Method for recovery of sodium sulfate from gas cleaning solution of electrolytic aluminum manufacturing

FIELD: non-iron metallurgy, in particular crystallizing of sodium sulfate.

SUBSTANCE: sodium sulfate from solution of electrolytic aluminum manufacturing is recovered by saturation of gas cleaning solution with sodium sulfate, cooling of obtained solution with cooler, and precipitate separation. Cooling of sulfate containing solution to 8-120C is carried out in refrigerator through a wall, and cooling to 0-(-2)0C is carried out by direct contact with cooler.

EFFECT: increased refrigerate durability, seduced labor cost, equipment cost, and energy consumption.

8 cl, 1 tbl, 3 ex

 

The present invention relates to the field of nonferrous metallurgy and can be used for crystallization of sodium sulfate from solution gas purification electrolytic production of aluminum.

Currently, in the electrolysis of aluminum fluoride in the exhaust gas is sulfur dioxide, which is captured soda solution in the wet gas cleaning system, is oxidized to the sulfate form and in large quantities accumulate in the solutions used for regeneration of cryolite.

The result of the accumulation of sodium sulfate in solution gas purification are loss of sodium fluoride, which is in units of wet gas purification forms a double salt NaF Na2SO4precipitated and can be removed along with slimes, and reduced quality of cryolite due to contamination of its sulphate.

Also, is the obliteration of rastvoroprovodov and gas treatment installations deposits of salt, which leads to the need to replace equipment.

A known way of separating sodium sulfate from solution gas purification electrolytic production of aluminum, whereby the gas purification solutions saturate to the concentration of Na2SO4=40-120 g/DM3and cool through the wall to a temperature 5--3°when mixing in the reactor for at least 2 hours (A.S. USSR №648518, the 01 D 5/00, 1979).

Upon cooling of the solution through the wall of the reactor internal surface is covered with crystals of sodium sulfate, resulting in the performance of the reactor decreases, and it is subject to washing and cleaning.

There is also known a method of crystallization of salts from solutions at low temperature (U.S. Pat. Of the Russian Federation No. 2102107, 6 01 D 9/02), according to which the process of crystallization of salts occurs due to contact of the cooling source solution, a cooling agent, which is used to partially or completely frozen solution of crystallizable salts.

However, this method is complex, labor - intensive and not amenable to mechanization and automation.

The closest in technical essence and the achieved result is a way of separating sodium sulfate from solution gas purification electrolytic aluminum production (U.S. Pat. Of the Russian Federation No. 2064891, publ. 10.08.96), according to which the cooling selfaddressed solution is performed using artificial cold in the crystallizer at a temperature of from 7 to -5°C, and the temperature of each subsequent mold is maintained at 4-6°lower than the previous one.

The disadvantage of this method is the high energy consumption for artificial cold, the complexity of hardware and technological schemes, inlaid on the orogovenia upon cooling through the wall of the mold, in the result, the equipment must also be cleaned.

The task of the invention is to eliminate inlay mold used for crystallization of salts.

The technical result of the invention is to increase the performance of the process of crystallization of sodium sulfate, duration of use of the equipment, reduce equipment costs, and reduce energy costs.

The technical result is achieved in that in the method of separation of sodium sulfate from solutions of electrolytic production of aluminum, including the saturation of the solution gas purification sodium sulfate, cooling the resulting solution with a cooling agent and separating the resulting precipitate, cooling selfaddressed solution up to t=8-12°To carry out in the cooling device through the wall, and the cooling selfaddressed solution up to t=0--2°C provide direct contact with a cooling agent, which during the cold season use natural cold air which is in contact with the solution by filing his or volume of the cooled solution or countercurrent to the spray cooled the solution and through the surface of the solution, in addition, direct contact with a cooling agent perform simultaneous submission is in his volume of the cooled solution and on its surface, and in the volume of the cooled solution in addition served to partially or completely frozen solution of sodium sulfate.

It should be borne in mind that under the cold period of the year you should understand this period (fall, winter, spring), when day and night temperature <-2°C.

The technical essence of the invention consists in the following.

The General condition of mass crystallization of salts from solutions is their oversaturation. To obtain a saturated solution of sodium sulfate was used the method of crystallization-based cooling solutions.

Now to implement this method on the aluminum plants use molds with the use of artificial cold, which represents a closed reactor, the side walls are provided with a "shirt". For cooling of the solution in a space formed by the outer wall of the reactor and the inner wall of the "shirts", submit a solution of calcium chloride, the temperature of which is supported by artificial cold.

When cooled selfaddressed solution of the prototype on the heat transfer surface of the mold from the cooled solution are formed over time, crystalline salt deposits (inlay). Thus the heat transfer surface is gradually reduced, and production is to smash the mould falls.

The proposed method due to the direct contact of the cooled solution with a cooling agent avoids the appearance of incrustation.

Production sulfadimidine solutions come on the crystallization of sodium sulfate with a temperature of ~40°C. the composition sulfidogenic solutions include, g/DM3: Na2SO460-120, NaF 5-25, Panso36-36, Na2CO35-32.

The proposed method initially provides a cooling solution to 8-12°C.

Research has shown that industrial sulfadimethoxine solution when cooled to ~8°do not form a crystalline coating on the heat transfer surface of the cooled solution. Therefore, this temperature limit for cooling through the wall.

Further cooling of the solution by the proposed method is carried out without contact with the cold surface, and provides direct contact selfaddressed solution with a cooling agent. And as a cooling agent during the cold season use natural cold air.

The cold air, as well as partially or fully frozen solution of sodium sulfate in the amount of the cooled solution allows you to evenly distribute the temperature at which the formation of crystalline zero is ISA salt.

It is known that the faster the heat transfer, the more intense the formation of nuclei of crystals.

The most intensive heat transfer occurs by direct contact of cold air with solfataras solution, supplied, for example, countercurrent to the spray solution.

Kinetics of crystallization of salts along with the formation of crystalline nuclei also includes the growth of crystals, i.e. their final formation, which occurs at t=0--2°C.

When the temperature drops below the proposed limit leads to freezing (crystallization) of water, which affects the performance of the process.

The stage of formation of the crystal is carried out in the vessel, the upper part of which is open with a large mirror surface of the solution.

Due to the fact that in the process of mass crystallization of sodium sulfate is an abrupt temperature increase to ~2°With mirror solution of the mould-thickener fanned the cold air using a fan.

Comparative analysis of the proposed solution with the prototype shows that the proposed solution differs from the well-known fact that:

- cooling sulfidogenic solutions to a temperature of 8-12°To carry out in the cooling device through the wall;

- cooling sulfidogenic solutions to pace atory 0--2° To carry out direct contact with a cooling agent;

- as a cooling agent during the cold season use natural cold air;

the contact of cold air with the solution is performed by feeding it countercurrent to the spray solution;

the contact of cold air with the solution is performed through the surface of the solution;

contact with a cooling agent perform simultaneous feeding it into the volume of the cooled solution and on the surface;

- as a cooling agent used partially or completely frozen solution of sodium sulfate;

additionally, when the contact of cold air with the solution through the surface into the volume of the cooled solution serves to partially or completely frozen solution of sodium sulfate.

Thus, the claimed technical solution meets the condition of patentability "novelty."

Analysis of the known technical solutions contained in the publicly available information sources, showed that in the prior art discovered information about the crystallization of sodium sulfate by cooling to a temperature 5--3° (A.S. USSR №648518, 2 01 D, 1979).

Famous is also information about the use of the refrigerant in the form of partially or completely frozen kristallizuetsya salts (U.S. Pat. Of the Russian Federation No. 2102107, 6B 01 D 9/02, from 20.01.98 year).

However, the known characteristics similar to distinguishing the claimed invention, together with previously unknown work inlay used equipment, to increase the duration of use of the equipment, reduce the additional costs of equipment and reduce energy and labor, i.e. to obtain a new technical result.

Thus, the claimed technical solution meets the condition of patentability "inventive step".

Example 1.

For the experiments we used the solution gas purification with mass composition, g/DM3: Na2SO4- 73,43; NaF - 15, 98; NaHCO3- 24,36; PA2CO3- 9,82.

Solfataras solution with a volumetric rate equal to 10 m3per hour, is supplied to the cooling temperature of ~40°C.

To effect the cooling of the solution through the wall up to 10°was used heat exchanger type AUG, is a hollow cylinder, inside of which there are bundles of thin tubes through which pass the cooled solution and on which the fan is served cold outside air volumetric flow rate of 15000 m3/hour.

Next solfataras solution with a temperature equal to 10°was admitted to the cooling to ~0°by direct contact with cold air is m flow countercurrent to the spray solution in a floor scrubber with a heat-insulated surface of the side walls.

For the final crystallization of sodium sulfate using the mold-thickener, representing the capacity of a cylindrical or rectangular shape with a conical or pyramidal bottom, which is along the Central axis provided with a discharge device for output of the thickened slurry of sodium sulfate.

The upper part of the mold-thickener is open, and the upper side surface of it are open drain for overflow obessolivanija solution.

The mold-thickener designed in such a way that its side surface and a conical bottom were well insulated to prevent heat transfer through the wall.

The crystallization process is completed already in the surface layer of the mold-thickener, the tapered part of it is the assertion of sodium sulfate.

In the process of mass crystallization of sodium sulfate is an abrupt temperature increase of ~2°so to compensate for the temperature jump mirror solution of the mould-thickener fanned the cold air using a fan.

After completion of the crystallization slurry enters the filter, resulting in a 900 kg of mirabilite with a humidity of 10%, and the filtrate concentration of sodium sulfate ~30 g/DM3popcorn is used in the gas purification process.

Example 2.

The solution of example 1 is also fed to a cooling of up to 10°in the heat exchanger and then into the mould-thickener with surface blowing cold air.

Example 3.

The solution of example 1 is also fed to a cooling of up to 10°in the heat exchanger and then into the mould-shuttel where cooling is served frozen solution of sodium sulfate.

The results of the experiments are given in the table.

Table
no PPMethodThe cost of equipment with capacity of 10 000 t/year Na2SO4, thousand rublesThe consumption of the electric energy at 1T Na2SO4, kWhKPI equipment during the cold season, %
12345
1the placeholder1150080082
2offer   
 1 example3800250100
 2 example5100300100
 3 example7800 280100

As follows from the table, in the proposed method, the cost of the equipment compared to the prototype is reduced to 1.5-3 times the cost of electricity is reduced to ~3 times, and equipment efficiency increases to 100%.

1. A way of separating sodium sulfate from solutions of electrolytic production of aluminum, including the saturation of the solution gas purification sodium sulfate, cooling the resulting solution with a cooling agent and separating the resulting precipitate, characterized in that the cooling sulfidogenic solutions up to t=8-12°C is carried out in cooling devices through the wall, and the cooling sulfidogenic solutions up to t=0-(-2)°C is carried out by direct contact with a cooling agent.

2. The method according to claim 1, characterized in that as a cooling agent during the cold season use natural cold air.

3. The method according to claim 2, characterized in that the contact of cold air with the solution is performed by feeding it into the volume of the cooled solution.

4. The method according to claim 2, characterized in that the contact of cold air with the solution is performed by feeding it countercurrent to the spray solution.

5. The method according to claim 2, characterized in that the contact of cold air with the solution is performed through the surface of the solution.

6. Pic is b according to claim 1, characterized in that the direct contact with a cooling agent perform simultaneous feeding it into the volume of the cooled solution and on its surface.

7. The method according to claim 1, characterized in that as a cooling agent used partially or completely frozen solution of sodium sulfate.

8. The method according to claim 5, characterized in that it further into the volume of the cooled solution serves to partially or completely frozen solution of sodium sulfate.



 

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SUBSTANCE: sodium sulfate from solution of electrolytic aluminum manufacturing is recovered by saturation of gas cleaning solution with sodium sulfate, cooling of obtained solution with cooler, and precipitate separation. Cooling of sulfate containing solution to 8-120C is carried out in refrigerator through a wall, and cooling to 0-(-2)0C is carried out by direct contact with cooler.

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