RU2247176C1 - Method for cleaning anode gases of electrolytical production of aluminum - Google Patents

Abstract

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.

Description

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

A known method of gas extraction from an aluminum electrolyzer with a continuous self-baking anode and an upper current lead, including collecting anode gases in a gas collector in a concentrated state with a temperature of 500 ° -900 ° C, burning resinous gugons in a gas receiving chamber, supplying gases to scrubbers to capture fluorine compounds, and then their release into the atmosphere (US Patent No. 2526875, MKI 204-67, 1950).

A known method of cleaning gases from an aluminum electrolyzer, including collecting anode gases and feeding them into a chamber equipped with a grill, on which there is a nozzle of finely divided petroleum coke, supplying gases through a nozzle heated to a temperature of 500-800 ° C, where oxide is burned carbon, moreover, to maintain combustion, air is supplied to the chamber, and resinous substances contained in the gas are cracked or pyrolyzed to form carbon (German Patent No. 1007069, 40 C., 4. 1957).

A known method of purification of exhaust gases by contacting with carbonaceous material at an elevated temperature of 350-450 ° C (Aut. St. USSR No. 1611419, CL. 01 D 53/34, 1990) and a method of purification of gases from carbon monoxide at elevated temperatures, including purging the cleaned gases through a layer of sinter having a temperature of 950-1000 ° C (Aut. St. USSR No. 982761, Cl. 01 D 53/34, 1983).

The main disadvantages of the known solutions are:

- insufficient purification from resinous substances and carbon, which creates difficulties in the further processing of anode gases, “overgrowing” of gas cleaning equipment, worsens the environmental situation;

- complex hardware design, significant costs and limited technological capabilities, which makes it extremely difficult to use aluminum in large industrial production.

The closest in technical essence and the presence of similar features is a method of exhausting gases from electrolytic cells with self-baking anodes, including collecting concentrated anode gases, supplying them to the burner and afterburning at a temperature of 600-700 ° C with limited air supply, supplying gases to a trap where it is separated coarse dust, and then - into a cyclone that traps the bulk of the dust. From a cyclone, gases are fed into a column with a nozzle, where they are chemically treated and fluorinated components are separated. After washing, the solution enriched in sodium fluoride is directed to the production of cryolite, and the gases, together with the solution carried by them, are fed into the ecguster and, after separation, a drop of liquid in the cyclone is released into the atmosphere (German Patent No. 1059667, 40 S., 6. 1959).

However, this method also does not have a sufficiently high degree of purification from resinous substances, which leads to "overgrowing" of dust and gas cleaning apparatuses, to a decrease in the efficiency of their work. In addition, residual concentrations of carbon and resinous substances pollute the secondary return product - regenerative cryolite, worsening its quality.

The objective of the proposed technical solution is to extract valuable components to return them to the production process in the form of secondary products, reduce emissions of harmful substances into the atmosphere and improve the quality of regenerative cryolite.

In the present invention, the technical result is to reduce the content of carbon, resinous substances and CO in the exhaust anode gases of the electrolytic production of aluminum.

This is achieved by the fact that the method of purification of anode gases from the electrolytic production of aluminum in electrolytic cells with self-burning anodes, including collecting anode gases, pre-burning them with air in burners installed on electrolysis cells, supplying a gas-air mixture after preliminary burning of anode gases through a gas duct to the dust and gas recovery stage and emission into the atmosphere, provides before feeding the gas-air mixture from the burner devices to the dust and gas collection stage, feeding it into the oki process Call duration calcination temperatures of 800-1100 ° C followed by cooling to 230-90 ° C with heat recovery at production needs.

The technical essence of the proposed solution is as follows.

The technology used in industry for cleaning anode gases includes collecting anode gases from the electrolyzer in a covered board-anode space, pre-burning them on each cell with burners when air is supplied (suction), evacuating after firing the mixture of anode gases with air through the flues to the “dry” stage and / or “wet” gas purification, where aluminum-fluorine-sodium-containing components are extracted for the purpose of their processing and return to the process in the form of secondary cryolite. The spent material from the gas treatment is partially discharged to the sludge fields, and partly in the form of a gas-air aerosol is emitted into the atmosphere. The existing scheme can provide a high degree of purification only at significant material and labor costs, the presence of expensive hardware and technological design, which increases the cost of commercial aluminum.

The proposed solution eliminates such a disadvantage as incomplete purification of anode gases from finely dispersed carbon, CO and resinous substances, which is achieved by additional afterburning of the air-gas mixture coming from burner devices installed on electrolytic cells at the dust and gas collection stage. Anode gases collected from the electrolyzer using a gas collection bell are burned in burners installed directly on the electrolysers at process temperatures of about 800 ° C. But, since the afterburning is carried out in a gas-air stream, the reaction time is limited, the afterburning of harmful components is incomplete. Then the gases along the gas duct, diluted with air (suction at the joints of the gas duct, etc.), cooled to a temperature of 300-400 ° C with condensation of some fractions of resinous substances, are supplied as a gas-air mixture to the dust and gas cleaning stage (“dry” and / or “wet” ”), Where fluorine-containing compounds are captured and recycled for the purpose of obtaining a secondary product (regenerative cryolite), carbon-containing dust and its discharge to the sludge field.

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

In the proposed technical solution, the gas-air mixture after the burner devices is supplied in the process of oxidative firing with heating to a temperature of 800-1100 ° C. This is due to the need for maximum conversion of PAHs into non-toxic and low-toxic compounds during their thermal decomposition. And at temperatures below 800 ° C, afterburning does not provide the required degree of decomposition of PAHs.

Gas cooling after firing is necessary and is associated with temperature limitations of the operation of electrostatic precipitators. The maximum temperature of the purified gases should be no more than 230 ° C to ensure uninterrupted and efficient operation of gas cleaning equipment. And the cooling of gases to temperatures below 90 ° C is unacceptable, since this can cause condensation of water vapor present in the gases, and this will lead to the formation of acids (hydrogen fluoride, sulfuric or sulfuric), which will cause corrosion of gas cleaning equipment.

The proposed technology is easily implemented at aluminum plants in the existing instrumentation-technological scheme of gas purification. For this, an energy-technological installation is installed in front of the electrostatic precipitators, for example, a fluidized bed furnace equipped with a heat recovery unit for cooling the gas-air mixture after oxidative firing and heat recovery using, for example, a recovery boiler of a hot-water or steam boiler and forwarding to the technological process. As a fuel, various carbon-containing fuels, such as propane, can be fed into the oxidative firing process. But it is preferable, from the point of view of economic and environmental, to use as a carbon-containing fuel the actual carbon-containing waste from the electrolytic production of aluminum suitable for burning: coke dust, defective anodes, pitch sediments, gas treatment sludge, flotation tailings and others.

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

- supply of the gas-air mixture from the burner devices to the oxidative firing process before feeding it to the dust and gas collection stage;

- heating the gas-air mixture to 800-1100 ° C;

- subsequent cooling of the gas-air mixture to 230-90 ° C with heat recovery for production needs.

The presence of these signs allows us to conclude that the claimed invention meets the patentability criterion of “novelty”.

The use in the proposed solution of a combination of known and distinctive features allows to achieve higher technical and economic results. The proposed technology is prepared for testing at the Irkutsk Aluminum Plant.

Claims (1)

The method of purification of anode gases from the electrolytic production of aluminum in electrolytic cells with self-baking anodes, including collecting anode gases, pre-burning them with air in burners installed on electrolysis cells, supplying a gas-air mixture after preliminary burning of anode gases through a gas duct to the dust and gas collection stage and emitting into the atmosphere, different the fact that before the gas-air mixture is supplied from the burner devices to the dust and gas collection stage, it is fed into the oxidative firing process, heated to a temperature of 800-1100 ° C, then cooled to 230-90 ° C with heat recovery for production needs.