Gas purification module in aluminum electrolysis process and purification method thereof

Abstract

The gas purification module is used for collecting and purifying gas generated by an aluminum production electrolytic cell and comprises at least two adsorption reactors (1) which are connected with a bag filter (2) through a transition pipeline (3), and the bag filter is composed of a dust-containing gas chamber (4), a gas purification chamber (5), a filter bag (6) and a fluorinated alumina stock bin (7). The module includes two adsorbent supply lines. The first adsorbent supply line is used for conveying pure aluminum oxide to the adsorption reactor (1) and the pneumatic lifting device (9), so that the pure aluminum oxide is sprayed on the filter bag (6). The second adsorbent feed line is configured to convey the fluorinated alumina into the adsorption reactor and the electrolysis cell through an airlift device (11). The device has the technical effect that the purification efficiency of fluorine-containing gas in a single electrolytic cell adopting different electrolysis processes is improved.

Description

Technical Field

[0001] This invention relates to the production of aluminum by molten salt electrolytic reduction and the purification of waste gas generated during the aluminum electrolytic reduction process, and particularly to a gas purification device that can be used for dry adsorption purification of waste gas from aluminum electrolytic cells. Background Technology

[0002] Methods and apparatuses for dry gas purification have been developed and widely applied for aluminum production, including cyclone separators, dust collectors, ash collectors and various types of electrostatic precipitators. These apparatuses utilize gravity, centrifugal force and electrostatic force to purify dust and other substances in the gas and then discharge them.

[0003] Known gas purification methods and apparatus have the following main drawbacks: they cannot remove hydrogen fluoride (HF) compounds; they cannot connect multiple electrolyzers in a centralized gas purification unit (GTU) for waste gas treatment; the performance of the recovered adsorbent is averaged out; and they have high capital expenditures (CAPEX).

[0004] A combined dust collection device (patent RU 2288782, publication date December 10, 2006) is known, which includes a horizontal electrostatic precipitator followed by a vertical tubular electrostatic precipitator. The effective volume ratio of the vertical to horizontal electrostatic precipitators is 0.1-0.9. The horizontal and vertical tubular electrostatic precipitators are housed within the same casing. The electrodes in the vertical tubular electrostatic precipitator are mechanically cleaned when airflow to that section is stopped. The sections of the tubular electrostatic precipitator are cleaned periodically by liquid flushing when airflow is interrupted.

[0005] The drawbacks of known technologies are increased structural size and the inability to connect filters to a single electrolytic cell for better purification regulation.

[0006] An electrolytic waste gas purification module (patent RU 2668926, publication date October 4, 2018) is known, comprising a bag filter and a reactor, wherein gas purification is performed by dry adsorption, and the adsorbent material is returned to production for use through at least one gas purification device. The gas purification device includes at least one reactor, which is a Venturi tube structure designed to achieve uniform airflow velocity distribution, and includes at least one self-supporting bag filter; the inlet pipe of the reactor is located on the opposite side of the outlet pipe of the corresponding filter.

[0007] A two-stage gas purification device for electrolytic gas purification is also known (RU 2749421, published June 9, 2021), which includes at least one reactor with a Venturi tube structure to achieve uniform airflow velocity. The reactor is connected to at least one bag filter via a connecting pipe. It also includes a chute for supplying adsorbent to the reactor, a dust-laden gas chamber and a clean gas chamber, filter bags, and a hopper. The device is characterized in that the dust-laden gas chamber and the clean gas chamber of the bag filter are divided into at least two partitions by a partition, and at least one partition can be closed. The gas purification device also includes an adsorbent spraying system with a clean air inlet pipe, designed to allow the adsorbent to be sprayed onto the filter bags via an additional chute. The connection point between the spraying system and the bag filter is located between the reactor and the filter. The hopper is divided into at least two partitions and equipped with an adsorbent discharge pipe.

[0008] The aforementioned chute is used for short-distance material conveying. The chute is an open or closed channel, typically with a circular or rectangular cross-section, installed at an incline to allow for gravity flow of materials. If a vibrator is used to vibrate the chute, its angle of inclination can be significantly reduced.

[0009] The common drawback of the known schemes is that multiple electrolytic cells are connected to a dry gas purification unit (DGTU). The system provides unified control over the gas purification process to ensure that the amount of adsorbent meets the needs of aluminum production. However, the performance parameters of the recovered adsorbent are average values, and the raw materials required for each electrolytic cell are not prepared individually.

[0010] Each electrolytic cell in the electrolysis workshop has its own independent production targets. The individuality of the targets depends on the amount of waste gas emitted from the electrolytic cell, the volume of pure alumina / circulated alumina directly added to the electrolytic cell, the voltage drop on the anode device, and the heat loss of the electrolytic cell.

[0011] When using a common gas purification unit, it is necessary to maintain the temperatures of both pure alumina and fluorinated alumina at a high level. Downstream of the gas purification unit, fluorinated alumina is returned to the electrolytic cell via a centralized alumina distribution system, typically arriving in the melt several hours later, by which time it has cooled. This process results in heat loss and a decrease in current in each electrolytic cell.

[0012] Because the cryolite ratio in the electrolytic cell melt is dependent on specific conditions, the fluorine content must be scientifically controlled to maintain its balance. Centralized gas purification in the electrolysis workshop has a time delay, only reflecting the average fluorine content. Due to the long cycle of feeding fluorinated alumina from the bag filter into the electrolytic cell, the required fluorine concentration when adding the adsorbent to the electrolytic cell melt often does not match the actual concentration. Therefore, it is necessary to solve the problem of the excessively long transportation distance of fluorinated alumina from the filter to the electrolytic cell.

[0013] To achieve the maximum production capacity of each electrolytic cell, it is necessary to equip each electrolytic cell with an independent gas purification device (or part thereof), including waste gas emission, gas purification, alumina storage, and alumina supply module to the electrolytic cell.

[0014] The closest prior art (prototype) to this invention is a process gas collection and pre-purification method for process gases generated in an electrolyzer (AU2020242088A1, published on October 28, 2021), which includes a pre-purification unit.

[0015] The prototype shares several features with this invention. The prototype includes a module immediately following the collection of waste gas from the electrolytic cell and a process gas pre-purification module. In one embodiment, an alumina fluidized bed reactor and a filtration module are used, the filtration module being connected to the pre-purification unit for reintroducing fluorinated alumina into the adsorption process. The prototype includes a pneumatic conveying system for transporting alumina to the gas purification module. The prototype device can be connected to at least one electrolytic cell. An exhaust system (fan or induced draft fan) is used. The prototype is equipped with a module for returning a portion of the fluorinated alumina and spraying it back into the electrolytic cell. The prototype aims to reduce the cost of the electrolysis process by configuring a separate purification device for each electrolytic cell. Furthermore, there is no system for centrally distributing alumina from a silo. The proposed concept and process flow also explicitly require the use of two reactors, with a filtration device downstream for deep gas purification. The prototype indicates that the amounts of pure alumina (PA) added to the reactor and the fluorinated alumina (FA) transported to the electrolytic cell can be adjusted.

[0016] To improve the efficiency of hydrogen fluoride (HF) removal, a second reactor is recommended in the prototype. Alternatively, a scrubber with a fluidized bed can be used, as described in the prototype. The entire process achieves thorough mixing of the exhaust gas with the fluorinated alumina.

[0017] The prototype operation described the possibility of installing the various components directly near the electrolyzer. It was suggested that the modules and components be arranged at a certain distance. That is, the prototype did not present a complete, integrated gas purification system, nor did it propose an overall solution.

[0018] The prototype's shortcoming lies in its application of only a single possible solution for electrolytic gas purification, failing to adapt the purification operation to other electrolytic reduction processes (such as prebaked anodes). Therefore, it lacks flexibility in improving the purification efficiency of fluorine-containing gases when electrolytic cell operating parameters may change. This is precisely the difference between this invention and the prototype in terms of objectives and achieved results.

[0019] The prototype is equipped with an electrolytic gas pre-purification unit, which is connected to a main filter, serving as the primary gas purification system. The prototype also envisions using a reactor or similar fluidized bed adsorption device within the electrolytic cell gas pre-purification module. Subsequently, the dust-laden gas mixture flows to a second-stage purification filter for dust separation, and some of the fluorinated alumina is returned to the first-stage purification unit for reuse. In summary, the device has a distributed layout on-site. Summary of the Invention

[0020] The technical problem solved and the effect achieved by this invention are: improving the purification efficiency of fluorine-containing gases from a single electrolytic cell and adapting to various electrolytic reduction processes occurring in aluminum electrolysis production, i.e., flexibility. It eliminates the need for additional process equipment to purify dust-laden gas mixtures, thereby reducing capital expenditure (CAPEX) compared to known equivalents.

[0021] The overall size of a gas purification module typically does not exceed that of a 20-foot shipping container. The "module" concept comprises the entire gas purification unit manufactured for a single electrolytic cell, allowing for relocation within an industrial site. The module utilizes essential equipment items, particularly bag filters, adsorption reactors, alumina conveying units, and fans. This approach minimizes capital expenditure during the retrofitting of aluminum production electrolytic plants.

[0022] The proposed problem is addressed by designing features and selecting the most suitable operating mode for the gas purification unit for a specific electrolytic reduction process, while taking into account the individual requirements and operating modes of each electrolyzer. This avoids the averaging of the circulating adsorbent parameters and performance of the electrolyzers connected to a centralized gas purification unit. Attached Figure Description

[0023] The content of this invention is illustrated with reference to the accompanying drawings.

[0024] Figure 1 This is a schematic diagram of the gas flow purification principle. Figure 2 The appearance of the gas purification module is shown; Figure 3 This is a schematic diagram of the gas passing through the gas purification module; Figures 4 to 8 The following are flow charts for gas purification under five process modes: 1 – Adsorption reactor; 2 – Bag filter; 3 – Transition pipe; 4 – Dust-laden gas chamber; 5 – Clean air chamber; 6 – Filter bags; 7 – Fluorinated alumina hopper for the filter; 8 – Horizontal partitions; 9 – Pneumatic lifting device for pure alumina; 10 – Fluorinated alumina silo; 11 – Pneumatic lifting device for fluorinated alumina; 12 – Pure alumina silo; 13.1, 13.2 – Purification Unit; 14.1, 14.2, 14.3 – Conveying devices; 15.1, 15.2, 15.3 – Dispensing boxes; 16 – Pure alumina inclined groove; 17 – Fluorinated alumina gas tank (for recirculation); 18 – Gas ring; 19 – Distributor; 20 – Heating element; 21 – Fan; 22 – Electrolytic cell.

[0025] The arrows in the attached diagram define the following flow directions: the direction of gas entering the inlet pipe, the direction of adsorbent (pure alumina and fluorinated alumina) addition, the flow direction of the dust-laden gas mixture, the flow direction of the purified gas, and the return direction of the alumina already used for purification. Detailed Implementation

[0026] The following provides examples of device structures in conjunction with the accompanying drawings to help those skilled in the art understand how the present invention is implemented.

[0027] The unit includes at least two identical adsorption reactors (1) which are rigidly connected to a bag filter (2) via a transition pipe (3) which is a tapered transition from the circular cross section of the adsorption reactor (1) to the rectangular cross section of the bag filter (2).

[0028] The bag filter (2) includes a dust-laden gas chamber (4), a clean gas chamber (5), a filter bag (6), and a fluorinated alumina hopper (7) for the filter. The dust-laden gas chamber of the gas purification module is divided into at least two zones by a transverse partition (8).

[0029] At least one pneumatic lifting device (9) for pure alumina (PA) is installed below the filter bag.

[0030] Used adsorbent (fluorinated alumina) is stored in an alumina (FA) silo (10). The silo is rigidly connected to a bag filter (2) via a pneumatic chute. The alumina silo (10) is equipped with a discharge pipe connected to an alumina (FA) pneumatic lifting device (11).

[0031] The silo (12) for pure alumina (PA) is integrated into the structure of the bag filter (2). The unit (12) has at least one discharge pipe, through which it is connected to the purification units (13.1, 13.2). Subsequently, the purification units (13.1, 13.2) are connected to the feeding devices (14.1, 14.2, 14.3) and the distribution boxes (15.1, 15.2, 15.3) via gas chute lines. One distribution box (15.1) is connected to the pure alumina (PA) pneumatic lifting device (9) via a pure alumina (PA) chute (16). The second distribution box (15.2) is connected to the gas ring (18) provided on the adsorption reactor (1) via a gas chute (17) for recirculation of fluorinated alumina (FA) and is connected to the chute.

[0032] A gas distributor is installed at the bottom of the bag filter (2), which is securely connected to the third distribution box (15.3) via a distributor (19).

[0033] The working principle of the gas purification module is as follows.

[0034] The gas purification module for electrolyzers employing electrolytic reduction technology (such as prebaked anodes) performs two-stage purification of the gas stream: an adsorption reactor (1) and a partitioned bag filter (2). In the first stage, fluorine compounds are adsorbed by mixing dust-laden gas with an adsorbent, while in the second stage, further purification is carried out and the purified gas is separated from the dust.

[0035] The gas stream generated by the electrolytic cell enters the feedstock fluorination unit through at least two identical adsorption reactors (1), which distribute the suitable gas stream evenly. The adsorption reactors are constructed in the form of Venturi tubes, which mix the dust-laden gas with the adsorbent (alumina) through the turbulence of the rising gas flow and ensure a uniform flow rate of the incoming dust-laden gas mixture. The reactor body is a conical tube with at least two inclined troughs for inputting fresh and / or fluorinated alumina, evenly distributed around the circumference and rising a certain distance above the small-diameter flange.

[0036] The dust-laden gas mixture then passes through a transition pipe (3), which reduces the velocity of the dust-laden gas flow and evenly distributes the volume of alumina particles and gas discharged from the reactor before entering the dust-laden gas chamber (4) and passing through a filter bag. The transition pipe (3) is inserted into the dust-laden gas chamber with a rectangular cross-section. The purified gas is collected in the clean gas chamber (5) and sent to the chimney.

[0037] The dust-laden gas chamber (4) is typically a parallelepiped structure, occupying most of the volume of the bag filter (2). Two rectangular flanges are located at the bottom of the chamber, which are connected to the adsorption reactor via transition pipes.

[0038] The clean air chamber (5) collects all gas flows from the two zones and discharges them through a common gas channel via a fan (21) directly mounted on the gas purification module, leading to the ventilation skylight of the electrolytic cell housing. The chamber is equipped with a pulse backflushing system consisting of air supply pipes leading to each filter bag.

[0039] The transition pipe (3), the dust-laden gas chamber (4), and the clean gas chamber (5) are structural components of the bag filter (2).

[0040] The bag filter (2) includes a pure alumina (PA) hopper (12). It shares a sidewall with the filter and is a vertical rectangular box with the same height and width as the filter. To prevent agglomeration and to transport the alumina to the downstream pipeline, at least one gas distributor with an outlet (chute) is installed at the bottom of the hopper. The chute distributes the adsorbent into two gas channels. The first gas channel is the main channel, ensuring the delivery of alumina to the adsorption reactor (1). The second gas channel is used to feed two pure alumina pneumatic lifting devices (9), which spray alumina onto the filter bags.

[0041] The gas duct (17) is an alumina conveying unit that can be installed at an angle within a horizontal range (0 to 3°). It is a profile pipe with a gas distributor at its bottom. The gas distributor is connected to the working section of the gas duct (17) via a flange. A breathable fabric is installed between these components, allowing air to pass through while intercepting adsorbents on the surface. Air is blown into the lower part of the gas distributor to ensure that the alumina can be smoothly conveyed through the breathable fabric.

[0042] The gas purification module uses two alumina supply lines: the first is a pure alumina supply line, and the second is a fluorinated alumina supply line.

[0043] The first feeding line (pure alumina feeding line) Pure alumina is supplied to the adsorption reactor (1). This line includes the following units: a purification unit (13.2), a feed device (14.1), a distribution box (15.2), a pure alumina (PA) chute (16), a fluorinated alumina (FA) gas chute (17) for recirculation, and a gas ring (18). The purification unit (13.2) is connected to the lower flange via the chute (which is a vertical conical transition pipe).

[0044] In this embodiment, the purification unit (13.2) is a vertical profile pipe, with pure alumina entering from the top of the inclined trough. Continuous airflow is applied to the breathable fabric at the bottom, promoting the formation of a bubbling layer. Alumina containing some impurities fills the entire space after entering the purification unit, forming a pseudo-fluidized layer. All heavier, finer impurities settle at the bottom, thus completing the purification of the alumina. As the liquid level gradually rises, the purified adsorbent enters the feeding device (14.1) through a pipe located at the top of the purification unit. An inspection hole is provided on one side of the profile pipe for unobstructed access and maintenance of the internal components.

[0045] For example, the feeding device (14.1) can be technically implemented as a roller feeder with an adjustable variable cross-section air trough at the bottom of its structure. This device has no continuously rotating parts, thus avoiding jamming and wear. The variable cross-section adjustment mechanism is a steel strip bent to a semi-circle along its length with a certain diameter, completely covering the working cross-section of the air trough. This component is mounted on a shaft and can rotate about its own axis. The steel strip has a tapered slit opening. Alumina flows through this opening through a breathable fabric. The adsorbent supply is adjusted by a reducer installed outside the air trough and connected to the steel strip shaft. For easy adjustment, a handwheel is provided; rotating the handwheel changes the internal opening angle, and an angle indicator displays the opening degree. The greater the angle of the steel strip deviating from its initial position, the larger the slit opening opens, thus supplying more alumina.

[0046] The adsorbent is fed through a feeding device and then transported to the distribution box (15.2) via an air trough. The distribution box is a rectangular silo structure with a discharge port. An air supply interface is installed at its lower part, while a dust suction interface and a pure alumina feed chute (16) are installed at its upper part. A sensor (vibration fork) is screwed into the upper part of the pure alumina feed chute in the alumina box to monitor the adsorbent loading level in the distribution box (15.2). A breathable fabric is stretched on the bottom cross section of the distribution box (15.2) so that the continuously supplied air and alumina can form a pseudo-fluidized layer. The discharge port on the wall of the distribution box (15.2) can distribute the adsorbent evenly to all parts of the system through the overflow effect. When the alumina is evenly distributed in the gas distributor and reaches the height of the chute, it will be transported in equal volume through two chutes, and then enter the adsorption reactors of the first and second sections via the air trough (17) and the air ring (18).

[0047] To ensure uniform mixing and distribution of the adsorbent in the reactor's inclined channels, a gas ring (18) is employed. The gas ring has a standard gas channel cross-section and is an overall ring structure. A longitudinal partition wall is provided inside the working cross-section of the gas ring (18). This partition wall divides the working cross-section of the gas ring in two and maintains a certain distance from the bottom of the gas distributor. This distance is determined based on parameters such as the material's flowability (bulkness) and density. This distance is selected experimentally to ensure that the material can flow unimpeded from one half of the working cross-section of the gas ring to the other. Alumina is fed from the upper inner side of the gas ring. Discharge is achieved through at least two side inclined channels located above the partition wall. This ensures uniform distribution of alumina at the bottom of the gas ring and thorough mixing of pure alumina and fluorinated alumina, while simultaneously achieving uniform distribution to each inclined channel. The inclined channels are circumferentially arranged pipe structures. Each pipe enters the reactor at a certain angle.

[0048] The second feeding line (fluorinated alumina feeding line) It is responsible for conveying fluorinated (recycled) alumina to the adsorption reactor (1), and consists of a distributor (19), a feeder (14), a distribution box (15.3), and a fluorinated alumina (FA) gas tank (17) for recycling.

[0049] The distributor (19) combines the discharges from the two-section bag filters into a single chute and is used to change the alumina flow direction from vertical (falling) to horizontal. Structurally, it consists of two chutes connected to a three-way body, which is a vertical pipe with a gas distributor. An air inlet pipe is provided at the bottom of the gas distributor. A lateral discharge port is provided at a certain distance above the breathable fabric and connected to the feeding device (14.3). The distance from the breathable fabric to the discharge port depends on the air inlet pressure. To achieve an overflow effect, the height of the alumina bubble layer must be maintained, and the discharge port is provided at this height. For easy maintenance of the internal unloading components, an inspection hole is provided on the side wall. After the alumina fills the space at the bottom of the gas distributor, it forms a bubble layer and flows into the discharge pipe in an overflow manner. It then enters the feeding device (14.3).

[0050] The feeding device (14.3) and the distribution box (15.3) have similar structures to those of the feeding device and distribution box of the first line.

[0051] In the bag filter (2), the fluorinated alumina hopper (bottom) (7) overflows and discharges from each section via chute. As the fluorinated alumina (shaken from the filter bag) gradually accumulates in the filter hopper, the adsorbent is distributed to the circulation air ring (18) and conveyed through at least one chute to a container called the fluorinated alumina hopper. The fluorinated alumina air trough for circulation participates in the adsorbent conveying and its structure is no different from the aforementioned air trough. This component is located below the bag filter and is connected to it via chute connecting the bottom of each section. The chute has a two-truncated cone structure. An inspection hole is provided in the upper center of the air trough for easy internal maintenance. The conveying of alumina on the breathable fabric can be checked through this inspection hole. The adsorbent then flows into the fluorinated alumina hopper (10).

[0052] The fluorinated alumina (FA) silo (10) is a container within the module that stores a portion of the adsorbent. It is a horizontal box, and its structure is entirely dependent on the space constraints of adjacent equipment and the daily fluorinated alumina production capacity required. To prevent clumping and ensure uniform material supply, the fluorinated alumina silo is equipped with a gas distributor. The gas distributor has an outlet at its end leading to the fluorinated alumina (FA) pneumatic lifting device (11). An exhaust vent may be provided on one wall of the fluorinated alumina silo (10). An inspection hole is also provided on the side wall. The tension of the breathable fabric can be checked through the inspection hole, and the outlet plate of the pneumatic lifting device can be accessed when necessary.

[0053] The alumina fluoride pneumatic lifting device (11) is used to vertically lift and transport waste materials to the electrolytic cell (22). The alumina fluoride pneumatic lifting device (11) has a vertical pipe structure. A gas distributor is installed at the bottom of the device. An inlet connected to the alumina fluoride silo (10) is provided on the upper side. The discharge is transported to the upper end of the alumina fluoride pneumatic lifting device (11) through a vertically installed stainless steel pipe. Inside the pneumatic lifting device, the vertical pipe is connected to the lower end of the high-pressure air inlet pipe to form a gap, which facilitates the air to carry the material into the vertical pipe to achieve lifting and discharge. The end of the high-pressure air inlet pipe is provided with a cylindrical sleeve with a threaded connection to adjust the air flow rate entering the vertical pipe. A second low-pressure air blower pipe is provided on the side wall of the aeration tank, which plays the role of stirring the alumina. The loaded adsorbent fills the space of the aeration fabric and rises to a certain height in the housing of the aeration lifting machine. By blowing air laterally, a bubble layer is formed at the bottom of the aeration tank to prevent the material from agglomerating. Air is supplied not only through lateral pipes but also through high-pressure pipes, which draw material from the bottom of the aeration tank and transport it through vertical stainless steel pipes. These pipes are free of buttresses and clamps to prevent abrasive wear from alumina on these components.

[0054] Downstream of the fluorinated alumina (FA) pneumatic lifting unit (11), the fluorinated alumina adsorbent enters the alumina centralized distribution system for loading into the electrolytic cells. In this stage, the alumina transported through the channel system is heated by heating elements (such as tubular coils) and gas supplied by a chimney fan. The heating scheme involves dividing the exhaust clean gas stream into two parts. The first part enters the alumina centralized distribution system. After heat exchange with the alumina, the exhaust gas returns to the chimney and is discharged into the atmosphere. The second part enters the ventilation system of the electrolysis workshop and is then discharged into the atmosphere.

[0055] To calculate the cross-section of the aeration channel, a formula is used based on the volume of alumina passing through the channel, the amount of air used to transport the alumina, and the physical properties of the transported material. During the calculation, the smallest possible aeration channel mass should be selected to reduce metal consumption. When selecting an airless chute, the shortest possible chute length and a larger inclination angle (no more than 38° for alumina) should be used to ensure minimal abrasion loss.

[0056] The gas purification module can operate in five modes to achieve maximum production capacity purification of waste gas discharged from different electrolytic reduction processes. The selection of each mode is determined experimentally based on the actual operating parameters of the electrolytic cell and the gas flow rate detection results. For different operating parameters of the electrolytic cell, such as exhaust volume, cryolite ratio, direct / circulating alumina feed rate, anode voltage drop, heat loss, etc., one operating mode is selected. According to the characteristics of the electrolysis process, this module can adjust the amount of adsorbent delivered to the space between the reactor and the filter bag. The flow rate of purified gas passing through the module can also be adjusted by the frequency converter of the fan (21). The operating modes and operating sequence are described below.

[0057] 1. Classic Mode This mode offers advantages when using prebaked anode processes. It is suitable for current output parameters (voltage drop).

[0058] Brief description of the working modes of the dry gas purification unit module: The waste gas from the electrolyzer is distributed as follows: 50% Q (gas volume) enters the first reactor; 50% Q (gas volume) enters the second reactor.

[0059] The flow rate of pure alumina (PA) is as follows: 50% of the pure alumina enters the first reactor; 50% of the pure alumina enters the second reactor.

[0060] Fluorinated alumina (FA) feed rate: up to 50% of fluorinated alumina is recycled to reactor 1; up to 50% of fluorinated alumina is recycled to reactor 2.

[0061] Fluorinated alumina is discharged into the electrolytic cell from the bag filters in sections 1 and 2.

[0062] Figure 4 The flowchart for the classic mode operation is displayed.

[0063] Dust-laden gas from a single electrolytic cell is uniformly fed to two adsorption reactors (1). In this process, pure alumina is fed into the purification unit (13.2) via a pure alumina hopper chute (12), and then into the feeding device (14.1). In this process, the feeding device is configured by adjusting the angle of its internal plates so that its cross-section can distribute 50% of the pure adsorbent to the two gas rings (18). The adsorbent is then conveyed to the distribution box (15.2) via the chute through the feeding device. Through the overflow effect, the adsorbent is circulated in the same proportion through the fluorinated alumina gas trough (17) into the gas rings (18) of the first and second zones.

[0064] Meanwhile, the fluorinated alumina from the bag filters in sections 1 and 2 is fed by the feeding device (14.3) through the fluorinated alumina distribution box (15.3) into the fluorinated alumina gas tank (17) for circulation, and then sent to the gas ring (18), with each gas ring distributing 50% of the adsorbent. The fluorinated alumina is discharged from the fluorinated alumina silo (7) from sections 1 and 2 (2) of the bag filter through the chute via an overflow method. Then the adsorbent enters the fluorinated alumina silo (10), and after accumulating a certain amount, it is transported to the electrolytic cell by the fluorinated alumina pneumatic lifting device (11) through the alumina distribution system.

[0065] 2. Sequential Mode This mode has advantages when using prebaked anode processes. It can be used to maintain the highest temperature of alumina.

[0066] A brief description of the module sequence mode of the dry gas purification device: The waste gas from the electrolyzer is distributed as follows: 50% Q (gas volume) enters the first reactor; 50% Q (gas volume) enters the second reactor.

[0067] Alumina feed rate: 100% pure alumina enters reactor 1.

[0068] Fluorinated alumina feed rate: 100% fluorinated alumina enters reactor 2. Fluorinated alumina from the bag filter in section 1 is fed into reactor 2.

[0069] Fluorinated alumina is discharged from the second section of the bag filter into the electrolytic cell.

[0070] Figure 5 The flowchart of the sequential mode operation is displayed.

[0071] Dust-laden gas from a single electrolytic cell is uniformly fed to two adsorption reactors (1). In this process, pure alumina is fed into the purification unit (13.2) via a pure alumina hopper chute (12), and then into the feeding device (14.1). Unlike the first working mode, in this process, the feeding device adjusts the angle of its internal plate so that its cross-section can feed 100% adsorbent (pure alumina) into the air ring (18) of the first zone bag filter. The adsorbent (pure alumina) is fed to the distribution box (15.2) via the chute through the feeding device (14.1), and then into the adsorption reactor (1) of the first zone bag filter. In this mode, the gate valve cuts off the channel for supplying pure alumina to the second adsorption reactor (1).

[0072] Meanwhile, 100% fluorinated alumina is fed from the first-section bag filter (2) through the feeding device (14.3) and the fluorinated alumina distribution box (15.3) into the fluorinated alumina gas tank of the second-section bag filter for circulation (17), and then sent to the gas ring (18) of the second adsorption reactor (1). Fluorinated alumina is discharged from the second section through the fluorinated alumina silo (7) of the bag filter via an overflow method. Then the adsorbent (fluorinated alumina) enters the fluorinated alumina silo (10), and after accumulating a certain amount, it is sent to the electrolytic cell by the fluorinated alumina pneumatic lifting device (11) through the alumina distribution system.

[0073] 3. Reverse Mode It is ideally suited for Soderberg or self-baking anode electrolysis processes. Suitable for current output parameters (voltage drop).

[0074] Brief explanation of the reverse mode of the dry gas purification unit module: The waste gas from the electrolyzer is distributed as follows: 50% Q (gas volume) enters the first reactor; 50% Q (gas volume) enters the second reactor.

[0075] The conveying capacity of pure alumina is as follows: 50% of the pure alumina enters the first pneumatic lifting device; 50% of the pure alumina enters the second pneumatic lifting device.

[0076] Fluorinated alumina feed rate: 50% fluorinated alumina is fed into reactor 1 from the first section of the bag filter; 50% fluorinated alumina is fed into reactor 2 from the second section of the bag filter.

[0077] Fluorinated alumina is discharged from the first and second sections of the bag filter into the electrolytic cell.

[0078] Figure 6 The flowchart of the reverse mode operation is shown.

[0079] Dust-laden gas from a single electrolytic cell is uniformly fed to two adsorption reactors (1). In this process, pure alumina is fed into the purification unit (13.1) via a pure alumina hopper chute (12), and then into the feeding device (14.2). The transport of pure alumina is achieved solely through a pneumatic lifting device (9) installed within the bag filter hopper (7). In this configuration, the conveying device (14.2) is configured by adjusting the inclination angle of its internal guide plate so that its cross-sectional structure can deliver 50% of the adsorbent (pure alumina) into the two pure alumina pneumatic lifting devices (9) respectively. In this mode, a gate valve cuts off the flow of pure alumina to the two reactors.

[0080] Meanwhile, 50% of the fluorinated alumina from each bag filter hopper (7) is fed into the fluorinated alumina gas tank for circulation (17) via the feeding device (14.3) and the fluorinated alumina distribution box (15.3), and then sent to the gas ring (18) of the two adsorption reactors (1). The method of unloading the fluorinated alumina from the bag filter hopper (7) and transporting the adsorbent to the electrolytic cell is the same as in the classic model.

[0081] 4. Efficiency Improvement Model This mode can be used to capture fluorine to the maximum extent (crystal ratio).

[0082] Brief description of the operation of this dry gas purification unit module in this mode: The waste gas from the electrolyzer is distributed as follows: 50% Q (gas volume) enters the first reactor; 50% Q (gas volume) enters the second reactor.

[0083] The flow rate of pure alumina is as follows: 25% pure alumina enters the first reactor; 25% pure alumina enters the second reactor; 25% pure alumina enters the first pneumatic lifting device; and 25% pure alumina enters the second pneumatic lifting device.

[0084] Fluorinated alumina feed rate: 50% fluorinated alumina is fed into reactor 1 from the first section of the bag filter; 50% fluorinated alumina is fed into reactor 2 from the second section of the bag filter.

[0085] Fluorinated alumina is discharged from the first and second sections of the bag filter into the electrolytic cell.

[0086] Figure 7 The flowchart of the efficiency improvement mode is displayed.

[0087] Dust-laden gas from a single electrolytic cell is uniformly fed to two adsorption reactors (1). In this scheme, pure alumina is fed into the gas ring (18) and the pure alumina pneumatic lifting device (9). The pure alumina is fed through two pure alumina hopper chutes (12), then distributed to purification units (13.1, 13.2) and fed into the feeding devices (14.1, 14.2). The two pure alumina feeding lines are described below. In this process, the two feeding devices (14.1, 14.2) are configured by adjusting the angle of their internal plates so that their cross-sections can distribute 25% adsorbent to each pneumatic lifting device ЧГ (9) and each gas ring (18). The adsorbent is transported to the distribution box (15.1, 15.2) via the feeding device (14.1, 14.2) through the inclined chute. The first feeding line enters the adsorption reactor (1) through the air ring (18), and the second feeding line enters the gap between the filter bags of the bag filter (2) through the pure alumina pneumatic lifting device (9).

[0088] Meanwhile, 50% of the fluorinated alumina in each bag filter hopper (7) is fed into the fluorinated alumina gas tank for circulation (17) via the feeding device (14.3) and the fluorinated alumina distribution box (15.3), and then sent to the gas ring (18) of the two adsorption reactors (1). The discharge of fluorinated alumina from the bag filter hopper (7) and the transport of the adsorbent are the same as in the classic model.

[0089] 5. Sequential unloading mode for adsorbent (fluorinated alumina) This mode has advantages when using prebaked anode processes. It can be used to maximize fluorine capture (cryolite ratio).

[0090] Brief description of the working modes of the dry gas purification unit module: The waste gas from the electrolyzer is distributed as follows: 50% Q (gas volume) enters the first reactor; 50% Q (gas volume) enters the second reactor.

[0091] The flow rate of pure alumina is as follows: 50% of the pure alumina enters the first reactor; 50% of the pure alumina enters the first pneumatic lifting device.

[0092] Fluorinated alumina feed rate: 100% fluorinated alumina is fed into the second reactor from the first section of the bag filter.

[0093] Fluorinated alumina is discharged from the second section of the bag filter into the electrolytic cell.

[0094] Figure 8 The flowchart of the sequential unloading mode of the adsorbent is shown.

[0095] Dust-laden gas from a single electrolytic cell is uniformly fed to two adsorption reactors (1). In this process, pure alumina is fed to a gas ring (18) in the first section and a pure alumina pneumatic lifting device (9) in the first section. Pure alumina is fed in through two pure alumina hopper chutes (12), then distributed to purification units (13.1, 13.2) and fed into feeding devices (14.1, 14.2). The two pure alumina feeding lines are described below. In this scheme, the two conveying devices (14.1, 14.2) are configured by adjusting the inclination angle of the internal guide plates so that their cross-sectional structure can feed 50% of the adsorbent into the pure alumina pneumatic lifting device (9) in the first section and the gas ring (18) in the first section, respectively. Downstream of the feeding device, the adsorbent is conveyed via a chute to the distribution boxes (15.1, 15.2), and then transported as follows: from line 1—through the air ring (18) to the adsorption reactor (1) in the first section, and from line 2—through the pure alumina pneumatic lifting device (9) in the first section of the bag filter to the space between the filter bags of the bag filter (2). In this mode, a knife gate valve cuts off the supply of pure alumina to the adsorption reactor (1) in the second section of the bag filter.

[0096] Simultaneously, 100% of the fluorinated alumina is supplied from the first section of the bag filter (2) via the feeding device (14.3) through the fluorinated alumina distribution box (15.3) to the fluorinated alumina gas tank (17) for recirculation in the second section, and then supplied to the air ring (18) of the adsorption reactor (1) in the second section. The fluorinated alumina is discharged from the filter hopper (7), and the adsorbent delivery method is similar to the sequential operation mode.

[0097] The fluorination device used for aluminum production shares several similarities with the prototype: The gas is mixed with the adsorbent through turbulent flow.

[0098] An adsorption reactor for fluorine adsorption is provided.

[0099] The equipment is equipped with a filter unit in the form of a bag filter.

[0100] The differences in device structure compared to the prototype are as follows: This equipment is not connected to a public centralized dry gas purification system, which solves the problem of independent operation. In this configuration, the gas purification module can be moved to connect to different electrolytic cells without the need for large-scale flue installations, offering flexibility. This advantage is achieved through the module's integral structure. The module can be moved using construction machinery.

[0101] This device is not a pre-purification unit, but has an independent working cycle that does not require external purification unit assistance, because the prototype's pre-purification was used for the operation of a centralized dry gas purification unit (which could not remove it from the adsorption process). Therefore, the proposed gas purification module can individually adjust gas adsorption according to the specific requirements of each electrolyzer. This advantage is achieved by adjusting the adsorbent entering the space between the filter bags of the adsorption reactor (1) and the bag filter (2) through the feeding device (14.1) and the knife gate valve.

[0102] The geometry of each component of the equipment is described in the instruction manual and the drawings are provided as examples only, and are not limited to the embodiments shown.

[0103] The preparation of raw materials for the electrolytic cells is carried out independently (without homogenization), thereby improving the technical and economic indicators of the entire series of electrolytic cells. Maximum energy efficiency of the electrolytic cells can be achieved. This advantage is realized through the real-time (without time delay) return of fluorinated alumina to the electrolytic cells via a gas channel.

[0104] This device is equipped with only one induced draft fan (blower) to achieve a complete gas purification cycle, unlike the prototype, which has one induced draft fan in the pre-purification unit and another in the common centralized dry gas purification unit. Therefore, the motor speed can be selected individually, thereby achieving high-quality regulation of the electrolytic cell gas extraction system.

[0105] In light of the specification and examples, a request is made to grant legal protection to a gas purification module for collecting and purifying gases generated in an aluminum production electrolytic cell, the module comprising: at least two adsorption reactors (1) connected to a bag filter (2) via a transition pipe (3), the bag filter (2) comprising a dust-laden gas chamber (4) divided into two partitions by a transverse partition (8), a clean gas chamber (5), a filter bag (6), and a fluorinated alumina silo (7); furthermore, the gas purification module includes two adsorbent supply lines, wherein a first adsorbent supply line is used to supply pure adsorbent. The first adsorbent supply line is equipped with a pure alumina silo (12) with a gas distributor and at least two inclined troughs to transport pure alumina to the adsorption reactor (1), and a pneumatic lifting device (9) to spray pure alumina onto the filter bag (6). The second adsorbent supply line includes a fluorinated alumina silo (7) located at the bottom of the bag filter (2), which is connected to the fluorinated alumina storage silo (7), and the fluorinated alumina is transported to the electrolytic cell and the adsorption reactor (1) by the pneumatic lifting device (11).

[0106] In addition, the first adsorbent supply line and the second adsorbent supply line are equipped with feeding devices (14.1, 14.2, 14.3) and distribution boxes (15.1, 15.2, 15.3).

[0107] It is suggested that the gas purification module be placed near the electrolytic cell and connected to the electrolytic cell via a delivery pipeline to transport fluorinated alumina as a raw material to the electrolytic cell.

[0108] Preferably, the gas purification module includes a fan (21) installed on the outlet gas pipeline leading to the atmosphere.

[0109] The scope of legal protection also includes a method for collecting and purifying gases generated in an aluminum production electrolytic cell using a provided gas purification module, comprising the following steps: (a) distributing the dust-laden gas generated by a single electrolytic cell equally to two adsorption reactors; (b) conveying pure alumina from a pure alumina silo to filter bags and / or adsorption reactors; (c) simultaneously feeding fluorinated alumina into a gas tank for recirculation via a feeding device and a distribution box, and then feeding it into the adsorption reactor; furthermore, after the fluorinated alumina in the bag filter silo is discharged from the first and / or second zones by overflow, the fluorinated alumina then accumulates in the fluorinated alumina silo for further conveying to the electrolytic cell.

[0110] The supply of pure alumina to a filter bag and / or adsorption reactor is set between 25% and 100% according to process requirements. The supply of fluorinated alumina to the adsorption reactor for recycling is between 50% and 100% according to the set operating mode of the production process. The fluorinated alumina is preheated before being fed into the electrolytic cell.

Claims

1. A gas purification module for collecting and purifying gases generated in an aluminum production electrolytic cell, comprising at least two adsorption reactors (1) connected to a bag filter (2) via a transition pipe (3), the bag filter (2) comprising a dust-laden gas chamber (4) divided into two partitions by a transverse partition (8), a clean gas chamber (5), a filter bag (6), and a fluorinated alumina silo (7), characterized in that, The gas purification module includes two adsorbent supply lines, wherein the first adsorbent supply line is used to transport pure alumina and the second supply line is used to transport fluorinated alumina. The first adsorbent supply line is provided with a pure alumina silo (12) with a gas distributor and at least two inclined troughs for transporting pure alumina to the adsorption reactor (1) and a pneumatic lifting device (9) for spraying pure alumina onto the filter bag (6). The second adsorbent supply line includes a fluorinated alumina silo (7) located at the bottom of the bag filter (2), which is connected to the fluorinated alumina storage silo (7) and transports fluorinated alumina to the electrolytic cell (22) and the adsorption reactor (1) through the pneumatic lifting device (11).

2. The gas purification module according to claim 1, characterized in that, The first adsorbent supply line and the second adsorbent supply line are equipped with feeding devices (14.1, 14.2, 14.3) and distribution boxes (15.1, 15.2, 15.3).

3. The gas purification module according to claim 1, characterized in that, The gas purification module can be arranged near the electrolytic cell and connected to the electrolytic cell through a conveying pipeline to transport fluorinated alumina as a raw material to the electrolytic cell.

4. The gas purification module according to claim 1, characterized in that, The gas purification module includes a fan (21) installed on the outlet gas pipeline leading to the atmosphere.

5. A method for collecting and purifying gases generated in an aluminum production electrolytic cell using a gas purification module according to any one of claims 1 to 4, comprising the following steps: (a) The dust-laden gas generated by a single electrolytic cell is equally distributed to two adsorption reactors; (b) Pure alumina is transported from the pure alumina silo to the filter bags and / or adsorption reactors; (c) Fluorinated alumina is simultaneously fed into the gas tank for recirculation via a feeding device and a distribution box, and then fed into the adsorption reactors; In addition, after the fluorinated alumina in the bag filter silo is discharged from the first and / or second zones by overflow, the fluorinated alumina then accumulates in the fluorinated alumina silo for further transport to the electrolytic cell.

6. The method according to claim 5, characterized in that, The supply of pure alumina to the filter bags and / or adsorption reactor is set between 25% and 100% according to process requirements.

7. The method according to claim 5, characterized in that, The amount of fluorinated alumina supplied to the adsorption reactor for recycling is between 50% and 100% depending on the set operating mode of the production process.

8. The method according to claim 5, characterized in that, Fluorinated alumina is preheated before being fed into the electrolytic cell.

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