JP2922985B2 - Needle coke manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a graphite raw material, in particular, needle coke used as a raw material for a graphite electrode for electric steelmaking. More specifically, by mixing petroleum heavy oil with coal tar stock oil that does not contain quinoline insolubles,
And a method for producing needle coke with low puffing and high calcined coke bulk density.

[Conventional technology]

Needle coke is mainly used as a raw material for electric steelmaking electrodes.
(Ultra high power) The operation and operating conditions are becoming more and more severe, and there is a demand for a graphite electrode having better performance and, consequently, a high quality needle coke.

In particular, CTE (coefficient of thermal expansion) is related to the thermal shock resistance when the electrode is used.
There is a demand for an electrode with low TE and coke.

On the other hand, the production side of graphite electrodes is also trying to shorten the graphitization time in order to save energy during the graphitization, and thus the irreversible thermal expansion phenomenon (puffing) that occurs when the electrodes are graphitized has become a problem. .

Puffing increases as the graphitization time decreases, and in extreme cases graphitization becomes impossible. Further, if the puffing is large, problems such as a decrease in the bulk density of the electrode obtained after graphitization occur. Therefore, not only the CTE of the graphite electrode, but also the puffing during graphitization is an important index of the needle coke quality.

At present, such needle coke is produced from coal tar heavy oil as a raw material and from petroleum heavy oil as a raw material. Coal tar needle coke is characterized by low CTE, but has the disadvantage of high nitrogen content and high puffing. In addition, petroleum-based needle coke has a drawback of high CTE due to low aromaticity of the raw material.

By the way, it has been considered that the puffing occurs because a sulfur compound or a nitrogen compound contained in the needle coke is rapidly decomposed and gasified when heated to a high temperature, and expands the coke structure.

Therefore, as a countermeasure against puffing, a method has been proposed in which a metal compound (for example, iron oxide) that forms a compound with sulfur is added to trap sulfur in a temperature range where puffing occurs.

However, even though this method is effective for petroleum needle coke obtained from petroleum-based raw materials containing a large amount of sulfur compounds, if the amount of sulfur compounds is too large, buffing becomes high. Is there. On the other hand, this method is not effective for coal-based needle coke obtained from a coal tar-based raw material having a small amount of sulfur compounds and a large amount of nitrogen compounds, and is insufficient as a measure for preventing puffing.

Regarding coal-based needle coke, although the sulfur content is lower than petroleum-based, puffing is not so low.Therefore, a detailed investigation of the cause of puffing in coal-based needle coke revealed that only sulfur was the cause of puffing. And nitrogen was also found to be the cause.

By the way, in order to produce needle coke from a coal tar-based raw material, it is necessary to remove a few percent of quinoline-insoluble matter (hereinafter abbreviated as QI content) contained in the coal tar-based raw material.

Needle coke obtained from such a QI-free coal tar-based raw material has a relatively small sulfur content, but has a large nitrogen content, and thus has little effect of the anti-puffing agent. For this reason, reduction of nitrogen in needle coke has become a major issue in reducing puffing.

On the other hand, the CTE level of coal tar needle coke is smaller than that of petroleum needle coke.
And puffing have an inverse correlation, and it was difficult to reduce CTE while reducing puffing by ordinary means.

Therefore, various methods for denitrifying coal tar-based raw materials have been conventionally proposed. For example, according to the hydrogenation method disclosed in JP-A-60-149690, it is shown that CTE and puffing can be simultaneously reduced. This method has the disadvantage that it requires large equipment and cost.

JP-B-62-45916 proposes a method for obtaining coke in which nitrogen in the coke is diffused by heating for a long time in a temperature range of 1430 to 1500 ° C., which is higher than a normal coke calcination temperature. ing. This method also has a disadvantage that it requires energy cost.

Japanese Patent Publication No. 57-61071 discloses that coal tar and thermal cracking treatment or contact cracking treatment residue are produced for the purpose of simultaneously producing high-grade coke (needle coke) and a raw material having a high aromatic content for producing carbon black. It discloses the use of a mixture consisting of oil.
However, this invention uses coal tar as a raw material,
Includes quinoline-insoluble matter that inhibits flow tissue development during coking and increases CTE. Also, as is clear from the comparative example in the example, by mixing the cracking residual oil with the coal tar, even in the coking raw material, the sulfur content in the obtained coke is significantly increased, and the puffing is reduced. It is clear that there is no connection.

Also, Japanese Patent Publication No. 49-26481 discloses a needle coke production method, after mixing coal-based coal tar pitch and petroleum heavy oil, heating and stirring at 200 to 320 ° C., and QI in the produced coal tar pitch. It discloses that a mixed solution obtained by separating and removing a precipitate containing is coked. However, when using this method, when a precipitate is generated by heating and stirring, a heavy component such as β resin, which is a main component of the carbonization reaction in the coal tar pitch, is simultaneously precipitated, so that it is contained in the carbonized raw material. Carbonized components derived from coal tar pitch
Not only does the yield of coke decrease, but the properties of the coke are close to those of carbonization of petroleum alone, resulting in an increase in CTE. (Comparative Example 4) [Problem to be Solved by the Invention] From the technical trend described in the conventional method, a large-scale apparatus,
There is a keen need for measures to reduce the nitrogen content of current needle coke feedstocks without the costly hydrogenation process and without spending energy costs such as high temperature and long time heating of the coke.

An object of the present invention is to remove quinoline-insoluble components from coal tar-based raw materials and to coke by mixing with different types of raw materials having a reduced nitrogen content while maintaining a low CTE characteristic of coal tar-based needle coke. Accordingly, it is an object of the present invention to provide a method for producing needle coke in which both CTE and puffing are excellent.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when a coal tar-based raw material from which quinoline-insoluble matter has been removed and a petroleum heavy oil having a low nitrogen content are mixed and carbonized, a coal tar-based The present invention has been completed by focusing on the fact that the flow structure is better than when the raw material is carbonized alone, the nitrogen in the raw material is reduced as compared with the coal tar-based raw material, and CTE is not different from that of coal-based needle coke.

That is, the present invention removes the quinoline insolubles from the coal tar heavy oil, and then mixes it with decant oil, which is a heavy component of the fluid catalytic cracking oil of petroleum having a nitrogen content of 0.5% by weight or less, to coke. This is a characteristic method for producing needle coke.

The coal tar-based raw material used in the present invention is coal tar produced when carbonizing coal, high-boiling tar oil and tar pitch separated from coal tar, and preferably tar pitch.

Tar pitch is a soft pitch with a softening point of 70 ° C or less.
There are a medium pitch of about 70 to 85 ° C. and a high pitch of a softening point of 85 ° C. or higher, and both can be used. However, it is advantageous to use a soft pitch in terms of handling. Further, a mixture of two or three types of tar pitch, coal tar and high boiling tar oil may be used.

Numerous documents have already been published on the method of removing the QI component from coal tar-based raw materials, but filtration and removal by mechanical methods such as centrifugation are also possible.
Since the particle size of QI is extremely small, the separation speed is slow,
The separation efficiency is low, such as clogging at the time of filtration, and cannot be carried out industrially. The same applies to the case where the viscosity is lowered by adding a solvent. As a method which can be carried out industrially, JP-A-57-30159
As disclosed in JP-A-53-66901 and JP-A-53-66901, hexane, octane, kerosene, naphtha, butanol and other aliphatic solvents and benzene,
An effective method is to add and mix a mixed solvent with an aromatic solvent such as toluene, xylene, methylnaphthalene, and phenol to generate insoluble products around the QI particles, increase the particles, and settle and remove the particles. is there.

The heavy petroleum oil used in the present invention is decant oil (FCC-DO), which is a heavy component of fluid catalytic cracking oil of petroleum. Further, from the viewpoint of the carbonization yield, these heavy oils may be previously removed by distillation of light components or heat-treated to be heavier by thermal polymerization.

Such petroleum heavy oil contains almost no QI.

FCC-DO has low CTE in any property, but nitrogen content of 0.4% or less and sulfur content of 1.2% or less,
The reduction in puffing is large and preferable.

The above-mentioned FCC-DO alone contains a large amount of sulfur which causes puffing of petroleum-based needle coke, and can only obtain coke having a higher CTE than that of coal-based needle coke.

In the present invention, by mixing such petroleum heavy oil with decoalized coal tar heavy oil and coking,
Puffing and CTE can be reduced at the same time.

In the present invention, the mixing ratio of petroleum heavy oil to coal tar heavy oil is 10 to ₈₀ wt _% , preferably 20 to 50 wt _%.
It is. If the mixing ratio is _less than 10 wt _% , the puffing is as high as that of coal tar needle coke, and if it is more than 80 wt _% , the CTE becomes higher than that of petroleum needle coke.

Also, when coal tar heavy oil and petroleum heavy oil are mixed and carbonized, nitrogen remaining in the needle coke,
The sulfur content is almost additive to the mixing ratio. Therefore, it can be seen that the nitrogen content causing the puffing can be surely reduced as compared with the coal tar raw material. Sulfur content increases compared to coal tar-based raw materials, but the amount of increase is within 0.5% by weight, and since puffing inhibitor is effective for puffing caused by sulfur, this increase is not a problem. .

In the present invention, the coal tar heavy oil from which the QI component has been removed is mixed with a petroleum heavy oil that does not contain the QI component, so that the compatibility between the both is very good, and an insoluble precipitate is generated during mixing. Never.

From these facts, it has become possible to produce needle coke excellent in both CTE and puffing by mixing petroleum heavy oil with coal tar heavy oil from which QI components have been removed and coking.

A known method can be adopted as a method of coking after mixing with a petroleum heavy oil after de-QI. For example, raw coke is produced at 450 to 550 ° C. under pressure (1 to 20 kg / cm ² G) in a delayed coker, and then the raw coke is calcined at 1200 to 1500 ° C. in a rotary kiln, shaft furnace, etc. to obtain needle coke. I do.

The needle coke obtained by the method of the present invention is pulverized, adjusted for particle size, and then mixed with a binder pitch to be molded. If this is calcined and then calcined at a temperature of 2500 ° C. or more, a graphite electrode having excellent performance can be efficiently obtained.

That is, the graphite electrode made from the needle coke obtained by the method of the present invention has a small CTE, and has excellent strength because it hardly causes puffing during production.

[Action]

In the present invention, the carbonization rate during coking, the gas generation state is changed by mixing and coking with heavy oil, thereby changing the carbonization rate during coking, the gas generation state, and the optical anisotropy showing low CTE. Needle coke with a texture can be manufactured. At the same time, the nitrogen content and the sulfur content that cause puffing are reduced, and low puffing is possible.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Example 1) FCC decant oil was mixed with coal tar pitch from which a QI component had been removed in advance at a mixing ratio of 9/1 to 2/8 by heating to a temperature of 100 ° C, and the obtained pitch was mixed with a small reactor at 480. At 8 ° C
Time coking, make raw coke, then 1450
Calcination was performed at 0 ° C. for 1 hour in an argon atmosphere.

With respect to the obtained coke, nitrogen, sulfur content, puffing, CTE and the like in the coke were measured. The results are shown in Table 1. The puffing was measured by adding 1% of Fe ₂ O ₃ as a puffing inhibitor.

(Comparative example 1) Except not mixing a petroleum heavy oil, it processed like Example 1. The results are shown in Table 1. The results of puffing measurement when Fe ₂ O ₃ was not added were also shown.

(Comparative example 2) Except not mixing a coal tar pitch, it processed like Example 1. The results are shown in Table 1. Also,
Puffing measurement results without addition of Fe ₂ O ₃ are also shown.

(Comparative Example 3) FCC-decant oil was mixed at a mixing ratio of 5/5 with coal tar pitch from which the QI component was not removed, followed by heating and stirring while refluxing light oil at 320 ° C for 3 hours, and then cooling to 180 ° C. An insoluble precipitate was formed, and the carbonized raw material mixture was recovered by decantation. The liquid yield at this time was 82%.

The same treatment as in Example 1 was performed except that the obtained carbonized raw material was coked.

 The results are shown in Table 1.

[Effects of the Invention] According to the method of the present invention, energy such as hydrogenation of coal tar-based feedstock and calcination of coke at high temperature for a long time is not required, and coke is produced by mixing with petroleum heavy oil without cost. Thereby, low CTE and low puffing needle coke can be manufactured at low cost. This is a major invention that contributes to the coke industry.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Taiji Oishi 4-7-1 Nakai, Kokurakita-ku, Kitakyushu-shi, Fukuoka (72) Inventor Shigeru Miwa 4--4-7 Nakai, Kokurakita-ku, Kitakyushu-shi, Fukuoka 6 (72) Inventor Kiichiro Miyata 4-17-16 Eidamarunishimachi, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Prefecture (58) Fields investigated (Int. Cl. ⁶ , DB name) C10B 57/04 C10B 31/00

Claims (1)

(57) [Claims] (1) removing quinoline-insoluble matter from coal tar heavy oil, and coking with a decant oil which is a heavy component of a fluid catalytic cracking oil of petroleum having a nitrogen content of 0.5% by weight or less. Characteristic method of producing needle coke.