Method for preparing polyaluminum chloride by cyclone atomization denitrogenation treatment of aluminum ash

Abstract

This invention belongs to the field of polyaluminum chloride preparation technology and discloses a method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification treatment. The method includes continuously and quantitatively feeding aluminum ash into a cyclone atomization reactor; forming a cyclone field within the reactor and spraying atomized water into the cyclone field, allowing the aluminum ash and atomized water to fully contact in a gas-solid cloud dynamic field, resulting in a hydrolysis reaction to generate aluminum hydroxide and ammonia; controlling the amount of water added to maintain a water-to-aluminum ash mass ratio of 0.1-0.5:1, and maintaining the reaction system temperature at 70-120℃; drawing the ammonia-containing tail gas generated by the hydrolysis reaction from the top of the cyclone atomization reactor and sending it to an ammonia absorption tower for multi-stage absorption; enhancing mass transfer through cyclone atomization, resulting in an extremely high hydrolysis conversion rate of aluminum nitride in the aluminum ash, reducing the ammonia nitrogen content of the polyaluminum chloride product; and completely eliminating the large amount of salt- and ammonia-containing wastewater generated by traditional water washing processes by precisely controlling the water-to-aluminum ash ratio to be near the stoichiometric ratio of the chemical reaction, without adding excess process water.

Description

Technical Field

[0001] This invention relates to the field of polyaluminum chloride preparation technology, specifically a method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification treatment. Background Technology

[0002] Aluminum ash is a slag produced during the electrolytic aluminum, aluminum processing, and recycled aluminum production processes. It is classified as hazardous solid waste, but it contains significant amounts of valuable components such as alumina and aluminum nitride, giving it resource utilization value. Using aluminum ash as a raw material to prepare polyaluminum chloride (PAC) is one of the important ways to achieve high-value utilization of aluminum ash. PAC is a water purification agent widely used in water and wastewater treatment. Its production process typically involves acid dissolution of aluminum-containing raw materials with hydrochloric acid, followed by hydrolysis, polymerization, and aging. The alumina and some active aluminum in aluminum ash can react with hydrochloric acid to form aluminum salts, theoretically serving as a low-cost alternative to bauxite or aluminum hydroxide in PAC production. However, aluminum ash also contains chemically active aluminum nitride, which can undergo side reactions with water or acid during acid dissolution, releasing ammonia and affecting the quality of PAC products. Therefore, effective denitrification pretreatment of the aluminum ash is essential before acid dissolution.

[0003] Currently, the denitrification processes used for preparing polyaluminum chloride from aluminum ash mainly include water washing and direct acid dissolution. Water washing involves mixing aluminum ash with water and utilizing the hydrolysis of aluminum nitride to generate aluminum hydroxide and ammonia (AlN + 3H₂O → Al(OH)₃↓ + NH₃↑), causing nitrogen to escape as ammonia, thus achieving denitrification. The denitrified aluminum ash is then acid-dissolved to prepare polyaluminum chloride. Direct acid dissolution involves simultaneous aluminum dissolution and aluminum nitride hydrolysis in a hydrochloric acid reaction system, but the reaction process is violent and difficult to control. In recent years, to improve denitrification efficiency and process controllability, researchers have proposed introducing cyclone atomization technology into the aluminum ash denitrification process. Cyclone atomization technology utilizes the centrifugal force field formed by a high-speed rotating airflow, causing solid particles to collide and contact violently with the atomized liquid in three-dimensional space, exhibiting high mass transfer efficiency, fast reaction speed, and short residence time. Applying this technology to aluminum ash denitrification can theoretically achieve rapid hydrolysis of aluminum nitride and efficient separation of ammonia under low water-ash ratio conditions, thereby overcoming some shortcomings of traditional immersion or stirring water washing processes.

[0004] However, existing methods for preparing polyaluminum chloride from aluminum ash still face several pressing technical challenges in practical applications. First, the ammonia nitrogen content in the polyaluminum chloride product easily exceeds the standard. Although cyclone atomization enhances the contact between water and aluminum ash, the aluminum hydroxide passivation film formed on the surface hinders the complete conversion of aluminum nitride in a single cyclone contact during the later stages of the aluminum nitride hydrolysis reaction. Residual ammonia nitrogen is released into the polyaluminum chloride product during subsequent acid dissolution, causing the product's ammonia nitrogen index to fail to meet the requirements of the national standard for industrial-grade polyaluminum chloride (GB / T22627-2022). Second, the wastewater generation is large. To ensure denitrification efficiency, existing cyclone atomization processes often require the addition of process water exceeding the stoichiometric ratio. This excess water is ultimately discharged as saline and ammonia-containing wastewater, which is difficult and costly to treat, becoming a key bottleneck restricting the economic and environmental performance of the process. Third, significant safety and environmental risks exist. In batch or semi-continuous operations, the reaction between aluminum ash and water still exhibits concentrated heat release and gas production. A sudden pressure surge within the reactor can easily trigger material overflow, causing burns from high-temperature materials and ammonia gas leakage, posing significant safety and environmental pollution risks. Fourth, energy consumption is high. Ammonia-containing tail gas generated during denitrification is typically recovered using water absorption. If further increasing the ammonia concentration or recovering ammonia gas is required, a steam-heated ammonia stripping device is needed, consuming a large amount of additional heat energy and increasing the process's operating costs and carbon footprint. Therefore, it is necessary to further improve and optimize the existing method of cyclone atomization denitrification treatment of aluminum ash to prepare polyaluminum chloride. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification includes the following steps:

[0008] S1: Continuously and quantitatively feed aluminum ash into the cyclone atomizing reactor;

[0009] S2: A swirling flow field is formed inside the swirling atomizing reactor, and atomized water is sprayed into the swirling flow field, so that aluminum ash and atomized water can fully contact each other in the gas-solid cloud dynamic field and undergo a hydrolysis reaction to generate aluminum hydroxide and ammonia gas; wherein, the swirling atomizing reactor is a vertical structure, aluminum ash enters tangentially from the top of the swirling atomizing reactor to form a downward spiral swirling flow, and atomized water is sprayed radially from the central axis or peripheral wall of the swirling atomizing reactor to fully collide and contact with the aluminum ash particles; the residence time of aluminum ash in the swirling atomizing reactor is 30 s-10 min;

[0010] S3: Control the amount of water added so that the mass ratio of water to aluminum ash is 0.1-0.5:1, maintain the temperature of the reaction system at 70-120℃, and control the material residence time through continuous feeding and discharging to ensure that the hydrolysis reaction proceeds fully;

[0011] S4: The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and sent to the ammonia absorption tower for multi-stage absorption to prepare ammonia water by-product; wherein, the multi-stage absorption is three-stage water absorption or three-stage dilute acid absorption to prepare ammonia water with a mass concentration of 15%-25%;

[0012] S5: The denitrified aluminum ash solid material discharged from the bottom of the cyclone atomizing reactor is reacted with hydrochloric acid using a conventional acid dissolution process to prepare polyaluminum chloride product. The ammonia nitrogen content of the polyaluminum chloride product is less than 500 mg / L.

[0013] Further detailed scheme: Replace step S2 with a multi-stage swirling shear collision coupling self-grinding surface renewal enhanced hydrolysis denitrification in a swirling atomizing reactor, including constructing a multi-stage series swirling shear zone in a vertical swirling atomizing reactor. The inner wall of the swirling atomizing reactor cylinder is provided with at least two stages of inwardly protruding spiral guide ribs along the axial direction. The protrusion height of the spiral guide ribs is 5%-15% of the cylinder diameter, and the spiral helix angle is 30-60 degrees. A roughened friction lining is provided in the cylinder wall area between two adjacent stages of spiral guide ribs. The surface roughness Ra value of the friction lining is 50-200μm.

[0014] The multi-stage tandem swirling shear zone includes a first-stage swirling shear zone, a second-stage swirling shear zone, and a third-stage swirling shear zone;

[0015] In the first-stage swirling shear zone, aluminum ash powder enters tangentially from the top of the swirling atomizing reactor at an inlet wind speed of 20-35 m / s, forming the first-stage high-speed swirling flow. The first set of dual-fluid nozzles sprays the first stream of atomized water downwards along the central axis of the reactor. The average diameter of the atomized droplets is 20-40 μm, and the mass ratio of water to aluminum ash is 0.05-0.10:1. In this zone, the centrifugal force generated by the high-speed swirling flow throws the aluminum ash particles toward the wall, where they collide with the fine water mist sprayed from the center, completing the initial wetting and rapidly initiating the hydrolysis reaction.

[0016] In the second-stage swirling shear zone, aluminum ash particles carrying some of the hydrolysis products of the aluminum hydroxide film move downwards along the first-stage spiral guide ridge with the airflow. Under the guidance and contraction of the spiral guide ridge, the particle flow is forcibly accelerated and forms a secondary swirling flow. Intense shearing friction and collisions occur between particles and between particles and the roughened friction liner. The second-stage swirling shear zone is used for in-situ mechanical peeling of the passivation film and self-grinding without additional energy consumption. The in-situ mechanical peeling of the passivation film utilizes the kinetic energy of the particles themselves and the shear force of the flow field. Through frictional collisions between particles and between particles and the wall, the loose aluminum hydroxide passivation film newly formed on the aluminum nitride surface is peeled off in real time, exposing the fresh aluminum nitride reaction interface. The self-grinding process without additional energy consumption does not require external grinding media or additional power. It is achieved entirely by the energy of the flow field itself and the structural design of the reactor.

[0017] In the third-stage swirling shear zone, below the second-stage spiral guide ridge, a second stream of atomized water is injected through a second set of radially opposed dual-fluid nozzles. The average diameter of the atomized droplets is 40-80 μm, and the water-to-aluminum ash mass ratio is 0.05-0.15:1. The surface-renewed aluminum nitride particles come into intense contact with the newly injected atomized water again in the third-stage swirling field, undergoing a deep hydrolysis reaction. At the same time, the lower conical section of the swirling atomizing reactor is equipped with adjustable swirling guide vanes. By adjusting the vane angle, the swirling intensity and residence time distribution of the material in the reactor can be changed.

[0018] The total water to aluminum ash mass ratio is controlled at 0.12-0.30:1; the mass flow rate ratio of the first atomized water to the second atomized water is 4:6-6:4; the total residence time of aluminum ash particles in the cyclone atomizing reactor is 45 s-8 min, with the residence time in the second-stage spiral guide zone accounting for 30%-50% of the total time; the cyclone atomizing reactor shell is equipped with a zoned temperature control jacket to control the temperature of each stage of the reaction zone as follows: 60-80℃ for the first-stage cyclone shear zone, 80-100℃ for the second-stage cyclone shear zone, and 70-90℃ for the third-stage cyclone shear zone.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. By enhancing mass transfer through swirl atomization, the hydrolysis conversion rate of aluminum nitride in aluminum ash is extremely high. The ammonia nitrogen content of polyaluminum chloride products prepared by acid dissolution of denitrified aluminum ash can be stably lower than 500 mg / L, thus reducing the ammonia nitrogen content of polyaluminum chloride products.

[0021] By precisely controlling the water-to-aluminum ash ratio to be close to the chemical reaction stoichiometry, without adding excessive process water, the large amount of salt and ammonia-containing wastewater generated by traditional water washing processes is completely eliminated, fundamentally solving the wastewater treatment problem and achieving zero discharge of process wastewater.

[0022] The continuous and quantitative feeding and water spraying methods avoid safety accidents such as overflow and splashing caused by concentrated and violent reactions of aluminum nitride; the system operates under slight negative pressure or in a closed state, and all ammonia is collected and recycled, resulting in no environmental pollution; the production process is safe and environmentally friendly.

[0023] Nitrogen in aluminum ash is recovered in the form of ammonia water, turning waste into treasure, without the need for additional ammonia stripping energy consumption, resulting in significant economic and environmental benefits; and full utilization of resources.

[0024] 2. By adding an auxiliary dissociation agent to enhance the pretreatment of raw materials and introducing a hydrolysis promoter to strengthen the reaction process, the encapsulation of aluminum nitride by inert components in aluminum ash is effectively destroyed, and the interfacial reaction on the surface of aluminum nitride is catalyzed. This results in a further reduction in the residual ammonia nitrogen content of the denitrified aluminum ash compared to the single cyclone atomization method, providing a guarantee for the subsequent preparation of ultra-low ammonia nitrogen polyaluminum chloride; the denitrification efficiency and depth are further improved.

[0025] By introducing a polymerization degree regulator into the acid dissolution process and hydrochloric acid reaction, the basicity and polymerization morphology of polyaluminum chloride products can be actively controlled, so that not only ammonia nitrogen meets the standards, but also the product performance indicators can be flexibly adjusted according to different water quality treatment needs such as high turbidity water and low temperature low turbidity water, which significantly improves the added value and market competitiveness of the products.

[0026] The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and first passes through a cyclone dust collector to recover the entrained fine aluminum dust. The recovered dust is returned to the feeding system in step S1. The addition of the cyclone dust collection and return step before the tail gas treatment not only recovers the effective aluminum components and improves the resource utilization rate, but also avoids dust from entering the absorption tower to block the packing or contaminate the ammonia water product, ensuring the long-term stable operation of the system.

[0027] The average diameter of the atomized droplets is controlled between 20-100μm. By limiting the droplet size and precisely controlling the temperature, the high consistency and stability of the denitrification effect of each batch of products is ensured, overcoming the defect of large quality fluctuations between batches in traditional processes.

[0028] 3. The ultrasonic in-situ stripping and passivation film technology solves the self-obstruction problem of aluminum nitride hydrolysis reaction, that is, the product layer hinders the reaction from continuing, which can make the aluminum nitride conversion rate approach 100%; combined with the lower stage carrier gas stripping technology, the physically adsorbed ammonia is completely separated.

[0029] The high-frequency vibration of ultrasound can effectively prevent the adhesion and bridging of damp aluminum ash powder on the reactor wall, ensuring the long-term stable operation of continuous production; the introduction of ultrasound greatly improves the efficiency and throughput of the hydrolysis reaction.

[0030] 4. Existing technologies require the addition of more water to achieve deep ammonia removal, but adding more water inevitably produces wastewater; however, this invention achieves deep conversion of aluminum nitride at an extremely low water-to-aluminum ash ratio by in-situ ultrasonic stripping of the passivation film, breaking the equilibrium limitation from the perspective of chemical reaction kinetics.

[0031] While the rapid-pass reaction in the prior art is highly efficient, the dissolved ammonia inside the particles and in the gel channels does not have enough time to escape. The present invention introduces a lower-stage carrier gas countercurrent stripping zone, which simultaneously completes the "reaction-separation" coupling process inside the reactor, minimizing the physical residual ammonia.

[0032] In existing technologies, enhanced mixing often requires the addition of internal components, and the handling of damp aluminum ash can easily lead to material buildup and blockage in the internal components; however, this invention uses an external ultrasonic transducer on the wall surface, which simultaneously achieves the dual functions of enhanced mass transfer and online anti-blocking and wall cleaning through a non-contact energy input method.

[0033] 5. Utilizing the energy of the flow field itself, self-grinding surface renewal is achieved through shearing collisions between particles, with zero additional energy consumption; the rough wall surface and spiral guide ridges actively induce turbulent eddies and particle collisions, resulting in a higher mass transfer coefficient; the purely passive internal component design of the spiral guide ridges and rough liner is simple in structure, maintenance-free, and has a long service life; the lower cone section of the swirl atomizing reactor is equipped with adjustable swirl guide vanes, and the addition of adjustable swirl guide vanes allows for independent control of swirl intensity and residence time distribution, making the process more adaptable;

[0034] 6. Online monitoring and feedback for dynamic water control, maintaining a water-to-aluminum ash ratio of 0.10-0.25:1 to keep the critical wetting state; upgrading from open-loop control to closed-loop adaptive control fundamentally ensures the reliability of zero wastewater discharge; independent and precise temperature control in three zones and recovery of reaction heat, with fluctuations of ±2℃, achieves cascade utilization and precise management of reaction heat, saving energy and reducing consumption, while improving reaction consistency; the multi-component synergistic system of main catalyst, co-catalyst, and dispersant / isolator has been upgraded from single pH adjustment to multi-dimensional synergy of kinetic, thermodynamic, and structural regulation, resulting in a qualitative leap in catalytic efficiency and depth; online monitoring, endpoint determination, and adaptive adjustment enable intelligent and unmanned operation of the process, ensuring batch-to-batch consistency of product quality;

[0035] 7. The dual-mode phase change circulation of liquid water and steam enables microporous permeation and closed-loop water recovery; it upgrades water conservation to water recycling, transforming zero wastewater discharge from a passive guarantee to an active closed-loop system; that is, traditional thinking holds that excessive water must be added to achieve full wetting of the particles, while this invention achieves full wetting of the particles through molecular-level permeation of gaseous water vapor without generating liquid free water, and at the same time, it recovers all evaporated water through condensation and recycling, forming a closed-loop water circulation.

[0036] The catalytic activity is staged, with immediate and latent components matched to the temporal and spatial progression of the reaction. The catalytic activity changes from constant throughout the process to on-demand release, solving the problem of strong catalysts being too strong in the early stages and weak in the later stages. Strong alkaline catalysts have a significant acceleration effect but are prone to causing the initial reaction to runaway. This invention uses microcapsule thermal response encapsulation technology to activate strong catalysts in situ at the required time and location, achieving a catalytic mode of mild start-up and strong mid-stage. Attached Figure Description

[0037] Figure 1 Line graphs showing the ammonia nitrogen content of polyaluminum chloride products in Comparative Example 1 and Experimental Examples 1-5;

[0038] Figure 2 A line graph showing the statistical wastewater generation of Comparative Example 1 and Experimental Examples 1-5;

[0039] Figure 3 A statistical line graph showing the basicity of the products in Comparative Example 1 and Experimental Examples 1-5;

[0040] Figure 4 The graph shows the statistical line graphs of ammonia nitrogen content in denitrified aluminum ash of Comparative Example 1 and Experimental Examples 1-5. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] A method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification includes the following steps:

[0044] S1: Continuously and quantitatively feed aluminum ash into the cyclone atomizing reactor;

[0045] S2: A swirling flow field is formed inside the swirling atomizing reactor, and atomized water is sprayed into the swirling flow field, so that aluminum ash and atomized water can fully contact each other in the gas-solid cloud dynamic field and undergo a hydrolysis reaction to generate aluminum hydroxide and ammonia gas; wherein, the swirling atomizing reactor is a vertical structure, aluminum ash enters tangentially from the top of the swirling atomizing reactor to form a downward spiral swirling flow, and atomized water is sprayed radially from the central axis or peripheral wall of the swirling atomizing reactor to fully collide and contact with the aluminum ash particles; the residence time of aluminum ash in the swirling atomizing reactor is 30 s-10 min;

[0046] S3: Control the amount of water added so that the mass ratio of water to aluminum ash is 0.1-0.5:1, maintain the temperature of the reaction system at 70-120℃, and control the material residence time through continuous feeding and discharging to ensure that the hydrolysis reaction proceeds fully;

[0047] S4: The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and sent to the ammonia absorption tower for multi-stage absorption to prepare ammonia water by-product; wherein, the multi-stage absorption is three-stage water absorption or three-stage dilute acid absorption to prepare ammonia water with a mass concentration of 15%-25%;

[0048] S5: The denitrified aluminum ash solid material discharged from the bottom of the cyclone atomizing reactor is reacted with hydrochloric acid using a conventional acid dissolution process to prepare polyaluminum chloride product. The ammonia nitrogen content of the polyaluminum chloride product is less than 500 mg / L.

[0049] By enhancing mass transfer through swirl atomization, the hydrolysis conversion rate of aluminum nitride in aluminum ash is extremely high. The ammonia nitrogen content of polyaluminum chloride product prepared by acid dissolution of denitrified aluminum ash can be stably lower than 500 mg / L, thus reducing the ammonia nitrogen content of polyaluminum chloride product.

[0050] By precisely controlling the water-to-aluminum ash ratio to be close to the chemical reaction stoichiometry, without adding excessive process water, the large amount of salt and ammonia-containing wastewater generated by traditional water washing processes is completely eliminated, fundamentally solving the wastewater treatment problem and achieving zero discharge of process wastewater.

[0051] The continuous and quantitative feeding and water spraying methods avoid safety accidents such as overflow and splashing caused by concentrated and violent reactions of aluminum nitride; the system operates under slight negative pressure or in a closed state, and all ammonia is collected and recycled, resulting in no environmental pollution; the production process is safe and environmentally friendly.

[0052] The nitrogen in aluminum ash is recovered in the form of ammonia water, turning waste into treasure, and no additional energy consumption for ammonia stripping is required, resulting in significant economic and environmental benefits; and full utilization of resources.

[0053] Example 2

[0054] This embodiment further elaborates on Embodiment 1:

[0055] A method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification includes the following steps:

[0056] S1. Raw material pretreatment and conditioning

[0057] Aluminum ash is crushed and ball-milled to obtain aluminum ash powder with a particle size of 40-200 mesh; 0.5%-5% of an auxiliary dissociation agent is added to the aluminum ash powder by its total mass, and after mixing evenly, it is allowed to stand and age for 30-120 min to obtain conditioned aluminum ash; then the conditioned aluminum ash is continuously and quantitatively fed into a cyclone atomizing reactor.

[0058] S2. A swirling flow field is formed inside the swirling atomizing reactor, and atomized water is sprayed into the swirling flow field, so that aluminum ash and atomized water can fully contact each other in the gas-solid cloud dynamic field and undergo a hydrolysis reaction to generate aluminum hydroxide and ammonia gas. The swirling atomizing reactor has a vertical structure, and aluminum ash enters tangentially from the top of the reactor to form a downward spiral swirling flow. The atomized water is sprayed out from a dual-fluid nozzle, and the Soder mean diameter of the atomized droplets is controlled at 20-100μm. The atomized water is sprayed radially from the central axis or peripheral wall of the reactor to fully collide and contact with the aluminum ash particles. The residence time of aluminum ash in the swirling atomizing reactor is 30 s-10 min.

[0059] S3. Control the amount of water added so that the mass ratio of water to aluminum ash is 0.1-0.5:1; through the heat exchange jacket or internal coil arranged on the wall of the cyclone atomizing reactor, the temperature of the reaction system is precisely maintained at a certain set value within the range of 70-120℃, with temperature fluctuation not exceeding ±5℃; the material residence time is controlled by continuous feeding and discharging to ensure that the hydrolysis reaction proceeds fully.

[0060] During the hydrolysis reaction, a hydrolysis accelerator of 0.01%-0.5% of the total mass of aluminum ash is introduced simultaneously through atomized water; the hydrolysis accelerator is any one or a combination of at least two of alkali metal hydroxides, alkali metal carbonates or organic amine compounds.

[0061] S4. The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and first passed through a cyclone dust collector to recover the entrained fine aluminum dust. The recovered dust is returned to the feeding system of step S1. The ammonia-containing tail gas after dust removal is sent to an ammonia absorption tower for multi-stage absorption to prepare ammonia water by-product. The multi-stage absorption is either three-stage water absorption or three-stage dilute acid absorption to prepare ammonia water with a mass concentration of 15%-25%.

[0062] S5. The denitrified aluminum ash solid material discharged from the bottom of the cyclone atomizing reactor is reacted with hydrochloric acid using an acid dissolution process to prepare polyaluminum chloride product. During the acid dissolution process and hydrochloric acid reaction, a polymerization degree regulator accounting for 0.1%-2% of the total mass of the denitrified aluminum ash solid material is added to the reaction system. The polymerization degree regulator is any one or a combination of at least two of sodium aluminate, sodium aluminate, and aluminum hydroxide gel. After the acid dissolution process and hydrochloric acid reaction are completed, a curing treatment is performed at a curing temperature of 60-90℃ for 2-8 hours. The final polyaluminum chloride product has a basicity of 45%-85% and an ammonia nitrogen content of less than 500 mg / L.

[0063] By adding an auxiliary dissociation agent to enhance the pretreatment of raw materials and introducing a hydrolysis promoter to strengthen the reaction process, the encapsulation of aluminum nitride by inert components in aluminum ash was effectively destroyed, and the interfacial reaction on the surface of aluminum nitride was catalyzed. This resulted in a further reduction in the residual ammonia nitrogen content of the denitrified aluminum ash compared to the single cyclone atomization method, providing a guarantee for the subsequent preparation of ultra-low ammonia nitrogen polyaluminum chloride; the denitrification efficiency and depth were further improved.

[0064] By introducing a polymerization degree regulator into the acid dissolution process and hydrochloric acid reaction, the basicity and polymerization morphology of polyaluminum chloride products can be actively controlled, so that not only ammonia nitrogen meets the standards, but also the product performance indicators can be flexibly adjusted according to different water quality treatment needs such as high turbidity water and low temperature low turbidity water, which significantly improves the added value and market competitiveness of the products.

[0065] The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and first passes through a cyclone dust collector to recover the entrained fine aluminum dust. The recovered dust is returned to the feeding system in step S1. The addition of the cyclone dust collection and return step before the tail gas treatment not only recovers the effective aluminum components and improves the resource utilization rate, but also avoids dust from entering the absorption tower to block the packing or contaminate the ammonia water product, ensuring the long-term stable operation of the system.

[0066] The average diameter of the atomized droplets is controlled between 20-100μm. By limiting the droplet size and precisely controlling the temperature, the high consistency and stability of the denitrification effect of each batch of products is ensured, overcoming the defect of large quality fluctuations between batches in traditional processes.

[0067] Further: In step S1, the auxiliary dissociation agent is any one or a mixture of at least two of calcium oxide, sodium hydroxide, and sodium carbonate; the auxiliary dissociation agent is used to pre-disrupt the dense coating layer formed by some salt fluxes in the aluminum ash, so that the aluminum nitride particles are more easily exposed and come into contact with water during the subsequent hydrolysis process, thereby increasing the depth of the denitrification reaction.

[0068] In step S3, the hydrolysis promoter is sodium hydroxide or triethanolamine. The trace alkaline substances in the hydrolysis promoter can change the local pH microenvironment of the aluminum nitride hydrolysis reaction, catalyze the dissolution or crystal transformation of the Al(OH)3 passivation film generated on the aluminum nitride surface, continuously expose fresh aluminum nitride reaction interface, shorten the time required for complete denitrification, and reduce residual ammonia nitrogen.

[0069] In step S5, the degree of polymerization regulator is used to precisely control the basicity and molecular morphology distribution during the hydrolysis and polymerization of aluminum salts after acid dissolution by introducing different forms of aluminum sources or alkaline components, so as to prepare polyaluminum chloride products with higher flocculation performance and stability under the premise of ensuring low ammonia nitrogen.

[0070] Example 3

[0071] The embodiment is another implementation of step S2 in embodiment 2: replacing step S2 with a swirl atomization reactor with cascaded swirl atomization coupled with acoustic vibration to enhance hydrolysis and denitrification, including constructing a three-stage cascaded reaction zone in the swirl atomization reactor: an upper turbulent mixing zone, a middle acoustic enhancement reaction zone, and a lower deep maturation and separation zone;

[0072] The upper turbulent mixing zone is where the conditioned aluminum ash powder is tangentially fed into the reactor from the top at an inlet air velocity of 15-30 m / s, forming an initial spiral swirling flow field. Simultaneously, the first stream of atomized water is sprayed downwards along the axis through the first set of dual-fluid nozzles arranged at the center of the top of the swirling atomizing reactor, with the Soder mean diameter of the atomized droplets controlled at 30-50 μm. The upper turbulent mixing zone is used to achieve intense turbulent collision and initial wetting of aluminum ash particles and fine water mist, rapidly initiating the hydrolysis reaction and releasing the heat of reaction.

[0073] In the central acoustic enhancement reaction zone, the material enters the middle section of the swirling atomizing reactor under the action of gravity and centrifugal force. Three to eight ultrasonic transducers are evenly arranged circumferentially on the outer wall of the cylinder in the middle section of the swirling atomizing reactor. An ultrasonic transducer with a frequency of 20-40 kHz and a power density of 0.5-2.0 W / cm² is applied into the swirling atomizing reactor. 2 High-frequency ultrasonic vibration; simultaneously, a second set of nozzles arranged on the cylinder wall of this area sprays a second stream of atomized water in a radial countercurrent manner, with the Sotter average diameter of the atomized droplets controlled at 50-80μm; ultrasonic vibration is used for cavitation effect stripping of passivation film and strengthening micromixing. Cavitation effect stripping of passivation film is formed by the collapse of transient cavitation bubbles generated by ultrasonic waves at the liquid-solid interface, forming microjets and shock waves, which can strip the aluminum hydroxide inert passivation film generated on the surface of aluminum nitride particles in situ due to initial hydrolysis, continuously exposing a fresh reaction interface; strengthening micromixing is that the acoustic flow effect induced by ultrasonic waves can eliminate the boundary layer on the particle surface and enhance the mass transfer rate of water molecules to the reaction interface;

[0074] In the lower deep maturation and separation zone, the material enters the lower conical section of the cyclone atomizing reactor. Water spraying is stopped in this area, and the reactor is kept at a temperature of 70-90℃ through the reactor jacket. A small amount of inert carrier gas preheated to 60-80℃ is introduced for gas stripping. The inert carrier gas includes nitrogen or purified hot air. The inert carrier gas flows from bottom to top at an apparent gas velocity of 0.5-2.0 m / s, and comes into countercurrent contact with the downward swirling solid material.

[0075] The mass flow rate ratio of the first atomized water to the second atomized water is 6-8:2-4; the mass ratio of total water to aluminum ash is controlled at 0.12-0.35:1; and the axial backmixing of aluminum ash particles in the swirl atomization reactor is controlled by adjusting the inlet wind speed, ultrasonic power and carrier gas flow rate.

[0076] The ultrasonic in-situ stripping and passivation film technology solves the self-obstruction problem of aluminum nitride hydrolysis reaction, that is, the product layer hinders the reaction from continuing, which can make the aluminum nitride conversion rate approach 100%. Combined with the lower stage carrier gas stripping technology, the physically adsorbed ammonia is completely separated. The ammonia nitrogen content of the denitrified aluminum ash can be stably lower than 150 mg / L, or even lower than 50 mg / L. The ammonia nitrogen content of the obtained polyaluminum chloride product is correspondingly greatly reduced, reaching the potential standard of drinking water grade polyaluminum chloride.

[0077] Existing technologies require the addition of more water to achieve deep ammonia removal, but this inevitably generates wastewater. In contrast, this invention achieves deep conversion of aluminum nitride at an extremely low water-to-aluminum ash ratio by in-situ ultrasonic stripping of the passivation film, thus breaking the equilibrium constraint from the perspective of chemical reaction kinetics.

[0078] While the rapid-pass reaction in the prior art is highly efficient, the dissolved ammonia inside the particles and in the gel channels does not have enough time to escape. The present invention introduces a lower-stage carrier gas countercurrent stripping zone, which simultaneously completes the "reaction-separation" coupling process inside the reactor, minimizing the physical residual ammonia.

[0079] In existing technologies, enhanced mixing often requires the addition of internal components, and the handling of damp aluminum ash can easily lead to material buildup and blockage of the internal components. However, this invention uses an external ultrasonic transducer on the wall surface, which simultaneously achieves the dual functions of enhanced mass transfer and online anti-blocking and wall cleaning through a non-contact energy input method.

[0080] The introduction of ultrasound increases the hydrolysis reaction rate constant by 3-5 times. At the same denitrification depth, the reactor volume can be reduced by more than 40%, and the processing throughput can be doubled. The reaction efficiency and throughput are greatly improved.

[0081] The high-frequency vibration of ultrasound can effectively prevent the adhesion and bridging of damp aluminum ash powder on the reactor wall, ensuring the long-term stable operation of continuous production.

[0082] Example 4

[0083] This embodiment is another implementation of step S2 in Embodiment 2:

[0084] The step S2 is replaced by a multi-stage swirling shear collision coupling self-grinding surface renewal enhanced hydrolysis denitrification reactor, which includes constructing a multi-stage series swirling shear zone in the vertical swirling atomizing reactor. The inner wall of the swirling atomizing reactor cylinder is provided with at least two stages of inwardly protruding spiral guide ribs along the axial direction. The protrusion height of the spiral guide ribs is 5%-15% of the cylinder diameter, and the spiral helix angle is 30-60 degrees. A roughened friction lining is provided in the cylinder wall area between two adjacent spiral guide ribs. The surface roughness Ra value of the friction lining is 50-200 μm.

[0085] The multi-stage tandem swirling shear zone includes a first-stage swirling shear zone, a second-stage swirling shear zone, and a third-stage swirling shear zone;

[0086] In the first-stage swirling shear zone, aluminum ash powder enters tangentially from the top of the swirling atomizing reactor at an inlet wind speed of 20-35 m / s, forming the first-stage high-speed swirling flow. The first set of dual-fluid nozzles sprays the first stream of atomized water downwards along the central axis of the reactor. The average diameter of the atomized droplets is 20-40 μm, and the mass ratio of water to aluminum ash is 0.05-0.10:1. In this zone, the centrifugal force generated by the high-speed swirling flow throws the aluminum ash particles toward the wall, where they collide with the fine water mist sprayed from the center, completing the initial wetting and rapidly initiating the hydrolysis reaction.

[0087] In the second-stage swirling shear zone, aluminum ash particles carrying some of the hydrolysis products of the aluminum hydroxide film move downwards along the first-stage spiral guide ridge with the airflow. Under the guidance and contraction of the spiral guide ridge, the particle flow is forcibly accelerated and forms a secondary swirling flow. Intense shearing friction and collisions occur between particles and between particles and the roughened friction liner. The second-stage swirling shear zone is used for in-situ mechanical peeling of the passivation film and self-grinding without additional energy consumption. The in-situ mechanical peeling of the passivation film utilizes the kinetic energy of the particles themselves and the shear force of the flow field. Through frictional collisions between particles and between particles and the wall, the loose aluminum hydroxide passivation film newly formed on the aluminum nitride surface is peeled off in real time, exposing the fresh aluminum nitride reaction interface. The self-grinding process without additional energy consumption does not require external grinding media or additional power. It is achieved entirely by the energy of the flow field itself and the structural design of the reactor.

[0088] In the third-stage swirling shear zone, below the second-stage spiral guide ridge, a second stream of atomized water is injected through a second set of radially opposed dual-fluid nozzles. The average diameter of the atomized droplets is 40-80 μm, and the water-to-aluminum ash mass ratio is 0.05-0.15:1. The surface-renewed aluminum nitride particles come into intense contact with the newly injected atomized water again in the third-stage swirling field, undergoing a deep hydrolysis reaction. At the same time, the lower conical section of the swirling atomizing reactor is equipped with adjustable swirling guide vanes. By adjusting the vane angle, the swirling intensity and residence time distribution of the material in the reactor can be changed.

[0089] The total water to aluminum ash mass ratio is controlled at 0.12-0.30:1; the mass flow rate ratio of the first atomized water to the second atomized water is 4:6-6:4; the total residence time of aluminum ash particles in the cyclone atomizing reactor is 45 s-8 min, with the residence time in the second-stage spiral guide zone accounting for 30%-50% of the total time; the cyclone atomizing reactor shell is equipped with a zoned temperature control jacket to control the temperature of each stage of the reaction zone as follows: 60-80℃ for the first-stage cyclone shear zone, 80-100℃ for the second-stage cyclone shear zone, and 70-90℃ for the third-stage cyclone shear zone.

[0090] A multi-stage series swirling shear zone is constructed within a vertical swirling atomizing reactor. The inner wall of the reactor cylinder is provided with at least two stages of spiral guide ribs, and a roughened friction lining is provided in the cylinder wall area between the guide ribs. Aluminum ash powder enters tangentially with an inlet wind speed of 20-35 m / s. In the first-stage swirling shear zone, it undergoes initial wetting by colliding with the first stream of fine atomized water sprayed along the axis. Subsequently, the material is accelerated under the guidance of the spiral guide ribs in the second-stage swirling shear zone to form a secondary swirling flow. Intense shearing friction occurs between particles and between particles and the rough wall surface, causing the aluminum hydroxide passivation film generated on the aluminum nitride surface to peel off in situ, achieving self-grinding and renewal of the reaction interface. The surface-renewed material enters the third-stage swirling shear zone, where it comes into intense contact again with the second stream of atomized water sprayed radially to complete deep hydrolysis.

[0091] Utilizing the energy of the flow field itself, self-grinding surface renewal is achieved through shearing collisions between particles, resulting in zero additional energy consumption. The rough wall surface and spiral guide ridges actively induce turbulent eddies and particle collisions, leading to a higher mass transfer coefficient. The purely passive internal component design of the spiral guide ridges and rough liner results in a simple structure, maintenance-free operation, and long service life. The lower conical section of the swirl atomizing reactor is equipped with adjustable swirl guide vanes, which allow for independent control of swirl intensity and residence time distribution, enhancing process adaptability.

[0092] Example 5

[0093] This embodiment is another implementation of step S3 in Embodiment 2: step S3 is replaced with precise water control based on online monitoring feedback and multi-component synergistic catalytic enhanced hydrolysis, including:

[0094] A. Online monitoring and feedback control system

[0095] Online humidity / moisture sensors and online temperature sensor arrays are respectively installed at the feed end, middle section, and discharge end of the cyclone atomizing reactor; the online humidity / moisture sensors and online temperature sensor arrays transmit the real-time collected material humidity signals and temperature distribution signals to the distributed control system;

[0096] B. Dynamic Zoning Water Control Strategy

[0097] The distributed control system executes dynamic water control logic, including feedforward control, feedback fine-tuning, and independent water control in different zones, based on online monitoring data.

[0098] Feedforward control calculates the theoretical water requirement based on the real-time mass flow rate of the fed aluminum ash and the pre-determined aluminum nitride content, and presets the basic flow rate of the first-stage atomized water. Feedback fine-tuning adjusts the injection volume of the second-stage atomized water in real time based on the material moisture content fed back by the humidity sensor in the middle of the reactor, ensuring that the material in the reaction system is always maintained in a critical wetting state where the surface is wetted and no free water is released internally. Zoned independent water control dynamically adjusts the mass flow rate ratio of the first-stage atomized water to the second-stage atomized water based on the temperature feedback signal, ranging from 3:7 to 7:3. The Sauter mean diameter of the atomized droplets of the first stream of atomized water is controlled at 20-40 μm, and the Sauter mean diameter of the atomized droplets of the second stream of atomized water is controlled at 40-80 μm. Through this dynamic water control strategy, the total water to aluminum ash mass ratio can be precisely controlled within a narrower range of 0.10:1 to 0.25:1, and the generation of free water caused by local over-wetting is completely eliminated.

[0099] C. Gradient temperature control and reaction heat management

[0100] The outer shell of the swirl atomizing reactor is divided into at least three independent temperature control zones along the axial direction. Each temperature control zone is equipped with an independent heat exchange jacket and temperature control loop. The three independent temperature control zones are the first temperature zone of the upper turbulent mixing zone, the second temperature zone of the middle enhanced reaction zone, and the third temperature zone of the lower ripening and separation zone.

[0101] The first temperature zone is controlled at 60-80℃ to receive the exothermic reaction from the initial hydrolysis and prevent local overheating that could lead to excessively rapid evaporation of moisture. The second temperature zone is controlled at 85-105℃ to utilize the concentrated exothermic reaction from aluminum nitride hydrolysis and to remove and recover excess heat through a heat exchange system for preheating the feed air or process water. The third temperature zone is controlled at 70-90℃ to maintain a suitable temperature for complete hydrolysis of residual gases. Temperature fluctuations are controlled within ±2℃.

[0102] D. Multi-component synergistic catalytic promoter system

[0103] A multi-component synergistic catalytic promoter system is introduced simultaneously via atomized water. This system consists of the following components in parts by mass:

[0104] Main catalyst: alkali metal hydroxide or alkali metal carbonate, 0.05-0.2 parts;

[0105] Co-catalyst: Organic amine compound, preferably triethanolamine or ethylenediamine, 0.01-0.1 parts;

[0106] Dispersing and separating agent: water-soluble polymer compound, preferably polyethylene glycol (PEG, molecular weight 400-2000) or polyvinyl alcohol, 0.005-0.05 parts;

[0107] The total amount of the multi-component synergistic catalytic promoter system added accounts for 0.015%-0.35% of the total mass of aluminum ash; the synergistic mechanism of each component is as follows:

[0108] Main catalyst: Adjusts the pH of the reaction micro-region to accelerate the hydrolysis kinetics of aluminum nitride;

[0109] Co-catalyst: By coordinating amine groups with aluminum atoms on the surface of aluminum nitride, the Al-N bond energy is weakened, thereby reducing the activation energy of the reaction;

[0110] Dispersing and separating agent: adsorbed on the surface of newly generated aluminum hydroxide particles, inhibiting their aggregation and densification, keeping them loose and porous, facilitating the inward diffusion of water molecules and the outward escape of ammonia;

[0111] E. Determination of reaction endpoint and adaptive adjustment

[0112] The distributed control system determines whether the hydrolysis reaction has reached its endpoint based on the signals from the online humidity sensor and gas sensor at the discharge end of the cyclone atomizing reactor. When the ammonia concentration at the discharge end is detected to be lower than the set threshold, the system automatically determines that the reaction is complete. If it is higher than the threshold, the system automatically extends the material residence time or finely adjusts and increases the amount of secondary atomizing water until the requirements are met.

[0113] An online monitoring and feedback control system was established, with humidity and temperature sensor arrays installed at the feed end, middle section, and discharge end of the cyclone atomizing reactor. The signals were connected to a distributed control system. The control system implemented a dynamic zoned water control strategy: the basic water volume was preset based on the feed flow rate, and the secondary water volume was fine-tuned based on the humidity feedback from the middle section, so that the material was always in a critically wetted state. The total water to aluminum ash mass ratio was precisely controlled at 0.10:1-0.25:1. The reactor was divided into three independent temperature control zones along the axial direction, with temperatures controlled at 60-80℃, 85-105℃, and 70-90℃ respectively, and temperature fluctuations not exceeding ±2℃. Excess reaction heat was recovered for preheating the process medium. A multi-component synergistic catalytic promoter system was introduced simultaneously through the atomized water, including a main catalyst (alkali metal hydroxide / carbonate), a co-catalyst (organic amine), and a dispersant (water-soluble polymer), with the total addition accounting for 0.015%-0.35% of the aluminum ash mass. The main catalyst accelerates the reaction, the co-catalyst weakens the Al-N bond energy, and the dispersing and isolating agent inhibits the agglomeration of aluminum hydroxide. The online monitoring and feedback control system adaptively adjusts the residence time or water volume based on the ammonia concentration signal at the discharge end to ensure complete hydrolysis.

[0114] Online monitoring and feedback enable dynamic water control, maintaining a water-to-aluminum ash ratio of 0.10-0.25:1 to keep the system in a critical wetting state. The system upgrades from open-loop control to closed-loop adaptive control, fundamentally ensuring the reliability of zero wastewater discharge. Three independent and precise temperature control in three zones allows for reaction heat recovery with fluctuations within ±2℃, enabling tiered utilization and precise management of reaction heat, saving energy and reducing consumption while improving reaction consistency. The multi-component synergistic system of the main catalyst, co-catalyst, and dispersant / isolator upgrades from simple pH adjustment to multi-dimensional synergistic regulation based on kinetics, thermodynamics, and structure, resulting in a qualitative leap in catalytic efficiency and depth. Online monitoring, endpoint determination, and adaptive adjustment enable intelligent and unmanned operation of the process, ensuring batch-to-batch consistency of product quality.

[0115] Example 6

[0116] This embodiment is another implementation of step S3 in Embodiment 2: replacing step S3 with phase change cycle water precise regulation and staged activation synergistic catalytic enhancement of hydrolysis, including:

[0117] A. Dual-mode phase change moisture control system

[0118] A dual-mode coordinated water supply system of liquid atomized water and gaseous water vapor was constructed in a swirl atomizing reactor. The dual-mode coordinated water supply system of liquid atomized water and gaseous water vapor includes a liquid atomized water supply subsystem and a gaseous water vapor supply subsystem.

[0119] The liquid atomized water supply subsystem injects liquid atomized water through the first set of dual-fluid nozzles. The average diameter of the atomized droplets is 20-50 μm, and it is used to initiate the hydrolysis reaction and provide the stoichiometric amount of water required for the reaction. The gaseous water vapor supply subsystem introduces low-pressure saturated water vapor at a temperature of 105-130℃ into the reaction chamber through a microporous steam distributor arranged in the lower section of the swirl atomizing reactor. The amount of water vapor introduced is 5%-20% of the mass of the liquid water.

[0120] The working mechanism of the dual-mode synergistic water supply system of liquid atomized water and gaseous water vapor is as follows: the liquid atomized water provides the main water required for rapid reaction, which is used to achieve efficient hydrolysis of aluminum nitride; the gaseous water vapor penetrates into the micropores and gaps of aluminum ash particles at the molecular level, replenishing the water in dead areas that are difficult for liquid water to wet, and at the same time, the latent heat released by steam condensation is used to provide in-situ heating for the reaction system to maintain temperature stability; the liquid water film formed by steam condensation is extremely thin and uniform, which effectively avoids the accumulation of free water caused by excessive liquid water.

[0121] B. Moisture Closed-Loop Recovery and Recycling Subsystem

[0122] A moisture condensation and recovery device is added between the tail gas outlet of the cyclone atomizing reactor and the ammonia absorption tower. The moisture condensation and recovery device includes a primary indirect condenser and a secondary deep dehumidifier. The primary indirect condenser uses circulating cooling water to reduce the tail gas temperature to 40-60℃, recovering most of the water vapor and vaporized process water carried in the tail gas. The condensate is collected in a recovery water storage tank. The secondary deep dehumidifier uses refrigerant direct cooling to reduce the tail gas temperature to 10-20℃, further recovering residual moisture. After the condensate in the recovery water storage tank passes the online water quality monitoring module, it is returned to the atomizing water supply system through the return water pipeline, mixed with fresh process water in a certain proportion, and reused for spraying. The online water quality monitoring module detects indicators including pH value, conductivity, and ammonia nitrogen concentration. When the ammonia nitrogen concentration exceeds the set threshold, it automatically switches to the ammonia absorption tower feed pipeline.

[0123] C. Staged activation of latent synergistic catalytic promoter system

[0124] The accelerator system is designed as a graded activation mode, which includes a first-stage accelerator and a second-stage accelerator.

[0125] The first-stage accelerator is an instant activation component, sprayed in with atomized water, and accounts for 60%-80% of the total mass of the accelerator system. The first-stage accelerator includes alkali metal carbonates and low molecular weight organic amines. The alkali metal carbonates include sodium carbonate and potassium carbonate, and the amount of alkali metal carbonates added is 0.02-0.15 parts per 100 parts of aluminum ash. The low molecular weight organic amine is triethanolamine, and the amount of low molecular weight organic amine added is 0.01-0.05 parts per 100 parts of aluminum ash.

[0126] The second-stage accelerator is a latent thermally activated component, premixed in aluminum ash powder, accounting for 20%-40% of the total mass of the accelerator system. The second-stage accelerator includes microencapsulated alkali metal hydroxides and thermally decomposable organic amine precursors. The microencapsulated alkali metal hydroxides use polymeric materials with melting points or solubilities of 60-90℃ as the capsule wall material, encapsulating sodium hydroxide or potassium hydroxide particles to form thermally responsive microcapsules. The polymeric materials include polyethylene glycol and polyvinyl alcohol. In the low-temperature zone at the reactor inlet, the capsule wall remains intact, and sodium hydroxide is not released. When the material enters the high-temperature zone (85-105℃) in the middle section, the capsule wall melts or dissolves, releasing a strongly alkaline catalytic component in situ.

[0127] The precursors of thermally decomposable organic amines are urea or hexamethylenetetramine, which have extremely low catalytic activity at room temperature. When the material enters the high-temperature zone, it decomposes and releases ammonia or amine active components, providing catalytic action at the stage most needed in the reaction.

[0128] The creative effects of hierarchical activation:

[0129] To avoid excessively violent local reactions: the strongly alkaline components are not released in the low-temperature zone to prevent the initial reaction from getting out of control and local overheating;

[0130] Precise matching between catalytic action and reaction process: In the middle and late stages of the reaction, when the passivation film has begun to form and the reaction rate decreases, the latent component releases a strong catalyst at specific points to maintain high reaction activity.

[0131] Extend the effective action time of the catalyst: avoid the catalyst being rapidly consumed or lost with the tail gas in the early stage of the reaction;

[0132] D. Dynamic zoning setting and adaptive adjustment of the water-to-aluminum-ash ratio

[0133] Based on online monitoring data, the distributed control system sets target values ​​for the water-to-aluminum ash ratio in each of the three reaction zones: the upper turbulent mixing zone, the middle acoustic enhancement reaction zone, and the lower deep curing and separation zone. Specifically, in the upper turbulent mixing zone, the mass ratio of liquid atomized water to aluminum ash is 0.03-0.08:1, with the water in the form of fine droplets; in the middle acoustic enhancement reaction zone, the mass ratio of liquid atomized water and steam condensate to aluminum ash is 0.05-0.12:1, with the water in the form of a combination of droplets and thin liquid films; and in the lower deep curing and separation zone, the mass ratio of steam condensate to aluminum ash is 0.02-0.05:1, with the water in the form of molecular-level adsorbed water.

[0134] E. Intelligent endpoint determination based on online analysis of product crystal phase

[0135] An online Raman or near-infrared spectroscopy probe is installed at the discharge end of the cyclone atomizing reactor to collect the spectral signals of the denitrified aluminum ash solid phase material in real time; the distributed control system has a built-in aluminum hydroxide crystal phase recognition model, which can distinguish the characteristic peaks of amorphous Al(OH)3, boehmite and Bayerite.

[0136] When the proportion of amorphous Al(OH)3 in the product is detected to be higher than 80% and there is no residual aluminum chloride characteristic peak, the hydrolysis reaction is determined to have reached the endpoint. If residual aluminum chloride peak or excessively high proportion of dense crystalline phase is detected, the following adjustment strategies are automatically executed: extend the material residence time, finely adjust and increase the amount of steam introduced in the middle section, and increase the activation rate of the second-stage latent promoter.

[0137] A dual-mode phase change moisture control system was constructed, including a liquid atomized water supply subsystem and a gaseous water vapor supply subsystem. The liquid atomized water (Soter average diameter 20-50μm) provides moisture for the main reaction. Low-pressure saturated water vapor at 105-130℃ is introduced in the middle and lower sections to replenish microporous moisture through molecular-level permeation and provide in-situ heating. The exhaust gas undergoes secondary condensation in a moisture condensation and recovery device, and the recovered water is returned to the water supply system after online water quality monitoring. The process water recycling rate reaches 85%-95%.

[0138] The accelerator adopts a graded activation mode: the first-stage immediate activation component (alkali metal carbonate, low molecular weight organic amine) is sprayed in with atomized water; the second-stage latent thermal activation component (microcapsule-encapsulated alkali metal hydroxide, thermally decomposable organic amine precursor) is premixed in aluminum ash and released in situ in the mid-stage high-temperature zone.

[0139] The distributed control system dynamically sets the water-to-aluminum ash ratio for each zone, with a total fresh water-to-aluminum ash mass ratio of 0.08-0.20:1. An online Raman spectroscopy probe is installed at the discharge end to intelligently determine the reaction endpoint based on an aluminum hydroxide crystal phase recognition model and adaptively adjust the process parameters.

[0140] The dual-mode phase change cycle of liquid water and steam enables microporous permeation and closed-loop water recovery; it upgrades water conservation to water recycling, transforming zero wastewater discharge from a passive guarantee to an active closed-loop system; that is, traditional thinking holds that excessive water must be added to achieve full wetting of the particles, while this invention achieves full wetting of the particles through molecular-level permeation of gaseous water vapor without generating liquid free water, and at the same time, it recovers all evaporated water through condensation and recycling, forming a closed-loop water cycle;

[0141] The catalytic activity is staged, with immediate and latent components matched to the temporal and spatial progression of the reaction. The catalytic activity changes from constant throughout the process to on-demand release, solving the problem of strong catalysts being too strong in the early stages and weak in the later stages. Strong alkaline catalysts have a significant acceleration effect but are prone to causing the initial reaction to runaway. This invention uses microcapsule thermal response encapsulation technology to activate strong catalysts in situ at the required time and location, achieving a catalytic mode of mild start-up and strong mid-stage.

[0142] Experimental objective: By comparing the various embodiments of the present invention (Examples 2-6) with the prior art (Comparative Example 1), and in accordance with the national standard GB / T 22627-2022 "Water Treatment Agent Polyaluminum Chloride" and related environmental protection indicators, this invention aims to verify its significant technological advancements and inventiveness in reducing ammonia nitrogen content in polyaluminum chloride products, achieving zero wastewater discharge, improving the controllability of product basicity, reducing energy consumption, and ensuring production safety and environmental protection.

[0143] Experimental materials: Secondary aluminum ash from an aluminum plant was used. Its main components, as determined by testing, were: Al2O3-65%, AlN-12%, metallic Al-8%, and chloride salts-15%. The aluminum ash was pre-crushed and ball-milled to a particle size of less than 80 mesh, serving as the uniform raw material for all examples and comparative examples.

[0144] Note: The following water-based ash refers to water and aluminum ash.

[0145] I. Comparative Example 1 (Existing Traditional Water Washing Denitrification Process)

[0146] Experimental steps:

[0147] 1000 kg of secondary aluminum ash was added to a stirred reactor, and 2000 kg of process water was added at a water-ash mass ratio of 2:1. The mixture was stirred and washed for 2 hours. During the reaction, the temperature, pressure, and ammonia gas emission within the reactor were monitored. After washing, the slurry was filtered through a filter press to obtain filter cake (denitrified aluminum ash) and filtrate (wastewater). The ammonia nitrogen content of the filter cake was tested, and the ammonia nitrogen concentration and pH value of the wastewater were measured and tested. The denitrified aluminum ash was processed using a conventional acid dissolution process, in which 20% industrial hydrochloric acid was added to the reactor for acid dissolution, polymerization, and aging, ultimately yielding liquid polyaluminum chloride. The product was tested according to GB / T 22627-2022 standard for various indicators. See Table 1 below for details.

[0148] Table 1

[0149] Testing items Detection value GB / T 22627-2022 Limits Compliance status Ammonia nitrogen content of polyaluminum chloride products 5500 mg / L ≤500 mg / L Substandard Wastewater generation 2.5 tons / ton aluminum ash - - wastewater ammonia nitrogen concentration 800-1500 mg / L - - Product basicity 52% 40%-90% Meets standards Safety status of the reaction process The production of large amounts of foam and ammonia gas increases the pressure in the reactor, necessitating the opening of the vent valve and posing a risk of overflow. - There are potential safety hazards. Energy consumption for ammonia stripping Wastewater needs to be heated to remove ammonia and recover ammonia, which consumes steam. - Additional energy consumption

[0150] Table 1 shows that the ammonia nitrogen content of polyaluminum chloride products prepared by the traditional water washing denitrification process is as high as 5500 mg / L, far exceeding the ≤500 mg / L requirement of GB / T 22627-2022 standard. Each ton of aluminum ash processed generates approximately 2.5 tons of high-concentration ammonia-containing wastewater, which is difficult and costly to treat subsequently. Batch-process reactions also exhibit concentrated exothermic and gas-generating phenomena, posing significant safety hazards.

[0151] II. Experimental Examples 1-5

[0152] Experimental Example 1 is Embodiment 2 of the present invention.

[0153] The process was carried out according to the scheme of Example 2. In the S1 raw material pretreatment and conditioning step, aluminum ash was crushed and ball-milled to a particle size of 40-200 mesh. Calcium oxide, accounting for 2% of its total mass, was added to the aluminum ash powder as an auxiliary dissociation agent. After mixing evenly, the mixture was allowed to stand for aging for 60 minutes to obtain conditioned aluminum ash. In the S3 hydrolysis reaction process, sodium hydroxide, accounting for 0.01% of the total mass of aluminum ash, was introduced simultaneously through atomized water as a hydrolysis promoter. In the S4 step, the ammonia-containing tail gas was first treated by a cyclone dust collector to recover the entrained fine aluminum ash dust, and the recovered dust was returned to the feeding system. In the S5 acid dissolution process, sodium aluminate, accounting for 1% of the total mass of the denitrified aluminum ash solid material, was added to the reaction system as a polymerization degree regulator. The aging temperature was 80℃, and the aging time was 4 hours. The water-ash mass ratio was controlled at 0.2:1, and the reaction temperature was maintained at 95-105℃. The parameters of the remaining steps were performed according to the range in Example 2. Specific experimental data are shown in Table 2.

[0154] Table 2

[0155] Testing items Detection value GB / T 22627-2022 Limits Compliance status Ammonia nitrogen content of polyaluminum chloride products 380 mg / L ≤500 mg / L Meets standards Wastewater generation 0 - Zero emissions Product basicity 68% 40%-90% Standards can be adjusted Dust recovery volume 3.5kg / ton aluminum ash - Improve resource utilization ammonia product concentration 20% - direct use Safety status of the reaction process Continuous, metered feeding and water spraying eliminate centralized heat release and gas generation, and reduce the risk of tank overflow. - Safe and controllable

[0156] Table 2 shows that: 1. The product's ammonia nitrogen content is 380 mg / L, which meets the requirements of GB / T 22627-2022 standard (ammonia nitrogen ≤0.05%, i.e. ≤500 mg / L); 2. No process wastewater is generated; 3. By adding a polymerization degree regulator, the product's basicity reaches 68%, and the basicity is adjustable within the standard range of 40%-90%, allowing for flexible adjustment of product performance indicators according to different water quality treatment needs; 4. Cyclone dust removal recovers effective aluminum components, improving resource utilization while preventing dust from entering the absorption tower, clogging the packing, or contaminating the ammonia product.

[0157] Experimental Example 2 is Example 3 of the present invention.

[0158] Based on Example 2, step S2 is replaced with the stepped swirl atomization coupled with acoustic vibration enhanced hydrolysis denitrification scheme of Example 3. A three-stage stepped reaction zone is constructed within the vertical swirl atomization reactor: an upper turbulent mixing zone, a middle acoustic enhancement reaction zone, and a lower deep curing and separation zone. Aluminum ash powder enters tangentially into the upper turbulent mixing zone at an inlet wind speed of 20 m / s. The first set of dual-fluid nozzles at the top center sprays the first stream of atomized water (SMD 30-50 μm) downwards along the axis. After the material enters the middle acoustic enhancement reaction zone, it is subjected to a 28 kHz frequency and a power density of 1.0 W / cm² through six ultrasonic transducers evenly arranged circumferentially on the outer wall of the reactor. 2 High-frequency ultrasonic vibration was applied, and a second stream of atomized water (SMD 50-80μm) was injected radially in a counter-current manner. Water spraying was stopped in the lower deep curing and separation zone, and the reactor was kept at 80℃ through the jacket. Preheated nitrogen to 70℃ was introduced as an inert carrier gas, and gas stripping was performed at an apparent gas velocity of 1.0 m / s. The mass flow ratio of the first to the second stream of atomized water was 7:3, and the total water-ash mass ratio was controlled at 0.15:1. The remaining steps were the same as in Example 2. Specific experimental data are shown in Table 3.

[0159] Table 3

[0160] Testing items Detection value Compared with Comparative Example 1 Compared with Experimental Example 1 Ammonia nitrogen content of polyaluminum chloride products 120 mg / L Reduced by 97.8% Reduced by 68.4% Ammonia nitrogen content of denitrified aluminum ash 95 mg / L - Reduced by 75% Wastewater generation 0 Zero emissions Zero emissions Product basicity 70% An increase of 18 percentage points Basically equivalent Reaction rate constant Increased by about 4 times - - The reactor volume can be reduced proportionally 40% - - Ammonia product concentration 22% - -

[0161] Table 3 shows that: 1. The ammonia nitrogen content of the product is reduced to 120 mg / L, meeting the potential standard requirements for drinking water grade polyaluminum chloride; 2. The ultrasonic in-situ stripping and passivation film technology solves the self-obstruction problem of aluminum nitride hydrolysis reaction (i.e., the product layer hinders the continued reaction), which can make the aluminum nitride conversion rate approach 100%; combined with the lower stage carrier gas stripping technology, the physically adsorbed ammonia is completely separated; 3. Deep conversion of aluminum nitride is achieved under extremely low water-ash ratio (0.15:1), breaking the technical contradiction of "adding more water to achieve deep ammonia removal, and adding more water will inevitably produce wastewater" from the perspective of chemical reaction kinetics; 4. The high-frequency vibration of ultrasound effectively prevents the adhesion and bridging of damp aluminum ash powder on the reactor wall; 5. The introduction of ultrasound increases the hydrolysis reaction rate constant by about 4 times, and under the same denitrification depth, the reactor volume can be reduced by more than 40%, and the processing throughput is greatly improved.

[0162] Experimental Example 3 is Example 4 of the present invention.

[0163] Based on Example 2, step S2 is replaced with the multi-stage swirling shear collision coupling self-grinding surface renewal enhanced hydrolysis denitrification scheme of Example 4. A multi-stage series swirling shear zone is constructed within a vertical swirling atomizing reactor. The inner wall of the reactor has two stages of inwardly protruding spiral guide ribs along the axial direction (the protrusion height is 10% of the reactor diameter, and the spiral angle is 45 degrees). A roughened friction lining (surface roughness Ra = 100 μm) is provided in the area of ​​the reactor wall between the guide ribs. Aluminum ash powder enters the first-stage swirling shear zone tangentially at an inlet wind speed of 25 m / s. The first set of dual-fluid nozzles sprays the first stream of atomized water (SMD 20-40 μm) downwards along the axis, with a water-ash ratio of 0.08:1. The material enters the second-stage swirling shear zone through the first-stage spiral guide ribs, where it is accelerated under the guiding and contraction action to form a secondary swirling flow, resulting in self-grinding surface renewal. The third-stage swirling shear zone is injected with a second stream of atomized water (SMD 40-80μm) through a second set of radially opposed nozzles, with a water-to-cement ratio of 0.10:1. The swirling guide vanes in the lower conical section of the reactor are adjusted to a medium opening. The total water-to-cement mass ratio is controlled at 0.18:1, and the total residence time is approximately 3 minutes. The reactor shell is equipped with a zoned temperature-controlled jacket to control the temperatures of the three reaction zones at 70℃, 90℃, and 80℃ respectively. The remaining steps are the same as in Example 2. Specific experimental data are shown in Table 4.

[0164] Table 4

[0165] Testing items Detection value Compared with Comparative Example 1 Compared with Experimental Example 1 Ammonia nitrogen content of polyaluminum chloride products 85 mg / L Reduced by 98.5% Reduced by 77.6% Ammonia nitrogen content of denitrified aluminum ash 65 mg / L - Reduced by 82.9% Wastewater generation 0 Zero emissions Zero emissions Product basicity 72% Increase by 20 percentage points Increased by 4 percentage points Self-grinding additional energy consumption 0 - - Mass transfer coefficient improvement Significant improvement - - Equipment maintenance cycle extend - Maintenance-free

[0166] Table 4 shows that: 1. The ammonia nitrogen content of the product is reduced to 85 mg / L, further approaching the drinking water grade polyaluminum chloride standard; 2. Utilizing the energy of the flow field itself, self-grinding surface renewal is achieved through shearing collisions between particles, with zero additional energy consumption, solving the problem of requiring external grinding media or ultrasonic energy in traditional technologies; 3. The rough wall surface and spiral guide ridges actively induce turbulent eddies and particle collisions, significantly improving the mass transfer coefficient; 4. The spiral guide ridges and rough liner are purely passive internal components, with a simple structure, maintenance-free operation, and long service life; 5. The addition of adjustable swirl guide vanes allows for independent control of swirl intensity and residence time distribution, resulting in stronger process adaptability; 6. The feasibility of the technical approach of "using mechanical energy to replace chemical potential to drive the reaction" in the field of aluminum ash denitrification is verified.

[0167] Experimental Example 4 is Example 5 of the present invention.

[0168] Based on Example 2, step S3 is replaced with the precise water control and multi-component synergistic catalytic enhanced hydrolysis scheme based on online monitoring feedback from Example 5. Online humidity / moisture sensors and online temperature sensor arrays are installed at the feed end, middle section, and discharge end of the cyclone atomizing reactor, respectively, and the signals are connected to a distributed control system (DCS). The control system executes a dynamic zoned water control strategy: feedforward control presets the basic flow rate of the first-stage atomized water, and feedback fine-tuning adjusts the injection volume of the second-stage atomized water in real time to maintain a "critical wetting" state. The total water-ash mass ratio is precisely controlled at 0.12:1. The reactor shell is divided into three independent temperature control zones along the axial direction: the first zone is 60-70℃, the second zone is 90-100℃, and the third zone is 80-85℃, with temperature fluctuations controlled within ±2℃. A multi-component synergistic catalytic promoter system was simultaneously introduced via atomized water: the main catalyst was 0.1 parts sodium carbonate / 100 parts aluminum ash, the co-catalyst was 0.03 parts triethanolamine / 100 parts aluminum ash, and the dispersant / isolating agent was 0.01 parts polyethylene glycol (PEG-1000) / 100 parts aluminum ash. The DCS system adaptively adjusted the residence time or water volume based on the ammonia concentration signal at the discharge end. The remaining steps were the same as in Example 2. Specific experimental data are shown in Table 5.

[0169] Table 5

[0170] Testing items Detection value Compared with Comparative Example 1 Compared with Experimental Example 1 Ammonia nitrogen content of polyaluminum chloride products 150 mg / L Reduced by 97.3% Reduce by 60% Wastewater generation 0 Zero emissions Zero emissions Actual water-cement mass ratio 0.12:1 Reduced by 94% Reduced by 40% Product basicity 75% Increased by 23 percentage points Increased by 7 percentage points Temperature control accuracy ±2℃ - Better than ±5℃ Product quality batch consistency high - Significant improvement Reaction heat recovery 15% - Energy saving and consumption reduction

[0171] Table 5 shows that: 1. The ammonia nitrogen content of the product is reduced to 150 mg / L; 2. Online monitoring and feedback dynamic water control, with the water-ash ratio precisely controlled at 0.12:1, upgrades from "open-loop control" to "closed-loop adaptive control," fundamentally ensuring the reliability of zero wastewater discharge; 3. Independent and precise temperature control and reaction heat recovery in three zones, with temperature fluctuations controlled within ±2℃, achieves cascade utilization and precise management of reaction heat, resulting in energy saving and consumption reduction; 4. The multi-component synergistic system of main catalyst, co-catalyst, and dispersant / isolator is upgraded from single pH adjustment to multi-dimensional synergy of kinetic, thermodynamic, and structural regulation; 5. Online monitoring, endpoint determination, and adaptive adjustment enable intelligent and unmanned operation of the process, ensuring batch-to-batch consistency of product quality.

[0172] Experimental Example 5 is Example 6 of the present invention.

[0173] Based on Example 2, step S3 is replaced with the phase change cycle moisture precise control and graded activation synergistic catalytic enhanced hydrolysis scheme of Example 6. A dual-mode phase change moisture control system is constructed: the liquid atomized water supply subsystem injects liquid atomized water (SMD 20-50μm) through the first set of dual-fluid nozzles, and the gaseous water vapor supply subsystem introduces low-pressure saturated water vapor at 120℃ into the reaction chamber through a microporous steam distributor, with the water vapor injection rate being 15% of the liquid water mass. A moisture condensation and recovery device is added between the tail gas outlet and the ammonia absorption tower (the first-stage indirect condenser cools the water to 50℃ and the second-stage deep dehumidifier cools it to 15℃). The condensate is returned to the water supply system after online water quality monitoring. A graded activation accelerator system was adopted: the first-stage immediate activating component consisted of 0.05 parts sodium carbonate / 100 parts aluminum ash and 0.02 parts triethanolamine / 100 parts aluminum ash, sprayed in with atomized water; the second-stage latent thermal activating component consisted of 0.03 parts polyethylene glycol-coated sodium hydroxide microcapsules / 100 parts aluminum ash, premixed in the aluminum ash and released in situ in the high-temperature zone of 85-105℃. An online Raman spectroscopy probe was installed at the discharge end, and the reaction endpoint was intelligently determined based on the aluminum hydroxide crystal phase recognition model. The total fresh water-ash mass ratio was controlled at 0.10:1. The remaining steps were the same as in Example 2. Specific experimental data are shown in Table 6:

[0174] Table 6

[0175] Testing items Detection value Compared with Comparative Example 1 Compared with Experimental Example 1 Ammonia nitrogen content of polyaluminum chloride products 70 mg / L Reduced by 98.7% Reduced by 81.6% Ammonia nitrogen content of denitrified aluminum ash 50 mg / L - Reduced by 86.8% Wastewater generation 0 Zero emissions Zero emissions Fresh water to water-ash ratio 0.10:1 Reduced by 95% Reduce by 50% Process water recycling rate 90% - - Product basicity 78% Increased by 26 percentage points Increase by 10 percentage points Aluminum nitride conversion rate Nearly 100% - - Initial reaction control status Mild and controllable - No localized overheating

[0176] Table 6 shows that: 1. The ammonia nitrogen content of the product was reduced to 70 mg / L, the lowest among all experimental examples, and the aluminum nitride conversion rate approached 100%; 2. A dual-mode phase change circulation system of liquid water and steam was constructed. Gaseous water vapor replenished the microporous water and provided in-situ heating through molecular-level permeation, achieving complete wetting of the particle interior without generating liquid free water; all evaporated water was reused through condensation recovery, and the process water recycling rate reached 90%, transforming zero wastewater discharge from a passive guarantee to an active closed-loop system; 3. A graded activation promoter system: the immediate component ensured the reaction start-up, and the latent component (microcapsule-coated alkali metal hydroxide) was released in-situ in the mid-stage high-temperature zone, achieving the ideal catalytic mode of "mild start-up and strong mid-stage", solving the problem of strong catalysts being too strong in the early stage and weak in the later stage; 4. The online Raman spectroscopy probe at the discharge end intelligently determined the reaction endpoint based on the crystal phase recognition model, upgrading from indirect determination by ammonia concentration to direct characterization; 5. The fresh water usage was reduced to 0.10:1, a 95% reduction compared to Comparative Example 1 and a 50% reduction compared to Experimental Example 1.

[0177] Table 7

[0178] Comparison indicators Comparative Example Experimental Example 1 Experiment Example 2 Experimental Example 3 Experiment Example 4 Experimental Example 5 GB / T 22627-202 requirements Ammonia nitrogen content (mg / L) of polyaluminum chloride products 5500 380 120 85 150 70 ≤500 Ammonia nitrogen compliance status Substandard Meets standards Meets standards Meets standards Meets standards Meets standards - Wastewater generation (tons / ton of aluminum ash) 2.5 0 0 0 0 0 - Water-cement ratio (fresh water) 2:1 0.2:1 0.15:1 0.18:1 0.12:1 0.10:1 - The amount of fresh water used was reduced compared to the control group. - 90% 92.5% 91% 94% 95% - Product basicity (%) 52 68 70 72 75 78 40-90 Ammonia nitrogen content in denitrified aluminum ash (mg / L) 2500 380 95 65 120 50 -

[0179] Table 7 shows that the mass fraction requirement for ammonia nitrogen (calculated as N) in GB / T 22627-2022 is ≤0.05%, i.e., ≤500 mg / L; the basicity standard range is 40%-90%. The ammonia nitrogen content of the products in each experimental example meets the national standard requirements, and the ammonia nitrogen content of experimental examples 3-6 is significantly lower than that of experimental example 1.

[0180] Through Table 1-7 and Figure 1-4 It can be known that:

[0181] The ammonia nitrogen content was significantly reduced, and the product quality met national standards: In Comparative Example 1, the ammonia nitrogen content of the polyaluminum chloride product prepared by the traditional process was 5500 mg / L, far exceeding the limit of GB / T 22627-2022 (≤500 mg / L). The ammonia nitrogen content of all experimental examples in this invention met the standards: Example 1 was 380 mg / L, Example 2 decreased to 120 mg / L, Example 3 decreased to 85 mg / L, Example 4 was 150 mg / L, and Example 5 decreased to 70 mg / L, a reduction of 98.7% compared to Comparative Example 1. This significant reduction in ammonia nitrogen content verifies the remarkable effectiveness of the swirl atomization-enhanced mass transfer and various optimization methods in improving the hydrolysis conversion rate of aluminum nitride in this invention.

[0182] Achieving zero discharge of process wastewater: Comparative Example 1 generates approximately 2.5 tons of high-concentration ammonia-containing wastewater for every ton of aluminum ash treated. In contrast, all experimental examples of this invention achieve zero wastewater discharge by precisely controlling the water-ash ratio within the range of 0.10-0.20:1. In particular, Experiment 5, through phase change circulation and condensation recovery technology, upgrades zero wastewater discharge from a passive guarantee to an active closed-loop system, achieving a process water recycling rate of 90% and reducing fresh water consumption by 95% compared to Comparative Example 1.

[0183] The basicity is adjustable and the product has wide applicability: The basicity of the product in Comparative Example 1 is 52%. In the experimental examples of this invention, the basicity can be flexibly adjusted within the range of 68%-78% by introducing a degree of polymerization regulator. All of them meet the requirements of GB / T 22627-2022 standard (40%-90%). The product performance can be adjusted according to different water quality treatment needs (such as high basicity for high turbidity water and low basicity for low temperature and low turbidity water).

[0184] Production process is safe and environmentally friendly: The comparative batch reaction has the risk of overflow and splashing caused by concentrated heat release and concentrated gas production. The present invention adopts continuous quantitative feeding and water spraying, and the material achieves controlled flow of "plastic flow as the main flow" in the swirl atomization reactor, which eliminates the safety hazards at the source.

[0185] Resource utilization is fully realized, and energy conservation and consumption reduction are significant: nitrogen in aluminum ash is recovered in the form of ammonia water, eliminating the need for additional ammonia stripping energy consumption. Experimental Example 5 further reduces fresh water consumption and ineffective catalyst loss through closed-loop water recovery and a graded activation promoter system.

[0186] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0187] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification, characterized in that, Includes the following steps: S1. Raw material pretreatment and conditioning Aluminum ash is crushed and ball-milled to obtain aluminum ash powder with a particle size of 40-200 mesh; 0.5%-5% of an auxiliary dissociation agent is added to the aluminum ash powder by its total mass, and after mixing evenly, it is allowed to stand and age for 30-120 min to obtain conditioned aluminum ash; then the conditioned aluminum ash is continuously and quantitatively fed into a cyclone atomizing reactor. S2. A swirling flow field is formed inside the swirling atomizing reactor, and atomized water is sprayed into the swirling flow field, so that aluminum ash and atomized water can fully contact each other in the gas-solid cloud dynamic field and undergo a hydrolysis reaction to generate aluminum hydroxide and ammonia gas. The swirling atomizing reactor has a vertical structure, and aluminum ash enters tangentially from the top of the reactor to form a downward spiral swirling flow. The atomized water is sprayed out from a dual-fluid nozzle, and the Soder mean diameter of the atomized droplets is controlled at 20-100μm. The atomized water is sprayed radially from the central axis or peripheral wall of the reactor to fully collide and contact with the aluminum ash particles. The residence time of aluminum ash in the swirling atomizing reactor is 30 s-10 min. S3. Control the amount of water added so that the mass ratio of water to aluminum ash is 0.1-0.5:1; through the heat exchange jacket or internal coil arranged on the wall of the cyclone atomizing reactor, the temperature of the reaction system is precisely maintained at a certain set value within the range of 70-120℃, with temperature fluctuation not exceeding ±5℃; the material residence time is controlled by continuous feeding and discharging to ensure that the hydrolysis reaction proceeds fully. During the hydrolysis reaction, a hydrolysis accelerator of 0.01%-0.5% of the total mass of aluminum ash is introduced simultaneously through atomized water; the hydrolysis accelerator is any one or a combination of at least two of alkali metal hydroxides, alkali metal carbonates or organic amine compounds. S4. The ammonia-containing tail gas generated by the hydrolysis reaction is drawn out from the top of the cyclone atomizing reactor and first passed through a cyclone dust collector to recover the entrained fine aluminum dust. The recovered dust is returned to the feeding system of step S1. The ammonia-containing tail gas after dust removal is sent to an ammonia absorption tower for multi-stage absorption to prepare ammonia water by-product. The multi-stage absorption is either three-stage water absorption or three-stage dilute acid absorption to prepare ammonia water with a mass concentration of 15%-25%. S5. The denitrified aluminum ash solid material discharged from the bottom of the cyclone atomizing reactor is reacted with hydrochloric acid using an acid dissolution process to prepare polyaluminum chloride product. During the acid dissolution process and hydrochloric acid reaction, a polymerization degree regulator accounting for 0.1%-2% of the total mass of the denitrified aluminum ash solid material is added to the reaction system. The polymerization degree regulator is any one or a combination of at least two of sodium aluminate, sodium aluminate, and aluminum hydroxide gel. After the acid dissolution process and hydrochloric acid reaction are completed, a curing treatment is performed at a curing temperature of 60-90℃ for 2-8 hours. The final polyaluminum chloride product has a basicity of 45%-85% and an ammonia nitrogen content of less than 500 mg / L.

2. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 1, characterized in that, In step S1, the auxiliary dissociation agent is any one or a mixture of at least two of calcium oxide, sodium hydroxide, and sodium carbonate. The auxiliary dissociation agent is used to pre-disrupt the dense coating layer formed by some salt fluxes in the aluminum ash, making the aluminum nitride particles more easily exposed and in contact with water during the subsequent hydrolysis process, thereby increasing the depth of the denitrification reaction.

3. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 1, characterized in that, In step S3, the hydrolysis promoter is sodium hydroxide or triethanolamine. The trace alkaline substances in the hydrolysis promoter can change the local pH microenvironment of the aluminum nitride hydrolysis reaction, catalyze the dissolution or crystal transformation of the Al(OH)3 passivation film generated on the aluminum nitride surface, continuously expose fresh aluminum nitride reaction interface, shorten the time required for complete denitrification, and reduce residual ammonia nitrogen.

4. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 1, characterized in that, In step S5, the degree of polymerization regulator is used to precisely control the basicity and molecular morphology distribution during the hydrolysis and polymerization of aluminum salts after acid dissolution by introducing different forms of aluminum sources or alkaline components, so as to prepare polyaluminum chloride products with higher flocculation performance and stability under the premise of ensuring low ammonia nitrogen.

5. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to any one of claims 1-4, characterized in that, The step S2 is replaced by a swirl atomization reactor with cascaded swirl atomization coupled with acoustic vibration to enhance hydrolysis and denitrification, including the construction of three cascaded reaction zones in the swirl atomization reactor: an upper turbulent mixing zone, a middle acoustic enhancement reaction zone, and a lower deep maturation and separation zone. The upper turbulent mixing zone is where the conditioned aluminum ash powder is tangentially fed into the reactor from the top at an inlet air velocity of 15-30 m / s, forming an initial spiral swirling flow field. Simultaneously, the first stream of atomized water is sprayed downwards along the axis through the first set of dual-fluid nozzles arranged at the center of the top of the swirling atomizing reactor, with the Soder mean diameter of the atomized droplets controlled at 30-50 μm. The upper turbulent mixing zone is used to achieve intense turbulent collision and initial wetting of aluminum ash particles and fine water mist, rapidly initiating the hydrolysis reaction and releasing the heat of reaction. In the central acoustic enhancement reaction zone, the material enters the middle section of the swirling atomizing reactor under the action of gravity and centrifugal force. Three to eight ultrasonic transducers are evenly arranged circumferentially on the outer wall of the cylinder in the middle section of the swirling atomizing reactor. An ultrasonic transducer with a frequency of 20-40 kHz and a power density of 0.5-2.0 W / cm² is applied into the swirling atomizing reactor. 2 High-frequency ultrasonic vibration; simultaneously, a second set of nozzles arranged on the cylinder wall of this area sprays a second stream of atomized water in a radial countercurrent manner, with the Sotter average diameter of the atomized droplets controlled at 50-80μm; ultrasonic vibration is used for cavitation effect stripping of passivation film and strengthening micromixing. Cavitation effect stripping of passivation film is formed by the collapse of transient cavitation bubbles generated by ultrasonic waves at the liquid-solid interface, forming microjets and shock waves, which can strip the aluminum hydroxide inert passivation film generated on the surface of aluminum nitride particles in situ due to initial hydrolysis, continuously exposing a fresh reaction interface; strengthening micromixing is that the acoustic flow effect induced by ultrasonic waves can eliminate the boundary layer on the particle surface and enhance the mass transfer rate of water molecules to the reaction interface; In the lower deep maturation and separation zone, the material enters the lower conical section of the cyclone atomizing reactor. Water spraying is stopped in this area, and the reactor is kept at a temperature of 70-90℃ through the reactor jacket. A small amount of inert carrier gas preheated to 60-80℃ is introduced for gas stripping. The inert carrier gas includes nitrogen or purified hot air. The inert carrier gas flows from bottom to top at an apparent gas velocity of 0.5-2.0 m / s, and comes into countercurrent contact with the downward swirling solid material. The mass flow rate ratio of the first atomized water to the second atomized water is 6-8:2-4; the mass ratio of total water to aluminum ash is controlled at 0.12-0.35:1; and the axial backmixing of aluminum ash particles in the swirl atomization reactor is controlled by adjusting the inlet wind speed, ultrasonic power and carrier gas flow rate.

6. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to any one of claims 1-4, characterized in that, The step S2 is replaced by a multi-stage swirling shear collision coupling self-grinding surface renewal enhanced hydrolysis denitrification reactor, which includes constructing a multi-stage series swirling shear zone in the vertical swirling atomizing reactor. The inner wall of the swirling atomizing reactor cylinder is provided with at least two stages of inwardly protruding spiral guide ribs along the axial direction. The protrusion height of the spiral guide ribs is 5%-15% of the cylinder diameter, and the spiral helix angle is 30-60 degrees. The cylinder wall area between two adjacent spiral guide ribs is provided with a roughened friction lining, and the surface roughness Ra value of the friction lining is 50-200 μm.

7. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 6, characterized in that, The multi-stage tandem swirling shear zone includes a first-stage swirling shear zone, a second-stage swirling shear zone, and a third-stage swirling shear zone; In the first-stage swirling shear zone, aluminum ash powder enters tangentially from the top of the swirling atomizing reactor at an inlet wind speed of 20-35 m / s, forming the first-stage high-speed swirling flow. The first set of dual-fluid nozzles sprays the first stream of atomized water downwards along the central axis of the reactor. The average diameter of the atomized droplets is 20-40 μm, and the mass ratio of water to aluminum ash is 0.05-0.10:

1. In this zone, the centrifugal force generated by the high-speed swirling flow throws the aluminum ash particles toward the wall, where they collide with the fine water mist sprayed from the center, completing the initial wetting and rapidly initiating the hydrolysis reaction. In the second-stage swirling shear zone, aluminum ash particles carrying some of the hydrolysis products of the aluminum hydroxide film move downwards along the first-stage spiral guide ridge with the airflow. Under the guidance and contraction of the spiral guide ridge, the particle flow is forcibly accelerated and forms a secondary swirling flow. Intense shearing friction and collisions occur between particles and between particles and the roughened friction liner. The second-stage swirling shear zone is used for in-situ mechanical peeling of the passivation film and self-grinding without additional energy consumption. The in-situ mechanical peeling of the passivation film utilizes the kinetic energy of the particles themselves and the shear force of the flow field. Through frictional collisions between particles and between particles and the wall, the loose aluminum hydroxide passivation film newly formed on the aluminum nitride surface is peeled off in real time, exposing the fresh aluminum nitride reaction interface. The self-grinding process without additional energy consumption does not require external grinding media or additional power. It is achieved entirely by the energy of the flow field itself and the structural design of the reactor. In the third-stage swirling shear zone, below the second-stage spiral guide ridge, a second stream of atomized water is injected through a second set of radially opposed dual-fluid nozzles. The average diameter of the atomized droplets is 40-80 μm, and the water-to-aluminum ash mass ratio is 0.05-0.15:

1. The surface-renewed aluminum nitride particles come into intense contact with the newly injected atomized water again in the third-stage swirling field, undergoing a deep hydrolysis reaction. At the same time, the lower conical section of the swirling atomizing reactor is equipped with adjustable swirling guide vanes. By adjusting the vane angle, the swirling intensity and residence time distribution of the material in the reactor can be changed. The total water to aluminum ash mass ratio is controlled at 0.12-0.30:1; the mass flow rate ratio of the first atomized water to the second atomized water is 4:6-6:4; the total residence time of aluminum ash particles in the cyclone atomizing reactor is 45 s-8 min, with the residence time in the second-stage spiral guide zone accounting for 30%-50% of the total time; the cyclone atomizing reactor shell is equipped with a zoned temperature control jacket to control the temperature of each stage of the reaction zone as follows: 60-80℃ for the first-stage cyclone shear zone, 80-100℃ for the second-stage cyclone shear zone, and 70-90℃ for the third-stage cyclone shear zone.

8. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 5, characterized in that, The step S3 is replaced with precise water control based on online monitoring feedback and multi-component synergistic catalytic enhanced hydrolysis, including: A. Online monitoring and feedback control system Online humidity / moisture sensors and online temperature sensor arrays are respectively installed at the feed end, middle section, and discharge end of the cyclone atomizing reactor; the online humidity / moisture sensors and online temperature sensor arrays transmit the real-time collected material humidity signals and temperature distribution signals to the distributed control system; B. Dynamic Zoning Water Control Strategy The distributed control system executes dynamic water control logic, including feedforward control, feedback fine-tuning, and independent water control in different zones, based on online monitoring data. Feedforward control calculates the theoretical water requirement based on the real-time mass flow rate of the fed aluminum ash and the pre-determined aluminum nitride content, and presets the basic flow rate of the first-stage atomized water. Feedback fine-tuning adjusts the injection volume of the second-stage atomized water in real time based on the material moisture content fed back by the humidity sensor in the middle of the reactor, ensuring that the material in the reaction system is always maintained in a critical wetting state where the surface is wetted and no free water is released internally. Zoned independent water control dynamically adjusts the mass flow rate ratio of the first-stage atomized water to the second-stage atomized water based on the temperature feedback signal, ranging from 3:7 to 7:

3. The Sauter mean diameter of the atomized droplets of the first stream of atomized water is controlled at 20-40 μm, and the Sauter mean diameter of the atomized droplets of the second stream of atomized water is controlled at 40-80 μm. Through this dynamic water control strategy, the total water to aluminum ash mass ratio can be precisely controlled within a narrower range of 0.10:1 to 0.25:1, and the generation of free water caused by local over-wetting is completely eliminated. C. Gradient temperature control and reaction heat management The outer shell of the swirl atomizing reactor is divided into at least three independent temperature control zones along the axial direction. Each temperature control zone is equipped with an independent heat exchange jacket and temperature control loop. The three independent temperature control zones are the first temperature zone of the upper turbulent mixing zone, the second temperature zone of the middle enhanced reaction zone, and the third temperature zone of the lower ripening and separation zone. The first temperature zone is controlled at 60-80℃ to receive the exothermic reaction from the initial hydrolysis and prevent local overheating that could lead to excessively rapid evaporation of moisture. The second temperature zone is controlled at 85-105℃ to utilize the concentrated exothermic reaction from aluminum nitride hydrolysis and to remove and recover excess heat through a heat exchange system for preheating the feed air or process water. The third temperature zone is controlled at 70-90℃ to maintain a suitable temperature for complete hydrolysis of residual gases. Temperature fluctuations are controlled within ±2℃. D. Multi-component synergistic catalytic promoter system A multi-component synergistic catalytic promoter system is introduced simultaneously via atomized water. This system consists of the following components in parts by mass: Main catalyst: alkali metal hydroxide or alkali metal carbonate, 0.05-0.2 parts; Co-catalyst: Organic amine compound, 0.01-0.1 parts; Dispersing and separating agent: water-soluble polymer compound, 0.005-0.05 parts; The total amount of the multi-component synergistic catalytic promoter system added accounts for 0.015%-0.35% of the total mass of aluminum ash; the synergistic mechanism of each component is as follows: Main catalyst: Adjusts the pH of the reaction microzone to accelerate the hydrolysis kinetics of aluminum chloride; Co-catalyst: By coordinating the amine group with the aluminum atoms on the surface of aluminum chloride, the Al-N bond energy is weakened, thereby reducing the activation energy of the reaction; Dispersing and separating agent: adsorbed on the surface of newly generated aluminum hydroxide particles, inhibiting their aggregation and densification, keeping them loose and porous, facilitating the inward diffusion of water molecules and the outward escape of ammonia; E. Determination of reaction endpoint and adaptive adjustment The distributed control system determines whether the hydrolysis reaction has reached its endpoint based on the signals from the online humidity sensor and gas sensor at the discharge end of the cyclone atomizing reactor. When the ammonia concentration at the discharge end is detected to be lower than the set threshold, the system automatically determines that the reaction is complete. If it is higher than the threshold, the system automatically extends the material residence time or finely adjusts and increases the amount of secondary atomizing water until the requirements are met.

9. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 5, characterized in that, The step S3 is replaced by a phase change cycle water precise regulation and graded activation synergistic catalytic enhancement of hydrolysis, including: A. Dual-mode phase change moisture control system A dual-mode coordinated water supply system of liquid atomized water and gaseous water vapor was constructed in a swirl atomizing reactor. The dual-mode coordinated water supply system of liquid atomized water and gaseous water vapor includes a liquid atomized water supply subsystem and a gaseous water vapor supply subsystem. The liquid atomized water supply subsystem injects liquid atomized water through the first set of dual-fluid nozzles. The average diameter of the atomized droplets is 20-50 μm, and it is used to initiate the hydrolysis reaction and provide the stoichiometric amount of water required for the reaction. The gaseous water vapor supply subsystem introduces low-pressure saturated water vapor at a temperature of 105-130℃ into the reaction chamber through a microporous steam distributor arranged in the lower section of the swirl atomizing reactor. The amount of water vapor introduced is 5%-20% of the mass of the liquid water. The working mechanism of the dual-mode synergistic water supply system of liquid atomized water and gaseous water vapor is as follows: the liquid atomized water provides the main water required for rapid reaction, which is used to achieve efficient hydrolysis of aluminum nitride; the gaseous water vapor penetrates into the micropores and gaps of aluminum ash particles at the molecular level, replenishing the water in dead areas that are difficult for liquid water to wet, and at the same time, the latent heat released by steam condensation is used to provide in-situ heating for the reaction system to maintain temperature stability; the liquid water film formed by steam condensation is extremely thin and uniform, which effectively avoids the accumulation of free water caused by excessive liquid water. B. Moisture Closed-Loop Recovery and Recycling Subsystem A moisture condensation and recovery device is added between the tail gas outlet of the cyclone atomizing reactor and the ammonia absorption tower. The moisture condensation and recovery device includes a primary indirect condenser and a secondary deep dehumidifier. The primary indirect condenser uses circulating cooling water to reduce the tail gas temperature to 40-60℃, recovering most of the water vapor and vaporized process water carried in the tail gas. The condensate is collected in a recovery water storage tank. The secondary deep dehumidifier uses refrigerant direct cooling to reduce the tail gas temperature to 10-20℃, further recovering residual moisture. After the condensate in the recovery water storage tank passes the online water quality monitoring module, it is returned to the atomizing water supply system through the return water pipeline, mixed with fresh process water in a certain proportion, and reused for spraying. The online water quality monitoring module detects indicators including pH value, conductivity, and ammonia nitrogen concentration. When the ammonia nitrogen concentration exceeds the set threshold, it automatically switches to the ammonia absorption tower feed pipeline. C. Staged activation of latent synergistic catalytic promoter system The accelerator system is designed as a graded activation mode, which includes a first-stage accelerator and a second-stage accelerator. The first-stage accelerator is an instant activation component, sprayed in with atomized water, and accounts for 60%-80% of the total mass of the accelerator system. The first-stage accelerator includes alkali metal carbonates and low molecular weight organic amines. The alkali metal carbonates include sodium carbonate and potassium carbonate, and the amount of alkali metal carbonates added is 0.02-0.15 parts per 100 parts of aluminum ash. The low molecular weight organic amine is triethanolamine, and the amount of low molecular weight organic amine added is 0.01-0.05 parts per 100 parts of aluminum ash. The second-stage accelerator is a latent thermally activated component, premixed in aluminum ash powder, accounting for 20%-40% of the total mass of the accelerator system. The second-stage accelerator includes microencapsulated alkali metal hydroxides and thermally decomposable organic amine precursors. The microencapsulated alkali metal hydroxides use polymeric materials with melting points or solubilities of 60-90℃ as the capsule wall material, encapsulating sodium hydroxide or potassium hydroxide particles to form thermally responsive microcapsules. The polymeric materials include polyethylene glycol and polyvinyl alcohol. In the low-temperature zone at the reactor inlet, the capsule wall remains intact, and sodium hydroxide is not released. When the material enters the high-temperature zone (85-105℃) in the middle section, the capsule wall melts or dissolves, releasing a strongly alkaline catalytic component in situ. The precursors of thermally decomposable organic amines are urea or hexamethylenetetramine, which have extremely low catalytic activity at room temperature. When the material enters the high-temperature zone, it decomposes and releases ammonia or amine active components, providing catalytic action at the stage most needed in the reaction.

10. The method for preparing polyaluminum chloride from aluminum ash by cyclone atomization denitrification according to claim 9, characterized in that, The step S3 is replaced by a phase change cycle moisture precise control and graded activation synergistic catalytic enhancement of hydrolysis, which also includes dynamic zoning setting and adaptive adjustment of the water-to-aluminum ash ratio. The dynamic zoning setting and adaptive adjustment of the water-to-aluminum ash ratio is as follows: Based on online monitoring data, the distributed control system sets target values ​​for the water-to-aluminum ash ratio in each of the three reaction zones: the upper turbulent mixing zone, the middle acoustic enhancement reaction zone, and the lower deep curing and separation zone. Specifically, in the upper turbulent mixing zone, the mass ratio of liquid atomized water to aluminum ash is 0.03-0.08:1, with the water in the form of fine droplets; in the middle acoustic enhancement reaction zone, the mass ratio of liquid atomized water and steam condensate to aluminum ash is 0.05-0.12:1, with the water in the form of a combination of droplets and thin liquid films; and in the lower deep curing and separation zone, the mass ratio of steam condensate to aluminum ash is 0.02-0.05:1, with the water in the form of molecular-level adsorbed water.

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