Thread Content
Acicular coke is an excellent material for manufacturing high-power and ultra-high-power electrodes. Graphite electrodes made from acicular coke possess advantages such as strong resistance to thermal shock, high mechanical strength, good oxidation resistance, low electrode consumption, and a high allowable current density. The needle coke produced today can be divided into two categories based on the raw materials used: petroleum-based and coal-based. The oil sector is represented by the United States, while the coal sector is represented by Japan. The production facilities of Mitsubishi Kasei and Shin Nihka in Japan came online in the late 1970s and early 1980s. However, the American company Great Lakes Carbon was the first to succeed in developing it in 1950. In 1964, United Carbon Corporation in the United States successfully manufactured ultra-high power electrodes using needle coke as raw material. According to the latest statistics, the domestic demand for high-power and ultra-high-power electrodes is 60,000–100,000 tons per year, while the corresponding demand for needle coke is 60,000–120,000 tons per year. At present, due to the limited amount of imported needle coke, Jinzhou Petrochemical Company’s production is only 30,000 t/year. Therefore, the production volume of ultra-high power electrodes in the domestic market is determined by the amount of needle coke available. The main production process technologies for coal-based needle coke are as follows: (1) Vacuum distillation method. In 1971, the American company LCI was the first to propose using vacuum separation to isolate needle coke from coal tar pitch, and filed a U.S. patent for this method. The core technique involves using vacuum distillation to select the raw materials suitable for producing needle coke; the process is relatively simple, but the yield of needle coke is low. (2) Solvent extraction method. In 1981, LCI Company filed a U.S. patent for a method using solvent treatment to remove the quinoline-insoluble (QI) components from asphalt. First, the QI is aggregated using a polymerization aid liquid, and the aggregates are separated in a gravity settler. This treatment technology is similar to the industrial plant used by Japan’s Shin Nihka Company to produce needle coke from coal tar pitch. The needle coke obtained through solvent treatment technology has a high yield and good quality, but the process is complex and the investment required is high. (3) M-L method. In 1985, LCI Company and Japan’s Mardzen Petrochemical Company applied for a U.S. patent for the M-L process, which combines specialized raw material pretreatment techniques with a unique two-stage delayed coking system; it was the first plant to produce needle coke using coal tar pitch as raw material. The needle coke produced has the best quality, but it also suffers from issues such as low yield, complex processing, and high costs. (4) Flash-polycondensation method. In 1985, Anshan Coking and Refining Institute, Anshan Iron and Steel University, and Shijiazhuang Coking Plant jointly developed the flash-evaporation-polycondensation process and applied for a Chinese patent. This method involves feeding the mixed crude oil into a specific flash tower, where it is flashed under certain temperature and vacuum conditions to produce flash oil; this flash oil then enters a polycondensation reactor where it undergoes polymerization to yield polycondensed asphalt. This process has a moderate yield and is simple. The Anshan Coastal Fertilizer Factory in China once carried out industrial-scale trials, but these were halted due to imperfect processes. In China, the main quality parameters for coal-based needle coke are based on the standards set by the Japanese company Shin Nihka. That is, the true specific gravity is ≥2.13, ash content ≤0.1%, volatile matter ≤0.5%, sulfur content ≤0.5%, thermal expansion coefficient CTE is 1×10-6/℃, and moisture content ≤0.2%.