Process for continuous hydrolysis of aluminum dross and purification of off-gas

Abstract

The application discloses a kind of aluminum ash slag continuous hydrolysis and tail gas recovery purification process, belong to electrolytic aluminum solid waste treatment technical field, including raw material slurry, hydrolysis, cooling, filtration, solid fluorine and so on Process system, still including auxiliary tail gas washing, tail gas recovery purification, dust removal, waste water recycling, circulating cooling water system, refrigeration system and so on Process unit;The application realizes not to block, continuous automatic operation, self purification eliminates three waste pollution, also has the characteristics of low energy consumption, process equipment mature, high feasibility.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic aluminum solid waste treatment technology, specifically relating to a continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag. Background Technology

[0002] Aluminum ash slag is a hazardous solid waste generated during electrolysis, aluminum processing, and recycled aluminum processing. It has a low aluminum content, complex impurities, high treatment costs, and is difficult to utilize comprehensively. In 2021, aluminum ash slag was listed as hazardous waste in the revised National Hazardous Waste List. The harmless disposal and resource utilization of aluminum ash slag is becoming a new opportunity and challenge for the aluminum profile industry.

[0003] Early high-temperature methods had high energy consumption issues and could not meet the requirements for harmless disposal. Currently, the preferred approach is to use a wet process for aluminum ash slag treatment, which generates high-alumina materials, ammonia water, and combustible gases, thus achieving full utilization of resources.

[0004] High-alumina materials can be sold to ceramic material factories, brick factories, and accelerator manufacturers, replacing bauxite in the production of ceramics, building materials, cement accelerators, and other products, offering significant economic and social benefits. Ammonia is an important basic chemical raw material with a wide range of applications. The recovered hydrogen can be used as fuel to partially replace natural gas in heating heat transfer oil, and in the long term, membrane filtration can be used to recover pure hydrogen as a green hydrogen energy feedstock. This project achieves zero emissions of wastewater, waste, and exhaust gas throughout the entire process, with an aluminum ash resource utilization rate exceeding 95%, thus extending the green industrial chain.

[0005] Research and development of wet processes are in full swing across various regions. The applicant has been deeply involved in waste treatment for many years and has accumulated rich experience. It has developed a continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag. This invention achieves non-clogging, continuous automatic operation, self-purification to eliminate pollution from waste gas, wastewater, and solid waste, and also features low energy consumption, mature process equipment, and high feasibility.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag includes the following process steps:

[0009] S1: Raw material preparation section, after the generated screen ash and secondary aluminum ash are collected, they are temporarily stored in the transfer silo and then transported to the high-level silo by tubular chain conveyor;

[0010] S2: Hydrolysis section. The aluminum ash raw material collected in step S1 is added to the slurry mixing tank, and then water is added. The mixing tank is stirred at room temperature, and the slurry pump circulates simultaneously, automatically controlling the slurry delivery to the hydrolysis tank. Heat transfer oil is introduced into the jacket of the hydrolysis tank for heating, and the temperature is controlled at 90-100℃. The hydrolysis reaction is carried out under stirring, and the slurry pump circulates simultaneously. A large amount of heat is released during hydrolysis, and the system automatically adjusts the flow rate of heat transfer oil to maintain a constant temperature. The hydrogen-containing and ammonia-containing water vapor exhaust gas discharged from the hydrolysis tank is sent to the exhaust gas recovery and purification device. When the liquid level in the hydrolysis tank rises, the slurry is automatically pumped to the series-connected hydrolysis tanks for continuous hydrolysis. The hydrolysis reaction residence time is 2-5 hours, and the hydrolyzed slurry is obtained.

[0011] S3: Filtration section, the hydrolyzed slurry obtained in step S2 is sent to the cooling kettle for cooling at a temperature of 45-60℃, and then automatically sent to the vacuum rotary filter. The high-alumina material obtained by separation is transported to the warehouse by belt for storage, and the filtrate is sent to the S4 section for further processing.

[0012] S4: In the solid fluoride section, the filtrate obtained in step S3 is added to calcium oxide powder for reaction. After being filtered and separated by a vertical centrifuge, calcium fluoride is obtained and transported to the warehouse by conveyor belt for storage. The filtrate is sent to the production circulating water tank. The circulating water is pressurized by a pump and sent to the hydrolysis preparation kettle in the S2 hydrolysis section for recycling. If it is insufficient, tap water is added externally.

[0013] S5: Tail gas recovery and purification section, the hydrogen-containing and ammonia-containing water vapor tail gas discharged from the hydrolysis kettle in step S2 is sent to the tail gas recovery and purification device, the ammonia recovery rate reaches 90-95%, and the by-products are ammonia water, diammonium phosphate solution or ammonium sulfate solution. After being washed with phosphoric acid or sulfuric acid, the residual ammonia is reduced to less than 20PPM and then sent to the heat transfer oil combustion furnace for use, or further purified for use as new energy green hydrogen.

[0014] S6: Treatment of waste gas, wastewater, and solid waste.

[0015] Waste liquid - Wastewater, water treatment wastewater and other production wastewater generated in the S2 hydrolysis process can all be reused in the hydrolysis reactor. All impurities in the water are sold with the filter cake, and there is no production wastewater discharge.

[0016] The exhaust gas is generated during the filter, powder conveying, and product loading and unloading, producing particulate matter and ammonia-containing gas. The thermal oil furnace burns natural gas, producing sulfur dioxide, nitrogen oxides, and particulate matter. All of the exhaust gases are recovered, purified, and discharged in compliance with standards.

[0017] The high-alumina filter cake and calcium fluoride filter cake produced in the waste residue-S3 section can be recycled by third parties.

[0018] Furthermore, in step S2, the mass ratio of aluminum ash raw material to water is 1:4-6.

[0019] Furthermore, in step S2, the venting of each hydrolysis vessel is carried out under a slight positive pressure to prevent air from entering the system and causing hydrogen to mix with air and reach the explosion limit.

[0020] Furthermore, the continuous hydrolysis in step S2 and the tail gas recovery and purification section in step S5 are controlled by PLC with full automation, requiring no manual intervention.

[0021] Furthermore, in step S4, the reaction is considered complete when the fluoride ion content is found to be lower than the industry standard after the fluoride ion removal.

[0022] Furthermore, the exhaust gas recovery and purification device in step S5 includes an exhaust gas pre-condensation purification unit, a rapid condensation unit, a concentrated ammonia recovery unit, a dilute ammonia recovery unit, an exhaust gas purification tower, and an acid washing purification tower.

[0023] Furthermore, the rapid condensation unit adopts a fully welded corrugated plate falling film condenser; the concentrated ammonia recovery unit adopts a fully welded corrugated plate falling film absorber; and the tail gas purification tower adopts a multi-section structured corrugated wire mesh packed tower.

[0024] The beneficial effects of the present invention are: (1) The present invention adopts a continuous hydrolysis process, changing from a single hydrolysis operation in multiple reactors to a continuous operation in multiple reactors, making the hydrolysis more thorough. In the hydrolysis reaction, the reactivity of aluminum nitride and elemental aluminum powder in aluminum ash with water is eliminated, and the automation level of the hydrolysis device is greatly improved. The continuous operation mode eliminates the possibility of scabbing and pipe blockage by the slurry without dead angle flow, and also eliminates the changes in temperature and reduces start-up and shutdown, resulting in significant energy saving and improved equipment reliability.

[0025] (2) In step S1, the present invention uses a tubular chain conveyor for transportation, which will not cause blockage or generate gas. In step S2, the slurry preparation, hydrolysis and cooling processes are all carried out without interruption by mechanical stirring, slurry circulation and subsequent delivery. The slurry pump is used for circulation, there are no dead corners in the system, eliminating the blockage of deposits and scale, and the production conditions are naturally maintained, so as to achieve unattended fully automatic operation and greatly improve efficiency. Moreover, the air entrained in the aluminum ash will not enter the hydrogen-containing tail gas generated by subsequent hydrolysis, ensuring safety. The aluminum ash slurry preparation is carried out in batches at room temperature, with short time and less hydrolysis reaction. Moreover, the water vapor eliminates the blockage of the aluminum ash feeding device, which also ensures the production conditions.

[0026] (3) The continuous operation of the filtration equipment in this invention reduces the number of equipment and directly jumps from the time-consuming and labor-intensive working mode of manual multi-pot intermittent material discharge filtration to a fully automated continuous operation with two disc vacuum filtration equipment operating and one on standby; and the moisture content of the filtered solid material is stable, as low as 15% and controllable.

[0027] (4) The tail gas recovery and purification device used in this invention includes a tail gas pre-condensation purification unit, which can condense a portion of the water vapor in the tail gas and use it as a washing liquid for cyclic washing, and control its return to the hydrolysis unit. It can also adjust the water balance function of the ammonia recovery system, intercept the aluminum ash carried out in the reaction vessel and return it to the slurry preparation process, ensuring the quality of the recovered ammonia water and preventing blockage of the tail gas purification system. The fast condensation unit uses a corrugated plate falling film condenser to condense water vapor at room temperature, reducing the cooling energy consumption for obtaining high-concentration ammonia water in the low-temperature high-concentration zone. The concentrated ammonia recovery unit adopts a fully welded corrugated plate falling film absorber, which integrates residual cooling recovery and low-temperature subcooling functions. It can quickly advance the absorption process to near gas-liquid equilibrium. The ammonia recovery efficiency in this unit reaches 65-75%, reducing the recovery load of the dilute ammonia recovery unit. Moreover, the recovered ammonia water concentration reaches more than 20%, which can be sold as an industrial product. The exhaust gas emission meets the national standard GB14554-93, the exhaust gas vent pipe emission height is 15-25m, and the total ammonia content in the exhaust gas can be as low as 0.5 kg / hour, which is lower than the national standard of 4.9 kg / hour.

[0028] The emission standards for odorous pollutants are shown in the table below.

[0029] Table 1

[0030]

[0031] The main reactions that occur in the hydrolysis reactor in this invention are as follows:

[0032] AlN + 3H2O == Al(OH)3↓ + NH3↑ (Main reaction)

[0033] Na₂O + H₂O == 2NaOH (side reaction)

[0034] K2O + H2O == 2KOH (side reaction)

[0035] 2Al + 6H₂O == 2Al(OH)₃↓ + 3H₂↑ (Side reaction)

[0036] 2NaOH + Al₂O₃ == 2NaAlO₂ + H₂O (side reaction)

[0037] 2Al + 2NaOH + 2H2O == 2NaAlO2 + 3H2↑ (side reaction)

[0038] 2NaF•SiF4 + H2O + 4NaOH == 6NaF + SiO2 + 3H2O (side reaction)

[0039] During hydrolysis, soluble NaCl and NaF in the aluminum ash also dissolve into the aqueous solution. The final filtrate after filtration consists of NaCl, NaF, NaAlO2, NaOH, and NH4+. 4+ composition.

[0040] The main reaction equations for the solid fluorine process in this invention are as follows:

[0041] Ca ++ + 2F - === CaF2. Attached Figure Description

[0042] Figure 1 This is a flow chart of the hydrolysis section;

[0043] Figure 2 This is a flowchart of the filtration section;

[0044] Figure 3 This is a flow chart for the exhaust gas scrubbing section. Detailed Implementation

[0045] To better understand the present invention, the embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Example

[0046] A continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag includes the following process steps:

[0047] S1: Raw material preparation section, after the generated screen ash and secondary aluminum ash are collected, they are temporarily stored in the transfer silo and then transported to the high-level silo by tubular chain conveyor;

[0048] S2: Hydrolysis section. The aluminum ash raw material collected in step S1 is added to the slurry mixing tank, and then water is added. The mass ratio of aluminum ash raw material to water is 1:5. The mixing tank is stirred at room temperature. The slurry is automatically controlled to be delivered to the hydrolysis tank. Heat transfer oil is introduced into the jacket of the hydrolysis tank for heating, and the temperature is controlled at 100°C. The hydrolysis reaction is carried out under stirring, and the slurry pump is circulated at the same time. A large amount of heat is released during hydrolysis. The system automatically adjusts the flow rate of heat transfer oil to maintain a constant temperature. The hydrogen-containing and ammonia-containing water vapor exhaust gas discharged from the hydrolysis tank is sent to the exhaust gas recovery and purification device. When the liquid level in the hydrolysis tank rises, the slurry is automatically pumped to the series of hydrolysis tanks for continuous hydrolysis. The hydrolysis reaction residence time is 5 hours, and the hydrolyzed slurry is obtained. The exhaust of each hydrolysis tank is carried out under a slight positive pressure to prevent air from entering the system and causing hydrogen to mix with air and reach the explosion limit.

[0049] S3: Filtration section, the hydrolyzed slurry obtained in step S2 is sent to the cooling kettle for cooling at 50°C, and then automatically sent to the vacuum rotary filter. The separated high-alumina material is transported to the warehouse by belt for storage, and the filtrate is sent to the S4 section for further processing.

[0050] S4: In the solid fluoride section, the filtrate obtained in step S3 is added to calcium hydroxide powder for reaction. After removing fluoride ions, the fluoride ion content is tested and found to be lower than the industry standard, indicating that the reaction is complete. After filtration and separation by a vertical centrifuge, calcium fluoride is obtained and transported to the warehouse by conveyor belt for storage. The filtrate is sent to the production circulating water tank, and the circulating water is pressurized by a pump and sent to the hydrolysis preparation kettle in the S2 hydrolysis section for recycling. If the water is insufficient, tap water is added externally.

[0051] S5: The exhaust gas scrubbing section sends the hydrogen- and ammonia-containing steam exhaust gas discharged from the hydrolysis reactor in step S2 to the exhaust gas recovery and purification device. The ammonia recovery rate reaches 95%, and the byproducts are ammonia water and diammonium phosphate solution. After being washed with phosphoric acid with residual ammonia below 20 PPM, it is sent to the heat transfer oil combustion furnace for utilization. The exhaust gas recovery and purification device includes an exhaust gas pre-condensation purification unit, a rapid condensation unit, a concentrated ammonia recovery unit, a dilute ammonia recovery unit, an exhaust gas purification tower, and an acid washing purification tower. The exhaust gas pre-condensation purification unit can wash away the materials entrained in the exhaust gas and partially condense the water in the exhaust gas. Steam is used as a washing liquid for cyclic washing and controlled to return to the hydrolysis unit, regulating the water balance function of the ammonia recovery system. The rapid condensation unit adopts a fully welded corrugated plate falling film condenser, which condenses water vapor at room temperature, reducing the cooling energy consumption for obtaining high-concentration ammonia water in the low-temperature, high-concentration zone. The concentrated ammonia recovery unit adopts a fully welded corrugated plate falling film absorber invented by Jiangsu Kaiding Chemical Technology Co., Ltd., which integrates residual cooling recovery and low-temperature subcooling functions, and can quickly advance the absorption process to near gas-liquid equilibrium. The ammonia recovery efficiency in this unit reaches 70%, reducing the dilute ammonia... The recovery unit recovers the load and achieves an ammonia concentration of over 20%, making it marketable as an industrial product. In the dilute ammonia recovery unit, the tail gas sequentially passes through a low-temperature dilute ammonia water pipeline for spray absorption, a structured packed tower for dilute ammonia water circulation absorption, and a low-temperature demineralized water scrubber in the upper section of the structured packed tower. This unit absorbs 20% of the ammonia, further reducing the ammonia load during acid washing, which is crucial for ensuring the recovery ratio and reducing the consumption of phosphoric acid, etc. The tail gas purification tower uses a multi-section structured corrugated wire mesh packed tower. The temperature of the ammonia-containing water collected at the bottom of each section is precisely controlled to ensure no freezing while minimizing the temperature of each section, thus shifting the ammonia recovery load downwards and reducing the purification load of the purification section. The acid washing purification tower uses chemical cleaning to reduce the ammonia content in the tail gas to the requirements of the environmental impact assessment. It employs in-pipe spraying and in-tower defoaming separation methods, with phosphoric acid replenishment automatically controlled by an online pH meter. There are two acid washing towers: one for washing hydrogen-containing hydrolysis tail gas and the other for washing other ammonia-containing gases containing air. The two must not be mixed to prevent explosion. The ammonium phosphate obtained from acid washing has high purity and can be sold as a product.

[0052] S6: Treatment of waste gas, wastewater, and solid waste.

[0053] Waste liquid - Wastewater, water treatment wastewater and other production wastewater generated in the S2 hydrolysis process can all be reused in the hydrolysis reactor. All impurities in the water are sold with the filter cake, and there is no production wastewater discharge.

[0054] The exhaust gas is generated during the filter, powder conveying, and product loading and unloading, producing particulate matter and ammonia-containing gas. The thermal oil furnace burns natural gas, producing sulfur dioxide, nitrogen oxides, and particulate matter. All of the exhaust gases are recovered, purified, and discharged in compliance with standards.

[0055] The high-alumina filter cake and calcium fluoride filter cake produced in the waste residue-S3 section can be recycled by third parties.

[0056] The continuous hydrolysis in step S2 and the tail gas recovery and purification section in step S5 are controlled by PLC with full automation, requiring no manual intervention. Example

[0057] A continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag includes the following process steps:

[0058] S1: Raw material preparation section, after the generated screen ash and secondary aluminum ash are collected, they are temporarily stored in the transfer silo and then transported to the high-level silo by tubular chain conveyor;

[0059] S2: Hydrolysis section. The aluminum ash raw material collected in step S1 is added to the slurry mixing tank, and then water is added. The mass ratio of aluminum ash raw material to water is 1:6. The mixing tank is stirred at room temperature. The slurry is automatically controlled to be delivered to the hydrolysis tank. Heat transfer oil is introduced into the jacket of the hydrolysis tank for heating, and the temperature is controlled at 98°C. The hydrolysis reaction is carried out under stirring, and the slurry pump is circulated at the same time. A large amount of heat is released during hydrolysis. The system automatically adjusts the flow rate of heat transfer oil to maintain a constant temperature. The hydrogen-containing and ammonia-containing water vapor exhaust gas discharged from the hydrolysis tank is sent to the exhaust gas recovery and purification device. When the liquid level in the hydrolysis tank rises, the slurry is automatically pumped to the series of hydrolysis tanks for continuous hydrolysis. The hydrolysis reaction residence time is 4 hours, and the hydrolyzed slurry is obtained. The exhaust of each hydrolysis tank is carried out under a slight positive pressure to prevent air from entering the system and causing hydrogen to mix with air and reach the explosion limit.

[0060] S3: Filtration section, the hydrolyzed slurry obtained in step S2 is sent to the cooling kettle for cooling at 45℃, and then automatically sent to the vacuum rotary filter. The separated high-alumina material is transported to the warehouse by belt for storage, and the filtrate is sent to the S4 section for further processing.

[0061] S4: In the solid fluoride section, the filtrate obtained in step S3 is added to calcium hydroxide powder for reaction. After removing fluoride ions, the fluoride ion content is tested and found to be lower than the industry standard, indicating that the reaction is complete. After filtration and separation by a vertical centrifuge, calcium fluoride is obtained and transported to the warehouse by conveyor belt for storage. The filtrate is sent to the production circulating water tank, and the circulating water is pressurized by a pump and sent to the hydrolysis preparation kettle in the S2 hydrolysis section for recycling. If the water is insufficient, tap water is added externally.

[0062] S5: The tail gas scrubbing section sends the hydrogen- and ammonia-containing steam tail gas discharged from the hydrolysis reactor in step S2 to the tail gas recovery and purification device. The ammonia recovery rate reaches 90%, and the byproducts are ammonia water and ammonium sulfate solution. After being washed with sulfuric acid to a residual ammonia level below 20 PPM, it is further purified for use as a new energy source, green hydrogen. The tail gas recovery and purification device includes a tail gas pre-condensation purification unit, a rapid condensation unit, a concentrated ammonia recovery unit, a dilute ammonia recovery unit, a tail gas purification tower, and an acid washing purification tower. The tail gas pre-condensation purification unit can wash away materials entrained in the tail gas and partially condense the tail gas. The water vapor in the ammonia is recycled as a washing liquid and returned to the hydrolysis unit to regulate the water balance of the ammonia recovery system. The rapid condensation unit uses a fully welded corrugated plate falling film condenser to condense water vapor at room temperature, reducing the cooling energy consumption for obtaining high-concentration ammonia water in the low-temperature, high-concentration zone. The concentrated ammonia recovery unit uses a fully welded corrugated plate falling film absorber invented by Jiangsu Kaiding Chemical Technology Co., Ltd., which integrates waste cooling recovery and low-temperature subcooling functions, and can quickly advance the absorption process to near gas-liquid equilibrium. The ammonia recovery efficiency in this unit reaches 65%, reducing the cooling energy consumption of the ammonia recovery system. The dilute ammonia recovery unit recovers the load and achieves an ammonia concentration of over 20%, making it suitable for sale as an industrial product. In this unit, the tail gas sequentially passes through a low-temperature dilute ammonia water pipeline for spray absorption, a structured packed tower for dilute ammonia water circulation absorption, and a low-temperature demineralized water scrubber in the upper section of the structured packed tower. This unit absorbs 23% of the ammonia, further reducing the ammonia load during acid washing, which is crucial for ensuring the recovery rate and reducing the consumption of sulfuric acid, etc. The tail gas purification tower uses a multi-section structured corrugated wire mesh packed tower, with precise temperature control of the ammonia-containing water collected at the bottom of each section. To ensure no freezing, the temperature of each section is reduced as much as possible, shifting the ammonia recovery load downwards and lowering the purification load of the purification section. The acid washing purification tower uses chemical cleaning to reduce the ammonia content in the tail gas to the requirements of the environmental impact assessment. It adopts pipeline spraying and in-tower defoaming separation methods, and the replenishment of sulfuric acid is automatically controlled by an online pH meter. There are two acid washing towers: one washes hydrogen hydrolysis tail gas, and the other washes other ammonia-containing gases containing air. The two must not be mixed to prevent explosion. The ammonium phosphate obtained from acid washing has high purity and can be sold as a product.

[0063] S6: Treatment of waste gas, wastewater, and solid waste.

[0064] Waste liquid - Wastewater, water treatment wastewater and other production wastewater generated in the S2 hydrolysis process can all be reused in the hydrolysis reactor. All impurities in the water are sold with the filter cake, and there is no production wastewater discharge.

[0065] The exhaust gas is generated during the filter, powder conveying, and product loading and unloading, producing particulate matter and ammonia-containing gas. The thermal oil furnace burns natural gas, producing sulfur dioxide, nitrogen oxides, and particulate matter. All of the exhaust gases are recovered, purified, and discharged in compliance with standards.

[0066] The high-alumina filter cake and calcium fluoride filter cake produced in the waste residue-S3 section can be recycled by third parties.

[0067] The continuous hydrolysis in step S2 and the tail gas recovery and purification section in step S5 are controlled by PLC with full automation, requiring no manual intervention. Example

[0068] A continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag includes the following process steps:

[0069] S1: Raw material preparation section, after the generated screen ash and secondary aluminum ash are collected, they are temporarily stored in the transfer silo and then transported to the high-level silo by tubular chain conveyor;

[0070] S2: Hydrolysis section. The aluminum ash raw material collected in step S1 is added to the slurry mixing tank, and then water is added. The mass ratio of aluminum ash raw material to water is 1:4. The mixing tank is stirred at room temperature. The slurry is automatically controlled to be delivered to the hydrolysis tank. Heat transfer oil is introduced into the jacket of the hydrolysis tank for heating, and the temperature is controlled at 90°C. The hydrolysis reaction is carried out under stirring, and the slurry pump is circulated at the same time. A large amount of heat is released during hydrolysis. The system automatically adjusts the flow rate of heat transfer oil to maintain a constant temperature. The hydrogen-containing and ammonia-containing water vapor exhaust gas discharged from the hydrolysis tank is sent to the exhaust gas recovery and purification device. When the liquid level in the hydrolysis tank rises, the slurry is automatically pumped to the series of hydrolysis tanks for continuous hydrolysis. The hydrolysis reaction residence time is 2 hours, and the hydrolyzed slurry is obtained. The exhaust of each hydrolysis tank is carried out under a slight positive pressure to prevent air from entering the system and causing hydrogen to mix with air and reach the explosion limit.

[0071] S3: Filtration section, the hydrolyzed slurry obtained in step S2 is sent to the cooling kettle for cooling at 60℃, and then automatically sent to the vacuum rotary filter. The separated high-alumina material is transported to the warehouse by belt for storage, and the filtrate is sent to the S4 section for further processing.

[0072] S4: In the solid fluoride section, the filtrate obtained in step S3 is added to calcium hydroxide powder for reaction. After removing fluoride ions, the fluoride ion content is tested and found to be lower than the industry standard, indicating that the reaction is complete. After filtration and separation by a vertical centrifuge, calcium fluoride is obtained and transported to the warehouse by conveyor belt for storage. The filtrate is sent to the production circulating water tank, and the circulating water is pressurized by a pump and sent to the hydrolysis preparation kettle in the S2 hydrolysis section for recycling. If the water is insufficient, tap water is added externally.

[0073] S5: The tail gas scrubbing section sends the hydrogen- and ammonia-containing steam tail gas discharged from the hydrolysis reactor in step S2 to the tail gas recovery and purification device. The ammonia recovery rate reaches 92%, and the byproducts are ammonia water and diammonium phosphate solution. After being washed with phosphoric acid and the residual ammonia is below 20 PPM, it is sent to the heat transfer oil combustion furnace for utilization. The tail gas recovery and purification device includes a tail gas pre-condensation purification unit, a rapid condensation unit, a concentrated ammonia recovery unit, a dilute ammonia recovery unit, a tail gas purification tower, and an acid washing purification tower. The tail gas pre-condensation purification unit can wash the materials entrained in the tail gas and partially condense the water in the tail gas. Steam is used as a washing liquid for cyclic washing and controlled to return to the hydrolysis unit, regulating the water balance function of the ammonia recovery system. The rapid condensation unit adopts a fully welded corrugated plate falling film condenser, which condenses water vapor at room temperature, reducing the cooling energy consumption for obtaining high-concentration ammonia water in the low-temperature, high-concentration zone. The concentrated ammonia recovery unit adopts a fully welded corrugated plate falling film absorber invented by Jiangsu Kaiding Chemical Technology Co., Ltd., which integrates residual cooling recovery and low-temperature subcooling functions, and can quickly advance the absorption process to near gas-liquid equilibrium. The ammonia recovery efficiency in this unit reaches 75%, reducing the dilute ammonia... The recovery unit recovers the load and achieves an ammonia concentration of over 20%, making it marketable as an industrial product. In the dilute ammonia recovery unit, the tail gas sequentially passes through a low-temperature dilute ammonia water pipeline for spray absorption, a structured packed tower for dilute ammonia water circulation absorption, and a low-temperature demineralized water scrubber in the upper section of the structured packed tower. This unit absorbs 25% of the ammonia, further reducing the ammonia load during acid washing, which is crucial for ensuring the recovery ratio and reducing the consumption of phosphoric acid, etc. The tail gas purification tower uses a multi-section structured corrugated wire mesh packed tower. The temperature of the ammonia-containing water collected at the bottom of each section is precisely controlled to ensure no freezing while minimizing the temperature of each section, thus shifting the ammonia recovery load downwards and reducing the purification load of the purification section. The acid washing purification tower uses chemical cleaning to reduce the ammonia content in the tail gas to the requirements of the environmental impact assessment. It employs in-pipe spraying and in-tower defoaming separation methods, with phosphoric acid replenishment automatically controlled by an online pH meter. There are two acid washing towers: one for washing hydrogen-containing hydrolysis tail gas and the other for washing other ammonia-containing gases containing air. The two must not be mixed to prevent explosion. The ammonium phosphate obtained from acid washing has high purity and can be sold as a product.

[0074] S6: Treatment of waste gas, wastewater, and solid waste.

[0075] Waste liquid - Wastewater, water treatment wastewater and other production wastewater generated in the S2 hydrolysis process can all be reused in the hydrolysis reactor. All impurities in the water are sold with the filter cake, and there is no production wastewater discharge.

[0076] The exhaust gas is generated during the filter, powder conveying, and product loading and unloading, producing particulate matter and ammonia-containing gas. The thermal oil furnace burns natural gas, producing sulfur dioxide, nitrogen oxides, and particulate matter. All of the exhaust gases are recovered, purified, and discharged in compliance with standards.

[0077] The high-alumina filter cake and calcium fluoride filter cake produced in the waste residue-S3 section can be recycled by third parties.

[0078] The continuous hydrolysis in step S2 and the tail gas recovery and purification section in step S5 are controlled by PLC with full automation, requiring no manual intervention.

[0079] The above description of the embodiments is intended to facilitate understanding and use of the present invention by those skilled in the art. Those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without inventive effort. 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 invention, should be within the protection scope of the present invention.

Claims

1. A continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag, characterized in that, The process includes the following steps: S1: Raw material preparation section, after the generated screen ash and secondary aluminum ash are collected, they are temporarily stored in the transfer silo and then transported to the high-level silo by tubular chain conveyor; S2: Hydrolysis section. The aluminum ash raw material collected in step S1 is added to the slurry mixing tank, and then water is added. The mixing tank is stirred at room temperature, and the slurry pump circulates simultaneously, automatically controlling the slurry delivery to the hydrolysis tank. Heat transfer oil is introduced into the jacket of the hydrolysis tank for heating, and the temperature is controlled at 90-100℃. The hydrolysis reaction is carried out under stirring, and the slurry pump circulates simultaneously. A large amount of heat is released during hydrolysis, and the system automatically adjusts the flow rate of heat transfer oil to maintain a constant temperature. The hydrogen-containing and ammonia-containing water vapor exhaust gas discharged from the hydrolysis tank is sent to the exhaust gas recovery and purification device. When the liquid level in the hydrolysis tank rises, the slurry is automatically pumped to the series-connected hydrolysis tanks for continuous hydrolysis. The hydrolysis reaction residence time is 2-5 hours, and the hydrolyzed slurry is obtained. S3: Filtration section, the hydrolyzed slurry obtained in step S2 is sent to the cooling kettle for cooling at a temperature of 45-60℃, and then automatically sent to the vacuum rotary filter. The high-alumina material obtained by separation is transported to the warehouse by belt for storage, and the filtrate is sent to the S4 section for further processing. S4: In the solid fluoride section, the filtrate obtained in step S3 is added to calcium oxide powder for reaction. After being filtered and separated by a vertical centrifuge, calcium fluoride is obtained and transported to the warehouse by conveyor belt for storage. The filtrate is sent to the production circulating water tank. The circulating water is pressurized by a pump and sent to the hydrolysis preparation kettle in the S2 hydrolysis section for recycling. If it is insufficient, tap water is added externally. S5: Tail gas recovery and purification section. The hydrogen- and ammonia-containing water vapor tail gas discharged from the hydrolysis kettle in step S2 is sent to the tail gas recovery and purification device. The ammonia recovery rate reaches 90-95%. The by-products are ammonia water, diammonium phosphate solution, or ammonium sulfate solution. After being washed with phosphoric acid or sulfuric acid to a residual ammonia level below 20 PPM, it is sent to the heat transfer oil combustion furnace for utilization, or further purified for use as a new energy source, green hydrogen. The tail gas recovery and purification device includes a tail gas pre-condensation purification unit, a rapid condensation unit, a concentrated ammonia recovery unit, a dilute ammonia recovery unit, a tail gas purification tower, and an acid washing purification tower. The concentrated ammonia recovery unit adopts a fully welded corrugated plate falling film absorber, which integrates residual cooling recovery and low-temperature subcooling functions, and can quickly advance the absorption process to near gas-liquid equilibrium. In the dilute ammonia recovery unit, the tail gas is sequentially absorbed by spray in a low-temperature dilute ammonia water pipeline, absorbed by dilute ammonia water circulation in a structured packed tower, and washed with low-temperature demineralized water in the upper section of the structured packed tower.

2. The continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag according to claim 1, characterized in that, In step S2, the mass ratio of aluminum ash raw material to water is 1:4-6.

3. The continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag according to claim 1, characterized in that, In step S2, the venting of each hydrolysis vessel is carried out under a slight positive pressure to prevent air from entering the system and causing hydrogen to mix with air, reaching the explosion limit.

4. The continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag according to claim 1, characterized in that, The S2 hydrolysis section and the S5 tail gas recovery and purification section are controlled by PLC with full automation, requiring no manual intervention.

5. The continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag according to claim 1, characterized in that, In step S4, the reaction is complete when the fluoride ion content is found to be lower than the industry standard after the fluoride ion removal.

6. The continuous hydrolysis and tail gas recovery and purification process for aluminum ash slag according to claim 1, characterized in that, The process also includes step S6: waste treatment. Waste liquid - All wastewater, water treatment wastewater and other production wastewater generated in the S2 hydrolysis process are recycled to the hydrolysis reactor. All impurities in the water are sold with the filter cake, and there is no production wastewater discharge. The exhaust gas filter, powder conveyor, and product loading and unloading will generate particulate matter and ammonia-containing gas. The thermal oil furnace will generate sulfur dioxide, nitrogen oxides, and particulate matter when burning natural gas. All the exhaust gases are recycled and purified to meet emission standards. The high-alumina filter cake and calcium fluoride filter cake produced in the waste residue-S3 section are recycled and reused by third parties.

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