Apparatus and method for controlled alumina supply

Abstract

Apparatus and methods for removing contaminants from process vent gas produced by electrolytic cells used in aluminum production apparatus to produce aluminum are disclosed. The apparatus and methods use flow control devices to control the supply of alumina to the electrolytic cells and to dry scrubber contact reactors.

Description

Technical Field

[0001] This disclosure relates to apparatus and methods for removing contaminants from process exhaust gases generated by electrolytic cells used in aluminum production equipment. More specifically, this disclosure relates to apparatus and methods for controlling the supply of alumina to the electrolytic cells, and to a separate dedicated dry scrubber. Background Technology

[0002] In processes used for the electrolytic production of aluminum, such as the Hall-Héroult process, aluminum is produced by reducing alumina in an electrolytic melting tank filled with a molten electrolyte in the form of fluoride minerals. This process generates emissions containing fluoride-containing substances such as hydrogen fluoride (HF) and fluoride-containing dust. Because these substances are extremely harmful to the environment, they must be separated before the process emissions can be released into the surrounding atmosphere. Simultaneously, the fluoride-containing melt is essential for the electrolytic process, therefore, the recovery of fluoride-containing substances is necessary for the recycling of the electrolytic process. This recycling can be achieved by adsorbing the fluoride-containing substances onto granular adsorbents.

[0003] As noted, the electrolytic reaction occurring in the electrolytic melting tank produces process exhaust gases in the form of hot, particulate-laden exhaust gases, which are typically cleaned in a gas cleaning unit before being released into the atmosphere. An example of a gas cleaning unit for cleaning exhaust gases generated in the electrolytic melting tank is disclosed in US 5,885,539. The gas cleaning unit disclosed in US 5,885,539 includes a first contact reactor and a second contact reactor. The exhaust gas from the electrolytic melting tank is first conveyed to the first contact reactor and contacted with recycled alumina in the first contact reactor. A portion of the cleaned exhaust gas is then conveyed to the second contact reactor and contacted with fresh alumina in the second contact reactor. A portion of the used alumina is recycled from the second contact reactor back to the first contact reactor. A dust collector removes the alumina from the exhaust gas, which is then released into the atmosphere.

[0004] Systems for recovering fluorides include a filter system contained within a closed system. It is important to stably deliver exhaust gases from the aluminum production process to the filter system. Stable delivery is achieved using gas pipelines through which the exhaust gases are transported by a large fan. The gas pipelines consist of a main pipe and branch pipes that are fluidly connected to the filter system. For each aluminum production electrolytic cell, branch pipes are introduced into or connected to the main pipe. As the amount of exhaust gas delivered increases, the cross-section of the main pipe gradually increases with the aid of diffusers. It is crucial, both environmentally and for the electrolysis process, that the exhaust gas distribution be as uniform as possible. Traditionally, uniform exhaust gas distribution is achieved by increasing the proximity of a particular branch pipe to the suction fan, thereby increasing the throttling of the exhaust gas delivered within the branch pipe. Throttling represents the loss of shear energy through pressure drop.

[0005] Gas cleaning units used to clean process exhaust gases generated during aluminum electrolysis include both centralized and decentralized systems. Centralized systems are typically connected to one or more halls comprising electrolytic cells, each hall potentially containing 70 to 200 cells, with cleaning equipment centrally located between or outside the halls. Centralized systems are connected to each electrolytic cell via a comprehensive and costly piping system. Alumina, used as an adsorbent in the exhaust gas cleaning process, is stored in separate silos—one for storage before use and another for storage after use. The alumina stored after use is then transported back to each cell via transport vehicles, cranes, or other aluminum transport systems such as those used for transporting aluminum in a compact phase.

[0006] A decentralized system is used to clean process exhaust gases from 5 to 40 electrolytic cells, more preferably 10 to 20 electrolytic cells. Therefore, less piping is required, and the transportation needs for alumina movement are significantly reduced. Greater flexibility is achieved at the start of operation, and the distance between the alumina storage unit and the electrolytic cells can be minimized. Additional beneficial effects achieved by the decentralized system are described in US6,406,524.

[0007] While systems for cleaning process exhaust gases generated during the electrolytic processing of aluminum are known, there remains a need in the aluminum production industry for improved systems that reduce operating costs, reduce equipment footprint, reduce capital costs, and / or increase adaptability to meet the specific system requirements of larger production facilities. Summary of the Invention

[0008] This disclosure relates to apparatus and methods for removing contaminants from process exhaust gases generated by electrolytic cells used in aluminum production equipment. More specifically, this disclosure relates to apparatus and methods for controlling the supply of alumina to the electrolytic cells, and to separate dedicated dry scrubber contact reactors. According to one embodiment of this disclosure, apparatus is provided in which each individual aluminum electrolytic cell is arranged at a level below that of a separate dedicated dry scrubber contact reactor used to remove gaseous contaminants such as hydrogen fluoride from exhaust gases generated by the aluminum production process. A single aluminum electrolytic cell includes a plurality of anode electrodes, typically six to thirty, generally arranged in two parallel rows extending along the length of the electrolytic cell and into the molten contents of the bath. The electrolytic cell also includes one or more cathode electrodes. The process occurring in the electrolytic cell can be the well-known Hall-Héroult process, in which alumina, also interchangeably referred to herein as “bauxite,” dissolves in a melt of a fluorinated mineral and electrolyzes to form aluminum. Thus, the electrolytic cell is used as an electrolytic cell. Powdered alumina is supplied to the electrolytic cell from an alumina hopper by gravity, fluidization, mechanical transport, and / or similar means. The powdered alumina is then supplied to the bath of the electrolytic cell via a feeder. Each feeder may be equipped with a feed pipe, a feed inlet, and a shell breaker operable to form an opening in the shell, typically on the surface of the contents of the bath. An example of a shell breaker is described in US 5,045,168.

[0009] The electrolysis process occurring in the electrolytic cell generates significant amounts of heat, particulate matter, and exhaust gases, including but not limited to hydrogen fluoride, sulfur dioxide, carbon dioxide, and perfluorinated compounds (PFCs), i.e., pollutants. The electrolytic cell is arranged within a closed enclosure defining an internal area. This internal area includes an outlet. A fan draws the exhaust gases from the enclosure into an exhaust gas treatment system via the outlet. The fan is preferably located downstream of the exhaust gas treatment system to create a negative pressure within it. However, other arrangements can be used for exhaust gas delivery. Due to the negative pressure generated by the fan, a volume of ambient air is drawn into the internal area of ​​the enclosure primarily through gaps or openings between the sidewall doors of the enclosure. The exhaust gases drawn from the internal area of ​​the enclosure thus include exhaust gases, particulate matter generated during the aluminum production process, and a volume of ambient air.

[0010] In a separate, dedicated exhaust gas treatment system arranged horizontally above the electrolytic cell, the exhaust gas flows upward through a dry scrubber contact reactor, where the adsorbent, typically alumina, is dispersed and subsequently used in aluminum production processes. The dispersed alumina mixes with the exhaust gas and interacts with some components of the exhaust gas, particularly hydrogen fluoride (HF) and sulfur dioxide (SO2), to generate a contact gas. Particulate adsorption products formed by the interaction of alumina with HF and SO2 are entrained in the contact gas, which flows vertically or upward from the dry scrubber contact reactor through the exhaust gas treatment system to a fabric filter. The particulate adsorption products are removed from the contact gas via the fabric filter to produce treated gas. In addition to removing HF and SO2 from the exhaust gas, the exhaust gas treatment system via the fabric filter also separates at least a portion of the dust particles entrained in the contact gas from the interior area of ​​the housing.

[0011] The dry scrubber contact reactor of the present invention is arranged downstream of an alumina hopper, which, according to one embodiment, extends horizontally across a portion of the porous bottom surface of an exhaust gas treatment system housing. A solid base wall is arranged at a distance vertically below the portion of the porous bottom surface. The exhaust gas treatment system housing includes a top, a portion of the porous bottom surface, and two opposing sidewalls, the portion of the porous bottom surface having a solid base wall just below it, the two opposing sidewalls defining an opening interior. Alumina is supplied to the dry scrubber contact reactor via the alumina hopper. Thus, alumina flows from a flow control device through the portion of the porous bottom surface of the exhaust gas treatment system to the dry scrubber contact reactor via gravity, fluidization, mechanical transport, and / or similar means. The dry scrubber contact reactor is equipped with an exhaust gas inlet through which exhaust gas flows, wherein alumina is dispersed into and mixed with the exhaust gas within the dry scrubber contact reactor. An exhaust gas inlet is arranged between a portion of the sidewall of the housing and a baffle wall adjacent to the free end of the porous bottom surface and the solid base wall, extending vertically upward from the free end to the free overflow edge. The baffle wall is located away from the sidewall to allow exhaust gas to flow therebetween into the dry scrubber contact reactor. Similarly, according to one embodiment, the dry scrubber contact reactor is arranged between movable non-scrubber walls extending generally parallel to the sidewalls from the free base end to the opposite free top end. The non-scrubber walls can be moved electronically and / or manually by adjusting arms equipped with hinges connected thereto. Arms connected to the sidewalls may have hinges at or near the sidewalls. Arms also connected to the non-scrubber walls may have hinges at or near the non-scrubber walls. Furthermore, the arms may also have hinges arranged between those of the sidewalls and the non-scrubber walls. Arms equipped with hinges or other moving mechanisms allow the non-scrubber walls to be moved electronically and / or manually, vertically (i.e., closer to or further away from the porous bottom surface) and horizontally (i.e., closer to or further away from the sidewalls). The supply of alumina to the dry scrubber contact reactor can be controlled or regulated by moving and positioning the scrubber wall. Therefore, if the scrubber wall is positioned relatively closer to the porous bottom surface, the alumina supply decreases. If the scrubber wall is positioned relatively further away from the porous bottom surface, the alumina supply increases. If the scrubber wall is positioned relatively closer to the sidewall, the alumina supply increases. If the scrubber wall is positioned relatively further away from the sidewall, the alumina supply decreases. A flow control device controls the flow of alumina to the alumina hopper. The flow control device includes a first section formed by a hollow structure of an elongated tubular or similar shape. The first section is vertically arranged, with its top inlet end fluidly connected to the primary alumina supply device. The opposite bottom outlet end of the first section is connected to or integrally formed with a vertically arranged second section. The second section defines an internal region of an opening extending from a free base edge on the side, which tapers inward and upward to an opposite connecting end. The connecting end of the second section is connected to the bottom outlet end of the first section.Therefore, primary alumina flows from the top inlet end of the first section to the base opening defined by the free base edge of the second section via a flow control device. The flow control device may be movable. It can be moved electronically and / or manually by adjusting an arm equipped with a hinge connected thereto. The arm is connected to a sidewall and may have a hinge at or near the sidewall. The arm is also connected to the flow control device and may have a hinge at or near the flow control device. Furthermore, the arm may have hinges arranged between those at the sidewall and the flow control device. The arm equipped with hinges or other such moving mechanisms allows the flow control device to be moved electronically and / or manually, both vertically (closer to or further from the porous bottom surface) and horizontally (closer to or further from the sidewall). By moving and positioning the flow control device, the supply of alumina to the alumina hopper can be controlled or regulated, thereby controlling or regulating the supply to the electrolytic cell and the dry scrubber contact reactor.

[0012] Since the electrolytic cell is supplied with alumina by an alumina hopper, which also supplies alumina to the dry scrubber contact reactor, the required alumina rate for the electrolytic cell is determined or controlled via a flow control device to supply alumina to a separate, dedicated dry scrubber contact reactor. Therefore, alumina is conveyed from the primary alumina supply device to a flow control device vertically arranged within the exhaust gas treatment system housing for gravity-fed alumina flow. The free base edge of the flow control device is arranged, according to system requirements, from a predetermined distance from a partially porous bottom surface of the exhaust gas treatment system housing to the top surface of the alumina within the alumina hopper or below it. According to this embodiment, an air supply device is fluidly connected to the housing to supply air between the solid base wall and the partially porous bottom surface. The air supply device can be a fan, blower, or similar device. The air supplied between the solid base wall and the partially porous bottom surface flows upward through openings arranged in one or more sections of the porous bottom surface, thereby fluidizing a portion of the alumina supported on the porous bottom surface. Therefore, a certain amount of static primary alumina is intentionally accumulated under the second section of the flow control device on the side wall adjacent to the exhaust gas treatment system housing. As the static amount of primary alumina accumulates in the internal region of the opening in the second section, the gravity flow of alumina through the first section becomes slowed or blocked. When a certain amount of alumina flows from below the second section via fluidization and / or gravity to the alumina hopper that supplies alumina to the electrolytic cell via the feed pipe, a portion of the static amount of primary alumina becomes free and displaced, allowing primary alumina to flow from the first section again. This flow of alumina continues unless or until the flow is again slowed or blocked by the accumulation of static primary alumina under the second section of the flow control device. The supply of alumina to the electrolytic cell and the flow of primary alumina from the flow control device is controlled by this ebb and the flow of primary alumina from the feed pipe downstream of the dry scrubber contact reactor. For an additional, possibly "on-demand" type intermittent booster, an air supply device may be connected to one or more air booster devices. According to one embodiment, the air booster device may be arranged on the side wall below the flow control device. An air booster device arranged below the flow control device can be intermittently used to locally increase the air supply to alter or enhance the fluidization conditions of alumina below the second part of the flow control device, thereby intermittently increasing the alumina supply to the alumina hopper. Alternatively, according to this embodiment, the air booster device can be arranged above the porous bottom surface of the retainer wall. An air booster device arranged on the retainer wall can be intermittently used to locally increase the air supply to alter or enhance the fluidization conditions, thereby intermittently increasing the alumina supply to the dry scrubber contact reactor.

[0013] The fabric filter of the present invention is arranged in the upper part of the exhaust gas treatment system housing, horizontally above the flow control device, alumina hopper, and dry scrubber contact reactor. The fabric filter includes a support wall arranged to extend across a portion of the exhaust gas treatment system housing to form a barrier separating a "post-filter" region on one side of the support wall from a "pre-filter" region on the opposite side of the support wall. A plurality of openings extend through the thickness of the support wall, each equipped with a replaceable fabric filter bag extending from the opening into the pre-filter region. An outlet is arranged in the post-filter region through which the treated gas flows outward from the post-filter region of the exhaust gas treatment system housing to another treatment device or the atmosphere.

[0014] A method of using the exhaust gas treatment system of the present invention includes: arranging the exhaust gas treatment system of the present invention horizontally above a horizontal electrolytic cell capable of operating to produce aluminum; fluidly connecting the exhaust gas treatment system of the present invention to the electrolytic cell via a feed pipe and an exhaust gas outlet, wherein the feed pipe is connected to an alumina hopper of the exhaust gas treatment system and the exhaust gas outlet is connected to a dry scrubber contact reactor; supplying alumina to the exhaust gas treatment system via a flow control device, wherein the flow control device supplies alumina to the electrolytic cell and the dry scrubber contact reactor at a rate based on the alumina demand of the electrolytic cell; causing the dispersed alumina to interact with the exhaust gas in the dry scrubber contact reactor to remove contaminants from the exhaust gas, thereby generating a contact gas carrying particulate adsorption products; and removing particulate adsorption products from the contact gas in a fabric filter to generate clean gas.

[0015] A method for supplying alumina using the flow control device of the present invention includes: providing a vertically arranged flow control device within an exhaust gas treatment system housing, the flow control device comprising a vertically arranged elongated first portion and a vertically arranged second portion and disposed at a predetermined distance above a portion of the porous bottom surface of the exhaust gas treatment system housing; supplying alumina from an alumina supply device to the flow control device to gravity supply alumina to an alumina hopper via the flow control device to supply alumina to an electrolytic cell and a dry scrubber contact reactor; and controlling the rate of alumina supply to the dry scrubber contact reactor based on the alumina demand of the electrolytic cell.

[0016] In summary, the exhaust gas treatment system of the present invention includes: a separate, dedicated exhaust gas treatment system arranged horizontally above a separate aluminum electrolysis cell; a housing defining an internal region of the separate exhaust gas treatment system; a flow control device vertically arranged within the internal region, the flow control device including an elongated hollow first portion and a tapered second portion and arranged at a predetermined distance from a partially porous bottom surface of the housing; an adsorbent hopper extending across the partially porous bottom surface of the housing between the flow control device and a dry scrubber contact reactor; a feed pipe fluidly connected between the adsorbent hopper and the separate aluminum electrolysis cell for supplying adsorbent to the separate aluminum electrolysis cell; and an exhaust gas outlet in the housing for the separate electrolysis cell, the exhaust gas outlet being fluidly connected to the dry scrubber contact reactor for interacting the exhaust gas with the adsorbent supplied from the adsorbent hopper to generate a contact gas. The exhaust gas treatment system also includes an air pressurization device to alter or promote adsorbent fluidization within the system. The exhaust gas treatment system of the present invention also includes a fabric filter operable to remove particulate adsorbent products and dust from the contact gas. The fabric filter comprises a plurality of removable fabric filter bags arranged horizontally within a housing, vertically above the flow control device, the adsorbent hopper, and the dry scrubber contact reactor. The flow control device and / or a portion of the dry scrubber contact reactor may be movable to influence adsorbent fluidization, and the flow control device of the exhaust gas treatment system controls the adsorbent supply rate to the dry scrubber contact reactor based on the adsorbent rate required by the electrolytic cell.

[0017] In summary, the flow control device of the present invention comprises: a vertically arranged elongated hollow first portion; a vertically arranged second portion defining an internal region of an opening, the second portion including a tapering wall extending between a base edge and a connecting top, wherein the connecting top is fluidly connected to the bottom opening end of the first portion; an adsorbent supply device fluidly connected to the top opening of the first portion; and a portion of an adsorbent hopper arranged at a predetermined distance vertically below the flow control device, wherein the flow control device is mechanically operable to control the rate of adsorbent supply to the dry scrubber contact reactor based on the adsorbent rate requirement of the aluminum electrolysis cell. The base edge of the second portion of the flow control device of the present invention is arranged vertically below the top surface of the adsorbent in the adsorbent hopper. Furthermore, the first portion of the flow control device of the present invention is a tubular or similar hollow structure. The dimension of the base edge of the second portion of the flow control device of the present invention is larger than the dimension of the connecting top of the second portion.

[0018] In summary, a method using the flow control device of the present invention includes: arranging the flow control device, which includes a vertically arranged elongated hollow first portion; a vertically arranged second portion defining an internal region of an opening, the second portion including a tapering wall extending between an opening free base edge and a connecting top, wherein the connecting top is fluidly connected to the bottom outlet end of the first portion; an adsorbent supply device fluidly connected to the opening top inlet end of the first portion; and a portion of an adsorbent hopper arranged at a predetermined distance vertically below the flow control device; and operating the flow control device to control the rate of adsorbent supply to the dry scrubber contact reactor based on the adsorbent rate requirement of the aluminum electrolysis cell. According to the method of the present invention, the adsorbent flows by gravity through the flow control device from the opening top inlet end of the first portion to the opening free base edge of the second portion. The adsorbent is alumina. The method of the present invention further includes increasing the rate of adsorbent supply to the dry scrubber contact reactor via an air pressurization device.

[0019] The method of the present invention further includes reducing the rate of adsorbent supply to the dry scrubber contact reactor by static adsorbent accumulation in the internal region of the opening defined by the second portion. The method also includes reducing the rate of the adsorbent flow supplied to the dry scrubber contact reactor via a flow control device by static adsorbent accumulation in the internal region of the opening defined by the second portion and static adsorbent accumulation below the second portion. According to the method of the present invention, the dimension of the free base edge of the opening of the second portion is larger than the dimension of the connecting top of the second portion. Additionally, according to the method of the present invention, the connecting top of the second portion has dimensions and construction similar to those of the bottom outlet end of the first portion.

[0020] The beneficial effect of the system of the present invention is that the control of the alumina and fluoride balance can be specific to the electrolytic cell. Therefore, if an electrolytic cell produces more hydrogen fluoride gas for some reason, the feeder can be actuated to supply more alumina to the electrolytic cell, thereby adsorbing more fluoride and reducing the amount of fluoride lost from the electrolytic cell. Furthermore, when the feeder is actuated, a shell breaker is first operated inside the bath to open an orifice through which alumina is supplied to the contents of the bath. This operation produces a significant amount of hydrogen fluoride gas. Therefore, during operation, the feeder supplies more alumina to the electrolytic cell. The additional alumina supplied to the electrolytic cell adsorbs more fluoride, reducing the amount of fluoride lost from the electrolytic cell during operation. Preferably, the hydrogen fluoride sensor, sulfur dioxide sensor, and / or perfluorinated compound sensor are mounted on or relatively close to the treated gas outlet for additional feeder control via a controller and emission control. Other objects and features of this disclosure will become apparent from the following detailed description and claims. Attached Figure Description

[0021] The present disclosure is described in more detail below with reference to the accompanying drawings, in which: Figure 1 This is a schematic side cross-sectional view of an aluminum production facility equipped with an embodiment of the exhaust gas treatment system of the present invention; and Figure 2 This is a schematic side cross-sectional view of an aluminum production facility equipped with another embodiment of the exhaust gas treatment system of the present invention. Detailed Implementation

[0022] Figure 1 and Figure 2 Each of the above is a schematic diagram of an aluminum production equipment 10. The main components of the aluminum production equipment 10 include an aluminum production electrolytic cell chamber 12 in which multiple aluminum production electrolytic cells 14 can be arranged. Figure 1 and Figure 2 In each figure, for clarity and simplicity, only one aluminum production electrolytic cell 14 is depicted, but it should be understood that the electrolytic cell chamber 12 may typically include 50 to 200 electrolytic cells 14. Each aluminum production electrolytic cell 14 includes a plurality of anode electrodes 16, typically six to thirty anode electrodes 16, usually arranged in two parallel rows extending along the length of the electrolytic cell 14 and into the contents 18 of the bath 20. The electrolytic cell 14 also includes one or more cathode electrodes 22. The process occurring in the electrolytic cell 14 may be the well-known Hall-Héroult process, in which alumina or bauxite A (used interchangeably herein) is dissolved in a melt of fluorine-containing minerals and electrolyzed to produce aluminum. Thus, the electrolytic cell 14 serves as an electrolytic cell. Powdered alumina A is supplied to the electrolytic cell 14 from an alumina hopper 24 integrated into a separate exhaust gas treatment system 26 dedicated to a single electrolytic cell 14. The powdered alumina A is supplied to the bath 20 by means of a feeder 28 controlled by a controller 126. Each feeder 28 is provided with a feed pipe 30, a feed inlet 32, and a shell breaker 34 operable to form an opening in the shell, which is typically formed on the surface 18A of the contents 18. An example of the shell breaker 34 is described in US 5,045,168. Each feeder 28 is electrically connected to a controller 126. The controller 126 may also be electrically connected to a hydrogen fluoride sensor 33 disposed in the treated gas outlet 102. An example of the hydrogen fluoride sensor 33 is disclosed in EP2181753. Other sensors 33 may also be disposed in the treated gas outlet 102, such as a sulfur dioxide sensor, a perfluorinated compound sensor, a carbon dioxide sensor, and / or similar contaminant sensors. The controller 126 may also be electrically connected to an air supply unit 120 and a pressurization unit 124. The controller 126 is discussed in more detail below.

[0023] The electrolysis process occurring in electrolytic cell 14 generates a large amount of heat H, particulate matter DP, and exhaust gas EG, including but not limited to hydrogen fluoride, sulfur dioxide, and carbon dioxide, i.e., pollutants. The cell housing 36 defines an internal region 36A in which the bath 20 is arranged. An exhaust gas EG inlet 66 is fluidly connected to the internal region 36A. A fan 40 draws exhaust gas EG from the internal region 36A and through an exhaust gas treatment system 26. The fan 40 is preferably located downstream of the exhaust gas treatment system 26 to create a negative pressure within the exhaust gas treatment system 26. However, alternatively, the fan 40 may be arranged elsewhere depending on the requirements of the equipment 10. The fan 40 creates suction in the internal region 36A of the cell housing 36 via the fluidly connected exhaust gas EG inlet 66. Due to the negative pressure in the cell housing 36, a volume of ambient air AA is drawn into the internal region 36A primarily through gaps or openings 42 at the side wall door 44. The exhaust gas EG drawn from the internal region 36A via the exhaust gas EG inlet 66 includes exhaust gas EG, particulate matter DP generated in the aluminum production process, and a volume of ambient air AA.

[0024] In the exhaust gas treatment system 26, the exhaust gas EG is mixed with an adsorbent, typically alumina A, in a dry scrubber contact reactor 46. Alumina A is subsequently used in aluminum production processes. Alumina A interacts with some components of the exhaust gas EG, particularly hydrogen fluoride (HF) and sulfur dioxide (SO2). Particulate adsorption products PP, formed by the reaction of alumina A with hydrogen fluoride and sulfur dioxide, are separated from the contact gas CG via a fabric filter 48. In addition to removing hydrogen fluoride and sulfur dioxide from the exhaust gas EG, the exhaust gas treatment system 26 via the fabric filter 48 also separates at least a portion of the dust particles DP entrained in the exhaust gas EG from the internal region 36A.

[0025] Optionally, the treated gas TG exiting the exhaust gas treatment system 26 via treated gas outlet 102 is further treated in a sulfur dioxide removal unit 50. The sulfur dioxide removal unit 50 removes most of the sulfur dioxide remaining in the treated gas TG after treatment in the exhaust gas treatment system 26. The sulfur dioxide removal unit 50 can be, for example, a seawater scrubber (such as the one disclosed in US 5,484,535), a limestone wet scrubber (such as the one disclosed in EP0162536), or another such device that utilizes an alkaline absorbent to remove sulfur dioxide from the production gas.

[0026] Optionally, the treated gas TG exiting from the exhaust gas treatment system 26 or from the sulfur dioxide removal unit 50 is further treated in a carbon dioxide removal unit 52, which is operable to remove at least some carbon dioxide from the treated gas TG. The carbon dioxide removal unit 52 can be of any type suitable for removing carbon dioxide gas from production gases. An example of a suitable carbon dioxide removal device 52 is one equipped for a refrigerated ammonia process. In the refrigerated ammonia process, the treated gas TG is contacted in an absorber 54 with, for example, a solution or slurry of ammonium carbonate and / or ammonium bicarbonate at a low temperature, such as 0°C to 10°C. The solution or slurry selectively absorbs the carbon dioxide gas from the treated gas TG. Thus, the treated gas TG, which mainly contains nitrogen and oxygen, flows from the absorber 54 to be released into the atmosphere. The used ammonium carbonate and / or ammonium bicarbonate solution or slurry is conveyed from the absorber 54 to a regenerator 56, where the ammonium carbonate and / or ammonium bicarbonate solution or slurry is heated to a temperature, for example, 50°C to 150°C, resulting in the release of carbon dioxide as a concentrated gas. The regenerated ammonium carbonate and / or ammonium bicarbonate solution or slurry is then returned to absorber 54. Concentrated carbon dioxide gas flows from regenerator 56 to gas treatment unit 58, where it is compressed. The compressed concentrated carbon dioxide (CC) can be disposed of, for example, by pumping to old mines, etc. An example of this type of carbon dioxide removal device 52 is disclosed in US2008 / 0072762. It should be understood that other carbon dioxide removal devices 52 may also be used.

[0027] Although the exhaust gas treatment system 26 of the present invention is described herein as being dedicated solely to the electrolytic cell 14, the scope of this disclosure covers applications in which the use of the exhaust gas treatment system 26 of the present invention can be dedicated to more than one electrolytic cell 14. In the dedicated exhaust gas treatment system 26 arranged horizontally above the level of the electrolytic cell 14, the exhaust gas EG flows upward through a dry scrubber contact reactor 46. The dry scrubber contact reactor 46 of the present invention is arranged downstream of an alumina hopper 24, which extends horizontally across the porous bottom surface 60A of the exhaust gas treatment system 26 housing 60. As used herein, the porous bottom surface 60A generally refers to a fully porous surface or a partially porous surface depending on the needs of the exhaust gas treatment system 26. A solid base wall 60D is arranged vertically below the porous bottom surface 60A at a certain distance. The exhaust gas treatment system 26 housing 60 includes a top 60B, a porous bottom surface 60A (below which is the solid base wall 60D), and two opposing side walls 60C defining an interior opening 62. The dry scrubber contact reactor 46 is supplied with a fluidized and / or gravity flow of alumina A by an alumina hopper 24. Thus, alumina A flows from the flow control device 64 through the porous bottom surface 60A of the exhaust gas treatment system 26 to the dry scrubber contact reactor 46 equipped with an exhaust gas EG inlet 66. Within the dry scrubber contact reactor 46, alumina A is dispersed into and mixed with the exhaust gas EG, which flows into the exhaust gas treatment system 26 housing 60 via the exhaust gas EG inlet 66. The exhaust gas EG inlet 66 is arranged between a portion of the sidewall 60C and the retaining wall 66A, wherein the base end 66B abuts the free end 61 of the porous bottom surface 60A and the solid base wall 60D, and extends vertically upward from the base end 66B to the free overflow edge 66C. The retaining wall 66A is spaced at a distance from the sidewall 60C to allow the flow of exhaust gas EG between them into the dry scrubber contact reactor 46. Similarly, the dry scrubber contact reactor 46 is arranged between movable scrubberless walls 46A, which extend vertically from the free base end 46B to the opposing free top end 46C, generally parallel to the sidewall 60C. The scrubberless walls 46A are electronically movable via controller 126 and / or manually movable by adjusting arms 49 equipped with hinges 47 connected thereto. Arms 49 connected to the sidewall 60C may have hinges 47 arranged at or near the sidewall 60C. Arms 49 connected to the scrubberless walls 46A may have hinges 47 arranged at or near the scrubberless walls 46A. Additionally, arms 49 may have hinges 47 arranged between those of the sidewall 60C and the scrubberless walls 46A.An arm 49 equipped with a hinge 47 or similar movable mechanical device allows the scrubber wall 46A to be moved electronically or manually via a controller 126, either vertically (closer to or further away from the porous bottom surface 60A) and horizontally (closer to or further away from the sidewall 60C). Therefore, when the scrubber wall 46A is arranged relatively closer to the porous bottom surface 60A, the supply of alumina A to the dry scrubber contact reactor 46 decreases. When the scrubber wall 46A is arranged relatively further away from the porous bottom surface 60A, the supply of alumina A to the dry scrubber contact reactor 46 increases. When the scrubber wall 46A is arranged relatively closer to the adjacent sidewall 60C, the supply of alumina A to the dry scrubber contact reactor 46 decreases. When the scrubber wall 46A is arranged relatively further away from the adjacent sidewall 60C, the supply of alumina A to the dry scrubber contact reactor 46 increases. The supply of alumina A to the dry scrubber contact reactor 46 can be controlled or regulated by moving and positioning the scrubber wall 46A. The flow control device 64 includes a first portion 68 formed of an elongated tubular or other similar hollow structure. The first portion 68 is vertically arranged, with its top inlet end 70 fluidly connected to the primary alumina supply device 72 via an adjustable conduit 74. The opposite bottom outlet end 76 of the first portion 68 is connected to or integrally formed with a vertically arranged second portion 78. The second portion 78 defines an open interior region 80 extending from a free base edge 82 of a side 84, which tapers inward and upward to a connecting end 86. The connecting end 86 of the second portion 78 is fluidly connected to the bottom outlet end 76 of the first portion 68. Thus, alumina A flows by gravity through the flow control device 64 from the top inlet end 70 of the first portion 68 to the base opening 88 defined by the free base edge 82 of the second portion 78. Although the flow control device 64 of the present invention is described herein as having a tubular first portion 68 and a tapered second portion 78 for controlling gravity flow, the scope of this disclosure covers other shapes and / or configurations that may function as the flow control device 64 of the present invention disclosed herein. The flow control device 64 may be movable. The flow control device 64 can be moved electronically via a controller 126 and / or can be moved manually by adjusting an arm 69 having a hinge 67 connected thereto. The arm 69 connected to the sidewall 60C may be equipped with a hinge 67 at or near the sidewall 60C. The arm 69 connected to the flow control device 64 may be equipped with a hinge 67 at or near the flow control device 64. Furthermore, the arm 69 may be equipped with a hinge 67 located between the sidewall 60C and those of the flow control device 64. The arm 69 equipped with hinge 67 enables the flow control device 64 to be moved electronically or manually via controller 126, either vertically (closer to or further away from the porous bottom surface 60A) or horizontally (closer to or further away from the sidewall 60C).Therefore, when the flow control device 64 is arranged relatively closer to the porous bottom surface 60A, the supply of alumina A to the alumina hopper decreases. When the flow control device 64 is arranged relatively further away from the porous bottom surface 60A, the supply of alumina A to the alumina hopper increases. When the flow control device 64 is arranged relatively closer to the adjacent sidewall 60C, the supply of alumina A to the alumina hopper decreases. When the flow control device 64 is arranged relatively further away from the adjacent sidewall 60C, the supply of alumina A to the alumina hopper increases. By moving and positioning the flow control device 64, the supply of alumina A to the electrolytic cell 14 and the dry scrubber contact reactor 46 can be controlled or regulated.

[0028] Since the electrolytic cell 14 is supplied with alumina A by an alumina hopper 24, which also supplies alumina A to the dry scrubber contact reactor 46, the required alumina A for the electrolytic cell 14 determines or controls the rate at which alumina is supplied to the separate dedicated dry scrubber contact reactor 46. Therefore, alumina A is conveyed from the primary alumina supply device 72 to a flow control device 64 vertically arranged within the exhaust gas treatment system housing 60 for gravity supply of alumina A. The free base edge 82 of the flow control device 64 is arranged at a predetermined distance D from the porous bottom surface 60A of the exhaust gas treatment system housing 60 within the alumina A flow in the alumina hopper 24. According to one embodiment, an air supply device 120 is fluidly connected to the housing 60 to supply air G at end 63, opposite the free end 61, between the solid base wall 60D and the porous bottom surface 60A. The air supply device 120 may be a fan, blower, or similar device. Air G supplied between the solid base wall 60D and the porous bottom surface 60A flows upward through openings 122 arranged on all, part or more of the porous bottom surface 60A, thereby fluidizing a portion of the alumina A supported by the porous bottom surface 60A. Thus, a certain static amount of alumina A intentionally accumulates under the adjacent sidewall 60C of the second section 78 of the flow control device 64 and the housing 60 of the exhaust gas treatment system 26. As the static amount of alumina A accumulates within the opening region 80 of the second section 78, the gravity flow of alumina A through the first section 68 is slowed or blocked. When a certain fluidized amount of alumina A flows from the second section 78 to the alumina hopper 24, alumina A is supplied to the electrolytic cell 14 via the feed pipe 30, and a portion of the static amount of alumina A is gravity-displaced to allow the flow of alumina A from the first section 68 again, unless or until the flow is again slowed or blocked by the static amount of alumina A accumulated below the second section 78 of the flow control device 64. Alumina A is supplied to electrolytic cell 14 via the ebb and the flow of alumina A from flow control device 64, and the flow of alumina A downstream of feed pipe 30 to dry scrubber contact reactor 46 is controlled to reach electrolytic cell 14. For an additional, possibly "on-demand" type of intermittent booster, air supply device 120 may be connected to one or more air booster devices 124. According to one embodiment, air booster device 124 may be arranged at the side wall 60C below flow control device 64. Air booster device 124 below flow control device 64 may be used intermittently to locally increase the air supply to intermittently change or increase the fluidization conditions below the second section 78 of flow control device 64. According to another embodiment, air booster device 124 may be arranged above the porous bottom surface 60A at retaining wall 66A.The air booster 124 can be used intermittently at the retaining wall 66A to locally increase the air supply G, thereby intermittently altering or increasing the supply of alumina A to the dry scrubber contact reactor 46.

[0029] The fabric filter 48 of the present invention is arranged in the upper portion 92 of the exhaust gas treatment system 26 housing 60, horizontally above the flow control device 64, the alumina hopper 24, and the dry scrubber contact reactor 46. The fabric filter 48 includes a support wall 90 arranged within the upper portion 92 of the exhaust gas treatment system 26, through which the housing 60 fluidly separates a "post-filter" region 94 on one side of the support wall 90 from a "pre-filter" region 96 on the opposite side of the support wall 90. A plurality of openings 98 extend through the thickness T of the support wall 90, each opening 98 being equipped with a replaceable fabric filter bag 100 extending from the opening 98 into the pre-filter region 96. Arranged within the post-filter region 94 is a treated gas outlet 102 through which the treated gas TG flows outward from the post-filter region 94 of the exhaust gas treatment system 26 housing 60 to optional additional treatment devices 50, 52 or the atmosphere.

[0030] exist Figure 1 In the middle, the lower part 78 of the flow control device 64 is arranged adjacent to the side wall 60C of the housing 60, and the fabric filter 48 is arranged vertically, that is, the fabric filter bag 100 extends vertically. Figure 2 Another embodiment is schematically shown, in which the lower portion 78 of the flow control device 64 has a simplified side 84 to allow for a closer proximity arrangement to the sidewall 60C of the housing 60, and the fabric filter 48 is arranged horizontally, i.e., the fabric filter bag 100 extends horizontally. Furthermore, the flow control device 64 (e.g., with its arrangement adjacent to the sidewall 60C of the housing 60) Figure 1 (as shown) and horizontally arranged fabric filters 48 (as shown) Figure 2 The implementation scheme shown, or the flow control device 64 in a simplified configuration (as shown) Figure 2 (as shown) and vertically arranged fabric filters 48 (as shown) Figure 1 (as shown) is also considered to be within the scope of this disclosure.

[0031] The method of using the exhaust gas treatment system 26 of the present invention includes arranging the exhaust gas treatment system 26 of the present invention horizontally above the level of the aluminum production electrolytic cell 14, and fluidly connecting the exhaust gas treatment system 26 of the present invention to the electrolytic cell 14 via a feed pipe 30 and an exhaust gas outlet 104. Thus, the feed pipe 30 is connected to an alumina hopper 24, and the exhaust gas outlet 104 is connected to an exhaust gas EG inlet 66 of a dry scrubber contact reactor 46. Alumina A is supplied to the exhaust gas treatment system 26 via a flow control device 64, wherein the flow control device 64 supplies alumina A to the electrolytic cell 14 and the dry scrubber contact reactor 46 at a rate based on the needs of the electrolytic cell 14. The alumina A supplied to the dry scrubber contact reactor 46 interacts with the exhaust gas EG in the dry scrubber contact reactor 26 to remove contaminants from the exhaust gas EG, thereby producing a contact gas CG entrained with particulate adsorption products PP. The method further includes removing the particulate adsorption products PP from the contact gas CG in a associated fabric filter 48 to produce treated gas TG.

[0032] A method of supplying alumina A using the flow control device 64 of the present invention includes: providing a vertically arranged flow control device 64 within the housing 60 of the exhaust gas treatment system 26, the flow control device 64 including a vertically arranged elongated first portion 68 and a vertically arranged second portion 78 and arranged at a predetermined distance D above a horizontally porous bottom surface 60A of the housing 60 of the exhaust gas treatment system 26; supplying alumina A from a primary alumina supply device 72 to the flow control device 64 to gravity supply alumina A to an alumina hopper 24 to supply alumina A to an electrolytic cell 14 and a dry scrubber contact reactor 46; and controlling the rate of supplying alumina A to the dry scrubber contact reactor 46 based on the demand for alumina A in the electrolytic cell 14.

[0033] The beneficial effect of the device 10 of the present invention is that the control of the alumina A and fluoride balance is specific to the electrolytic cell 14. Therefore, if the electrolytic cell 14 produces more hydrogen fluoride gas for some reason, the hydrogen fluoride sensor 33 electronically transmits the measured value of hydrogen fluoride to the controller 126, and through electronic control by the controller 126, the feeder 28 will supply more alumina A to the electrolytic cell 14 to adsorb more fluoride, thereby reducing the amount of fluoride lost from the electrolytic cell 14. Furthermore, when the feeder 28 is actuated, the shell breaker 34 is first operated inside the bath 20 to open an orifice through which alumina A is supplied to the contents 18 of the bath 20. This operation produces a significant amount of hydrogen fluoride gas. Therefore, during operation, the feeder 28 will supply more alumina A to the electrolytic cell 14. The additional alumina A supplied to the electrolytic cell 14 adsorbs more fluoride, thus reducing the amount of fluoride lost from the electrolytic cell 14 during operation. Preferably, the hydrogen fluoride sensor 33 is arranged on or relatively close to the exhaust gas EG outlet 102 for the controller 126 to control the feeder 28 to supply alumina A to the electrolytic cell 14. Alternatively, one or more hydrogen fluoride sensors 33 may be arranged in various other locations within the aluminum production equipment 10, such as, but not limited to, adjacent feeders 28 and / or adjacent exhaust gas outlets 104. Similar to the hydrogen fluoride sensor 33, other sensors 33 may also be arranged in the equipment 10, such as sulfur dioxide sensors, carbon dioxide sensors, perfluorinated compound sensors, and / or similar pollutant sensors, for emission control.

[0034] In summary, the exhaust gas treatment system 26 of the present invention includes: a separate, dedicated exhaust gas treatment system 26 arranged vertically above a separate aluminum electrolysis cell 14; a housing 60 defining an internal region 62 of the separate exhaust gas treatment system 26; a flow control device 64 vertically arranged within the internal region 62, the flow control device including an elongated hollow first portion 68 and a tapered second portion 78 and arranged at a predetermined distance D from the horizontal porous bottom surface 60A of the housing 60; and an adsorbent hopper 24, the adsorbent hopper being used in the flow control... A horizontally porous bottom surface 60A extends across the housing 60 between the device 64 and the dry scrubber contact reactor 46; a feed pipe 30, fluidly connected between the adsorbent hopper 24 and the separate aluminum electrolysis cell 14, for supplying adsorbent to the separate aluminum electrolysis cell 14; and an exhaust gas outlet 104 in the housing 36 for the separate electrolysis cell 14, fluidly connected to the exhaust gas EG inlet 66 of the dry scrubber contact reactor 46, for reacting the exhaust gas EG with the adsorbent supplied from the adsorbent hopper 24 to produce contact gas CG. The exhaust gas treatment system 26 of the present invention also includes an air pressurization device 124 to alter or promote adsorbent fluidization within the system 26. The exhaust gas treatment system 26 of the present invention also includes a fabric filter 48 operable to remove particulate adsorption products PP and dust DP from the contact gas CG. The fabric filter 48 includes a plurality of removable fabric filter bags 100 arranged within the housing 60 at a horizontal position vertically above the flow control device 64, the adsorbent hopper 24, and the dry scrubber contact reactor 46. The flow control device and / or a portion of the dry scrubber contact reactor are movable to influence adsorbent fluidization and / or flow, and the flow control device 64 of the exhaust gas treatment system 26 controls the adsorbent supply rate to the dry scrubber contact reactor 46 based on the adsorbent rate required by the electrolyzer 14.

[0035] In summary, the flow control device 64 of the present invention includes: a vertically arranged elongated hollow first portion 68; a vertically arranged second portion 78 defining an open interior region 80, the second portion 78 including a tapering wall 84 extending between a base edge 82 and a connecting top 86, wherein the connecting top 86 is fluidly connected to the bottom open end 76 of the first portion 68; an adsorbent supply device 72 fluidly connected to the open top 70 of the first portion 68; and a portion of an adsorbent hopper 24 arranged at a predetermined distance D vertically below the flow control device 64, wherein the flow control device 64 is mechanically operable to control the rate of adsorbent supply to the dry scrubber contact reactor 46 based on the adsorbent rate requirement of the aluminum electrolysis cell 14. The base edge 82 of the second portion 78 of the flow control device 64 of the present invention is arranged vertically below the top surface S of the adsorbent in the adsorbent hopper 24. Furthermore, the first portion 68 of the flow control device 64 of the present invention is a tubular or similar hollow structure. The size of the base edge 82 of the second part 78 of the flow control device 64 of the present invention is larger than the size of the connecting top 86 of the second part 78.

[0036] In summary, the method of using the flow control device 64 of the present invention includes: arranging the flow control device 64, which includes a vertically arranged elongated hollow first portion 68; a vertically arranged second portion 78 defining an internal region 80 of an opening, the second portion 78 including a tapering wall 84 extending between an opening free base edge 82 and a connecting top 86, wherein the connecting top 86 is fluidly connected to a bottom outlet end 76 of the first portion 68; an adsorbent supply device 72 fluidly connected to an opening top inlet end 70 of the first portion 68; and a portion of an adsorbent hopper 24 arranged at a predetermined distance D vertically below the flow control device 64; and operating the flow control device 64 to control the rate at which adsorbent is supplied to the dry scrubber contact reactor 46 based on the adsorbent rate requirement of the aluminum electrolysis cell 14. According to the method of the present invention, the adsorbent flows by gravity through the flow control device 64 from the opening top inlet end 70 of the first portion 68 to the opening free base edge 82 of the second portion 78. The adsorbent is alumina A. The method of the present invention further includes increasing the rate at which the adsorbent is supplied to the dry scrubber contact reactor 46 via the air pressurization device 124. The method of the present invention also includes reducing the rate at which the adsorbent is supplied to the dry scrubber contact reactor 46 by static adsorbent accumulation in the internal region 80 of the opening defined by the second portion 78. The method further includes reducing the rate of the adsorbent flow supplied to the dry scrubber contact reactor 46 via the flow control device 64 by static adsorbent accumulation in the internal region 80 of the opening defined by the second portion 78 and static adsorbent accumulation below the second portion 78. According to the method of the present invention, the dimension of the free base edge 82 of the opening of the second portion 78 is larger than the dimension of the connecting top 86 of the second portion 78. Additionally, according to the method of the present invention, the connecting top 86 of the second portion 78 has dimensions and construction similar to those of the bottom outlet end 76 of the first portion 68.

[0037] Although this disclosure has been described with reference to several embodiments, those skilled in the art will understand that various changes can be made and elements can be substituted with equivalents without departing from the scope of the invention. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the basic scope of this disclosure. Therefore, this disclosure is not intended to be limited to the specific embodiments disclosed as the best mode for carrying out the present disclosure, but rather to include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms "first," "second," etc., does not indicate any order or importance, but rather the terms "first," "second," etc., are used to distinguish one element from another.

Claims

1. An exhaust gas treatment system (26) for at least one aluminum electrolysis cell (14), comprising: A dedicated exhaust gas treatment system (26) is provided, which is dedicated to the aluminum electrolysis cell (14) and is arranged horizontally above the aluminum electrolysis cell (14) at a height of 100 mm. The housing (60) has at least a partially porous bottom (60A) and defines an internal region (62) of the dedicated exhaust gas treatment system (26). A flow control device (64) is vertically arranged within the internal region (62), the flow control device comprising an elongated hollow first portion (68) and a tapered second portion (78), the flow control device (64) being arranged at a predetermined distance (D) from the at least part of the porous bottom (60A) of the housing (60); Adsorbent hopper (24) extends across at least part of the porous bottom (60A) of the housing (60) between the flow control device (64) and the dry scrubber contact reactor (46); A feed pipe (30), fluidly connected between the adsorbent hopper (24) and the aluminum electrolysis cell (14), is used to supply adsorbent (A) to the aluminum electrolysis cell (14); and An exhaust gas outlet (104) is located in the outer shell (36) of the aluminum electrolysis cell (14), which is fluidly connected to the dry scrubber contact reactor (46) for interacting the exhaust gas (EG) with the adsorbent (A) supplied from the adsorbent hopper (24) to generate contact gas (CG).

2. The exhaust gas treatment system (26) according to claim 1 further includes a pressurization device (124) to alter or promote the fluidization of the adsorbent (A) within the exhaust gas treatment system (26).

3. The exhaust gas treatment system (26) according to claim 1 further includes a fabric filter (48) comprising a plurality of removable fabric filter bags (100) arranged within the housing (60) at a horizontal position vertically above the flow control device (64), the adsorbent hopper (24) and the dry scrubber contact reactor (46).

4. The exhaust gas treatment system (26) according to claim 1, wherein the flow control device (64) and / or a portion of the dry scrubber contact reactor (46) are movable to influence the supply rate of the adsorbent (A).

5. The exhaust gas treatment system (26) according to any one of claims 1 to 4, wherein the flow control device (64) comprises: A vertically arranged slender hollow first part (68) has an open bottom end (76) and an open top end (70). A vertically arranged second portion (78) defining the interior region (80) of the opening, the second portion (78) including a tapered wall (84) extending between a base edge (82) and a connecting top (86), wherein the connecting top (86) is fluidly connected to the bottom end (76) of the opening of the first portion (68). Adsorbent supply device (72), which is fluidly connected to the top opening (70) of the first portion (68); and A portion of the adsorbent hopper (24) is arranged at a predetermined distance (D) vertically below the flow control device (64); The flow control device (64) is mechanically operable to control the supply rate of adsorbent (A) to the dry scrubber contact reactor (46) based on the rate at which the aluminum electrolysis cell (14) requires adsorbent (A).

6. The exhaust gas treatment system (26) according to claim 5, wherein the base edge (82) of the second part (78) is arranged vertically below the top surface (S) of the adsorbent (A) in the adsorbent hopper (24).

7. The exhaust gas treatment system (26) according to claim 5, wherein the first portion (68) is tubular.

8. The exhaust gas treatment system (26) according to claim 5, wherein the size of the base edge (82) of the second part (78) is greater than the size of the connecting top (86) of the second part (78).

9. A method for treating exhaust gases from at least one aluminum electrolysis cell using the exhaust gas treatment system (26) of claim 5, the method comprising: Adsorbent (A) is supplied from the adsorbent supply device (72) to the adsorbent hopper (24) via the flow control device (64). Adsorbent (A) is fed from the adsorbent hopper (24) across the at least part of the porous bottom (60A) of the outer shell (60) into the dry scrubber contact reactor (46). The adsorbent (A) is fed from the adsorbent hopper (24) through the feed pipe (30) into the aluminum electrolysis cell (14). Exhaust gas (EG) flows from the aluminum electrolysis cell (14) through exhaust gas inlet (66) to the dry scrubber contact reactor (46) for reacting the exhaust gas (EG) with adsorbent (A) fed from the adsorbent hopper (24); and The flow control device (64) is operated to control the supply rate of adsorbent (A) to the dry scrubber contact reactor (46) based on the rate at which the aluminum electrolysis cell (14) requires adsorbent (A).

10. The method according to claim 9, wherein the adsorbent (A) flows by gravity through the flow control device (64) from the top opening (70) of the first portion (68) to the base edge (82) of the second portion (78).

11. The method according to claim 9, further comprising increasing the supply rate of adsorbent (A) to the dry scrubber contact reactor (46) by means of a pressurizing device (124).

12. The method of claim 11, further comprising reducing the rate of supplying adsorbent (A) to the dry scrubber contact reactor (46) by accumulating static adsorbent (A) in the interior region (80) of the opening defined by the second portion (78).

13. The method of claim 11, further comprising reducing the rate of the adsorbent (A) flow supplied to the dry scrubber contact reactor (46) by the flow control device (64) by the accumulation of static adsorbent (A) in the interior region (80) of the opening defined by the second portion (78) and the accumulation of static adsorbent (A) below the second portion (78).

14. The method according to claim 9, wherein the size of the base edge (82) of the second portion (78) is greater than the size of the connecting top (86) of the second portion (78).

15. The method of claim 9, wherein the connecting top (86) of the second portion (78) has a similar size and construction to the opening bottom (76) of the first portion (68).

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