Recovery treatment system and method for flue gas generated by inert anode electrolysis of aluminum chloride

Abstract

The invention relates to the technical field of aluminum smelting tail gas recovery treatment, in particular to a flue gas recovery treatment system and method for inert anode electrolysis of aluminum chloride. Flue gas comprises chlorine, hydrogen fluoride and hydrogen chloride, and the recovery treatment method comprises the following steps: carrying out first recovery treatment on the flue gas by using first absorption liquid to obtain first absorption liquid and first treated tail gas; the component of the first absorption liquid comprises a sodium hydroxide solution or a saturated sodium chloride solution; performing second recovery treatment on the first treated tail gas by using second absorption liquid to obtain second absorption liquid and second treated tail gas; the component of the second absorption liquid comprises a sodium hydroxide solution or a concentrated sulfuric acid solution; according to the treatment mode of the second treatment tail gas, whether the second absorption liquid needs to be subjected to thermal refining or not is judged, and a thermal refining liquid is obtained; sequentially evaporating and drying the conditioning liquid to obtain a mixture of chlorate and fluoride salt. According to the recovery treatment method, the recovery efficiency of the chlorine element and the fluorine element in the flue gas is remarkably improved.

Description

Technical Field

[0001] This application relates to the technical field of aluminum smelting tail gas recovery and treatment, and particularly relates to a flue gas recovery and treatment system and method for inert anode electrolysis of aluminum chloride. Background Art

[0002] Conventional aluminum chloride electrolysis usually uses a carbonaceous anode and a vertical multi-chamber structure. The carbon anode does not participate in the reaction during the aluminum chloride decomposition process, making it difficult for the carbon anode to be consumed. However, once the aluminum chloride raw material contains oxygen substances (such as water or oxide impurities), these oxygen will react with aluminum chloride in the aluminum chloride electrolyte melt to form aluminum oxide. The decomposition voltage of aluminum oxide at the carbon anode is less than that of aluminum chloride, which causes the decomposition reaction of aluminum oxide to occur immediately during the normal operation of the carbon anode, resulting in continuous consumption of the carbon anode, an increase in the anode-cathode distance, and uneven current distribution. In addition, these oxygen-containing substances continuously participate in the electrochemical reaction, generating an AlOCl crust on the cathode surface, and the presence of this crust will cause a short circuit between the anode and cathode of the aluminum chloride electrolytic cell. Therefore, generally, high-purity anhydrous aluminum chloride (with an oxygen content of less than 0.03% by mass) is required, but the preparation, storage, and transportation of high-purity anhydrous aluminum chloride are difficult, and the production cost of high-purity anhydrous aluminum chloride is relatively high.

[0003] Inert anode aluminum electrolysis is generally carried out in a fluoride electrolyte system for alumina electrolysis. The inert anode used can be a cermet inert anode, and the cermet inert anode has good corrosion resistance in both fluoride electrolyte systems and chloride electrolyte systems. If the cermet inert anode is used for aluminum chloride electrolysis, the decomposition voltage of alumina will be higher than that of aluminum chloride, which means that after the aluminum chloride raw material containing oxygen substances enters the electrolyte melt, it will not affect the normal decomposition reaction of aluminum chloride, thereby reducing the purity requirement for anhydrous aluminum chloride.

[0004] However, when using a cermet inert anode during aluminum chloride electrolysis, a small amount of fluoride needs to be added and flue gas containing volatiles such as chlorine, hydrogen chloride, aluminum chloride, hydrogen fluoride, and fluoride salts is generated. Due to the complex composition of these electrolytic flue gases, it is difficult to effectively recover and utilize them. Summary of the Invention

[0005] This application provides a flue gas recovery and treatment system and method for inert anode electrolysis of aluminum chloride to solve the following technical problem: how to improve the recovery and utilization rate of aluminum chloride electrolytic flue gas.

[0006] In the first aspect, an embodiment of this application provides a method for recovering and treating flue gas from inert anode electrolysis of aluminum chloride, where the flue gas includes chlorine, hydrogen fluoride, and hydrogen chloride, and the recovery and treatment method includes:

[0007] The flue gas is subjected to a first recovery treatment using a first absorption liquid to absorb the hydrogen fluoride and hydrogen chloride, obtaining a first absorption liquid and a first treated tail gas; wherein, the components of the first absorption liquid include a sodium hydroxide solution or a saturated sodium chloride solution;

[0008] The first treated tail gas is subjected to a second recovery treatment using a second absorption liquid, obtaining a second absorption liquid and a second treated tail gas; wherein, the components of the second absorption liquid include a sodium hydroxide solution or a concentrated sulfuric acid solution;

[0009] Judge whether it is necessary to temper the second absorption liquid according to the treatment method of the second treated tail gas;

[0010] If so, use a tempering agent to temper the first absorption liquid and the second absorption liquid to obtain a tempered liquid;

[0011] If not, use a tempering agent to temper the first absorption liquid to obtain a tempered liquid;

[0012] The tempered liquid is evaporated and dried in sequence to obtain a mixture of chloride salts and fluoride salts.

[0013] Optionally, when the component of the first absorption liquid is a sodium hydroxide solution and the component of the second absorption liquid is a sodium hydroxide solution, the second treated tail gas is a harmless gas; or

[0014] When the component of the first absorption liquid is a saturated sodium chloride solution and the component of the second absorption liquid is a concentrated sulfuric acid solution, the second treated tail gas is chlorine gas.

[0015] Optionally, the judging whether it is necessary to temper the second absorption liquid according to the treatment method of the second treated tail gas includes the steps of:

[0016] If the treatment method of the second treated tail gas is direct emission, it is necessary to temper the second absorption liquid;

[0017] Mix the first absorption liquid and the second absorption liquid to obtain a mixed absorption liquid;

[0018] Use a tempering agent to temper the mixed absorption liquid to obtain a tempered liquid; or

[0019] If the treatment method of the second treated tail gas is recycling, directly use a tempering agent to temper the first absorption liquid to obtain a tempered liquid.

[0020] Optionally, the pH value of the tempering treatment is greater than 6; and / or

[0021] The tempering agent includes sodium hydroxide and / or sodium carbonate.

[0022] Optionally, the temperature of the flue gas is less than 180°C.

[0023] In a second aspect, an embodiment of the present application provides a recovery and treatment system for the flue gas of electrolyzing aluminum chloride with an inert anode. The recovery and treatment system is arranged at the gas outlet end of an aluminum chloride electrolytic cell with an inert anode. The recovery and treatment system is adapted to the recovery and treatment method described in the first aspect. The recovery and treatment system includes:

[0024] A gas guiding part, including a gas guiding straight pipe and a bifurcated pipe. The feeding end of the gas guiding straight pipe is connected to the gas outlet end of the aluminum chloride electrolytic cell, and the gas outlet end of the gas guiding straight pipe communicates with the intake end of the bifurcated pipe;

[0025] An absorption part, including a first absorption unit and a second absorption unit. The feeding end of the first absorption unit communicates with the gas outlet end of the bifurcated pipe, and the discharging end of the first absorption unit communicates with the feeding end of the second absorption unit.

[0026] Optionally, the first absorption unit includes a first intake pipe, a first outlet pipe, and a first absorption liquid layer. The intake end of the first intake pipe communicates with the gas outlet end of the bifurcated pipe, the outlet end of the first intake pipe extends into the first absorption liquid layer, the intake end of the first outlet pipe is arranged above the first absorption liquid layer, and the outlet end of the first outlet pipe communicates with the second absorption unit.

[0027] Optionally, the second absorption unit includes a second intake pipe, a second outlet pipe, and a second absorption liquid layer. The intake end of the second intake pipe communicates with the outlet end of the first outlet pipe, the outlet end of the second intake pipe extends into the second absorption liquid layer, and the intake end of the second outlet pipe is arranged above the second absorption liquid layer.

[0028] Optionally, the absorption part further includes a collection airbag, and the collection airbag is arranged at the outlet end of the second outlet pipe.

[0029] Optionally, the recovery and treatment system further includes:

[0030] A cleaning unit, including a back-blowing device or a ramming rod; when the cleaning unit includes a back-blowing device, the back-blowing device is arranged at the gas outlet end of the gas guiding straight pipe;

[0031] When the cleaning unit includes a ramming rod, the ramming rod is arranged in the gas guiding straight pipe, and the ramming rod expands and contracts in the gas guiding straight pipe to push the electrolyte volatiles adhered in the gas guiding straight pipe into the aluminum chloride electrolytic cell.

[0032] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0033] A method for recycling and treating the flue gas of inert anode electrolysis of aluminum chloride provided by an embodiment of the present application. For the flue gas generated by inert anode electrolysis of aluminum chloride, first, a first absorbent solution of sodium hydroxide solution or saturated sodium chloride solution is used to fully absorb the hydrogen chloride and hydrogen fluoride gases in the flue gas, so that the first absorbent solution forms chloride salts and some chlorate ions, to recover some chlorine and fluorine elements in the flue gas. Then, a second absorbent solution of sodium hydroxide solution can selectively absorb the chlorine gas in the flue gas, so that the second absorbent solution forms chloride salts and some chlorate ions, to realize the recovery of chlorine elements in the flue gas; or a second absorbent solution of concentrated sulfuric acid is used to dry the chlorine gas in the flue gas to realize the recovery of chlorine gas in the flue gas. Through the conditioning treatment with a conditioner, the chlorate ions in the first absorbent solution or the second absorbent solution can be converted into chloride salts. Through subsequent evaporation and drying treatments, these chloride salts can be separated from the first absorbent solution and the second absorbent solution, thereby improving the recovery utilization rate of the flue gas of aluminum chloride electrolysis. In addition, using the first absorbent solution of saturated sodium chloride solution can inhibit the dissolution of chlorine gas in the first absorbent solution through the common ion effect, reduce the loss of available chlorine, and improve the recovery amount of chlorine gas in the subsequent flue gas, thereby further improving the recovery utilization rate of the flue gas of aluminum chloride electrolysis. Description of the Drawings

[0034] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present application, and are used together with the specification to explain the principles of the present application.

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a schematic flow chart of a method for recycling and treating the flue gas of inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0037] Figure 2 It is a detailed schematic flow chart of a method for recycling and treating the flue gas of inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0038] Figure 3 It is a detailed schematic flow chart of another method for recycling and treating the flue gas of inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0039] Figure 4 It is a logical structure diagram of a system for recycling and treating the flue gas of inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0040] Figure 5 Structural diagram of a recovery and treatment system for the flue gas of inert anode electrolytic aluminum chloride containing a ramming rod provided by an embodiment of the present application;

[0041] Figure 6 Structural diagram of a recovery and treatment system for the flue gas of inert anode electrolytic aluminum chloride for collecting chlorine provided by an embodiment of the present application;

[0042] Figure 7 Structural diagram of a recovery and treatment system for the flue gas of inert anode electrolytic aluminum chloride with a backwashing device and direct evacuation provided by an embodiment of the present application;

[0043] Among them, 1 - aluminum chloride electrolytic cell, 2 - straight gas guide pipe, 3 - bifurcated pipe, 4 - first absorption unit, 401 - first intake pipe, 402 - first outlet pipe, 403 - first absorption liquid layer, 5 - second absorption unit, 501 - second intake pipe, 502 - second outlet pipe, 503 - second absorption liquid layer, 6 - collection airbag, 7 - backwashing device, 8 - ramming rod. Specific embodiments

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0045] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub - ranges and the individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub - ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of what the range is; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0046] In this text, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or", which describes the associated relationship of associated objects, indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as parts by weight and parts by mass represent the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by the ratio should be understood as the antecedents of the ratio formula in the order of description, and the ratio numbers should be understood as the consequents of the ratio formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the ratio numbers in the ratio formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0047] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in this text can be obtained through market purchases or can be prepared by existing methods.

[0048] Figure 1 Exemplarily shown is a schematic flow chart of a method for recovering and treating the flue gas of an inert anode electrolytic aluminum chloride provided by an embodiment of the present application;

[0049] As Figure 1 shown, for a method for recovering and treating the flue gas of an inert anode electrolytic aluminum chloride provided by an embodiment of the present application, the flue gas includes chlorine, hydrogen fluoride, and hydrogen chloride, and the recovery and treatment method includes:

[0050] S1. Using a first absorption liquid to perform a first recovery treatment on the flue gas to absorb the hydrogen fluoride and hydrogen chloride, obtaining a first absorption liquid and a first treated tail gas; wherein, the components of the first absorption liquid include a sodium hydroxide solution or a saturated sodium chloride solution;

[0051] S2. Use the second absorption liquid to perform a second recovery treatment on the first treated tail gas to obtain a second absorption liquid and a second treated tail gas; wherein, the components of the second absorption liquid include a sodium hydroxide solution or a concentrated sulfuric acid solution;

[0052] S3. According to the treatment method of the second treated tail gas, determine whether it is necessary to perform conditioning treatment on the second absorption liquid;

[0053] If so, use a conditioner to perform conditioning treatment on the first absorption liquid and the second absorption liquid to obtain a conditioned liquid;

[0054] If not, use a conditioner to perform conditioning treatment on the first absorption liquid to obtain a conditioned liquid;

[0055] S4. Evaporate and dry the conditioned liquid in sequence to obtain a mixture of chloride salts and fluoride salts.

[0056] It should be noted that since chlorine, hydrogen chloride, hydrogen fluoride, etc. in the flue gas dissolve in the solution to form a large number of acid radicals, resulting in a certain degree of acidity in the first absorption liquid or the second absorption liquid, and according to the components of the first absorption liquid and the second absorption liquid, the conditioner can use sodium hydroxide and / or sodium carbonate to effectively adjust the pH value of the first absorption or the second absorption liquid, so that there are a large number of chloride salts and a small amount of fluoride salts in the first absorption liquid and the second absorption liquid finally. The components of these chloride salts and fluoride salts are close to those of the aluminum chloride electrolyte and can be recycled as the aluminum chloride electrolyte after evaporation and drying treatment.

[0057] It should be noted that the first absorption liquid will also absorb the solid volatiles present in the flue gas to improve the recovery utilization rate of the flue gas.

[0058] It should be noted that when the first absorption liquid is a saturated sodium chlorate solution and the saturated sodium chlorate solution becomes turbid and viscous, it is necessary to replace the new first absorption liquid in time; when the second absorption liquid is a sodium hydroxide solution and the pH value of the second absorption liquid is less than 6, it is necessary to replace the new second absorption liquid in time.

[0059] It should be noted that the embodiment of the present application provides a method for reclaiming and treating the flue gas of an inert anode electrolytic aluminum chloride. The reclaiming and treating method improves the recovery utilization rate through the following technical means:

[0060] 1. Use sodium hydroxide or saturated sodium chloride solution as the first absorption liquid to preferentially and efficiently absorb hydrogen chloride and hydrogen fluoride in the flue gas and convert them into chloride salts to achieve the preliminary recovery of chlorine and fluorine elements.

[0061] 2. Selectively recover chlorine through the second-stage recovery treatment:

[0062] (1) Absorb chlorine gas using sodium hydroxide solution to generate chloride salts;

[0063] (2) Or dry and recover high-purity chlorine gas using concentrated sulfuric acid.

[0064] 3. Innovatively utilize the common ion effect of saturated sodium chloride solution to inhibit the dissolution tendency of chlorine gas in the first absorption liquid, so as to reduce the loss of available chlorine and create favorable conditions for subsequent chlorine recovery.

[0065] 4. Quenching and conversion process:

[0066] Convert the chlorate ions in the first absorption liquid and the second absorption liquid into chloride salts, and separate the salts through evaporation and drying.

[0067] Therefore, through the process design of hierarchical absorption and selective recovery, and by optimizing the absorption sequence and reaction conditions, this method significantly improves the recovery efficiency of chlorine and fluorine elements in flue gas.

[0068] In some alternative embodiments, when the component of the first absorption liquid is sodium hydroxide solution and the component of the second absorption liquid is sodium hydroxide solution, the second treated tail gas is a harmless gas; or

[0069] When the component of the first absorption liquid is saturated sodium chloride solution and the component of the second absorption liquid is concentrated sulfuric acid solution, the second treated tail gas is chlorine gas.

[0070] In these embodiments, the first absorption liquid and the second absorption liquid of sodium hydroxide solution can fully absorb the chlorine gas, hydrogen chloride, and hydrogen fluoride in the flue gas through multi-stage absorption to make the second treated tail gas a harmless gas. Additionally, the first absorption liquid of saturated sodium chloride solution can absorb the hydrogen chloride and hydrogen fluoride in the flue gas to initially improve the purity of chlorine gas in the flue gas, and then the second absorption liquid of concentrated sulfuric acid can effectively dry the chlorine gas in the first tail gas to obtain pure chlorine gas.

[0071] Figure 2 Exemplarily shows a detailed process flow diagram of a method for recovering and treating the flue gas of an inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0072] Figure 3 Exemplarily shows another detailed process flow diagram of a method for recovering and treating the flue gas of an inert anode electrolysis of aluminum chloride provided by an embodiment of the present application;

[0073] In some alternative embodiments, such as Figure 2 Or as Figure 3 shown, judging whether it is necessary to perform quenching treatment on the second absorption liquid according to the treatment method of the second treated tail gas includes the steps:

[0074] S301. If the treatment method of the second treated tail gas is direct emission, the second absorbent needs to be conditioned;

[0075] S302. Mix the first absorbent and the second absorbent to obtain a mixed absorbent;

[0076] S303. Use a conditioner to condition the mixed absorbent to obtain a conditioned liquid; or

[0077] S301. If the treatment method of the second treated tail gas is recycling, directly use a conditioner to condition the first absorbent to obtain a conditioned liquid.

[0078] In these embodiments, according to the treatment method of the second treated tail gas (direct emission or recycling), it can be determined whether the second absorbent needs to be conditioned: when the second treated tail gas needs to be directly emitted, at this time the first absorbent and the second absorbent need to completely absorb the harmful gases in the flue gas, which will cause the pH of the first absorbent and the second absorbent to tend to be acidic. Therefore, through conditioning, the pH of the first absorbent and the second absorbent can be improved, and the chlorate ions in the first absorbent or the second absorbent can be converted into chlorides; when the second treated tail gas needs to be recycled, at this time the first absorbent needs to avoid absorbing chlorine gas, which will cause the pH of the first absorbent to decrease. Therefore, through conditioning, the pH of the first absorbent can be improved, and the chlorate ions in the first absorbent can be converted into chlorides.

[0079] In some alternative embodiments, the pH of the conditioning treatment is greater than 6; and / or

[0080] The conditioner includes sodium hydroxide and / or sodium carbonate.

[0081] In these embodiments, the pH of the conditioning treatment is above 6. At this time, the pH of the conditioned liquid tends to be neutral, so that the chlorate in the conditioned liquid is converted into chloride, which can facilitate the subsequent evaporation and drying to finally obtain a mixture of chloride and fluoride. The composition of these mixtures is close to that of the aluminum chloride electrolyte, so they can be recycled as a supplement to the aluminum chloride electrolyte. In addition, sodium hydroxide or sodium carbonate as a conditioner can, while adjusting the pH of the first absorbent or the second absorbent, avoid introducing other impurity ions into the first absorbent or the second absorbent, so as to ensure that the purity of the chloride is within a certain range, thus facilitating the direct use of the chloride subsequently and improving the recycling rate of the aluminum chloride electrolysis flue gas.

[0082] In some alternative embodiments, the temperature of the flue gas is less than 180°C.

[0083] In these embodiments, flue gas at a temperature lower than 180 °C can effectively reduce the temperature of the flue gas entering the first absorption liquid, causing the gaseous phase of aluminum chloride in the flue gas to condense on the inner wall of the straight gas guide pipe, forming a solid phase of aluminum chloride.

[0084] Figure 4 Exemplarily, a logic structure diagram of a recovery and treatment system for the flue gas of an inert anode electrolysis of aluminum chloride provided by an embodiment of the present application is shown;

[0085] Based on a general inventive concept, as Figure 4 shown, an embodiment of the present application provides a recovery and treatment system for the flue gas of an inert anode electrolysis of aluminum chloride. The recovery and treatment system is provided at the gas outlet end of an aluminum chloride electrolytic cell 1 with an inert anode. The recovery and treatment system is adapted to the recovery and treatment method. The recovery and treatment system includes:

[0086] A gas guiding part, including a straight gas guide pipe 2 and a bifurcated pipe 3. The feed end of the straight gas guide pipe 2 is connected to the gas outlet end of the aluminum chloride electrolytic cell 1, and the gas outlet end of the straight gas guide pipe 2 communicates with the inlet end of the bifurcated pipe 3;

[0087] An absorption part, including a first absorption unit 4 and a second absorption unit 5. The feed end of the first absorption unit 4 communicates with the gas outlet end of the bifurcated pipe 3, and the discharge end of the first absorption unit 4 communicates with the feed end of the second absorption unit 5.

[0088] This recovery and treatment system is implemented based on the above recovery and treatment method. The specific steps of this recovery and treatment method can refer to the above embodiments. Since this recovery and treatment system adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0089] It should be noted that the materials of the straight gas guide pipe 2 and the bifurcated pipe 3 can both use corundum materials. Based on the corrosion resistance characteristics of corundum materials, corrosion of the straight gas guide pipe 2 and the bifurcated pipe 3 by flue gas can be avoided; in addition, corundum materials have certain thermal conductivity, which can effectively reduce the temperature of the flue gas.

[0090] In some alternative embodiments, the first absorption unit 4 includes a first inlet pipe 401, a first outlet pipe 402, and a first absorption liquid layer 403. The inlet end of the first inlet pipe 401 communicates with the gas outlet end of the bifurcated pipe 3, the outlet end of the first inlet pipe 401 extends into the first absorption liquid layer 403, the inlet end of the first outlet pipe 402 is provided above the first absorption liquid layer 403, and the outlet end of the first outlet pipe 402 communicates with the second absorption unit 5.

[0091] In these embodiments, the first absorption unit 4 including the first intake pipe 401, the first outlet pipe 402, and the first absorption liquid layer 403 can increase the contact area between the flue gas and the first absorption liquid by extending the outlet end of the first intake pipe 401 into the first absorption liquid layer 403, so that the flue gas is fully absorbed.

[0092] In some alternative embodiments, the second absorption unit 5 includes a second intake pipe 501, a second outlet pipe 502, and a second absorption liquid layer 503. The intake end of the second intake pipe 501 is connected to the outlet end of the first outlet pipe 402. The outlet end of the second intake pipe 501 extends into the second absorption liquid layer 503, and the intake end of the second outlet pipe 502 is provided above the second absorption liquid layer 503.

[0093] In these embodiments, the second absorption unit 5 including the second intake pipe 501, the second outlet pipe 502, and the second absorption liquid layer 503 can increase the contact area between the flue gas and the second absorption liquid by extending the outlet end of the second intake pipe 501 into the second absorption liquid layer 503, so that the first treated tail gas is fully absorbed.

[0094] It should be noted that the second intake pipe 501 and the first outlet pipe 402 can be connected through a flexible hose.

[0095] In some alternative embodiments, the absorption part further includes a collection airbag 6, and the collection airbag 6 is provided at the outlet end of the second outlet pipe 502.

[0096] In these embodiments, introducing the collection airbag 6 into the absorption part can effectively recover chlorine through the collection airbag 6 when the second tail gas is chlorine.

[0097] Figure 5 Exemplarily shown is a structural diagram of a recovery and treatment system for the flue gas of inert anode electrolysis of aluminum chloride including a ramming rod provided by an embodiment of the present application;

[0098] Figure 6 Exemplarily shown is a structural diagram of a recovery and treatment system for the flue gas of inert anode electrolysis of aluminum chloride for collecting chlorine provided by an embodiment of the present application;

[0099] Figure 7 Exemplarily shown is a structural diagram of a recovery and treatment system for the flue gas of inert anode electrolysis of aluminum chloride including a back-blowing device and direct venting provided by an embodiment of the present application;

[0100] In some alternative embodiments, as Figure 5 、 Figure 6 and Figure 7 shown, the recovery and treatment system further includes:

[0101] The cleaning unit includes a back-blowing device 7 or a ramming rod 8; when the cleaning unit includes the back-blowing device 7, the back-blowing device 7 is arranged at the air outlet end of the air guiding straight pipe 2;

[0102] When the cleaning unit includes the ramming rod 8, the ramming rod 8 is arranged in the air guiding straight pipe 2, and the ramming rod 8 expands and contracts in the air guiding straight pipe 2 to push the electrolyte volatiles adhered in the air guiding straight pipe 2 into the aluminum chloride electrolytic cell 1.

[0103] In these embodiments, by introducing the back-blowing device 7 or the ramming rod 8 into the recovery treatment system, the aluminum chloride solid phase adhered to the air guiding straight pipe 2 can be pushed into the aluminum chloride electrolytic cell 1 by the action of the back-blowing gas or the ramming rod 8, and the aluminum chloride component in the flue gas can be further recovered.

[0104] It should be noted that when the first absorption liquid is saturated sodium chloride solution and the second absorption liquid is concentrated sulfuric acid, the second treated tail gas is chlorine gas, and the second treated tail gas needs to be collected. If the back-blowing device 7 is used, the back-blowing gas of the back-blowing device 7 needs to be controlled as dry chlorine gas to avoid introducing impurities; when both the first absorption liquid and the second absorption liquid are sodium hydroxide solution, the second treated tail gas is a harmless gas. If the back-blowing device 7 is used, the back-blowing gas of the back-blowing device 7 needs to be controlled as dry chlorine gas, dry air or dry inert gas.

[0105] The present application will be further described below in conjunction with specific embodiments. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0106] Example 1

[0107] As Figure 2 shown, a method for recovering and treating the flue gas of an inert anode electrolyzing aluminum chloride, the flue gas includes chlorine gas, hydrogen fluoride and hydrogen chloride, and includes:

[0108] S1. Using a first absorption liquid to perform a first recovery treatment on the flue gas to absorb hydrogen fluoride and hydrogen chloride, obtaining a first absorption liquid and a first treated tail gas; wherein, the components of the first absorption liquid include sodium hydroxide solution;

[0109] S2. Using a second absorption liquid to perform a second recovery treatment on the first treated tail gas, obtaining a second absorption liquid and a second treated tail gas; wherein, the components of the second absorption liquid include sodium hydroxide solution;

[0110] S301. If the treatment method of the second treated tail gas is direct emission, then the second absorption liquid needs to be conditioned;

[0111] S302. Mix the first absorbent liquid and the second absorbent liquid to obtain a mixed absorbent liquid;

[0112] S303. Use a tempering agent to temper the mixed absorbent liquid to obtain a tempered liquid;

[0113] S4. Evaporate and dry the tempered liquid in sequence to obtain a mixture of chloride salts and fluoride salts.

[0114] The pH of the tempering treatment is greater than 6;

[0115] The tempering agent includes sodium hydroxide or sodium carbonate.

[0116] The temperature of the flue gas is 150 °C.

[0117] A recovery and treatment system for the flue gas of an inert anode electrolysis of aluminum chloride. The recovery and treatment system is arranged at the gas outlet end of an aluminum chloride electrolytic cell 1 with an inert anode. The recovery and treatment system is adapted to the recovery and treatment method, and includes:

[0118] A gas guiding part, including a gas guiding straight pipe 2 and a bifurcated pipe 3. The feeding end of the gas guiding straight pipe 2 is connected to the gas outlet end of the aluminum chloride electrolytic cell 1, and the gas outlet end of the gas guiding straight pipe 2 communicates with the intake end of the bifurcated pipe 3;

[0119] An absorption part, including a first absorption unit 4 and a second absorption unit 5. The feeding end of the first absorption unit 4 communicates with the gas outlet end of the bifurcated pipe 3, and the discharging end of the first absorption unit 4 communicates with the feeding end of the second absorption unit 5.

[0120] The first absorption unit 4 includes a first intake pipe 401, a first outlet pipe 402 and a first absorbent liquid layer 403. The intake end of the first intake pipe 401 communicates with the gas outlet end of the bifurcated pipe 3, the outlet end of the first intake pipe 401 extends into the first absorbent liquid layer 403, the intake end of the first outlet pipe 402 is arranged above the first absorbent liquid layer 403, and the outlet end of the first outlet pipe 402 communicates with the second absorption unit 5.

[0121] The second absorption unit 5 includes a second intake pipe 501, a second outlet pipe 502 and a second absorbent liquid layer 503. The intake end of the second intake pipe 501 communicates with the outlet end of the first outlet pipe 402, the outlet end of the second intake pipe 501 extends into the second absorbent liquid layer 503, and the intake end of the second outlet pipe 502 is arranged above the second absorbent liquid layer 503.

[0122] The absorption part further includes a collection airbag 6, and the collection airbag 6 is arranged at the outlet end of the second outlet pipe 502.

[0123] The recovery and treatment system further includes:

[0124] The cleaning unit includes a ramming rod 8; when the cleaning unit includes the ramming rod 8, the ramming rod 8 is arranged in the direct gas guide pipe 2, and the ramming rod 8 expands and contracts in the direct gas guide pipe 2 to push the electrolyte volatiles adhering in the direct gas guide pipe 2 into the aluminum chloride electrolytic cell 1.

[0125] Example 2

[0126] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0127] The components of the first absorption liquid include saturated sodium chloride solution;

[0128] The components of the second absorption liquid include concentrated sulfuric acid solution;

[0129] S301. If the treatment method of the second treated tail gas is recycling, directly use a conditioning agent to condition the first absorption liquid to obtain a conditioned liquid.

[0130] The temperature of the flue gas is 160 °C.

[0131] The recovery treatment system further includes:

[0132] The cleaning unit includes a backwashing device 7; when the cleaning unit includes the backwashing device 7, the backwashing device 7 is arranged at the gas outlet end of the direct gas guide pipe. Dry chlorine gas is used as the backwashing gas for the backwashing device 7.

[0133] Example 3

[0134] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0135] The components of the first absorption liquid include sodium hydroxide solution;

[0136] The components of the second absorption liquid include sodium hydroxide solution.

[0137] S301. If the treatment method of the second treated tail gas is direct emission, it is necessary to condition the second absorption liquid;

[0138] S302. Mix the first absorption liquid and the second absorption liquid to obtain a mixed absorption liquid;

[0139] S303. Use a conditioning agent to condition the mixed absorption liquid to obtain a conditioned liquid.

[0140] The temperature of the flue gas is 160 °C.

[0141] The recovery treatment system further includes:

[0142] The cleaning unit includes a backwashing device 7; when the cleaning unit includes the backwashing device 7, the backwashing device 7 is arranged at the gas outlet end of the direct gas guide pipe. Dry chlorine gas is used as the backwashing gas for the backwashing device 7.

[0143] Comparative Example 1

[0144] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0145] Do not use the recycling treatment method, that is, do not use the recycling treatment system, and directly recycle the flue gas generated by the electrolysis of aluminum chloride.

[0146] Related experimental and effect data:

[0147] Respectively count the recovery products (mixture of chloride salts and fluoride salts and chlorine gas) of each example, and use the flue gas of the comparative example as the blank control to count the recovery rates of the flue gas components of these examples. The results are shown in Table 1.

[0148] Table 1 Flue gas recovery rate situation table of each example

[0149]

[0150] As can be seen from Table 1, a method for recycling and treating the flue gas of an inert anode for electrolyzing aluminum chloride provided by the embodiment of the present application. Through the two-stage recycling treatment of the first absorption liquid and the second absorption liquid, and then cooperating with the conditioning treatment and evaporation and drying, the materials of the first absorption liquid and the second absorption liquid can be recycled, so as to significantly improve the recovery efficiency of chlorine and fluorine elements in the flue gas to more than 99%.

[0151] In summary, a method for recycling and treating the flue gas of an inert anode for electrolyzing aluminum chloride provided by the embodiment of the present application. Through the process design of hierarchical absorption and selective recovery, and simultaneously optimizing the absorption sequence and reaction conditions, the recovery efficiency of chlorine and fluorine elements in the flue gas is significantly improved.

[0152] In addition, a method for recycling and treating the flue gas of an inert anode for electrolyzing aluminum chloride provided by the embodiment of the present application effectively fills the technical gap in the collection and treatment of the flue gas of an inert anode for electrolyzing aluminum chloride.

[0153] In addition, a method for recycling and treating the flue gas of an inert anode for electrolyzing aluminum chloride provided by the embodiment of the present application can effectively recycle all the chloride salts in the flue gas and will not cause any pollution to the environment.

[0154] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but rather to the broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for recovering and treating flue gas from the electrolysis of aluminum chloride using an inert anode, wherein the flue gas comprises chlorine, hydrogen fluoride, and hydrogen chloride, and the method comprises: The flue gas is subjected to a first recovery treatment using a first absorption liquid to absorb the hydrogen fluoride and hydrogen chloride to obtain a first absorption liquid and a first treated tail gas; wherein the first absorption liquid comprises a sodium hydroxide solution or a saturated sodium chloride solution; Using a second absorption liquid to perform a second recovery treatment on the first treated tail gas to obtain a second absorption liquid and a second treated tail gas; wherein the second absorption liquid comprises a sodium hydroxide solution or a concentrated sulfuric acid solution; determining whether the second absorption liquid needs to be tempered according to the treatment method of the second treated tail gas; If yes, tempering the first absorption liquid and the second absorption liquid with a tempering agent to obtain a tempered liquid; If not, tempering the first absorption liquid with a tempering agent to obtain a tempered liquid; The conditioning solution is evaporated and dried in sequence to obtain a mixture of chloride salt and fluoride salt.

2. The recycling and treatment method according to claim 1, wherein In the case where the first absorption liquid is composed of a sodium hydroxide solution and the second absorption liquid is composed of a sodium hydroxide solution, the second treated tail gas is a harmless gas; or In the case where the component of the first absorption liquid is a saturated sodium chloride solution and the component of the second absorption liquid is a concentrated sulfuric acid solution, the second treated tail gas is chlorine gas.

3. The recycling method according to claim 1, characterized in that: The method of determining whether the second absorption liquid needs to be tempered according to the treatment method of the second treated tail gas comprises the following steps: If the second treated tail gas is directly discharged, the second absorption liquid needs to be tempered; mixing the first absorption liquid and the second absorption liquid to obtain a mixed absorption liquid; Using a conditioning agent to condition the mixed absorption liquid to obtain a tempered liquid; or If the second treated tail gas is to be recycled, the first absorption liquid is directly tempered using a tempering agent to obtain a tempered liquid.

4. The recycling and treatment method according to claim 1, characterized in that, The pH value of the conditioning treatment is greater than 6; and / or The conditioning agent includes sodium hydroxide and / or sodium carbonate.

5. The recycling and treatment method according to claim 1, wherein, The temperature of the flue gas is less than 180°C.

6. A system for recovering and treating flue gas from the electrolysis of aluminum chloride using an inert anode, the system being disposed at the gas outlet of an aluminum chloride electrolytic cell having an inert anode, the system being adapted to the recovery method according to any one of claims 1 to 5, the system comprising: An air guide portion, comprising an air guide straight pipe and a bifurcated pipe, wherein the feed end of the air guide straight pipe is connected to the air outlet end of the aluminum chloride electrolytic cell, and the air outlet end of the air guide straight pipe is connected to the air inlet end of the bifurcated pipe; The absorption part includes a first absorption unit and a second absorption unit, wherein the feed end of the first absorption unit is connected to the gas outlet end of the bifurcated pipe, and the discharge end of the first absorption unit is connected to the feed end of the second absorption unit.

7. The recycling and treatment system according to claim 6, characterized in that, The first absorption unit includes a first intake pipe, a first outlet pipe, and a first absorption liquid layer. The intake end of the first intake pipe is connected to the outlet end of the bifurcated pipe. The outlet end of the first intake pipe extends into the first absorption liquid layer. The intake end of the first outlet pipe is arranged above the first absorption liquid layer, and the outlet end of the first outlet pipe is connected to the second absorption unit.

8. The recycling and treatment system according to claim 6, characterized in that, The second absorption unit includes a second intake pipe, a second outlet pipe, and a second absorption liquid layer. The intake end of the second intake pipe is connected to the outlet end of the first outlet pipe. The outlet end of the second intake pipe extends into the second absorption liquid layer. The intake end of the second outlet pipe is arranged above the second absorption liquid layer.

9. The recycling and treatment system according to claim 8, wherein, The absorption part further includes a collection airbag, and the collection airbag is arranged at the outlet end of the second outlet pipe.

10. The recycling system according to claim 6, characterized in that: The recovery and treatment system further includes: a cleaning unit, including a back-blowing device or a pushing rod; when the cleaning unit includes a back-blowing device, the back-blowing device is arranged at the outlet end of the straight air guide pipe; when the cleaning unit includes a pushing rod, the pushing rod is arranged in the straight air guide pipe, and the pushing rod extends and retracts in the straight air guide pipe to push the electrolyte volatiles adhered to the inside of the straight air guide pipe into the aluminum chloride electrolytic cell.

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