JPH05163491A - Production of needle coke - Google Patents

Abstract

PURPOSE:To obtain the subject coke having excellent coefficient of thermal expansion and puffing by blending a coal tar-based heavy oil with a petroleum- based heavy oil in a specific ratio, making the blend into raw coke by a delayed coker, calcining, cooling and calcining again at a higher temperature. CONSTITUTION:A coal tar-based heavy oil and a petroleum-based heavy oil from which a quinoline-insoluble component is preremoved are blended in a range of <=1.0wt.% nitrogen content and <=1.4wt.% sulfur content to give a raw material oil. The raw material oil is fed to a delayed coker to produce raw coke, which is firstly calcined in a temperature range of 700-900 deg.C, cooled <=100 deg.C once to adsorb oxygen in air on the raw coke and calcined again in a temperature range of 1,200-1,600 deg.C to give the objective excellent needle coke having extremely low coefficient of thermal expansion and extremely low puffing by co-carbonizing effects of the coal tar-based heavy oil and the petroleum- based heavy oil and the calcining at two stages.

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 needle coke having a low coefficient of thermal expansion (CTE) and a low irreversible expansion (puffing). More specifically, a specific amount of petroleum heavy oil is combined and mixed with a coal heavy oil, and a raw coke produced from this is combined with two-stage calcination, so that the conventional CTE is low, but the conventional CTE is low. The present invention relates to a method for producing low-puffing needle coke from a coal-based raw material having a high puffing.

[0002]

2. Description of the Related Art Conventionally, needle coke is produced from coal tar, coal tar pitch or heavy petroleum oil as a raw material and used as an aggregate for graphite electrodes. Generally, a graphite electrode is manufactured by extrusion-molding after adding coke particles and powder in a predetermined ratio and adding a suitable amount of binder pitch while mixing. Firing this raw electrode,
After graphitization, it is processed to produce graphite electrode products.

In recent years, due to the soaring power cost, an electrode with a low unit consumption is desired, and efforts are being made to reduce the power cost during graphitization, which consumes a large amount of power. As a method for this, a method called an ultra high power (UHP) method is used, in which a large current is passed during graphitization to increase the temperature rising rate and shorten the graphitization time. Needle coke causes irreversible expansion (referred to as puffing) during graphitization, especially during energy-saving rapid graphitization, which causes problems such as product cracking and low bulk density. Currently, the rate of temperature rise cannot be increased. Therefore, the appearance of needle coke with low puffing is desired.

Since the graphite electrode is used under severe conditions (high temperature atmosphere), it has a good thermal shock resistance, that is, a low C content.
TE's are desired. Petroleum needle coke has a relatively high sulfur content and a low nitrogen content. On the other hand, coal-based needle coke has a low sulfur content but a high nitrogen content. It is known that the thermal decomposition of the compound containing both of them causes puffing. However, with respect to the released sulfur content, since an anti-puffing agent such as iron oxide is effective, petroleum-based needle coke is focused on reducing the coefficient of thermal expansion (CTE) rather than puffing.

On the other hand, the cause of the puffing of the coal-based needle coke is that the sulfur content is originally low, so that the thermal decomposition of nitrogen compounds is the cause of the puffing. Originally, CTE is low, so we are focusing on reducing puffing.

Japanese Patent Publication No. 63-28477 discloses that needle coke with reduced puffing can be obtained by using a hydrogenated coal tar raw material. However, in order to hydrogenate coal tar-based raw materials, not only large equipment and cost are required, but also
There is a problem that the coke yield decreases, and efforts have been made to improve the coke yield by heat-treating a hydrogenated product (Japanese Patent Laid-Open No. 63-156885).

Further, in JP-A-60-33208 and JP-A-60-208392, puffing is reduced by heat-treating coal-based raw coke at a high temperature of 1,500 ° C. or higher to denitrify it. The method to do is proposed. This method has the drawback that the energy consumption per unit of heating at high temperature becomes large, and the wear of the refractory of the heating furnace is also large, and after pretreatment such as oxidation treatment of the raw coke in advance,
Efforts such as calcination at normal calcination temperature are being made.
(Japanese Patent Laid-Open No. 1-134895, Japanese Patent Publication No. 63-13
5486 publication).

However, in any of the above methods, the process is more complicated, the cost is higher, and the puffing is required to be reduced at a lower cost than the conventional methods.

On the other hand, the raw material made from heavy petroleum oil is
Due to the low coke yield and the above-mentioned circumstances, the emphasis is placed on the production of low CTE coke in good yield and at low cost. However, since anti-puffing agents such as iron oxide also become impurities, it is also required to produce low-puffing coke in good yield at low cost without using them.

In Japanese Examined Patent Publication No. Sho 53-35801, raw coke obtained by the delayed coke method is first calcined in a temperature range lower than a normal calcination temperature, and once cooled,
Again, a method for producing high-quality coke is disclosed in which calcination is performed within the normal calcination temperature range. In this specification, both Examples and Comparative Examples focus on reducing the coefficient of thermal expansion of petroleum-based needle coke using petroleum-based feedstock, and literally, the raw coke obtained using a coal-based feedstock is used. Although it is described that it can also be applied, there is no possibility that it can be applied as it is to coal-based needle coke with a different puffing generation mechanism,
In fact, even if the two-stage calcination is performed on the coal-based needle coke itself as described in Comparative Examples 4 and 6 of the present application, the reduction of puffing is slight.

On the other hand, in Japanese Patent Laid-Open No. 2-145689, a mixture of 10 to 90% by weight of a coal-based feedstock and 90 to 10% by weight of a vacuum distillation residual oil of ethylene heavy end oil is produced after heat treatment. A coke crystal growth inhibiting substance is removed, and then delayed coking is performed to form coke. A method for producing high-quality coke in which both the thermal expansion coefficient and the puffing, which are inversely related to each other due to the coke crystal structure, are reduced, has been proposed. .. However, in the example in which 50 to 30% by weight of ethylene heavy end oil distillation residual oil was blended, the puffing was 1.1 to 1.5%, which was not so low.
It is lower than that of the plain coal type.

JP-A-3-250090 discloses a low CTE in which coal tar pitch from which quinoline insoluble matter is substantially removed and petroleum heavy oil are mixed and the mixture is carbonized.
And a method of manufacturing a needle coke with low puffing is disclosed. Looking at this example, looking at the case where 50:50 petroleum heavy oil (catalytic cracking oil) was added to coal tar pitch, both CTE and puffing showed that
The results are relatively good.

However, as a result of repeated trials by the present inventors, even when a catalytically cracked oil is used as the petroleum heavy oil, such coal heavy oil and petroleum heavy oil are It has been found that the CTE and puffing can be improved only by adding them (hereinafter referred to as co-carbonization) as shown in Comparative Example of the present application. It is considered that this is due to the difference in the quality of the heavy oil such as the content of nitrogen and sulfur in the heavy oil. Both denitrification from coal-based heavy oil and desulfurization from petroleum-based heavy oil have drawbacks that require large equipment and cost.

[0014]

The object of the present invention is to achieve a low CTE and a significantly low puffing without going through costly steps such as denitrification of coal-based heavy oil and desulfurization of petroleum-based heavy oil. It is intended to provide a method for producing needle coke with high yield.

[0015]

[Means for Solving the Problems] The inventors of the present invention selected a raw material prepared by mixing a coal-based heavy oil and a petroleum-based heavy oil and adjusting and blending them so that the nitrogen content and the sulfur content are both below specific values. By producing raw coke and carrying out two-stage calcination including intermediate cooling on this raw coke, the two-stage calcination, which had little effect on the coal-based heavy oil alone, is a co-carbonized product. The present invention has been completed by discovering that the coke produced in this manner has an extremely large synergistic effect, that the coke produced in this way is not affected by the graphitization rate, and the puffing does not increase.

That is, according to the present invention, (1) a coal tar-based heavy oil and a petroleum-based heavy oil are mixed in a ratio within a range of a nitrogen content of 1.0% by weight or less and a sulfur content of 1.4% by weight or less. A raw oil was prepared, and this raw oil was charged into a delayed coker to produce raw coke. The raw coke obtained was calcined in the temperature range of 700 to 900 ° C, cooled once, and then cooled again. A method for producing needle coke, which comprises calcination in a temperature range of 1200 to 1600 ° C.

(2) Production of needle coke according to item (1), wherein the quinoline insoluble matter (QI) is substantially removed from the coal tar heavy oil in advance, or is substantially removed after mixing with the petroleum heavy oil. Is the way

(3) The method for producing needle coke according to the above (1), wherein the once cooling is performed by cooling to 100 ° C. or lower to adsorb oxygen in the air.

The present invention will be described in detail below. Examples of the coal tar used as a starting material in the present invention include ordinary coal tar produced as a by-product during coke production, while coal tar pitch contains a quinoline insoluble component (hereinafter referred to as QI) and has a softening point of 100. A soft pitch or a medium pitch of not higher than 0 ° C, preferably 20 to 100 ° C is used. When the softening point exceeds 100 ° C, by adding an aromatic oil such as anthracene oil,
Workability can be improved by setting the softening point to 100 ° C. or lower.

In the method of the present invention, the QI component is substantially removed from such coal tar or coal tar pitch, or is substantially removed after mixing with the petroleum heavy oil. That is, the QI content is usually removed to 0.5% by weight or less, preferably 0.3% by weight or less, and optimally 0.1% by weight or less. As a means therefor, a method known per se which has already been described in various documents can be applied. For example, the heavy tar oil is treated with a mixed solvent of an aromatic oil and an aliphatic oil.

As the aliphatic oil, cyclic compounds such as cyclohexane and cyclopentane, compounds having a carbonyl group such as acetone and ether, kerosene and light oil can be used. In particular, it is preferable to use this aliphatic compound and an aromatic oil such as tar-based cleaning oil or anthracene oil in an appropriate ratio, since the solubility can be appropriately adjusted depending on the mixing ratio.

The weight ratio of pitch: solvent is 1: 2
1: 0.3, preferably 1: 1 to 1: 0.4 and mixed. The mixing temperature can be from room temperature to about 350 ° C, but is preferably 100 to 300 ° C from the viewpoint of mixing efficiency. The stationary separation can be performed at a temperature from room temperature to 350 ° C., but the range of 100 to 300 ° C. is preferable from the viewpoint of separation efficiency, and the stationary time varies depending on the type of solvent, the amount of solvent, the temperature, etc. , Usually about 10 minutes to 10 hours,
It is preferably 30 minutes to 5 hours.

In the method of the present invention, the above-mentioned supernatant liquid (comprising reformed coal tar or coal tar pitch and a solvent) from which QI is substantially removed is obtained, and this is mixed with heavy petroleum oil. Although it can be used as a raw material for needle coke production, it is usually used by mixing the above supernatant with a petroleum heavy oil after removing the solvent by distillation. Distillation is carried out at the boiling point of the solvent, the distillation temperature of 95% by volume, etc.,
The distillate is collected and reused as a solvent if necessary.

Examples of the petroleum heavy oil to be mixed with coal tar or coal tar pitch include catalytic cracking oil, atmospheric residual oil, vacuum residual oil and the like, but they are desulfurized even a little and their aromaticity is enhanced. Contact cracked oil is preferred. Ethylene bottom oil and the like are also preferable.

The mixing ratio is calculated from the nitrogen content in the coal tar or coal tar pitch, the sulfur content, the nitrogen content in the petroleum heavy oil and the sulfur content, and the nitrogen content in the mixed oil is 1.0% by weight. Hereinafter, the sulfur content is mixed in a ratio of 1.4% by weight or less. It goes without saying that it is mainly determined by the nitrogen content in tar pitch and the like and the sulfur content in heavy petroleum oil. Actually, from the usual contents of nitrogen and sulfur, coal tar or coal tar pitch 4 was used as shown in the examples.
It is 0 to 90% by weight, and the heavy petroleum oil is about 60 to 10% by weight. Coal tar or coal tar pitch is preferably 50 to 80% by weight, and petroleum heavy oil is 50 to 20% by weight.

The obtained mixed raw material oil is coked as a coking charging raw material by a conventional needle coke production method. That is, 450 to 4 depending on the delayed coker
Raw coke is prepared at a temperature of about 90 ° C.

Usually, this raw coke is calcined in a rotary kiln or the like in one step to 1300 to 1500 ° C. to obtain needle coke, but in the present invention, this is not carried out in one step but is calcined in two steps. Is characteristic. That is, the raw coke is first calcined in the temperature range of 700 to 900 ° C., once cooled to 300 ° C. or lower, and then again 1200 to
Calcination in the temperature range of 1600 ° C. The first stage calcination is performed in a non-oxidizing atmosphere at a temperature rise time of about 200 ° C./hr for 70
Heat to 0-900 ° C and then cool. Cooling at 100 ℃
Hereinafter, it is preferably cooled to about room temperature. 700
The temperature of ~ 900 ° C is the temperature at which the raw coke rapidly generates volatile matter, but once the calcination is stopped at this temperature, the cracks generated on the surface of the coke by cooling under the atmosphere open the oxygen in the air. Is adsorbed, and the oxygen during the second calcination,
By increasing the pores by oxidizing the coke,
It is considered to reduce CTE and puffing.
Therefore, for cooling after the first-stage calcination, it is preferable to lower the temperature to room temperature as much as possible and adsorb oxygen in the air as much as possible. After cooling, the temperature is again raised to a normal calcination temperature or slightly higher temperature of 1300 to 1600 ° C. at a rate of 200 ° C./hour to obtain needle coke.

The obtained needle coke is blended in a predetermined proportion of particle size, and while being heated and mixed, an appropriate amount of binder pitch is added, and the mixture is extrusion-molded to produce a raw electrode.
It goes without saying that iron oxide may be added as a puffing inhibitor at the time of mating, if necessary. The raw electrode can be graphitized by firing and then processed to produce a product graphite electrode.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Examples 1, 2 and Comparative Examples 1, 2, 3) As coal tar pitch, specific gravity 1.173 (100 ° C.), H / C
0.72, nitrogen content 1.10% by weight, sulfur content 0.37% by weight, Conradson residual carbon (CCR) 30.0% by weight,
Coal tar soft pitch having a softening point of 37 ° C. was used. This is heated to 170 ° C., a mixed solvent of kerosene and tar cleaning oil is added to deposit a heavy pitch-like precipitate, which is allowed to stand and separate, a QI component is separated and distilled to remove the solvent. Separate
De-QI coal tar pitch (CTP) was obtained. The QI content was 0.01% by weight or less. As heavy petroleum oil,
Fluid catalytic cracking residual oil (FCC-DO) was used. H / C
0.94, Conradson carbon residue (CCR) 11.3
% By weight, nitrogen 0.14% by weight, sulfur content 0.96% by weight,
The QI content was 0.01% by weight.

These were mixed at the compounding ratio shown in Table 1 and heated at a coking temperature of 480 to 490 ° C. for 8 hours using a small reactor of 5 kg per batch to obtain raw coke. Using this laboratory coke in a laboratory calcination furnace (Siliconit furnace, 4 kg / batch), one-stage calcination temperature 800 ° C, two-stage calcination temperature 1300 to 1400 ° C, intermediate cooling temperature, room temperature open to the atmosphere, furnace atmosphere Was subjected to two-step calcination as shown in Table 1 in an argon gas stream. Table 1 shows the coke yield and the nitrogen content in the coke.

CTE is measured by crushing calcined coke,
About 100 parts of this, with 100 parts of this mixture, 25 parts of coal tar binder pitch was mixed, heated and bonded, then molded, fired at 1000 ° C. and test pieces graphitized at 2500 ° C. It was measured. Puffing was carried out on a test piece similarly molded and fired using a Tammann furnace at a temperature rising rate of 10 ° C./min (standard) at a temperature of room temperature to 2500 ° C. between the measured temperature and the dimension of the fired body perpendicular to the extrusion direction. The elongation is shown as puffing. The results are shown in Table 1.

In Table 1, Example 1 and Comparative Example 1 are CT
2 is a comparison of the physical properties of Example 1 in which two-step calcination was performed and Comparative Example 1 in which one-step calcination was performed on a co-carbonized product in which P and FCC-DO were mixed in 50% by weight. Example 2 and Comparative Example 2 are Example 2 in which two-step calcination was performed and Comparative Example 2 in which one-step calcination was performed on the co-carbonized product in which CTP and FCC-DO were mixed at 70/30 wt% each. It is a physical property comparison. Comparative Example 3 shows the physical properties of a conventional coal tar-based coke obtained by calcining a single CTP in one stage.

[0033]

[Table 1]

(Example 3, Comparative Examples 4, 5 and 6) CTP / FCC-DO of the present invention when the graphitization rate was doubled in order to see the effect of co-carbonization-2 step calcination in the present invention. (50
Example 3 in which the co-carbonized product of 50/50) was calcined in the two steps described above.
And Comparative Example 4 in which the same co-carbonized product was calcined in one step, Comparative Example 5 in which tar-based plain fresh coke having a high CTE but low puffing was calcined in two steps, and the same tar-based plain raw coke in one step For the calcined Comparative Example 6, the graphitization rate was 10
Table 2 shows the puffing measurement results for the cases of ℃ / min and 20 ℃ / min.

[0035]

[Table 2]

[0036]

EFFECTS OF THE INVENTION According to the method of the present invention, co-carbonization in which both CTE and puffing are not sufficiently reduced only by ordinary one-step calcination of coal-based heavy oil and petroleum-based heavy oil. By calcination of the product in two steps, a sufficiently low CTE and puffing coke was obtained, and in the case of calcination only by two steps, CTE and puffing were remarkably improved by combining co-carbonization. .. That is, a significant synergistic effect was observed between co-carbonization and two-step calcination, and needle coke with low CTE and puffing was obtained. In addition, this needle coke is not affected even when the graphitization rate required for rapid graphitization is increased,
The puffing has the surprisingly excellent property of not rising.

Claims (3)

[Claims] 1. A feedstock oil is prepared by mixing coal tar heavy oil and petroleum heavy oil in a ratio such that the nitrogen content is 1.0 wt% or less and the sulfur content is 1.4 wt% or less. This raw material oil is charged into a delayed coker to produce raw coke, and the obtained raw coke is first calcined in a temperature range of 700 to 900 ° C., cooled once, and then cooled again to 1200 to 1600 ° C. A method for producing needle coke, which comprises calcination within a temperature range. 2. The method for producing needle coke according to claim 1, wherein the quinoline insoluble matter (QI) is substantially removed from the coal tar heavy oil in advance, or the quinoline insoluble matter (QI) is substantially removed after mixing with the petroleum heavy oil. 3. The method for producing needle coke according to claim 1, wherein the once cooling is performed by cooling to 100 ° C. or lower to adsorb oxygen in the air.