Anhydrous magnesium chloride preparation system and process

Abstract

The application discloses anhydrous magnesium chloride preparation system and process, the system includes first fluidized bed dryer, second fluidized bed dryer and cooling bin, the material outlet of first fluidized bed dryer is connected with the material import of second fluidized bed dryer, the material outlet of second fluidized bed dryer and the material import of cooling bin are connected, the waste gas outlet of first fluidized bed dryer and second fluidized bed dryer is connected with first tail gas treatment device and second tail gas treatment device respectively, the purification gas outlet of second tail gas treatment device is connected with the gas import of second fluidized bed dryer, the application solves the equipment parking problem caused by material melting, air distribution plate blockage, dead bed, has good stability, can long-period operation, is suitable for large-scale production, meanwhile, the matching between fluidized bed dryers is good, the adjustable range is large, solves the problem that process parameter fluctuation between fluidized bed dryers is large, long-period operation cannot be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anhydrous magnesium chloride preparation, in particular to an anhydrous magnesium chloride preparation system and process. BACKGROUND

[0002] Anhydrous magnesium chloride is an important inorganic raw material, which is used for producing magnesium products such as magnesium carbonate, magnesium hydroxide and magnesium oxide, and also used as a raw material for antifreeze. At present, there are four main methods for preparing anhydrous magnesium chloride: one is to produce anhydrous magnesium chloride by dehydrating bischofite (MgCl2·6H2O) under hydrogen chloride atmosphere; one is ammonia method, that is, dissolving hydrated magnesium chloride in an organic solvent, removing water from the solvent, forming a magnesium chloride complex by reacting the anhydrous magnesium chloride with a precipitating agent, and heating the magnesium chloride complex to produce anhydrous magnesium chloride. This method is also called "ammonia method". One is to produce anhydrous magnesium chloride by calcining magnesite. Magnesite is calcined at high temperature to produce magnesium oxide, which reacts with chlorine at high temperature to produce anhydrous magnesium chloride. One is to produce anhydrous magnesium chloride by double salt method. Bischofite can form ammonium light halite with ammonium chloride, and anhydrous magnesium chloride can be obtained by stepwise dehydration and deamination of ammonium light halite.

[0003] Among them, the ammonia method has low efficiency and high energy consumption; the magnesite calcination method has low efficiency, and safety and environmental protection problems are prominent; the double salt method has difficulty in recovering ammonium chloride and the purity of anhydrous magnesium chloride is not high; at present, the bischofite dehydration method for producing anhydrous magnesium chloride is more popular, although the product quality meets the requirements, but there are problems of long process flow, many operation points and high operation requirements; in addition, the existing technology also uses a fluidized bed to produce anhydrous magnesium chloride, and only the material quantity and temperature parameters of the feed and air inlet of the entire fluidized bed dryer can be adjusted, the temperature of each bed layer cannot be adjusted, which may cause a certain layer or several layers to deviate from the set working condition of the fluidized bed, and further cause unstable working condition, dead bed and frequent shutdown. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides an anhydrous magnesium chloride preparation system and process, which solves the problems of equipment shutdown caused by material melting, air distribution plate blockage and dead bed, has good stability, can be operated for a long period, and is suitable for large-scale production; at the same time, the matching between the fluidized bed dryers is good, and the adjustable range is large, which solves the problem of large process parameter fluctuation between the fluidized bed dryers, and realizes long-period operation.

[0005] The technical scheme of the present application is as follows:

[0006] In a first aspect of the present application, a system for preparing anhydrous magnesium chloride is provided, comprising 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 to a material inlet of the second fluidized bed dryer, a material outlet of the second fluidized bed dryer is connected to a material inlet of the cooling bin; a waste gas outlet of the first fluidized bed dryer is connected to a first tail gas treatment device, and a waste gas outlet of the second fluidized bed dryer is connected to a second tail gas treatment device; 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 application, a plurality of air distribution plates are arranged in the first fluidized bed dryer, and the air distribution plates are uniformly provided with air holes; the bottom of each air distribution plate is provided with a cooling pipe, and the cooling pipes of different air distribution plates are connected to cooling media of different temperatures.

[0008] In some embodiments of the present application, the upper part of each air distribution plate is provided with two partitions, the two partitions are arranged at a distance and are staggered, the partitions are perpendicular to the upper surface of the air distribution plate, and the height of each partition is less than the distance between two adjacent air distribution plates.

[0009] In some embodiments of the present application, 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 application, the lower part of each of the first fluidized bed dryer and the second fluidized bed dryer is provided with an air inlet, and the upper part of each of the first fluidized bed dryer and the second fluidized bed dryer is provided with a material inlet, and the material inlet is connected to a conveying device.

[0011] In some embodiments of the present application, a first mist removal device and a second mist removal device are arranged at the waste gas outlet of the first fluidized bed dryer and the second fluidized bed dryer, respectively.

[0012] In some embodiments of the present application, the second fluidized bed dryer is provided with a hydrogen chloride / chlorine gas supplement inlet.

[0013] In some embodiments of the present application, the cooling bin 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 application, a process for preparing anhydrous magnesium chloride is provided, which is implemented by using the system of the first aspect, comprising:

[0015] The magnesium chloride hydrate is dried in the first fluidized bed dryer to form magnesium chloride tetrahydrate, and then the magnesium chloride tetrahydrate is converted into magnesium chloride dihydrate.

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

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

[0018] The one or more technical solutions of the present application have the following beneficial effects:

[0019] (1) The anhydrous magnesium chloride preparation system provided by the present application adopts two fluidized bed dryers to perform two dehydration treatments on the magnesium chloride hydrate and cooling bin cooling treatment, and then obtains anhydrous magnesium chloride, the whole system structure is simple, and operation is convenient; the exhaust gas outlet of each fluidized bed dryer is connected with the corresponding tail gas treatment device to realize purification treatment of the exhaust gas, wherein the exhaust gas generated by the second fluidized bed dryer can return to the second fluidized bed dryer for recycling after purification treatment by the tail gas treatment device, and the resource utilization efficiency is improved; the material waste heat recovered by the cooling bin can enter the first fluidized bed dryer for recycling, and the heat energy utilization efficiency is improved.

[0020] (2) The anhydrous magnesium chloride preparation system provided by the present application adopts active regulation means, sets cooling pipes in a certain layer or several layers of the bed, and independently adjusts the temperature of the bed layer, so as to overcome the difficulty in adjusting the overall temperature field of the large dryer and the situation that a certain layer or several layers are overheated or deviate from the set working condition; at the same time, the bed layer structure of the fluidized bed dryer is improved, and a multi-layer bed layer structure is arranged, the movement path and residence time of the material on each air distribution plate can be changed by setting a partition plate on the air distribution plate, and the working efficiency of the fluidized bed dryer is improved.

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

[0022] (4) The anhydrous magnesium chloride preparation process provided by the application is as follows: wet material (magnesium chloride hydrate containing 5.0-6.0 crystal water) is dehydrated to generate semi-dry material (magnesium chloride hydrate containing 1.6-2.2 crystal water) in an air atmosphere; then secondary dehydration is carried out in a high-temperature hydrogen chloride or chlorine atmosphere to remove the remaining crystal water to obtain dry material (anhydrous magnesium chloride), the whole process is simple, the preparation of anhydrous magnesium chloride can be realized through two steps of dehydration, and the preparation efficiency of anhydrous magnesium chloride is improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The working principle diagram of the anhydrous magnesium chloride preparation system of the application is shown in the figure.

[0024] Figure 2 The top view of the air distribution plate of the application is shown in the figure.

[0025] Figure 3 The side view of the air distribution plate of the application is shown in the figure.

[0026] Figure 4 The schematic diagram of the arrangement of the cooling pipeline below the air distribution plate of the application is shown in the figure.

[0027] In the figure: 1, conveying device; 2, first mist removal device; 3, first fluidized bed dryer; 4, first air distribution plate; 5, first air inlet; 6, discharge outlet; 7, waste gas outlet; 8, stock bin; 9, second air distribution plate; 10, second mist removal device; 11, second air inlet; 12, first tail gas treatment device; 13, second tail gas treatment device; 14, third air inlet; 15, cooling stock bin; 16, feeding inlet; 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 application will be further described below in combination with the accompanying drawings and examples.

[0029] Example 1

[0030] In a typical embodiment of the application, an anhydrous magnesium chloride preparation system is provided, as shown in the figure. Figure 1As shown, including the first fluidized bed dryer 3, the second fluidized bed dryer 17 and the cooling bin 15; the material outlet of the first fluidized bed dryer 3 is connected with the material inlet of the second fluidized bed dryer 17, and the material outlet of the second fluidized bed dryer 17 is connected with the material inlet of the cooling bin 15; the exhaust gas outlet 7 of the first fluidized bed dryer 3 and the second fluidized bed dryer 17 is connected with the first tail gas treatment device 12 and the second tail gas treatment device 13 respectively; the purified gas outlet of the second tail gas treatment device 13 is connected with the gas inlet of the second fluidized bed dryer 17; the wet material is dehydrated to form semi-dry material by the first fluidized bed dryer 3, and the semi-dry material is dehydrated to form dry material by the second fluidized bed dryer 17, so as to obtain anhydrous magnesium chloride.

[0031] Because the internal structure of the existing fluidized bed dryer is not reasonably designed, and lacks active control means, the flow field and temperature field in the dryer are not uniformly distributed, which is easy to cause the accumulation of materials, local or even the whole bed over-temperature, resulting in dead bed, dryer shutdown, and the need to open the manhole for manual cleaning before starting again. However, the dryer is full of high-temperature hydrogen chloride gas, which must be cooled and replaced with qualified gas before entering the operation, and the cooling and replacement cycle is long, the cleaning cycle is short, and it is time-consuming and labor-intensive, which is very unfavorable for production and seriously affects the preparation of anhydrous magnesium chloride.

[0032] Therefore, in the present embodiment, a plurality of bed layers are arranged in the first fluidized bed dryer 3 and the second fluidized bed dryer 17, specifically, a plurality of first air distribution plates 4 are arranged in the first fluidized bed dryer 3, and a plurality of second air distribution plates 9 are arranged in the second fluidized bed dryer, the air distribution plate 20 is used for the bed layer structure, and the structure of the air distribution plate 20 is as shown in Figures 2-4 As shown, the air distribution plate 20 is uniformly distributed with air holes 19, and the bottom of the air distribution plate 20 is provided with a cooling pipeline 23. Different layers of the cooling pipeline 23 at the bottom of the air distribution plate are connected with cooling media of different temperatures, so as to control the temperature of the bed layer in the fluidized bed dryer. The cooling pipeline 23 is provided with a pipeline inlet 21 and a pipeline outlet 22. Optionally, air or water can be used as the cooling medium, and the cooling pipeline 23 can be installed above a certain layer or several layers of the bed layer (air distribution plate) of the dryer according to the temperature control needs.

[0033] Further, the upper part of the air distribution plate 20 is provided with two partitions 18, the two partitions 18 are arranged at 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 the adjacent two air distribution plates 20. The Z-shaped channel is formed between the two air distribution plates by the partition 18. The partition 18 plays a guiding role in the movement of the particles in the fluidized bed dryer, increases the movement path of the particles, and improves the drying efficiency of the fluidized bed dryer.

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

[0035] In the present embodiment, the bed layer 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. Specifically, the number of bed layers in the first fluidized bed dryer 3 is less than that in the second fluidized bed dryer 17. In practice, the number of bed layers can be selected according to the residence time of the material and the function of the fluidized bed dryer.

[0036] In the present embodiment, the lower part of the first fluidized bed dryer 3 is provided with a first air inlet 5, the lower part of the second fluidized bed dryer 17 is provided with a second air inlet 11, and the upper part of the first fluidized bed dryer 3 and the second fluidized bed dryer 17 is provided with a material inlet. Hot air / hot flue gas enters the first air inlet 5 at the lower part of the first fluidized bed dryer 3, passes through the bed layers of the first fluidized bed dryer from bottom to top, and the wet material passes through each bed layer of the first fluidized bed dryer from top to bottom, and the gas-solid two-phase flow moves in the opposite direction; hot hydrogen chloride / chlorine gas enters the second air inlet 11 at the lower part of the second fluidized bed dryer 17, passes through the bed layers of the first fluidized bed dryer 17 from bottom to top, and the semi-dry material passes through each bed layer of the second fluidized bed dryer from top to bottom, and the gas-solid two-phase flow moves in the opposite direction, which is beneficial to the full reaction.

[0037] In the present embodiment, the inlet temperature of the hot air / hot flue gas is 300-450℃, and the outlet temperature is 120-160℃; the inlet temperature of the hot hydrogen chloride / chlorine gas is 300-450℃, and the outlet temperature is 120-160℃. By limiting the temperature range, the energy utilization rate of the fluidized bed is high, and the moisture content of the discharged material (semi-dry material) can also meet the specified requirements.

[0038] In the present embodiment, the material inlets of the first fluidized bed dryer 3 and the second fluidized bed dryer 17 are connected to the conveying device 1, which can be a screw conveyor, a belt conveyor, a pipe chain conveyor, etc., or can be a pneumatic conveying device. The conveying device 1 conveys the material into the fluidized bed dryer.

[0039] In the embodiment, the first mist eliminator 2 and the second mist eliminator 10 are arranged at the exhaust gas outlets in the first fluidized bed dryer 3 and the second fluidized bed dryer 17 respectively, for performing mist removal treatment on the exhaust gas generated by the first fluidized bed dryer 3 and the second fluidized bed dryer 17; further, the first tail gas treatment device 12 is arranged to perform dust removal, condensation, moisture removal and purification on the exhaust gas generated by the first fluidized bed dryer 3, and then discharge the exhaust gas; the second tail gas treatment device 13 is arranged to perform dust removal, condensation and moisture removal on the exhaust gas generated by the second fluidized bed dryer 17, and then return the exhaust gas to the second fluidized bed dryer 17 through a hydrogen chloride compressor and a heater for heat exchange, and recycle the exhaust gas, meanwhile, the second fluidized bed dryer 17 is provided with a hydrogen chloride / chlorine gas supplement port for supplementing hydrogen chloride / chlorine.

[0040] In the embodiment, the cooling bin 15 is used for cooling the material, and the cooling bin is provided with a third air inlet 14 and an air outlet connected with the first fluidized bed dryer 3; the top of the cooling bin 15 is provided with a feeding port 16; the cooling bin 15 uses air as a cooling medium to cool the material to below 75℃; and the air with increased temperature is transported to the first fluidized bed dryer 3 as high-temperature gas, so that the residual heat in the material is recycled.

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

[0042] The feeding port of the first fluidized bed dryer 3 is connected with the conveying device 1; the wet material (magnesium chloride hydrate containing 5.0-6.0 crystal water) in the conveying device is dehydrated to generate semi-dry material (magnesium chloride hydrate containing 1.6-2.2 crystal water) in the air atmosphere in the first fluidized bed dryer 3; the semi-dry material is discharged from the discharging port 6 of the first fluidized bed dryer 3 and stored in the bin 8; then the semi-dry material is transported to the second fluidized bed dryer 17 by the conveying device 1; the semi-dry material is subjected to secondary dehydration in the high-temperature hydrogen chloride or chlorine gas atmosphere in the second fluidized bed dryer 17 to remove the residual crystal water and obtain dry material (anhydrous magnesium chloride MgCl2); the water content of the dry particles of the anhydrous magnesium chloride is ≤0.1%, and the MgOHCl is ≤0.4%; the dry particles are cooled to below 75℃ in the particle cooler, and then enter the finished product bin.

[0043] Embodiment 2

[0044] In a typical embodiment of the present application, an anhydrous magnesium chloride preparation process is provided, which is realized by using the system described in Embodiment 1, and includes the following steps:

[0045] The magnesium chloride hydrate is dried in the first fluidized bed dryer to form magnesium chloride tetrahydrate, and the magnesium chloride tetrahydrate is then dried to form magnesium chloride dihydrate;

[0046] The magnesium chloride dihydrate is dried in the second fluidized bed dryer to form magnesium chloride monohydrate, and the magnesium chloride monohydrate is then dried to form anhydrous magnesium chloride, and meanwhile, the magnesium chloride dihydrate is prevented from high-temperature hydrolysis under the hydrogen chloride atmosphere.

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

[0048] MgCl2·nH2O→MgCl2+nH2O (n=2, 4, 6)

[0049] In the first fluidized bed dryer, the following reactions mainly occur: the magnesium chloride hexahydrate is stepwise dried to form magnesium chloride tetrahydrate (MgCl2·4H2O) and magnesium chloride dihydrate (MgCl2·2H2O), and the magnesium chloride tetrahydrate (MgCl2·4H2O) is dried to form the magnesium chloride dihydrate (MgCl2·2H2O).

[0050] In the second fluidized bed dryer, the following reactions mainly occur: the magnesium chloride dihydrate (MgCl2·2H2O) is dried to form the magnesium chloride monohydrate (MgCl2·H2O), the magnesium chloride monohydrate (MgCl2·H2O) is dried to form the anhydrous magnesium chloride MgCl2, and the magnesium chloride dihydrate (MgCl2·2H2O) is prone to the following hydrolysis reaction at high temperature to generate MgOHCl which is not conducive to electrolysis.

[0051] MgCl2·2H2O→MgOHCl+HCl(g)+H2O(g)

[0052] Therefore, the semi-dry particles in the second fluidized bed dryer are fully contacted with the hydrogen chloride gas in a certain temperature range, and the following reaction occurs to prevent the hydrolysis reaction from occurring, and at the same time, complete dehydration. When hydrogen is introduced, the introduced hydrogen and the removed water react to generate HCl, which has the same effect as the hydrogen chloride gas.

[0053] MgOHCl+HCl(g)→MgCl2+H2O(g)

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

[0055] The above describes the specific embodiments of the present application in conjunction with the drawings, but is not a limitation on the scope of protection of the present application. Those skilled in the art should understand that various modifications or variations made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A process for the preparation of anhydrous magnesium chloride, characterized in that, The system comprises a first fluidized bed dryer, a second fluidized bed dryer and a cooling bin; the material outlet of the first fluidized bed dryer is connected with the material inlet of the second fluidized bed dryer, and the material outlet of the second fluidized bed dryer is connected with the material inlet of the cooling bin; the exhaust gas outlets of the first fluidized bed dryer and the second fluidized bed dryer are respectively connected with first and second tail gas treatment devices; the purified gas outlet of the second tail gas treatment device is connected with the gas inlet of the second fluidized bed dryer. The first fluidized bed dryer is provided with multiple layers of air distribution plates, and the air distribution plates are uniformly provided with air holes; the bottom of the air distribution plate is provided with a cooling pipeline, and the cooling pipelines at the bottoms of different layers of air distribution plates are connected with cooling media of different temperatures. The upper part of the air distribution plate is provided with two partitions, which are arranged at a set 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 the adjacent two air distribution plates. The number of bed layers in the first fluidized bed dryer is less than that in the second fluidized bed dryer. The preparation process comprises: drying the magnesium chloride hydrate in the first fluidized bed dryer to form magnesium chloride tetrahydrate, and then converting the magnesium chloride tetrahydrate into magnesium chloride dihydrate; The magnesium chloride dihydrate is fed into the second fluidized bed dryer to form magnesium chloride monohydrate, and then the magnesium chloride monohydrate is converted into anhydrous magnesium chloride; at the same time, the magnesium chloride dihydrate is inhibited from high-temperature hydrolysis reaction under the hydrogen chloride atmosphere. The high-temperature gas inlet temperature of the first fluidized bed dryer is 300-450℃, and the gas outlet temperature of the first fluidized bed dryer is controlled at 120-160℃ by adjusting the temperature of the cooling pipelines on the distribution plates; the high-temperature gas inlet temperature of the second fluidized bed dryer is 300-450℃, and the gas outlet temperature of the second fluidized bed dryer is controlled at 120-160℃ by adjusting the temperature of the cooling pipelines on the distribution plates.

2. The anhydrous magnesium chloride production process of claim 1, wherein, The lower part of the first fluidized bed dryer and the second fluidized bed dryer is provided with an air inlet, and the upper part of the first fluidized bed dryer and the second fluidized bed dryer is provided with a material inlet, which is connected with a conveying device.

3. The anhydrous magnesium chloride production process of claim 1, wherein, The exhaust gas outlets in the first fluidized bed dryer and the second fluidized bed dryer are respectively provided with first and second mist removal devices.

4. The anhydrous magnesium chloride production process of claim 1, wherein, The second fluidized bed dryer is provided with a hydrogen chloride / chlorine gas supplement inlet.

5. The anhydrous magnesium chloride production process of claim 1 wherein, The cooling bin is provided with an air inlet and an air outlet, and the air outlet is connected with the first fluidized bed dryer.

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