtained from pig iron by burning carbon and adding alloying elements.
Raw materials
The basis for producing cast iron in the blast furnace process is iron ores. Since iron has a relatively high affinity for oxygen, it is not found in its pure form in the earth’s crust, but is found in the form of compounds with oxygen and carbon dioxide.
The main iron ores that are used in metallurgical production are iron oxide (Fe3O4 - magnetite, magnetic iron ore), iron oxide (Fe2O3 - red iron ore, 2Fe2O3 * 3H2O - brown iron ore) and iron carbonate FeCO3.
Naturally, these substances are not found in their pure form, but contain admixtures of other elements (most often sulfur and phosphorus) and other substances in the form of accompanying rocks that do not form chemical compounds with the target product (usually SiO2, Al2O3, CaO, MgO).
In addition, iron pyrite FeS2 is available in large quantities in the form of ores, but it is very rarely used in metallurgy, since the iron smelted from it is of very low quality due to its high sulfur content.
As a result of special technologies for ore crushing and the flotation process, a significant part of the waste rock can be separated from the target product, as a result of which in some cases it is possible to increase the iron content in the ore to 63-67%, and sometimes to 69-72%.
However, it is not possible to completely remove waste rock; this operation is carried out in the blast furnace process itself by converting waste rock into slag, which is separated from the cast iron.
Process and diagrams
The blast furnace process (the process of producing pig iron) is carried out in shaft furnaces (blast furnaces). The blast furnace, a schematic section of which is shown in Fig. 5.
1, is a device in the form of a cone in the upper part several tens of meters high, lined with fire-resistant bricks on the inside and tied together with iron hoops on the outside or surrounded by a solid iron shell.
The upper part of the blast furnace is called the shaft and ends at the top with a hole - the top, which is closed by a movable funnel - the top gate. The widest part of the blast furnace is called the steam chamber. The lower part of the blast furnace forms the forge. The forge has holes - tuyeres - through which hot air is blown into the furnace.
When starting up, the blast furnace is loaded first with coal (coke), and then layer by layer with a mixture of ore with flux and coal and clean coal. The lower layers of coal are ignited, after which combustion and the temperature required for smelting are maintained by blowing air heated in heat recuperators into the hearth. The latter enters an annular pipe located around the bottom of the furnace, and from it through distribution pipes through tuyeres into the hearth.
In the forge, coal burns, turning into carbon dioxide, which, rising up and passing through a layer of hot coal, turns into carbon monoxide. This carbon monoxide reduces the bulk of the ore, turning back into carbon dioxide. However, such a scheme does not fully reflect the variety of chemical reactions occurring in the furnace. The order of transformation of ore into cast iron and the temperature distribution are shown in Fig. 5.2.
Rice. 5.1. Schematic representation of a shaft furnace for producing cast iron (blast furnace).
Rice. 5.2. Scheme of chemical reactions occurring along the height of a blast furnace.
In the lower part of the furnace, as already mentioned, coke combustion occurs according to the reaction:
< C > + { O2 } = { CO2 }
Here, angle brackets indicate the solid state, and curly brackets indicate the gaseous state.
Passing upward further through a layer of hot coal, CO2 turns into carbon monoxide:
{ CO2 } + < C > = 2 { CO }
Carbon monoxide is a strong reducing agent and is what reduces iron from ores. The reaction occurs in stages, as shown in the figure. As a result, grains of solid iron are formed.
As the coal burns, this iron falls down the furnace into its hotter part - steam, and here at a temperature of about 1200 ° C it melts in contact with coal, partially dissolving it and forming hypereutectic cast iron with a carbon content of 4-4.5%.
While pure iron melts at 1535°C, cast iron at the eutectic point melts at 1150°C, so drops of liquid iron flow down to the bottom of the hearth. In order to save the thermal energy of the exhaust gases and return it to the process, the exhaust gases from the blast furnace are sent to the so-called. “coopers”, where gases give off some of the heat.
First, these gases are sent to one of the cowpers, while air is blown through the second to be subsequently fed into the blast furnace, where it is heated. At certain intervals the flows change places.
Simultaneously with the reduction of iron, processes of separation of waste rock from the target product occur through the formation of slag during the interaction of impurities with flux additives.
The final slag consists of 85-95% SiO2, Al2O3 and CaO; the rest is MgO (2-10%), FeO (0.2-0.6%), MnO (0.3-2%) and 1.5-2.5% sulfur in the form of CaS.
They strive to create the most fusible slag, therefore, depending on the type of impurities in the ore used, either acidic (SiO2) or alkaline components (calcium and magnesium oxides) are added to the charge.
To produce liquid smelting products, cast iron and slag tapholes are used separately.
Since slag is a multicomponent system, in addition, the process of transition from solid to liquid state occurs in a fairly large temperature range, the viscosity of the slag is determined not only by temperature, but also by the composition of the slag, therefore each type of charge has its own characteristics.
Another problem that is observed in the blast furnace process and which is solved differently for each type of charge is the problem of sulfur. Sulfur is a harmful element that deteriorates the quality of metal. It causes red brittleness in steel and deteriorates the quality of cast iron, increasing the likelihood of cavities forming in castings.
The restrictions on sulfur for steel and cast iron are very serious - these materials should not contain more than a few hundredths of a percent. However, if no special measures are taken, up to 0.9% sulfur can accumulate in cast iron.
Since sulfur is easier to remove from ores and cast irons than from steel, it is at the stage of preparation of charge components and in blast furnace production that these operations are carried out.
Although a significant amount of sulfur is removed during fire processing of ores (sintering and pellet roasting), a lot of sulfur is introduced into the blast furnace with coke and iron ore materials in the form of iron sulfide (pyrite FeS2), barite BaSO4 and gypsum CaSO4 * H2O.
Part of the sulfur is removed naturally during technological processes through the formation of gases (SO2, H2S, etc.), but this is only a small part, estimated at about 15% for a conventional blast furnace process. Therefore, the main attention is paid to the conversion of sulfur compounds that dissolve in cast iron into compounds that do not dissolve in it, for example, according to the reaction:
FeS + CaO = CaS + FeO
FeO + C = Fe + CO
FeS +CaO + C = CaS +Fe + CO
There are other desulfurization methods that can generally solve this problem when using a wide variety of ores.
The end products of blast furnace smelting are pig iron (target product) and slag and blast furnace gases (production by-products). In this case, we are only interested in cast iron, so we will focus on it.
Cast iron is a multicomponent alloy of iron with carbon, silicon, manganese and sulfur. Depending on the purpose of cast iron, it may contain other substances, the content of which is regulated by relevant standards.
The main type of cast iron produced in blast furnace production is pig iron (up to 90% of all cast iron produced), which is then used to produce various types of steel.
The production of cast iron is also of independent importance, since some types are used for castings. A small part of pig iron is also used to produce cast iron castings. Some types of cast iron products can be galvanized, but we'll talk about that later.
Depending on the purpose of the cast iron, the latter is transported from blast furnaces by iron carriers in liquid form either to steelmaking shops or to casting machines (when smelting commercial cast iron).
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Source: https://ECM-zink.ru/info/stati/domennyij-proczess-pechi.html
Blast furnace. Iron smelting. Furnace for smelting cast iron. Blast furnace diagram. Construction of a blast furnace. Blast furnace operation. Parameters and design of a blast furnace. | mtomd.info
Cast iron is smelted in shaft-type furnaces - blast furnaces . The essence of the process of producing cast iron in blast furnaces is the reduction of iron oxides that make up the ore with carbon monoxide, hydrogen and solid carbon released during fuel combustion.
When smelting cast iron, the following problems are solved:
- Reduction of iron from ore oxides, carburizing it and removing it in the form of liquid cast iron of a certain chemical composition.
- Melting of waste ore, formation of slag, dissolution of coke ash in it and removal of it from the furnace.
Design and operation of a blast furnace
The blast furnace has a steel casing lined with refractory fireclay bricks. The working space of the furnace includes a top 6, a shaft 5, a steam chamber 4, shoulders 3, a hearth 1, a flange 15. In the upper part of the top there is a filling apparatus 8, through which the charge is loaded into the furnace.
The charge is fed into lift cars 9, which move along bridge 12 to the filling apparatus and, tipping over, pour the charge into the receiving funnel 7 of the charge distributor.
When lowering the small cone 10, the charge enters the bowl 11, and when lowering the large cone 13, it enters the blast furnace, which prevents the release of gases from the blast furnace into the atmosphere.
Blast furnace diagram
When the furnace is operating, the charge materials are melted and lowered, and new portions of the charge are fed through the loading device so that the entire useful volume is filled.
Iron production. Blast furnace production of cast iron. Cast iron production technology. Cast iron production process.
The useful volume of a blast furnace is the volume occupied by the charge from the flange to the lower edge of the large cone of the filling apparatus when it is lowered. The useful height of the blast furnace (H) reaches 35 m, and the useful volume is 20,005,000 m3.
In the upper part of the hearth there are tuyere devices 14, through which the heated air necessary for fuel combustion enters the furnace. The air comes from an air heater, inside of which there is a combustion chamber and a nozzle made of refractory bricks, in which there are vertical channels.
Purified blast furnace gas is supplied to the combustion chamber to the burner, which, when burned, forms hot gases. Passing through the nozzle, the gases heat it and are removed through the chimney. Air is passed through the nozzle, it is heated to a temperature of 1000-1200 0C and enters the tuyere device, and from there through tuyeres 2 into the working space of the furnace.
After the nozzles have cooled, the heaters are switched.
Fuel combustion. Near the tuyeres, natural gas and carbon coke, interacting with oxygen in the air, burn:
C + O2 = CO2 + Q
CH4 + 2O2 = CO2 + 2H2O(steam) + Q
As a result of combustion, a large amount of heat is released; in the furnace above the level of the tuyeres, temperatures above 2000 0C develop. Combustion products interact with hot coke according to the following reactions:
CO2 + C = 2CO - Q
H2O + C = CO + H2 - Q
A mixture of reducing gases is formed, in which carbon monoxide CO is the main reducer of iron from its oxides.
To increase productivity, the air supplied to the blast furnace is humidified, which leads to an increase in the reducing agent content. Hot gases, rising, give off heat to the charge materials and heat them, cooling to 300-400 0C at the top.
The charge (sinter, coke) falls towards the gas flow, and at a temperature of about 570 0C the reduction of iron oxides begins.
Reduction of iron in a blast furnace. The reduction of iron occurs as the charge moves down the mine and the temperature rises from the highest oxide to the lowest, in several stages:
Fe2O3 —> Fe3O4 —> FeO —> Fe
Temperature determines the nature of chemical reactions. The reducing agents for iron oxides are solid carbon, carbon monoxide and hydrogen. Reduction with solid carbon (coke) is called direct reduction and occurs in the lower part of the furnace (steam zone), where temperatures are higher, according to the reaction:
FeO + C = Fe + CO – Q
Reduction by gases (CO and H2) is called indirect reduction , it occurs in the upper part of the furnace at relatively low temperatures, according to the reactions:
3Fe2O3 + CO = 2Fe3O4 + CO2 + Q
Fe3O4 + CO = 3FeO + CO2 - Q
FeO + CO = Fe + CO2 + Q
Due to CO and H2, all higher iron oxides are reduced to lower and 40-60% metallic iron.
At a temperature of 1000-1100 0C, solid iron reduced from ore, interacting with carbon monoxide, coke and black carbon, intensively dissolves carbon. When saturated with carbon, the melting point decreases and at the level of steam and shoulders, iron melts (at a temperature of about 1300 0C).
Drops of the iron-carbon alloy, flowing over pieces of coke, are additionally saturated with carbon (up to 4%), manganese, silicon, phosphorus, which are reduced from ore at a temperature of 1200 0C, and sulfur contained in the coke.
At the bottom of the blast furnace, slag is formed as a result of the fusion of gangue ore oxides, fluxes and fuel ash. Slags contain Al2O3, CaO, MgO, SiO2, MnO, FeO, CaS. Slag is formed gradually, its composition changes as it flows into the furnace, where it accumulates on the surface of liquid cast iron, due to its lower density. The composition of the slag depends on the composition of the charge materials used and the cast iron being smelted.
Cast iron is released from the furnace every 34 hours through cast iron tap hole 16, and slag is released every 11.5 hours through slag tap hole 17 (a tap hole is a hole in the masonry located above the flange). The tap hole is opened with a drilling machine, then covered with a fire-resistant mass. The cast iron and slag are poured into cast iron ladles and slag bowls.
Pig iron enters oxygen converter (see Oxygen converter) or open-hearth shops (see Open-hearth furnace), or is poured into molds by a casting machine, where it solidifies in the form of ingots weighing 45 kg.
Source: http://www.mtomd.info/archives/1828
We build small and large businesses in the production of cast iron
The chemical composition of cast iron is close to the composition of steel, but differs from it in its increased, more than 2%, carbon content. It also necessarily includes silicon, manganese, phosphorus and sulfur.
When smelting steel from iron ore, it is an intermediate product of the production process, since its melting point is 300 degrees lower than the melting point of steel.
At the next stage of the process, steel is obtained from it by increasing the melting temperature and removing impurities. About 85% of all cast iron produced is used for this purpose.
Due to these circumstances, it costs much less than steel.
The high carbon content makes cast iron brittle and vulnerable to impact. But at the same time, it has great stability under compression. Due to its structure, products made from this material are not sensitive to damage to their surface and such damage does not lead to deformation or destruction of the entire product as a whole.
These properties make cast iron easier to cut than steel, especially when processed on a lathe. Therefore, it is often used for the manufacture of parts for various devices that are not subject to shock and tensile influences. The history of industrial production of cast iron in Russia goes back almost 300 years. In the 20th century, the USSR ranked first in the world in the production of iron and steel.
During this time, the gross production of ferrous metals in Russia together with Ukraine reached 153 million tons. After the collapse of the USSR, smelting decreased by more than half. In 2008, 68.5 million tons were smelted in Russia. Russia now holds fourth place in the ranking of ferrous steel producers after China, Japan and the USA.
The peculiarity of the current state of affairs in the iron foundry industry in Russia is that it mostly works for export, producing cast iron mainly in the form of pigs sent abroad for further processing. As a result, a situation has arisen where in Russia, despite the large volume of gross production of cast iron, there is a constant shortage of finished products from cast iron.
Thanks to this, a niche has been created in Russia for small businesses engaged in shaped iron casting. It should be said that this production is one of the complex ones and places high demands on technical literacy and technological discipline of both managers and ordinary workers.
We will try to give a general idea of the main methods of making cast iron and their attractiveness for small businesses.
Blast furnace method of cast iron production
Blast furnace production aims to smelt iron from ore, while waste rock and harmful impurities are removed during smelting.
The basic operating diagram of a blast furnace has remained unchanged since the creation of iron foundries in Russia.
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- The furnace itself is a structure with a vertical working chamber, the inner surface of which is lined with refractory bricks.
- The charge, the raw material for smelting, is fed into the upper part of the blast furnace, called the top.
The top is equipped with gas outlets, through which a mixture of top gases and charge dust accumulated during smelting is removed from the blast furnace. Then the mixture is separated, and the dust goes into agglomeration, again entering the charge, and the gas is used for use in auxiliary production.
- The main part of the working chamber, the shaft, is made in the form of a truncated cone, located base down.
- Under the shaft there is a cylindrical container - steam. The charge melts in the steam; it rests on pillars that are fixed directly to the foundation of the blast furnace.
- Under the steam there is another cylindrical container - a forge. In the upper part of the hearth there is a taphole for releasing slag, and in the lower part there is a taphole for tapping cast iron. Through tapholes during smelting, pig iron and slag are periodically removed from the blast furnace.
- Above the slag tap hole there are holes - tuyeres, through which oxygen, heated air and other additives are supplied.
Smelting in a blast furnace occurs as follows:
- Oxygen supplied through tuyeres reacts with the carbon contained in the charge, and the combustion temperature is up to 2000 degrees.
- Molten iron, freed from burnt carbon, accumulates in a cone-shaped transition chamber between the furnace and the steam - the shoulders. Here, part of the carbon released from the charge combines with iron, carburizing it. Here, manganese with silicon, sulfur, phosphorus and other elements released from the charge are combined with iron.
- The cast iron thus formed flows from the shoulders into the hearth, and the molten slag accumulates above it.
- Pig iron and slag are discharged from the blast furnace through appropriate tapholes.
- From the tap hole, molten cast iron, the temperature of which is about 1500 degrees, flows through a chute into the transfer ladle.
Melted cast iron is divided depending on its purpose into the following types:
- Pig iron, which will later be converted into steel.
- Foundry cast iron, which is characterized by an increased silicon content and reduced sulfur content, is used for the production of iron castings.
- Special (ferroalloy) cast iron, in which the content of elements such as manganese or chromium can be increased, is used to produce special steels.
When poured from the dispensing ladle, the pig iron is sent to the mixer, from where it is taken for processing into steel. Foundry cast iron is poured into molds for the production of pig iron.
The volume of a blast furnace ranges from 1500 to 5000 m3, its height can reach several tens of meters. The blast furnace operates in a continuous mode for several years, which requires a constant supply of a huge amount of charge and fuel.
At the same time, the functioning of a blast furnace is ensured by a complex and highly developed infrastructure, consisting of auxiliary production and communications for the transportation of raw materials and the final product. The investments required to organize blast furnace production amount to billions of rubles. Therefore, its organization is only possible for large corporations.
Based on all of the above, we can summarize that the organization of blast furnace production of cast iron is too far beyond the capabilities of small businesses.
Remelting cast iron in a cupola furnace
Unlike blast furnace melting, remelting cast iron in a cupola furnace, with the right approach, can generate profit with relatively small investments and is of undoubted interest for small businesses. The cupola furnace, like the blast furnace, belongs to the shaft-type furnaces.
It uses coke as a fuel; recently, gas-powered cupola furnaces have become increasingly widespread. To achieve a high combustion temperature, air is forced into the working chamber.
Unlike a blast furnace, where metal is smelted from ore, scrap iron and pig iron are melted in a cupola furnace, followed by pouring the melt into molds to produce finished products.
Due to their small size, servicing such furnaces is orders of magnitude easier than servicing a blast furnace. For the same reason, their repair and stopping procedure have been simplified.
The schematic diagram of a cupola furnace operating on coke looks like this:
- The main part of the cupola is a metal cylinder - a casing made of 6-12 mm steel sheets. Its internal surface is lined with heat-resistant bricks or other fire-resistant material, the thickness of which is 200-300 mm.
- The base for the casing is a hearth slab, which is supported by four columns. To remove cast iron residues during repairs, there is a hole located in the center of the plate, closed with a damper.
- A loading window is used to load pieces of cast iron, coke and additives.
- The part of the working space from the bottom plate to the filling window is called the shaft.
- The part of the casing space located above the filling hole is called a pipe.
- The lower part of the shaft is called the forge. The forge has tuyeres for supplying air or oxygen, as well as tap holes, cast iron and slag.
- The part of the hearth in the tuyere area is the melting belt.
- Ignition is carried out through the working window using firewood.
The melting process goes like this:
- Through the loading window, pieces of cast iron and coke, as well as flux and other additives are loaded into the shaft.
- When coke is burned, the combustion temperature of which increases due to the air pumped through the tuyeres, the cast iron melts, which exits through the cast iron tap hole.
- The slag, which due to its lightness floats on top of the cast iron, exits through the slag tap hole.
- The gaseous mixture formed during combustion, going up the shaft, heats the charge descending from the filling window and goes into the pipe.
To facilitate the pouring of large molds and maintain a constant chemical composition of cast iron, cupola furnaces are usually equipped with another hearth - a hoarder, in which the cast iron coming out of the casing tap hole is accumulated. In this case, the melt is distributed from the hoarder. The operating cycle is from 10 to 20 hours, after which the cupola is extinguished and the heat-resistant lining of its inner surface is repaired.
The productivity of such a furnace can be from 0.2 to 25 t/hour, respectively, with a shaft diameter of 500 to 2000 mm, with a useful shaft height of 3 to 5 meters.
Investments required to start cupola casting production
Let's try to determine the profitability of foundry production when using a cupola furnace with a productivity of 0.2-0.35 t/hour. The electricity consumption of such a furnace is 2 kW/h. It is capable of smelting several types of cast iron - foundry, modified and refined. This occurs due to the use of SPR technology - loop blowing of the melt.
In a month, such a furnace is capable of producing 22 heats with a finished product yield per heat of 5400 kg. That is 118 tons of cast iron per month. The cost of such a furnace is about 4,500,000 rubles. This figure, in addition to equipment, includes the cost of its delivery and installation, as well as employee training.
Rent of production premises and their preparation for installation of equipment, as well as the purchase of tools, workwear and the like - 45,000 rubles.
Source: https://bisnesideya.ru/nestandartny-e-idei-biznesa/stroim-malyj-i-bolshoj-biznes-na-proizvodstve-chuguna.html
Blast furnace - design and operation
editorial
Categories: blast furnace production
Purpose. Furnace design. Technological process of cast iron smelting.
Blast furnace
Cast iron is smelted in shaft-type furnaces - blast furnaces .
The essence of the process of producing cast iron in blast furnaces is the reduction of iron oxides that make up the ore with carbon monoxide, hydrogen and solid carbon released during fuel combustion. When smelting cast iron, the following problems are solved:
- Reduction of iron from ore oxides, carburizing it and removing it in the form of liquid cast iron of a certain chemical composition.
- Melting of waste ore, formation of slag, dissolution of coke ash in it and removal of it from the furnace.
Design and operation of a blast furnace
The blast furnace has a steel casing lined with refractory fireclay bricks. The working space of the furnace includes a top 6, shaft 5, steam 4, shoulders 3, hearth 1, flange 15. In the upper part of the top there is a filling apparatus 8, through which the charge is loaded into the furnace.
The charge is fed into lift cars 9, which move along bridge 12 to the filling apparatus and, tipping over, pour the charge into the receiving funnel 7 of the charge distributor.
When the small cone 10 is lowered, the charge enters the bowl 11, and when the large cone 13 is lowered, it enters the blast furnace, which prevents the release of gases from the blast furnace into the atmosphere.
Blast furnace diagram
When the furnace is operating, the charge materials are melted and lowered, and new portions of the charge are fed through the loading device so that the entire useful volume is filled. Iron production. Blast furnace production of cast iron. Cast iron production technology.
Cast iron production process.
The useful volume of a blast furnace is the volume occupied by the charge from the flange to the lower edge of the large cone of the filling apparatus when it is lowered.
The useful height of the blast furnace (H) reaches 35 m, and the useful volume is 20,005,000 m3.
In the upper part of the hearth there are tuyere devices 14, through which the heated air necessary for fuel combustion enters the furnace. The air comes from an air heater, inside of which there is a combustion chamber and a nozzle made of refractory bricks, in which there are vertical channels. Purified blast furnace gas is supplied to the combustion chamber to the burner, which, when burned, forms hot gases. Passing through the nozzle, the gases heat it and are removed through the chimney. Air is passed through the nozzle, it is heated to a temperature of 1000-1200 0C and enters the tuyere device, and from there through tuyeres 2 into the working space of the furnace. After the nozzles have cooled, the heaters are switched. Fuel combustion. Near the tuyeres, natural gas and coke carbon, interacting with oxygen in the air, burn: C + O2 = CO2 + Q CH4 + 2O2 = CO2 + 2H2O(steam) + Q As a result of combustion, a large amount of heat is released, in the furnace above the level of the tuyeres a higher temperature develops 2000 0C. Combustion products interact with hot coke according to the reactions: CO2 + C = 2CO - Q H2O + C = CO + H2 - Q A mixture of reducing gases is formed, in which carbon monoxide CO is the main reducer of iron from its oxides. To increase productivity, the air supplied to the blast furnace is humidified, which leads to an increase in the reducing agent content. Hot gases, rising, give off heat to the charge materials and heat them, cooling to 300-400 0C at the top. The charge (sinter, coke) falls towards the gas flow, and at a temperature of about 570 0C the reduction of iron oxides begins.
Reduction of iron in a blast furnace. The reduction of iron occurs as the charge moves down the mine and the temperature rises from the highest oxide to the lowest, in several stages:
Fe2O3 —> Fe3O4 —> FeO —> Fe
Temperature determines the nature of chemical reactions. The reducing agents for iron oxides are solid carbon, carbon monoxide and hydrogen. Reduction with solid carbon (coke) is called direct reduction and occurs in the lower part of the furnace (steam zone), where temperatures are higher, according to the reaction:
FeO + C = Fe + CO – Q
Reduction by gases (CO and H2) is called indirect reduction , it occurs in the upper part of the furnace at relatively low temperatures, according to the reactions:
3Fe2O3 + CO = 2Fe3O4 + CO2 + Q Fe3O4 + CO = 3FeO + CO2 - Q FeO + CO = Fe + CO2 + Q Due to CO and H2, all higher iron oxides are reduced to lower and 4060% metallic iron. At a temperature of 1000-1100 0C, solid iron reduced from ore, interacting with carbon monoxide, coke and black carbon, intensively dissolves carbon. When saturated with carbon, the melting point decreases and at the level of steam and shoulders, iron melts (at a temperature of about 1300 0C). Drops of the iron-carbon alloy, flowing over pieces of coke, are additionally saturated with carbon (up to 4%), manganese, silicon, phosphorus, which are reduced from ore at a temperature of 1200 0C, and sulfur contained in the coke. At the bottom of the blast furnace, slag is formed as a result of the fusion of gangue ore oxides, fluxes and fuel ash. Slags contain Al2O3, CaO, MgO, SiO2, MnO, FeO, CaS. Slag is formed gradually, its composition changes as it flows into the furnace, where it accumulates on the surface of liquid cast iron, due to its lower density. The composition of the slag depends on the composition of the charge materials used and the cast iron being smelted.
Cast iron is released from the furnace every 34 hours through cast iron tap hole 16, and slag is released every 11.5 hours through slag tap hole 17 (a tap hole is a hole in the masonry located above the flange). The tap hole is opened with a drilling machine, then covered with a fire-resistant mass. The cast iron and slag are poured into cast iron ladles and slag bowls.
Cast iron enters oxygen converter or open-hearth shops, or is poured into molds by a casting machine, where it solidifies in the form of ingots weighing 45 kg.
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Source: https://www.metaljournal.com.ua/blast-furnace/
Basic processes of a blast furnace. Features of cast iron production
Let's talk about the role of coke in the blast furnace process. Let's take a closer look at the essence of this metallurgical production.
Nowadays, the production of iron and steel uses the blast furnace process, in which the furnace is an important component.
Unit specifics
Let's look at the features of the device and its purpose. The main processes of a blast furnace involve smelting coke. It is a porous material that is sintered from a mass of carbon obtained by calcining coal without the presence of atmospheric oxygen.
A blast furnace is a powerful and highly productive unit, where a significant amount of blast and charge is consumed.
raw materials
A modern blast furnace requires materials to remain in it for 4-6 hours, and gaseous substances for 3-12 seconds. If the gases are completely distributed over the cross-section of the furnace, you can count on high melting rates, and cast iron production is underway. The blast furnace process involves taking into account the movement of gases through zones that have lower resistance of the charge.
Therefore, when loading it into the furnace, adjustment and redistribution of coke and agglomerate across the cross section of the furnace is carried out so that they differ in gas permeability. Otherwise, a larger percentage of gases will leave the furnace at a significant temperature, which will negatively affect the use of thermal energy, and the blast furnace process will not be fully effective.
In those areas that have high resistance, the gas mixture will be slightly heated, additional heat consumption will be required in the lower part of the furnace, as a result, the consumption of raw materials will increase significantly.
What other features are important to consider when loading? The blast furnace process for producing cast iron is an energy-intensive production. That is why a layer of less gas-permeable agglomerate is used near the walls of the furnace, and in the center they increase the layer of coke, due to which the gas flow is redistributed to the center. The materials are placed evenly around the circumference.
the charge is carried out in separate portions - feeds. One portion consists of several skips, the ore part (agglomerate), and coke. The ratio of the starting ingredients is determined by specialists.
The blast furnace process allows for co-feeding, whereby skips of coke and sinter are accumulated on a large cone, which is then loaded into the furnace.
Adjustment of charge distribution
The distribution of coke and agglomerate over the cross section of the tops is controlled by the following methods:
- the order of arrangement of raw materials on a large cone changes;
- split and separate feeds are used;
- movable plates are installed near the walls of the fire pit.
The blast furnace process involves taking into account certain patterns of adding bulk materials:
- laying raw materials falling from a large cone on a flue with a raised ridge;
- fines accumulate at the ridge (at the point of fall) of the charge, large pieces roll down to the foot of the ridge, therefore, in this zone the gas permeability of the charge is greater;
- the ridge is affected by the level of backfill on the top, as well as the distance with a large cone;
- The large cone does not descend completely, causing small pieces of coke to fall to the periphery.
For the most part, the center of the kiln receives material from the feed skips that were last loaded into the large cone. If you change the loading order, you can achieve a redistribution of materials across the cross section of the top.
To regulate the process of distribution of the used charge throughout the volume of the furnace, two cone devices are used. Recently, some blast furnaces have been equipped with movable plates near the walls of the top, allowing them to change the angle of inclination and move them along a horizontal plane.
Pieces of the charge that fall on the slabs are reflected from them, which makes it possible to direct the raw material to certain zones of the top.
Options for ovens without a cone
In furnaces that do not have a conical loading device, raw materials are passed through two sluice hoppers that open alternately. Raw materials are delivered to them by inclined belt conveyors, on which coke and sinter are placed at clear intervals. One portion comes from the belt into one hopper, then is unloaded onto the furnace top along a rotating inclined tray. During the unloading period, they make about ten full revolutions around a fixed central axis.
Boot cycle
It is commonly referred to as the repeating number of portions of charge materials. The maximum portion is determined by the volume of the sluice hopper of the filling mechanism. The number of servings in one cycle can range from 5 to 14.
How to obtain the products of the blast furnace process in full? In order to answer this question, let's take a closer look at the essence of the process. With an increased content of carbon dioxide in the mixture, low temperature promotes the completeness of heat exchange and chemical processes in the blast furnace.
In order for the device to work economically and intensively, the quantitative content of carbon dioxide along the axis and at the periphery of the furnace must be reduced, and at a height of one or two meters from the walls it must be increased.
Temperature control in new furnaces is carried out by inserting probes through holes in the casing. It is mandatory for all processes to control the level of filling at the top.
Among the innovations is the use of non-contact methods of level measurement based on readings from microwave and infrared sensors.
Features of temperature distribution
In addition to the heat that is introduced by the heated blast, as the main source of heat for heating the gases and charge, carrying out recovery and compensating for heat losses, losses can be compensated for by the heat that is released during the combustion of fuel in the upper part of the hearth. As gaseous products move upward from the hearth, heat drops to the cold charge materials, and heat exchange occurs. A similar process explains the decrease from 1400 to 200 degrees in the temperature at the outlet of the furnace top.
Removing excess moisture
Let's look at the basic physical and chemical processes in a blast furnace. The charge that is loaded into a blast furnace contains hygroscopic moisture. For example, in coke its content can be up to five percent. Moisture evaporates quickly at the top, so additional heat is required to remove it.
Hydrate moisture appears when brown iron ore, as well as kaolin, is loaded into a blast furnace. To solve the problem in modern cast iron production, these ores are practically not used as raw materials.
Carbonate decomposition processes
Carbonic acid salts can enter the blast furnace. As they heat up, they decompose into oxides of calcium and carbon, and the process is accompanied by the release of a sufficient amount of energy.
Lately, almost no ore has been loaded into blast furnaces. What is the role of fluxes in the blast furnace process? They increase its efficiency and reduce production costs. Thanks to the use of fluxed sinter and complete removal of limestone from the blast furnace charge, significant coke savings can be achieved. The process of limestone decomposition during agglomeration is ensured by the combustion of low-grade fuel.
Iron is introduced into the blast furnace in the form of oxides. The main objective of the process is to maximize the extraction of iron from oxides by reduction. The essence of the process is to remove oxygen; carbon, carbon monoxide, and hydrogen are used for this.
The reduction of carbon is called a direct process, and the reaction with gaseous substances is called an indirect reaction. What are their distinctive features? The direct reaction consumes carbon, resulting in a significant reduction in its quantity.
The second type of reduction of iron from oxides requires an excess amount of hydrogen.
During the process, solid iron is formed. The recovery rate in cast iron is 99.8%. Thus, only 0.2 -1% turns into slag.
Smelting of manganese cast iron
During the smelting of converted cast iron, manganese enters the blast furnace in the form of an agglomerate. In some quantities, manganese ores in the form of manganese silicates contribute to the production of manganese cast iron.
Reduction from manganese oxides occurs in stages. In order to fully carry out the process, the forge must be set to high temperatures. The process of smelting pig iron is accompanied by the reduction of manganese only in a ratio of 55-65%.
Currently, due to the scarcity of manganese ores and manganese, a small amount of manganese cast iron has begun to be used in the technological chain.
When switching to low-manganese cast iron, you can save not only manganese itself, but also coke, since its consumption for direct metal reduction will be reduced.
