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What are the carbon materials used as recarburizers?

The recarburizer is a material used to increase the carbon content. The main component is carbon. There are many materials that can be used as a recarburizer. Commonly used are coke and anthracite, calcined petroleum coke, graphitized petroleum coke, and graphite (artificial graphite). , natural graphite) and mixtures made from such materials.

1. Coke and anthracite
Coke is a type of solid fuel. It is obtained by dry distillation of coal under high temperature conditions of about 1000 °C. The main component is fixed carbon, followed by ash, and contains less volatile matter and sulfur. Silver-gray, metallic luster. Hard and porous. In addition to a large amount of coke and iron non-ferrous metal smelting (metallurgical coke), coke is also used in foundry, chemical, calcium carbide and ferroalloys, and its quality requirements are different. For example, for casting coke, it is generally required to have large particle size, low porosity, high fixed carbon and low sulfur content; coking for chemical gasification is not strict with strength, but requires good reactivity, high ash melting point, and coke requirement for calcium carbide production. Try to increase the fixed carbon content.

Anthracite is a hard, dense and high-gloss coal mine. The main applications of anthracite lump coal are chemical fertilizer (nitrogen fertilizer, synthetic ammonia), ceramics, manufacturing forging and other industries; anthracite coal is mainly used in the metallurgical industry for blast furnace injection (blast furnace coal mainly includes anthracite, lean coal, lean coal and gas coal) ).

2. Calcined petroleum coke (calcined coke or calcined coke)
Calcined petroleum coke is a widely used recarburizer, which is obtained by calcining petroleum coke. Petroleum coke is a by-product of refined crude oil. Residual oil and petroleum asphalt obtained by vacuum distillation or vacuum distillation can be used as raw materials for petroleum coke, and then coke is obtained to obtain raw petroleum coke. The annual production of American petroleum coke is about 30 million T. The raw petroleum coke has high impurity content and cannot be directly used as a recarburizer. It must be calcined first.

Raw petroleum coke has spongy, needle-like, granular and fluid states.
Sponge petroleum coke is produced by delayed coking. Because of its high sulfur and metal content, it is usually used as a fuel for calcination and as a raw material for calcined petroleum coke. The calcined plum cotton coke is mainly used in the aluminum industry and as a recarburizer.
The acicular petroleum coke is obtained by a delayed coking process using a raw material having a high content of aromatic hydrocarbons and a low impurity content. This coke has a needle-like structure that is easily broken, sometimes referred to as graphite coke, and is mainly used for the manufacture of graphite electrodes after calcination.
Granular petroleum coke is a hard granule. It is a raw material with a high content of sulfur and bitumen. It is produced by delayed coking and is mainly used as a fuel.
The fluid petroleum coke is obtained by continuous coking in a fluidized bed. It is in the form of fine particles, has no directional structure, high sulfur content and low volatile content.
The burning of petroleum coke is to remove sulfur, moisture, and volatiles. The raw petroleum coke is burned at 1200 ° C - 1350 t ° C to make it substantially pure carbon.
The largest user of smoked petroleum coke is the aluminum industry, 7 which is used to make anodes for the reduction of bauxite. The United States produces smoked petroleum coke, which accounts for about 6% of cast iron enhancers.

3. Graphitized petroleum coke
Graphitized petroleum coke refers to the high-temperature graphitization of petroleum coke. Under the high temperature of 3000 °C, the carbon molecular form in the petroleum coke is changed from an irregular arrangement to a hexagonal uniform arrangement. The agent is most easily decomposed in molten iron.

Characteristics of graphitized recarburizer
    1) The low-sulfur graphitization recarburizer has a high decomposition rate and a high absorption rate, and can reach more than 90%.
    2) High carbon, low sulfur, low nitrogen, and extremely harmful components.
    3) Adding graphite nucleus to molten steel and molten iron, more uniform and finer distribution in molten steel and molten iron, so that the performance is more excellent and stable.

4. Graphite is an allotrope of elemental carbon. Each carbon atom is connected with three other carbon atoms (multiple hexagons arranged in a honeycomb shape) to form a covalent molecule by covalent bonding. . Graphite and carbon products have excellent performance, are increasingly used, and the production capacity and benefits are growing rapidly. There are more enterprises of graphite and carbon products above the scale of China, and the concentration is low. With the rapid development of China's metallurgy, chemical, machinery, medical equipment, nuclear power, automotive, aerospace and other industries, the demand for graphite and carbon products will continue to grow in these industries, and China's graphite and carbon products industry will maintain rapid growth. . Graphite is mainly divided into natural graphite and artificial graphite.

4.1. Natural graphite
Natural graphite can be divided into two types: flake graphite and microcrystalline graphite. Microcrystalline graphite has a high ash content and is generally not used as a carbon reinforcer for cast iron. There are many varieties of flake graphite. High-carbon flake graphite needs to be extracted by chemical methods, or heated to high temperature to decompose and volatilize the oxides. This flake graphite has low yield and high price, and generally does not act as a recarburizer; low carbon scales Graphite has a high ash content and should not be used as a recarburizer; it is mainly used as a carbon reinforcer for medium carbon graphite, but it is not used in large amounts.

4.2. Artificial graphite
Among the above various recarburizing agents, the best quality is artificial graphite. The main raw material for the manufacture of artificial graphite is powdered high-quality simmered petroleum coke, in which asphalt is added as a binder, and a small amount of other auxiliary materials are added. After the various raw materials are combined, they are press-formed and then treated in a non-oxidizing atmosphere at 2500 to 3000 ° C to be graphitized. After high temperature treatment, the ash, sulfur and gas contents are greatly reduced. Due to the high price of artificial graphite products, the artificial graphite breakers commonly used in foundries are mostly cut when manufacturing graphite electrodes.
Recycled materials such as chips, used electrodes and graphite blocks to reduce production costs. In the smelting of ductile iron, in order to make the metallurgical quality of cast iron superior, the carbon-reducing agent should be the first choice of artificial graphite. For this reason, it is better to purchase scrap electrodes from nearby companies that use electric arc furnace steelmaking or electrolytic aluminum production enterprises, and crush them to the required particle size. .

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