Graphite electrode and needle coke

The production process of carbon materials is a strictly controlled system engineering. The production of graphite electrodes, special carbon materials, carbon for aluminum, new high-end carbon materials, etc. are inseparable from the four production elements of raw materials, equipment, technology, management and related proprietary Combination of technology.

 

The raw material is the key element that determines the basic characteristics of the carbon material, and the performance of the raw material determines the performance of the manufactured carbon material. For the production of UHP and HP graphite electrodes, high-quality needle coke is the first choice, as well as high-quality binder pitch and impregnant pitch. But only with high-quality raw materials, lack of equipment, technology, management elements and related proprietary technologies, it is also impossible to produce high-quality UHP and HP graphite electrodes.

 

This article focuses on explaining some personal views on some characteristics of high-quality needle coke, for discussion and discussion with colleagues from needle coke manufacturers, electrode manufacturers, and research institutes.

 

Although the industrial production of needle coke in my country is later than that of foreign companies, it has developed rapidly in recent years and has begun to take shape. In terms of total production, it can basically meet the needs of domestic carbon companies to produce UHP and HP graphite electrodes for needle coke. Demand. However, there is still a certain gap in the quality of needle coke compared with foreign companies. The fluctuation of batch performance affects the demand for high-quality needle coke in the production of large-size UHP and HP graphite electrodes, especially the graphite electrode joints are not yet available. High-quality joint needle coke used in production.

 

Foreign carbon companies producing large-size UHP and HP graphite electrodes often prefer high-quality petroleum needle coke as the main raw material coke. Japanese carbon companies also use some coal-based needle coke as raw materials, but they are only used in the production of graphite electrodes with specifications below Φ600 mm. my country’s needle coke is currently mainly coal-based needle coke. The production of high-quality large-size UHP graphite electrodes by various carbon companies often relies on imported petroleum-based needle coke, especially the production of high-quality joints are imported from Japan’s Mizushima oil. Needle coke and British HSP oil-based needle coke are used as raw materials.

 

At present, the needle coke produced by various enterprises is usually compared with the commercial performance indicators of foreign needle coke by conventional performance indicators, such as ash content, true density, sulfur content, nitrogen content, particle size distribution, and thermal expansion coefficient. However, compared with foreign countries, there is still a lack of needle coke classification with different levels of performance in the needle coke classification. Therefore, most of the needle coke produced is generally "all goods", which does not reflect the quality and price of needle coke by grade.

 

In the comparison of needle coke performance, in addition to the conventional performance comparison, carbon companies should also pay attention to the classification of needle coke's coefficient of thermal expansion (CTE), particle strength, anisotropy, non-inhibited state and expansion data in inhibited state The characteristics of needle coke, such as the temperature range during expansion and contraction. Because these thermal properties of needle coke are very important for the control of the graphitization process in the production of graphite electrodes, of course the influence of the thermal properties of pitch coke formed after the binder and impregnant pitch is roasted is not ruled out.

 

1 Comparison of anisotropy of needle coke

 

(A)  Sample: Φ500 mm UHP electrode body of a domestic carbon factory;

 

Raw material needle coke: Japan's new daily chemical LPC-U grade, ratio: 100% LPC-U grade; analysis: SGL Griesheim factory; performance indicators are shown in Table 1.

 

(B)   Sample: Φ450 mmHP electrode body of a domestic carbon factory; raw needle coke: petroleum needle coke of a domestic factory, ratio: 100%; analysis: Shandong Bayan Carbon Factory; performance indicators are shown in Table 2.

 

From the comparison of Table 1 and Table 2, it can be seen that the thermal performance anisotropy of the LPC-U grade of Xinrihua coal series needle coke is relatively large, and the CTE anisotropy can reach 3.61~4.55, and the resistivity is anisotropy. The degree of anisotropy is also relatively large, reaching 2.06~2.25. The domestic petroleum needle coke is far lower in the evaluation of anisotropy than the new one, except that the flexural strength of the domestic petroleum needle coke is better than that of the new daily chemical LPC-U level coal needle coke. Daily chemical LPC-U coal series needle coke.

 

The anisotropy performance analysis of ultra-high-power graphite electrode products is a very important analysis method to evaluate the quality of raw needle coke. Of course, the anisotropy also has a certain impact on the electrode production process. , The thermal shock resistance of the electrode with large anisotropy is much better than that of the ordinary power electrode with small anisotropy.

 

At present, the domestic coal-based needle coke production volume is far greater than the petroleum needle coke production volume. Due to the current dilemma of high raw material cost and price factors faced by various carbon companies, it is difficult to use 100% domestic needle coke in the production of UHP electrodes. For coke production, it is difficult to evaluate the anisotropy performance of domestic needle coke by mixing a certain proportion of calcined petroleum coke and graphite crushed to produce electrodes.

 

2 The linearity and volume change performance of needle coke

 

The linear and volume change performance of needle coke is mainly reflected in the graphitization process of electrode production. As the temperature changes, the needle coke will undergo linear and volume expansion and contraction changes during the heating process of the graphitization process, which directly affects When it comes to the linear and volume changes of the calcined electrode blanks in graphitization production, the changes that take place with different properties of raw coke and different grades of needle coke are different. Moreover, the linearity and volume change of different grades of needle coke and calcined petroleum coke have different temperature ranges. Only by mastering this characteristic of raw coke can we better control and optimize the production of graphitization process. This is particularly evident in the production process of tandem graphitization.

 

Table 3 shows some of the linearity and volume changes and temperature ranges of the three grades of petroleum needle coke produced by ConocoPhillips' UK plant. When the oil-based needle coke starts to heat up, linear expansion occurs first, but the temperature at which the linear contraction begins often lags behind the maximum calcination temperature. The linear contraction starts from 1525°C to 1725°C and then begins to expand again. The temperature range of the entire linear contraction is narrow. 200°C. The temperature range of the general delayed petroleum coke's entire linear shrinkage is much larger than that of needle coke. Coal-based needle coke is somewhere in between, and slightly larger than oil-based needle coke. The test results of the Osaka Institute of Industrial Technology Test Institute in Japan show that the worse the thermal performance of coke, the larger the linear shrinkage temperature range, which can reach the linear shrinkage temperature range of 500-600℃, and the starting temperature of linear shrinkage is low. Linear shrinkage begins at 1150～1200℃, which is also the characteristic of ordinary delayed petroleum coke.

 

The better the thermal performance of needle coke and the greater the degree of anisotropy, the narrower the temperature range of linear shrinkage. Some high-quality oil-based needle coke only has a linear shrinkage temperature range of 100～150℃. After understanding the characteristics of various raw coke, such as expansion, contraction and expansion after heating, it is very useful for carbon companies to guide graphitization process production, which can avoid some unnecessary quality waste products caused by the traditional empirical power transmission mode. .

 

3 Conclusion

 

Master the various characteristics of raw materials, select reasonable equipment matching, good process technology combination, and the company's management becomes more scientific and reasonable. This series of whole processes are systematically controlled and stable, and it can be said to have high-quality production. The basis of ultra-high power and high power graphite electrodes.