The bituminous coal is heated to 950-1050°C under the condition of isolating the air, and finally becomes coke after drying, pyrolysis, melting, bonding, solidification, and shrinking. This process is called high-temperature coking.
Metallurgical coke is a collective term for blast furnace coke, foundry coke, ferroalloy coke and coke for non-ferrous metal smelting. Since more than 90% of metallurgical coke is used for blast furnace iron-making, blast furnace coke is often referred to as metallurgical coke.
Coke is mainly used for blast furnace iron smelting and blast furnace smelting for copper, lead, zinc, titanium, antimony, mercury and other non-ferrous metals, acting as a reducing agent, heating agent and material column skeleton. The use of coke instead of charcoal in iron-making blast furnaces laid the foundation for the large-scale modern blast furnace and was a major milestone in the history of metallurgy. In order to achieve better technical and economic indicators for blast furnace operation, the metallurgical coke used for smelting must have appropriate chemical and physical properties, including the thermal properties during the smelting process. In addition to a large amount of coke used in iron-making and non-ferrous metal smelting (metallurgical coke), it is also used in foundry, chemical industry, calcium carbide and ferroalloys, with different quality requirements. For example, coke for foundry generally requires large particle size, low porosity, high fixed carbon and low sulfur ingredient; coke for chemical gasification does not have strict requirements on strength, but requires good reactivity and high ash melting point; requirements for coke for calcium carbide production Maximize the fixed carbon ingredient.
The ability of coke to react chemically with carbon dioxide, oxygen and water vapor, CRI = (G0—G1)/G0×100% 。 The strength of coke after reaction refers to the ability of the coke to resist chipping and abrasion under the action of mechanical and thermal stress. Coke chemically reacts with carbon dioxide, oxygen and water vapor in the process of blast furnace iron-making, cast iron and fixed bed gasification. Since the reaction of coke with oxygen and water vapor has a similar regularity to that of carbon dioxide, most countries use the characteristics of the reaction between coke and carbon dioxide to assess coke reactivity.
The Chinese standard (GB/T4000-1996) specifies the test method for coke reactivity and strength after reaction. The method is to make the coke react with carbon dioxide at a high temperature, and then measure the weight loss rate and mechanical strength of the coke after the reaction. The repeatability of coke reactive CRI and strength CSR after reaction shall not exceed the following values:
The test results of coke reactivity and strength after reaction are taken as the arithmetic mean of parallel test results.
1. Sulfur in coke: Sulfur is one of the harmful impurities in pig iron smelting, which reduces the quality of pig iron. If the sulfur ingredient steel-making pig iron is greater than 0.07%, it is a waste product. About 11% of the sulfur brought into the furnace comes from ore; 3.5% comes from limestone; 82.5% comes from coke, so coke is the main source of sulfur in the oven. The level of coke sulfur directly affects blast furnace iron-making production. When the sulfur of coke is greater than 1.6%, for every 0.1% increase in sulfur , the amount of coke used increases by 1.8%; the amount of limestone added increases by 3.7%, and the amount of ore added increases by 0.3%. The output of blast furnace is reduced by 1.5-2.0%. The sulfur ingredient of metallurgical coke shall not exceed 1%, and the sulfur of metallurgical coke used in large and medium-sized blast furnaces shall be less than 0.4-0.7%.
2. Phosphorus ingredient in coke: The phosphorus content of metallurgical coke used for iron-making should be below 0.02—0.03%.
3. Ash in coke: The ash ingredient of coke has a significant influence on blast furnace smelting. The ash in coke is increased by 1%, and the amount of coke is increased by 2-2.5%. Therefore, it is very necessary to reduce the ash content of coke.
4. Volatile ingredient in coke: The maturity of coke can be judged according to the volatile ingredient of coke. If the volatile ingredient is greater than 1.5%, it means coke is produced; if the volatile content is less than 0.5—0.7%, it means over fire. Generally, the volatile content of mature metallurgical coke is about 1%.
5. Moisture in coke: Fluctuations of moisture will make the coke measurement inaccurate and cause fluctuations in furnace conditions. In addition, the increase in coke moisture will make M04 higher and M10 lower, which will bring errors to the drum index.
6. Screening composition of coke: The particle size of coke is also important in blast furnace smelting. Our country’s past requirements for coke particle size were: the coke particle size for large coke ovens (1300-2000 square meters) was greater than 30 mm; the coke particle size for medium and small blast furnaces was greater than 20 mm. However, some steel mill tests show that the coke particle size is 30-60 mm. Coke larger than 80 mm should be granulated so that the particle size range does not change much. In this way, the coke lump is uniform, the gap is large, the resistance is small, and the furnace runs well.
Coke is a solid product of high-temperature dry distillation. The main component is carbon. It is a porous structure with cracks and irregularities .
The index to measure the pore structure is mainly expressed by the porosity (referring to the percentage of the coke pore volume to the total volume), which affects the reactivity and strength of the coke. Coke for different purposes has different requirements for porosity index. Generally, the porosity of metallurgical coke is required to be 40-45%, foundry coke is 35-40%, and the export coke is about 30%.
Coke strength is usually expressed by two indicators: crushing strength and abrasion resistance. The crushing strength of coke refers to the ability of coke to resist external impact without breaking along the cracks or defects of the structure. The abrasion resistance of coke refers to the ability of coke to resist external friction without producing surface glass to form debris or powder