I. Definition of coke
Bituminous coal is heated to 950-1050°C in the condition of being isolated from air, and finally made into coke after drying, pyrolysis, melting, bonding, solidification and shrinkage. This process is called high-temperature coking. The coke obtained from high-temperature coking is used in blast furnace smelting, casting and gasification. The recovered and purified coke oven gas produced in the coking process is not only a high calorific value fuel but also an important organic synthesis industrial raw material.
Metallurgical coke is a collective term for blast furnace coke, foundry coke, ferroalloy coke and non-ferrous metal smelting coke. Since more than 90% of metallurgical coke is used for blast furnace ironmaking, blast furnace coke is often referred to as metallurgical coke.
Foundry coke is a special coke with iron melting iron. Foundry coke is the main fuel for molten iron in chemical melting furnaces. Its role is to melt the charge and superheat the molten iron and support the column to maintain its good air permeability. Therefore, the casting coke should have the characteristics of large block size, low reactivity, low porosity, sufficient impact crushing strength, ash content, and low score.
Second, the distribution of coke
From the perspective of the distribution of coke production in China, the regional distribution of coking enterprises in China is uneven, mainly distributed in North China, East China and Northeast China.
Third, coke use
Coke is mainly used in blast furnace ironmaking and blast furnace smelting of non-ferrous metals such as copper, lead, zinc, Titanium, Niobium , and mercury, and acts as a reducing agent, heat-generating agent, and material column skeleton. The use of coke instead of charcoal in ironmaking blast furnaces laid the foundation for the modernization of modern blast furnaces and is a major milestone in the history of metallurgy. In order to achieve a good technical and economical index for blast furnace operation, the coke (metallurgical coke) used for smelting must have appropriate chemical and physical properties, including the thermal properties during the smelting process. In addition to the large amount of coke used in iron and non-ferrous metal smelting (metallurgical coke), but also used in casting, chemical, calcium carbide and iron alloys, their quality requirements are different. Such as casting coke, generally require large size, low porosity, high carbon and low * fixed points; chemical gasification coke, strict requirements on the strength, but requires good reactivity, high ash melting point; carbide production coke requirements Try to increase the fixed carbon content.
Fourth, the physical properties of coke
Coke physical properties include coke screening composition, coke bulk density, coke density, coke apparent relative density, coke porosity, coke specific heat capacity, coke thermal conductivity, coke thermal stress, coke ignition temperature, coke thermal expansion coefficient, coke shrinkage Rate, coke resistivity and coke permeability.
The physical properties of coke are closely related to its room temperature mechanical strength and thermal strength and chemical properties. The main physical properties of coke are as follows:
The true density is 1.8-1.95g/cm3;
The apparent density is 0.88-1.08g/cm3;
Porosity is 35-55%;
The bulk density is 400-500kg/ m3;
The average specific heat capacity is 0.808kj/(kgk) (100°C), 1.465kj/(kgk) (1000°C);
The thermal conductivity is 2.64kj/(mhk) (normal temperature), 6.91kg/(mhk) (900°C);
The ignition temperature (in the air) is 450-650°C;
Dry ash-free low calorific value of 30-32KJ/g;
The specific surface area is 0.6-0.8 m2/g.
Fifth, coke reactivity and reaction intensity
The reactivity of coke reactivity with carbon dioxide, oxygen and water vapor, etc. The strength after coke reaction refers to the ability of the coke after reaction to resist cracking and wear under the re-mechanical and thermal stress. In the process of blast furnace ironmaking, cast iron and fixed bed gasification, coke reacts with carbon dioxide, oxygen and water vapor. Because the reaction of coke with oxygen and water vapor has a similar reaction with carbon dioxide, most countries use the reaction characteristics between coke and carbon dioxide to assess coke reactivity.
China Standard (GB/T4000-1996) specifies the coke reactivity and post-reaction strength test method. The method is to make coke not react with carbon dioxide at high temperature, and then measure the coke weight loss rate and its mechanical strength after the reaction. The reproducibility of coke reactive CRI and post-reaction strength CSR must not exceed the following values:
CRIr≤2.4%
CSR: ≤3.2%
The test results of coke reactivity and post-reaction strength are all arithmetic averages of parallel test results.
Six, coke quality indicators
Coke is a solid product produced by high-temperature dry distillation. The main component is carbon, which is a spore structure (or porous spore body) with cracks and irregularities. The number of cracks directly affects the strength and crushing strength of coke, and its index is generally measured by the degree of cracking (referring to the length of cracks per unit volume of coke). Measure the index of the structure of the sporangium, which is mainly expressed by the porosity (only the percentage of the volume of coke pores in the total volume), which affects the reactivity and strength of the coke. Different uses of coke, the porosity of the requirements of different indicators, the general metallurgical coke porosity requirements of 40 to 45%, casting coke requirements in 35 to 40%, export coke requirements in 30%. The degree of coke cracking and porosity are directly related to the type of coal used for coking. For example, coal-based coke has many cracks, high porosity, and low strength; coke cracks derived from coke as a base coal Less, low porosity, high strength. The strength of coke is usually expressed in terms of crushing strength and abrasion resistance. The crushing strength of coke refers to the ability of coke to resist cracking or imperfection along the structure by external impact, and is expressed by M40 value; the abrasion resistance of coke is that coke can resist external friction without producing surface. The ability of the glass to form crumbs or powder, expressed as M10 value. The degree of cracking of coke affects the value of its crush strength, M40, and the structure of the coccus of the coke affects the wear resistance strength M10. M40 and M10 values ​​are measured in many ways. Our country uses the German Migon drum test method.
VII. Evaluation of coke quality
1. The * points in coke: * is one of the harmful impurities in pig iron smelting, which reduces the quality of pig iron. The content of the * in the steel-making pig iron is more than 0.07% that is waste. About 11% of the * brought into the furnace by the blast furnace charge comes from ore; 3.5% comes from limestone; 82.5% comes from coke, so coke is the main source of * in the charge. The level of coke* directly affects the production of blast furnace ironmaking. When the coke* content is greater than 1.6%, *0.1% for each increment, coke usage increases by 1.8%, limestone addition increases by 3.7%, ore addition increases by 0.3%, and blast furnace output decreases by 1.5-2.0%. Less than 1%, the amount of metallurgical coke used in large and medium-sized blast furnaces is less than 0.4-0.7%.
2. Phosphorus in coke: The metallurgical coke used in ironmaking should have a phosphorus content of 0.02-0.03%.
3. Ash in coke: The effect of coke ash on blast furnace smelting is very significant. The ash content of coke increased by 1%, and the amount of coke used increased by 2-2.5%. Therefore, it is necessary to reduce the ash content of coke.
4, volatiles in coke: according to the volatile content of coke can determine coke maturity. If the volatile content is greater than 1.5%, it means raw coke. If the volatile content is less than 0.5-0.7%, it means that the fire has occurred. Generally, the mature metallurgical coke volatilizes into about 1%.
5, coke moisture: Moisture fluctuations will make coke measurement inaccurate, causing furnace conditions fluctuations. In addition, the increase in coke moisture will make M04 high, M10 is low, giving errors in the drum index.
6, the coke screening composition: In the blast furnace smelting coke particle size is also very important. In the past, the coke particle size requirements in China were: coke particle size greater than 40 mm for coke ovens (1300-2000 m2) and coke particle size greater than 25 mm for medium and small furnaces. However, some steel mills' experiments show that the coke particle size is 40-25 mm. Coke larger than 80 mm is to be sized so that its particle size range does not change much. In this way, the coke has a uniform block size, large gaps, low resistance, and good furnace conditions.
Bituminous coal is heated to 950-1050°C in the condition of being isolated from air, and finally made into coke after drying, pyrolysis, melting, bonding, solidification and shrinkage. This process is called high-temperature coking. The coke obtained from high-temperature coking is used in blast furnace smelting, casting and gasification. The recovered and purified coke oven gas produced in the coking process is not only a high calorific value fuel but also an important organic synthesis industrial raw material.
Metallurgical coke is a collective term for blast furnace coke, foundry coke, ferroalloy coke and non-ferrous metal smelting coke. Since more than 90% of metallurgical coke is used for blast furnace ironmaking, blast furnace coke is often referred to as metallurgical coke.
Foundry coke is a special coke with iron melting iron. Foundry coke is the main fuel for molten iron in chemical melting furnaces. Its role is to melt the charge and superheat the molten iron and support the column to maintain its good air permeability. Therefore, the casting coke should have the characteristics of large block size, low reactivity, low porosity, sufficient impact crushing strength, ash content, and low score.
Second, the distribution of coke
From the perspective of the distribution of coke production in China, the regional distribution of coking enterprises in China is uneven, mainly distributed in North China, East China and Northeast China.
Third, coke use
Coke is mainly used in blast furnace ironmaking and blast furnace smelting of non-ferrous metals such as copper, lead, zinc, Titanium, Niobium , and mercury, and acts as a reducing agent, heat-generating agent, and material column skeleton. The use of coke instead of charcoal in ironmaking blast furnaces laid the foundation for the modernization of modern blast furnaces and is a major milestone in the history of metallurgy. In order to achieve a good technical and economical index for blast furnace operation, the coke (metallurgical coke) used for smelting must have appropriate chemical and physical properties, including the thermal properties during the smelting process. In addition to the large amount of coke used in iron and non-ferrous metal smelting (metallurgical coke), but also used in casting, chemical, calcium carbide and iron alloys, their quality requirements are different. Such as casting coke, generally require large size, low porosity, high carbon and low * fixed points; chemical gasification coke, strict requirements on the strength, but requires good reactivity, high ash melting point; carbide production coke requirements Try to increase the fixed carbon content.
Fourth, the physical properties of coke
Coke physical properties include coke screening composition, coke bulk density, coke density, coke apparent relative density, coke porosity, coke specific heat capacity, coke thermal conductivity, coke thermal stress, coke ignition temperature, coke thermal expansion coefficient, coke shrinkage Rate, coke resistivity and coke permeability.
The physical properties of coke are closely related to its room temperature mechanical strength and thermal strength and chemical properties. The main physical properties of coke are as follows:
The true density is 1.8-1.95g/cm3;
The apparent density is 0.88-1.08g/cm3;
Porosity is 35-55%;
The bulk density is 400-500kg/ m3;
The average specific heat capacity is 0.808kj/(kgk) (100°C), 1.465kj/(kgk) (1000°C);
The thermal conductivity is 2.64kj/(mhk) (normal temperature), 6.91kg/(mhk) (900°C);
The ignition temperature (in the air) is 450-650°C;
Dry ash-free low calorific value of 30-32KJ/g;
The specific surface area is 0.6-0.8 m2/g.
Fifth, coke reactivity and reaction intensity
The reactivity of coke reactivity with carbon dioxide, oxygen and water vapor, etc. The strength after coke reaction refers to the ability of the coke after reaction to resist cracking and wear under the re-mechanical and thermal stress. In the process of blast furnace ironmaking, cast iron and fixed bed gasification, coke reacts with carbon dioxide, oxygen and water vapor. Because the reaction of coke with oxygen and water vapor has a similar reaction with carbon dioxide, most countries use the reaction characteristics between coke and carbon dioxide to assess coke reactivity.
China Standard (GB/T4000-1996) specifies the coke reactivity and post-reaction strength test method. The method is to make coke not react with carbon dioxide at high temperature, and then measure the coke weight loss rate and its mechanical strength after the reaction. The reproducibility of coke reactive CRI and post-reaction strength CSR must not exceed the following values:
CRIr≤2.4%
CSR: ≤3.2%
The test results of coke reactivity and post-reaction strength are all arithmetic averages of parallel test results.
Six, coke quality indicators
Coke is a solid product produced by high-temperature dry distillation. The main component is carbon, which is a spore structure (or porous spore body) with cracks and irregularities. The number of cracks directly affects the strength and crushing strength of coke, and its index is generally measured by the degree of cracking (referring to the length of cracks per unit volume of coke). Measure the index of the structure of the sporangium, which is mainly expressed by the porosity (only the percentage of the volume of coke pores in the total volume), which affects the reactivity and strength of the coke. Different uses of coke, the porosity of the requirements of different indicators, the general metallurgical coke porosity requirements of 40 to 45%, casting coke requirements in 35 to 40%, export coke requirements in 30%. The degree of coke cracking and porosity are directly related to the type of coal used for coking. For example, coal-based coke has many cracks, high porosity, and low strength; coke cracks derived from coke as a base coal Less, low porosity, high strength. The strength of coke is usually expressed in terms of crushing strength and abrasion resistance. The crushing strength of coke refers to the ability of coke to resist cracking or imperfection along the structure by external impact, and is expressed by M40 value; the abrasion resistance of coke is that coke can resist external friction without producing surface. The ability of the glass to form crumbs or powder, expressed as M10 value. The degree of cracking of coke affects the value of its crush strength, M40, and the structure of the coccus of the coke affects the wear resistance strength M10. M40 and M10 values ​​are measured in many ways. Our country uses the German Migon drum test method.
VII. Evaluation of coke quality
1. The * points in coke: * is one of the harmful impurities in pig iron smelting, which reduces the quality of pig iron. The content of the * in the steel-making pig iron is more than 0.07% that is waste. About 11% of the * brought into the furnace by the blast furnace charge comes from ore; 3.5% comes from limestone; 82.5% comes from coke, so coke is the main source of * in the charge. The level of coke* directly affects the production of blast furnace ironmaking. When the coke* content is greater than 1.6%, *0.1% for each increment, coke usage increases by 1.8%, limestone addition increases by 3.7%, ore addition increases by 0.3%, and blast furnace output decreases by 1.5-2.0%. Less than 1%, the amount of metallurgical coke used in large and medium-sized blast furnaces is less than 0.4-0.7%.
2. Phosphorus in coke: The metallurgical coke used in ironmaking should have a phosphorus content of 0.02-0.03%.
3. Ash in coke: The effect of coke ash on blast furnace smelting is very significant. The ash content of coke increased by 1%, and the amount of coke used increased by 2-2.5%. Therefore, it is necessary to reduce the ash content of coke.
4, volatiles in coke: according to the volatile content of coke can determine coke maturity. If the volatile content is greater than 1.5%, it means raw coke. If the volatile content is less than 0.5-0.7%, it means that the fire has occurred. Generally, the mature metallurgical coke volatilizes into about 1%.
5, coke moisture: Moisture fluctuations will make coke measurement inaccurate, causing furnace conditions fluctuations. In addition, the increase in coke moisture will make M04 high, M10 is low, giving errors in the drum index.
6, the coke screening composition: In the blast furnace smelting coke particle size is also very important. In the past, the coke particle size requirements in China were: coke particle size greater than 40 mm for coke ovens (1300-2000 m2) and coke particle size greater than 25 mm for medium and small furnaces. However, some steel mills' experiments show that the coke particle size is 40-25 mm. Coke larger than 80 mm is to be sized so that its particle size range does not change much. In this way, the coke has a uniform block size, large gaps, low resistance, and good furnace conditions.
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