JP2001329271A - Needle coke for graphite electrode and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide needle coke for a graphite electrode which enables inhibition of puffing of the needle coke even in a small amount of a puffing inhibitor and improves the yield and the properties of the graphite electrode, and a method of manufacturing the same. SOLUTION: The needle coke for a graphite electrode has a controlled particle size, and coarse particulate coke having a particle size of at least not smaller than 1.0 mm which contains 0.1-15 wt.% metallic component or oxide of a metallic component as the ash, and the method of manufacturing the needle coke for a graphite electrode comprises pulverizing calcined coke, screening the pulverized coke into coarse particulate coke having a large particle diameter and fine powder coke having a particle size of not greater than the size of the coarse particulate coke or the like, attaching a metallic compound in a molten state to the particulate coke, conducting heat treatment at 300-1,500 deg.C to attach 0.1-15% ash composed of an oxide of the metallic compound to the particulate coke, and then mixing the resulting particulate coke with the remaining fine powder coke or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a needle coke for a graphite electrode and a method for producing the same.

[0002]

2. Description of the Related Art Artificial graphite electrodes are obtained by pulverizing coal-based coke or petroleum-based coke, adjusting the particle size distribution to a predetermined value, kneading the mixture with a binder pitch, extruding, firing, impregnating, secondary firing, and graphitizing. To manufacture. Graphitization is about 300
This is a step of performing heat treatment at 0 ° C., and a method using an LWG furnace (direct energization type) is generally used. However, this LWG
When graphitized in a furnace, the rate of temperature rise is high, so the rate of gas generation is high, and an abnormal expansion phenomenon called puffing tends to occur. Puffing not only lowers the density of the electrode, but can also damage the electrode in extreme cases,
The development of a puffing inhibitor that suppresses this puffing and a low-puffing needle coke have been demanded, and development has been carried out.

[0003] Puffing is mainly initiated by graphitization.
It is believed that at temperatures between 0 and 2000 ° C. sulfur occurs due to elimination. For this reason, as the puffing inhibitor, a compound which traps such sulfur to form a compound such as iron sulfide and shifts the desorption timing until its decomposition temperature is desirable. For example, iron oxide (Japanese Patent Laid-Open No. 55-110190)
JP, JP-A-60-190491, and titanium oxide (JP-A-2-51409) have been proposed and implemented.

Further, iron sulfate soluble in water or alcohol,
Although a method using iron nitrate is also disclosed, these puffing inhibitors and the like have been added at the same time at the stage of kneading the binder pitch and coke. However, these methods have different effects depending on the type of raw coke, such as the fact that coal-based coke shows only a slight effect. There was a problem that lowering. Furthermore, although a method of directly adding iron sulfate or the like to coke is also disclosed, when added to the entire coke used as an electrode aggregate, when the ash content becomes high, the resistance value of the electrode is increased. There was a problem.

[0005] As a method for producing low-puffing needle coke, pitch in which quinoline-insoluble matter has been removed is removed in the presence of a hydrogenation catalyst in order to remove nitrogen or sulfur in the raw material pitch, which is a cause of puffing. A method for coking after hydrogenation and production is disclosed (JP-A-59-122585). On the other hand, after the first stage calcination of the raw coke is performed at a temperature lower than the normal calcination temperature, for example, around 800 ° C., it is cooled once and then again in the temperature range of 1200 to 1500 ° C. (Japanese Patent Application Laid-Open No. 53-35801) has also been proposed.

[0006]

However, these methods for producing a low-puffing needle coke are not economical in any case and have not been put into practical use.
Alternatively, there is a problem that a sufficient puffing reduction effect cannot always be obtained. Therefore, from the present situation, an object of the present invention is to reduce the needle coke puffing and to increase the production yield and characteristics of a carbon electrode without increasing the cost of producing needle coke. The aim is to provide a method.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, coarse coke (lump or granular coke) mainly causes puffing. Focuses on hardly causing puffing, and adds a metal compound used as a puffing inhibitor in solution only to the lump and granular coke surfaces before kneading with binder pitch, etc., and heat-treats it to add the inhibitor. The inventors have found that the effect of suppressing puffing is increased despite the decrease in the amount, and the present invention has been completed.

[0008] That is, the needle coke for graphite electrode according to claim 1 of the present invention is a coke for graphite electrode whose particle size has been adjusted (before kneading the binder pitch),
The coarse coke having a particle size of at least 1.0 mm contains a metal component or an oxide of the metal component in an amount of 0.1 to 15% by weight as ash.

In the present invention, at least a particle size of 0.3
It is preferable that the fine ash coke of not more than mm does not contain the ash. The metal component in the present invention is preferably one or more selected from iron, magnesium, aluminum, titanium, cobalt, manganese, nickel and the like.

The method for producing needle coke for a graphite electrode according to the present invention is characterized in that calcined coke is finely pulverized and adjusted to a predetermined particle size distribution, and then is converted into a coarse coke having a large particle size and a fine coke smaller than that. After sieving (or classification), the metal compound is attached to the coarse coke in a solution state,
The heat treatment is performed at ℃ 1500 ° C. so that 0.1 to 15% by weight of an ash composed of a metal component or an oxide of the metal component is adhered, and then mixed with the remaining fine coke or the like.

The metal compound in the present invention may be at least one salt selected from the group consisting of iron sulfate, magnesium sulfate, aluminum sulfate, titanium sulfate, cobalt sulfate, manganese sulfate, nickel sulfate and the like. It is advantageous.

[0012]

Embodiments of the present invention will be described below in detail. The needle coke for the graphite electrode of the present invention and the coke used in the method for producing the same are made of one or both of petroleum-based or coal-based heavy oil as raw materials, and raw coke produced by a delayed coking method, for example, from 1200 to 1200. Coke calcined in a temperature range of 1500 ° C. is used. The calcined coke is not only obtained by only one calcining (usually 1200 to 1600 ° C.), but also at the temperature lower than the normal calcining temperature (for example, around 800 ° C.). After baking, it is once cooled and again heated to a higher temperature (e.g.
(0 to 1600 ° C.) in the case of employing the method of performing the second-stage calcination, including those obtained by the first-stage calcination and those obtained by the second-stage calcination. Incidentally, even if the raw coke is treated according to the present invention, no effect is obtained. Thereafter, usually, the calcined coke is reduced, finely pulverized, sieved, and adjusted in particle size, and then kneaded (kneaded) with a binder pitch as appropriate to be formed into various shapes and graphitized.

The calcined coke is finely pulverized and adjusted to the particle size distribution before kneading the binder pitch. In this case, the particle size distribution and the amount of the calcined coke vary depending on the size of the electrode to be produced. Because the effect of reducing puffing by the puffing inhibitor also changes,
The particle size ranges of coarse coke (including granular / bulk coke) having a large particle diameter to which an inhibitor is added and fine powder coke to which no inhibitor is added are not limited. However, the standard of coarse coke in the present invention may be at least 1.0 mm or more in particle diameter, and the maximum diameter may be appropriately adjusted according to the electrode size, and is not particularly limited.

The standard of the fine powder coke to which no inhibitor is added may be in the range of the smallest compounded particle size of the electrode to be produced, or 25% by weight in the particle size distribution of the whole coke used. %. However, it is preferable that the fine powder has a particle size of 0.3 mm or less regardless of whether or not it corresponds to this standard. In the present invention described above, “coarse powder coke having a particle diameter of at least 1.0 mm” refers to a particle diameter of 1.0 mm or more.
All of the above are included, but it means that even if the particle diameter is less than 1.0 mm, the addition of the inhibitor according to the present invention may be included. Similarly, "fine coke having a particle size of at least 0.3 mm or less" includes all those having a particle size of 0.3 mm or less, but those having no inhibitor according to the present invention even if the particle size exceeds 0.3 mm. It means that it may be included. In particular, a particle size of 0.3 to
With respect to coke equivalent to 1.0 mm, whether or not an inhibitor is added may be arbitrary, and is not particularly limited.
In this case, also in the coke to which the inhibitor according to the present invention is added, coarse coke having a particle diameter of 1.0 mm or more accounts for 40% by weight or more, more preferably 70% by weight.
It is good to do above.

The metal compound used in the present invention is a compound which reacts or decomposes by heating to produce one or more metal components or metal oxides (including composite oxides), and is used in the form of a solution. And then heat-treated at 300 to 1500 ° C. after adhering to the surface of massive and granular calcined coke. Therefore, the metal compound serving as a puffing inhibitor may be attached to calcined coke as an aqueous solution, or if it is not soluble in water, it is dissolved in a volatile liquid such as alcohol or benzene as a solvent and then attached to coke. You may.

As a specific puffing inhibitor, at least one selected from the group consisting of iron sulfate, magnesium sulfate, aluminum sulfate, titanium sulfate, cobalt sulfate, manganese sulfate, nickel sulfate and the like, which are easily dissolved in water, is used. It is desirable. What is important here is that these metal compounds are directly adhered to coarse-grained coke (including granular / bulk coke), and the inhibitor is applied to all calcined coke (needle coke), which is a graphite electrode aggregate, as in the past. Even if it is added, the effect is not different from the case where the inhibitor is added only to coarse coke.

In the production method of the present invention, a compound, which reacts or decomposes by heating to produce one or more metal components or metal oxides, etc., in the form of a solution in the form of coarse calcined coke (including granular / bulk coke) It is important to heat-treat at 300 to 1500 ° C. after adhering to the surface of (1).
The heat treatment removes the water of crystallization of the attached compound and converts the compound into one or more metal oxides. If the water of crystallization is not removed by heat treatment, or if it is not converted into a metal oxide, not only does the compound generate moisture during firing in the electrode manufacturing process, causing defects in the electrode, but also the compound decomposes during firing and gas is generated. Occurs and lowers the bulk density of the electrode. For this reason, the strength of the electrode is insufficient,
The electrode may be damaged when used in an electric furnace.

Therefore, by carrying out a heat treatment in advance at 300 ° C. or higher, moisture and generated gas from the metal compound at the time of firing the electrode are removed, and these problems are solved. When the heat treatment temperature is lower than 300 ° C., the water of crystallization of the compound is hard to be desorbed, so the heat treatment temperature is preferably 300 ° C. or higher, and more preferably the heat treatment at 500 ° C. or higher so that the compound reacts with oxygen in the air or the compound itself is decomposed. . On the other hand, 15
When the temperature exceeds 00 ° C., graphitization of the needle coke starts during the heat treatment of the compound, and it is difficult to effectively suppress the puffing.

The amount of the metal compound adhered to 100 parts by weight of the coarse coke (including granular / bulk coke) thus heat-treated is determined by the amount of ash (metal component or metal oxide, etc.).
0.1 to 15 parts by weight, more preferably 0.1 to 15 parts by weight.
The content is preferably 5 to 3 parts by weight. If the amount of adhesion is insufficient outside these ranges, the effect of reducing puffing is not practically sufficient, while if the amount of adhesion is excessive, the effect of increasing the amount of addition is not remarkable and the remaining ash is not preferable on the electrode product. Affect.

The ash in the heat-treated coarse-grained coke (including granular / bulk coke) includes one or more metal components or metal components selected from magnesium, aluminum, titanium, manganese, cobalt and nickel. And the like. The ash content referred to in the present invention shall be obtained by the ash measurement method described later. The ash content of ordinary graphite electrode needle coke is 0.1% by weight.
However, in the present invention, coarse coke (granular /
The amount of ash contained in lump coke is 0.1
-15% by weight.

The coarse coke containing the metal oxide or the like is mixed with the remaining fine coke or the like to obtain coke for graphite electrode whose particle size has been adjusted before kneading the binder pitch.
In this case, the fine-powder coke to be mixed is preferably 25% by weight or less, more preferably 50% by weight or less, based on the total amount of the coke for graphite electrode. When a graphite electrode is manufactured using the calcined coke having the particle size adjusted before the binder pitch kneading obtained by the above method, a usual method can be applied. That is, the binder pitch is kneaded with the graphite electrode coke of the present invention whose particle size has been adjusted, and if necessary, iron oxide is further added. After kneading (kneading), extrusion molding, primary baking, impregnation, and secondary baking are performed. Then, a graphite electrode can be manufactured by a conventional means such as graphitization.

In addition, an inhibitor may be added to coarse-grain coke whose particle size has not been adjusted, and a pulverizing step may be appropriately performed again after the heat treatment. In this case, fine powder is generated,
This fine powder may or may not be mixed with fine powder to which no inhibitor is added at the time of particle size adjustment. That is, since it is not directly related to the effect of reducing puffing, it may be appropriately selected in consideration of electrode quality such as ash content and economic efficiency.

Further, when kneading (kneading) the binder pitch, the use of iron oxide which is usually used as a puffing inhibitor may be omitted, but if it is used, a further effect of reducing puffing can be obtained. Therefore, it may be appropriately selected in consideration of required quality and economy.

In the present invention, by limiting the coke to which the puffing inhibitor is added to coarse coke having a large particle diameter, the effect of suppressing the puffing even though the amount of the puffing inhibitor is reduced can be obtained. This is a characteristic that the effect is obtained, and at the same time, leads to a drastic reduction in the amount of ash contained in the electrode, which is a very economical and industrially useful technique.

[0025]

The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to these examples. The methods of measuring puffing, graphitized BD and ash used in the examples are shown below.

(1) Method of Measuring Puffing The samples of Examples and Comparative Examples are kneaded for 20 minutes at 160 ° C. by adding a binder pitch of 30% (outer portion) and, if necessary, a predetermined amount of iron oxide. This is 20mmφ
It is molded into a size of 100 mm. The molded test piece is fired in a firing furnace to 900 ° C., impregnated with the impregnation pitch, and fired again at 900 ° C. for 2 hours.
This was used as a sample for puffing measurement. In the puffing measurement, the temperature is raised to 2500 ° C. at a rate of 10 ° C./min, and expressed by the maximum elongation from 1500 ° C. to 2500 ° C.

(2) Measuring method of graphitized BD The volume of the test piece, which has been processed by the measuring method of (1) above, is calculated from the diameter and length, while the weight is measured, and the weight is measured by volume. Divide and calculate the bulk density.

(3) Ash Content Measurement Method Regarding the samples of Examples 1 to 5, Comparative Examples 1 to 4 and Comparative Examples 9 to 12, a metal compound was adhered before kneading the binder, and after heat-treated calcined coke was reduced, 0.25mm
Crush below to obtain an average sample. Weigh at least about 1 g of sample into a pre-weighed magnetic dish. 800
Keep the sample in a muffle furnace at a temperature of 0 ° C (the door of the furnace is slightly opened so as to create an oxidizing atmosphere) until the sample is completely incinerated. After complete incineration, cool in a desiccator and weigh the entire dish to calculate the ash content. In the same manner, the amount of ash of only calcined coke to which no metal compound was attached before kneading the binder was calculated, and the amount of metal oxide or the like attached to coke was calculated from the difference between the former and the latter.

Examples 1 to 4 Calcined coke obtained by calcining raw coke produced by the delayed coking method using coal-based heavy oil as a raw material was used. Finely pulverize calcined coke and adjust particle size (2.4 to 1m
m = 40%, 0.3-0.07 mm = 35%, 0.07
mm or less = 25%), of which the particle diameter is 2.4 to 1 m
m calcined coke (130 g), an aqueous solution of iron sulfate (3.5 g) having a concentration of 3.5% by weight was added and left for 30 minutes.
After drying at 150 ° C., it was further heated at 900 ° C. Table 1 shows the results obtained by measuring the puffing and graphitized bulk density (bulk density; BD) of the mixture of the untreated fine coke and the mixture. Examples 1-4 were compared by changing the amount of iron oxide added during kneading.

Example 5 A calcined coke obtained by calcining raw coke produced by a delayed coking method using coal-based heavy oil as a raw material was used. An aqueous solution of iron sulfate (2.3 g) having a concentration of 1.75% by weight was added to calcined coke (130 g) of 2.4 to 1 mm in the same manner as in Example 1, left for 30 minutes, dried at 150 ° C., and then dried. Further, heat treatment was performed at 900 ° C. to this,
About what mixed the fine coke which was not treated,
Puffing and graphitized bulk density (bulk density; B
Table 1 shows the measurement results of D).

Comparative Example 1 Calcined coke obtained by calcining raw coke produced by the delayed coking method using coal-based heavy oil as a raw material was used. 0.3-0.07 mm (175 g) and 0.07 mm with a particle size of less than 1 mm sieved in Example 1
To a mixture (300 g) of calcined coke such as fine coke (125 g) described below (3.5 g), an aqueous solution of iron sulfate (17.5 g) having a concentration of 3.5% by weight was added.
And then heat-treated at 900 ° C. Table 2 shows the results of measuring the puffing and graphitized bulk density (bulk density; BD) of the mixture obtained by mixing the untreated coarse coke.

Comparative Examples 2 and 3 Calcined coke obtained by calcining raw coke produced by delayed coking using heavy coal-based oil as a raw material was used. No calcined coke (3k
g) was added with a 3.5% by weight aqueous solution of iron sulfate (750 g), left for 30 minutes, dried at 150 ° C, and further heated at 900 ° C. The results of measuring the puffing and graphitized bulk density (bulk density; BD) are shown in Table 2. Comparative Examples 2 and 3 were compared by changing the amount of iron oxide added during kneading.

Comparative Example 4 Calcined coke obtained by calcining raw coke produced by a delayed coking method using coal-based heavy oil as a raw material was used. An aqueous solution of cobalt sulfate (750 g) having a concentration of 3.75% by weight was added to all of the calcined coke (3 kg) which had not been subjected to particle size adjustment as in Comparative Example 3 and left for 30 minutes.
After drying at 50 ° C., it was further heated at 900 ° C. The results of measuring the puffing and graphitized bulk density (bulk density; BD) are shown in Table 2.

Comparative Examples 5 to 8 In a conventional electrode preparation method using a coal-based calcined coke not according to the present invention, iron oxide was not added to 100 parts by weight of coke during kneading of binder pitch (Comparative Example 5). After adding 1 to 3 parts by weight of iron oxide (Comparative Examples 6 to 8), electrodes were prepared. Table 3 shows the results of measuring the puffing and graphitized bulk density (bulk density; BD).

Comparative Examples 9 to 12 Calcined coke obtained by calcining raw coke produced by the delayed coking method using coal-based heavy oil as a raw material was used. An aqueous solution of iron sulfate having a concentration of 3.5% by weight was added to calcined coke of 2.4 to 1 mm and 0.3 to 0.07 mm, left for 30 minutes, dried at 150 ° C., and then heated at 900 ° C. Processed. Table 4 shows the results of measuring the puffing and graphitized bulk density (bulk density; BD) of the mixture obtained by mixing the untreated fine powder. Comparative Examples 9 to 12 were compared by changing the amount of iron oxide added during kneading.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

As is clear from Tables 1, 2, 3 and 4, each of the examples of the present invention has a smaller amount of phosphating inhibitor (ash content) than the corresponding comparative example. It can be seen that the puffing was also significantly improved. That is, when the puffing inhibitor of the present invention is attached to coarse powder having a particle size range of 2.4 to 1 mm, the entire particle size range (2.4 to 1 mm, 0.3 to 0.0
As compared with the case where the puffing inhibitor is similarly adhered to the powder of 7 mm or less, 0.07 mm or less, the same amount of puffing reduction effect can be obtained with approximately half the ash content (Example 1v).
s. Comparative Example 2). Also, when iron oxide was added during kneading, the same level of puffing reduction effect was obtained with approximately half the ash content (Example 3 vs. Comparative Examples 3 and 4), and practically even with approximately 1/4 ash content. An effect of reducing puffing to the extent that there is no problem is obtained (Example 5). When the puffing inhibitor of the present invention is attached only to fine powder having a particle size of less than 1 mm (0.3 to 0.07 mm, 0.07 mm or less), the entire particle size range (2.4 to 1 mm, 0.3-0.0
Only a low puffing reduction effect can be obtained as compared with the case where a puffing inhibitor is similarly attached to powder having a diameter of 7 mm or 0.07 mm or less (Comparative Example 1 vs. Comparative Examples 2, 3,
4). By the way, when the puffing inhibitor of the present invention is not used, the effect of reducing puffing to a practically acceptable level cannot be obtained unless 3 wt% of iron oxide is added during kneading (Comparative Examples 5 to 8, especially Comparative Examples 8). In addition, not only coarse powder having a particle size range of 2.4 to 1 mm, but also a particle size range of 0.3 to
When the puffing inhibitor of the present invention is also attached to fine powder of 0.07 mm, the total attached amount (ash content)
Despite the large amount, only a low puffing reduction effect can be obtained (Example 1 vs. Comparative Example 9, Example 2 vs. Comparative Example 1).
0, Example 3, 5 vs. Comparative Example 11, Example 4 vs. Comparative Example 1
2). The graphitized needle coke of each of Examples 1 to 5 also had a bulk density (graphitized BD) of 1.6 g / cm.
^{It was} about ³ , which was a value that would be acceptable for practical use.

[0041]

According to the present invention, although the amount of the puffing inhibitor is reduced by limiting the particle size of the coke to which the puffing inhibitor is added, the electrode production is the same as when the puffing inhibitor is added to the entire coke. Needle coke for graphite electrodes that effectively suppresses puffing during the graphitization process, has a high bulk specific gravity (BD) after graphitization, has excellent strength characteristics, and can sufficiently satisfy the required characteristics in manufacturing and quality. Can be provided. In addition, the yield of the electrodes can be improved and the product characteristics can be improved, which can provide great industrial and economic benefits.

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Claims (5)

[Claims] 1. A coke for a graphite electrode whose particle size has been adjusted, wherein a coarse component coke having a particle size of at least 1.0 mm has a metal component or an oxide of the metal component in an amount of 0.1 to ash.
Needle coke for graphite electrodes characterized by containing 15% by weight. 2. The needle coke for a graphite electrode according to claim 1, wherein said fine ash having a particle diameter of at least 0.3 mm does not contain said ash. 3. The needle coke for a graphite electrode according to claim 1, wherein the metal component is at least one selected from iron, magnesium, aluminum, titanium, cobalt, manganese, nickel and the like. 4. The calcined coke is finely pulverized and adjusted to a predetermined particle size distribution, and then sieved (or classified) into a coarse-grained coke having a large particle size and a fine-grained coke having a smaller particle size. Adheres a metal compound in a solution state,
Needle coke for a graphite electrode, wherein 0.1 to 15% by weight of ash composed of a metal component or an oxide of a metal component is adhered by heat treatment at 500 ° C., and then mixed with the remaining fine powder coke. Manufacturing method. 5. The metal compound is at least one kind of salt selected from the group consisting of iron sulfate, magnesium sulfate, aluminum sulfate, titanium sulfate, cobalt sulfate, manganese sulfate, nickel sulfate, and the like. Of producing needle coke for graphite electrodes.