Foundry coke is mainly applied to blast furnace ironmaking and air furnace smelting of copper, lead, zinc and other non-ferrous metals as the low sulfur coke , acting as reductant, exothermic compound and stock column skeleton. Blast furnace is using coke instead of charcoal for ironmaking, which lays foundation for upsizing the modern blast furnaces, and it is a major milestone in the history of metallurgy.
To achieve better technical-economic indicator in blast furnace operation, coke for smelting (metallurgical coke) must have suitable chemical and physical properties, including thermal property in smelting process. Besides ironmaking and non-ferrous metal smelting (metallurgical coke), coke is also used for casting, chemical industry, calcium carbide and ferroalloy with varied quality requirements. For example, the casting coke generally requires large particle size, low porosity, high fixed carbon and low sulfur content. Chemical gasification coke doesn’t require strict strength, but should be well reactive, with high ash fusion point. The coke used for calcium carbide production shall have as high fixed carbon content as possible.
As a solid product of high temperature retorting, coke is mainly composed of carbon, with cracks and irregular pore. The number of cracks directly determines the force and crushing strength of coke, whose indicator is generally measured by crack degree (crack length per unit volume of coke). The main indicator to measure pore structure is porosity (Percentage of coke pore volume in total volume), which would affect the coke reactivity and strength.
The requirements of porosity vary with coke applications. The porosity of metallurgical coke is generally 40～45%, and that of foundry coke is required to be 35～40%, and outlet coke is about 30%.
The crack degree and porosity of coke is directly related to the coal used in coking. For example, the coke mainly produced by gas coal has more cracks, high porosity and low strength, while that produced with coking coal as basic coal has less crack, low porosity and high strength. Coke strengthen is generally expressed by two indicators of crushing strength iron and steel abrasive resistance. The crushing strength of coke refers to the ability of coke resisting external impact force without cracking along the crack or defect of the structure, represented by M40 value. The abrasive resistance of coke refers to the ability of coke resisting external friction without causing chips or powder of surface glass, represented by M10 value. The crack degree of coke affects the crushing strength (M40 value), while its pore structure affects the abrasive resistance (M10 value).
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