RU2317944C2 - Anode mass preparation process - Google Patents

Abstract

FIELD: electrical power sources.

SUBSTANCE: invention relates to preparation of self-burning anodes of aluminum electrolyzers. To that purpose, coke is separated into at least two fractions: > 1.0 mm and <1.0 mm. First, fraction <1.0 mm is mixed with molten pitch and simultaneously coke is reduced into dustlike fraction <0.045 mm being exposed to hydraulic shock-cavitation field, optionally at pressure below 100 mbar. Then, the other fraction is added, optionally being preliminarily mixed with molten pitch at pressure below 100 mbar. Resulting anode mass is homogenous and has stable composition. Fired anode mass is characterized by density 1.54 kg/cm3, compression strength 50.9 MPa, total porosity 22.0%, specific resistivity 59 μOhm/m, and relative elongation 114.6%.

EFFECT: improved performance characteristics of anode mass.

3 cl, 1 dwg, 1 tbl

Description

The invention relates to electrode production, in particular to the production of anode paste for self-baking anodes of aluminum electrolysis cells.

The anode paste is a composition of petroleum or pitch coke with pitch of coal or petroleum origin. The main requirement for the anode mass for self-firing anodes is plasticity, which determines its ability to self-seal in the conditions of the upper molten zone of the anode. The anode mass refers to highly concentrated disperse systems, the sedimentation stability of which and the ability to self-compaction is determined by the concentration of coke-filler and its interaction with the pitch-binder. Particular attention in the production of anode masses is given to the quantity and composition of the dust fraction in the charge. The dust fraction has the highest adsorption surface and is crucial in determining the need for pitch binder to provide the necessary plasticity of the anode mass. The composition of the dust fraction and pitch binder forms a matrix structure in the anode mass in which the grain fractions are distributed. The properties of the matrix structure determine the sedimentation stability of the anode mass and the ability to self-compact in the molten state. It is known that an increase in the content in the charge or an increase in the fineness of grinding the dust fraction leads to an improvement in the quality of the anode mass and increases its resistance to delamination in a self-baking anode. However, poor wettability and the tendency of small particles to agglomerate when mixed with pitch do not allow to obtain a high-quality anode mass.

A known method of producing anode mass for a self-burning anode (M.A. Korobov, A.A.Dmitriev. Self-burning anodes of aluminum electrolysis cells. M .: Metallurgy, 1982), in which the dust fraction is prepared by grinding coke in ball mills, mixed with coarse fractions, heated and mixed with molten coal tar pitch.

The disadvantage of this method is the instability of the composition of the fraction of 0.075 mm, which is the reason for large fluctuations in ductility and sedimentary instability of the anode mass. A disadvantage of the known method is the uneven distribution of the pitch binder between the particles of the dust fraction when mixed due to the low wettability of the particles and their high ability to form agglomerates. The heterogeneity of mixing leads to unpredictable behavior of the anode mass under conditions of a self-burning anode.

Closest to the proposed invention is a known method for the preparation of a coke-pitch composition for carbon products (Auth. St. USSR No. 816956, IPC СВВ 31/02, 1981), which includes grinding and separation of coke into fractions, mixing a fine fraction of coke (-0, 09 + 0.01 mm) with molten pitch, and then introducing into the prepared mixture a fraction of coke -3.0 + 0.09 mm.

However, the known method does not ensure the stability of the composition of the fraction -0.09 + 0.01 mm and requires a long mixing time to obtain a homogeneous composition (the process of preparing a coke-pitch composition takes one hour). The instability of the fraction composition of -0.09 + 0.01 mm leads to instability of the properties of the anode mass, and the duration of the process is not compatible with the requirements of the large-tonnage production of the anode mass in the aluminum industry.

The objective of the invention is to increase the productivity of the process of preparing the anode mass and reduce the duration of the process.

The technical result consists in obtaining an anode mass with high physical and mechanical properties based on a homogeneous finely divided coke pitch pitch composition of a stable composition.

The specified technical result is achieved by the fact that in the method of producing the anode mass, including crushing and separating coke into fractions, mixing one coke fraction with molten pitch, adding another coke fraction to the resulting mixture and then mixing the mixture, according to the claimed solution, the coke is separated not less than than two fractions larger than 1.0 mm and less than 1.0 mm in size, and first, the coke fraction of less than 1.0 mm is mixed with molten pitch and, at the same time, the coke is crushed to a dusty fr ktsii size less than 0.045 mm under the influence of hydraulic-cavitation field, whereupon another coke fraction and stirred again.

The method is supplemented by private distinctive features, also aimed at achieving the specified technical result.

Mixing the coke fraction of less than 1.0 mm and at the same time its grinding is carried out at a pressure of less than 100 mbar.

The coke fraction of more than 1.0 mm before being added to the mixture is pre-mixed with molten pitch at a pressure of less than 100 mbar.

In relation to the prototype of the proposed method has the following differences. The crushed coke is separated into at least two fractions: a fraction with a particle size of more than 1.0 mm and a fraction with a particle size of less than 1.0 mm. Fraction - 1.0 mm is used to obtain a homogeneous finely divided coke-pitch composition with a coke particle size of less than 0.045 mm. A homogeneous finely divided coke-pitch composition is obtained by combining the processes of mixing and grinding of coke in a molten pitch medium in a centrifugal hydropercussion disperser generating a field of successive hydropercussion and cavitation pulses with a frequency of resonant particle breakdown. Under the influence of a series of resonant loads in the compression-rarefaction mode, coke particles are destroyed to a size of less than 0.045 mm. The formation of a new surface during the destruction of coke particles directly in the environment of the molten pitch ensures the absence of oxidation and adsorption of atmospheric gases on the surface, which ensures good wetting of the coke particles. Cavitation pulses prevent the formation of conglomerates of coke particles in the molten pitch, which ensures the homogeneity of the dust-dust composition. High dispersion of the solid phase and effective wetting of the fracture surface contribute to the appearance of a movable structural network in the binder volume, in the nodes of which coke particles are located. The introduction of coarse particles into such a structured matrix ensures their sedimentation stability in the molten anode mass. The anode mass on the basis of a homogeneous finely divided coke-pitch composition is similar in structure and stability to concentrated colloidal systems, therefore it can conditionally be called "colloid".

The analysis carried out by the applicant showed that the set of features is new, and the method and device for its implementation satisfy the condition of an inventive step due to the novelty of the cause-effect relationship “distinctive features - technical result”.

The invention is illustrated in the diagram of the composition of coke fractions less than 1.0 mm before and after processing the coke pitch pitch in a centrifugal hydropercussion dispersant, shown in the drawing.

The proposed method for the production of "colloidal" anode mass is implemented as follows. Pre-crushed coke is divided into fractions of +1.0 mm and -1.0 mm. The coke fraction -1.0 mm and the molten pitch are dosed together in a centrifugal hydropercussion dispersant. The coke fraction -1.0 mm is crushed under the influence of hydroshock and cavitation pulses to a size of less than 0.045 mm and at the same time is homogenized in a molten pitch medium. To remove volatile components and atmospheric gases, the preparation of finely dispersed coke pitch pitch can be carried out at a residual pressure of less than 100 mbar. Finished finely divided coke pitch pitch enters the storage tank, from which it is used for mixing with a coarse fraction of coke more than 1.0 mm in a batch or continuous mixer. The coarse fraction of coke more than 1.0 mm before being mixed with the finely divided coke-pitch composition can be pre-evacuated to a residual pressure of less than 100 mbar to remove air from the pore space of the coke.

Performed laboratory experiments confirm the effectiveness of the proposed method. The finely dispersed coke pitch pitch was processed for 10 minutes in a centrifugal hydropercussion disperser from coal tar pitch and the initial coke fraction of -1.0 mm in size. The solid content in the finely divided coke-pitch composition was 58%. Based on the obtained finely divided coke-pitch composition, an anode mass was prepared. The table shows the comparative test results of the calcined anode masses prepared by known (prototype) and the proposed methods.

From the data presented in the table, it is seen that the production of the anode mass according to the proposed method allows to reduce the electrical resistivity and gas permeability, increase the density and strength of the anode mass. Reducing electrical resistivity and gas permeability will reduce the consumption of electricity and carbon during the electrolysis of aluminum.

Table Indicator Units The method of preparation of the anode mass Famous Proposed Apparent density kg / cm ³ 1.51 1,54 Compressive strength MPa 47.8 50.9 Total porosity % 26.8 22.0 Electrical resistivity μΩm 66 59 Gas permeability nPm 7.4 2,8 Elongation coefficient % 15.6 114.6

Claims (3)

1. Method for the production of anode paste, including crushing and separating coke into fractions, mixing one coke fraction with molten pitch, adding another coke fraction to the resulting mixture and then mixing the mixture, characterized in that the coke is separated into at least two fractions: size more than 1.0 mm and less than 1.0 mm, moreover, first, a fraction of coke less than 1.0 mm is mixed with molten pitch and simultaneously with mixing, coke is crushed to a pulverulent fraction of size less than 0.045 mm under the influence of hydrocavity field, after which another coke fraction is added. 2. The method according to claim 1, characterized in that the mixing of the coke fraction of less than 1.0 mm and its simultaneous grinding is carried out at a pressure of less than 100 mbar. 3. The method according to claim 1, characterized in that the coke fraction of more than 1.0 mm before being added to the mixture is pre-mixed with molten pitch at a pressure of less than 100 mbar.