Basic questions and answers on ironmaking production technology

1. What types of iron ores are commonly used in blast furnaces? What are their characteristics?
Answer: Industrial iron ore is named after the iron-containing mineral deposits in which the iron content accounts for more than 85% of the total iron.
Iron-bearing mineral deposits are divided into oxide iron ore (Fe2O3, Fe3O4), hydrous iron oxide ore (Fe2O3.nH2O) and carbonate iron ore (FeCO3). The iron ores used in blast furnace ironmaking are divided into hematite (red ore) Fe2O3, magnetite (black ore) Fe3O4, limonite Fe2O3nH2O and siderite FeCO3.
The characteristic of hematite is that its scratches on the porcelain cross-section are reddish brown and non-magnetic. Soft, easily broken and easy to recover. The highest iron content is 70%. However, there is a kind of hematite that exists in the form of γ-Fe2O3. It has fine crystal structure, dark brown scratches, and strong magnetism, similar to magnetite.
The scratches of magnetite on the porcelain cross-section are black, the structure is fine and firm, the porosity is small, and recovery is difficult. Magnetite can be regarded as a combination of Fe2O3 and FeO, of which Fe2O369%, FeO31%, and the theoretical iron content is 72.4%. Pure magnetite is rarely seen in nature. Due to varying degrees of oxidation, the Fe2O3 component in magnetite increases and the FeO component decreases. Magnetite is magnetic, which is its most outstanding feature.
Limonite is an iron oxide ore containing crystal water. Its color is generally light brown to dark brown or black, with loose organization and good recovery properties. The theoretical iron content of limonite is not high, generally 37% to 55%, but after heating, the crystallization water is removed, the iron content is relatively increased, the porosity is increased, and the recoverability is improved.
Siderite is a carbonate iron ore with a color ranging from gray to light yellow to medium brown. The theoretical iron content is not high, only 48.2%, but after being decomposed by heat and releasing CO2, it not only increases the iron content, but also forms a porous structure with good recovery properties. Therefore, although the iron content is low, it still has high smelting value.
2. What is pig iron?
Answer: Pig iron is a general term for iron-carbon alloys containing more than 1.7% carbon and a certain amount of silicon, manganese, phosphorus, sulfur and other elements. It is mainly produced in a blast furnace.
3. What types of pig iron are there?
Answer: Pig iron is generally divided into three categories: steel for making steel; cast iron fordie die bcasting thin wall and tools (including pig iron for making ductile iron); and special pig iron, such as blast furnace manganese for ferroalloys. Iron and ferrosilicon etc. In addition, there is also vanadium-containing pig iron containing the special element vanadium.
4. What are the products and by-products produced by blast furnaces?
Answer: The product produced by the blast furnace is pig iron. The by-products are slag, blast furnace gas and furnace dust (gas ash).
5. What materials are used in blast furnace production?
Answer: The main raw materials produced by blast furnaces are iron ore and its substitutes, manganese ore, fuel and flux.
Iron ore contains natural ores and artificial rich ores. Generally, natural rich ores with an iron content of more than 50% can be directly put into the furnace; while ores with an iron content of less than 30% to 50% are not economical and must be processed into artificial rich ores through beneficiation and agglomeration before being put into the furnace.
Iron ore substitutes mainly include: blast furnace dust, oxygen converter dust, steel rolling scale, sulfuric acid slag and some high-speed iron tailings for non-ferrous metal ore dressing. These materials are generally used in block making.
Manganese ore is generally only used in the production of blast furnace ferromanganese.
6. Why does a blast furnace use flux? What are the commonly used fluxes? What are the requirements for flux?
Answer: Due to the need for blast furnace slag production, a certain amount of flux, referred to as flux, is often added to the blast furnace configuration. The purpose is to generate low melting point compounds from high melting point oxides (SiO2 1713°C, Al2O3 2050°C, CaO 2570°C) in the gangue to form slag with good fluidity, thereby achieving the purpose of separating slag and iron and removing harmful impurities.
According to the different compositions of gangue and fuel ash in the ore, as well as the type and quality requirements of smelting pig iron, the fluxes used in the blast furnace include alkaline limestone (CaCO3), dolomite [(Ca, Mg)CO3]; acidic silica (SiO2). There are also forsterite and serpentine (3MgO·2SiO2·2H2O) that serve as MgO-containing and acidic fluxes, as well as fluorite (CaF2) for furnace cleaning. In recent years, converter steel slag has also been used to replace limestone and dolomite as a flux to adjust the alkalinity of the slag.
With the advancement of fine material technology and the widespread promotion of the charge structure of high alkalinity sinter plus acid materials (natural lump ore, pellets and acidic sinter), the possibility of direct addition of flux to the blast furnace is getting smaller and smaller. Now a small number of people enter the blast furnace. The flux of the furnace is only used as a means to stabilize the furnace conditions and adjust the alkalinity of the slag.
The requirements for flux directly put into the furnace are: 1. The useful flux must be high. 2. The lower the content of harmful impurities S and P, the better. 3. The particle size should be uniform.
7. What fuels are used in blast furnaces? What are the advantages and disadvantages of each?
Answer: 1. Charcoal. Charcoal is made by dry distillation of wood at a satisfactory temperature. It has high fixed carbon content, low ash content, almost no sulfur, and high porosity. However, charcoal has poor mechanical strength and high price, so it has been screened out as a blast furnace fuel.
2. Anthracite (or white coal). Its chemical composition can basically meet the requirements of ironmaking; it has good low-temperature strength and can be transported over long distances; but its porosity is very low and its thermal stability is poor. It breaks into powder after being heated in the blast furnace, and its sulfur content is generally high. . It is no longer used.
3. Coke. It is made by carbonization of coal at high temperature (900℃~1000℃). Its composition can fully meet the requirements of blast furnace ironmaking; its mechanical strength is much higher than that of charcoal; its thermal stability is better than that of white coal; its porosity is not as good as that of charcoal, but it is much larger than that of white coal. Coke is the ideal fuel for modern blast furnaces and is also the main fuel for blast furnaces today.
Fuel for injection. In order to reduce the coke ratio, countries around the world now generally choose to inject part of the fuel from the blast furnace tuyere to replace skate parts . Injection fuels include pulverized coal, heavy oil and natural gas.
4. Type focus. As an alternative fuel, the molding technology of non-caking coal such as anthracite, lean coal, lignite, etc. is currently being studied at home and abroad. According to the production process, it can be divided into two categories: hot press forming and cold press forming. (The use of molded coke in blast furnaces is still in the experimental stage of smelting).
8. What is the role of coke in blast furnace production?
Answer: 1. Supply most of the heat required for blast furnace smelting;
2. Supply the reducing agent required for blast furnace smelting;
3. Coke is the skeleton of the blast furnace material column;
4. The carbon source for carburization during the formation of pig iron.
9. What are the requirements for coke quality during the blast furnace smelting process?
Answer: In order to ensure the smoothness of the blast furnace smelting process and obtain good production targets, coke quality must meet the following requirements:
1. The fixed carbon content should be high and the ash content should be low. The general experience is that when the coke ash content is increased by 1%, the coke ratio increases by 2% and the output value decreases by 3%.
2. Contain less S and P impurities. More than 80% of S in the blast furnace smelting process comes from coke. Therefore, reducing the S content in coke is of great significance to reducing the S content in pig iron. Coke contains less P and has no significant impact on the quality of pig iron. The P content of coke in my country is generally less than 0.05%.
3. The mechanical strength of coke should be better. Coke acts as a skeleton to support the material column in the lower high-temperature zone of the blast furnace. With the huge pressure of the upper material column, if the mechanical strength of the coke is not high, it will form a lot of broken coke, worsen the air permeability of the hearth, damage the operation of the blast furnace, and in severe cases, normal production cannot be carried out. . In addition, coke with poor strength produces a lot of powder during transportation, causing losses.
4. The particle size should be uniform and the powder should be small. Aerodynamics research shows that bulk materials with uneven particle sizes have the smallest open space and poor air permeability. Bulk materials with uniform particle size have large open space and small gas resistance. Therefore, in order to improve the permeability of the blast furnace and ensure reasonable gas flow and smooth operation of the blast furnace, not only the coke particle size is required, but also the particle size is uniform and there is less powder. Generally, blast furnaces use large pieces of coke of 40 to 60 mm.
5. The moisture should be stable. The moisture in coke enters during wet coke quenching, generally reaching 2% to 6%. Moisture has no effect on blast furnace smelting, but because coke is fed into the furnace by weight, moisture fluctuations will inevitably cause fluctuations in the amount of dry coke, which will then cause fluctuations in furnace conditions.
6. Coke should have low reactivity and strong alkali resistance. Coke reactivity refers to the ability of coke to react with CO2 at high temperatures to form CO (C coke + CO2 = 2CO). During the reaction of coke with CO2, the pore walls inside the coke will become thinner, thereby reducing the strength of the coke and accelerating the damage of the coke, which will have the following effects on blast furnace smelting: the direct recovery of iron develops, the use of gas deteriorates, and the coke ratio increases; At the same time, the coke powder produced by coke damage worsens the air permeability of the blast furnace column and affects the smooth operation of the blast furnace. The methods to reduce the reactivity of coke are: appropriately use low and medium evaporation coal in coking coal blending; increase the final temperature of coking; operate the furnace in a stuffy furnace; use dry quenching; reduce the ash content of coke, etc.
Coke’s alkali resistance is the ability of coke to resist the effects of alkali, sodium and their salts in the blast furnace. Potassium and sodium are catalysts for the C+CO2=2CO reaction, and can also react with coke to produce C8K, C36K, etc. Therefore, alkali corrosion will reduce the strength of coke and cause damage to blast furnace production. Methods to improve the alkali resistance of coke include: appropriately using low-density, weakly cohesive gas coal in coal blending, and taking measures to reduce the reactivity of coke.
10. What is fine material? What are its policies?
Answer: Concentrate refers to measures taken to optimize the quality of the raw fuel before entering the blast furnace to become charge that meets the requirements of intensive smelting in the blast furnace. Excellent technical and economic indicators and higher economic benefits can be obtained after using concentrate in blast furnace smelting. There are many ideas for doing a good job in fine material operations, such as “high, cooked, clean, small, uniform, and stable”, which means that the grade of the furnace should be higher, sinter and pellets should be used more often, and powders smaller than 5mm should be screened out and controlled. The upper limit of the ore entering the furnace ensures uniform particle size and stable chemical composition. A more comprehensive formulation is “the slag volume is less than 300kg/t; the composition is stable and the particle size is uniform; it has excellent metallurgical properties; and the charge structure is reasonable.”
11. What is iron-containing ore powder sintering?
Answer: Sintering in a broad sense is the process of consolidating bulk powder into blocks by solid combined forces at a certain temperature. Sintering in the field of ironmaking refers to the process of consolidating iron ore powder and other iron-containing materials through the melt into artificial lumps with excellent metallurgical properties, and its product is sinter.
12. What is the significance of the sintering production of iron ore powder?
Answer: First of all, sintering production is an artificial rich ore production process. With this block making method, many poor ores existing in nature can be transformed into high-quality artificial rich ores that can meet the requirements of blast furnace smelting through mineral processing and sintering, and then used Natural resources are fully utilized. Secondly, some waste materials from other steel and chemical industries such as rich ore powder, blast furnace dust, converter dust, steel rolling scale, iron filings, sulfuric acid slag, etc. can be used in the sintering process to effectively utilize these waste materials and turn “waste” into Treasure, turn “harm” into benefit.
Compared with natural ore, sinter produced through sintering has suitable particle size, good recovery and reflow properties, stable composition, and excellent slagging performance, ensuring the smooth flow of blast furnace production.
Ultimately, the sintering process can remove 80% to 90% of S and some F, As and other harmful impurities, greatly reducing the desulfurization task during the blast furnace smelting process and improving the quality of pig iron.
13. What fluxes are used in sinter production? What are the requirements for them?
Answer: Fluxes used in sinter production include: limestone, quicklime, slaked lime, dolomite, light burnt dolomite, serpentine, etc. The general requirements for them are high useful ingredients, low harmful ingredients, and suitable particle size (1 to 3 mm).
14. What are the quality targets for sinter?
Answer: 1. Sinter grade. It refers to the iron content of sinter, generally referring to the iron content after deducting the alkaline oxide content in sinter.
2. Sinter mineral alkalinity.
3. Restorability of sinter. Sinter drum index refers to the index of sinter’s resistance to wear and peeling and impact resistance at room temperature.
4. Sinter drop strength: an indicator of the impact resistance of sinter.
5. Thermal recovery powdering rate of sinter ore. It refers to the mechanical strength of sinter under recovery conditions of 400~600℃.
6. Soft melting function.
15. What are pellets? What are its characteristics?
Answer: Pellets are fine concentrate powder (-200 mesh, that is, the mineral powder with a particle size of 0.074mm accounts for more than 80%, and the specific surface area is more than 1500cm2/g). After mixing with a small amount of additives, water is added to the pellets, relying on capillary The force and the mechanical force of rotation form a green ball with a diameter of 8 to 16 mm, which is then dried on the roasting equipment. The crystal bridge bonds of Fe2O3 recrystallized in a high-temperature oxidizing atmosphere are consolidated into a spherical shape with high grade, good strength and uniform particle size. Ironmaking materials. It has the following features:
1. Produced by using high-grade concentrate powder, the grade of acidic oxidation pellets can reach 68%, and SiO2 is between 1% and 2%;
2. There are no large pores like sinter, and all pores exist in the form of micropores, which is conducive to the recovery of the gas-solid phase;
3. The FeO content is low (usually around 1%), the mineral deposits are mainly Fe2O3, and the recovery is good;
4. Good cold strength, each ball can withstand 2800~3600N (300~400kg·f) pressure, uniform particle size, and good transportation performance;
5. The natural pile angle is as small as 24° to 27°, and the material in the blast furnace is easy to roll toward the center of the furnace;
6. The sulfur content is very low, because roasting in a strong oxidizing atmosphere can remove 95 to 99% of the sulfur in the mass;
7. It has the defect of recovery expansion, and abnormal expansion will occur under the catalytic effect of K2O, Na2O, etc.;
8. The reflow performance of acidic oxidized pellets is poor, that is, its softening starting temperature is low and the reflow temperature range is narrow. However, it is still better than natural rich lump ores and is still suitable for high-alkalinity sinter in the charge structure. Best ingredients.

16. How does concentrate powder become 8~16mm green balls?
Answer: The balling of concentrate powder is caused by its characteristics of dripping water into balls under natural conditions and its ability to be densely packed under the action of mechanical force. The process of forming balls on the balling machine is carried out in the following three stages:
Cue ball composition. The material loaded into the pelletizing tray generally has a moisture content of 8% to 10% and is in a relatively loose state. Each mineral powder particle is covered by adsorbed water and film water, and capillary water only exists at the contact points between the particles. The other spaces are filled with air, and the contact between particles is not tight, so the film water cannot be effective. In addition, because the amount of capillary water is too small, the capillary pores are too large, the capillary pressure is small, and the binding force between particles is weak, it cannot form a ball. For this reason, uneven dripping of moisture must be carried out, and through the effect of mechanical force, part of the The particles are in closer contact, forming finer capillary pores and greater capillary pressure, which pull the surrounding mineral particles toward the center of the water droplet to form a tighter particle aggregate, and then form a cue ball.
The cue ball grows. The cue ball continues to roll on the ball-making disc, and the cue ball is further compressed, and the internal capillary tube becomes thinner. The excess capillary water is squeezed to the surface of the cue ball. In this way, the over-wet cue ball uses the capillary force to absorb the surrounding mineral powder with less water content. Glue them together to make the cue ball grow. When the cue ball reaches the required particle size, additional water spray must be applied to the surface of the cue ball. However, the amount of water spray should be moderate. If it is too large, the particles will be completely saturated with water and produce gravity water, which will cause the particles to break out of contact and break the cue ball, which is extremely ineffective in making balls.
Green ball compaction. Raw balls that are only held together by capillary force are not very strong. In order to improve the strength of the green balls, it is necessary to stop spraying water to make the green balls roll on the ball-making disk, squeeze out all the capillary water inside the green balls, and be absorbed by the surrounding mineral powder; at the same time, the mineral powder particles in the green balls are oscillated Place it more tightly so that the film water layers may contact each other and form

The hydration film shared by many particles strengthens the binding force, thereby greatly improving the strength of the green balls. When the green balls reach a certain particle size and density, they will be automatically thrown out of the ball-making disc due to the centrifugal force of the ball-making disc.
The green balls coming out of the pelletizing machine are screened with a porcelain roller screen to remove those with particle sizes larger than 16mm and 8mm. The compressive strength of the green balls should reach 15~20N/ball, and the drop strength (a single green ball falls from a height of 0.5m to the steel plate Repeatedly falling until the green ball is damaged and stopped (the number of times) is not less than 4 times. If the above two indicators are met, the green ball is qualified.
17. What are the main pellet roasting methods currently available?
Answer: There are currently three methods for roasting pellets at home and abroad: shaft furnace roasting; belt roasting; chain grate machine-rotary kiln roasting.
The shaft furnace was the earliest pellet roasting equipment. Modern shaft furnaces have a drying bed at the top and a wind guide wall in the center of the roasting chamber. The high-temperature gas generated in the combustion chamber is sprayed into the roasting chamber from both sides and moves toward the top. The green balls are evenly spread on the drying bed from the top and are dried and preheated by the rising hot gas. Then they slide into the roasting chamber along the slope of the drying bed for roasting and solidification. After exiting the roasting chamber, it encounters the cold air blowing in from the bottom and is cooled. Finally, the ore discharge machine is used to discharge the shaft furnace.
The structure of the shaft furnace is simple and has no special requirements for raw materials. The disadvantage is that the output value of a single furnace is low and it is only suitable for roasting magnetic powder pellets. Because the gas flow in the shaft furnace is difficult to control, uneven roasting results in uneven pellet quality.
Belt roasting machine is currently the most widely used roasting method. Features of belt roasting:

1. Use bottom material and edge material to improve the roasting quality, while protecting the trolley and extending its life;

2. Using a combination of blast and exhaust drying to improve the drying process and advance the pellets. The quality;

3. Air blast cooling pellets, direct use of the hot air obtained in the cooling zone to assist fuel combustion in the roasting zone, and use in the drying zone; only exhaust gas with low temperature and high moisture content is discharged into the chimney;

5. Suitable for various applications Roasting of raw material (hematite flotation concentrate, magnetite magnetic separation concentrate or mixed powder) pellets.
18. The difference between steel and iron
Iron is extremely abundant in nature, accounting for 5% of the element content in the earth’s crust, ranking fourth among the earth’s substances. Iron is very active and easily combined with other substances. It is customary to refer to steel as a general term for steel and iron. There is a difference between steel and iron. The so-called steel is mainly composed of two elements, namely iron and carbon. Generally, carbon and the element iron form a compound, which is called iron-carbon alloy. The carbon content has a great influence on the properties of steel. When the carbon content is increased to a certain level, it will cause qualitative changes. A substance composed of iron atoms is called pure iron. Pure iron has very few impurities. The carbon content is the primary criterion for differentiating steel. The carbon content of pig iron is greater than 2.0%; the carbon content of steel is less than 2.0%. Pig iron contains high carbon content, is hard and brittle, and has almost no plasticity. Steel not only has good plasticity, but also steel products have excellent physical and chemical properties such as high strength, good toughness, high temperature resistance, corrosion resistance, easy processing, impact resistance, and easy refining, so they are widely used.
19. The difference between white iron and gray iron
Carbon (C) has two forms in iron: graphite and iron carbide. Graphite is a form of carbon. Graphite is flake carbon, smooth and soft, like coal dust, very unstable, dispersed in iron, splitting the iron matrix, as if there are many strip-shaped holes in the iron, destroying the solidity of the iron. This kind of carbon that exists in iron in the form of graphite dyes iron gray, so it is called gray iron. Gray iron contains soft graphite and is easily cut by machine tools when used as machine parts. Graphite has a “smooth” effect in liquid molten iron, which improves the fluidity of the molten iron and is suitable for pouring castings, so gray iron is also called cast iron.
Iron carbide is white, hard and brittle. When there is too much iron carbide, the iron becomes like stone. Loss of plasticity. Parts made of this kind of iron are difficult to cut, so white iron is mainly used to make steel, so it is also called steel making.
Graphite and iron carbide can also transform into each other. There are two decisive conditions: first, the chemical composition of the molten iron. If the molten iron contains high silicon content, it can promote the decomposition of iron carbide and turn into graphite, so the silicon content of cast iron is always high; Another factor is the speed at which the molten iron solidifies. When the composition is suitable, if it is cooled too quickly, the iron carbide in the molten iron will not have time to decompose and it will become white iron. If it is cooled slowly, the iron carbide will decompose into graphite and iron, thus turning into 65kg gray iron sand casting parts.
20. Smelting principles of blast furnace ironmaking
Blast furnace production is carried out continuously. A generation of blast furnace (from opening to overhaul and shutdown is a generation) can continue to produce for several years to more than ten years. During production, iron ore, coke, and flux are continuously loaded from the top of the furnace (generally the top of the furnace is composed of materials and hoppers, and modern blast furnaces are bell valve tops and bellless furnace tops), and are blown from the tuyere at the lower part of the blast furnace. Inject hot air and spray fuel such as oil, coal or natural gas. The iron ore loaded into the blast furnace is mainly a compound of iron and oxygen. At high temperatures, the coke neutralizes the carbon in the injection material and the carbon generated by combustion takes out the oxygen in the iron ore and obtains iron. This process is called recovery. The iron ore produces pig iron through the recovery reaction, and the molten iron is released from the tap hole. The gangue, coke and ash in the injection material in the iron ore combine with fluxes such as limestone in the furnace to form slag, which is discharged from the tap hole and the slag hole respectively. The gas is exported from the top of the furnace, and after dust removal, it is used as industrial gas. Modern blast furnaces can also use the high pressure at the top of the furnace to generate electricity using part of the exported gas.
The recovery gas in the blast furnace is generated by the combustion of fuel in front of the tuyere. This process generates two major flow flows: one is the rising hot gas flow, and the other is the falling furnace material flow (iron ore, coke, flux, etc.). All reactions in the blast furnace occur in the mutual movement and mutual interaction of gas and charge. It includes the heating, transpiration, evaporation and decomposition of the charge; the recovery of iron and other elements; the melting, slagging and desulfurization of non-iron oxides in the furnace; the carburization of iron and the formation of pig iron; the relationship between the charge and gas The heat exchange, etc., is the sum of a series of physical and chemical reaction processes.
21. What is blast furnace gas?
Answer: The high-pressure blower (axial flow fan) blows air, and enters the blast furnace after being heated by the hot air furnace. This hot air and coke support combustion, producing carbon dioxide and carbon dioxide. The carbon dioxide reacts with the hot coke and recovers during the rising process. The iron element in the iron ore is removed and turned into pig iron. This is the chemical process of iron making. The molten iron is temporarily stored at the bottom of the furnace and is released regularly for direct steelmaking or ingot casting. At this time, there is still a lot of excess gas in the blast furnace. This mixed gas is “blast furnace gas”.
This kind of flammable gas is a low calorific value gas fuel that can be used for self-use gas of metallurgical manufacturers, such as heating hot-rolled cnc machining 1215 steel ingots, preheating ladles, etc. It can also be provided for civilian use. If coke oven gas can be added, it is called “mixed gas”, which increases the calorific value.
22. Composition of blast furnace gas
Answer: Blast furnace gas is a by-product produced during the ironmaking process. The main components are: CO, C02, N2, H2, CH4, etc. Among them, the combustible component CO content accounts for about 25%, and the content of H2 and CH4 is very small. CO2, N2 The content accounts for 15% and 55% respectively, and the calorific value is only about 3500KJ/m3.
The composition and calorific value of blast furnace gas are related to the fuel used in the blast furnace, the type of pig iron smelted and the smelting process. Modern iron-making production generally adopts production processes with large volume, high air temperature, high smelting intensity and high amount of pulverized coal injection. The use of these advanced production processes improves labor productivity and reduces energy consumption, but the calorific value of the blast furnace gas produced is lower, making it more difficult to use. The CO2 and N2 in blast furnace gas neither participate in the heat generated by combustion nor can they support combustion. On the contrary, they also absorb a lot of heat generated during the combustion process, resulting in a low theoretical combustion temperature of blast furnace gas. The ignition point of blast furnace gas is not high, and there seems to be no obstacle to ignition. However, in the actual combustion process, affected by various factors, the temperature of the mixed gas must be much greater than the ignition point to ensure the stability of combustion. The theoretical combustion temperature of blast furnace gas is low, and a large amount of blast furnace gas is added to the combustion, resulting in a very slow heating rate of the mixed gas, low temperature, and poor combustion stability.
Another condition for the occurrence of an ignition reaction is that effective collisions can occur between gas molecules, that is, collisions between molecules that have sufficient energy to produce oxidation reactions. The presence of a large amount of C02 and N2 reduces the effective collision between molecules. The probability of collision is manifested in microscopically slow burning speed and unstable burning.
There is a lot of CO2 and N2 in the blast furnace gas, which does not participate in chemical reactions at all during the combustion process. Almost the same amount is transferred to the flue gas generated by the combustion. The amount of flue gas generated by burning blast furnace gas is much more than that of burning coal.
23. Conventional gas classification
Blast furnace gas: CO, CO2, N2, ———————–Ironmaking furnace exhaust gas
Steelmaking brown flue gas: Fe2O3,CO———————steelmaking furnace exhaust gas
, natural gas: CH4
Coke oven gas: H2, CH4, a small amount of CO, CO2, C2H4, N2 – tail gas from the carbonization of coal
Cracked gas: ethylene, butadiene, etc.
Table of composition and calorific value of several common gas generators and furnace gases

Coal Type│Project

Jiayang coking coal

Datong bituminous coal

Fushun gas coal

Hebi poor coal

Tongchuan poor coal

Yangquan anthracite

Yingcheng Changyan Coal

Huainan gas coal

Jiaozuo anthracite coal

Hegang Gas Coal

Xishan anthracite

Gas volume composition %

24. Melting recovery method to produce iron
melted yet
The iron ore method refers to a method of recovering iron ore in a high-temperature molten state without using a blast furnace. The product is liquid molten iron with a composition similar to that of the blast furnace molten iron. The purpose of developing the smelting recovery method is to replace or compensate for the blast furnace method of ironmaking. Compared with the blast furnace method, the melting method has the following characteristics:
(l) Coal is used as fuel instead of coke, so no coke ovens can be built to reduce pollution. ​
(2) The same massive iron-containing raw materials as those used in blast furnaces can be used or mineral powder can be used directly as raw materials. If mineral powder is used as raw material, there is no need to build a sintering plant or pelletizing plant.
(3) All oxygen is used instead of air, which consumes a lot of oxygen.
(4) Molten iron with basically the same composition and temperature as the molten iron in the blast furnace can be produced for converter steelmaking.
(5) In addition to producing molten iron, a large amount of high calorific value gas is also produced.
There are many melt recovery methods in the world, among which only the Corex method is relatively mature and has formed an industrial production scale, while other methods are still in the process of development and industrialization. The melt recovery method has not been widely developed in our country and is now in the stage of laboratory experiments and semi-industrial experiments.

25. Types of iron-making products
Iron-making products can be divided into pig iron, direct reconstituted iron, smelting reconstituted iron, iron-making by-products, ductile iron and cast iron pipes according to their production methods, uses and types.

26. Start the direct recovery method of iron deficiency
It refers to the iron-making production process that restores iron ore into sponge iron below the melting temperature. The product is directly restored iron (DRI), also known as sponge iron.
This product has not been melted, but still maintains the shape of the ore. It is named after the recovery of oxygen loss and the formation of many pores, which look like a sponge when observed under a microscope. Sponge iron is characterized by low carbon content (<1%) and preservation of gangue in the ore. These characteristics make it unsuitable for large-scale use in converter steelmaking and is only suitable for replacing scrap steel as raw material for electric furnace steelmaking.
The direct restoration method is divided into two categories: gas-based method and coal-based method. The former uses natural gas to produce H2 and CO gas through cracking, which is used as a reducing agent to restore iron oxide in iron ore into sponge iron in a shaft furnace, tank furnace or fluidized bed. There are mainly Midrex method, HYL III method, FIOR method, etc. The latter uses coal as a restoring agent to restore iron oxide in iron ore in equipment such as rotary kilns and tunnel kilns. The main ones are the FASMET method and so on.
The advantages of direct recovery include:
​ (1) The process is short, directly recovering iron and adding electric furnace to make steel;
(2) No coke is required, and it is not affected by the shortage of coking coal;
(3) Less pollution, eliminating coke oven, sintering and other processes;
(4) The content of harmful impurities such as sulfur and phosphorus and non-ferrous metals in sponge iron is low, which is beneficial to the smelting of high-quality steel in electric furnaces. The shortcomings of the direct restoration method are:
(l) The requirements for raw materials are relatively high: the gas base must contain natural gas; the coal base must use coal with a high ash melting point and good reactivity;
(2) The price of sponge iron is generally higher than that of scrap steel.
The direct restoration method has a history of hundreds of years of development, but it was not until the 1960s that it made a major breakthrough. In the 1990s, its production technology became increasingly mature and achieved rapid development. The primary reasons are:
(1) Many developments and applications of natural gas, especially the use of high-efficiency natural gas conversion methods, have provided practical recovery gas, giving the direct recovery method new impetus with rich sources and relatively cheap prices.
(2) The rapid development of electric furnace steelmaking and the demand for smelting a variety of high-quality steels have greatly expanded the demand for sponge iron.
(3) The improvement of mineral processing technology can provide a large number of high-grade concentrates. The amount of gangue in the ore has been reduced to a level that does not need to be removed during the recovery and smelting process, thus simplifying the direct recovery technology.
At that time, more than 90% of the world’s directly recovered iron was produced using the gas-based method.
my country’s natural gas is mainly sold directly to the chemical industry and civil use, and cannot be widely used in the steel industry. Due to the relatively abundant coal reserves in my country, the direct coal-based restoration method has formed a certain production scale in Tianjin, Liaoning, Jilin, Shandong and other places since the 1990s.
27. Non-steelmaking pig iron
Non-steelmaking pig iron includes:
(l) Casting pig iron has a higher silicon content than steelmaking pig iron. Generally, the silicon content is greater than 1.25%. There are many grades and it is mainly used in casting production.
Casting pig iron can be divided into pig iron for ductile iron and pig iron for ordinary casting (pig iron for other castings). Pig iron for ductile iron and pig iron for ordinary casting