Bituminous coal is heated to 950-1050 C under the condition of isolating air. It is finally made into coke through drying, pyrolysis, melting, bonding, solidification and shrinkage. This process is called high temperature coking (high temperature dry distillation). Coke obtained by high temperature coking is used for 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 synthetic industrial raw material.
Types of coke: Coke is usually divided into metallurgical coke (including blast furnace coke, casting coke and ferroalloy coke, etc.), gasified coke and calcium carbide coke. A new type of coke made from coal briquetting and pressing after carbonization and so on is called type coke. Metallurgical coke is a general term for coke used in blast furnace, coke making, iron alloy coke and non-ferrous metal smelting. Because more than 90% of the metallurgical coke is used for blast furnace ironmaking, coke oven coke is often called metallurgical coke.
Coke quality evaluation
1. Sulfur content in coke: sulfur is one of the harmful impurities in pig iron smelting, and it reduces the quality of pig iron. In steelmaking pig iron, the sulphur content is greater than 0.07%. Eleven percent of the sulfur carried into the burden comes from ore, 3.5 percent from limestone and 82.5 percent from coke, so coke is the main source of sulfur in the burden. The sulfur content of coke directly affects the production of blast furnace ironmaking. When the sulphur content of coke exceeds 1.6%, the sulphur content of coke increases by 0.1%, the usage of coke increases by 1.8%, the limestone content increases by 3.7%, the ore content increases by 0.3% and the output of blast furnace decreases by 1.5-2.0%. The sulphur content of metallurgical coke is not more than 1%, and the sulphur content of metallurgical coke used in large and medium blast furnaces is less than 0.4-0.7%.
2. Phosphorus content in coke: phosphorus content in metallurgical coke used for ironmaking should be below 0.02 - 0.03%.
3. Ash content in coke: the ash content of coke is very significant for blast furnace smelting. The ash content of coke increases by 1% and the coke consumption increases by 2-2.5%. Therefore, it is necessary to reduce the ash content of coke.
4. Volatile matter in coke: Coke maturity can be determined according to the volatile content of coke. If the volatile matter is more than 1.5%, it means coking; if the volatile matter is less than 0.5-0.7%, it means overheating. Generally, the volatile matter of mature metallurgical coke is about 1%.
5. Moisture in coke: moisture fluctuation makes coke measurement inaccurate, resulting in fluctuations in furnace conditions. In addition, the increase of coke moisture will make the M04 high and M10 low, which will bring errors to drum index.
6, coke screening composition: in blast furnace smelting, the size of coke is also very important. In the past, the coke granularity requirements in China were as follows: the coke granularity of large coke oven (1300-2000 square meters) was greater than 40 mm; the coke granularity of medium and small blast furnaces was greater than 25 mm. But at present some steel mill tests show that the coke size is between 40 and 25 millimeters. The coke size greater than 80 millimeter should be whole grains, so that the size range of the coke will not change much. Thus, the size of the coke is uniform, the air gap is large, the resistance is small, and the furnace condition is running well.
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