Anhydrous magnesium chloride preparation system and process

Abstract

The invention discloses an anhydrous magnesium chloride preparation system and process. The system comprises a first fluidized bed dryer, a second fluidized bed dryer and a cooling bin, a material outlet of the first fluidized bed dryer is connected with a material inlet of the second fluidized bed dryer; a material outlet of the second fluidized bed dryer is connected with a material inlet of the cooling bin; waste gas outlets of the first fluidized bed dryer and the second fluidized bed dryer are respectively connected with a first tail gas treatment device and a second tail gas treatment device; a purified gas outlet of the second tail gas treatment device is connected with a gas inlet of the second fluidized bed dryer; the device solves the problem of equipment shutdown caused by material melting, air distribution plate blocking and bed blocking, is good in stability, can operate for a long period, and is suitable for large-scale production; meanwhile, the fluidized bed dryers are good in matching performance and large in adjustable range, and the problems that technological parameters of the fluidized bed dryers are large in fluctuation, and long-period operation cannot be achieved are solved.

Description

Technical Field

[0001] The invention relates to the technical field of anhydrous magnesium chloride preparation, and in particular to an anhydrous magnesium chloride preparation system and process. Background Art

[0002] Anhydrous magnesium chloride is an important inorganic raw material used to produce magnesium products such as magnesium carbonate, magnesium hydroxide, magnesium oxide, and is also used as a raw material for antifreeze. At present, there are four main methods for preparing anhydrous magnesium chloride: one is to use bischofite (MgCl 2 6H 2 O) Dehydration to produce anhydrous magnesium chloride. One is the ammoniation method, that is, hydrated magnesium chloride is dissolved in an organic solvent, water is removed from the solvent, and the alcohol solution of the anhydrous magnesium chloride reacts with a precipitant to form a magnesium chloride complex, and the magnesium chloride complex is heated to produce anhydrous magnesium chloride. This method is also called "ammoniation method". One is the production of anhydrous magnesium chloride by calcining and chlorinating magnesite. Magnesite is calcined at high temperature to produce magnesium oxide, and magnesium oxide reacts with chlorine at high temperature to produce anhydrous magnesium chloride. One is the double salt method to produce anhydrous magnesium chloride. Hydrochlorite and ammonium chloride can form ammonia carnallites, and ammonia carnallites can be dehydrated and deamined in steps to obtain anhydrous magnesium chloride.

[0003] Among them, the ammoniation method is inefficient and has high energy consumption; the calcination method of magnesite is inefficient and has prominent safety and environmental protection issues; the recovery of ammonium chloride by the double salt method is difficult and the purity of anhydrous magnesium chloride is not high; the more popular method is to dehydrate bischofite to produce anhydrous magnesium chloride. Although the product quality meets the requirements, there are problems such as long process flow, many control points and high operation requirements; in addition, the prior art also uses a fluidized bed to produce anhydrous magnesium chloride, but only the material amount and temperature parameters of the feed and air inlet of the entire fluidized bed dryer can be adjusted, and the temperature of each bed layer cannot be adjusted, which may cause one or several layers to deviate from the set working condition of the fluidized bed, thereby causing unstable working conditions and frequent parking due to dead beds. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides an anhydrous magnesium chloride preparation system and process, which solves the problem of equipment shutdown caused by material melting, air distribution plate blockage and dead bed, has good stability, can operate for a long period of time, and is suitable for large-scale production; at the same time, the fluidized bed dryers have good matching and a large adjustability range, which solves the problem that the process parameters of the fluidized bed dryers fluctuate greatly and long-term operation cannot be achieved.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect of the present invention, a system for preparing anhydrous magnesium chloride is provided, comprising a first fluidized bed dryer, a second fluidized bed dryer and a cooling silo; a material outlet of the first fluidized bed dryer is connected to a material inlet of the second fluidized bed dryer, and a material outlet of the second fluidized bed dryer is connected to a material inlet of the cooling silo; exhaust gas outlets of the first fluidized bed dryer and the second fluidized bed dryer are connected to a first tail gas treatment device and a second tail gas treatment device, respectively; and a purified gas outlet of the second tail gas treatment device is connected to a gas inlet of the second fluidized bed dryer.

[0007] In some embodiments of the present invention, a plurality of layers of air distribution plates are disposed in the first fluidized bed dryer, air holes are evenly distributed on the air distribution plates, cooling pipes are disposed at the bottom of the air distribution plates, and cooling media of different temperatures are passed through the cooling pipes at the bottom of air distribution plates of different layers.

[0008] In some embodiments of the present invention, two partitions are arranged on the upper part of the air distribution plate, the two partitions are separated by a certain distance and staggered, the partitions are perpendicular to the upper surface of the air distribution plate, and the height of the partitions is less than the distance between two adjacent air distribution plates.

[0009] In some embodiments of the present invention, the number of bed layers in the first fluidized bed dryer is less than the number of bed layers in the second fluidized bed dryer.

[0010] In some embodiments of the present invention, an air inlet is disposed at the lower portion of the first fluidized bed dryer and the second fluidized bed dryer, a material inlet is disposed at the upper portion of the first fluidized bed dryer and the second fluidized bed dryer, and the material inlet is connected to a conveying device.

[0011] In some embodiments of the present invention, a first demister and a second demister are respectively provided at the exhaust gas outlets inside the first fluidized bed dryer and the second fluidized bed dryer.

[0012] In some embodiments of the present invention, a hydrogen chloride / chlorine gas supply port is provided on the second fluidized bed dryer.

[0013] In some embodiments of the present invention, the cooling silo is provided with an air inlet and an air outlet, and the air outlet is connected to the first fluidized bed dryer.

[0014] In a second aspect of the present invention, a process for preparing anhydrous magnesium chloride is provided, which is implemented by the system described in the first aspect, comprising:

[0015] The magnesium chloride hydrate enters the first fluidized bed dryer for drying to form magnesium chloride tetrahydrate, and then the magnesium chloride tetrahydrate forms magnesium chloride dihydrate;

[0016] The magnesium chloride dihydrate enters the second fluidized bed dryer, where the magnesium chloride dihydrate forms magnesium chloride monohydrate, and the magnesium chloride monohydrate forms anhydrous magnesium chloride. Meanwhile, the magnesium chloride dihydrate inhibits the occurrence of high-temperature hydrolysis reaction in the hydrogen chloride atmosphere.

[0017] In some embodiments of the present invention, the high-temperature gas inlet temperature of the first fluidized bed dryer is 300-450°C, and the gas outlet temperature of the first fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the first fluidized bed dryer; the high-temperature gas inlet temperature of the second fluidized bed dryer is 300-450°C, and the gas outlet temperature of the second fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the second fluidized bed dryer.

[0018] One or more technical solutions of the present invention have the following beneficial effects:

[0019] (1) The anhydrous magnesium chloride preparation system provided by the present invention uses two fluidized bed dryers to perform two dehydration treatments on magnesium chloride hydrate and cooling treatment on a cooling silo to obtain anhydrous magnesium chloride. The entire system has a simple structure and is easy to operate. The exhaust gas outlet of each fluidized bed dryer is connected to a corresponding tail gas treatment device to achieve exhaust gas purification treatment. The exhaust gas generated by the second fluidized bed dryer can be returned to the second fluidized bed dryer for recycling after being purified by the tail gas treatment device, thereby improving resource utilization efficiency. The waste heat of the material recovered from the cooling silo can enter the first fluidized bed dryer for recycling, thereby improving thermal energy utilization efficiency.

[0020] (2) In the anhydrous magnesium chloride preparation system provided by the present invention, the fluidized bed dryer adopts active control means, and cooling pipes are set in one or several layers of the bed to autonomously adjust the temperature of the bed, thereby overcoming the problem that the overall temperature field of the large dryer is difficult to adjust, and one or several layers may overheat or deviate from the set working condition; at the same time, the bed structure of the fluidized bed dryer is improved, and a multi-layer bed structure is set. By setting partitions on the air distribution plates, the movement path and residence time of the material on each layer of the air distribution plates can be changed, thereby improving the working efficiency of the fluidized bed dryer.

[0021] (3) The anhydrous magnesium chloride preparation system provided by the present invention overcomes the problem of equipment shutdown caused by material melting, air distribution plate blockage, and dead bed, has good stability, can operate for a long period of time, and is suitable for large-scale production; at the same time, the fluidized bed dryers have good matching and a large adjustability range, which overcomes the problem that the process parameters of the fluidized bed dryers fluctuate greatly and cannot achieve long-term operation.

[0022] (4) The present invention provides a process for preparing anhydrous magnesium chloride. The wet material (magnesium chloride hydrate containing 5.0-6.0 crystal waters) is dehydrated in an air atmosphere to generate a semi-dry material (magnesium chloride hydrate containing 1.6-2.2 crystal waters); then, the material is subjected to a secondary dehydration in a high-temperature hydrogen chloride or chlorine atmosphere to remove the remaining crystal water to obtain a dry material (anhydrous magnesium chloride). The entire process is simple, and the preparation of anhydrous magnesium chloride can be achieved through two dehydration steps, thereby improving the preparation efficiency of anhydrous magnesium chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a working principle diagram of the anhydrous magnesium chloride preparation system of the present invention;

[0024] Figure 2 A top view of the air distribution plate of the present invention;

[0025] Figure 3 is a side view of the air distribution plate of the present invention;

[0026] Figure 4 It is a schematic diagram of the arrangement of cooling ducts below the air distribution plate of the present invention.

[0027] In the figure: 1. conveying device; 2. first demisting device; 3. first fluidized bed dryer; 4. first air distribution plate; 5. first air inlet; 6. discharge port; 7. exhaust gas outlet; 8. silo; 9. second air distribution plate; 10. second demisting device; 11. second air inlet; 12. first tail gas treatment device; 13. second tail gas treatment device; 14. third air inlet; 15. cooling silo; 16. feed port; 17. second fluidized bed dryer; 18. partition; 19. air hole; 20. air distribution plate; 21. pipeline inlet; 22. pipeline outlet; 23. cooling pipeline. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] Example 1

[0030] In a typical embodiment of the present invention, a system for preparing anhydrous magnesium chloride is provided, such as Figure 1As shown, it includes a first fluidized bed dryer 3, a second fluidized bed dryer 17 and a cooling silo 15; the material outlet of the first fluidized bed dryer 3 is connected to the material inlet of the second fluidized bed dryer 17, and the material outlet of the second fluidized bed dryer 17 is connected to the material inlet of the cooling silo 15; the exhaust gas outlet 7 of the first fluidized bed dryer 3 and the second fluidized bed dryer 17 are respectively connected to the first tail gas treatment device 12 and the second tail gas treatment device 13; the purified gas outlet of the second tail gas treatment device 13 is connected to the gas inlet of the second fluidized bed dryer 17; the wet material is dehydrated to form a semi-dry material by the first fluidized bed dryer 3, and the semi-dry material is dehydrated to form a dry material by the second fluidized bed dryer 17, so as to obtain anhydrous magnesium chloride.

[0031] Due to the unreasonable internal structure design of the existing fluidized bed dryer and the lack of active control means, the flow field and temperature field in the dryer are unevenly distributed, which can easily cause material accumulation, partial or even entire bed overheating, resulting in dead bed and dryer shutdown. It is necessary to open the manhole for manual cleaning before restarting. The dryer is full of high-temperature hydrogen chloride gas and must be cooled and gas replaced before entering the operation. The cooling and replacement cycle is long, and the cleaning cycle is short, time-consuming and labor-intensive, which is very unfavorable for production and seriously affects the preparation of anhydrous magnesium chloride.

[0032] To this end, in this embodiment, a multi-layer bed structure is provided in the first fluidized bed dryer 3 and the second fluidized bed dryer 17. Specifically, a multi-layer first air distribution plate 4 is provided in the first fluidized bed dryer 3, and a multi-layer second air distribution plate 9 is provided in the second fluidized bed dryer. The bed structure adopts an air distribution plate 20. The structure of the air distribution plate 20 is as follows: Figure 2-4 As shown, the air distribution plate 20 is evenly distributed with air holes 19, and a cooling pipe 23 is arranged at the bottom of the air distribution plate 20. Cooling media of different temperatures are introduced into the cooling pipes 23 at the bottom of different layers of air distribution plates to control the bed temperature in the fluidized bed dryer. The cooling pipe 23 is provided with a pipe inlet 21 and a pipe outlet 22. Optionally, air or water can be used as the cooling medium. The cooling pipe 23 can be installed above one or several layers of the bed (air distribution plate) of the dryer according to the temperature control requirements.

[0033] Furthermore, two partitions 18 are arranged on the upper part of the air distribution plate 20, and the two partitions 18 are separated by a certain distance and staggered. The partition 18 is perpendicular to the upper surface of the air distribution plate 20, and the height of the partition 18 is less than the distance between two adjacent air distribution plates 20. The partition 18 is arranged to form a Z-shaped channel between the two air distribution plates; the partition 18 is arranged to guide the movement of particles in the fluidized bed dryer, thereby increasing the movement path of the particles and improving the drying efficiency of the fluidized bed dryer.

[0034] In a specific implementation of this embodiment, the air distribution plate 20 is made of 5mm-15mm steel plate, on which a number of pores are evenly distributed, the size of the pores is φ2-10mm, and the opening rate is 30-45%. The particle movement trajectory and residence time in the dryer bed are controlled by the partition, fluidization speed, etc. The partition is made of 5mm-10mm steel plate, and the height of the partition is determined by the bed height.

[0035] In this embodiment, the bed structures in the first fluidized bed dryer 3 and the second fluidized bed dryer 17 are the same, but the number of bed layers is different. The number of bed layers in the first fluidized bed dryer 3 is less than the number of bed layers in the second fluidized bed dryer 17. Specifically, the number of bed layers in the first fluidized bed dryer 3 is generally 1-3 layers, and the number of bed layers in the second fluidized bed dryer 17 is generally 7-10 layers. In actual application, the corresponding number of bed layers can be selected according to the residence time of the material and the function of the fluidized bed.

[0036] In this embodiment, the first fluidized bed dryer 3 is provided with a first air inlet 5 at the bottom, the second fluidized bed dryer 17 is provided with a second air inlet 11 at the bottom, and the first fluidized bed dryer 3 and the second fluidized bed dryer 17 are provided with material inlets at the top. Hot air / hot flue gas enters from the first air inlet 5 at the bottom of the first fluidized bed dryer 3 and passes through the bed layers of the first fluidized bed dryer from bottom to top in sequence, and wet materials pass through the various beds of the first fluidized bed dryer from top to bottom in sequence, and the gas-solid two-phase flow runs in reverse direction; hot hydrogen chloride / chlorine gas enters from the second air inlet 11 at the bottom of the second fluidized bed dryer 17 and passes through the bed layers of the first fluidized bed dryer 17 from bottom to top in sequence, and semi-dry materials pass through the various beds of the second fluidized bed dryer from top to bottom in sequence, and the gas-solid two-phase flow runs in reverse direction, which is conducive to the full progress of the reaction.

[0037] In this embodiment, the inlet temperature of the hot air / hot flue gas is 300-450°C, and the outlet temperature is 120-160°C; the inlet temperature of the hot hydrogen chloride / chlorine gas is 300-450°C, and the outlet temperature is 120-160°C. By limiting the temperature range, while ensuring the high energy utilization rate of the fluidized bed, it can also ensure that the output material (semi-dry material) meets the specified moisture content index.

[0038] In this embodiment, the material inlets of the first fluidized bed dryer 3 and the second fluidized bed dryer 17 are both connected to the conveying device 1. The conveying device 1 can be a screw conveyor, a belt conveyor, a tube chain conveyor, etc., or it can be a pneumatic conveying device. The material is transported to the fluidized bed dryer through the conveying device 1.

[0039] In this embodiment, the first and second demisting devices 2 and 10 are respectively provided at the exhaust gas outlets inside the first fluidized bed dryer 3 and the second fluidized bed dryer 17, which are used to perform demisting treatment on the exhaust gas generated by the first fluidized bed dryer 3 and the second fluidized bed dryer 17; further, the exhaust gas generated by the first fluidized bed dryer 3 is dedusted, condensed, and purified by the first tail gas treatment device 12 before being discharged; the exhaust gas generated by the second fluidized bed dryer 17 is dedusted, condensed, and purified by the second tail gas treatment device 13, and then returns to the second fluidized bed dryer 17 for recycling after entering the heater through the hydrogen chloride compressor for heat exchange. At the same time, the second fluidized bed dryer 17 is provided with a hydrogen chloride / chlorine gas replenishment port for replenishing hydrogen chloride / chlorine.

[0040] In this embodiment, the cooling silo 15 is used to cool the material. The cooling silo is provided with a third air inlet 14 and an air outlet. The air outlet is connected to the first fluidized bed dryer 3. The top of the cooling silo 15 is provided with a feed inlet 16. The cooling silo 15 uses air as a cooling medium to cool the material. When the air temperature is cooled to below 75°C, it is transported to the first fluidized bed dryer 3 as a high-temperature gas input after the air temperature is increased, thereby realizing the recovery of waste heat in the material.

[0041] The working principle of the anhydrous magnesium chloride preparation system provided in this embodiment is:

[0042] The feed inlet of the first fluidized bed dryer 3 is connected to the conveying device 1, through which the wet material, i.e., magnesium chloride hydrate containing 5.0-6.0 crystal waters, is dehydrated in the air atmosphere in the first fluidized bed dryer 3 to generate semi-dry material (magnesium chloride hydrate containing 1.6-2.2 crystal waters). The semi-dry material is discharged from the discharge port 6 of the first fluidized bed dryer 3 and enters the silo 8 for temporary storage, and then the semi-dry material is transported to the second fluidized bed dryer 17 by the conveying device 1. The semi-dry material is dehydrated for a second time in the high-temperature hydrogen chloride or chlorine atmosphere of the second fluidized bed dryer 17 to remove the remaining crystal water to obtain a dry material (anhydrous magnesium chloride MgCl 2 ), the water content of the dry particles of anhydrous magnesium chloride is ≤0.1%, MgOHCl ≤0.4%, the dry particles enter the particle cooler and are cooled to below 75°C, and then enter the finished product silo.

[0043] Example 2

[0044] In a typical embodiment of the present invention, a process for preparing anhydrous magnesium chloride is provided, which is implemented using the system described in Example 1, comprising:

[0045] The magnesium chloride hydrate enters the first fluidized bed dryer for drying to form magnesium chloride tetrahydrate, and then the magnesium chloride tetrahydrate forms magnesium chloride dihydrate;

[0046] The magnesium chloride dihydrate enters the second fluidized bed dryer, where the magnesium chloride dihydrate forms magnesium chloride monohydrate, and the magnesium chloride monohydrate forms anhydrous magnesium chloride. Meanwhile, the magnesium chloride dihydrate inhibits the occurrence of high-temperature hydrolysis reaction in the hydrogen chloride atmosphere.

[0047] The dehydration of magnesium chloride hydrate is not the traditional drying dehydration, but a complex chemical reaction. It mainly includes the following reactions:

[0048] MgCl 2 ·nH 2 O→MgCl 2 +nH 2 O(n=2,4,6)

[0049] The following reactions mainly occur in the first fluidized bed dryer: magnesium chloride hexahydrate is converted into magnesium chloride tetrahydrate (MgCl 2 ·4H 2 O) and magnesium chloride dihydrate (MgCl 2 ·2H 2 O), magnesium chloride tetrahydrate (MgCl 2 ·4H 2 O) to produce magnesium chloride dihydrate (MgCl 2 ·2H 2 O).

[0050] In the second fluidized bed dryer, magnesium chloride dihydrate (MgCl 2 ·2H 2 O) to produce magnesium chloride monohydrate (MgCl 2 ·H 2 O), magnesium chloride monohydrate (MgCl 2 ·H 2 O) to generate anhydrous magnesium chloride MgCl 2 、Magnesium chloride dihydrate (MgCl 2 ·2H 2 O) is prone to undergo the following hydrolysis reaction at high temperature to produce MgOHCl which is not conducive to electrolysis.

[0051] MgCl 2 ·2H 2 O→MgOHCl+HCl(g)+H 2 O(g)

[0052] Therefore, the semi-dried particles in the second fluidized bed dryer are fully contacted with the hydrogen chloride gas within a certain temperature range, and the following reaction occurs to inhibit the occurrence of hydrolysis reaction and completely dehydrate. When hydrogen is introduced, the introduced hydrogen and the removed water react chemically to generate HCl, which has the same effect as hydrogen chloride gas.

[0053] MgOHCl+HCl(g)→MgCl 2 +H 2 O(g)

[0054] Furthermore, the high-temperature gas inlet temperature of the first fluidized bed dryer is 300-450°C, and the gas outlet temperature of the first fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the first fluidized bed dryer; the high-temperature gas inlet temperature of the second fluidized bed dryer is 300-450°C, and the gas outlet temperature of the second fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the second fluidized bed dryer.

[0055] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A system for preparing anhydrous magnesium chloride, characterized in that: It includes a first fluidized bed dryer, a second fluidized bed dryer and a cooling silo; the material outlet of the first fluidized bed dryer is connected to the material inlet of the second fluidized bed dryer, and the material outlet of the second fluidized bed dryer is connected to the material inlet of the cooling silo; the exhaust gas outlets of the first fluidized bed dryer and the second fluidized bed dryer are connected to the first tail gas treatment device and the second tail gas treatment device respectively; the purified gas outlet of the second tail gas treatment device is connected to the gas inlet of the second fluidized bed dryer.

2. The anhydrous magnesium chloride preparation system according to claim 1, characterized in that, The first fluidized bed dryer is provided with multiple layers of air distribution plates, on which air holes are evenly distributed, and cooling pipes are provided at the bottom of the air distribution plates, and cooling media of different temperatures are passed through the cooling pipes at the bottom of the air distribution plates with different layers.

3. The anhydrous magnesium chloride preparation system according to claim 2, characterized in that, Two partitions are arranged on the upper part of the air distribution plate, the two partitions are spaced a certain distance apart and staggered, the partitions are perpendicular to the upper surface of the air distribution plate, and the height of the partitions is less than the distance between two adjacent air distribution plates.

4. The anhydrous magnesium chloride preparation system according to claim 2, characterized in that, The number of bed layers in the first fluidized bed dryer is less than the number of bed layers in the second fluidized bed dryer.

5. The anhydrous magnesium chloride preparation system according to claim 1, characterized in that, An air inlet is disposed at the lower portion of the first fluidized bed dryer and the second fluidized bed dryer, and a material inlet is disposed at the upper portion of the first fluidized bed dryer and the second fluidized bed dryer, and the material inlet is connected to a conveying device.

6. The anhydrous magnesium chloride preparation system according to claim 1, characterized in that, A first demister and a second demister are respectively provided at the exhaust gas outlets inside the first fluidized bed dryer and the second fluidized bed dryer.

7. The anhydrous magnesium chloride preparation system according to claim 1, characterized in that: The second fluidized bed dryer is provided with a hydrogen chloride / chlorine gas supply port.

8. The anhydrous magnesium chloride preparation system according to claim 1, characterized in that, The cooling silo is provided with an air inlet and an air outlet, and the air outlet is connected to the first fluidized bed dryer.

9. A process for preparing anhydrous magnesium chloride, implemented by the system according to any one of claims 1 to 8, characterized in that: include: The magnesium chloride hydrate enters the first fluidized bed dryer for drying to form magnesium chloride tetrahydrate, and then the magnesium chloride tetrahydrate forms magnesium chloride dihydrate; The magnesium chloride dihydrate enters the second fluidized bed dryer, where the magnesium chloride dihydrate forms magnesium chloride monohydrate, and the magnesium chloride monohydrate forms anhydrous magnesium chloride. Meanwhile, the magnesium chloride dihydrate inhibits the occurrence of high-temperature hydrolysis reaction in the hydrogen chloride atmosphere.

10. The process for preparing anhydrous magnesium chloride according to claim 9, wherein: The high-temperature gas inlet temperature of the first fluidized bed dryer is 300-450°C, and the gas outlet temperature of the first fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the first fluidized bed dryer; the high-temperature gas inlet temperature of the second fluidized bed dryer is 300-450°C, and the gas outlet temperature of the second fluidized bed dryer is controlled at 120-160°C by adjusting the temperature of the cooling pipes on each distribution plate in the second fluidized bed dryer.

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