Aluminum hydroxide low-temperature roasting system and technology

Abstract

An aluminum hydroxide low-temperature roasting system comprises a feeding system, a roasting system, a multi-stage separation system, a cyclone recycling system and the like, the feeding system is used for conveying Al (OH) 3 materials, the roasting system is used for roasting aluminum hydroxide materials and outputting alpha-Al2O3, the multi-stage separation system is used for cooling high-temperature alpha-Al2O3, and the cyclone recycling system is used for recycling the high-temperature alpha-Al2O3. And the cyclone recovery system is used for recovering flue gas generated by the roasting system. The interior of the suspension roasting furnace is divided into different areas through the stepped functional belt from bottom to top, Al2O3 particles with attached water removed pass through the different areas in sequence, temperature control is conducted on the areas through different combustion chambers, therefore, dynamic balance of materials is achieved in the roasting process, the roasting temperature is reduced, and the roasting efficiency is improved. Compared with the traditional roasting temperature, the highest roasting temperature does not exceed 900 DEG C, and the roasting energy consumption is lower at the low temperature. Secondly, the alpha-Al2O3 stays for 1-10 min through a buffer, the ignition loss rate of the alpha-Al2O3 is reduced in the process, and meanwhile energy consumption in the roasting process is reduced.

Description

Technical Field

[0001] The present invention relates to the field of alumina production, and particularly to a low-temperature roasting system and process for aluminum hydroxide. Background Art

[0002] Traditional alumina roasting processes generally refer to the process of converting aluminum hydroxide (Al(OH) 3 ) into alumina (Al 2 O 3 ) under high-temperature conditions. In the production process, alumina (Al 2 O 3 ) can be further regulated to generate different alumina crystal forms according to different roasting temperatures and times, including γ-Al 2 O 3 and α-Al 2 O 3 . Due to their different crystal structures, thermal stabilities, specific surface areas, and mechanical properties, the two alumina crystal forms have different application scenarios.

[0003] In industrial production, α-Al 2 O 3 is mainly converted from γ-Al 2 O 3 . In traditional processes, the crystal form conversion is carried out in a rotary kiln or a roasting furnace, and the internal temperature is generally around 900 - 1200 °C. At this temperature, γ-Al 2 O 3 will gradually transform into α-Al 2 O 3 . The higher the temperature, the higher the conversion efficiency. However, as the temperature increases, the loss-on-ignition rate of α-Al 2 O 3 will decrease, and the loss-on-ignition rate of α-Al 2 O 3 is the main quality control parameter. A low loss-on-ignition rate usually means higher purity. Therefore, generally to ensure product quality, within a certain range of loss-on-ignition rate, it is necessary to ensure the conversion efficiency as much as possible without causing excessive energy consumption and increasing production costs.

[0004] The existing patent CN119569093A discloses an energy-saving suspension roasting device for aluminum hydroxide and its roasting method. The device includes a cooling component, a preheating component, a suspension roasting furnace, an SCR reactor, a dryer, a feeding component, an exhaust gas emission component, and a heat supply device; the heat supply device can provide heat for the SCR reactor. It mainly solves the problem that the flue gas is not cooled sufficiently during the heat exchange process, resulting in a relatively high temperature of the flue gas discharged from the chimney, thus causing heat waste. Through the technical solution of this patent, although the problem of heat waste can be reduced, it does not disclose a related solution for controlling low-temperature roasting in the suspension roasting furnace, that is, it is impossible to ensure the conversion efficiency and excessive energy consumption while ensuring the product quality.

[0005] Secondly, the existing patent CN108751244A discloses an integrated device for roasting crystalline aluminum salt to prepare industrial-grade alumina, and specifically discloses that the raw material crystalline aluminum salt enters the material crushing and storage feeding and conveying system, and after crushing, it enters the low-temperature section of the fluidized integrated roasting furnace through multiple feeding pipelines; the acid-containing corrosive flue gas and entrained solid particles from the fluidized integrated roasting furnace enter the dry dust collector through the second flue, and the solid particles after gas-solid separation enter the high-temperature section of the fluidized integrated roasting furnace again through the fourth pipeline; the acid-containing corrosive flue gas after gas-solid separation enters the waste heat boiler through the third flue to recover the waste heat of the flue gas, and then enters the acid recovery system through the fourth flue, and the by-product finished acid is recovered through the processes of cooling, washing, and absorption, and the tail gas is discharged up to the environmental protection standards. It mainly solves the problems of poor adaptability of the crystalline aluminum salt roasting process to materials, high roasting energy consumption, and possible environmental pollution caused by acidic gases.

[0006] Through the above patent analysis, the high-temperature roasting process requires a large amount of energy input, which not only increases the production cost but also has low energy utilization efficiency, resulting in untransformed alumina particles in the discharged flue gas and a decrease in product output. Secondly, during the production process, there is also a problem of a relatively high ignition loss rate of the product in the current process. Summary of the Invention

[0007] The purpose of the present invention is to provide a low-temperature roasting system and process for aluminum hydroxide, which adopts a stepped roasting method, conducts controllable low-temperature monitoring and control inside the suspension furnace, and can ensure the conversion efficiency of crystal forms at a relatively low temperature, while reducing energy consumption and ignition loss rate, and also ensuring product output and quality.

[0008] The present invention adopts the following technical solutions:

[0009] A low-temperature roasting system for aluminum hydroxide includes a feeding system, a roasting system, a multi-stage separation system, and a cyclone recovery system, wherein the feeding system is used to convey Al(OH) 3Materials, specifically including a blanking bin, a variable-speed conveyor, and a screw conveyor; the roasting system is used to roast aluminum hydroxide materials and output α-Al 2 O 3 , specifically including a Venturi dryer, a preheater, a first solid-gas separator, a second solid-gas separator, a suspension roaster, a third solid-gas separator, a combustion station, and a buffer. The inside of the suspension roaster is stepped from bottom to top, and is successively a preheating zone A, a heating zone B, a crystal form conversion zone C, an activity maintenance zone D, and a quenching zone E. Moreover, the diameter of each step gradually increases from bottom to top; the multi-stage separation system is used to cool high-temperature α-Al 2 O 3 , specifically including a first cyclone cooler, a second cyclone cooler, a third cyclone cooler, a fourth cyclone cooler, and a fluidized bed; the cyclone recovery system is used to recover the flue gas generated by the roasting system, specifically including a bag filter, a induced draft fan, an air lift pump, and a recovery chimney.

[0010] Preferably, the bottom of the blanking bin is connected to the variable-speed conveyor, the output end of the variable-speed conveyor is communicated with the output end of the screw conveyor, and the output end of the screw conveyor is also communicated with the Venturi dryer.

[0011] Preferably, the Venturi dryer is also connected to the preheater, the output end of the Venturi dryer is connected to the first solid-gas separator, the output end of the first solid-gas separator is connected to the input end of the second solid-gas separator, the output end of the second solid-gas separator is connected to the suspension roaster, the output end of the suspension roaster is connected to the input end of the third solid-gas separator, the output end of the third solid-gas separator is connected to the buffer, the output end of the buffer is connected to the input end of the first cyclone cooler, and flue gas return channels are provided on the first solid-gas separator, the second solid-gas separator, and the third solid-gas separator. The first solid-gas separator is connected to the bag filter through the flue gas return channel, the second solid-gas separator is connected to the preheater through the flue gas return channel, and the third solid-gas separator is connected to the second solid-gas separator through the flue gas return channel.

[0012] Preferably, inside the suspension roasting furnace, from bottom to top, there are a preheating zone A, a heating zone B, a crystal form transformation zone C, an activity maintenance zone D, and a quenching zone E respectively. Graphite sealing rings are provided between adjacent stepped sections. A plurality of burners are also arranged in an array on the preheating zone A and the heating zone B. Along the circumference of the furnace wall in the crystal form transformation zone C, several porous air plates are distributed in a staggered manner. The porosity of the porous air plates is not less than 60%. Along the radial direction of the suspension roasting furnace in the activity maintenance zone D, honeycomb ceramic regenerators are arranged, and the honeycomb ceramic regenerators are assembled in a modular manner. Two groups of interconnected nitrogen curtain walls are also distributed above and below the activity maintenance zone D. The nitrogen in the two groups of nitrogen curtain walls forms an annular closed air curtain, and each group of nitrogen curtain walls is connected to an external nitrogen supply system. The suspension roasting furnace is also connected to a combustion station.

[0013] Preferably, the combustion station includes a start-up combustion station, a main combustion station, an auxiliary combustion station, and a drying combustion station. Among them, the start-up combustion station is used to heat the crystal form transformation zone C inside the suspension roasting furnace. The main combustion station is mainly used to heat the heating zone B. The auxiliary combustion station is used to heat the preheating zone A. The drying combustion station is used to heat the Venturi dryer.

[0014] Preferably, the input end of the first cyclone cooler is connected to the output end of the buffer. The output end of the first cyclone cooler is connected to the input end of the second cyclone cooler. The output end of the second cyclone cooler is connected to the input end of the third cyclone cooler. The output end of the third cyclone cooler is connected to the input end of the fourth cyclone cooler. The output end of the fourth cyclone cooler is connected to the input end of the fluidized bed. The number of fluidized beds is not less than two.

[0015] Preferably, the first cyclone cooler, the second cyclone cooler, the third cyclone cooler, and the fourth cyclone cooler are all provided with circulation channels. The first cyclone cooler is connected to the suspension roasting furnace through the circulation channel. The second cyclone cooler is connected to the first cyclone cooler through the circulation channel. The third cyclone cooler is also connected to the second cyclone cooler through the circulation channel. The fourth cyclone cooler is also connected to the third cyclone cooler through the circulation channel.

[0016] Preferably, the bag filter is also connected to the recovery chimney through an induced draft fan. The bottom output end of the bag filter is connected to the first cyclone cooler through several air lift pumps.

[0017] Preferably, the present invention also provides a low-temperature roasting process for aluminum hydroxide. The main steps include:

[0018] S1: Drying. Al(OH) with a moisture content of 4 - 6% is fed through the automatic feeding port at the bottom of the feeding bin. 3The material is conveyed to a variable-speed conveyor, then weighed and metered, and then conveyed to a Venturi dryer through a screw conveyor for heat exchange drying. Among them, the solid material is carried into the first solid-gas separator by flue gas and water vapor. During this process, the preheating temperature of the preheater is controlled at 110 - 160 °C, and the pressure difference during the drying process of the Venturi dryer is controlled < 1.5 kPa;

[0019] S2: Remove the attached water. After being separated by the first solid-gas separator, it is heated and separated by the second solid-gas separator, so that the attached water in the Al(OH) 3 in the material is removed. Then, the Al(OH) after removing the attached water 3 is conveyed to a suspension roasting furnace for roasting. During this process, the temperature of the first solid-gas separator is controlled at 160 - 200 °C, and the temperature of the second solid-gas separator is controlled at 320 - 350 °C;

[0020] S3: Low-temperature roasting. The Al 2 O 3 particles formed after removing the attached water are subjected to stepped suspension roasting from bottom to top in the suspension roasting furnace, and the roasting temperature and residence time of the material in each step in the suspension roasting furnace are monitored and controlled in real time through low-temperature monitoring and control, so that the crystal form of the material is fully transformed at a relatively low temperature;

[0021] S4: Buffer residence. The α-Al 2 O 3 is separated by the third solid-gas separator, and then the solid material is allowed to stay through a buffer. The residence time is 1 - 10 min, and the buffer temperature is 860 - 890 °C;

[0022] S5: Cooling and output. After buffering, the solid material is gradually cooled down through the first cyclone cooler, the second cyclone cooler, the third cyclone cooler and the fourth cyclone cooler respectively, and the cooled solid material is collected through a fluidized bed, and the crystalline α-Al 2 O 3 particles are output.

[0023] Preferably, the specific steps of the low-temperature monitoring and control are as follows:

[0024] S30: First, according to the requirements of the produced product, control the auxiliary combustion station to preheat the preheating zone A. During this process, the Al 2 O 3 particles after removing the attached water are subjected to secondary removal again to ensure that the attached water is completely removed. Among them, the temperature of the preheating zone A is not lower than 300 - 350 °C, and the preheating residence time is 8 - 15 min;

[0025] S31: After the preheating is completed, first control the main combustion station to heat the heating zone B, so that the Al 2 O3 The particles begin to remove the crystal water, and during this process, Al 2 O 3 The particles will remove all the crystal water to form γ-Al 2 O 3 , the temperature of heating zone B is not lower than 500 - 560 °C, and the residence time is 5 - 10 min;

[0026] S32: Pass the formed γ-Al 2 O 3 through the crystal form transformation zone C. Through the staggered distributed porous air plates, hot air can continuously and evenly heat γ-Al 2 O 3 . And by adjusting the gas flow rate and temperature entering the porous air plates, the temperature gradient of the crystal form transformation zone C in the furnace can be adjusted more precisely, so that the crystal form transformation of γ-Al 2 O 3 to α-Al 2 O 3 can be completed at a lower temperature. The temperature of the crystal form transformation zone C is controlled at 820 - 880 °C, and the residence time is 18 - 24 min;

[0027] S33: Pass the formed α-Al 2 O 3 through the activity maintenance zone D, so that α-Al 2 O 3 forms a stable crystal form. Among them, the oxygen can be isolated by the nitrogen curtain wall to avoid the oxidation of the material at high temperature, and heat conduction is carried out through the porous surface of the honeycomb ceramic regenerator to maintain a stable temperature, which can reduce the external heat demand. And the temperature of the activity maintenance zone D is controlled at 850 - 880 °C, and the residence time is 10 - 15 min;

[0028] S34: Cool down the stable α-Al 2 O 3 formed in S33 in the quenching zone E, and convey the α-Al 2 O 3 obtained after cooling down to the third solid-gas separator for separation. Among them, the temperature of the quenching zone E is 600 - 660 °C, and the residence time is 3 - 5 min.

[0029] The beneficial effects of the present invention are as follows:

[0030] First, through the feeding system, the Al(OH) material with a certain moisture content can be conveyed to the roasting system, and the raw material is dried by the Churri dryer and the preheater, reducing the Al(OH) 3 material, and reducing the Al(OH) 3The influence of moisture in the material on the roasting process. Secondly, through the first solid-gas separator and the second solid-gas separator, the separation and removal of attached water are carried out, and the flue gas recycling is realized. While reducing the Al 2 O 3 particle content in the flue gas, it also avoids the entry of moisture and attached water into the suspension roaster, enabling the complete removal of crystal water from the Al 2 O 3 particles during the roasting process, directly reducing the energy consumption of the suspension roaster.

[0031] Second, through the step-by-step working area from bottom to top, the inside of the suspension roaster is divided into different regions, enabling the Al 2 O 3 particles with attached water removed to pass through different regions in sequence, and the temperature of each region is controlled by different combustion chambers, so as to achieve a dynamic balance of the material during the roasting process, reduce the roasting temperature while ensuring the product quality. Compared with the traditional roasting temperature, through this solution, the highest roasting temperature does not exceed 900 °C. At such a low temperature, the roasting has low energy consumption, high conversion efficiency, and the generated nitrogen oxides are also reduced.

[0032] Third, through the buffer, the α-Al 2 O 3 separated and discharged by the third solid-gas separator stays for 1 - 10 minutes, thereby extending the residence time of the roasted α-Al 2 O 3 , further reducing the ignition loss rate of α-Al 2 O 3 , also reducing the roasting temperature and energy consumption. At the same time, the low temperature inhibits the production of nitrogen oxides and reduces the emission pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The process flow chart of the present invention;

[0034] Figure 2 The system composition diagram of the present invention;

[0035] Figure 3 The internal structure schematic diagram of the suspension roaster;

[0036] Figure 4 For Figure 3 The enlarged structure diagram of part C in;

[0037] Figure 5 For Figure 3 The enlarged structure diagram of part D in;

[0038] In the figure: feeding system 1, roasting system 2, multi-stage separation system 3, cyclone recovery system 4, blanking bin 10, adjustable-speed conveyor 11, screw conveyor 12, Venturi dryer 20, preheater 21, first solid-gas separator 22, second solid-gas separator 23, suspension roasting furnace 24, preheating zone A, heating zone B, crystal form conversion zone C, activity maintenance zone D, quenching zone E, third solid-gas separator 25, combustion station 26, buffer 27, first cyclone cooler 30, second cyclone cooler 31, third cyclone cooler 32, fourth cyclone cooler 33, fluidized bed 34, bag filter 40, induced draft fan 41, air lift pump 42, recovery chimney 43, start-up combustion station 260, main combustion station 261, auxiliary combustion station 262, drying combustion station 263, graphite sealing ring 6, porous air plate 7, honeycomb ceramic regenerator 8, nitrogen curtain wall 9 and blanking valve 51. Detailed implementation mode

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In the description of the present invention, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0041] Embodiment 1:

[0042] Please refer to Figures 1-5 , a low-temperature roasting system for aluminum hydroxide, comprising a feeding system 1, a roasting system 2, a multi-stage separation system 3 and a cyclone recovery system 4, wherein the feeding system 1 is used for conveying Al(OH) 3 material, and the Al(OH) 3 material is Al(OH) with a moisture content of 4-6% and a particle size of 100-200 μm 3 , specifically including a blanking bin 10, an adjustable-speed conveyor 11 and a screw conveyor 12; wherein the blanking bin 10 is mainly used for storing aluminum hydroxide materials generated in wet metallurgy processes such as the Bayer process, and the supply rate of the materials is controlled by the adjustable-speed conveyor 11. The roasting system 2 is used for roasting aluminum hydroxide materials and outputs α-Al 2 O3 , specifically including a Venturi dryer 20, a preheater 21, a first solid-gas separator 22, a second solid-gas separator 23, a suspension roaster 24, a third solid-gas separator 25, a combustion station 26 and a buffer 27. Among them, the Venturi dryer 20 and the preheater 21 mainly dry the Al(OH) 3 material to make it better for solid-gas separation, and then remove the attached water through the first solid-gas separator 22 and the second solid-gas separator 23. The interior of the suspension roaster 24 is stepped from bottom to top, and is successively a preheating zone A, a heating zone B, a crystal form transformation zone C, an activity maintenance zone D and a quenching zone E. Moreover, the diameter of each step gradually increases from bottom to top. Through the stepped shape from bottom to top, the temperature gradient can be controlled step by step, and the attached water and crystal water can be removed step by step. Through the gradual temperature control of the roasting system 2, phase transformation at a lower temperature can be achieved, and multi-stage solid-gas separation is adopted, and the Al 2 O 3 particles in the flue gas of each stage of the solid-gas separator can be recycled, reducing the content of Al 2 O 3 particles in the flue gas, and this process has lower energy consumption compared with traditional roasting.

[0043] The multi-stage separation system 3 is used to cool the high-temperature α-Al 2 O 3 , specifically including a first cyclone cooler 30, a second cyclone cooler 31, a third cyclone cooler 32, a fourth cyclone cooler 33 and a fluidized bed 34. During the multi-stage separation process, the flue gas generated at each stage can be returned to the previous stage cyclone separator, so as to ensure that the fluidized bed 34 can separate and extract pure α-Al 2 O 3 . In this process, solid particles are not prone to agglomeration in the fluidized state; the cyclone recovery system 4 is used to recover the flue gas generated by the roasting system 2 and the multi-stage separation system 3, specifically including a bag filter 40, a draft fan 41, an air lift pump 42 and a recovery chimney 43. The bag filter 40 is used to collect waste gas and send the purified waste gas into the recovery chimney 43 through the draft fan 41, and the dust concentration discharged from the recovery chimney 43 is less than 10mg / Nm 3 .

[0044] The bottom of the feeding bin 10 is connected to the adjustable-speed conveyor 11, the output end of the adjustable-speed conveyor 11 is communicated with the output end of the screw conveyor 12, and the output end of the screw conveyor 12 is also communicated with the Venturi dryer 20.

[0045] Through the above technical solution, first, the material reaches the adjustable-speed conveyor 11 through the feeding bin 10. After automatic weighing and metering by the adjustable-speed conveyor 11, a certain mass of the material is conveyed to the Venturi dryer 20 through the screw conveyor 12. The Venturi dryer 20 mainly uses the hot air flow generated by the preheater 21 and the drying combustion station 263 to disperse Al(OH) 3 material, so that the moisture in the Al(OH) 3 material evaporates. The solid material is sent into the first solid-gas separator 22 by the flue gas and water vapor. A differential pressure transmitter is also set on the Venturi dryer 20 to monitor whether it is blocked inside and control the internal differential pressure to be < 1.5 kPa. This process ensures that the Venturi dryer 20 can quickly dry the Al(OH) 3 material and reduces the influence of moisture in the roasting system 2.

[0046] The Venturi dryer 20 is also connected to the preheater 21. The output end of the Venturi dryer 20 is connected to the first solid-gas separator 22. The output end of the first solid-gas separator 22 is connected to the input end of the second solid-gas separator 23. The output end of the second solid-gas separator 23 is connected to the suspension roasting furnace 24. The output end of the suspension roasting furnace 24 is connected to the input end of the third solid-gas separator 25. The output end of the third solid-gas separator 25 is connected to the buffer 27. The output end of the buffer 27 is connected to the input end of the first cyclone cooler 30. Smoke return channels are provided on the first solid-gas separator 22, the second solid-gas separator 23, and the third solid-gas separator 25. The first solid-gas separator 22 is connected to the bag filter 40 through the smoke return channel. The second solid-gas separator 23 is connected to the preheater 21 through the smoke return channel. The third solid-gas separator 25 is connected to the second solid-gas separator 23 through the smoke return channel.

[0047] Through the above technical solution, the solid-gas mixed material processed by the Venturi dryer 20 enters the first solid-gas separator 22. Under the action of centrifugal force and gravity, the solid particles in the flue gas rotate downward along the inner wall of the first solid-gas separator 22 and the solid particles are discharged from the bottom downcomer. In addition, the purified flue gas at the rotation center is pushed to the top and discharged, and the flue gas is collected through the cyclone recovery system 4. The second solid-gas separator 23 receives the solid particles at the bottom of the first solid-gas separator 22, and then the attached water is removed in the second solid-gas separator 23. The flue gas generated in this process directly enters the preheater 21 and then returns to the Venturi dryer 20 for re-drying. Then, the solid particles with the attached water removed are discharged from the bottom of the second solid-gas separator 23 and conveyed into the suspension roasting furnace 24 for roasting, so that Al 2 O 3 removes the crystal water and completes the crystal form transformation. Then, the α-Al 2 O3 It is sent to the third solid-gas separator 25 for solid-gas separation again. The flue gas generated by the third solid-gas separator 25 will also enter the second solid-gas separator 23 for re-separation. α-Al is separated in the third solid-gas separator 25 2 O 3 , and finally the separated α-Al 2 O 3 is sent into the buffer 27 for buffer residence. In the buffer 27, the ignition loss rate of α-Al 2 O 3 can be reduced.

[0048] Referring to Figure 3 , from bottom to top inside the suspension roasting furnace 24 are a preheating zone A, a heating zone B, a crystal form transformation zone C, an activity maintenance zone D, and a quenching zone E. The parameters of each functional zone inside the suspension roasting furnace 24 are shown in the following table:

[0049]

[0050] Among them, infrared temperature measurement arrays and pneumatic valve channels for isolating each functional zone are provided at the preheating zone A, heating zone B, crystal form transformation zone C, activity maintenance zone D, and quenching zone E. Each infrared temperature measurement array is used to monitor the real-time temperature of different steps in real time, and the average real-time temperature of each functional zone is calculated through a calculation program. The average real-time temperature is the main parameter for measuring the heat of each functional zone.

[0051] The pneumatic valve channel mainly controls the opening and closing time of the pneumatic valve channel according to actual requirements to control the residence time of the particulate material. The control logic of the residence time is based on the change rate of the average real-time temperature. That is, when the change rate of the average real-time temperature of each functional zone is large, it means that the temperature of this functional zone is unstable. In this case, the control logic unit will extend the opening time of the pneumatic valve channel to make up for the heat loss caused by the low temperature. Graphite sealing rings 6 are provided between adjacent stepped sections. The graphite sealing rings 6 are mainly used to isolate adjacent functional zones. A plurality of burners are also arranged in an array on the preheating zone A and the heating zone B. The burners are mainly used to spray hot gas flow, and in this process, the main combustion chamber 261 and the auxiliary combustion chamber 262 play a role. At the heating zone B, the Al 2 O 3 particles begin to remove the crystal water of themselves, that is, γ-Al 2 O 3 is formed. After formation, it enters the crystal form transformation zone C through the pneumatic valve channel. The heat at the crystal form transformation zone C is mainly controlled by the start combustion chamber 260. In this process, γ-Al 2 O 3 will release a small amount of physically adsorbed water and other possible volatile impurities. When γ-Al 2 O3 When entering the crystal form conversion zone C, start the combustion chamber 260 to control the high-temperature gas flow to enter the crystal form conversion zone C through the porous gas plate 7. The main purpose of the porous gas plate 7 is to provide sufficient oxygen supply and carry away the generated water vapor and other volatile substances, preventing them from accumulating in the material and affecting the crystal form conversion of the product. The experimental data of the porosity of the porous gas distribution plate 7 and the gas distribution uniformity are shown in the following table:

[0052]

[0053]

[0054] From the above experimental data, it can be seen that when the porosity of the porous gas plate 7 is greater than 60%, the coefficient of variation of its gas flow velocity is lower than 7%, which can provide a stable flow field environment for crystal form conversion. Secondly, as the porosity increases, its phase conversion rate increases significantly, and the activation energy is in a decreasing state, that is, it shows that by controlling the porosity efficiency of the porous gas plate 7, the energy consumption can be reduced while increasing the phase conversion rate. Secondly, the gas flow rate and temperature entering the porous gas plate 7 can also be controlled by starting the combustion chamber 260. The combination of the two can accurately control the phase conversion efficiency and stability of the crystal form conversion zone C.

[0055] Refer to Figure 4 , the honeycomb ceramic regenerator 8 is arranged along the radial direction of the suspension roasting furnace 24 in the active maintenance zone D, and is divided into upper and lower groups in the vertical direction. The honeycomb ceramic regenerator 8 is assembled modularly, and each piece has a size of 150×150×300 mm. The honeycomb ceramic regenerator 8 is also alternately connected to the start-up combustion station 260 and periodically reverses the direction (the gas flow direction is switched every 5-8 minutes). Its purpose is to dynamically control the temperature, including the heat storage stage and the heat release stage. During the formation process of crystal form conversion, when the infrared temperature measurement array in the active maintenance zone D monitors that the temperature is higher than the set temperature, the start-up combustion station 260 will make the high-temperature flue gas flow reversely through the honeycomb ceramic regenerator 8, and the heat is absorbed by the ceramic body, that is, the excess heat is absorbed during the heating period, and when the temperature is relatively low, the start-up combustion station 260 releases the gas flow forward, so as to release the stored heat again, so that the temperature fluctuation in the active maintenance zone D is controlled within ±3°C / m. This process maintains the temperature stability and avoids the influence of temperature change on the crystal form.

[0056] Refer to Figure 5, two sets of interconnected nitrogen curtain walls 9 are distributed above and below the activity maintenance zone D, and the nitrogen in the two sets of nitrogen curtain walls 9 forms an annular closed air curtain. Each set of nitrogen curtain walls 9 is connected to an external nitrogen supply system. Nitrogen can be supplied to the nitrogen curtain walls 9 through the external nitrogen supply system. Nitrogen enters the activity maintenance zone D through the upper nitrogen curtain wall 9 and flows out through the lower nitrogen curtain wall 9, so that the nitrogen curtain walls 9 form an annular closed air curtain barrier perpendicular to the material direction around the material flow, thereby isolating the influence of air and avoiding the following side reactions when the oxygen content is <500 ppm:

[0057] 4AL 2 O 3 ·H 2 O+3O 2 →2AL 4 O 6 +4H 2 O

[0058] Circular protection is achieved. Secondly, due to the laminar flow characteristics of the nitrogen curtain wall 9, the nitrogen curtain wall 9 can weaken convective heat transfer and reduce the axial temperature gradient <3 °C / m, thereby reducing the thermal interference between adjacent temperature zones. The suspension roaster 24 is also connected to the combustion station 26.

[0059] The suspension roaster 24 is also connected to the combustion station 26. The combustion station 26 includes a start-up combustion station 260, a main combustion station 261, an auxiliary combustion station 262, and a drying combustion station 263. Among them, the start-up combustion station 260 is used to heat the crystal form conversion zone C inside the suspension roaster 24, the main combustion station 261 is mainly used to heat the heating zone B, the auxiliary combustion station 262 is used to heat the preheating zone A, and the drying combustion station 263 is used to heat the Venturi dryer 20.

[0060] Through the above technical solutions, the combustion station 26 can simultaneously achieve temperature control of different functional zones in the suspension roaster 24 and drying control of the Venturi dryer 20, which improves the stability of the system and does not affect each other.

[0061] The input end of the first cyclone cooler 30 is connected to the output end of the buffer 27, the output end of the first cyclone cooler 30 is connected to the input end of the second cyclone cooler 31, the output end of the second cyclone cooler 31 is connected to the input end of the third cyclone cooler 32, the output end of the third cyclone cooler 32 is connected to the input end of the fourth cyclone cooler 33, the output end of the fourth cyclone cooler 33 is connected to the input end of the fluidized bed 34, and the number of fluidized beds 34 is not less than two.

[0062] Through the above technical solutions, when α-Al 2 O 3After the particles flow out of the buffer 27, the solid particles will successively pass through the first cyclone cooler 30, the second cyclone cooler 31, the third cyclone cooler 32, and the fourth cyclone cooler 33, and finally be processed by the fluidized bed 34 to form α-Al 2 O 3 finished product.

[0063] Among them, the relationship between the roasting temperature inside the suspension roasting furnace 24 and the loss-on-ignition rate of Al 2 O 3 is shown in the following table:

[0064]

[0065]

[0066] As can be seen from the above table, as the roasting temperature decreases, the loss-on-ignition rate of its product will increase. Although it can ensure that the loss-on-ignition rate is less than 1.0%, the loss-on-ignition rate of α-Al 2 O 3 is still greater than 0.9. And a lower loss-on-ignition rate means higher purity and better performance stability. Especially in the fields of high-purity electronic ceramics or high-end abrasives, a very low loss-on-ignition rate is often required.

[0067] In this technical solution, after the material is roasted, solid-gas separation is first carried out by the third solid-gas separator 25, and then buffering is carried out in the buffer 27. The main purpose of the buffer 27 is to reduce the temperature of the material while prolonging the residence time of the material particles, and further reduce the loss-on-ignition rate, roasting temperature and the generation amount of nitrogen oxides of α-Al 2 O 3 . In this solution, the experimental data of the residence time of the buffer 27 and the loss-on-ignition rate of α-Al 2 O 3 are shown in the following table:

[0068]

[0069] From the above data, it can be seen that after roasting, the loss-on-ignition rate of α-Al 2 O 3 will decrease with the increase of the residence time and temperature in the buffer 27, that is, the buffer 27 can further reduce the loss-on-ignition rate.

[0070] In this solution, two temperature drops are carried out through the quenching zone E and the buffer 27. Among them, the first temperature drop is carried out in the quenching zone E, and the stable α-Al 2 O 3 transformed from the active maintenance zone D is cooled from a temperature of 850 - 880 °C to 600 - 660 °C. During the quenching process, as the temperature decreases, the conversion rate of its crystal form changes as shown in the following table:

[0071]

[0072]

[0073] From the above data, it can be seen that the lower the temperature and the longer the residence time, the higher the α-Al 2 O 3 The higher the phase content, the lower the specific surface area. In order to ensure the purity and quality of the product, the temperature of the quench zone E is generally controlled at 600-660℃, which can not only ensure the α-Al 2 O 3 Purity and specific surface area can also be maintained within a certain range.

[0074] The first cyclone cooler 30, the second cyclone cooler 31, the third cyclone cooler 32 and the fourth cyclone cooler 33 are all provided with circulation channels. The first cyclone cooler 30 is connected to the suspension roasting furnace 24 through the circulation channel, the second cyclone cooler 31 is connected to the first cyclone cooler 30 through the circulation channel, the third cyclone cooler 32 is also connected to the second cyclone cooler 31 through the circulation channel, and the fourth cyclone cooler 33 is also connected to the third cyclone cooler 32 through the circulation channel. In this process, the second cyclone cooler 31, the third cyclone cooler 32 and the fourth cyclone cooler 33 are in the process of cooling and forming, and each stage will generate waste gas in the cooling process, and these waste gases include α-Al 2 O 3 The particles and the unconverted Al collected by the bag filter 40 2 O 3 The particles will enter the suspension roasting furnace 24 again for roasting, which further improves the output and quality of the product.

[0075] The bag dust collector 40 is also connected to a recovery chimney 43 via an induced draft fan 41 , and the bottom output end of the bag dust collector 40 is connected to the first cyclone cooler 30 via a plurality of air lift pumps 42 .

[0076] A low-temperature roasting process for aluminum hydroxide, the main steps of which include:

[0077] S1: Drying: Al(OH) with a moisture content of 4% is discharged through the automatic discharge port at the bottom of the discharge bin 10. 3 The material is conveyed to the adjustable speed conveyor 11, and then after being weighed and metered, it is conveyed to the Venturi dryer 20 through the screw conveyor 12 for heat exchange drying, wherein the solid material is brought into the first solid-gas separator 22 by the flue gas and water vapor. During this process, the preheating temperature of the preheater 21 is controlled at 110°C, and the pressure difference is controlled to be less than 1.5 kPa during the drying process of the Venturi dryer 20;

[0078] S2: Remove the adsorbed water. After separation by the first solid-gas separator 22, it is heated and separated by the second solid-gas separator 23 to remove the adsorbed water in the Al(OH) 3 material. Then, the Al(OH) after removing the adsorbed water 3 is conveyed to the suspension roasting furnace 24 for roasting. During this process, the temperature of the first solid-gas separator 22 is controlled at 170 °C, and the temperature of the second solid-gas separator 23 is controlled at 320 °C;

[0079] S3: Low-temperature roasting. The Al 2 O 3 particles formed after removing the adsorbed water are subjected to stepwise suspension roasting from bottom to top in the suspension roasting furnace 24, and the roasting temperature and residence time of the material in each step in the suspension roasting furnace 24 are monitored and controlled in real time through low-temperature monitoring and control, so that the crystal form of the material is fully transformed at a relatively low temperature;

[0080] S4: Buffer residence. The α-Al 2 O 3 is separated by the third solid-gas separator 25, and then the solid material is allowed to stay through the buffer 27 for 4 minutes at a buffer temperature of 860 °C;

[0081] S5: Cooling and output. After buffering, the solid material is gradually cooled down through the first cyclone cooler 30, the second cyclone cooler 31, the third cyclone cooler 32 and the fourth cyclone cooler 33 respectively, and the cooled solid material is collected through the fluidized bed 34, and the crystalline α-Al 2 O 3 particles are output.

[0082] The main steps of the low-temperature monitoring and control are as follows:

[0083] S30: First, according to the requirements of the produced product, control the auxiliary combustion station 262 to preheat the preheating zone A. During this process, the Al 2 O 3 particles after removing the adsorbed water are subjected to secondary removal again to ensure that the adsorbed water is completely removed. The temperature of the preheating zone A is 320 °C, and the preheating residence time is 8 minutes;

[0084] S31: After the preheating is completed, first control the main combustion station 261 to heat the heating zone B, so that the Al 2 O 3 particles start to remove the crystal water. During this process, the Al 2 O 3 particles will remove all the crystal water to form γ-Al 2 O 3 , the temperature of the heating zone is 510 °C, and the residence time is 5 minutes;

[0085] S32: Form the γ-Al 2 O 3 Through the crystal form transformation zone C, the hot air can continuously and evenly heat the γ-Al 2 O 3 by means of the staggered distributed porous air plates 7, and by adjusting the gas flow rate and temperature entering the porous air plates 7, the temperature gradient of the crystal form transformation zone C in the furnace can be adjusted more precisely, so that the crystal form transformation of γ-Al 2 O 3 to α-Al 2 O 3 can be completed at a lower temperature, where the temperature of the crystal form transformation zone C is controlled at 820 °C and the residence time is 18 min;

[0086] S33: Form the α-Al 2 O 3 Through the activity maintenance zone D, the α-Al 2 O 3 forms a stable crystal form, where the oxygen can be isolated by the nitrogen curtain wall 9 to avoid oxidation of the material at high temperature, and heat conduction is carried out through the porous surface of the honeycomb ceramic regenerator 8 to maintain a stable temperature, which can reduce the external heat demand, and the temperature of the activity maintenance zone D is controlled at 850 °C and the residence time is 10 min;

[0087] S34: Cool down the stable α-Al 2 O 3 formed in S33 in the quenching zone E, and convey the α-Al 2 O 3 obtained after cooling down to the third solid-gas separator 25 for separation, where the temperature of the quenching zone E is 600 °C and the residence time is 3 min.

[0088] Through the above process steps, the comparison of the product indexes obtained with the traditional indexes is shown in the following table:

[0089]

[0090] Example 2:

[0091] The difference from Example 1 is:

[0092] S1: Drying, the Al(OH) with a moisture content of 5% is fed through the automatic feeding port at the bottom of the feeding bin 10 3The material is conveyed to the adjustable-speed conveyor 11, then weighed and metered, and then conveyed to the Venturi dryer 20 through the screw conveyor 12 for heat exchange drying. Among them, the solid material is carried into the first solid-gas separator 22 by flue gas and water vapor. During this process, the preheating temperature of the preheater 21 is controlled at 140 °C, and the pressure difference during the drying process of the Venturi dryer 20 is controlled to be < 1.5 kPa;

[0093] S2: Remove the attached water. After being separated by the first solid-gas separator 22, it is heated and separated by the second solid-gas separator 23, so that the attached water in the Al(OH) 3 in the material is removed, and then the Al(OH) after removing the attached water 3 is conveyed to the suspension roasting furnace 24 for roasting. During this process, the temperature of the first solid-gas separator 22 is controlled at 200 °C, and the temperature of the second solid-gas separator 23 is controlled at 340 °C;

[0094] S3: Low-temperature roasting. The Al 2 O 3 particles formed after removing the attached water are subjected to step-by-step suspension roasting from bottom to top in the suspension roasting furnace 24, and the roasting temperature and residence time of the material in each step in the suspension roasting furnace 24 are monitored and controlled in real time through low-temperature monitoring and control, so that the crystal form of the material is fully transformed at a relatively low temperature;

[0095] S4: Buffer residence. The α-Al 2 O 3 is separated by the third solid-gas separator 25, and then the solid material is allowed to stay through the buffer 27 for a residence time of 4 min and a buffer temperature of 880 °C;

[0096] S5: Cooling and output. After buffering, the solid material is gradually cooled down through the first cyclone cooler 30, the second cyclone cooler 31, the third cyclone cooler 32 and the fourth cyclone cooler 33 respectively, and the cooled solid material is collected by the fluidized bed 34, and the crystalline α-Al 2 O 3 particles are output.

[0097] The main steps of the low-temperature monitoring and control are as follows:

[0098] S30: First, according to the requirements of the produced product, control the auxiliary combustion station 262 to preheat the preheating zone A. During this process, the Al 2 O 3 particles after removing the attached water are subjected to secondary removal again to ensure that the attached water is completely removed. Among them, the temperature of the preheating zone A is 350 °C, and the preheating residence time is 10 min;

[0099] S31: After the preheating is completed, first control the main combustion station 261 to heat the heating zone B, so that the Al2 O 3 The particles begin to remove the crystal water, and during this process, Al 2 O 3 The particles will remove all the crystal water to form γ-Al 2 O 3 , the temperature of the heating zone is 540 °C, and the residence time is 10 min;

[0100] S32: Pass the formed γ-Al 2 O 3 through the crystal form transformation zone C. Through the staggered porous air plates 7, hot air can continuously and evenly heat the γ-Al 2 O 3 , and by adjusting the gas flow rate and temperature entering the porous air plates 7, the temperature gradient of the crystal form transformation zone C in the furnace can be adjusted more precisely, so that the crystal form transformation of γ-Al 2 O 3 to α-Al 2 O 3 can be completed at a lower temperature. Among them, the temperature of the crystal form transformation zone C is controlled at 840 °C, and the residence time is 20 min;

[0101] S33: Pass the formed α-Al 2 O 3 through the activity maintenance zone D, so that α-Al 2 O 3 forms a stable crystal form. Among them, the oxygen can be isolated by the nitrogen curtain wall 9 to avoid oxidation of the material at high temperature, and heat conduction is carried out through the porous surface of the honeycomb ceramic regenerator 8 to maintain a stable temperature, which can reduce the external heat demand, and the temperature of the activity maintenance zone D is controlled at 850 °C, and the residence time is 10 min;

[0102] S34: Cool down the stable α-Al 2 O 3 formed in S33 in the quenching zone E, and convey the α-Al 2 O 3 obtained after cooling down to the third solid-gas separator 25 for separation. Among them, the temperature of the quenching zone E is 660 °C, and the residence time is 5 min.

[0103] Through the process steps of Example 2, the key data indexes of the obtained product are shown in the following table:

[0104]

[0105] The above are only the preferred embodiments of the present invention and do not limit the present invention in other forms. Any person skilled in the relevant art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A low-temperature roasting system for aluminum hydroxide, characterized in that: The invention comprises a feeding system (1), a roasting system (2), a multi-stage separation system (3) and a cyclone recovery system (4), wherein the feeding system (1) is used for conveying Al(OH)3 materials, and specifically comprises a lower hopper (10), an adjustable speed conveyor (11) and a screw conveyor (12); the roasting system (2) is used for roasting aluminum hydroxide materials and outputting α-Al2O3, and specifically comprises a venturi dryer (20), a preheater (21), a first solid-gas separator (22), a second solid-gas separator (23), a suspension roasting furnace (24), a third solid-gas separator (25), a combustion station (26) and a buffer (27), wherein the suspension The interior of the roasting furnace (24) is stepped from bottom to top, and is sequentially composed of a preheating zone A, a heating zone B, a crystal transformation zone C, an activity maintenance zone D and a quenching zone E, and the diameter of each step gradually increases from bottom to top; the multi-stage separation system (3) is used to cool the high-temperature α-Al2O3, and specifically includes a first cyclone cooler (30), a second cyclone cooler (31), a third cyclone cooler (32), a fourth cyclone cooler (33) and a fluidized bed (34); the cyclone recovery system (4) is used to recover the flue gas generated by the roasting system, and specifically includes a bag dust collector (40), an induced draft fan (41), an air lift pump (42) and a recovery chimney (43).

2. The aluminum hydroxide low temperature roasting system according to claim 1, characterized in that: The bottom of the lower bin (10) is connected to an adjustable-speed conveyor (11), the output end of the adjustable-speed conveyor (11) is connected to the output end of a screw conveyor (12), and the output end of the screw conveyor (12) is also connected to a Venturi dryer (20).

3. The aluminum hydroxide low temperature roasting system according to claim 1, characterized in that: The venturi dryer (20) is also connected to the preheater (21), the output end of the venturi dryer (20) is connected to the first solid-gas separator (22), the output end of the first solid-gas separator (22) is connected to the input end of the second solid-gas separator (23), the output end of the second solid-gas separator (23) is connected to the suspension roasting furnace (24), the output end of the suspension roasting furnace (24) is connected to the input end of the third solid-gas separator (25), and the output end of the third solid-gas separator (25) is connected to the buffer (27). The output end of the buffer (27) is connected to the input end of the first cyclone cooler (30); a flue gas reflux channel is provided on the first solid-gas separator (22), the second solid-gas separator (23) and the third solid-gas separator (25); the first solid-gas separator (22) is connected to the bag filter (40) through the flue gas reflux channel; the second solid-gas separator (23) is connected to the preheater (21) through the flue gas reflux channel; and the third solid-gas separator (25) is connected to the second solid-gas separator (23) through the flue gas reflux channel.

4. The aluminum hydroxide low temperature roasting system according to claim 3, characterized in that: The suspension roasting furnace (24) comprises a preheating zone A, a heating zone B, a crystal conversion zone C, an activity maintenance zone D and a quenching zone E from bottom to top, and graphite sealing rings (6) are arranged between adjacent stepped sections. A plurality of burners are arranged in an array on the preheating zone A and the heating zone B. A plurality of porous gas plates (7) are staggeredly distributed along the circumference of the furnace wall in the crystal conversion zone C, and the opening rate of the porous gas plates (7) is not less than 60%. Honeycomb ceramic heat storage bodies (8) are arranged along the radial direction of the suspension roasting furnace (24) in the activity maintenance zone D, and the honeycomb ceramic heat storage bodies (8) are assembled in a modular manner. Two groups of interconnected nitrogen curtain walls (9) are distributed above and below the activity maintenance zone D, and the nitrogen in the two groups of nitrogen curtain walls (9) forms an annular closed air curtain, and each group of nitrogen curtain walls (9) is connected to an external nitrogen supply system. The suspension roasting furnace (24) is also connected to a combustion station (26).

5. The aluminum hydroxide low temperature roasting system according to claim 3, characterized in that: The combustion station (26) includes a starting combustion station (260), a main combustion station (261), an auxiliary combustion station (262) and a drying combustion station (263), wherein the starting combustion station (260) is used to heat the crystal transformation zone C inside the suspension roasting furnace (24), the main combustion station (261) is mainly used to heat the heating zone B, the auxiliary combustion station (262) is used to heat the preheating zone A, and the drying combustion station (263) is used to heat the Venturi dryer (20).

6. The aluminum hydroxide low temperature roasting system according to claim 3, characterized in that: The output end of the first cyclone cooler (30) is connected to the input end of the second cyclone cooler (31), the output end of the second cyclone cooler (31) is connected to the input end of the third cyclone cooler (32), the output end of the third cyclone cooler (32) is connected to the input end of the fourth cyclone cooler (33), the output end of the fourth cyclone cooler (33) is connected to the input end of the fluidized bed (34), and the number of the fluidized beds (34) is not less than two.

7. The aluminum hydroxide low temperature roasting system according to claim 6, characterized in that: The first cyclone cooler (30), the second cyclone cooler (31), the third cyclone cooler (32) and the fourth cyclone cooler (33) are all provided with circulation channels; the first cyclone cooler (30) is connected to the suspension roasting furnace (24) through the circulation channel; the second cyclone cooler (31) is connected to the first cyclone cooler (30) through the circulation channel; the third cyclone cooler (32) is also connected to the second cyclone cooler (31) through the circulation channel; and the fourth cyclone cooler (33) is also connected to the third cyclone cooler (32) through the circulation channel.

8. The aluminum hydroxide low temperature roasting system according to claim 1, characterized in that: The bag dust collector (40) is connected to a recovery chimney (43) via an induced draft fan (41), and the bottom output end of the bag dust collector (40) is connected to a first cyclone cooler (30) via a plurality of air lift pumps (42).

9. A low-temperature roasting process for aluminum hydroxide, using the low-temperature roasting system for aluminum hydroxide according to claims 1-8, characterized in that: The main steps include: S1: Drying, Al(OH)3 material with a moisture content of 4-6% is conveyed to an adjustable speed conveyor (11) through an automatic discharge port at the bottom of a discharge bin (10), and then conveyed to a venturi dryer (20) through a screw conveyor (12) for heat exchange drying after weighing, wherein the solid material is brought into a first solid-gas separator (22) by flue gas and water vapor, and during this process, the preheating temperature of the preheater (21) is controlled at 110-160°C, and the pressure difference during the drying process of the venturi dryer (20) is controlled to be less than 1.5 kPa; S2: removing attached water, separating in the first solid-gas separator (22) and heating and separating in the second solid-gas separator (23) to remove attached water in the Al(OH)3 material, and then delivering the Al(OH)3 after the attached water is removed to the suspension roasting furnace (24) for roasting. In this process, the temperature of the first solid-gas separator (22) is controlled at 160-200°C, and the temperature of the second solid-gas separator (23) is controlled at 320-350°C; S3: low-temperature calcination, wherein the Al2O3 particles formed after the attached water is removed are subjected to step-by-step suspension calcination from bottom to top in a suspension calcination furnace (24), and the calcination temperature and residence time of the material in each step in the suspension calcination furnace (24) are monitored and controlled in real time through low-temperature monitoring and control, so that the material can be fully converted into a crystal form at a relatively low temperature; S4: buffer retention, the obtained α-Al2O3 is separated by a third solid-gas separator (25), and then the solid material is retained by a buffer (27), wherein the retention time is 1-10 minutes and the buffer temperature is 860-890°C; S5: Cooling and outputting. After buffering, the solid material is cooled step by step through a first cyclone cooler (30), a second cyclone cooler (31), a third cyclone cooler (32) and a fourth cyclone cooler (33), and the cooled solid material is collected through a fluidized bed (34) and output as crystalline α-Al2O3 particles.

10. A low-temperature roasting process for aluminum hydroxide according to claim 9, characterized in that: The specific steps of the low temperature monitoring control are as follows: S30: First, according to the output product requirements, the auxiliary combustion station (262) is controlled to preheat the preheating zone A. During this process, the Al2O3 particles from which the attached water has been removed are subjected to secondary removal to ensure that the attached water is completely removed. The temperature of the preheating zone A is not lower than 300-350°C, and the preheating residence time is 8-15 minutes. S31: After the preheating is completed, the main combustion station (261) is first controlled to heat the heating zone B so that the Al2O3 particles begin to remove crystal water. In this process, the Al2O3 particles will remove all crystal water to form γ-Al2O3. The temperature of the heating zone B is not less than 500-560°C, and the residence time is 5-10 minutes; S32: passing the formed γ-Al2O3 through the crystal transformation zone C, and the hot air can continuously and evenly heat the γ-Al2O3 through the staggered porous gas plates (7), and by adjusting the gas flow and temperature entering the porous gas plates (7), the temperature gradient of the crystal transformation zone C in the furnace can be finely adjusted, so that the crystal transformation of γ-Al2O3 to α-Al2O3 can be completed at a lower temperature, wherein the temperature of the crystal transformation zone C is controlled at 820-880°C, and the residence time is 18-24min; S33: passing the formed α-Al2O3 through the active maintenance zone D, so that the α-Al2O3 forms a stable crystal form, wherein the nitrogen curtain wall (9) can isolate oxygen to prevent the material from being oxidized at high temperature, and heat is conducted through the porous surface of the honeycomb ceramic heat storage body (8) to maintain a stable temperature, which can reduce the external heat demand, and the temperature of the active maintenance zone D is controlled at 850-880°C, and the residence time is 10-15min; S34: The stable α-Al2O3 formed in S33 is cooled in the quenching zone E, and the α-Al2O3 obtained by cooling is transported to the third solid-gas separator (25) for separation, wherein the temperature of the quenching zone E is 600-660°C and the residence time is 3-5 minutes.

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