DE19702783A1 - Large carbon component production giving improved quality - Google Patents

Abstract

The production of large carbon components, particularly carbon anodes for aluminium electrolysis cells, out of a carbon mass containing pitch comprises mixing solid carbon raw materials as a filler with liquid pitch at elevated temperatures, then compacting the green carbon mass into solid carbon components. The filler material and the binder pitch are ready-mixed discontinuously or continuously at temperatures of 300-450 deg C and atmospheric pressure. Immediately afterwards, discontinuously or continuously, the green carbon mass is subjected to a vacuum treatment at approximately the same temperatures, but at pressures less than 50 mbar. As a result, more volatile constituents of the binding pitch, whose softening temperature is raised by a factor of 1.5-2.2, are distilled away.

Description

The invention relates to a method for producing large format tiger carbon body, especially electrodes for light arc furnaces, blocks for the lining of electrolysis cells and Blast furnaces as well as carbon anodes for the aluminum smelting river electrolysis, from pitch-containing carbon masses by Ver mix solid carbon raw materials as filler with liquid pitch at elevated temperature and subsequent compression of the carbon masses to solid carbon bodies.

According to the process for the production of synthetic carbon body (see Fig. 1) solid carbon raw materials, for. B. coke of various types, processed to a grain size and the individual grain fractions in a defined composition as a so-called drying aggregate or filler with liquid electrode pitch as a binder at temperatures up to about 200 ° C to a green carbon mass.

The processing properties of the electrode pitches are through their softening point or their viscosity as a function of Characterized temperature. The currently in the mentioned product Pitch used mainly have softening points (according to the "Mettler" DIN method) from 100 to 120 ° C or about that. The mixing temperature of drying unit and pitch rich mainly depends on the pitch viscosity.  

The technically used viscosity range is for mixing between 100 and 1000 mPa.s, the low viscosity range from 100 to 500 mPa.s regarded as particularly favorable must become. As the viscosity drops, it doesn't just decrease the effort for the mixing process, also the wetting ability speed of the drying unit, especially the fine powder partly, increases considerably. Two other important Eigen properties of the electrode pitches are the coking residue and the strength of the binding coke formed. Both together agree to a high degree the strength and porosity of the by Pitch carbonization of the binding structure formed in the carbon body by.

In principle, the coking value of the electrode pitches increases increasing softening point; but the increase in Coke residue with softening points according to Mettler of over 110 ° C. If you want another gain in coke yield achieve, one would not only have to disproportionate the softening points tionally, but also the optimal mixing temperatures, which are usually almost twice as high as the Erwei points of interest, according to Mettler, would be extremely high Temperature level.

The main obstacle to such a procedural goal However, the fact is that the very highly softening pitches are the most suitable desired mixed viscosities of 100-500 mPa.s before the on set the pitch pyrolysis no longer achieve and that ins special their wetting ability for the coke filler drastically worsened. The result is that the fountain pen has a considerable impact demands higher pitch addition and the compressibility of the green ones Carbon mass decreases noticeably. The end result will then be despite increased coke yield from the pitch and enormous ver driving technical effort no overall qualitative ver get better carbon body.  

Nowadays, electrode pitches are because technical and economical economically advantageous, with softening points up to 120 ° C Mettler in the liquid state in tankers or tankers Temperatures of 200-250 ° C also over long distances to Über sea and transported to remote areas and in heated Tanks stored liquid. The transport of pitch in solid, lumpy form loses importance. If you look in advance practice the liquid transport of the extraordinarily high melting point pitches with softening points of more than, for example 130 ° C, would be at the required transport temperatures of over 300 ° C in addition to the greater technical effort and other There are hardly insurmountable problems: the peche learn from such high temperatures relatively quickly chemical and structural real changes, e.g. B. the formation of mesophase. It could therefore only very short, practically not feasible transport and storage times are permitted. It would also be very difficult rigorous and extremely risky, the pumpability of the bad luck and the Safe transport from the pitch manufacturer to the consumer guarantee.

The object of the present invention is in a method the coke yield of the type used Improve pitches and shorten processing time as well in the Koh produced by the process according to the invention the strength, electrical and thermal Conductivity and the apparent density (bulk density) of the ge to burn burned carbon body. Beyond that the carbon body has a significant reduction in deformity tion, shrinkage and susceptibility to cracking.

This object is achieved by the claims specified features solved.

The starting point for the method according to the invention is that of common pitches with softening points from 90 to  maximum 120 ° C according to Mettler. They can be made easily set, transport, handle, store and fulfill in terms of viscosity and wettability they directed requirements. Generated from these conventionally According to the invention, ten pitch is a maximum of binding power to get out.

While for the usual pitches with softening points of 90 to 120 ° C nowadays mixed temperatures of approx. 150 to 200 ° C are used, the inventive method for the above mentioned mixing temperatures between 300 and 450 ° C, preferably between 350 and 400 ° C before. The dynamic visco Pitches decrease exponentially with increasing temperature and arrives at a certain, narrow temperature interval Minimum viscosity. In the range of the minimum viscosity, each according to external conditions, the evaporation of pitch components a.

The loss of distillation on low-boiling pitch components - these are usually the so-called low-molecular tar oils - leads to an increase in viscosity. That explains it minimum viscosity mentioned above. The bad luck First boiling tar oils are not just low for reaching responsible viscosities, but support before especially the wetting ability of the liquid pitches.

According to the invention, the temperature range around the viscose minimum for optimal, intensive wetting and impregnation unlucky enough to use the coke filler. In said tempe rature viscosity range for viscosities below 100 mPa.s who the surprisingly strong capillary when distillation begins forces of bad luck that affect the mixing work and duration around the Reduce factor 5-10.  

On the one hand, the temperature of the viscosity minimum can be read out thermogravimetric distillation of the pitches or otherwise from the temperature-dependent, evaporation-permitting viscose determine the physical activity.

After wetting and mixing at the minimum viscosity the tar oils contained in the binding pitch have their function in Principle fulfilled and can be distilled off. The increase in Pitch viscosity by distilling off the more volatile Pitch components can also be increased by the Erwei point of expression. Compared to the bad luck used the softening point rises to 1.5-2.2 times.

The subsequent process, shaping, is carried out at Visko tities of over 500 mPa.s, for example between 500 and 3000 mPa.s performed. Keep the temperature of the green coals mass of material for shaping at the lower temperature level mixing, namely at about 350 ° C, so they can be easier distilling components of the pitch without further ado desired upper limit of the impression viscosity are removed.

The technical implementation of the method according to the invention happens as follows: That with a coordinated grit band Existing filling material is except for approx. 350-400 ° C preheated by electrical resistance heating and in a corresponding heated continuous or discontinuous animal mixer (batch mixer). The bad luck is over a tube heater also to a preheating temperature of brought about 350 ° C and added to the filler. Alternatively, leave filling material and pitch together in the mixer except for the Heat the desired mixing temperature. It is also practical advantage, the coke filler up to 400-450 ° C and the bad luck only preheat to 350 ° C. The right mixing temperature is then only set in the mixer. The information on the previous heating and mixing temperatures serve as preferred examples. The target mixing temperature should be the minimum viscosity of the bad luck match.  

The pitch is basically in at temperatures above 200 ° C closed vessels or pipes because it is kept at the processing temperatures an unpleasant, the breathable organs irritating smoke that is not harmless to health developed.

For the preparation of green carbon masses according to the classic The procedure is based on 100% of the filler on average 15-25% pitch additives required. They essentially hang on the fineness of the filler material or the grain structure of the Filler. For the mixing technique according to the invention, the Pitch additions beyond the specified range by about 2-5% raised. Depending on the softening point of the pitch used evaporated from its amount 5-20%.

The general sequence of the method according to the invention is shown in the flow diagram in FIG. 1.

Liquid pitch is fed into a tube furnace 2 at approximately 220 ° C., which it leaves at approximately 350 ° C. The heated pitch material reaches the continuous mixer 4 without significant cooling, where it is mixed with the drying unit, via a container differential balance 3 .

The drying unit 5 is also preheated to approximately 400 ° C. via a continuous electric preheater 6 before it is entered into the continuous mixer 4 . The mix well then has a temperature of approximately 375 ° C. in the continuous mixer 4 .

After mixing, the mix is placed in an evacuation vessel 7 , where it is evacuated at approximately 350 ° C. Then it reaches a container scale 8 and cools down to approx. 325 ° C.

In a vibration former 9 , the mix is treated under vacuum at approx. 300 ° C. The flow chart in Fig. 1 thus shows the "green line" in the bulk factory.

In FIG. 2, in a general overview of a machine-technical solution is illustrated for the inventive method. It means:

Process stage I

• a Preheat the filler coke up to 400 ° C
• b Preheat the pitch up to 350 ° C

Process stage II

• c Hot mixing at 350-400 ° C
• d Evacuate and distill off Tar vapors at approx. 375 ° C and 50 TORR
• e Condensation of tar vapors

Process stage III

• f Impression at approx. 250-350 ° C.

At 10 , cold filler is entered into an electrical resistance heating screw 11 and leaves it as a hot filler 12 with a temperature of approximately 400 ° C. The hot filler is fed with liquid pitch 15 , which was heated in a tube furnace 16 , via lines 17 a, 17 b into the vacuum mixer 13 , 14 .

The tar vapors 18 are removed from the vacuum mixers 13 , 14 and introduced into a tar vapor condenser 19 which is connected to a vacuum pump 20 . The tar condensate leaves the tar vapor condenser 19 via line 21 .

A green electrode mass is transferred hot from the vacuum mixers 13 , 14 via line 22 into the vibration compressor 23 . There the electrode mass is compressed and an electrode 24 is obtained after the method has ended.

Fig. 2 thus shows an inventive process scheme with two alternately used vacuum batch mixers in procedural stage II. In the batch mixer, the hot mixing of filler material and pitch is first carried out under atmospheric pressure at a viscosity minimum of about 375 ° C. The interior of the mixer is then placed under a vacuum of <50 mbar. The green carbon mass is easily moved by the mixer blades. The more volatile components of the pitch are extracted in a few seconds. The process diagram does not show the weighing and dosing of filler and pitch as well as the weighing of the green electrode mass.

The process scheme described in FIG. 2 can also be designed continuously using known process technology and with the appropriate machines.

Claims (5)

1. A process for the production of large-sized carbon bodies, in particular carbon anodes for the aluminum melt flow electrolysis, from pitch-containing carbon masses by mixing solid carbon raw materials as filler material with liquid pitch at elevated temperature and then compressing the green carbon masses to form solid carbon bodies, characterized in that First the filler material and the binding pitch at temperatures of 300-450 ° C under atmospheric pressure are mixed continuously or continuously and the green carbon masses are then immediately subjected to a discontinuous or continuous vacuum treatment at approximately the same temperature but pressures of <50 mbar, whereby the more volatile constituents of the binding pitch are distilled to 1.5 to 2.2 times as their softening point increases (according to Mettler). 2. The method according to claim 1, characterized, that the mixing takes place up to a temperature level at who is not yet using pitch pyrolysis.   3. The method according to any one of the preceding claims, characterized, that the mixing of the pitch-containing carbon masses inside half of a temperature interval at which the visco minimum values of binding pitch. 4. The method according to any one of the preceding claims, characterized, that the mixing time is reduced by 5 to 10 times Compared to the current state of the art Mixing times. 5. The method according to any one of the preceding claims, characterized, that the shaping and compression of the vacuum treated Carbon mass occurs in a temperature interval, in which the pitch viscosity is preferably 500-3000 mPa.s.