RU2196192C2 - Anodic mass production method - Google Patents

Abstract

FIELD: nonferrous metallurgy. SUBSTANCE: method involves preparing burden of pitch and/or oil cokes, receiving, thermostatically controlling and homogenizing hydrocarbon binder comprising mixture of coal tar and/or oil pitches; dosing and mixing while heating cokes and pitches. Coal tar and/or oil pitches are separately received from suppliers and thermostatically controlled with following preparing of mixture comprising different grades of pitches and homogenizing thereof under turbulence mode. Pitches are dosed in an amount providing content of α- fraction in pitch mixture within the range of 26-28% and of α₁- fraction within the range of 6-8%. Method is used for manufacture of anodes for aluminum electrolyzers. EFFECT: wider range of raw materials, improved and stabilized quality of binders used for manufacture of anodic mass and, as a consequence, increased technical and economic efficiency of anodic mass and electolyzer. 4 cl, 2 tbl

Description

 The present invention relates to electrode production, in particular to the production of anode paste for self-baking anodes of aluminum electrolysis cells, and can be used in the production of baked anodes.

 It is known that a general trend in the coke industry is a decrease in the production of coal tar pitch and an increase in their pyrolysis. As a result, there is an acute shortage of coal tar pitch and they become heavier and less ductile.

 Oil pitch can be considered an alternative binder, but medium-temperature oil sands produced at refineries have a low coke residue, which does not allow to obtain anode mass on their basis and, accordingly, self-baking anodes of the required quality.

On the other hand, a significant volume of production of the anode mass, due to its high consumption in electrolysis (up to 500-600 kg / t A1), requires a steady supply of binder materials in an amount that cannot be provided by one or two domestic suppliers. As a result, aluminum smelters are forced to simultaneously process the sands of various suppliers, differing both in origin (oil, coal) and in their physical and chemical properties, due to the technological characteristics of the supplier-manufacturer:
- softening temperature,
- the content of substances insoluble in quinoline (α ₁ fraction),
- the content of substances insoluble in toluene (α-fraction),
- release of volatile substances.

 So, for coal tar pitch GOST 10200-83 provides for the release of three brands of pitch: "A" and "B" (medium temperature pitch), "B" (pitch with a softening point).

 A number of methods are known aimed at simultaneously involving in the production process the anode mass of pitch with various physicochemical characteristics, including oil pitch (AS USSR N 1520899, C 25 C 3/12, 10.11.87, "Anode mass for self-baking anodes of aluminum electrolytic cells "; AC USSR N 1512180, С 25 С 3/12, 08/26/87," Carbon anode mass "; A. S. USSR N 824691, С 25 С 3/12, 08.10.76," Method production of the anode mass ").

 The closest in technical essence and the achieved result is the technical solution according to the patent of the Russian Federation N 2080418, С 25 С 3/12, 05/27/97, "Method for the production of the anode mass of aluminum electrolysis cells", which consists in the fact that in the production of the anode mass as a carbon-containing binder use a homogeneous mixture obtained by mixing coal tar pitch with oil pitch at a ratio of 19: 1 to 2: 1. Mixing coal tar pitch with oil pitch is carried out by pumping the mixture from the lower zone of the tank to the upper one based on a 1-3-fold deception by a common stream in a turbulent mode.

 The disadvantage of this method is the complexity of its real technological implementation, since the authors, stating for a homogeneous mixture a sufficiently wide range of ratios of various pitch (19: 1-2: 1), did not specify by what principle this or that ratio is selected, by what parameter is carried out control on stabilization of which technological indicator the claimed technology is directed.

 It is known that the main task of any technology for the production of anode paste is to achieve a stable quality of the anode paste that meets the requirements of TU 48-5-80-86.

 It is not possible to achieve this by the known technology due to the fact that the pitches are accepted and thermostated as they arrive from the suppliers in a common flow, not paying attention to changes in the suppliers' time and supply volumes, and therefore, the qualitative characteristics of the incoming raw materials.

 The objective of the invention is to expand the raw material base for the production of anode paste, improve and stabilize the quality of the binder used to produce the anode paste, and, as a result, increase the technical and economic indicators of the production of the anode paste and electrolysis as a whole.

The technical result of the proposed method is the ability to stabilize the physicochemical properties of the binder by using an additive pitch mixture in the production of the anode mass, the composition of which is determined based on the goal of stabilizing the control quality indicators of the mixture, namely, stabilizing the content of α and α ₁ fractions.

The specified technical result is achieved by the fact that in the method for the production of the anode mass for the electrolytic production of aluminum, including the preparation of a mixture from pitch and / or petroleum coke, acceptance, temperature control, homogenization of a hydrocarbon binder from a mixture of coal and / or petroleum pitch, dosing of coke and pitch and mixing when heated, acceptance from suppliers and thermostating of coal and / or oil pitch are carried out separately, then an additive mixture of various pitch is prepared and homogenized in the turbulent regime, the dosing is different pitches in the mixture is carried out in an amount providing a content of α-fraction in the additive mixture of pitches in the range 26-28%, and the fraction α ₁ in the range of 6-8%, the homogenization additive mixture is carried out at pitches a temperature 1.7–2 times higher than the softening temperature of coal tar pitch, while thermostat is subjected to a pitch with a volatile content of more than 58%; moreover, dust of electrostatic precipitators with a fraction of -0.05 mm is added to the additive pitch mixture not less than 70-75% and / Whether pitch fraction precipitates -1 mm, wherein the total content of α ₁ fraction in the additive mixture of the aforementioned pitches and the additives in the form of electrostatic dust and / or precipitation of pitch is maintained in the range of 6-8%.

 Briefly, the technical essence of the present invention lies in the fact that knowledge of the properties of the starting pitch, the accuracy of their dosing in an additive mixture, taking into account recommendations for the implementation of the method, homogenization of the mixture in small volumes and guaranteed mixing parameters allow to obtain a mass with guaranteed stable properties.

It is known that the yield of coke from the binder primarily depends on the content of the α-fraction in it, and more recently, the α-fraction has been divided into α ₁ and α ₂ fractions:
-α ₁ fraction (or carboids) contains particles of semicoke, coke and mineral impurities. Carboids are an inert filler. They do not have binding properties, but serve as centers of coke formation, activate the coking process and contribute to an increase in the yield of coke from the lower molecular weight components of the pitch fractions and;
-α ₂ fraction (or carbenes) is considered one of the most important, since its content in the electrode pitch can give a partial assessment of its quality and suitability for the anode mass. This component of the pitch melts when heated and has the properties of a binder, with an increase in its content, the quality of the binder improves.

For the practical implementation of the proposed method at the manufacturing plants of the anode mass, it is necessary, in addition to the input control of the pitch arriving for processing, to determine the α and α ₁ fractions immediately before the pitch is put into production.

Common features of the proposed method and the prototype method is the following:
1) acceptance of incoming oil pitch is carried out separately from coal;
2) prepare a hydrocarbon binder in the form of a mixture of pitch with various physico-chemical properties;
3) homogenize the mixture in a turbulent mode.

But, as mentioned above, to implement the prototype method in practice is not possible, since:
- firstly, the control parameter for choosing the optimal ratio of mixed pitch is not defined;
- secondly, it is proposed to perform homogenization by pumping the pitch mixture from the lower zone of the tank to the upper common stream in a turbulent mode, which, as practice has shown, does not allow to average the physicochemical parameters of the pitch mixture due to insufficient turbulence when working with large volumes. The pitch is practically pumped in layers without mixing.

Therefore, the main distinguishing features of the invention are:
firstly, it is not a spontaneous choice of the ratio of various pitch in the additive mixture, but selection based on their initial properties, while dosing into the mixture and controlling its quality is carried out according to the most important indicator that affects the coke yield from the binder, the content of the fraction in the mixture,
secondly, the additive mixture is prepared and homogenized in small volumes in the pecotrass. That is, the mixing of the pitches and their averaging occurs during the simultaneous metered pumping of the pitches from the pitch warehouse into the main building in the pitch line and in the pressure tank, where the prepared additive mixture is supplied from the bakers. Turbulization in the peck-road is ensured by introducing into the additive mixture its pitch peaks in the flows directed at an angle to each other and at a speed that ensures turbulent mode in the pek-pipe.

The distinguishing features include the following:
- if according to the prototype separate reception of pitch is carried out only on the basis of its origin (oil or coal), then in the claimed invention, the reception of pitch from all suppliers is carried out separately, since even among coal or oil pitch the quality indicators are very different. Separately, thermostating is also carried out, and the peaks are thermostated to a content of “volatile” substances of less than 58%. It is advisable to control the pitch for the α and α ₁ fractions after temperature control;
- to ensure the homogeneity of the hydrocarbon binder mixture, it is proposed to carry out homogenization in a turbulent mode at a temperature that is 1.7-2 times higher than the softening temperature of coal tar pitch, that is, if medium and high temperature peaks are sent to prepare the mixture, then the homogenization temperature is selected based on the temperature softening high-temperature pitch;
- if necessary, to involve in the production of the anode mass oil pitch, characterized by a low content of α-fraction, the authors propose to carry out its adjustment for this indicator, and more specifically for the α ₁ fraction, by adding dust from electrostatic precipitators and / or pitch sediments.

However, a comparison of the proposed method with similar solutions in this area revealed a number of similar features:
- an increase in the centers of coke formation due to the introduction of carbon into the anode mass is known from A.S. USSR N 1014307, C 25 C 3/12, 09.09.81, "The mixture for obtaining the anode mass";
- heating the hydrocarbon binder to a temperature 1.5-2 times higher than the softening temperature of the pitch, it is known from A.S. USSR N 1520899, С 25 С 3/12, 10.11.87, "Anode mass for self-baking anodes of aluminum electrolysis cells".

 A new set of features, both known and unknown, in their close relationship allows to obtain a technical result of a higher level.

The main advantage of the proposed method for the production of the anode mass is the ability to maintain the stability of the specified quality indicators of the electrode binder after homogenization of the pitch dosed according to the proposed method, which allows:
- improve and stabilize the quality of the anode mass;
- reduce the consumption of raw materials for the production of anode paste;
- reduce the consumption of the anode mass during electrolysis;
- increase the productivity of the cell;
- reduce energy consumption for the production of 1 ton of aluminum.

In the proposed method, a number of parameters are stated, expressed in absolute terms. The selected parameter value is justified by the following:
1) "... the content of the α-fraction in the additive pitch mixture in the range of 26-28% ..."
This parameter is determined on the basis of many years of experience working at the pitch of various suppliers. The factories of the aluminum sub-industry process mainly coal sands, which meet the requirements of GOST 10200-83. The lower limit on the content of α-fraction for brand "A" pitch ("light" pitch) is 24% with a "volatile" content of about 60%. Map “A” from coal tar pitch is less preferable for the production of anode paste, but nevertheless this pitch is referred to GOST as electrode. In the process of temperature control, the volatile fractions are distilled off and, accordingly, the pitch is enriched in the α fraction. As a rule, a pitch with an α-fraction of at least 25% is fed to the mixing apparatus.

-фракции в пеке. В работе "Микроскопические исследования пекового кокса и некоторые особенности его формирования" Смирнов Б.Н., Фиалков А.С. (ХТТ, 1969, 6, с.60-66) показано, что взвешенные в пеке частицы затрудняют рост частиц мезофазы и препятствуют их слиянию, что приводит к изотропности структуры кокса и плохой его графитируемости.2) ".... α ₁ fractions within 6-8%."
The upper limit of the content of α ₁ - fraction in the electrode pitch is set by GOST 10200-83 and equal to 12%. This limit is established on the basis of the following theoretical principles: the process of coalescence of mesophase particles depends on the presence of suspended dispersed particles

fractions in the pitch. In the work "Microscopic studies of pitch coke and some features of its formation" Smirnov BN, Fialkov AS (KhTT, 1969, 6, pp. 60-66), it was shown that particles suspended in the pitch impede the growth of mesophase particles and prevent their coalescence, which leads to isotropy of the coke structure and poor graphitizability.

Practical experience has shown that the content of α ₁ fraction above 12% significantly reduces the quality indicators of the anode mass. When the content of α ₁ fraction is less than 6%, the quality of the anode mass also deteriorates. In the pitch arriving for processing, this indicator varies within wide limits, and when preparing additive mixtures, it is necessary to control this parameter, preferably maintaining it within 6–8%.

As for oil pitch, the content of α ₁ fraction is possible at a level of 2% with a fraction content of about 28%, so the yield of coke from the oil binder is low and can only be recommended as an additive to the coal tar pitch mixture, while it can be improved by α ₁ fractions due to the addition of carbon-containing components, such as dust of electrostatic precipitators, pitch precipitation;
3) "... The homogenization of the additive pitch mixture is carried out at a temperature 1.7-2 times higher than the softening temperature of coal tar pitch."
Practice has shown that qualitative homogenization can be achieved only with good heating of the material to ensure minimum viscosity of the mixed materials in a turbulent mode;
4) "... add dust to electrostatic precipitators with a fraction content of -0.05 mm not less than 70-75% ..."
This dust fraction of electrostatic precipitators has a high surface activity and, in its function, can replace the α ₁ fraction with a low content in the initial pitch.

The study of the fractional composition of dust of electrostatic precipitators showed that, as a rule, 70-75% of its volume is dust of a fraction of -0.05 mm, which, to a greater extent, approaches the α ₁ fraction of electrode pitch in its surface properties.

5) ^" ... add pitch precipitates of a fraction of -1 mm ..." It is known that pitch precipitates contain 35-40% α ₁ fractions, from this point of view, pitch precipitates are more preferred corrective additives to the additive pitch mixture than the specified higher dust electrostatic precipitators.

The experimental part was carried out on a coke charge traditional for IrkAZ with grain composition, mm:
+6 - <3%
-6 + 4 - 7-15%
-4 + 1 - 28-36%
-1 + 0.08 - 17-29%
-0.08 - 27-33%
When using a coke charge of the aforementioned grain composition and as a binder of the medium-temperature coal tar pitch of Magnitogorsk MK (the characteristics of the pitch are shown in Table 1), experimentally the best results on the quality of the anode mass were obtained with its content of 26.5% (see Table 2). Hence, the content of α and α ₁ fractions, respectively, was 68.37 kg and 17.49 kg per 1 ton of the anode mass.

Based on the concept of the present invention, in order to ensure stable quality of the mass during processing of the pitch mixture, it is necessary to maintain a balance of α and α ₁ fractions.

 The proposed method has been tested in an industrial environment. Magnitogorsk and N-Tagil peaks with the following characteristics were separately placed in two bakeers, with the following characteristics (see Table 3).

 As can be seen from the characteristics of the pitch, one (Magnitogorsk) refers to the "light", and the other (N-Tagil) - to the "heavy."

 After thermostating of Magnitogorsk pitch for three days, and N-Tagilsky pitch - during the day, the peaks were fed into the production of the anode mass in a ratio of 50: 50%. Control samples of the pitch were taken from the pressure tank every 4 hours and had the following characteristics (see table).

 As follows from the results, pitch averaging was quite complete and allowed us to obtain a homogenized binder with good characteristics. The values obtained are somewhat different from the calculated ones, which may be caused by a change in the characteristics of Magnitogorsk pitch during thermostating. The coefficient of fluidity of the anode mass for the period of operation on the average pitch was 2.15 Rel. units with a binder content of 26.2%.

 The proposed method is practically implemented as follows.

1. Suppose the following peaks are available at the factory (see table 1):
ZSMK - α = 26.0%; α ₁ = 4.9%
N-Tagil - α = 27%; α ₁ = 11%
Magnitogorsk - α = 25.8%; α ₁ = 6.6%
Suppose that the scope of supply of Magnitogorsk pitch allows it to be added to the additive pitch mixture up to 50%, then the mixture of N-Tagil pitch and ZSMK pitch should contain α = 34.19 kg / 1 t am, α ₁ = 8.75 kg / 1 t a.m.

The number of "light" and "heavy" pitches of the suppliers in question is determined by the weighted average percentage of these pitches in the additive mixture based on the content of the α-fraction in them:
1) we determine the weighted average percentage of these peaks in the additive mixture:
Peck ZSMK
26.0 • 100% / 53.0 • 2 = 124.53%
Peak N-Tagil
27 • 100% / 53.0 • 2-25.47%.

2) from here the content of the pitch, respectively:
Peck ZSMK
265 • 24.53 / 100 = 65.00 kg
Peak N-Tagil
265 • 25.47 / 100 = 67.50 kg.

Thus, the optimal additive homogeneous mixture contains peaks in the following ratio,%:
Magnitogorsk - 50
ZSMK - 24.53
N-Tagil - 25.47
Moreover, by α ₁ fraction we obtain the following results:
Magnitogorsk
265 • 50 • 6.6 / 100 • 100 = 8.74 kg
ZSMK
265 • 24.53 • 4.9 / 100 • 100 = 3.18 kg
N-Tagil
265 • 25.47 • 11/100 • 100 = 7.42 kg
Total = 19.34 kg
As a result of the calculation, we obtain the content in the additive pitch mixture: α-fraction 68.37 kg or 26%, and fraction α ₁ 19.34 kg or 7%, which is consistent with the claims.

 If it is necessary to process the mixture of ZSMK pitch and Nizhne-Tagilsky, their content in the mixture should be ~ 1: 1.

 The proposed calculation method for the preparation of additive mixtures is fully consistent with laboratory tests of the anode mass based on these mixtures. When using this method in the production of the anode mass, the mass flow coefficient (Kt) was stabilized. The number of CT violations decreased by more than 2 times. The amount of pitch leaks in the anode under the pins and the anode casing decreased by about the same amount.

 The proposed calculation method for determining the amount of individual pitch in an additive mixture allows dosing the pitch in the mixture with sufficient accuracy and on its basis to obtain an anode mass with a quality that meets the requirements of TU 48-5-80-86.

Claims (4)

1. The method of production of the anode mass for the electrolytic production of aluminum, including the preparation of a mixture of pitch and / or petroleum coke, acceptance, temperature control, homogenization of a hydrocarbon binder from a mixture of coal and / or petroleum pitch, dosing of coke and pitch and mixing them when heated, characterized in that the acceptance from suppliers and thermostating of coal and / or oil pitch are carried out separately, then an additive mixture of various pitch is prepared and homogenized in a turbulent mode, and up to different peaks are blended into the mixture in an amount that ensures the content of the α-fraction in the additive pitch mixture in the range of 26–28%, and the α ₁ fraction in the range of 6–8%.  2. The method according to p. 1, characterized in that the homogenization of the additive pitch mixture is carried out at a temperature 1.7-2 times higher than the softening temperature of coal tar pitch. 3. The method according to claim 1, characterized in that dust of the electrostatic precipitators with a content of -0.05 mm fraction of not less than 70-75% is added to the additive pitch mixture, and the total content of the α ₁ fraction in the additive mixture of pitch and dust of electrostatic precipitators is maintained in the range of 6-8%. 4. The method according to p. 1, characterized in that in the additive pitch mixture add pitch precipitation fraction -1 mm, and the total content of the α ₁ fraction in the additive mixture of pitch and pitch precipitation is maintained within 6-8%.

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