Method for comprehensively recycling secondary aluminum ash and co-producing high-purity hydrogen

Abstract

The invention provides a method for comprehensively recycling secondary aluminum ash and co-producing high-purity hydrogen, which comprises the following steps of: pretreating the secondary aluminum ash by using an ammonium chloride solution, hydrolyzing substances such as aluminum nitride and aluminum carbide in the aluminum ash, dissolving and recycling salt, and increasing the process safety; the waste liquid is recycled for multiple times, evaporative crystallization, carbon reduction and salt recovery are performed, and the utilization efficiency of the sodium element in the alkaline treatment process is improved; and then gas recycling in the aluminum ash hydrolysis process is optimized, low-concentration ammonia water obtained through absorption is used for absorbing carbon dioxide, ammonium chloride is recycled through cyclic accumulation, strong acid absorption is avoided, and the equipment cost is reduced. And performing hydrogen purification on the gas component by adopting pressure swing adsorption until the purity is required by the fuel cell. According to the method provided by the invention, the high-temperature-resistant and corrosion-resistant requirements on equipment in the process of treating the secondary aluminum ash by the alkaline wet method are reduced, sodium elements fed in the process of treating the secondary aluminum ash by the alkaline method and soluble salts in the secondary aluminum ash are fully recycled, harmless treatment of the aluminum ash is realized, and the economic and environment-friendly benefits are outstanding.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment, and in particular, relates to a method for comprehensive recycling of secondary aluminum ash and co-production of high-purity hydrogen. Background Art

[0002] China is the world's largest aluminum producer and consumer. For a long time, China's aluminum production has accounted for more than half of the world's total. The solid waste produced by the oxidation of molten aluminum in contact with air during aluminum electrolysis, regeneration and processing is called aluminum ash. According to statistics, 110 kg of aluminum ash is produced for every ton of aluminum produced. When smelting aluminum metal at high temperature, aluminum will react with O2, N2, CO, etc. at high temperature to produce oxides, nitrides, carbides, etc. Generally speaking, aluminum ash usually contains Al, Al2O3, AlN, magnesium aluminum spinel, metal salts, etc. The harm of aluminum ash mainly lies in nitrides (AlN, FeN, etc.). For example, AlN reacts with water to produce irritating and toxic gas ammonia. Ammonia is irritating and will cause serious air pollution, aggravating the irritation and causing various diseases such as lung infection. Aluminum ash has long been included in the "National Hazardous Substances List" and has been identified as HW48 non-ferrous metal smelting waste.

[0003] The treatment methods of aluminum ash are divided into pyrolysis, wet treatment and combined wet and pyrolysis processes. The core of pyrolysis treatment is to make the reactive active components in the secondary aluminum ash fully react with O2 by heating to eliminate the reactivity of the aluminum ash. The aluminum ash is mixed with limestone and added to the rotary kiln, sintered at 1200~1350℃ to prepare calcium aluminate refining slag for steelmaking: 7Al2O3+12CaCO3=12CaO∙7Al2O3+12CO2. This method requires coal or natural gas as fuel and has high energy consumption. Wet treatment is the most effective method for removing active components from secondary aluminum ash, and it is also the most commonly used harmless treatment method. Wet treatment includes acid leaching and alkaline leaching. The acid leaching method uses a strong acid solution to dissolve all the soluble components in the secondary aluminum ash, and then filters and adds excess sodium hydroxide to the filtrate to make Al 3+It is converted into aluminate, and then goes through pH adjustment precipitation, filtration, calcination and other processes to finally obtain Al2O3 products. The acid method can remove nitrogen and form ammonium salts to avoid the harm of ammonia to people, equipment and the environment, and fully recover the aluminum element. However, the acid method requires a large amount of solvent, resulting in high raw material costs, and alkaline oxides such as Fe and Ca will dissolve into the solution, resulting in complex solution components, cumbersome subsequent purification processes, and a large amount of acidic waste liquid to be treated. The alkaline leaching method adds alkali as a catalyst to catalyze the deammoniation of secondary aluminum ash by water leaching. During the alkaline treatment process, negative trivalent nitrogen evaporates in the form of ammonia, and the ammonia is recovered by the absorption device. When the alkaline leaching method recovers aluminum products, less impurities (mainly Si) are brought in, and the resulting aluminum products have a higher purity, but the recovery rate of aluminum is low, with only about 30% of aluminum entering the solution. If the recovery rate is to be improved, the reaction needs to be carried out under a high temperature, high pressure and high alkali environment. In general, the pyrometallurgical treatment of aluminum ash consumes a lot of energy, and both acid and alkali methods have their own advantages and disadvantages. Summary of the invention

[0004] In view of the problems of acid leaching treatment with large amount of waste liquid, alkaline leaching treatment with large consumption of sodium hydroxide, low aluminum extraction rate, low ammonia concentration, and low efficiency of combustible gas recovery in wet treatment, a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen was proposed. Compared with the traditional alkaline wet process, this process has the advantages of high safety, less three wastes, diversified products, and high element recovery rate.

[0005] To solve the above problems, the technical solution of the present invention is as follows:

[0006] A method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0007] Step S1, raw material preparation process, using a grinder to grind the secondary aluminum ash, grinding the large particles agglomerated in the aluminum ash, the particle size of the ground secondary aluminum ash is 60-100 mesh, increasing the reaction contact area, and using a magnetic suction device to recover the magnetic iron element in the aluminum ash;

[0008] Step S2, a first-stage hydrolysis process, wherein the aluminum ash treated in step S1 is transported into a reactor through a pipe chain, and then an ammonium chloride solution at 50-80° C. is added, and a hydrolysis reaction is carried out for 1-3 hours under stirring, and an acid pretreatment is carried out to remove some active substances, improve the purity of hydrogen during the second-stage hydrolysis, and recover the soluble salt in the aluminum ash at the same time, and the reaction liquid is simply filtered and recovered into a salt solution storage tank;

[0009] Step S3, a second-stage hydrolysis process, when the temperature in the reactor drops to 25-30°C, a sodium hydroxide solution is pumped into the reactor, and a hydrolysis reaction is carried out for 2-6 hours under stirring, and circulating water is used for heat transfer, and the reaction temperature is controlled not to be higher than 90°C; the process is carried out under a slight positive pressure to prevent air from entering the system and causing an explosion;

[0010] Step S4, filtering process, when the hydrolyzed slurry is cooled to below 45°C, it is sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery;

[0011] Step S5, a dealkalization process, introducing CO2 gas into the filtrate obtained in step S4 to make the solution pH <11, and filtering and recovering the aluminum hydroxide product using a plate and frame filter;

[0012] Step S6, a concentration and carbonization process, wherein CO2 gas and ammonia gas are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated ammonium chloride solution are recovered by evaporation and crystallization;

[0013] Step S7, tail gas recovery process, for the gas phase components after the reaction, use the low concentration of ammonium chloride solution in the brine storage tank to absorb ammonia and reduce the temperature; the mixed gas mainly composed of hydrogen, methane and nitrogen is purified by pressure swing adsorption to obtain high-purity hydrogen, with high-quality hydrogen as the product, and low-quality exhaust gas is burned for heat supply.

[0014] Furthermore, in step S2, the ammonium chloride solution includes ammonium chloride, ammonia water, and sodium chloride, and is obtained from a brine storage tank. The mass fraction of ammonium chloride in the ammonium chloride solution is not less than 1%; the mass ratio of the ammonium chloride solution put into the reactor to the aluminum ash is 2-4:1.

[0015] Furthermore, in step S3, the sodium hydroxide solution is recycled for 3 to 5 times, and the solutes contained are NaOH, NaAlO2, and NH3; the NaOH concentration in the sodium hydroxide solution used should be greater than 2.5 mol / L, and the mass ratio of the added sodium hydroxide solution to the aluminum ash is 2 to 5:1.

[0016] Furthermore, in step S3, the slightly positive pressure condition refers to being 1-10 kPa higher than the standard atmospheric pressure.

[0017] Furthermore, in step S6, the heat required for the evaporation and crystallization is provided by the by-product H2 and CH4 mixed gas; the ammonia gas is preferably a low-concentration ammonia water produced by the absorption tower.

[0018] Furthermore, in step S7, the solution in the brine storage tank is used to absorb ammonia and cool down, the mass fraction of ammonium chloride in the solution is less than 1%, the solution temperature is preferably 20-30°C, and the volume liquid-to-gas ratio of the solution in the brine storage tank to ammonia is 3-7:1.

[0019] The mechanism of the present invention includes:

[0020] The method provided by the present invention first uses an acidic ammonium chloride solution to consume a portion of the active components of aluminum ash, dissolve and extract the soluble salts in the aluminum ash, and then uses a high-concentration sodium hydroxide solution for efficient denitrification and aluminum extraction, completely converting AlN into aluminate and ammonia, and converting the aluminum element in the aluminum ash into the form of aluminic acid. After the recovered high-pH filtrate is used multiple times, it is passed through carbon dioxide for treatment, and the aluminate is completely converted into aluminum hydroxide. Finally, carbon dioxide and low-concentration ammonia water are added to produce sodium bicarbonate to recover the sodium element, and a low-solubility ammonium chloride solution is produced to recover chlorine and nitrogen. The hydrogen-rich gas produced by hydrolysis is further purified by pressure swing adsorption.

[0021] The above method involves the following reactions:

[0022] Al2O3+NaOH→NaAlO2+ H2O

[0023] Al + NaOH → H2↑ + NaAlO2

[0024] AlN+NaOH→NH3↑+NaAlO2

[0025] NaAlO2+CO2→Na2CO3+ Al(OH)3↓

[0026] Na2CO3+CO2+ H2O→2NaHCO3

[0027] NaCl+NH3+CO2→NaHCO3↓+ NH4Cl

[0028] Due to the addition of the first-stage hydrolysis, the reactive components in the aluminum ash are reduced, the second-stage hydrolysis reaction releases less heat, the temperature is easier to control, and it is more convenient for large-scale production. The sodium and chlorine elements added to the reaction system are recovered, the production efficiency is improved, and it is more environmentally friendly. The ammonia absorption tower uses the solution recovered from the salt liquid storage tank instead of the traditional sulfuric acid, which reduces equipment corrosion and production costs. The entire process can obtain high-quality aluminum hydroxide, hydrogen, and sodium bicarbonate, with good economic benefits and broad prospects for industrial application.

[0029] The recovered high pH filtrate contains NaOH, NaAlO2, and NH3. During the hydrolysis of aluminum ash, the pure sodium hydroxide solution reacts violently with the aluminum ash. NaAlO2 and NH3 can play a certain buffering role on the pH of the system, so that the pH of the system is maintained in a relatively stable range, which is conducive to the continuous hydrolysis of aluminum ash and reduces local overheating, thereby reducing the safety risks that may be caused by excessive reaction, such as solution splashing. In addition, the presence of sodium metaaluminate can promote the dissolution and reaction of aluminum in aluminum ash. Under appropriate conditions, it can react with some insoluble aluminum compounds in aluminum ash to convert more aluminum into soluble aluminate forms, thereby improving the recovery rate of aluminum. NH3 may also react with some impurities in aluminum ash (such as metal ions forming complexes, etc.), so that aluminum and impurities are better separated, which is conducive to improving the purity and recovery rate of aluminum.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) The present invention reduces the reaction temperature of the secondary aluminum ash alkali treatment reaction by a two-stage reaction method, thereby increasing the reaction ignition point and reducing the heat transfer burden.

[0032] (2) The present invention uses a new process concept to utilize the waste liquid generated in the original alkali leaching process, thereby achieving efficient recovery of sodium, chlorine, aluminum and ammonia nitrogen.

[0033] (3) The present invention optimizes the ammonia absorption process and uses ammonium chloride solution to absorb ammonia. Different from the existing aluminum ash nitrogen resource utilization method, it achieves high-quality recovery of nitrogen resources without increasing operating costs and equipment costs.

[0034] (4) The present invention adds a high-quality hydrogen recovery process, greatly improves the purity of the recovered hydrogen, and increases the product value.

[0035] (5) The present invention recycles and utilizes the generated carbon dioxide, which meets the needs of the national dual carbon strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the method provided by the present invention

[0037] Figure 2 The main process flow diagram of the present invention is

[0038] Figure 3 This is a schematic diagram of the triple-effect evaporation crystallization process of the present invention.

[0039] Figure 4 Schematic diagram of dual-bed pressure swing adsorption model DETAILED DESCRIPTION

[0040] In order to make researchers more clearly understand the technical solutions and technical advantages of the present invention, the present invention will be described in detail below in conjunction with the embodiments. It is particularly noted that the embodiments are only used to clearly and completely describe the present invention and should not be regarded as limiting the scope of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0043] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, taking the secondary aluminum ash between 60 and 100 meshes after grinding, and using a magnetic suction device to recover the magnetic iron element in the secondary aluminum ash.

[0044] S2: A hydrolysis process, the secondary aluminum ash treated by S1 is transported into the reactor through a pipe chain, and then a 70°C, 1wt% ammonium chloride solution is added. The mass ratio of the added ammonium chloride solution to the aluminum ash is 2:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 1 hour. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salt in the aluminum ash dissolves in the reaction solution, and the mass loss rate of the aluminum ash is 7~15% (the statistical results of 6 experiments are due to the differences in the component content in the aluminum ash).

[0045] S3: Secondary hydrolysis process, when the temperature in the reactor drops to 28°C, simple filtration and separation are performed. After N2 is introduced for oxygen replacement, a 5 mol / L sodium hydroxide solution at room temperature is pumped into the reactor. The mass ratio of the added sodium hydroxide solution to the aluminum ash is 5:1. The hydrolysis reaction is carried out for 2 hours under stirring. Circulating water is used for heat transfer. The temperature of the reactor is controlled below 90°C to obtain a completely hydrolyzed slurry. The reaction is carried out under a slight positive pressure (106.4 kPa) to prevent air from entering the system and causing an explosion. The gas composition collected after the reaction and ammonia removal is H2:CH4:N2=90.89%:0.75%:8.36%.

[0046] S4: Filtration process: the hydrolyzed slurry is cooled to 40°C and sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery.

[0047] S5: dealkalization process, slowly introducing CO2 gas into the filtrate obtained in step S4 to make the solution pH <11, after standing and settling, using a plate and frame filter to filter and recover the aluminum hydroxide product.

[0048] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0049] S7: Tail gas recovery process, for the gases NH3, H2, CH4, water vapor and exhaust nitrogen produced by the second stage hydrolysis, the following method is used to separate them: for NH3, use 20℃, 0.5wt% ammonium chloride solution for absorption, with a volume liquid-to-gas ratio of 6:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen, the waste gas is used for combustion and heating, and the carbon dioxide is used for S5 and S6 processes.

[0050] Example 2

[0051] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0052] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, taking the secondary aluminum ash between 60 and 100 meshes after grinding, and using a magnetic suction device to recover the magnetic iron element in the secondary aluminum ash.

[0053] S2: a hydrolysis process, the aluminum ash treated in step S1 is transported into the reactor through a pipe chain, and then a 1.5wt% ammonium chloride solution is added at 60°C, and the mass ratio of the added ammonium chloride solution to the aluminum ash is 2.5:1. No external heating treatment is performed, and the hydrolysis reaction is carried out for 2 hours under stirring. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salt in the aluminum ash dissolves in the reaction solution, and the mass loss rate of the aluminum ash is 6-14%.

[0054] S3: Secondary hydrolysis process, wait for the temperature in the reactor to drop to 28°C, and then filter and separate simply. Add NaOH to the sodium hydroxide solution (containing NaOH, NaAlO2, and NH3) recovered in step S3 to obtain a 4 mol / L sodium hydroxide solution, which is transported into the reactor by a pump. The mass ratio of the added sodium hydroxide solution to the aluminum ash is 4:1. The hydrolysis reaction is carried out for 3 hours under stirring, and circulating water is used for heat transfer. The temperature of the reactor is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (106.3 kPa) to prevent air from entering the system and causing an explosion. The gas composition collected after the reaction and ammonia removal is H2:CH4:N2=92.46%:0.67%:6.87%.

[0055] S4: Filtration process: the hydrolyzed slurry is cooled to 38°C and sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery.

[0056] S5: de-alkali process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0057] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0058] S7: Tail gas recovery process, for the gases NH3, H2, CH4, water vapor and exhaust nitrogen produced by the second stage hydrolysis, the following method is used to separate: for NH3, use 25℃, 0.2wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 7:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen, the waste gas is used for combustion and heating, and the carbon dioxide is used for S5 and S6 processes.

[0059] Example 3

[0060] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0061] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, taking the secondary aluminum ash between 60 and 100 meshes after grinding, and using a magnetic suction device to recover the magnetic iron element in the secondary aluminum ash.

[0062] S2: a hydrolysis process, the aluminum ash treated in step S1 is transported to the reactor through a pipe chain, and then the ammonium chloride solution (ammonium chloride, ammonia water mixture) recovered from step S7 is added, 60°C, 1wt%, the mass ratio of the added ammonium chloride solution to the aluminum ash is 3:1, no external heating treatment is performed, and the hydrolysis reaction is carried out for 3 hours under stirring. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salt in the aluminum ash dissolves in the reaction solution, and the mass loss rate of the aluminum ash is 5-15%.

[0063] S3: Secondary hydrolysis process, wait for the temperature in the reactor to drop to 25°C, and then filter and separate simply. A 3 mol / L sodium hydroxide solution at room temperature is pumped into the reactor, and the mass ratio of the added sodium hydroxide solution to the aluminum ash is 2:1. The hydrolysis reaction is carried out for 6 hours under stirring, and circulating water is used for heat transfer. The temperature of the reactor is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (106.1 kPa) to prevent air from entering the system and causing an explosion. The gas composition collected after the reaction and ammonia removal is H2:CH4:N2=90.97%:0.83%:9.2%.

[0064] S4: Filtration process: the hydrolyzed slurry is cooled to 38°C and sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery.

[0065] S5: de-alkali process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0066] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0067] S7: Tail gas recovery process, for the gases NH3, H2, CH4, water vapor and exhaust nitrogen produced by the second-stage hydrolysis, the following method is used to separate them: for NH3, use 20℃, 0.1wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 5:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen, the waste gas is used for combustion and heating, and the carbon dioxide is used for S5 and S6 processes.

[0068] Example 4

[0069] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0070] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, taking the secondary aluminum ash between 60 and 100 meshes after grinding, and using a magnetic suction device to recover the magnetic iron element in the secondary aluminum ash.

[0071] S2: A hydrolysis process, the aluminum ash treated by S1 is transported to the reactor through a pipe chain, and then the ammonium chloride solution recovered from the S7 process is added, 55°C, 2wt%, the mass ratio of the added ammonium chloride solution to the aluminum ash is 4:1, no external heating treatment is done, and the hydrolysis reaction is carried out for 2 hours under stirring. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salt in the aluminum ash dissolves in the reaction solution. The mass loss rate of aluminum ash is 5~11%.

[0072] S3: Secondary hydrolysis process, wait for the temperature in the reactor to drop to 30°C, and then filter and separate simply. Add NaOH to the sodium hydroxide solution (containing NaOH, NaAlO2, and NH3) recovered in step S3 to obtain a 3 mol / L sodium hydroxide solution, which is transported by a pump and added to the reactor. The mass ratio of the added sodium hydroxide solution to the aluminum ash is 3:1. The hydrolysis reaction is carried out for 4 hours under stirring, and circulating water is used for heat transfer. The reaction temperature is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (104.67 kPa) to prevent air from entering the system and causing an explosion. The gas composition collected after the reaction and ammonia removal is H2:CH4:N2=91.67%:0.53%:7.8%.

[0073] S4: Filtration process: the hydrolyzed slurry is cooled to 43°C and sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery.

[0074] S5: de-alkali process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0075] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0076] S7: Tail gas recovery process, for the gases NH3, H2, CH4, water vapor and exhaust nitrogen produced by the second-stage hydrolysis, the following method is used to separate them: for NH3, use 20℃, 0.3wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 3:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen, the waste gas is used for combustion and heating, and the carbon dioxide is used for S5 and S6 processes.

[0077] Comparative Example 1

[0078] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, taking the secondary aluminum ash between 60 and 100 meshes after grinding, and using a magnetic suction device to recover the magnetic iron element in the secondary aluminum ash.

[0079] S2: A hydrolysis process, the aluminum ash treated in S1 is transported to the reactor through a pipe chain, and then 70°C water is added. The mass ratio of the added water to the aluminum ash is 2:1. No external heating treatment is performed, and the hydrolysis reaction is carried out for 1 hour under stirring.

[0080] Phenomenon: After adding the 70℃ aqueous solution, the temperature continued to rise within 20 minutes, and at 22 minutes, the temperature rose to 175℃.

[0081] Table 1 Hydrogen content and aluminum ash mass loss rate in Examples 1-4

[0082] Hydrogen content (%) Aluminum ash mass loss rate (%) Example 1 90.89 7~ 15 Example 2 92.46 6~ 14 Example 3 90.97 5~ 15 Example 4 91.67 5~ 11

[0083] The above results show that: Examples 1 to 4 reflect the different effects of secondary aluminum ash hydrolysis under different conditions. The results show that the two-stage wet treatment of aluminum ash is beneficial to controlling the reaction temperature of the secondary aluminum ash alkali treatment reaction, so that the reaction ignition point is increased and the heat transfer burden is reduced. The first-stage hydrolysis process is beneficial to the hydrolysis of active substances such as aluminum nitride and aluminum carbide, thereby improving the purity of hydrogen in the second-stage hydrolysis. The purity of hydrogen produced after adding sodium hydroxide solution can reach more than 90%.

[0084] Pressure swing adsorption tail gas treatment and purification

[0085] For the gas components in Examples 1 to 4, Aspen Adsorption was used to perform numerical simulation analysis using a dual adsorption bed pressure swing adsorption process to create two parallel adsorption beds to simulate the purification of hydrogen to the standard for fuel cell proton membrane hydrogen.

[0086] Ⅰ. Bed 1 feed pressurization and bed 2 depressurization (Pressurization Bed1, Depressurization Bed2): The feed gas will be introduced into the adsorption bed Bed1 through the air inlet valve F1, and the pressure in the adsorption bed will gradually increase from the pressure after the pressure equalization stage to the adsorption pressure. The waste gas in the adsorption bed Bed2 will be discharged from the waste gas outlet W2. The pressure will drop rapidly to atmospheric pressure, and the impurity gas in the adsorption bed will also be desorbed from the adsorbent due to the pressure drop and flow out from the waste gas outlet.

[0087] Ⅱ. Adsorption Bed 1, Purge Bed 2: In this process, the pressure in the adsorption bed is the higher pressure formed after the feed gas is introduced, and the adsorption bed maintains this pressure unchanged during the entire adsorption process. As the adsorption process proceeds, a large amount of impurity gas will be absorbed into the pores of the adsorbent to complete the purification of hydrogen. Hydrogen with low adsorption will flow out of the adsorption bed, part of which will be enriched at the Product outlet, and the other part will flow to Bed 2 for flushing.

[0088] Ⅲ. Pressure equalization (PPE): Close all valves except the purge valve. The gas in the adsorption bed will flow automatically due to the pressure difference between the two towers. The pressure in the adsorption bed Bed1 with a higher pressure will decrease, and the pressure in the adsorption bed Bed2 will increase, and finally the pressure equalization will be completed.

[0089] IV. Bed 2 Feed Pressurization Bed 1 Depressurization (Pressurization Bed2, Depressurization Bed1): The feed gas will be introduced into the adsorption bed Bed2 through the air inlet valve F2, and the pressure in the adsorption bed will gradually increase from the pressure after the pressure equalization stage to the adsorption pressure. The waste gas in the adsorption bed Bed2 will be discharged from the waste gas outlet W2. The pressure will drop rapidly to atmospheric pressure, and the impurity gas in the adsorption bed will also be desorbed from the adsorbent due to the pressure reduction and flow out from the waste gas outlet.

[0090] V. Bed 2 Adsorption Bed 1 Purge (Adsorption Bed2, Purge Bed1): In this process, the pressure in the adsorption bed is the higher pressure formed after the feed gas is introduced, and the adsorption bed maintains this pressure unchanged during the entire adsorption process. As the adsorption process proceeds, a large amount of impurity gas will be absorbed into the pores of the adsorbent to complete the purification of hydrogen. Hydrogen with low adsorption will flow out of the adsorption bed, part of which will pass through P2 to the product tank, and the other part (determined by the purge ratio) will flow to Bed1 to flush it.

[0091] Ⅵ. Pressure equalization (PPE): Close all valves except the purge valve. The gas in the adsorption bed will flow automatically due to the pressure difference between the two towers. The pressure in the adsorption bed Bed1 will rise and eventually the pressure equalization will be completed.

[0092] The initial stage of the cycle is the adsorption step, in which the adsorbent adsorbs the mixed gas. Therefore, the pressure of the adsorption bed will be kept at an adsorption pressure of 10 bar. Then the second stage of the pressure reduction pressure equalization step is entered. The two adsorption beds with different pressures are equalized through the valve, and the pressure of the adsorption bed Bed1 is reduced. The third step is the purge. The exhaust valve connected to the outside is opened, and the pressure is rapidly reduced to atmospheric pressure. The residual impurity gas in the adsorption bed is desorbed and flows into the exhaust tank through the exhaust valve. The fourth stage is flushing. The other adsorption bed is in the adsorption stage at this time. Part of the generated hydrogen flows into the adsorption bed through the valve, flushing out the remaining impurity gas and filling the adsorption bed with hydrogen, which can be reused. The pressure in this stage is kept at atmospheric pressure, and the exhaust valve is kept open. The fifth stage is the boost pressure equalization. In contrast to the pressure reduction pressure equalization step, the gas in the adsorption bed increases due to the equalization. Finally, it is the feed pressurization stage. A large amount of feed gas enters the adsorption bed through the valve, and the gas in the bed also rises back to the adsorption pressure of 10 bar, so that a cycle ends.

[0093] Example 5

[0094] A three-component mixed gas (H2:CH4:N2=84.67:0.53:14.8) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.15, the adsorption time was 3 s and the temperature was 298.15 K.

[0095] Example 6

[0096] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 3 s and the temperature was 298.15 K.

[0097] Example 7

[0098] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.25, the adsorption time was 3 s and the temperature was 298.15 K.

[0099] Example 8

[0100] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 5 s and the temperature was 298.15 K.

[0101] Example 9

[0102] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 7 s and the temperature was 298.15 K.

[0103] Example 10

[0104] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 15 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 3 s and the temperature was 298.15 K.

[0105] Table 2 Activated carbon adsorption bed purification performance parameters in Examples 5 to 10

[0106] Hydrogen purity% Hydrogen yield% Example 5 96.734 71.31 Example 6 99.995 64.35 Example 7 98.853 64.08 Example 8 98.943 61.52 Example 9 98.858 64.08 Example 10 99.996 52.51

[0107] The above results show that: Examples 5 to 10 reflect the results of pressure swing adsorption of secondary aluminum ash hydrolysis gas under different conditions. The results show that under the conditions of adsorption pressure of 10 bar, P / F ratio of 0.2, and adsorption time of 3 s, a gas separation effect of hydrogen purity greater than 99.99% and a yield of 64.35% was achieved, which meets the standard of GB / T 34872-2017 "Technical Requirements for Hydrogen Supply Systems of Proton Exchange Membrane Fuel Cells" and achieves high-value recovery of aluminum ash wet gas production.

[0108] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, characterized in that: The following steps are involved: Step S1, a raw material preparation process, using a grinder to grind the secondary aluminum ash, grinding the large particles agglomerated in the aluminum ash to increase the reaction contact area, and using a magnetic suction device to recover the magnetic iron element in the aluminum ash; Step S2, a hydrolysis process, the secondary aluminum ash treated in step S1 is transported into a reactor through a pipe chain, and then an ammonium chloride solution at 50-80°C is added to perform a hydrolysis reaction under stirring, at which time part of the aluminum, aluminum carbide, and aluminum nitride react with water, the generated ammonia gas dissolves in the reaction solution, and the soluble salt in the aluminum ash dissolves in the reaction solution, and the reaction solution is filtered and recovered into a salt solution storage tank; Step S3, a second-stage hydrolysis process, when the temperature in the reactor drops to 25-30°C, a sodium hydroxide solution is pumped into the reactor, and a secondary hydrolysis reaction is carried out under stirring, and circulating water is used for heat transfer, and the reaction temperature is controlled not to be higher than 90°C; the process needs to be carried out under a slight positive pressure to prevent air from entering the system and causing an explosion; Step S4, filtering process, the slurry after hydrolysis in step S3 is cooled and sent to a vacuum rotary filter, the solid is recovered, and the filtrate is sent to the next stage for further recovery; Step S5, a dealkalization process, introducing carbon dioxide gas into the filtrate obtained in step S4 to make the solution pH <11, and filtering and recovering the aluminum hydroxide product using a plate and frame filter; Step S6, a concentration process, introducing carbon dioxide gas and ammonia gas into the filtrate obtained in step S5, evaporating and crystallizing to recover the sodium bicarbonate product and the concentrated ammonium chloride solution; Step S7, the tail gas recovery process, for ammonia, use the solution in the brine storage tank to absorb it to increase the mass fraction of ammonia nitrogen in the absorption liquid; for hydrogen, after drying and removing water, use pressure swing adsorption technology to continuously produce new energy green hydrogen products.

2. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S1, the particle size of the ground secondary aluminum ash is 60-100 mesh.

3. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S2, the ammonium chloride solution comes from a brine storage tank, the mass fraction of ammonium chloride in the ammonium chloride solution is required to be not less than 1%, and the mass ratio of the added ammonium chloride solution to the secondary aluminum ash is 2-4:

1.

4. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S2, the primary hydrolysis reaction takes 1 to 3 hours.

5. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S3, the NaOH concentration in the sodium hydroxide solution should be no less than 2.5 mol / L, the sodium hydroxide solution is recycled, the number of recycling times is 3 to 5 times, and the mass ratio of the added sodium hydroxide solution to the secondary aluminum ash is 2 to 5:

1.

6. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S3, the secondary hydrolysis reaction time is 2 to 6 hours; the slightly positive pressure refers to being 1 to 10 kPa higher than the standard atmospheric pressure.

7. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S4, the temperature of the slurry fed into the vacuum rotary filter should be lower than 45°C.

8. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S7, the volume liquid-gas ratio of the solution in the brine storage tank to the ammonia gas is 3-7:

1.

9. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S7, the high-quality hydrogen produced by the pressure swing adsorption technology can be used in fuel cells, and the low-quality hydrogen is used for combustion and heat generation.

Images