JPS6245916B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high quality electrode coke. More specifically, coal-based raw pitch coke containing 5 to 12% volatile content is manufactured in a delayed coker from coal tar and/or coal tar pitch, which is a raw material containing nitrogen compounds, or petroleum-based heavy oil, etc. In the sintering method used to produce high-grade electrode coke by sintering green pitch coke (hereinafter referred to as raw pitt coke) or raw petroleum coke, a sufficient holding time is allowed at the sintering temperature to reduce or remove the nitrogen content. , relates to a method for producing high-grade electrode coke. Coke for electrodes is generally made from coal tar and/or coal tar pitch or heavy petroleum oil and heated at 450°C to 500°C in a Delade coker.
The raw pitch coke or raw petroleum coke containing 5 to 12% volatile matter is produced by heating and carbonizing in the temperature range of
It is manufactured by firing in a firing furnace such as a shaft furnace or a rotary hearth furnace at a firing temperature in the temperature range of 1100°C to 1400°C in order to remove volatile matter and increase the degree of carbonization. At that time, if the raw material coal tar and/or coal tar pitch or petroleum heavy oil contains a nitrogen-containing compound, nitrogen content will remain in the produced electrode coke. On the other hand, graphite electrodes are made by crushing and sieving the electrode coke produced by the method described above, adjusting the particle size to an appropriate particle size, adding binder pitch for electrodes to it, kneading it, and then molding the mixture using an extrusion molding machine or press molding machine. It is manufactured by molding, then firing and graphitizing. However, if electrode coke contains nitrogen, sulfur, etc., gases such as nitrogen and nitrogen compounds, sulfur and sulfur compounds will be generated during the graphitization process, and the gas pressure may cause cracks in the graphite electrode. It is recognized that this causes a decrease in the strength etc. of the electrode. In recent years, electric steel manufacturing has adopted large electric furnaces to improve productivity, and as ultra high power operations have become commonplace, the graphite electrodes used are In order to reduce manufacturing costs as electricity costs rise, direct current furnaces have been increasingly used as graphitization furnaces instead of the conventional Acheson furnaces with the intention of improving productivity and reducing power consumption. In the case of a direct current furnace, the graphitization time is shorter than that in an Acheson furnace.
Because it is shortened to about 1/2 to 1/3 of the conventional time,
During graphitization, it is necessary to increase the temperature gradient, and as a result, the expansion of coke during graphitization due to the generated gas pressure increases, causing problems such as cracks in the product or a decrease in the strength of the electrode. Therefore, the requirements for the quality of coke for electrodes have become increasingly strict. The present inventors conducted a detailed study on the calcination temperature of coke, and found that if the coke for electrodes contains nitrogen, the graphitization temperature during electrode manufacturing will be lower than 1400°C.
It was discovered that in the temperature range of 1800°C, the generation of nitrogen gas and nitrogen compound gases (cyanide, ammonia, etc.) increases, and the electrode during graphitization expands due to the gas pressure. Therefore, the present inventors removed the nitrogen content from the coke, which causes the generation of nitrogen gas and nitrogen compound gas, which adversely affects the graphitization of the graphite electrode as described above.
As a result of intensive research into how to reduce or eliminate this problem, we have completed the present invention. In other words, the present invention uses raw coal-based pitch coke or raw petroleum coke containing nitrogen at a temperature range of 1430°C to 1500°C.
This is a method for producing high-quality electrode coke, which is characterized by obtaining coke that has been kept for 48 hours to dissipate the nitrogen content in the coke. Next, the present invention will be explained in detail. Table 1 shows the analytical values of various types of coke. Also the first
The figure shows the results of making fired electrodes (diameter 25 mm x 100 mm) using the various types of coke listed in Table 1, and measuring the longitudinal expansion of the fired electrodes at each temperature during the graphitization process. It is something. This shows that there are differences in expansion depending on the nitrogen content of coke. Table 2 shows examples of elemental analysis values when raw pitch coke is baked at various temperatures. As you can see from this table, the nitrogen content is
It shows that it is dissipated in the temperature range from 1400℃ to 1800℃. Table 3 shows the results for pitch coke A and petroleum coke A shown in Table 1 in an argon atmosphere.
This is an analysis value of gas generated in the temperature range of graphitization process from ℃ to 1800℃. Hydrogen gas is detected regardless of the nitrogen content, but this shows that a large amount of nitrogen and nitrogen compounds are detected in coke with a relatively high nitrogen content. From these facts, it can be easily inferred that nitrogen and nitrogen compound gases play a major role in the expansion of the electrode during graphite electrode manufacturing, especially in the temperature range of 1400°C to 1800°C during the graphitization process. I can do it.

【table】

【table】

【table】

〔Example〕

Raw pitch coke obtained by converting coal tar soft pitch into coke using a delayed coker is used in the fourth stage.
Burnt coke was produced under the temperature conditions listed in the table. Next, the calcined coke is pulverized, 50% by weight of the 20-70 mesh pulverized product and 50% by weight of the pulverized product of 100 mesh or less are thoroughly mixed together with binder pitch, and extrusion molded to form a compact (diameter 25 mm, length 100 mm).
mm) was created. Then, using a graphitizing crucible,
Each molded body was fired at 900℃ for 6 hours, then further heated to 2300℃.
Graphitization was carried out for 5 minutes. The results are shown in Table 4. As can be seen from this table, it is difficult to reduce the nitrogen content of pitch coke baked at a temperature of 1300℃ for a short holding time.
Furthermore, although it is possible to reduce the nitrogen content by baking at a temperature higher than the temperature conditions of the present invention,
A graphite molded body made from such coke has a low bulk density, which leads to a decrease in the performance of the electrode, making it undesirable. As explained above, in coke baking, the present invention has a coke baking temperature at which the nitrogen compounds that cause puffing are rapidly decomposed and denitrification occurs rapidly, and a coke baking temperature at which pores begin to increase rapidly. It was discovered that there is a gap between the two, and this gap is utilized to perform calcination for a relatively long period of time, that is, denitrification for a long period of time, at an intermediate temperature. By using this coke, it is possible to manufacture the most well-balanced electrode, which has a low coefficient of thermal expansion and a small pore volume when used as an electrode, and therefore has a large bulk density and high electrode strength.

【table】 [Brief explanation of the drawing]

Figure 1 shows the coefficient of thermal expansion during graphitization of graphite compacts using various types of coke, Figure 2 shows the coefficient of thermal expansion during graphitization of graphite compacts using pitch coke at different firing temperatures, The figure shows the pore volume of coke baked at various temperatures.

Claims (1)

[Claims] 1 Coal-based raw pitch coke or raw petroleum coke whose nitrogen content is the main cause of puffing is heated to 1430℃
Hold in a temperature range of 1500℃ for 4 to 48 hours,
A method for producing high-grade electrode coke, which is characterized by obtaining coke from which nitrogen content in the coke has been diffused.