Method for cleaning anode gases of electrolytical production of aluminum

FIELD: production of aluminum in cells with self-fired anodes, possibly processes for cleaning anode gases.

SUBSTANCE: method comprises steps of accumulating anode gases, preliminarily combusting them together with air in burner devices mounted in cells; supplying gas-air mixture after preliminary combustion of anode gases along gas duct to stage of dust and gas trapping and blowing out to atmosphere. Before supplying gas-air mixture from burner devices to stage of dust and gas trapping, it is fed to process for oxidizing roasting; heated up to temperature 800-1100°C and then it is cooled until 230-290°C and heat is used for production needs.

EFFECT: lowered content of carbon, resin and CO in exhaust gases.

 

The invention relates to the electrolytic production of aluminum electrolysis cells with self-baking anodes and can be used for cleaning the anode gases.

Known way off gas suction of the aluminum electrolytic cell with a continuous self-baking anode and the upper conductors, including the collection anode gas in gazosbornik in a concentrated state with a temperature of 500°-900°With burning resinous goganov in gasolene chamber, flow of gases in the scrubber for recovery of fluorine compounds, and then release them into the atmosphere (U.S. Patent No. 2526875, MKI 204-67, 1950).

A known method of purification of gases from aluminum electrolysis cell, including the collection anode gas and feeding them into the camera, equipped with a grating on which the nozzle of finely chopped petroleum coke, flow of gases through the nozzle is heated to a temperature of 500-800°C, where the combustion of carbon monoxide, and to maintain combustion in the chamber to deliver air, and resinous substances contained in the gas are subjected to cracking or pyrolysis with the formation of carbon (the Federal Republic of Germany Patent No. 1007069, 40 C., 4. 1957).

A known method of purification of waste gases by contacting the carbonaceous material at an elevated temperature of 350 to 450° (Ed. St. The USSR №1611419, CL. 01 D 53/34, 1990) and the method of purification of gases from carbon monoxide at elevated so is the temperature value, including blowing the cleaned gases through a layer of sinter having a temperature of 950-1000° (Ed. St. The USSR №982761, CL. 01 D 53/34, 1983).

The main disadvantages of the known solutions are:

insufficient cleaning of tar and carbon, which creates difficulties in the further processing of anode gases, “overgrowing” purifying equipment, degrades the environment;

- complex instrumentation, significant costs and limited technological capabilities, making it very difficult to use in large-scale industrial production of aluminum.

The closest in technical essence and the presence of similar features is the way of the exhaust gases from the electrolysis cells with self-baking anodes, including the collection of concentrated anode gas, feeding them into the burner and the oxidation at a temperature of 600-700°With a limited supply of air, flow of gases into the trap which removes larger dust and then into a cyclone, catching the main part of the dust. From the cyclone gases fed to the column with a nozzle, where it is chemical treatment and isolation of fluorine-containing components. After washing solution, enriched with fluoride sodium direct the production of cryolite, and gases, together with passionate about their solution are fed into exhauster and after separation of the liquid drop in a cyclone in the joyful atmosphere (the Federal Republic of Germany Patent No. 1059667, 40 S., 6. 1959).

However, this approach is not high enough degree of purification from resinous substances, which leads to the “obliteration” of the dust removal apparatus, to decrease the effectiveness of their work. Furthermore, the residual concentration of carbon and tarry substances contaminate the secondary return the product - regeneration cryolite, degrades its quality.

The objective of the proposed technical solution is the extraction of valuable components to return them into the production process in the form of recycled products, reducing emissions of harmful substances into the atmosphere and improving the quality of the recovery of cryolite.

In the present invention the technical result is to decrease the content of carbon, tar, and CO in the exhaust anode gas electrolytic production of aluminum.

This is achieved by the purification method of the anode gases electrolytic production of aluminum electrolysis cells with self-baking anodes, including the collection anode gas, the preliminary burning them with air in the burner devices installed in the electrolytic cells, the feed gas mixture after the preliminary combustion of anode gases pass through the gas trapping and emission in the atmosphere, provides before serving gas-air mixture from the burner devices on stage, pylea is oluline feed her in the process of oxidative roasting, heating to a temperature of 800-1100°C, followed by cooling to 230-90°with heat recovery on the needs of production.

The technical essence of the proposed solution is as follows.

Used in the industry, the anode gas cleaning technology enables the collection anode gas from the electrolyzer in the covered space Board-anode, pre-burning at each cell burners at submission (choke) air evacuation after firing a mixture of anode gases with air ducts on stage “dry” and/or “wet” gas purification, where the extraction of aluminium-fluoride-sodium components with the purpose of their processing and return to the process in the form of secondary cryolite. Waste material from the gas purification partially displayed on sludge fields, and partly in the form of gas-aerosol emitted into the atmosphere. The current scheme can provide a high degree of purification only when significant material and labor costs, the availability of expensive equipment and process design, which increases the cost of commercial aluminum.

The proposed solution eliminates such a disadvantage as incomplete cleaning of the anode gases from fine carbon, and resinous substances, which is achieved by the additional ignition of the gas mixture coming from the burner the device, installed on the cells at the stage of gas trapping. The anode gases collected from the cell using the gas bell, burnt in burners that are installed directly on the cells, at process temperatures of about 800°C. But, because the oxidation is conducted in the gas stream, the reaction time is limited, catalysers of harmful components is incomplete. Then the gases in the flue, razbavlyali air (intake in the joints of the flue and other), being cooled to a temperature of 300-400°C, condensation of some fractions of tar, served in the form of gas-air mixture at the stage of gas cleaning (“dry” and/or “wet”), where the recovery of fluorine compounds and return them for recycling with the aim of obtaining a secondary product (recovery of cryolite, carbon capture dust and reset it on the sludge field.

In the composition of the resinous substances are carcinogenic polycyclic aromatic hydrocarbons (PAHs), which are the most dangerous component of the anode gas. The most effective way to remove PAHs from the gases of electrolysis is their thermal deactivation at elevated temperature process (pyrolysis).

The proposed technical solution, the gas-air mixture after burners are served in the process of the oxidative roasting by heating it to a temperature of 800-1100° C. This is due to the need for maximum transfer of PAH in non-toxic and toxic compounds during their thermal decomposition. And at a temperature of at least 800°With the ignition does not provide the desired degree of decomposition of PAH.

The cooling gas after firing is necessary and due to the temperature limitations of electrostatic precipitators. The maximum temperature of the cleaned gases should be no more than 230°to ensure the smooth and efficient operation of gas-cleaning equipment. And cooling gases to temperatures below 90°C is unacceptable as this can cause condensation of water vapor, present in the gases, and this will lead to the formation of acid (fluoride-hydrogen, sulfur or sulfur), which will cause corrosion of the gas-cleaning equipment.

The proposed technology is easily implementable on aluminium smelters in the existing apparatus and process flow of the gas purification. To do this, before electrostatic precipitators installed energy technology installation, for example fluidized bed furnace, equipped with a heat exchanger for cooling the gas-air mixture after oxidation firing and heat recovery using, for example, boiler hot water or steam boiler and direction in the process. As fuel in the process of oxidation on the yoke can be made of various carbonaceous fuel, for example, propane. But it is preferable, from the point of view of economic and environmental, to use as the carbonaceous fuel actually carbonaceous waste electrolytic production of aluminum, suitable for combustion of coke dust, defective anodes, pitch sediment, sludge gas cleaning, flotation tailings and other.

Distinctive features of the proposed technical solutions from the prototype are:

the feed gas mixture from the burner units in the process of oxidative roasting before submitting it to the stage of gas trapping;

the heated gas mixture to 800-1100°C;

further cooling of the gas-air mixture to 230-90°with heat recovery on the needs of production.

The presence of these features allows you to make a conclusion on the compliance of the claimed invention, the patentability criteria of “novelty”.

Using the proposed solution together well-known and distinctive characteristics allows to achieve higher technical and economic results. The proposed technology is prepared for testing at the Irkutsk aluminium smelter.

The purification method of the anode gases electrolytic production of aluminum electrolysis cells with self-baking anodes, including the collection anode gas, the preliminary burning them in the spirit in combustion devices, installed on the pots, the feed gas mixture after the preliminary combustion of anode gases pass through the gas trapping and emission in the atmosphere, characterized in that before applying the gas-air mixture from the burner devices on stage gas trapping it serves in the process of oxidative roasting, heated to a temperature of 800-1100°, then cooled to 230-90°with heat recovery on the needs of production.



 

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FIELD: production of aluminum in cells with self-fired anodes, possibly processes for cleaning anode gases.

SUBSTANCE: method comprises steps of accumulating anode gases, preliminarily combusting them together with air in burner devices mounted in cells; supplying gas-air mixture after preliminary combustion of anode gases along gas duct to stage of dust and gas trapping and blowing out to atmosphere. Before supplying gas-air mixture from burner devices to stage of dust and gas trapping, it is fed to process for oxidizing roasting; heated up to temperature 800-1100°C and then it is cooled until 230-290°C and heat is used for production needs.

EFFECT: lowered content of carbon, resin and CO in exhaust gases.

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