JPH02272095A - Method for control of puffing of coke produced from coal tar pitch - Google Patents

Abstract

PURPOSE: To produce a coal pitch premium coke suitable for the production of high-load-withstanding graphite by adding at least partially soluble compound of Mg, Ca or the like to a starting coking material.

CONSTITUTION: Desirably 0,05-0.5 wt.% at least partially soluble compound such as a carboxylate, sulfonate or phenolate of a metal selected from the group consisting of magnesium, calcium, strontium and barium is added to a starting coking material comprising coal tar pitch.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for suppressing puffing (irreversible volumetric expansion that occurs in the temperature range of 1400 to 2000°C) in coke produced from coal tar pitch.

The present invention particularly relates to coke used as a raw material for producing graphitized bodies (hereinafter referred to as graphite bodies) made of carbon.

[Prior Art] This type of coke is made by mixing hydrocarbons or hydrocarbon mixtures with a high carbon content, such as hot tar, decant oil, pyrolysis oil, lubricating oil extract or coal tar pitch, with sufficient air exclusion. In particular, it is produced by pyrolysis using a delayed coking process. Furthermore, a chamber furnace method can also be used, although on a smaller scale.

Graphite bodies have good electrical and thermal conductivity, high thermal shock resistance, corrosion resistance, mechanical strength and outstanding temperature stability.

Graphite bodies are therefore used in large quantities in electrothermal and electrochemical processes or processing technology. The main field of use is diameter 7
This is a field of electric steel making in which an arc is generated between graphite electrodes up to 00 mm and up to 2700 cm in length to obtain heat of fusion.

The production of graphite bodies, which takes several weeks, involves a number of expensive processing steps. The raw materials required are expensive.

As a result, graphite bodies become increasingly expensive. Therefore, one of the most important objectives of graphite manufacturers is to minimize the occurrence of defective products and to produce products with high utility value.

Graphite bodies are produced from coke, a carbonizable binder and optionally various auxiliary additives. From the coke fraction obtained after crushing and sieving, a batch of dry material is produced according to the above recipe, which is generally mixed with a binder under heat and the mixture is processed under compression, e.g. by extrusion method. Processed into a molded body. 700 to 1 molded body
The coke body is calcined at a temperature of up to 000°C, converting the binder into a coke matrix, and the coke body is converted into a graphite body by heating to 2500-3000°C in an electric furnace.

The most important coke raw material is currently petroleum coke, especially anisotropic petroleum premium coke, which is often also called needle coke because of its external structure. This needle coke has very good properties such as low coefficient of thermal expansion, low electrical resistance, good mechanical strength and high thermal conductivity. This needle coke is therefore used for producing graphite bodies capable of maximum loading, such as electrodes for electric steelmaking furnaces.

In recent years, expensive coke produced from coal tar pitch, so-called St needle coke, has become available. However, the production of large, loadable graphite bodies made of this type of coke is uneconomical, since cracks occur during graphitization, resulting in a large number of rejects.

Premium coke is manufactured using the delayed coking method. In this case, a high-boiling hydrocarbon mixture as aromatic as possible is heated in a furnace, often in a tube furnace, to approximately 500°C and then sent to a coke drum.
Coking is now carried out gradually over a period of several hours.

This process is carried out with air excluded. After the coking process is completed, the obtained raw coke is taken out from the coke drum and calcined at 1200-1400°C. The final pore system of the coke is then formed and the content of volatile substances falls to less than 1%.

The usability of coke is critically influenced, in addition to its structure, raw materials, manufacturing conditions, etc., by a phenomenon that those skilled in the art refer to as "puffing". What is puffing?1400~2
It refers to irreversible volume expansion that occurs rapidly in the temperature range of 1,000°C. This puffing creates mechanical stresses within the molded body made from coke, which generates micro- and macroscopic cracks in the structure and at the same time causes the molded body to rupture, resulting in rejects. Furthermore, important properties of the graphite body, such as mechanical strength, electrical resistance and thermal conductivity, are deteriorated. Puffing can be reduced by gradual heating. However, this is uneconomical and also impairs quality.

In the case of petroleum coke, the cause of puffing is the sulfur content of 0.3-1.5% in commercial products.

For example, during graphitization, the carbon molded body has a
When heated to temperatures of It can be significantly reduced or suppressed by adding suitable inhibitors. A large number of puffing inhibitors have been proposed, and their use always poses a problem of fine distribution into the shaped bodies to be graphitized. The amount of inhibitor material actually added is 1-2% based on the coke component of the mixture batch. A significant drawback in the use of puffing inhibitors is that they increase the coefficient of thermal expansion of graphite. This degrades its stability to changes in temperature and increases the usage of graphite in steelmaking electrodes.

The aim must therefore be to use as effective a substance as possible in the smallest possible amount. This problem cannot be solved by packaging, and many proposals have been made in this regard.

German Patent Application No. 1073368 describes the use of alkali metal salts, such as sodium or potassium carbonate, as puffing inhibitors. The electrode raw material cooled after firing is impregnated with a sodium carbonate or potassium carbonate solution, and then graphitized.

FR 1 491 497 discloses adding chromium oxide to coke-pitch mixtures. In addition to its anti-puffing effect, this additive also acts as a graphitization catalyst.

GB 733073 describes a method in which oxides of chromium, iron, copper or nickel are added to the coke during crushing and are thus finely distributed on the surface of the coke when mixed with the subsequent pitch. ing. These oxides act as puffing inhibitors during the graphitization of the shaped and fired compacts.

U.S. Pat. No. 3,563,705 discloses a method for inhibiting puffing by adding a mixture of iron or calcium compounds and trace amounts of titanium and zirconium compounds to a mixture of coke and binder. be.

U.S. Pat. No. 3,338,993 describes adding calcium fluoride, magnesium fluoride, strontium fluoride and barium fluoride to a mixture of raw coke or calcined coke and a binder for the same purpose. There is.

According to US Pat. No. 4,308,177, chlorinated naphthalene additives, in addition to acting as pressing aids and condensing agents for pitch, also have anti-puffing effects. Especially chloronaphthalene and iron oxide, chromium oxide, copper oxide,
When a metal compound having an inhibitory effect such as cobal I oxide or manganese oxide and an alkaline earth metal fluoride are simultaneously added to the mixture of each manufacturing component before molding, the puffing inhibiting effect becomes remarkable due to the synergistic effect. 1-3
Adding % of calcium cyanamide or calcium carbide to green coke before firing as an agent to bind sulfur and inhibit puffing is described in U.S. Pat. No. 3,642,962.
It is disclosed in the specification of No.

US Pat. No. 4,312,745 and US Pat. No. 4,334,980 relate to a method for producing coke that does not cause puffing. For this purpose, the sulfur-containing substances used are chromium compounds, preferably chromium oxide (US Pat. No. 43,127).
45) or an iron compound, advantageously iron oxide or calcium fluoride (US Pat. No. 4,334,980), and then the coke is produced by a delayed coking process.

All these known methods involve adding inhibitors during the production or processing of petroleum coke.

These methods are compromise solutions and some have significant drawbacks. In other words, the amount of ash generated within the graphite body increases with the addition of the metal compound. The graphite products thus produced cannot be used for purposes requiring pure graphite or can only be used after expensive purification treatments, associated with increasing the coefficient of thermal expansion. This drawback has already been detailed. Many of the previously proposed anti-puffing agents have problems in their handling or their manufacturing process produces harmful, corrosive, and environmentally polluting emissions (fluorides, chlorides, nitrates, chromium compounds, copper). compounds, nickel compounds, cobalt compounds, chloronaphthalene). Alkali metals and alkaline earth metals, as well as iron compounds, catalyze the oxidation of carbon and are undesirable for all high-temperature applications, and finally all additives require expense in their procurement, preparation and use.

Special problems exist when using coke made from coal tar pitch.

Various studies (K, W, Tucker and others) r13th Biennial Conference on Carbon in Two Bins/California
ce on Carbonin Irvine / C
a1if,) J Extended Abstract
ts, pages 191 and 192 and Letizia (T, Let
R16th Annual Conference on Carbon in San Diego, California (1
6th Biennial Conference on
Carbon in San Diego / Ca
1if,) J Extended Abstract
s, 593.594 true and Morris (E, G, Mo
(ibid., pp. 595 and 596)
and experience in industrial processing shows that the correlation that exists between high sulfur content and puffing for petroleum coke does not hold true for coal pitch coke, and in particular for St coke and St needle coke. Containing sulfur indicates that the puffing of petroleum coke is not reduced at all or cannot be reduced sufficiently by the addition of conventional inhibitors such as iron oxide or chromium oxide for petroleum coke. Coke does not actually cause puffing, but St coke or St needle coke causes significant puffing.

It is therefore not possible to compare the puffing of petroleum coke with the puffing of coke produced from coal tar pitch, and it is therefore clear to those skilled in the art that in the case of coke produced from coal tar pitch, in addition to sulfur, in particular Other shadow 1 factors such as 1 are also considered to be the cause of puffing and have been discussed as 1 abnormal buffing of St coke.

This property of abnormal puffing is advantageous for reasons regarding the availability and quality of its raw materials as well as for economic reasons, despite the existence of a large number of puffing inhibitors for petroleum coke and petroleum premium. This has hitherto prevented the use of St needle coke, which is approximately equivalent to coke, for the economical production of large graphite bodies, such as electrodes for steel production.

(Problem H to be Solved by the Invention) Therefore, the problems of the present invention are as follows: To provide a method for producing coke; (2) to reduce the amount of added inhibitor metal compared to methods actually used in petroleum coke; (3)
The object of the present invention is to use inhibitors which no longer generate harmful emissions and which practically do not suffer from the other drawbacks mentioned above.

[Means to solve the problem]

Second tlIN! According to the invention, I is added to the starting material for producing coke before or during coking,
The solution is to add at least one compound of a metal from the group of magnesium, calcium, strontium and barium which is at least partially soluble in these starting materials. As additives according to the invention, in particular alkaline earth metal compounds from the group of sulfonates, carboxylates and carbonates are used, alone or in mixtures. The sulfonate has the general formula 2 (R-3o,)-metal (where R
is an alkyl chain having 25 to 70 carbon atoms, and the metal is M
g s Ca % S r and a metal from the group of Ba). The carboxylic acid salt has the general formula 2 (R-Coo)"metal, where R is an alkyl group having at least 8 and up to 400 carbon atoms, and the metal is a metal from the group Mg, Ca, Sr and Ba. The carbonate is represented by the general formula 2 (R-C,H,
-0)-metal, where R is a side chain of at least 8 and up to 400 carbon atoms attached to the aromatic ring of the phenol, and the metal is a metal from the group Mg, Ca, Sr and Ba. ). This type of compound is Lub
rizol Corporation<29400
Lak @ 1 and Boulavard, Wickl
It can be purchased from ifL 0hio 44092 (located in the US). These compounds advantageously have a content of alkaline earth metals of zero in the material to be coked.
．． 05-0.5% by weight. Instead of each of the above-mentioned compounds, other alkaline earth metal compounds with organic groups can be used, which are at least partially soluble in the material to be coked, such as xanthates of the type (R-OC3S), [(RO)I PSS)-type dithiophosphates,
(R,NC55)-type dithiocarbamate, RSH
mercaptans of the type (R3Oz)-, alkyl-substituted arylsulfonates of the (R3Oz)-type, alkyl sulfates of the (RO3O3)-type, where R is an aliphatic group or a mixed aliphatic-aromatic group having at least 7 carbon atoms; ) and aryl sulfonates and aryl-substituted carbonates can also be used. By being dissolved in the material to be coked, the puffing inhibitor is present as finely as possible, ie in a molecularly distributed manner.

The addition of these substances must be carried out in such a way that they are evenly distributed over the entire volume of material to be coked, so that they are later evenly distributed in each volumetric component of the coke and suppress puffing there. be able to. This procedure consists of dissolving or dispersing in a material that is at least partially soluble in the use substance and then using a conveying device suitable for the use substance, e.g. via a placement pump. This can be advantageously carried out by adding continuously and in suitable weight ratios during the course of the process. The inhibitor can, of course, also be stirred into the material to be used in a corresponding amount and dissolved in a batchwise or incrementally continuous operation.

The addition of the inhibitor to the materials used can be carried out at various points in the process and using known arrangements and conveying devices. In the delayed coking process, this addition is advantageously carried out upstream of the conveying device or pump that conveys the material to the heater or tube furnace.Optionally, this addition is carried out, for example, from the heater to the inlet to the coke drum. It can also be carried out directly during the filling process into the coke drum or together with substances that regulate the formation of air bubbles in the coke drum. Furthermore, other possibilities exist which are well known to the person skilled in the art and can be used appropriately.

The alkaline earth metal compounds according to the invention are added in such amounts that the respective alkaline earth metal content in the material to be coked is at least 0.05% by weight. The upper limit for the amount of inhibitor added depends on the desired properties of the coke and must be confirmed experimentally. This is generally 0.5% by weight, based on the respective alkaline earth metal content in the toilet material.

(Effects of the Invention) An advantage of the present invention is that the coal pitch coke, especially the coal pitch premium, is suitable for suppressing puffing and thereby producing graphite bodies capable of high loads such as high load electric bridges for electric steel manufacturing. The purpose is to enable the production of coke.

Furthermore, the amount of inhibitor metal added in the case of the process according to the invention differs from that in the process with petroleum coke and in the process with coal pitch coke using insoluble additives according to DE 39 07 156 A1. Compared to the method
The amount can be reduced by at least half to obtain the same effect. As a result, the content of substances that require oxidation to form ash is extremely reduced. The deterioration of the coefficient of thermal expansion is so slight that it can be ignored industrially.

Harmful emissions no longer occur.

〔Example〕

The present invention will be explained below based on Examples.

Finely powdered coal tar pitch suitable for producing needle coke [α resin 0.5%, β resin 1i 31.2%, γ resin 29.0%, coking residue 54.1% (D[N51
905), softening point 84.0°C (DIN52025
)], magnesium sulfonate (2 carbon atoms)
Calcium carboxylate (alkyl side chain component having 8 to 12 carbon atoms, calcium content 15%)
Weight%, density 1.15 g/Cl5Lubrizo1
0368150), and barium carbonate (alkyl side chain component having 8 to 12 carbon atoms, barium content 2
7°5% by weight, density 1.31 g/(1m”, Lu
brizo 1 (trade name L2106) in an amount corresponding to 0.5% by weight of the inhibitor metal based on the coal tar pitch. another one
Inhibitor metal 0 for coal tar pitch in one batch
．． Barium carbonate of the same type was added in an amount corresponding to 25% by weight. One batch had no additives added for comparison. Each batch was individually mixed in a heatable kneader and then heated to 1050° C. in an annular chamber furnace. The temperature gradient in the coking phase was 2/h. The coal pitch cokes thus obtained were the same except for their puffing behavior, and had the following characteristic values. Sulfur content 0.34±0.02% <according to DIN51724T1), hydrogen content 0.066±0.0 O8% (DI8
51912), density 2.122±O, OO4g/
cm" (according to D IN51901), coefficient of linear thermal expansion (CTE) α35±0.05xlO-"xK-' (
D [according to N51909], to prepare the samples, each coke was ground separately according to the batch in a hammer mill to a maximum particle size of 1 ounce, and then 100 parts by weight of coke was ground with coal tar pitch (softening point 89°C). DIN5202
5), coking residue 59% (DI851905)
(according to DIN 51921), quinoline solubility 12% (according to DIN 51921)].
Mixed for 20 minutes at 30°C. This mixture was molded into a block press molding having a diameter of 50 cm and a length of 80 cm at a compounding temperature of 110°C. This press-formed body is heated under a temperature gradient of 4
It was heated at temperatures up to 800° C. in an indoor furnace at 1/h. A sample of 8X8X60 size was cut from the coke body thus obtained, and the dynamic puffing was measured by Wagner (LH).

"High Temperat 1 High 0 Pressures" by Wagner and others.
ures (formerly GH Pressures) J 13.1
53. It was carried out in the temperature range of 1400 to 2400°C using a high temperature articulating rod dilatometer described in 1981. The volume expansion coefficient summed over the measurement range was used as a measure of puffing. These values are calculated from the coefficient of linear expansion of the sample by Δvolume−
Summer mountain based on 3Δ length. The results are shown in the table below.

These values in the table indicate that alkaline earth metals, especially barium, work well as puffing inhibitors in coal pitch coke.

Furthermore, it is clear that iron, which is useful as an inhibitor, is of no use in petroleum coke, which shows that it can be treated with significantly lower concentrations of inhibitor than in petroleum coke.

Claims (1)

[Claims] 1) Puffing in coal pitch coke (140
In a method for suppressing the irreversible volumetric expansion (occurring in the temperature range from 0 to 2000°C) by means of additives, the starting materials for producing coke are at least partially added to the starting materials before or during coking. 1. A method for suppressing puffing of coke produced from coal tar pitch, characterized in that at least one compound of a metal from the group of magnesium, calcium, strontium and barium is dissolved in the coal tar pitch. 2) Process according to claim 1, characterized in that a compound from the group of alkaline earth metal sulfonates is added. 3) Process according to claim 1, characterized in that a compound from the group of alkaline earth metal carboxylates is added. 4) Process according to claim 1, characterized in that a compound from the group of alkaline earth metal carbonates is added. 5) Claim 1, characterized in that at least two of the compounds according to one of claims 1 to 4 are added in the form of a mixture.
Method described. 6) The compound is added in an amount corresponding to an alkaline earth metal content of 0.05 to 0.5% by weight based on the material to be coked.
The method described in. 7) Before adding the compound according to one of claims 1 to 4 to the materials to be coked, it is dissolved in a substance that is at least partially soluble in those materials or at least partially dissolved in said material. 7. A method according to claim 1, characterized in that the method is dispersed in a substance that contains 8) Process according to one of claims 1 to 7, characterized in that the compound according to one of claims 1 to 4 is added to the material to be coked continuously during the conveying process and at a suitable weight rate. . 9) When applying the delayed coking method, claim 1
9. Process according to claim 1, characterized in that the compound according to one of claims 1 to 4 is added to the material to be coked before the tube furnace. 10) When the delayed coking method is applied, the compound according to any one of claims 1 to 4 is added to the material to be coked before or during press-fitting into a coke drum. The method described in one.