JP3025540B2 - Needle coke manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing graphite raw material, in particular, needle coke used as a raw material for a graphite electrode for electric steelmaking. More specifically, the present invention relates to a method for producing a needle coke having a low CTE and a low puffing and a high calcined coke bulk density by mixing a petroleum heavy oil with a coal tar stock oil containing no quinoline-insoluble matter.

[0002]

2. Description of the Related Art Needle coke is mainly used as a raw material for electric steelmaking electrodes. However, in the electric steelmaking industry, electric furnaces have become larger, and UHP (ultra high power) operations and operating conditions have become increasingly severe. There is a demand for graphite electrodes having better performance and, consequently, high quality needle coke. In particular, CTE (coefficient of thermal expansion) is related to thermal shock resistance when an electrode is used, and when CTE is low, the unit consumption of the electrode is improved. Therefore, an electrode and coke having a low CTE are demanded.

[0003] On the other hand, the graphite electrode production side has also tried to shorten the graphitization time in order to save energy during the graphitization, and the irreversible thermal expansion phenomenon (puffing) caused by the electrode during graphitization has become a problem. Has become. 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.

[0004] 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 a low CTE, but has the disadvantage of high nitrogen content and high puffing. In addition, petroleum-based needle coke has a low aromaticity as a raw material,
Has the disadvantage of being expensive.

[0005] By the way, puffing is considered to occur because sulfur compounds and nitrogen compounds contained in needle coke are rapidly decomposed and gasified when heated to a high temperature, and the coke structure is expanded. Was. 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.

[0006] However, even if this method is effective for petroleum needle coke obtained from petroleum raw materials containing a large amount of sulfur compounds, if the amount of the sulfur compounds is too large, puffing becomes high, so that a raw material having a low sulfur content is used. You need to choose. 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 that of petroleum-based, the puffing is not so low. Not only sulfur but also nitrogen was found to be the cause.

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) contained in the coal tar-based raw material.

[0009] Needle coke obtained from such a QI-free coal tar-based raw material has a relatively small sulfur content but a large nitrogen content, and thus has little effect of an anti-puffing agent.
For this reason, reduction of nitrogen in needle coke has become a major issue in reducing puffing.

[0010] On the other hand, the CTE level of coal tar needle coke is smaller than that of petroleum needle coke, but CTE and puffing are in an inverse correlation, and it is difficult to reduce CTE while reducing puffing by ordinary means. It was difficult.

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

Japanese Patent Publication No. 62-45916 discloses 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. Has been proposed. This method also has a disadvantage that it requires energy cost.

Further, Japanese Patent Publication No. 57-61071 discloses
Disclosed is the use of a mixture of coal tar and residual oil subjected to thermal cracking or catalytic cracking for the purpose of simultaneously producing high-grade coke (needle coke) and a raw material having a high aromatic content for producing carbon black. ing. However, in the present invention, since coal tar is used as a raw material, a quinoline-insoluble component that inhibits the development of a flow structure during coking is contained, and the CTE is increased. Also, as is clear from the comparative example in that example, by mixing the cracking residual oil with coal tar,
It is clear that the sulfur content in both the coking raw material and the obtained coke is significantly increased, and does not lead to a decrease in puffing.

Japanese Patent Publication No. 49-26481 discloses a needle coke production method in which coal-based coal tar pitch and petroleum heavy oil are mixed and then mixed at 200 to 320 ° C.
And coke the mixed solution obtained by separating and removing the precipitate containing QI in the generated coal tar pitch. 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. The carbonized component derived from coal tar pitch decreases, and not only the coke yield decreases, but also the properties of the coke become closer to those obtained when carbonized by petroleum alone, resulting in an increase in CTE.

[0015]

According to the technical trends described in the conventional methods, energy costs such as high-temperature and long-time heating of coke are consumed without using a hydrogenation method requiring large-scale equipment and cost. Therefore, there is an eager need for a measure to reduce the nitrogen content from the current raw material for needle coke.

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

[0017]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have found that coal tar-based raw materials from which quinoline insolubles have been removed and petroleum heavy oil having a low nitrogen content. When mixed and carbonized, the flow structure is better than when coal tar-based raw material is carbonized alone, nitrogen in the raw material is reduced compared to coal tar-based raw material, and CTE is not different from coal-based needle coke. Thus, the present invention has been completed.

That is, the present invention relates to (1) a coal tar heavy oil from which quinoline insoluble matter has been removed in advance, and a quinoline insoluble matter having a sulfur content of 1.2% by weight or less and a nitrogen content of 0.5% by weight or less. Containing no H
/ C is 1.06 or less, Conradson carbon residue CCR is 10
A method for producing needle coke, characterized by mixing coke by mixing with decant oil which is a heavy component of fluid catalytic cracking oil of petroleum adjusted to not less than weight%,

(2) Decant oil, which is a heavy component of fluid catalytic cracking oil of petroleum, is subjected to vacuum distillation of the heavy component of fluid catalytic cracking in advance to cut light components, and specific gravity d ¹⁰⁰ at 100 ° C.
₄ is a method for producing a needle coke according to the above (1), wherein the needle coke is prepared to be 1.020 or more.

The coal tar-based raw material used in the present invention is coal tar produced during carbonization of coal, high boiling tar oil and tar pitch separated from coal tar, and preferably tar pitch. Tar pitch is a soft pitch having a softening point of 70 ° C. or less, and a softening point of 7.
There are a medium pitch of about 0 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.

Although a number of literatures have already been published on the method of removing QI from coal tar-based raw materials,
It is also possible to remove by mechanical methods such as paste and centrifugation, but the particle size of the QI is extremely small, so the separation speed is slow, and the separation efficiency is low, such as clogging during paste. It cannot be carried out industrially. The same applies to the case where the viscosity is lowered by adding a solvent.

An industrially applicable method is disclosed in
As disclosed in JP-A-7-30159 and JP-A-53-66901, an aliphatic solvent such as hexane, octane, kerosene, naphtha, butanol and the like, benzene, toluene, xylene, methyl An effective method is to add and mix a mixed solvent with an aromatic solvent such as naphthalene or phenol to form an insoluble product around the QI particles, increase the particles, and settle and remove the particles.

An important point of the present invention is that a decant oil (fluid catalytic cracker oil, commonly called FC), which is a heavy component of a fluid catalytic cracking oil of petroleum which has been adjusted to specific properties thereafter, is used.
C-DO) to form coke.

According to the results of investigations by the present inventors, in this case, depending on the properties of FCC-DO, puffing is reduced as compared with the case of coal tar needle coke alone, but on the other hand, CTE of CTE is reduced. It turned out that there was a thing where the up rate became high.

Therefore, as a result of a detailed study, it was found that the nitrogen content was 0.1%.
5% by weight or less, sulfur content of 1.2% by weight or less and H / C
FCC-D adjusted to a specific range such that the Conradson residual carbon content CCR is 10% by weight or more and the Conradson residual carbon content CCR is 106% or less.
It was found that by mixing O, as compared with the case where the raw material oil was a coal-tar heavy oil alone, it was possible to reduce the puffing and at the same time reduce the CTE increase rate as much as possible. However, H / C represents the atomic ratio of hydrogen and carbon in the decant oil.

Usually, FCC-DO, which is a bottom heavy oil from a fluid catalytic cracking unit for petroleum, has a nitrogen content of 0.5% by weight or less, a sulfur content of 0.5 to 4% by weight, and an H / C Is 1.
1 to 1.2, Conradson residual carbon content CCR is in the range of 2 to 10% by weight. FCC-DO used in the present invention is:
H / C is 1.06 or less and Conradson residual carbon amount CCR
Is adjusted to 10% by weight or more.

Even if the H / C is 1.06 or less, the Conradson residual carbon content CCR is less than 10% by weight, or even if the Conradson residual carbon content CCR is 10% by weight or more, H / C is 1.0% or more.
If it exceeds 6, depending on the coking conditions, the CTE may be worse than when using coal tar heavy oil as the raw material oil.

This is because light FCC-DO having an H / C of more than 1.06 or a Conradson residual carbon amount CCR of less than 10% by weight has a very high carbonization rate and a coal tar heavy oil. It is considered that even when mixing and coking, the balance between the carbonization rate and the gas generation that generates an anisotropic structure exhibiting a low CTE cannot be obtained.

As a method for adjusting the FCC-DO,
Either use a raw material (petroleum) with as high aromaticity as possible in the fluid catalytic cracking unit, increase the cracking temperature of the fluid catalytic cracking unit, or use FCC, which is a bottom heavy oil from a general petroleum fluid catalytic cracking unit. -It is possible to utilize the method of cutting light components of DO by distillation under reduced pressure or heat treatment.

The FCC-DO used in the present invention
Does not substantially contain a quinoline-insoluble component, but it is desirable to carry out a dequinoline-insoluble component treatment as necessary.

By mixing FCC-DO with coal tar heavy oil, the coke produced from this base oil has a nitrogen content of not more than 0.4% by weight and a sulfur content of not more than 1.0% by weight. Are preferred since they greatly reduce puffing.

When the above-mentioned FCC-DO is used alone as a coke feedstock, it contains a large amount of sulfur which causes puffing of petroleum-based needle coke, and can obtain only coke having a higher CTE than that of coal-based needle coke. .

In the present invention, such a petroleum heavy oil is de-QI
By mixing with coal tar-based heavy oil and coking it as a raw material oil, puffing is greatly reduced without deteriorating the low effect of CTE, which is the characteristic of coal-tar based heavy oil. Can be done.
In the present invention, FCC for coal tar heavy oil
-The mixing ratio of DO is coal tar heavy oil 90 to 20 wt.
% Of FCC-DO, preferably 80 to 50% by weight of coal-tar heavy oil,
C-DO is 20 to 50 wt%. When the mixing ratio of FCC-DO is lower than 10 wt%, the puffing is as high as that of coal tar needle coke, and when the mixing ratio of FCC-DO is higher than 80 wt%, the CTE becomes as high as that of petroleum needle coke. .

Further, coal tar heavy oil and FCC-D
When O is mixed and carbonized, the content of nitrogen and sulfur remaining in the needle coke is substantially additive with respect 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. Although the sulfur content increases compared to coal tar-based raw materials,
The increase is within 0.5% by weight, and since the anti-puffing agent is effective against the 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 FCC-DO having a characteristic property substantially not containing the QI component, so that the compatibility between the two is very good. No insoluble precipitates form on mixing.
From these facts, it is possible to produce a needle coke excellent in both CTE and puffing by mixing the coal tar heavy oil from which the QI component has been removed with the FCC-DO adjusted to a specific property and coking. became.

FCC-D adjusted to specific properties after de-QI
A known method can be employed for coking after mixing with O. For example, under pressure (1 ~
Raw coke is produced at 450 to 550 ° C. at 20 kg / cm ² G), and then the raw coke is calcined at 1200 to 1500 ° C. in a rotary kiln, shaft furnace or the like to obtain needle coke.

The needle coke obtained by the method of the present invention is pulverized, adjusted for particle size, mixed with a binder pitch and molded. If this is fired 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,
Since puffing hardly occurs during production, the strength is excellent.

[0038]

In the present invention, the carbonization rate during coking,
By mixing and coking heavy oils having different gas generation states, it is possible to produce a needle coke having an optically anisotropic structure exhibiting a low CTE by changing the carbonization rate and the gas generation state during coking. . At the same time, the nitrogen content and the sulfur content that cause puffing are reduced, and low puffing is possible.

[0039]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. (Example 1) Coal tar pitch (CTP) from which QI was removed was adjusted to 0.1% by weight of nitrogen, 0.67% by weight of sulfur, 0.94 of H / C, and 11.3% by weight of CCR. The FCC decant oil is mixed at a mixing ratio of 7/3 to 3/7 by heating to a temperature of 100 ° C., and the obtained pitch is coked in a small reactor at 480 to 485 ° C. for 8 hours to produce raw coke. After that, calcination was performed at 1450 ° C. for 1 hour in an argon atmosphere. With respect to the obtained coke, nitrogen, sulfur content, puffing, CTE, etc. in the coke were measured. Table 1 shows the results. The puffing was measured by adding 1% of Fe ₂ O ₃ as a puffing inhibitor.

(Example 2) FCC-DO used was H / C = 1.0
The results were shown in Table 1, except that the treatment was performed in the same manner as in Example 1 except that the CCR was 11.1 wt%.

Examples and Comparative Examples

[Table 1]

(Comparative Example 1) A process was performed in the same manner as in Example 1 except that FCC-DO was not mixed. Table 2 shows the results.

(Comparative Example 2) A treatment was performed in the same manner as in Example 1 except that no coal tar pitch was mixed. Table 2 shows the results. The results of the puffing measurement are also shown.

(Comparative Example 3) FCC-DO used was H / C = 1.1
The treatment was carried out in the same manner as in Example 1 except for 1, CCR = 10.6 wt%. The results are shown in Table 2.

(Comparative Example 4) FCC-DO used was H / C = 1.0
2, The treatment was performed in the same manner as in Example 1 except that CCR = 7.0 wt%. The results are shown in Table 2.

[0046]

[Table 2]

(Example 3) Coal tar pitch from which the QI component had been removed in advance was added to various FCC-DOs having different CCRs adjusted according to the distillation cut rate for the light boiling point (however, H / C <1.06, d
¹⁰⁰ ₄ ≧ 1.02) Heat the mixture to a temperature of 100 ° C. at a mixing ratio of 1/1 and mix.
Coke at 90 ° C. for 8 hours, then 145
Calcination was performed at 0 ° C. for 1 hour under an argon atmosphere.

The obtained coke was measured for CTE and puffing. Table 3 shows the results. In FIG. 1, the increase in CTE as compared with the CTE of coal tar pitch alone is plotted against CCR. With this relationship,
It can be seen that when the CCR becomes 10 wt% or less, the puffing does not change much and the CTE sharply increases. When the CCR is 10 wt% or more, the increase in CTE is
It is maintained at a nearly constant level.

Example 4 A process was performed in the same manner as in Example 1 except that various types of FCC-DO having a constant CCR of 11 wt% and different H / C were used. Note that the FCC-DO used here is d ¹⁰⁰ ₄ ≧ 1.02 when H / C ≦ 1.06.
When /C>1.06, d ¹⁰⁰ ₄ <1.02. Table 4 shows the results. FIG. 2 plots the increase in CTE with respect to H / C. From this relationship, H / C is 1.06
It can be seen that the CTE sharply increases when the value exceeds the limit.

[0050]

[Table 3]

[0051]

[Table 4]

[0052]

According to the method of the present invention, it is possible to mix with FCC-DO adjusted to a specific property without requiring energy and cost such as hydrogenation of coal tar-based feedstock and calcination of coke at high temperature for a long time. By coking,
Needle coke with low CTE and low puffing can be manufactured at low cost. This is a major invention that contributes to the coke industry.

[Brief description of the drawings]

FIG. 1 When FCC-DO / CTP = 1/1, FCC-
It is the graph which showed the relationship between CCR of DO and CTE of coke.

[Fig. 2] When FCC-DO / CTP = 1/1, FCC-
It is the graph which showed the relationship between H / C of DO, and CTE of coke.

Continuation of the front page (72) Inventor Satoru Kawano 2-4-5-306 Nakai, Kokurakita-ku, Kitakyushu-shi, Fukuoka (56) References JP-A-61-293292 (JP, A) JP-A-58-118889 (JP) JP-A-2-202989 (JP, A) JP-B-49-26481 (JP, B2) JP-B-57-61071 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C10B 57/04

Claims (2)

(57) [Claims] 1. A coal tar heavy oil from which quinoline insolubles have been removed in advance, a sulfur content of 1.2% by weight or less and a nitrogen content of 0.1%.
5% by weight or less, containing substantially no quinoline-insoluble matter,
And the atomic ratio of hydrogen to carbon (H / C) is 1.06 or less;
A method for producing needle coke, comprising mixing coke with a decant oil which is a heavy component of fluidized catalytic cracking oil of petroleum whose Conradson residual carbon content CCR is adjusted to 10% by weight or more. 2. A decant oil, which is a heavy component of a fluid catalytic cracking oil of petroleum, is subjected to vacuum distillation of a heavy component of the fluid catalytic cracking in advance to cut light components, and has a specific gravity of 1.020 at 100 ° C.
The method for producing needle coke according to claim 1, which is prepared as described above.