RU2816389C1 - Method for purifying waste gases from alumina production kilns - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to methods for purifying exhaust gases from rotary kilns for alumina production. To purify gases, it is proposed to use multi-stage purification in a dust chamber, electric precipitators, and subsequent “wet” purification in two parallel scrubbers. The scrubbers are equipped with gas distribution grids and spray nozzles, to which sludge water is supplied through separate pipelines. The volume of sub-sludge water on the gas distribution grid is maintained in the range from 70 to 90 m³/h. When supplying mud water to the nozzle, the volume of mud water is maintained in the range from 10 to 30 m³/h, respectively. Then the purified gases are sent to centrifugal separators to separate excess moisture and water vapour from them.

EFFECT: invention ensures purification of atmospheric air from dust, carbon dioxide and water vapour contained in emissions from rotating kilns.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to methods for purifying exhaust gases from rotary sintering furnaces at alumina and cement plants.

There is a known method for purifying gases from sulfur dioxide and high-resistivity dust; for this, part of the dust and gas flow, humidified to a value of at least 90%, containing sulfur dioxide, is passed through a barrier discharge zone [RF Patent 2077391, publ. 04/20/1997].

The disadvantage of this known method is the lack of effective cleaning of exhaust gases from dust and carbon dioxide.

There is a known method for cleaning the exhaust gases of rotary kilns using electric precipitators installed behind the kilns. The gases leaving the furnace are drawn through electric precipitators with the help of baking smoke exhausters, where they are cleaned of solid dust inclusions. Then the gases are fed into a reactor with a nozzle, where, in the presence of water vapor, harmful gaseous oxides are neutralized by the alkaline components of residual cement dust [RF Patent 2013112, publ. 05/30/1994].

The disadvantage of this known method is the lack of effective purification of exhaust gas components from fine dust and carbon dioxide.

The closest to the invention in technical essence is a method for cleaning exhaust gases from sintering furnaces of alumina production, including their sequential multi-stage cleaning in a dust chamber, cyclones, electric precipitators and subsequent “wet” cleaning in a scrubber, in which sludge water is used as a gas cleaning solution [Druzhinin K.E. Improvement of the main and auxiliary equipment of pyrometallurgical processes and its testing in the conditions of existing production / K.E. Druzhinin, N.V. Nemchinova, N.V. Vasyunina // Bulletin of ISTU, 2016, No. 5, p. 144-152].

The disadvantage of this method is the insufficient efficiency of cleaning the exhaust gases of rotary sintering kilns from fine dust and greenhouse gases, including carbon dioxide and water vapor.

The purpose of the invention is to obtain a high degree of gas purification from fine dust and greenhouse gases.

The problem to be solved by the invention is the development of an effective method for cleaning exhaust gases from sintering furnaces from fine dust and reducing emissions of greenhouse gases (carbon dioxide and water vapor).

The task is achieved by the fact that to clean exhaust gases from fine dust after cleaning the gases in the dust chamber and electrostatic precipitators, an additional stage of “wet” cleaning is used in two parallel scrubbers with gas distribution grids installed in them and spray nozzles, to which sub-sludge is supplied through separate pipelines water, then the purified gases are sent to centrifugal separators to separate excess moisture and water vapor from them.

The technical result of the proposed method is the purification of atmospheric air from dust and greenhouse gases emitted by rotating sintering kilns. The essence of the method is that the purification of gases from rotating sintering kilns from their constituent ingredients is carried out using a multi-stage method, which makes it possible to first purify the gases from coarse dust in a dust chamber and multi-field electrostatic precipitators, then purify them from fine dust in scrubbers, and then send the purified gases gases into a separator to capture water vapor. In contrast to the method adopted as a prototype, the claimed method in the multi-stage cleaning scheme excludes cleaning in cyclones, but uses cleaning in two parallel scrubbers with gas distribution grids installed in them and spray nozzles, to which sub-sludge water is supplied through separate pipelines, while the volume of sub-sludge water on the gas distribution grid is maintained in the range from 70 to 90 m ³ / h, and when subsludge water is supplied to the nozzle, respectively, from 10 to 30 m ³ / h, and then the purified gases are sent to centrifugal separators to separate excess moisture from the gas flow and collect vapors water. The exhaust gas emissions from sintering furnaces after cleaning using the proposed method ensure a lower content of dust and greenhouse gases.

A comparable analysis of methods for purifying waste gases from rotary sintering furnaces of alumina production with the proposed one shows the fundamental difference between the latter, both in terms of its novelty and in terms of the use of the constituent waste gases. Previously proposed technical solution for cleaning the exhaust gases of rotary sintering furnaces using multi-stage cleaning of the exhaust gases of the sintering furnaces, including cleaning in a dust chamber, electric precipitators and an additional cleaning stage in two parallel scrubbers with gas distribution grids installed in them and spray nozzles, which are fed through separate pipelines subsludge water, while the volume of subsludge water on the gas distribution grid is maintained in the range from 70 to 90 m ³ /h, and when supplying subsludge water to the nozzle, respectively, from 10 to 30 m ³ /h, and then the purified gases are sent to centrifugal separators to separate excess moisture from the gas flow and the capture of water vapor was not claimed and therefore the claimed method meets the “novelty” criterion. Comparison of the proposed method with other technical solutions allows us to conclude that the features that distinguish it from existing methods of purifying gases from rotary kilns were identified during the study of this field of technology and, therefore, ensures that the proposed solution meets the “significant differences” criterion.

The inventive method was tested at alumina production at JSC RUSAL Achinsk. The method of purifying exhaust gases from sintering furnaces of alumina production was carried out as follows.

The sinter formed as a result of sintering the raw material charge in rotary kilns enters the grate coolers, and the gases from the sintering furnaces 1, containing mainly sinter dust, are sent to a gas purification system, including a dust chamber 2, electric precipitators 3 of which gas enters through exit flues 5 in There are 4 smoke exhausters, and of these there are 9 scrubbers in the incoming flues. The gas passes through the first stage of irrigation 8 before entering the scrubber 6 and enters the main irrigation 7 with subsludge water in the scrubber, where it is cleaned of dust. The gas, passing through the separator 11, is cleared of the droplet suspension of sludge water and enters the exhaust gas duct 10 of the scrubber, then discharged into the atmosphere through the chimney 12 (Fig. 1).

To solve the problem, in a “wet” gas purification installation containing two centrifugal scrubbers, additional nozzles spraying sludge water were installed in the incoming gas duct to slow down the gas flow and increase the ability to purify and absorb gases. Purification of gases meant their passage through two scrubbers, into which mud water was supplied through two separate pipelines: through one pipeline, mud water was supplied under the gas distribution grid, while the volume of water was maintained in the range from 70 to 90 m ³ /h, through the other pipeline, mud water was supplied was supplied to the nozzle and the volume of water was accordingly maintained from 10 to 30 m ³ /h. The sludge water falling on the dissecting element under the gas distribution grid irrigates the gas flow according to the principle of a shower; the exiting gas duct with three-leaf gate valves was supplemented with centrifugal separators to separate excess moisture from the gas flow and capture water vapor.

Furnace gas enters through the gas duct 9 into the lower part of the scrubber into the hopper 13 on the side and enters it tangentially to create a gas turbulence. Solid heavy particles from the gas fall into the scrubber cone, which is filled with water; the level is monitored by a radar level gauge installed on top of pipe 18 and is sealed on flange 23. In order for the water level to rise freely inside the pipe, a breather 19 is installed. Passing through the gas distribution grille, the wetted dust particles increase in mass and, due to the resulting centrifugal force, are pressed against the wall of the chamber 14 and flow down the pipe 17, entering the cone through outlet 21. Next, the purified gas moves to the upper part of the scrubber to the separator 11 and then to the exiting flue. The contaminated water is drained into the scrubber cone through pipe 28 (Fig. 2). In each scrubber, above the incoming gas duct, there is a water-dispersing element 15 (nozzle) and a gas distribution grid 16. The gas distribution grid consists of blades 24 arranged in rows in a circle at an angle of 11 degrees, and holes for the passage of gas 25, its purpose is to reduce the speed of the gas flow and increase turbulence of gas to create centrifugal force in it. (Fig. 3) Dividing the supply of the irrigating solution of sub-sludge water into two flows (to the gas distribution grid and to the nozzle) ensures more effective cleaning of gas emissions from fine dust and carbon dioxide.

Sludge water is recycled water from alumina production, which contains 7-10 g/l Na ₂ O _ku . The essence of the process of purifying gas emissions from sintering furnaces from CO ₂ is to neutralize the gas with a circulating solution of highly alkaline sub-sludge water to form soda:

The resulting sludge is pumped out to a sludge field, and gases cleared of dust and CO ₂ are sent into the atmosphere through a chimney (Fig. 1).

During industrial testing, gases from sintering furnaces, after additional purification in scrubbers, were sent to a separator to separate excess moisture from the gas flow and capture water vapor. The principle of collecting dust in a scrubber is based on the wettability properties of the dust contained in the gas. The dusty gas enters the scrubber from the bottom up through the inlet pipe, where dust particles come into contact with water. To increase contact, water enters the scrubber through a nozzle (Fig. 2). The crushing of water into small drops occurs on grates with rings laid in one layer (Fig. 3).

Gases that passed all three stages of purification were released into the atmosphere, and the content of pollutants in them was controlled.

Examples of the implementation of the method for purifying waste gases from sintering furnaces of alumina production at JSC RUSAL Achinsk are given in Table 1 (experiment No. 1 - prototype method, experiments No. 2-7 - claimed method.

Analysis of the table 1 showed that the implementation of the method according to the prototype (experiment No. 1) provides a sufficiently high efficiency of purification from inorganic dust (98.0%), but does not lead to the required degree of purification of exhaust gases from sintering furnaces from carbon dioxide, while the carbon dioxide content in emissions into the atmosphere is 12.8%.

The optimal volume of supply of sub-sludge water to the scrubber was as follows: supply to the gas distribution grid from 70 to 90 m ³ /h, supply to the nozzle from 10 to 30 m ³ /h. This ensured fairly high rates of purification of gas emissions from sintering furnaces from fine dust and carbon dioxide, which is confirmed by the data in Table 1. The supply of sub-sludge water to the gas distribution grid was less than 70 m ³ /h and to the nozzle less than 10 m ³ /h (experiment No. 2) did not led to effective removal of carbon dioxide, which was explained by the lack of an alkaline irrigating solution to bind carbon dioxide and allow it to pass through the scrubber. An increase in the supply of sub-sludge water to the gas distribution grid by more than 70 m ³ /h and to the nozzle by more than 10 m ³ /h (experiment No. 6) led to a deterioration in the efficiency of cleaning gas emissions from dust. In this mode of operation of “wet” cleaning installations, during sampling, emissions of dirt and large drops of water were visually observed, while the level of sludge in the scrubber was constantly increasing. Purification of gases by supplying water only to a gas distribution grid of 80 m ³ /h (without supplying water to the nozzle), even at an optimal volume, did not lead to a relatively high degree of purification of gas emissions from carbon dioxide (experiment No. 7). The proposed method for cleaning exhaust gases from sintering furnaces provided effective cleaning from dust and carbon dioxide according to the proposed scheme using an additional stage of a “wet” gas purification installation, which was carried out in two parallel scrubbers with gas distribution grids installed in them and spray nozzles, which Sub-sludge water was supplied to separate pipelines, while the volume of sub-slurry water to the gas distribution grid was maintained in the range from 70 to 90 m ³ /h, and when feeding sub-sludge water to the nozzle, respectively, from 10 to 30 m ³ /h. At the same time, in the exhaust gas emissions after purification according to the proposed method and according to the stated parameters of the volumes of sub-sludge water supply, a lower content of carbon dioxide and fine dust is ensured.

According to the proposed cleaning scheme (Fig. 1), the exhaust gases of the sintering furnaces entered the dust chamber and then into electric precipitators, with the gas temperature reaching 230-270°C. After the electric precipitators, the gases were sent for “wet” cleaning in the scrubber and, taking into account the high temperature of the gases after the electric precipitators, there was a significant release of vapor from an aqueous solution of the irrigating liquid. At the same time, the main greenhouse gas is water vapor, the relative content of which in the atmosphere is much higher than carbon dioxide. It is known from literary sources that the greenhouse effect on average is up to 78% due to water vapor and only 22% due to carbon dioxide, so the proposed method included a separator to separate excess moisture and water vapor from them. During pilot tests, it was found that a device for “wet” purification of gas emissions with an additionally installed separator provides higher efficiency in the separation of aerosol particles and spray liquid vapors.

Claims (1)

A method for cleaning waste gases from alumina production sintering furnaces, including their multi-stage cleaning in a dust chamber, an electric precipitator and subsequent “wet” cleaning in a scrubber, in which sludge water is used as a gas cleaning solution, characterized in that “wet” gas cleaning is carried out in two parallel located scrubbers with gas distribution grids and spray nozzles installed in them, to which sub-sludge water is supplied through separate pipelines, while the volume of sub-sludge water on the gas distribution grid is maintained in the range from 70 to 90 m ³ /h, and when supplying sub-sludge water to the nozzle, accordingly from 10 to 30 m ³ /h, then the purified gases are sent to centrifugal separators to separate excess moisture and water vapor from them.

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