System and process for preparing high-whiteness calcined kaolin

Abstract

The system comprises a preheater, a rotary kiln, a hot blast stove, a bleaching machine, a cooling air pipe and a dust collector, a clinker outlet of the rotary kiln is connected with the bleaching machine, a water spraying pipeline is arranged in the bleaching machine, a discharging port of the bleaching machine is connected with the cooling air pipe, cooling air is introduced into the cooling air pipe, and the dust collector is connected with the hot blast stove. An outlet of the cooling air pipe is connected with the dust collector, an air outlet of the dust collector is connected with the hot-blast stove, an air outlet of the hot-blast stove is connected with the rotary kiln, and hot air generated by combustion of fuel in the hot-blast stove enters the rotary kiln. Through cooperation of three-stage whitening, two-stage cooling and heat recovery processes, high-whiteness kaolin is obtained, hot air in the system is efficiently utilized, energy consumption of the system is reduced, the whiteness of the product is improved through the whole production system, the production line is energy-saving and low-carbon, the product quality is stable, the process and equipment are simple, the production line is suitable for large-scale industrial production, and the production cost is reduced. The cost is reduced and the cost performance is high.

Description

Technical Field

[0001] The present invention relates to the technical field of kaolin preparation, in particular to a system and process for preparing high-whiteness calcined kaolin. Background Art

[0002] Calcined kaolin is a process in which kaolin is sintered in a furnace to a specific temperature and time, causing its physical and chemical properties to change to meet specific requirements. Due to its excellent plasticity and refractory properties, it is widely used in a variety of industries, including ceramics, papermaking, coatings, rubber, plastics, and building materials. However, with the continued mining of high-grade conventional kaolin, the raw ore required to produce refined kaolin that meets industrial requirements has become increasingly scarce.

[0003] Gangue is solid waste emitted during coal mining and washing. Its main components are Al2O3 and SiO2. Produced in large quantities, it is typically stored in piles, significantly impacting the environment and causing spontaneous combustion, acid rain, underground seepage, river siltation, photochemical smog, and mudslides. Kaolinite is the most important mineral component of gangue. Using gangue to produce calcined kaolin can significantly improve the utilization efficiency of gangue resources, reduce environmental pollution from gangue accumulation or discharge, increase its added value, and generate significant economic benefits.

[0004] However, coal gangue has a high carbon content and low natural whiteness. The associated carbon and organic matter are difficult to remove, and incomplete carbon removal will seriously affect the whiteness of kaolin. At present, when using coal gangue to prepare calcined kaolin, calcination process equipment is mainly used. Chinese Patent Publication No. CN104150497A discloses a method for preparing ultra-high whiteness calcined kaolin from all coal gangue. It uses an ultra-long calcination kiln of 180m, and the raw materials composed entirely of coal gangue are calcined at a temperature between 945-955℃ using a muffle flame for more than 6 hours. This patent achieves whitening of coal gangue, but the calcination time is too long, requiring more than 6 hours, and it is a muffle flame calcination, with poor temperature controllability, low heat utilization efficiency, and relatively high cost. Chinese patent publication number CN105692639A discloses a method for preparing kaolin from coal gangue, which includes washing the ore, adding calcium oxide, suspending and preheating, adding titanium dioxide to mix, calcining, feeding a mixed gas for cooling and breaking up and classifying. Although this method improves the whiteness of the calcined kaolin, it uses hot nitrogen to preheat the material and adds calcium oxide and titanium dioxide additives, which increases production costs.

[0005] In summary, the problems existing in the prior art are:

[0006] (1) The production process of calcined kaolin prepared from coal gangue is complex, the temperature controllability of the rotary kiln is poor, the product is easy to sinter, the system energy consumption is high, and the heat utilization efficiency is low.

[0007] (2) It is difficult to prepare high-whiteness calcined kaolin using coal gangue. In order to further improve the whiteness of calcined kaolin, the production cost is high and the economic efficiency is poor. Summary of the Invention

[0008] In order to solve the problems of low whiteness value and high energy consumption of kaolin prepared by calcining coal gangue, the present invention provides a system and process for preparing high-whiteness calcined kaolin. Through the cooperation of three-stage whitening, two-stage cooling and heat recovery processes, while obtaining high-whiteness kaolin, the hot air in the system is efficiently utilized, and the energy consumption of the system is reduced. The entire production system improves the whiteness of the product, and the production line is energy-saving and low-carbon, the product quality is stable, the process and equipment are simple, it is suitable for large-scale industrial production, reduces costs, and is cost-effective.

[0009] The present invention is achieved as follows: a system for preparing high-whiteness calcined kaolin includes a preheater, a rotary kiln, a hot blast furnace, a bleaching machine, a cooling air duct, and a dust collector. The clinker outlet of the rotary kiln is connected to the bleaching machine, a water spray pipe is provided in the bleaching machine, the material outlet of the bleaching machine is connected to the cooling air duct, cooling air is introduced into the cooling air duct, the outlet of the cooling air duct is connected to the dust collector, the air outlet of the dust collector is connected to the hot blast furnace, the air outlet of the hot blast furnace is connected to the rotary kiln, and the hot air generated by the combustion of fuel in the hot blast furnace enters the rotary kiln.

[0010] In the above technical solution, preferably, an exhaust duct is further provided in the bleaching machine, and the exhaust duct is connected to the inlet of the dust collector.

[0011] In the above technical solution, it is further preferred that the exhaust duct is also connected to the water vapor treatment system to allow excess water vapor to enter the water vapor treatment system.

[0012] In the above technical solution, preferably, the water spray pipe extends from the bleaching machine smoke chamber into the bleaching machine, and a water spray amount regulating device is provided on the water spray pipe.

[0013] In the above technical solution, preferably, the dust collector outlet is connected to the heat recovery air duct, and the heat recovery air duct is provided with a primary air branch pipe and a secondary air branch pipe. The primary air branch pipe is connected to the burner at the head of the hot blast furnace, and the secondary air branch pipe is connected to the air inlet of the hot blast furnace.

[0014] In the above technical solution, it is further preferred that a first induced draft fan is provided on the main pipe of the heat recovery air duct, a second induced draft fan is provided on the primary air branch pipe, and a third induced draft fan is provided on the secondary air branch pipe.

[0015] In the above technical solution, preferably, the heat recovery air duct is further provided with a bypass branch pipe, and the bypass branch pipe is connected to the waste heat utilization system or the chimney.

[0016] In the above technical solution, preferably, the preheater is a multi-stage cyclone heat exchange structure, the air inlet duct of the last cyclone of the preheater is connected to the tail smoke chamber of the rotary kiln, the discharge pipe of the last cyclone is connected to the tail smoke chamber of the rotary kiln, and the discharge pipe of the penultimate cyclone is connected to the air inlet duct of the last cyclone.

[0017] A process for preparing high-whiteness calcined kaolin, comprising a three-stage whitening process, a two-stage cooling process, and a heat recovery process;

[0018] The three-stage whitening process is as follows: the first-stage whitening is to feed the gangue treated by the raw material processing system into the preheater for multiple heat exchanges with the flue gas leaving the rotary kiln to remove moisture, part of the hydroxyl group and carbon. The flue gas temperature leaving the rotary kiln is 650-900℃. The second-stage whitening is to feed the hot air generated by the combustion of fuel in the hot blast furnace into the rotary kiln, exchange heat with the flue gas, and feed the gangue after gas-solid separation into the rotary kiln for calcination at a temperature of 800-1200℃ and a residence time of 30-100 minutes to completely remove carbon. The third-stage whitening is to feed the kaolin leaving the rotary kiln into the bleaching machine for quenching and whitening by spraying water to further improve the whiteness of the kaolin.

[0019] The two-stage cooling process is as follows: the first stage cooling is to spray water in the bleaching machine to quench the kaolin leaving the rotary kiln at a temperature of 800-1100℃. The water spraying system is used to adjust the water spraying volume to control the temperature of the kaolin entering the cooling air duct at 600-800℃. The second stage cooling is to enter the cooling air duct to further cool the kaolin leaving the bleaching machine. The amount of cold air entering the cooling air duct is adjusted according to the required air volume in the hot air furnace.

[0020] The heat recovery process is as follows: the air temperature out of the cooling air duct is less than 250°C, and the material is recovered through the dust collector. The hot air out of the dust collector enters the burner as primary air in one way and enters the hot air furnace as secondary air in the other way, realizing efficient heat recovery and utilization.

[0021] In the above technical solution, preferably, the water vapor exiting the bleaching machine enters a dust collector or a water vapor treatment system.

[0022] The advantages and positive effects of the present invention are:

[0023] 1. The present invention combines the functions of calcining, bleaching, cooling and heat recovery of kaolin, thereby obtaining a high-whiteness kaolin product. At the same time, it realizes full heat recovery and utilization, improves the thermal utilization efficiency of the system, reduces the energy consumption of the system, and achieves energy saving and efficiency improvement.

[0024] 2. The present invention realizes efficient decarbonization and improves the whiteness of kaolin through a three-stage whitening process of partial decarbonization and pre-whitening in a preheater, calcination and decarbonization and whitening in a rotary kiln, and water spraying and quenching and whitening in a bleaching machine. The heat source for calcination in the rotary kiln comes from the hot flue gas generated by the combustion of fuel in the hot blast furnace. The temperature of the flue gas entering the rotary kiln can be controlled by regulating the amount of secondary air entering the hot blast furnace, thereby realizing precise controllable and adjustable temperature in the rotary kiln, avoiding direct contact between the gangue raw materials and the high-temperature flame, which would lead to a significant reduction in the activity of the kaolin product.

[0025] 3. The present invention cooperates with the two-stage cooling of the bleaching machine through water spray cooling and cooling duct air cooling, which does not affect the whiteness of the product while recovering the heat of the kaolin leaving the kiln; the temperature of the material entering the cooling duct is adjusted in real time by the amount of water sprayed, ensuring that the hot air energy after heat exchange of the cold air entering the cooling duct can be fully utilized.

[0026] 4. The present invention can recycle all the hot air from the cooling air duct after dust collection treatment. Part of it is used as primary air and the other part is used as secondary air. Since the temperature of the above two parts of air is much higher than that of normal temperature air, it is conducive to combustion and can reduce the energy consumption of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the system for preparing high-whiteness calcined kaolin provided in Example 1 of the present invention.

[0028] In the picture:

[0029] 1-preheater, 101-first stage cyclone, 102-second stage cyclone, 103-third stage cyclone, 104-air lock valve;

[0030] 2-hot air stove, 3-burner;

[0031] 4-rotary kiln, 401-kiln tail smoke chamber, 402-kiln door cover,

[0032] 5-bleaching machine, 501-bleaching machine smoke room;

[0033] 6-cooling air duct, 7-dust collector;

[0034] 8-heat recovery air duct, 801-primary air branch pipe, 802-secondary air branch pipe, 803-bypass branch pipe;

[0035] 901-first induced draft fan, 902-second induced draft fan, 903-third induced draft fan;

[0036] 10-water spray pipe, 11-water spray system, 12-water vapor treatment system;

[0037] A-coal gangue, B-kaolin, C-cooling air;

[0038] The dotted line with an arrow is the direction of airflow, and the solid line with an arrow is the direction of material flow. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0041] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0042] Example 1

[0043] See also Figure 1 An embodiment of the present invention provides a low-energy consumption system for preparing high-whiteness calcined kaolin, comprising a preheater 1, a hot blast furnace 2, a burner 3, a rotary kiln 4, a bleaching machine 5, a cooling air duct 6, a dust collector 7, and a heat recovery air duct 8. This embodiment uses a three-stage cyclone separation preheater as an example. The rotary kiln 4 includes a kiln tail smoke chamber 401 and a kiln door cover 402. The rotary kiln 4 is not equipped with a burner (i.e., no fuel inlet). The burner 3 on the hot blast furnace 2 is located at the head of the hot blast furnace 2.

[0044] A raw material inlet is provided on the connecting air duct between the first-stage cyclone 101 and the second-stage cyclone 102 of the preheater 1, the discharge pipe of the second-stage cyclone 102 is connected to the air inlet duct of the third-stage cyclone 103, the kiln tail smoke chamber 401 is connected to the air inlet duct of the third-stage cyclone 103, the discharge pipe of the third-stage cyclone 103 is connected to the kiln tail smoke chamber 401, the clinker outlet of the rotary kiln 4 is located at the kiln door cover 402, and the feed port of the bleaching machine 5 is located at the bleaching machine smoke chamber 501. The kiln door cover 402 is connected to the feeding port of the bleaching machine 5. A water spray pipe 10 is provided in the bleaching machine 5. The water spray pipe 10 extends from the bleaching machine smoke chamber 501 into the bleaching machine. Preferably, the water spray pipe 10 extends to the middle section of the bleaching machine 5. A water spray amount regulating device is provided on the water spray pipe 10. The water spray pipe 10 is connected to the water spray system 11. The feeding port of the bleaching machine 5 is connected to the cooling air duct 6. A cold air inlet is provided on the cooling air duct 6. Cooling air C is introduced into the cooling air duct 6. The outlet of the cooling air duct 6 is connected to the inlet of the dust collector 7. The outlet of the dust collector 7 is connected to the hot blast furnace 2. The outlet of the hot blast furnace 2 is connected to the kiln door cover 402, so that the hot air generated by the combustion of fuel in the hot blast furnace 2 enters the rotary kiln 4.

[0045] Raw coal gangue A is fed into the preheater 1, where it exchanges heat with the flue gas exiting the rotary kiln to remove moisture, some hydroxyl groups, and carbon. Hot air generated by fuel combustion in the hot blast furnace 2 enters the rotary kiln 4, where it undergoes heat exchange with the flue gas, achieving gas-solid separation and is then fed into the rotary kiln 4 for calcination. High-temperature kaolin emerging from the rotary kiln 4 falls into the bleaching unit 5, where it undergoes two cooling stages and is separated in the dust collector 7 to yield finished low-temperature kaolin. The two cooling stages work in tandem. In the first stage, the kaolin exiting the rotary kiln 4 is sprayed with water for cooling within the bleaching unit 5. Adjusting the water spray rate controls the kaolin temperature and the volume of cold air C entering the cooling duct 6, ensuring that all hot air exiting the cooling duct 6 is fully recycled. In the second stage, the kaolin exiting the bleaching unit 4 is further cooled by air cooling. Furthermore, the water spraying in the bleaching unit 5 improves the whiteness of the calcined kaolin. The hot air from the dust collector 7 enters the hot air furnace 2, thereby realizing efficient heat recovery and utilization and reducing system energy consumption.

[0046] Because the central flame temperature generated by the fuel combustion is high, if it comes into direct contact with the gangue, the kaolin product will be mainly mullite, and the product activity will be greatly reduced. Therefore, in order to ensure the activity of the calcined kaolin, an indirect calcination method is adopted. The hot air generated in the hot blast furnace 2 with an appropriate heat and air volume enters the rotary kiln 4 for calcining the gangue.

[0047] As a preferred embodiment, an exhaust duct is further provided in the bleaching machine 5 , which extends from the discharge port of the bleaching machine 5 into the bleaching machine. When the water spraying amount of the bleaching machine is small, the exhaust duct is connected to the inlet of the dust collector 7 .

[0048] As a preferred embodiment, when the amount of water sprayed in the bleaching machine is large, the exhaust duct is connected to the water vapor treatment system 12 to allow excess water vapor to enter the water vapor treatment system 12.

[0049] The destination of water vapor from the bleaching machine 5 is determined based on the range of flue gas moisture content that the dust collector 7 can tolerate. Kaolin leaving the rotary kiln 4 at a temperature of 800-1100°C is cooled by spraying water within the bleaching machine 5. By adjusting the amount of water sprayed, the temperature of the kaolin entering the cooling duct 6 can be controlled to be between 600-800°C. Specifically, when the amount of water sprayed is low, the generated water vapor is diluted by the hot air exiting the cooling duct 6, resulting in a low water vapor content in the flue gas. Therefore, the water vapor leaving the bleaching machine 5 can enter the dust collector 7 directly without further treatment. When the amount of water sprayed is high, the amount of steam generated is high, and the water vapor content can cause condensation in the dust collector 7, requiring it to enter the water vapor treatment system 12.

[0050] As a preferred embodiment, the air outlet of the dust collector 7 is connected to the heat recovery air duct 8, and the heat recovery air duct 8 is provided with a primary air branch 801 and a secondary air branch 802. The primary air branch 801 is connected to the burner 3, and the secondary air branch 802 is connected to the air inlet of the hot blast furnace 2. One stream of hot air from the dust collector 7 enters the burner 3 as the primary air, and the other stream enters the hot blast furnace 2 as the secondary air, thereby realizing efficient heat recovery and reducing system energy consumption. In order to reduce the impact of residual carbon in solid combustion on the whiteness of calcined kaolin, the fuel fed into the burner 3 is preferably gas fuel, and the gas fuel can be natural gas, coal gas, etc. The gas fuel is fed into the hot blast furnace 2 through the burner 3 along with the primary air. With the help of the secondary air, hot air with appropriate heat and air volume is generated and enters the rotary kiln 4 for use in calcining coal gangue.

[0051] As a preferred embodiment, a first induced draft fan 901 is provided on the main pipe of the heat recovery air duct 8, a second induced draft fan 902 is provided on the primary air branch duct 801, and a third induced draft fan 903 is provided on the secondary air branch duct 802. Part of the hot air coming out of the cooling air duct 6 is used as primary air to enter the burner 3 to assist combustion, and the other part is used as secondary air to enter the hot blast furnace 2. If the amount of primary air and secondary air just meets the fuel combustion requirements, the hot air generated by the combustion will usually be higher than 1200°C, and when it enters the rotary kiln 4 to calcine the coal gangue, it will produce mullite and deactivate the kaolin. Therefore, in order to avoid the hot air temperature entering the rotary kiln being too high, a certain amount of low-temperature air needs to be added. In addition to assisting combustion, this part of the hot air entering the hot blast furnace through the secondary air branch duct 802 also plays the role of cooling and regulating the air temperature of the hot blast furnace and protecting the side walls of the hot blast furnace, thereby realizing efficient heat recovery and reducing system energy consumption. Under normal working conditions, all the hot air coming out of the cooling air duct 6 can enter the hot air furnace 2, realizing full utilization of thermal enthalpy, improving the heat utilization efficiency of the system and reducing the energy consumption of the system.

[0052] As a preferred embodiment, heat recovery duct 8 is further provided with a bypass branch 803, which is connected to a waste heat recovery system or chimney. If abnormal operating conditions occur, such as unstable fuel calorific value or fuel supply, resulting in incomplete utilization of the hot air exiting cooling duct 6, the hot air must be discharged through the chimney or used to dry raw materials in the waste heat recovery system to ensure stable system operation.

[0053] As a preferred embodiment, the preheater 1 is a three- to five-stage cyclone separation preheater, and one to two air lock valves 104 are provided on the discharge pipes of the cyclones at each stage.

[0054] Example 2

[0055] See also Figure 1 The present invention provides a process for preparing high-whiteness calcined kaolin, which includes a three-stage whitening process, a two-stage cooling process, and a heat recovery process.

[0056] The three-stage whitening process is as follows: the first-stage whitening occurs in the preheater 1. The first-stage whitening is that the gangue A treated by the raw material processing system is fed into the preheater 1 and undergoes multiple heat exchanges with the flue gas out of the rotary kiln 4 to remove moisture, part of the hydroxyl groups and carbon. The flue gas temperature out of the rotary kiln 4 is 650-900°C; the second-stage whitening is that the hot air generated by the combustion of the fuel in the hot blast furnace 2 enters the rotary kiln 4, and the gangue after heat exchange with the flue gas and solid separation is fed into the rotary kiln 4 for calcination. The calcination temperature is 800-1200°C, the residence time is 30-100 minutes, and all carbon is removed; the third-stage whitening is that the kaolin out of the rotary kiln 4 enters the bleaching machine 5, is sprayed with water for rapid cooling and whitening, and further improves the whiteness of the kaolin.

[0057] The two-stage cooling process is as follows: First, the kaolin leaving the rotary kiln 4 at a temperature of 800-1100°C is sprayed with water in the bleaching machine 5. The water spraying system 11 regulates the water volume, controlling the kaolin temperature entering the cooling duct 6 to between 600-800°C. Second, the kaolin leaving the bleaching machine 4 is further cooled by air after entering the cooling duct 6. The amount of cold air entering the cooling duct 6 is adjusted based on the required air volume in the hot air furnace 2. Cooling air C enters the cooling duct 6 and flows in the same direction as the kaolin leaving the bleaching machine 5 before entering the dust collector 7.

[0058] The two-stage cooling cooperates with each other. By adjusting the amount of water sprayed, the temperature of the kaolin entering the cooling air duct 6 and the amount of cold air C entering the cooling air duct 6 can be controlled, ensuring that all the hot air out of the cooling air duct 6 can be recycled.

[0059] The heat recovery process is as follows: the air temperature out of the cooling air duct 6 is less than 250°C, and the product kaolin B is recovered through the dust collector 7. One stream of hot air out of the dust collector 7 enters the burner 3 as primary air, and the other stream enters the hot blast furnace 2 as secondary air. In addition to supporting combustion, the secondary air also plays a role in cooling, regulating the air temperature and protecting the side walls of the hot blast furnace, thereby realizing efficient heat recovery and utilization and reducing system energy consumption.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for preparing high-whiteness calcined kaolin, characterized by: It includes a preheater, a rotary kiln, a hot blast furnace, a bleaching machine, a cooling air duct, and a dust collector. The clinker outlet of the rotary kiln is connected to the bleaching machine. A water spray pipe is provided in the bleaching machine. The discharge port of the bleaching machine is connected to the cooling air duct. Cooling air is introduced into the cooling air duct. The outlet of the cooling air duct is connected to the dust collector. The air outlet of the dust collector is connected to the hot blast furnace. The air outlet of the hot blast furnace is connected to the rotary kiln. The hot air generated by the combustion of fuel in the hot blast furnace enters the rotary kiln.

2. The system for preparing high-whiteness calcined kaolin according to claim 1, characterized in that: An exhaust duct is also provided in the bleaching machine, and the exhaust duct is connected to the inlet of the dust collector.

3. The system for preparing high-whiteness calcined kaolin according to claim 2, characterized in that: The exhaust duct is also connected to the water vapor processing system, so that excess water vapor enters the water vapor processing system.

4. The system for preparing high-whiteness calcined kaolin according to claim 1, characterized in that: The water spraying pipe extends from the smoke chamber of the bleaching machine into the bleaching machine, and a water spraying amount regulating device is provided on the water spraying pipe.

5. The system for preparing high-whiteness calcined kaolin according to claim 1, characterized in that: The air outlet of the dust collector is connected to the heat recovery air duct, which is provided with a primary air branch pipe and a secondary air branch pipe. The primary air branch pipe is connected to the burner at the head of the hot blast furnace, and the secondary air branch pipe is connected to the air inlet of the hot blast furnace.

6. The system for preparing high-whiteness calcined kaolin according to claim 5, characterized in that: The main pipe of the heat recovery air duct is provided with a first induced draft fan, the primary air branch pipe is provided with a second induced draft fan, and the secondary air branch pipe is provided with a third induced draft fan.

7. The system for preparing high-whiteness calcined kaolin according to claim 5, characterized in that: The heat recovery air duct is also provided with a bypass branch pipe, which is connected to the waste heat utilization system or the chimney.

8. The system for preparing high-whiteness calcined kaolin according to claim 1, characterized in that: The preheater is a multi-stage cyclone heat exchange structure. The air inlet pipe of the last cyclone of the preheater is connected to the tail smoke chamber of the rotary kiln, the discharge pipe of the last cyclone is connected to the tail smoke chamber, and the discharge pipe of the penultimate cyclone is connected to the air inlet pipe of the last cyclone.

9. A process for preparing high-whiteness calcined kaolin using the system according to any one of claims 1 to 8, characterized in that: It includes three-stage whitening process, two-stage cooling process and heat recovery process; The three-stage whitening process is as follows: the first-stage whitening is to feed the gangue treated by the raw material processing system into the preheater for multiple heat exchanges with the flue gas leaving the rotary kiln to remove moisture, part of the hydroxyl group and carbon. The flue gas temperature leaving the rotary kiln is 650-900℃. The second-stage whitening is to feed the hot air generated by the combustion of fuel in the hot blast furnace into the rotary kiln, exchange heat with the flue gas, and feed the gangue after gas-solid separation into the rotary kiln for calcination at a temperature of 800-1200℃ and a residence time of 30-100 minutes to completely remove carbon. The third-stage whitening is to feed the kaolin leaving the rotary kiln into the bleaching machine for quenching and whitening by spraying water to further improve the whiteness of the kaolin. The two-stage cooling process is as follows: the first stage cooling is to spray water in the bleaching machine to quench the kaolin leaving the rotary kiln at a temperature of 800-1100℃. The water spraying system is used to adjust the water spraying volume to control the temperature of the kaolin entering the cooling air duct at 600-800℃. The second stage cooling is to enter the cooling air duct to further cool the kaolin leaving the bleaching machine. The amount of cold air entering the cooling air duct is adjusted according to the required air volume in the hot air furnace. The heat recovery process is as follows: the air temperature out of the cooling air duct is less than 250°C, and the material is recovered through the dust collector. The hot air out of the dust collector enters the burner as primary air in one way and enters the hot air furnace as secondary air in the other way, realizing efficient heat recovery and utilization.

10. The process for preparing high-whiteness calcined kaolin according to claim 9, characterized in that: The water vapor leaving the bleaching machine enters the dust collector or water vapor treatment system.

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