Graphite electrode refers to petroleum coke and asphalt coke as the main material, coal tar pitch as binder, which is made by raw material calcination, crushing milling, compounding, kneading, forming, roasting, impregnating, graphitization and mechanical processing. High-temperature graphite conductive material, called artificial graphite electrode, is distinguished from natural graphite electrode prepared by using natural graphite as raw material. There are several types of graphite electrodes used:
(1) Used in electric arc furnace
Electric furnace steelmaking is the largest use of graphite electrodes. The output of China's electric furnace steel accounts for about 18% of the crude steel output, and the graphite electrode for steelmaking accounts for 70% to 80% of the total graphite electrode. Electric furnace steelmaking uses a graphite electrode to introduce a current into the furnace, and smelting is performed by a high-temperature heat source generated by an arc between the electrode end and the charge.
(2) Used in mine electric furnace
The ore electric furnace is mainly used for the production of industrial silicon and yellow phosphorus. It is characterized in that the lower part of the conductive electrode is buried in the charge, an electric arc is formed in the material layer, and the heat generated by the resistance of the charge itself is used to heat the charge, wherein current is required. Graphite electrodes are required for higher density electric furnaces. For example, about 100 kg of graphite electrode is consumed for each 1T of silicon produced, and about 40 kg of graphite electrode is consumed for each 1T of yellow phosphorus produced.
(3) For resistance furnace
The graphitization furnace for producing graphite products, the melting furnace for melting glass, and the electric furnace for producing silicon carbide are all electric resistance furnaces. The materials contained in the furnace are both heating resistors and objects to be heated. Usually, graphite electrodes for electric conduction are embedded in the resistance furnace end. In the furnace wall of the department, the graphite electrode used here is not continuously consumed.
(4) For the preparation of shaped graphite products
The graphite electrode blank is also used to process a variety of shaped graphite products such as enamel, mold, boat and heating element. For example, in the quartz glass industry, for every 1T electrofusion tube produced, a graphite electrode blank 10T is required; for every 1T quartz brick produced, 100 kg of graphite electrode blank is consumed.
Graphite products have been widely used in industrial sectors such as metallurgy, machinery, electrical, chemical, textile, and defense because of their many excellent properties.
Two important changes in the graphite refractory industry are the widespread use of magnesia carbon bricks in steelmaking linings and the application of aluminum carbon bricks in continuous casting. One of the main uses of graphite is in the production of refractory materials, including refractory bricks. , crucible, continuous casting powder, mold core, mold, detergent and high temperature resistant materials.
Graphite products are currently used in large quantities in the world for magnesia carbon bricks, and have become a traditional use of graphite. Conventional graphite clays are made of flake graphite with a carbon content greater than that of graphite, which is currently produced in foreign countries. Important improvements in technology.
The type of graphite used, the size and quality of the graphite have greater flexibility. Secondly, the traditional clay graphite crucible is replaced by silicon carbide graphite crucible. The products are increasingly used in mining systems, diesel systems, railway systems and high-tech. industry.
Graphite particles are mainly derived from the scraps generated during the machining of graphite electrodes and the waste products generated by the graphitization process. They are one kind of graphite products. Because graphite scraps have electrical conductivity, thermal conductivity, high temperature resistance, low ash content and high carbon content. It has a good chemical stability and is widely used as a recarburizer for steelmaking furnaces.
The combination of domestic graphite column and self-produced wear-resistant plate technology has made outstanding contributions to the development of China's automobile industry, greatly improving the production efficiency of automobiles, and lowering the cost of automobiles. It is used in guide bushes, guide columns and self-control. Lubricating the graphite column on the bearing and wear plate, the graphite product can also be made by carbonizing the carbon refractory material in a resistance furnace at 2500 ° C ~ 2800 ° C to make it graphitized.
Graphite products can be used as reaction tanks and autoclave linings in the chemical industry. They are also widely used in the manufacture of corrosion-resistant heat exchangers and masonry high-temperature furnaces. Graphite has a high scattering cross section and a very low thermal neutron absorption cross section. The high scattering cross section is used to slow down the neutrons, the low absorption cross section prevents the neutrons from being absorbed, allowing the nuclear reactor to achieve critical or normal operation with a small amount of fuel, which is used in graphite materials for the nuclear industry.
As of the end of June 2018, China's graphite electrode production capacity is about 1.5 million tons / year, of which effective capacity of 1.234 million tons / year. From January to June 2018, the total output of graphite electrodes in China was 310,400 tons (up 19.11% over the same period of last year), including 74,200 tons of ordinary graphite electrodes (up 23.47% over the same period of last year) and 86,000 tons of high power (up 3.28 compared with the same period of last year). %), the super high is 150,100 tons (up 28.13% over the same period last year).
Since the price of graphite electrode has risen in the second quarter of 2017, although the price has dropped before, the graphite electrode has always had a high profit margin. Therefore, the graphite electrode enterprise is doing its full capacity production, and the monthly supply is increasing. In the first half of 2018, the operating rate of electric furnace steel showed a turbulent trend. In the following six months, the country's demand for steel market will increase, which will help the operating rate of electric furnace steel.
The guiding role of national policies on electric furnace steel. Xinhua News Agency reported on July 25 that Luo Tiejun, inspector of the Raw Materials Division of the Ministry of Industry and Information Technology, said at the expansion meeting of the executive director of the China Iron and Steel Association that promoting the conversion of "long process" steelmaking to "short process" will further reduce the steel industry. The impact on the atmospheric environment. The state will study relevant policies and measures to support the development of electric furnace steel, and effectively improve the market competitiveness of electric furnace enterprises.
The outward transfer of steel production capacity in the Beijing-Tianjin-Hebei region may become an important source of short-process steelmaking capacity indicators. "Luo Tiejun said, "We will work with relevant departments such as the Development and Reform Commission to encourage and guide the transfer of production capacity to meet the needs of the development of electric furnace steel outside the region. ”
“South China, Southwest China, Northwest China and other regions with large capacity, abundant scrap resources and sufficient power supply have the advantage of developing electric furnace steel. We will guide the relevant regions to strengthen communication and convergence on the basis of strict implementation of capacity replacement policy, and actively undertake from The production capacity of Beijing-Tianjin-Hebei and surrounding areas will be rationally planned to develop electric furnace steel."
The national policy on the advancement of electric furnace steel will be conducive to the development of electric furnace steel, which will also drive the development of the graphite electrode industry. In the fourth quarter of 2018, during the heating season, Hebei, Henan and Shandong provinces will face the problem of limited production. At that time, the output will be reduced. In addition, the state's investment in infrastructure and the guiding policy for electric furnace steel, we believe that the fourth quarter graphite electrode Resources may tighten and prices will rise slightly.
The petroleum coke from the delayed coking unit is called raw coke, and the process of heat treatment of high temperature (1250~1380 °C) under the condition of insulating air is called calcination. The petroleum coke after calcination is called calcined petroleum coke, also called Calcined coke and calcined petcoke, they have different names but are the same product. The purpose of calcination is to discharge moisture and volatiles in the raw materials, so that the petroleum coke raw materials are sufficiently shrunk to improve their physical and chemical properties.
Under normal circumstances, the petroleum coke starts to escape volatiles from 200 ° C. When the temperature reaches 1100 ° C, the volatiles basically escape. In the range of 500 ° C to 800 ° C, the volatiles of petroleum cokes escape the most. At about 700 °C, the petroleum coke volatiles are mainly hydrogen decomposed by hydrocarbons and hydrocarbon pyrolysis. As the temperature continues to increase, the gas escape amount decreases, and the pyrolysis temperature increases, further promoting the structure. Tightening. In the calcination of petroleum coke, the O2, N2, CO, CO2, and S elements are sequentially removed by heat, and a planar network structure is formed inside the petroleum coke at 1350 °C. This change in microstructure reflects an improvement in the physical properties of the calcined coke (such as true density, electrical conductivity, strength, etc.).
Calcined petroleum coke is mainly used for prebaked anode and cathode used in electrolytic aluminum, carbonizing agent for production in metallurgical steel industry, graphite electrode, carbon electrode for industrial silicon, yellow phosphorus and iron alloy. Therefore, both electrolytic aluminum plants, independent carbon plants and refineries are concerned about the progress and development of petroleum coke calcination technology.
Why is petroleum coke need calcined?
The purpose of calcination:
1. Eliminate volatiles and moisture in petroleum coke raw materials. After calcination, the volatile matter is 0.5% or less, and the water content is 0.3% or less.
The calcined volatiles and moisture represent the degree of calcination, which does not require secondary shrinkage and crack formation during calcination.
2. Improve the density and mechanical strength of petroleum coke raw materials. The true density is 2.00 g/cm3 or more.
The true density of the calcined coke affects the true density of the final product, and the mechanical strength is low. The bulk density is low, which affects the molding. The main performance is difficult to form. The height of the green block does not meet the requirements within the required time, which affects the operation of the aluminum electrolytic cell.
3. Improve the electrical conductivity of petroleum coke raw materials.
The calcined coke specific resistance affects the final product resistivity.
4. Improve the chemical stability of petroleum coke raw materials. Improved oxidation resistance.