Aluminum hydroxide roasting system with zero carbon emission

Abstract

The invention discloses an aluminum hydroxide roasting system with zero carbon emission, and relates to the technical field of aluminum hydroxide roasting. An aluminum hydroxide material enters a drying unit through a feeding device and exchanges heat with dust-removed recovered flue gas and high-temperature flue gas generated by a secondary preheater; the dried material sequentially enters a first-stage preheater, a second-stage preheater and a third-stage preheater and then enters a roasting furnace, the roasted material enters a fourth-stage preheater to be subjected to gas-solid separation and then enters a suspension reactor and a multi-stage cooling unit to be subjected to multi-stage cooling, the cooled material enters a solid-solid heat exchanger, and finished aluminum oxide is obtained. Through collaborative design of the multi-stage preheating unit, the drying unit, the solid-solid heat exchanger and the steam recovery device, whole-process secondary utilization of flue gas and heat of finished product materials is achieved, hydrogen serves as the only fuel, a hydrogen combustion product is only water, and emission of CO and NOx pollutants generated by combustion of traditional fossil fuel is completely eradicated from the source.

Description

Technical Field

[0001] This invention relates to the field of aluminum hydroxide calcination technology, specifically to a zero-carbon-emission aluminum hydroxide calcination system. Background Technology

[0002] Aluminum hydroxide roasting is a core and critical process in alumina production. Its core function is to remove the water of crystallization from aluminum hydroxide and complete its crystal transformation through high-temperature heating, ultimately producing alumina products that meet industrial standards. The energy consumption level and pollutant emission intensity of this process directly determine the overall environmental protection level, economic cost, and market competitiveness of alumina production, making it a key control point for alumina enterprises to achieve green and low-carbon development. Currently, domestic alumina enterprises mainly use equipment such as gas-state suspension roasting furnaces and rotary kilns for roasting operations. Their heat supply methods still heavily rely on fossil fuels such as natural gas and heavy oil, resulting in a single energy structure and high carbon emission intensity.

[0003] Traditional fossil fuel roasting processes face two major bottlenecks: First, the combustion of fossil fuels inevitably produces large amounts of carbon dioxide, making it impossible to achieve zero carbon emissions during roasting. Furthermore, long-term reliance on fossil fuels makes them susceptible to energy price fluctuations, increasing production and operating costs. Second, the combustion of fossil fuels also produces nitrogen oxides (NOx). x The generation of pollutants such as exhaust gas not only requires additional investment in exhaust gas treatment equipment and costs, but also poses risks to environmental compliance, thus hindering the green development process of enterprises.

[0004] Hydrogen, as an ideal clean fuel, has significant advantages such as combustion products consisting only of water, zero carbon dioxide emissions, fast flame speed, and high calorific value. It can eliminate carbon emissions from the roasting process at the source, perfectly meeting the green and low-carbon transformation needs of the alumina industry and providing a new technical path for the zero-carbon upgrade of the aluminum hydroxide roasting process.

[0005] The roasting process of aluminum hydroxide produces a large amount of high-temperature flue gas and high-temperature alumina products. Although the existing technology is equipped with basic preheating and cooling heat exchange devices, the heat recovery efficiency is limited, and a large amount of waste heat is directly lost, failing to achieve the cascade secondary utilization of heat, which further increases the system energy consumption. Summary of the Invention

[0006] In view of the above-mentioned shortcomings and deficiencies, this invention provides a zero-carbon emission aluminum hydroxide roasting system. Through the coordinated design of multi-stage preheating units, drying units, solid-solid heat exchangers, and steam recovery devices, it achieves full-process secondary utilization of heat from flue gas and finished materials. Using hydrogen as the sole fuel, the only combustion product of hydrogen is water, thus eliminating CO2 and NO produced by the combustion of traditional fossil fuels from the source. x Pollutant emissions.

[0007] To achieve the above objectives, the main technical solution adopted by the present invention is a zero-carbon emission aluminum hydroxide roasting system, comprising a feeding device, a drying unit, a multi-stage preheating unit, a roasting furnace, a multi-stage cooling unit, a suspension reactor, and a dust removal and recovery unit, wherein the multi-stage preheating unit includes a first- to fourth-stage preheater; the dust removal and recovery unit includes a solid-solid heat exchanger, a dust collector, and a steam recovery device, a fan, and a flue gas duct connected in sequence to the dust collector; Aluminum hydroxide material enters the drying unit through a feeding device, where it exchanges heat with the high-temperature flue gas recovered by the dust removal and recovery unit and generated by the secondary preheater. After heat exchange, the material sequentially enters the primary, secondary, and tertiary preheaters before entering the calcining furnace. After calcination, the material enters the quaternary preheater for gas-solid separation and then enters the suspension reactor. After undergoing high-temperature suspension reaction, the material enters the multi-stage cooling unit for multi-stage cooling. The cooled material enters the solid-solid heat exchanger to obtain the finished alumina. The finished alumina indirectly exchanges heat and cools with soft water before entering the receiving device below.

[0008] The drying unit includes a hydrate dryer and a dryer connected to its discharge port. High-temperature flue gas from the outlet of the steam recovery unit flows through the hydrate dryer. After passing through the hydrate dryer, the high-temperature flue gas is connected to the inlet pipe of the primary preheater. After the material is initially dried by the hydrate dryer, it enters the dryer for further drying. The material after passing through the dryer is sent to the primary preheater.

[0009] The high-temperature flue gas from the outlet of the steam recovery device is transported to the hydrate dryer by a fan, and a flue gas flow regulating valve is installed on the connecting pipe between the fan and the hydrate dryer.

[0010] In the primary preheater, high-temperature flue gas and materials undergo gas-solid separation. The high-temperature flue gas enters the dust collector, and the collected dust is sent to the quaternary preheater. The flue gas after dust removal enters the steam recovery device, with part of it entering the drying unit and part entering the exhaust duct.

[0011] The discharge port of the primary preheater and the air outlet of the tertiary preheater are both connected to the secondary preheater; the air outlet of the secondary preheater is connected to the drying unit, and its discharge port and the air outlet of the quaternary preheater are connected to the tertiary preheater; the discharge port of the tertiary preheater is connected to the roasting furnace, and the discharge port of the roasting furnace is connected to the quaternary preheater.

[0012] The roasting furnace is equipped with hydrogen nozzles in both the conical and straight sections, which are connected to hydrogen. A hydrogen flow regulating valve is installed on the hydrogen pipeline. The air inlet at the bottom of the roasting furnace is connected to the high-temperature air outlet of the solid-solid heat exchanger, and an air flow regulating valve is installed on the connecting pipeline.

[0013] The discharge port of the fourth-stage preheater is connected to the suspension reactor. The lower part of the suspension reactor is equipped with a fluidizing air inlet. The high-temperature air generated after the air passes through the solid-solid heat exchanger is connected to the fluidizing air inlet. The discharge port of the suspension reactor is connected to the multi-stage cooling unit.

[0014] The solid-solid heat exchanger is equipped with a feed inlet, a discharge outlet, a soft water inlet, a high-temperature and high-pressure steam outlet, an air inlet, and a high-temperature air outlet.

[0015] The multi-stage cooling unit includes a primary cooler and a secondary cooler. The material passing through the suspension reactor enters the primary cooler and the secondary cooler in sequence for cooling before entering the solid-solid heat exchanger. The material exchanges heat indirectly with soft water in the solid-solid heat exchanger before entering the material collection device. The steam generated in the solid-solid heat exchanger is discharged through the high-temperature and high-pressure steam outlet of the solid-solid heat exchanger.

[0016] The discharge port of the primary cooler is connected to the secondary cooler along with the air; the air outlet of the primary cooler is connected to the air inlet of the roasting furnace; and the air outlet of the secondary cooler is connected to the air inlet of the primary cooler.

[0017] The present invention has the following beneficial effects and advantages: 1. This system is equipped with hydrogen nozzles in both the conical and straight sections of the roasting furnace, using hydrogen as the sole fuel. The only combustion product of hydrogen is water, thus eliminating CO2 and NO produced by the combustion of traditional fossil fuels at the source. x Pollutant emissions are reduced, while the hydrogen supply is precisely controlled by a flow regulating valve on the hydrogen pipeline. Combined with a high-temperature air intake channel and air flow regulating valve connected to the solid-solid heat exchanger below the roasting furnace, the adjustable ratio of hydrogen to high-temperature air is achieved. This effectively solves the problems of poor flame stability and easy backfire and flameout of hydrogen combustion, ensuring continuous and stable operation of the roasting process.

[0018] 2. This system achieves full-process secondary utilization of heat from flue gas and finished materials through the coordinated design of multi-stage preheating units, drying units, solid-solid heat exchangers, and steam recovery devices. On the one hand, the drying unit uses high-temperature flue gas from the steam recovery device outlet and high-temperature flue gas from the secondary preheater to dry the materials. The flue gas, after passing through the hydrate dryer, can be recycled back to the primary preheater inlet pipe. Combined with precise temperature control via a flue gas flow regulating valve, this solves the problem of direct heat loss in traditional processes. On the other hand, the finished alumina, after being cooled by multi-stage cooling units, enters the solid-solid heat exchanger, where it indirectly exchanges heat with soft water to generate high-temperature, high-pressure steam. Simultaneously, it heats air to provide a high-temperature gas source for the calcining furnace and suspension reactor. The fluidizing air in the suspension reactor and the combustion air in the calcining furnace both come from the high-temperature air heated by the solid-solid heat exchanger, forming a closed loop of heat, material, and gas source recycling. This reduces the overall energy consumption of the system and solves the problem of insufficient heat recovery in existing processes.

[0019] 3. The system is equipped with four stages of preheaters. The gas-solid flow design, where the outlets of the first and third stage preheaters are connected to the second stage preheater, and the outlets of the second and fourth stage preheaters are connected to the third stage preheater, ensures that the material and the high-temperature flue gas have sufficient contact and heat exchange, ensuring uniform material heating and thorough removal of adsorbed moisture, laying the foundation for subsequent roasting processes. At the same time, after gas-solid separation is achieved in the first stage preheater, the collected dust is returned to the fourth stage preheater to participate in roasting again, avoiding material loss, improving raw material utilization, and solving the problems of uneven material heat exchange and dust waste in traditional preheating processes.

[0020] 4. After being roasted in the calcining furnace, the material enters the suspension reactor. High-temperature air heated by the solid-solid heat exchanger is used as fluidizing air, allowing the material to complete subsequent crystal transformation in a high-temperature suspension state, thereby improving the purity and crystal consistency of the alumina product. The multi-stage cooling unit adopts a series design of primary and secondary coolers, and the coolers form an air source circulation with the calcining furnace and suspension reactor. This not only achieves gradient cooling of the material, avoiding crystal damage caused by direct cooling of high-temperature materials, but also recovers the heat during the cooling process for system circulation. At the same time, in conjunction with the final heat exchange of the solid-solid heat exchanger, it ensures that the temperature of the finished alumina meets the standard, ensuring the stability of subsequent material collection and storage.

[0021] 5. This system does not rely on fossil fuels, thus avoiding operational risks caused by energy price fluctuations and eliminating the need for CO2 and NO emissions. x The investment and maintenance costs of exhaust gas treatment equipment; the cascade heat recovery and recycling design significantly reduces energy consumption; the high-temperature and high-pressure steam generated by the solid-solid heat exchanger can also be recycled as a by-product; the entire system has a modular structure and can be upgraded based on existing alumina calcination equipment, with low modification costs and strong adaptability. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention.

[0023] The components are as follows: 1. Feeding device; 2. Hydrate dryer; 3. Dryer; 4. Primary preheater; 5. Secondary preheater; 6. Tertiary preheater; 7. Quaternary preheater; 8. Calcining furnace; 9. Hydrogen nozzle; 10. Hydrogen flow regulating valve; 11. Suspension reactor; 12. Air flow regulating valve; 13. Primary cooler; 14. Secondary cooler; 15. Solid-solid heat exchanger; 16. Dust collector; 17. Steam recovery device; 18. Fan; 19. Flue gas duct; 20. Flue gas flow regulating valve. Detailed Implementation

[0024] The invention will now be further described with reference to the accompanying drawings. Figure 1As shown, this invention is a zero-carbon emission aluminum hydroxide calcination system. The feeding device 1 is the core component of the system's inlet, used to receive aluminum hydroxide material transported from the upstream process. Its outlet is sealed and connected to the inlet of the hydrate dryer 2. The feeding device 1 can precisely control the material feeding rate, avoiding the impact of feeding fluctuations on subsequent drying and calcination processes, ensuring continuous and stable system operation. Its advantage lies in achieving quantitative and continuous material feeding, laying the foundation for stable control of process parameters throughout the entire process.

[0025] Hydrate dryer 2 and dryer 3 are connected in series to form a two-stage drying unit. The discharge port of hydrate dryer 2 is sealed to the inlet of dryer 3, realizing progressive drying of the material. This gradually removes the water attached to the material, avoiding agglomeration or crystal damage caused by excessive drying intensity in a single step. Simultaneously, the air inlet of hydrate dryer 2 is connected to the outlet of steam recovery device 17 via a pipeline. Along the flue gas flow direction, a fan 18 and a flue gas flow regulating valve 20 are sequentially installed on this pipeline. The fan 18 provides stable power for flue gas delivery, ensuring that waste heat flue gas can smoothly enter hydrate dryer 2. The flue gas flow regulating valve 20 can precisely adjust the flue gas flow rate according to the moisture content and temperature parameters of the material inside hydrate dryer 2, achieving dynamic matching of drying intensity. Its advantage lies in ensuring drying effect while avoiding waste of flue gas heat. The outlet of the hydrate dryer 2 is connected to the inlet pipe of the primary preheater 4, so that the low-temperature flue gas after drying and heat exchange can participate in the preheating process again, realizing the recycling of flue gas waste heat and further improving energy utilization.

[0026] A multi-stage gradient preheating unit is constructed sequentially using a primary preheater 4, a secondary preheater 5, a tertiary preheater 6, and a quaternary preheater 7. An efficient heat exchange system is formed through optimized gas-solid flow design: the outlet of the primary preheater 4 and the outlet of the tertiary preheater 6 are both sealed and connected to the secondary preheater 5; the outlet of the secondary preheater 5 is connected to the inlet of the dryer 3; the outlet of the secondary preheater 5 and the outlet of the quaternary preheater 7 are both sealed and connected to the tertiary preheater 6; and the outlet of the tertiary preheater 6 is directly and sealed to the inlet of the calcining furnace 8. This layout allows the material and high-temperature flue gas to form a counter-current heat exchange, extending the heat exchange time and increasing the heat exchange area, ensuring a gradual and stable increase in material temperature. Its advantages include avoiding localized overheating or excessively rapid temperature rise in the material, ensuring the uniformity of subsequent calcination crystal transformation, maximizing the recovery of waste heat from the flue gas, and reducing system energy consumption.

[0027] The roasting furnace 8 is the core roasting component of the system. Hydrogen nozzles 9 are evenly distributed in its conical and straight sections. All hydrogen nozzles 9 are connected to an external hydrogen source through pipelines, and hydrogen flow regulating valves 10 are connected in series on the pipelines. The advantage of the regional arrangement of hydrogen nozzles 9 is that it can evenly disperse hydrogen in the inner cavity of the roasting furnace 8, fully mix with high-temperature air for combustion, avoid local flame concentration that could damage the furnace body, and improve combustion stability, thus solving the technical problems of easy backfire and flameout during hydrogen combustion. The hydrogen flow regulating valve 10 can precisely control the hydrogen supply according to the roasting temperature requirements, realize dynamic regulation of combustion heat, and ensure that the roasting temperature is stable within the process range.

[0028] The lower air inlet of the roasting furnace 8 is connected to the high-temperature air outlet of the solid-solid heat exchanger 15. An air flow regulating valve 12 is provided on the connecting pipeline to precisely regulate the amount of combustion air. The advantage of this setting is that it achieves the best ratio of hydrogen to air, which ensures that hydrogen is fully combusted and avoids excessive air carrying away a large amount of heat, thereby improving combustion efficiency.

[0029] The discharge port of the calcining furnace 8 is sealed to the inlet of the four-stage preheater 7, allowing the high-temperature calcined material and flue gas to enter the four-stage preheater 7 together for gas-solid separation. The discharge port of the four-stage preheater 7 is sealed to the inlet of the suspension reactor 11. The lower part of the suspension reactor 11 is equipped with a fluidizing air inlet, which is connected to the high-temperature air outlet of the solid-solid heat exchanger 15 through a branch pipe, receiving heated high-temperature air as fluidization power. The suspension reactor 11 keeps the material in a high-temperature suspended state, which can further promote crystal transformation, ensure uniform alumina product quality, and avoid material accumulation leading to incomplete local reactions.

[0030] The discharge port of the suspension reactor 11 is sealed to the inlet of the primary cooler 13. The primary cooler 13 and the secondary cooler 14 are connected in series to form a multi-stage cooling unit. The discharge port of the primary cooler 13 is connected to the inlet of the secondary cooler 14, and the discharge port of the primary cooler 13 is connected to the secondary cooler 14 after merging with the external air pipe. The air outlet of the primary cooler 13 is connected to the air inlet of the calcining furnace 8, and the air outlet of the secondary cooler 14 is connected to the air inlet of the primary cooler 13. The advantage of setting up a multi-stage cooling unit is that it can achieve gradient cooling of materials, avoid rapid cooling of high-temperature materials that may cause crystal damage, and recover the heat released during the cooling process to provide an auxiliary heat source for the calcining furnace 8, further reducing energy consumption.

[0031] The discharge port of the secondary cooler 14 is sealed to the inlet of the solid-solid heat exchanger 15. The solid-solid heat exchanger 15 integrates an inlet, a discharge port, a soft water inlet, a high-temperature and high-pressure steam outlet, an air inlet, and a high-temperature air outlet. Its discharge port is connected to the receiving device below. The soft water inlet is connected to an external soft water source. The high-temperature and high-pressure steam outlet is used to discharge the steam generated by the heat exchange (which can be recycled as a by-product). The air inlet is connected to an external air source. The high-temperature air outlet is split into two paths, connected to the air inlet below the roasting furnace 8 and the fluidizing air inlet of the suspension reactor 11, respectively. The solid-solid heat exchanger 15 realizes multi-media heat exchange between the waste heat of the material and soft water and air, maximizing the recovery of waste heat from the finished material. The generated high-temperature and high-pressure steam can create additional economic benefits, and the heated air provides a heat source for the roasting and fluidization processes, forming a closed-loop heat cycle and reducing the overall energy consumption of the system.

[0032] The outlet of the primary preheater 4 is sealed and connected to the inlet of the dust collector 16. The outlet of the dust collector 16 is connected to the quaternary preheater 7, which allows the collected alumina dust to be returned to the system for re-combustion, reducing material loss and improving raw material utilization. This also prevents dust from causing pollution and waste when emitted with the flue gas. Since hydrogen produces a large amount of steam after combustion, the flue gas exiting the dust collector 16 enters the steam recovery device 17 to recover the steam. The outlet of the steam recovery device 17 is arranged in two paths: one path connects to the hydrate dryer 2 via the fan 18 and the flue gas flow regulating valve 20, enabling flue gas recycling; the other path connects to the exhaust pipe 19, allowing the low-temperature flue gas, after multi-stage waste heat recovery, to be treated to meet emission standards. The advantage of the exhaust pipe 19 is that it ensures a standardized flue gas emission path, meeting environmental emission requirements.

[0033] In operation, aluminum hydroxide material is precisely metered by the feeding device 1 and stably conveyed into the hydrate dryer 2. High-temperature waste heat flue gas from the outlet of the steam recovery device 17, driven by the fan 18, is regulated to a suitable flow rate by the flue gas flow regulating valve 20 and introduced into the hydrate dryer 2 to exchange heat with the material, completing the initial drying. The initially dried material then enters the dryer 3 through the outlet of the hydrate dryer 2, where it undergoes a second deep drying process using the high-temperature flue gas discharged from the secondary preheater 5, thoroughly removing any attached water (reducing the moisture content to the required range). The dried material then sequentially enters the primary preheater 4, secondary preheater 5, and tertiary preheater 6, where it undergoes counter-current heat exchange with the high-temperature flue gas in each preheater, gradually increasing the material temperature to the calcination preheating temperature. Finally, it is sent to the calcination furnace 8 via the tertiary preheater 6. This process, through the gradient heat exchange design of the four preheaters, maximizes the recovery of waste heat from the flue gas, saving energy and reducing consumption in the calcination process.

[0034] Hydrogen gas is introduced into the roasting furnace 8 through hydrogen nozzles 9 evenly distributed in conical and straight sections. The hydrogen flow regulating valve 10 precisely controls the hydrogen supply according to the roasting temperature parameters. Simultaneously, high-temperature air heated by the solid-solid heat exchanger 15 is regulated by the air flow regulating valve 12 and sent to the bottom of the roasting furnace 8 to mix with the hydrogen. The hydrogen is fully combusted, releasing heat (the combustion product is only water, achieving zero carbon emissions in the roasting process), providing a stable high-temperature environment for the material roasting. The high-temperature material after roasting enters the fourth-stage preheater 7 together with the flue gas. Gas-solid separation is completed in the fourth-stage preheater 7. The separated flue gas enters the third-stage preheater 6 to participate in subsequent heat exchange and recover waste heat, while the separated material is sent to the suspension reactor 11. This process, through the uniform arrangement of the hydrogen nozzles 9 and the coordinated regulation of the flow regulating valves 10 and 12, ensures a stable and zero-carbon roasting process.

[0035] The suspension reactor 11 receives high-temperature air heated by the solid-solid heat exchanger 15 through the lower fluidizing air inlet, keeping the material in a high-temperature suspension state and fully completing the crystal transformation reaction. The reacted material enters the primary cooler 13 and the secondary cooler 14 in sequence, where it undergoes gradient cooling with the circulating cooling air. After the cooling air absorbs heat and heats up in the primary cooler 13, it is sent to the calcining furnace 8 as a supplementary combustion gas source to achieve waste heat recovery. This process takes into account both material cooling effect and heat recovery through the circulation design of the multi-stage coolers 13 and 14.

[0036] After being cooled by the secondary cooler 14, the material enters the solid-solid heat exchanger 15, where it undergoes indirect heat exchange with soft water. The soft water absorbs the waste heat from the material to generate high-temperature, high-pressure steam, which is then discharged through the high-temperature, high-pressure steam outlet of the solid-solid heat exchanger 15 for recycling. Simultaneously, the solid-solid heat exchanger 15 heats the incoming air, providing a high-temperature gas source for the calcining furnace 8 and the suspension reactor 11, thus achieving cascaded utilization of waste heat. The material cooled by heat exchange is the qualified finished alumina, which is sent to the collection device for collection through the outlet of the solid-solid heat exchanger 15. This process maximizes the utilization of the waste heat value of the finished material through the multi-media heat exchange design of the solid-solid heat exchanger 15.

[0037] The flue gas discharged from the primary preheater 4 enters the dust collector 16 to remove alumina dust impurities from the flue gas. After being collected by the dust collector 16, the dust is returned to the quaternary preheater 7 to participate in the roasting again. The flue gas after dust removal is sent to the steam recovery device 17 to recover waste heat. Part of the flue gas after recovering waste heat is circulated to the hydrate dryer 2 for reuse via the fan 18 and the flue gas flow regulating valve 20, while the other part is discharged through the exhaust pipe 19 (the discharge temperature is reduced to the environmental protection requirement range). This process achieves full utilization of waste heat and environmental compliance through flue gas circulation and multi-stage treatment.

[0038] This embodiment utilizes the coordinated control of hydrogen flow regulating valve 10, air flow regulating valve 12, and flue gas flow regulating valve 20 to dynamically adjust the hydrogen supply, combustion air volume, and flue gas circulation volume based on real-time operating parameters such as material moisture content, roasting temperature, and heat exchange efficiency. This ensures stable operation of the system under different production loads and guarantees consistent product quality. Simultaneously, the multi-media heat exchange design of the solid-solid heat exchanger 15, along with the circulating layout of multi-stage preheating and cooling units, constructs a closed-loop heat recovery system throughout the entire process. Combined with zero-carbon combustion technology featuring a 9-zone arrangement of hydrogen nozzles, this completely solves the technical defects of traditional roasting processes, such as high carbon emissions, severe heat waste, and poor hydrogen compatibility. It combines environmental friendliness, high efficiency, and stability, possessing significant industrial application value.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the concept and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A zero-carbon emission aluminum hydroxide calcination system, characterized in that: It includes a feeding device, a drying unit, a multi-stage preheating unit, a calcining furnace, a multi-stage cooling unit, a suspension reactor, and a dust removal and recovery unit. The multi-stage preheating unit includes a first- to fourth-stage preheater. The dust removal and recovery unit includes a solid-solid heat exchanger, a dust collector, and a steam recovery device, a fan, and a flue gas duct connected in sequence to the dust collector. Aluminum hydroxide material enters the drying unit through a feeding device, where it exchanges heat with the high-temperature flue gas recovered by the dust removal and recovery unit and generated by the secondary preheater. After heat exchange, the material sequentially enters the primary, secondary, and tertiary preheaters before entering the calcining furnace. After calcination, the material enters the quaternary preheater for gas-solid separation and then enters the suspension reactor. After undergoing high-temperature suspension reaction, the material enters the multi-stage cooling unit for multi-stage cooling. The cooled material enters the solid-solid heat exchanger to obtain the finished alumina. The finished alumina indirectly exchanges heat and cools with soft water before entering the receiving device below.

2. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The drying unit includes a hydrate dryer and a dryer connected to its discharge port. High-temperature flue gas from the outlet of the steam recovery unit flows through the hydrate dryer. After passing through the hydrate dryer, the high-temperature flue gas is connected to the inlet pipe of the primary preheater. After the material is initially dried by the hydrate dryer, it enters the dryer for further drying. The material after passing through the dryer is sent to the primary preheater.

3. The zero-carbon emission aluminum hydroxide calcination system according to claim 2, characterized in that: The high-temperature flue gas from the outlet of the steam recovery device is transported to the hydrate dryer by a fan, and a flue gas flow regulating valve is installed on the connecting pipe between the fan and the hydrate dryer.

4. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: In the primary preheater, high-temperature flue gas and materials undergo gas-solid separation. The high-temperature flue gas enters the dust collector, and the collected dust is sent to the quaternary preheater. The flue gas after dust removal enters the steam recovery device, with part of it entering the drying unit and part entering the exhaust duct.

5. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The discharge port of the primary preheater and the air outlet of the tertiary preheater are both connected to the secondary preheater; the air outlet of the secondary preheater is connected to the drying unit, and its discharge port and the air outlet of the quaternary preheater are connected to the tertiary preheater; the discharge port of the tertiary preheater is connected to the roasting furnace, and the discharge port of the roasting furnace is connected to the quaternary preheater.

6. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The roasting furnace is equipped with hydrogen nozzles in both the conical and straight sections, which are connected to hydrogen. A hydrogen flow regulating valve is installed on the hydrogen pipeline. The air inlet at the bottom of the roasting furnace is connected to the high-temperature air outlet of the solid-solid heat exchanger, and an air flow regulating valve is installed on the connecting pipeline.

7. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The discharge port of the fourth-stage preheater is connected to the suspension reactor. The lower part of the suspension reactor is equipped with a fluidizing air inlet. The high-temperature air generated after the air passes through the solid-solid heat exchanger is connected to the fluidizing air inlet. The discharge port of the suspension reactor is connected to the multi-stage cooling unit.

8. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The solid-solid heat exchanger is equipped with a feed inlet, a discharge outlet, a soft water inlet, a high-temperature and high-pressure steam outlet, an air inlet, and a high-temperature air outlet.

9. The zero-carbon emission aluminum hydroxide calcination system according to claim 1, characterized in that: The multi-stage cooling unit includes a primary cooler and a secondary cooler. The material passing through the suspension reactor enters the primary cooler and the secondary cooler in sequence for cooling before entering the solid-solid heat exchanger. The material exchanges heat indirectly with soft water in the solid-solid heat exchanger before entering the material collection device. The steam generated in the solid-solid heat exchanger is discharged through the high-temperature and high-pressure steam outlet of the solid-solid heat exchanger.

10. The zero-carbon emission aluminum hydroxide calcination system according to claim 9, characterized in that: The discharge port of the primary cooler is connected to the secondary cooler along with the air; the air outlet of the primary cooler is connected to the air inlet of the roasting furnace; and the air outlet of the secondary cooler is connected to the air inlet of the primary cooler.

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