CN111356788A - Apparatus for collecting and removing gases from aluminium reduction tanks - Google Patents

Abstract

The present invention relates to the production of aluminium in a reduction cell having a baked anode. An apparatus includes a gas piping system and a gas collection cap. Each of the caps is connected to a horizontal gas conduit by a first passage to form a primary deaeration circuit and to an additional gas conduit by a second passage to form an additional deaeration circuit. The height of each subsequent channel of the main circuit is increased by 16% to 24% of the height of the previous channel, and the height of each subsequent channel of the additional circuit is increased by 24% to 26% of the height of the previous channel. A divider plate is mounted inside the cap. The length of each subsequent plate is reduced by 25% to 35% relative to the preceding plate. The technical effect is to reduce the amount of gas removed from the reduction cell and maintain the degassing efficiency.

Description

Apparatus for collecting and removing gases from aluminium reduction tanks

technical field

The present invention relates to non-ferrous metallurgy, and in particular to the production of aluminum in reduction tanks with prebaked anodes, and can be used to reduce the amount of gas removed from the reduction tank while at the High removal efficiency is maintained between operations and during regular operations.

Background technique

A device is known in which a plenum cap is in contact with the casing at the casing opening. The purpose of this invention is to collect the waste gas from the reduction tank in order to remove the waste gas from the aluminium fluorine compound (Patent US 4,770,752,1988).

Disadvantages of the known device include the limitations of the described invention related to maintenance of the alumina feed system located within the cap and possible damage during anode replacement due to the location of the cap close to the anode and housing.

An arrangement is known in which a standard amount of process gas is removed between regular operations and an increased amount of process gas is removed by actuating an additional exhaust fan when the anode casing lid is opened. A divider wall is installed inside the hood to direct the flow upwards into the gas channel to reduce emissions into the potroom (Patent No. RU2251593C2, IPCC25C3/20, published on 15.11.2000).

A disadvantage of similar devices is that when the reduction tank is opened, the air flow drawn under the hood moves the electrolytic gas along the reduction tank and creates a stagnant area of elevated electrolytic gas concentration under the bottom flange of the collector beam. In these areas, the gas escapes into the working area of the electrolysis plant through the gaps between the anode rods and the flanges and through the gaps between the hoods.

As disclosed in patent RU 2553137, C25C 3/22, published on June 10, 2015, a device is known for collecting and removing gas from an aluminum reduction tank, the device comprising a top reinforcement ring and a bottom A reinforcing ring and a double vertical walled collector beam, between which, along the vertical wall in the top of the collector beam, a main gas duct channel of variable cross-section is formed with located along the longitudinal axis of the collector beam A condenser above the anode, fixed at one end at the cowl inlet and at the other end with an opening at the bottom reinforcement ring, the height of the main gas duct channel increases towards the end of the collector beam connected to the gas stripping system. Two additional gas duct passages of variable cross-section are positioned symmetrically with respect to the longitudinal axis of the collector beam between the top and bottom reinforcing rings, these gas duct passages are connected to a collector with a shutter equipped. A bottom reinforcement ring is positioned along the longitudinal axis above the anode between the collectors of the main gas duct channels, wherein each main gas duct channel has a collector mounted at the front side in the metal extraction area.

A disadvantage of the provided device is that a local increase in the sparseness in the anode replacement area is provided in the device without equalizing the sparseness under the entire hood. For this purpose, additional gas pipes are included, which are connected to the collectors equipped with automatic shutters. Through these openings, the door for anode replacement is removed, and a large amount of air is drawn under the hood, creating and spreading vortices throughout the hood. As a result, collectors in other areas of the hood cannot manage the removal of gas, and gas escapes into the electrolysis plant through leaks in the hood. The provided device does not ensure efficient outgassing during anode replacement.

In terms of technical substance, the closest invention to the claimed invention is one disclosed in patent WO 2010/033037A1, IPCC25C3/22, published on March 25, 2010, for collecting Device for hot exhaust gas, the patent was selected as prior art. In this unit, the degassing cap is located directly above the housing opening and ensures a lower total gas removal from the reduction tank at higher _CO2 concentrations and elevated temperatures to reduce the number of gas stripping units and Increased heat exchange potential. Additionally, the plenum cap has at least two inlets, ie the plenum cap has double walls. The inlet velocity between the double walls significantly exceeds the velocity at the center of the cap to provide an additional draft that forms an artificial air wall, ensuring more efficient collection of exhaust gases and reducing disturbances from cross flow.

Disadvantages of prior art devices:

The cap design of the prior art ensures efficient removal of the electrolysis gas through the double wall, which creates an artificial air wall and reduces disturbances from the lateral flow. In this case, displacement of the cap away from the breaker would result in inefficient outgassing, and during operation in an aggressive environment, positioning the cap immediately above the housing opening would result in increased use of the reduction trough reflector and Damage to the flow control mechanism of the feeder.

The desired range for the cap to be positioned above the housing is 10mm to 1000mm, determined by the rate at which the alumina remains and the possibility to replace the anode. To meet this requirement, the mounting height of the cap should be changed for different operations, which affects the tightness of the device for gas removal.

Effective degassing from the reduction tank requires the removal of an equal amount of gas from all caps positioned under the hood of the reduction tank. This requires equal sparseness at each cap inlet; however, prior art devices do not have a system to control uniform air intake under the hood of the reduction tank.

In the device disclosed in WO 2010/033037, the cap for process gas collection can be mounted beside the feeder rather than being an integral part of the feeder. In this case, most of the gas will be drawn in at the periphery of the cap; however, this requires a uniform intake along the base length of the cap.

When replacing the anode, the hood door is opened and the air drawn in through the openings created creates vortices that move the gas into one end of the reduction tank, making the cap in that area unable to manage the removal of the increased gas volume. In addition, the air wall prevents the suction of the transverse air flow, which is formed through the large cracks formed in the casing from which the electrolyte of the anode is removed.

Therefore, the prior art devices do not ensure efficient removal of electrolysis gas between and during normal operations of the reduction tank operation. Furthermore, the equipment positioned under the hood is subjected to high stresses from the aggressive environment.

SUMMARY OF THE INVENTION

The present invention aims to reduce the heat loss of the exhaust gas from the reduction tank and relieve the stress on the gas stripping unit, while maintaining the degassing efficiency.

The stress on the gas stripping facility is determined by the amount of gas removed from the reduction tank. The total amount of gas removed from the reduction cell with the fired anode is 3000 nm ³ /h to 20000 nm ³ /h, of which only 1 to 2% are electrolysis gases and the rest is air. The efficiency of gas removal from the reduction tank is determined by the efficiency factor of the system that removes gas from the reduction tank. This value is usually 98%.

The technical result of the claimed invention is that the total amount of gas removed from the reduction tank is reduced several times due to the reduction in the amount of air, while ensuring the following conditions.

1. The efficiency factor of the degassing system is maintained at 98% or higher between and during normal operation of the reduction tank operation.

2. The aggressive environment imposes no increased stress on equipment positioned under the hood.

In order to ensure the first condition, the technical solution provided maintains the uniformity of the intake air along the length of the reduction tank hood and along the length of the base of each plenum cap between regular operations of the reduction tank operation.

In order to ensure the second condition, the plenum caps are positioned such that the mechanism for feeding the alumina is outside the intake area, and for said positioning - outside the intake area, the design of the cap ensures that along the respective plenums The length of the base of the cap evenly intakes air.

In one of the embodiments, the problem presented is solved by an apparatus for collecting and removing gas in an aluminium reduction tank, the apparatus comprising: a gas piping system comprising a horizontal main gas piping and additional gas piping, The horizontal main gas duct and the additional gas duct are configured to cut in/out of the main gas duct and the additional gas duct; and gas collecting caps, wherein each gas collecting cap is connected to the horizontal main gas duct through the first passage to form the main degassing loop, and is connected to an additional vertical gas duct through a second channel to form an additional degassing loop. The height of each subsequent first channel of the main circuit increases along the airflow by 16% to 24% of the height of the previous first channel, and the height of each subsequent second channel of the additional circuit increases along the airflow of the previous first channel. 24% to 26% of the height of the second channel. A divider plate is installed at the bottom of the inner surface of the longitudinal side of the at least one plenum cap in the direction of airflow, the divider plate having a length not greater than 50% of the height of the plenum cap, wherein at least two divider plates Mounted symmetrically on each side of the central axis of the gas collection cap, and the length of each subsequent plate in the direction of the central axis of the cap is reduced by 25% to 35% relative to the previous plate.

According to one embodiment of the proposed invention, the cap is made in the form of a collector.

According to one embodiment of the proposed invention, the main circuit and the additional circuit are combined at the top of the cap.

According to one embodiment of the proposed invention, the distance between the divider plates is at least 15% of the length of the base of the plenum cap.

Additionally, there is provided a system for collecting and removing gas from an aluminum reduction tank, the system comprising: a reduction tank including at least an anode and an electrolyte casing breaker; a cover of the reduction tank, the cover consisting of a removable the cover composition of the , the gas collecting cap is positioned along the longitudinal axis of the reduction tank below the hood of the reduction tank, between the electrolyte shell breakers, to form an air intake area in the center of the reduction tank. The guide elements are mounted horizontally on the inside of the removable cover with respect to the electrolyte housing and are configured to direct airflow into the intake area; wherein each of the plenum caps is connected to the horizontal main cap via a first channel Gas piping to form a main degassing circuit and connected to additional vertical gas piping via a second passage to form an additional degassing circuit. The height of each subsequent first channel of the main circuit increases along the airflow by 16% to 24% of the height of the previous first channel, and the height of each subsequent second channel of the additional circuit increases along the airflow of the previous first channel. 24% to 26% of the height of the second channel. A divider plate is installed at the bottom of the inner surface of the longitudinal side of the at least one plenum cap along the direction of airflow, the divider plate having a length not greater than 50% of the height of the plenum cap. At least two divider plates are mounted symmetrically on each side of the central axis of the plenum cap, with the length of each subsequent plate being reduced by 25% to 35% relative to the preceding plate in the direction of the central axis of the cap.

According to one embodiment of the proposed invention, the gas collecting cap in the system is positioned above the electrolyte casing at a distance equal to 0.5 to 1.5 of the height of the new anode of the reduction tank.

According to one embodiment of the proposed invention, the height of the cover relative to the electrolyte level is equal to 1.5 to 2 of the height of the new anode.

In addition, there is provided a reduction tank comprising the above-described means for collecting and removing gas in the aluminum reduction tank.

The listed embodiments of the present invention are not the only possible embodiments. Various modifications and improvements are envisaged without departing from the scope of the invention as defined in the independent claims.

Description of drawings

The essence of the present invention is illustrated by the following figures.

Figure 1 shows a general view of a reduction tank including means for collecting and removing gases.

Figure 2 shows the arrangement of the elements of the structure for collecting and removing the gas inside the reduction tank.

Figure 3 shows the elements of the main degassing circuit and the additional degassing circuit.

FIG. 4 shows an embodiment of a guide element made in the form of a protrusion of the device for collecting and removing gas (section view of the reduction groove).

Figure 5 shows an embodiment of a guide element made in the form of a plate (section view of the reduction tank) of the device for collecting and removing gases.

Figure 6 shows the arrangement of the divider plates in the plenum cap (cutaway view of the cap).

Figure 7 shows a longitudinal view of the main degassing circuit and the additional degassing circuit with the plenum cap.

Detailed ways

A device for collecting and removing gas is installed in the reduction tank. A reduction tank is a device that produces aluminum by reducing the melt, and typically includes an anode, a point alumina feeder with a crusher, a collector beam with gas conduits and gas caps, and a hood. All structural elements of the claimed device are fastened to the collector beam 1 . The cover of the reduction tank 2 is made of a separate cover, inside which the guide element 3 is mounted firmly horizontally with respect to the electrolyte housing of the melt. The guide elements may be structurally made in the form of plates or protrusions (Figs. 4 and 5) made of the material used to manufacture the cover, such as aluminum. The number of guide elements is determined by the velocity of the flow between the guides and needs to be ensured that the gas flow velocity is higher than 2m/s and lower than 7m/s in order to exclude the gas escaping from the reduction tank and carry the alumina away from the shell surface . The location and length of the guide elements are determined by the configuration of the hood and the uniform flow provided around the anode.

The gas collecting cap 4 is positioned along the longitudinal axis of the reduction tank below the reduction tank hood, between the electrolyte shell breakers and between the breakers 6 above the anode 5 to form an air intake area in the center of the reduction tank.

Each gas collecting cap 4 is connected to a horizontal main gas duct 9 through a first channel 8 to form a main degassing circuit, and to an additional vertical gas duct 10 through a second channel 8' to form an additional degassing circuit (Fig. 3) . The height of each subsequent first channel of the main circuit increases along the airflow by 16% to 24% of the height of the previous first channel, and the height of each subsequent second channel of the additional circuit increases along the airflow of the previous first channel. 24% to 26% of the height of the second channel. The main horizontal gas line 9 and the additional horizontal gas line 10 are connected to the electrolysis plant degassing system (not shown).

A divider plate is installed at the bottom of the inner surface of the longitudinal side of the at least one plenum cap in the direction of the air flow, the divider plate having a length not greater than 50% of the height of the plenum cap (Fig. 7). The divider plates are securely fastened to each side of the central axis of the gas collection cap, and the length of each subsequent plate is reduced by 25% to 35% relative to the preceding plate in the direction of the central axis of the cap. The plates are positioned symmetrically with respect to the central axis of the cap to ensure the same intake conditions along the length of the base of the cap. The number of plates needs to be at least two on each side of the central axis to exclude stagnant areas in the cap. A divider plate installed in this way divides the volume of the cap into regions (channels) of equal velocity at the base of the cap, without forming a stagnant area (through which gas is not removed) to ensure that the cap center and periphery the same intake efficiency. The width of each parallel channel should preferably be at least 15% of the length of the base of the cap. The effect obtained allows the cap to be positioned between the breakers, while the mechanism for feeding the alumina is outside the intake zone and therefore the stress from the aggressive environment is minimal.

The inventors have unexpectedly found that for different plate positions and sizes, the effect of uniform air intake at the base of the cap cannot be obtained.

Thus, an increase in the length of the plate or directing the plate towards the center of the cap causes the flow from the channels to collide and thus create a positive pressure zone. In this case, the gas escapes back into the hood. Positioning the plate on top of the cap results in increased velocity when exiting the cap. As a result, the aerodynamic resistance of the cap is increased, and thus the stress on the gas stripping resistance is also increased. Since, in this case, areas with different degrees of sparseness are formed at the cap inlet, the air intake non-uniformity at the base of the cap also increases. Furthermore, an air wall similar to that in prior art devices can be formed to prevent the ingress of gas at the periphery of the cap.

The gas collecting cap 4 is mounted over the electrolyte casing, eg, at a distance equal to 0.5 to 1.5 of the height of the new anode, and the height of the hood is equal to 1.5 to 2.0 of the height of the new anode. An increase in hood height will increase the amount of air in the removal gas, which will require an increase in rarefaction to the level present in current designs of reduction tanks, which increases the stress on the gas stripping facility and increases heat losses. In the case of a reduced amount, the anode cannot be replaced.

In one of the embodiments devised during the development of the present invention, the gas collection cap is made in the form of a collector - a collector in which the channels are gradually narrowed, which increases the velocity of the gas being removed And reduce the loss of energy spent on degassing. The cap height is 800mm, and the base length is 1800mm and the base width is 170mm. The divider plates are fixed at a height of 30mm from the base of the cap and are oriented along the side walls, forming parallel channels for airflow. The length of the first plate is 400mm, which is 50% of the height of the cap. The lengths of the second and third plates are 260mm and 170mm, respectively. The rectangular shape of the base of the cap is defined by the positioning mechanism needed to perform anode replacement and feed alumina under the hood, the cap covers the entire space in the center of the reduction tank between the anodes, excluding the space for operating the crusher and feeder . The width of each channel in the parallel channels is 180mm. The cap is mounted at a height of 50mm above the anode.

The device operates as follows. Between normal operations of the reduction tank operation, the gas entering under the hood of the reduction tank 2 through the casing opening pierced by the breaker 6 mixes with the air leaked in through the hood and is drawn into the cap 4 of the main horizontal gas duct 9 , for degassing and further into the electrolysis plant degassing system (not shown). The divider plate 7 in the cap 4 evenly distributes the airflow over the base of the cap. By varying the heights of the channels 8 and 8' to the main gas duct, distributing the resistance along the length of the main horizontal gas duct 9, it is possible to ensure an even distribution of gas flow between the caps 4. The cap 4 is preferably positioned above the housing at a height of 0.5 to 1.5 of the height of the anode 5, between the breakers 6, to ensure that the degree of thinning is sufficient to completely remove the gas.

When performing operations on the reduction tank that involve partially opening the reduction tank, air is drawn under the hood 2 and mixed with the anode gas to form vertical and horizontal vortices. The guide element 3 fixed to the inside of the cover breaks up the vortex and guides it to the cap 4 . When performing operations, such as replacing the anode, gas is removed through both the main gas conduit 9 and the additional gas conduit 10 . Thus, the sparseness under the hood can be increased by a factor of 3 to 4, which is sufficient to remove gas when the hood is partially opened. Known mechanisms, such as dampers, cut the main and additional gas ducts in and out.

Achieving the claimed device, due to the combined effect of reducing the amount of gas to be removed, redistributing the gas flow into the intake area, and positioning the cap close to where the electrolysis gas is exhausted under the hood, allows the removal of gas from a reduction tank. The amount of gas is reduced by a factor of 2 to 4. The degassing efficiency coefficients obtained ranged from 98% to 99%, depending on the operation performed by the reduction tank.

Mounting the cap under the hood, close to where the electrolysis gas exits, increases degassing efficiency with a smaller amount of gas removed, and the stated height at which the cap is mounted above the electrolyte housing ensures anode replacement without damaging the cap possibility. Plates inside the cap ensure even air intake along the length of the base of the cap.

Caps are included in both the main degassing system and the additional degassing system to ensure effective degassing between and during routine operations.

Said range of variation in the height of the channels connected to the caps ensures efficient operation of all caps, ie efficient degassing along the length of the reduction tank.

The main gas conduit and additional gas conduits are connected to the cap at the top of the cap (at the collector apex). The velocity of the flow at the outlet of the accumulator has reached equilibrium and switching in the additional loop will not change the characteristics of the gas flow inside the accumulator, ie will not affect the uniformity of the intake air at the base of the cap. The gas redistribution in the loop is proportional to the sparseness in the loop and the cross-sectional area of the gas pipes.

The positioning of the cap between the breakers at a height equal to 0.5 to 1.5 of the anode height allows the anode to be replaced without damaging the structural elements of the device used for gas removal, and reduces the temperature and impact of abrasive particles on the breakers and the reduction tank. effects on the normal operation of the feeder.

Claims (11)

1. A device for collecting and removing gas in an aluminum reduction tank, the device comprising: a gas duct system including a horizontal main gas duct and an additional gas duct, the horizontal main gas duct and the additional gas duct being configured to cut in/out of the main gas duct and the additional gas duct; as well as gas cap; Wherein, each of the gas collecting caps is connected to a horizontal main gas pipeline through a first channel to form a main degassing circuit, and is connected to an additional vertical gas pipeline through a second channel to form an additional degassing circuit; where the height of each subsequent first channel of the main circuit increases along the airflow by 16% to 24% of the height of the previous first channel, and the height of each subsequent second channel of the additional circuit along the Airflow increased by 24% to 26% of the height of the previous second channel; wherein a divider plate is installed at the bottom of the inner surface of the longitudinal side of at least one air collecting cap along the direction of the air flow, and the length of the divider plate is not greater than 50% of the height of the air collecting cap; wherein at least two divider plates are mounted symmetrically on each side of the central axis of the plenum cap, with each subsequent plate decreasing in length relative to the preceding plate in the direction of the central axis of the cap 25% to 35%. 2. The device of claim 1, wherein the primary circuit and the additional circuit are combined at the top of the cap. 3. The device of claim 1, wherein the cap is made in the form of a collector. 4. The apparatus of claim 1, wherein the distance between the divider plates is at least 15% of the length of the base of the plenum cap. 5. A system for collecting and removing gas in an aluminum reduction tank, the system comprising: a reduction tank comprising at least an anode and an electrolyte shell breaker, a cover of the reduction tank, the cover is constituted by a removable cover; a gas duct system including a horizontal main gas duct and an additional gas duct, the horizontal main gas duct and the additional gas duct being configured to cut in/out of the main gas duct and the additional gas duct; a gas collecting cap positioned along the longitudinal axis of the reduction tank below the hood of the reduction tank, between the electrolyte shell breakers, to be centered on the reduction tank forming an air intake area; wherein a guide element is mounted horizontally on the inside of the removable cover with respect to the electrolyte housing, the guide element being configured to direct airflow into the air intake area; Wherein, each of the gas collecting caps is connected to a horizontal main gas pipeline through a first channel to form a main degassing circuit, and is connected to an additional vertical gas pipeline through a second channel to form an additional degassing circuit; where the height of each subsequent first channel of the main circuit increases along the airflow by 16% to 24% of the height of the previous first channel, and the height of each subsequent second channel of the additional circuit along the Airflow increased by 24% to 26% of the height of the previous second channel; wherein a divider plate is installed at the bottom of the inner surface of the longitudinal side of at least one air collecting cap along the direction of the air flow, and the length of the divider plate is not greater than 50% of the height of the air collecting cap; wherein at least two divider plates are mounted symmetrically on each side of the central axis of the plenum cap, with each subsequent plate decreasing in length relative to the preceding plate in the direction of the central axis of the cap 25% to 35%. 6. The system of claim 5, wherein the cap is made in the form of a collector. 7. The system of claim 5, wherein the gas collection cap is positioned above the electrolyte housing by a distance equal to 0.5 to 1.5 of the height of the new anode. 8. The system of claim 5, wherein the height of the cover relative to the level of the electrolyte is equal to 1.5 to 2 of the height of the new anode. 9. The system of claim 5, wherein the primary circuit and the additional circuit are combined at the top of the cap. 10. The system of claim 5, wherein the distance between the divider plates is at least 15% of the length of the base of the plenum cap. 11. A reduction tank comprising the apparatus of claim 1 for collecting and removing gas.

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