Process for drying slurry into powder and drying system thereof

Abstract

The invention provides a process for drying slurry into powder and a drying system, and relates to the technical field of material preparation, the drying method comprises the following steps: providing slurry which comprises dispersion liquid and powder dispersed in the dispersion liquid; carrying out filter pressing on the slurry to form a filter cake, and breaking the filter cake into a filter block with the particle size of not more than 3mm; and sequentially heating and drying the filter block by using infrared rays and microwaves, so that the filter block spontaneously explodes into powder. The invention further provides a drying system capable of being used for the method. According to the technical scheme provided by the invention, the problem that in the prior art, a drying mode of slurry spray granulation needs to be ground again is solved.

Description

Technical Field

[0001] The invention relates to the field of battery materials, and in particular to a process for drying slurry into powder and a drying system thereof. Background Art

[0002] In the prior art, the preparation process of alumina powder usually requires first preparing a precursor, then drying it into powder, and deciding whether to calcine to remove the crystal water therein according to the desired alumina powder. It can be seen that drying into alumina powder is a common process in the preparation of alumina powder.

[0003] In the prior art, spray granulation is usually used for drying into powder. The process is mature, the drying is rapid, and the particle size and morphology (spherical or quasi-spherical) of the obtained particles can be controlled by controlling the parameters of the spray process. However, spray granulation requires that the prepared precursor be first configured into a slurry suitable for spray granulation; in addition, since spray granulation is to atomize the suspension formed by the precursor into tiny droplets through a nozzle, and these droplets are then dried and solidified under appropriate conditions to form spherical or quasi-spherical particles, the particles formed are larger in particle size than the particle size of the raw materials, and their morphology will also mostly show a spherical or quasi-spherical morphology, making it difficult to maintain the original particle size and morphology of the raw materials. To this end, if the particle size and morphology of the raw materials need to be maintained, the spray-dried particles need to be crushed again. For example, when preparing alumina powder, the precursor is often slurried and then spray-granulated, and then crushed into powder and calcined. This process involves many steps and is likely to introduce more impurities into the powder. Furthermore, when the spray-dried particles need to be crushed again, it is not conducive to maintaining the integrity of the powder particles and is likely to lead to an increase in fine powder. Summary of the invention

[0004] The object of the present invention is to provide a process for drying slurry into powder, which does not require spray granulation or crushing after drying, has a simple process and is not prone to introducing other impurities.

[0005] Another object of the present invention is to provide a drying system for drying slurry into powder.

[0006] In a first aspect, the present application provides a process for drying a slurry into powder, comprising the following steps:

[0007] Providing a slurry, the slurry comprising a dispersion liquid and a powder dispersed in the dispersion liquid;

[0008] The slurry is filtered into a filter cake, and the filter cake is broken into filter blocks with a particle size not higher than 3 mm;

[0009] The filter block is heated and dried in sequence by infrared rays and microwaves, so that the filter block spontaneously explodes into powder.

[0010] Further, in some embodiments of the present application, the infrared heating of the filter block sequentially includes a low-temperature heating stage and a medium-temperature heating stage;

[0011] In the low-temperature heating stage, the temperature to which the filter block is heated is lower than the temperature to which the filter block is heated in the medium-temperature heating stage;

[0012] The microwave heating causes the filter block to reach a temperature higher than the temperature to which the filter block is heated in the medium temperature heating stage.

[0013] Further, in some embodiments of the present application, in the low-temperature heating stage, the filter block is heated to 70-100° C. and maintained for at least 5 minutes;

[0014] In the medium temperature heating stage, the filter block is heated to 110-140° C. and maintained at this temperature for at least 5 minutes.

[0015] Further, in some embodiments of the present application, in the low-temperature heating stage, the filter block is heated to 70-100° C. and maintained for 5 min to 20 min;

[0016] In the medium temperature heating stage, the filter block is heated to 110-140° C. and maintained for 5-10 minutes.

[0017] Furthermore, in some embodiments of the present application, in the microwave heating, the microwave wavelength used is 12.2CM; the frequency is 2450M.

[0018] Furthermore, in some embodiments of the present application, in the infrared heating, the wavelength of the infrared rays used is 2.5 μm-15 μm, and the power is 65 KW.

[0019] Further, in some embodiments of the present application, during the microwave heating, the filter block is heated to at least 150°C.

[0020] Further, in some embodiments of the present application, after the infrared heating, the water content of the filter block is not higher than 0.2% and not lower than 0.05%.

[0021] Furthermore, in some embodiments of the present application, the solid content in the filter cake is not less than 65%.

[0022] Furthermore, in some embodiments of the present application, the thickness of the filter cake is 3 to 5 cm, and the spreading thickness of the filter block is not higher than 1 cm.

[0023] In a second aspect, the present application also provides a drying system for drying a slurry into powder, comprising:

[0024] A filter press mechanism, used to filter the slurry into a filter cake;

[0025] A crushing mechanism, disposed downstream of the filter pressing mechanism, for crushing the filter cake into filter blocks;

[0026] An infrared drying mechanism is arranged downstream of the crushing mechanism, and comprises a first infrared drying device and a second infrared drying device arranged in sequence; the first infrared drying device and the second infrared drying device are both used for drying the filter block;

[0027] The microwave drying mechanism is arranged downstream of the infrared drying mechanism and is used for drying the filter block and spontaneously exploding it into powder.

[0028] The embodiment of the present application provides a process for drying slurry into powder and a drying system. The drying process uses infrared rays and microwaves to sequentially dry filter blocks of the powder, reduces the water content in the filter blocks to a certain level through infrared radiation, and then uses microwave drying to automatically explode the filter blocks to form powder. The raw materials can be dispersed into powder without grinding or crushing. The process is simple, and the dispersion effect is good, and grain agglomeration is not obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention provides a flow chart of the process for drying the slurry into powder. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. 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 creative work are within the scope of protection of the present invention.

[0031] Infrared drying is a process of drying by infrared radiation. It is a drying method with fast drying speed and high energy utilization rate. Microwave drying is a drying method with strong penetrating power. It uses high-frequency electromagnetic waves to make the water molecules inside the material rotate violently as the direction of the microwave electric field changes, thereby generating violent collisions and friction, generating heat and leaving the material, thereby achieving material drying.

[0032] The intermediates used to prepare alumina easily absorb water and undergo hydration reactions, which in turn produce strong adhesion forces. The particles easily adhere and agglomerate in the slurry, resulting in difficulty in dispersion. In order to make the particle size distribution of the alumina particles after calcination narrower and the agglomeration smaller, the alumina needs to be dispersed as much as possible before calcination. In this regard, the spray drying provided in the prior art forms spherical or quasi-spherical particles formed by the agglomeration of multiple alumina particles, which need to be crushed again before entering the calcination process. The process is complicated and it is easy to introduce other impurities during the crushing process. On this basis, the inventor wants to find a drying method with a simpler process. Although infrared microwave drying has a simple process and a fast drying speed, the inventor found that the alumina particles obtained by directly using infrared microwave drying to treat the intermediates after the reaction or the reaction system containing the intermediates are obviously agglomerated, and the particle sizes are different, making it difficult to obtain alumina particles with a narrow particle size distribution. On this basis, the inventors proposed a new process for drying slurry into powder, in which the slurry containing the product is filtered and crushed into filter blocks of a certain specification, and then the moisture on the surface of the filter blocks and the moisture inside the filter blocks are dried in stages by infrared radiation. When the moisture inside and outside the filter blocks is reduced to a certain level, microwave drying is used to make the filter blocks automatically explode and crush to form product powder.

[0033] The solution provided in this application is Figure 1 , specifically including the following steps:

[0034] (1) providing a slurry, wherein the slurry comprises a dispersion liquid and a powder dispersed in the dispersion liquid;

[0035] (2) filtering the slurry into a filter cake, and breaking the filter cake into filter blocks with a particle size not greater than 3 mm;

[0036] (3) Using infrared rays and microwaves to heat and dry the filter blocks in sequence, so that the filter blocks spontaneously explode into powder.

[0037] The slurry in this application refers to a solid-liquid mixture containing a product, which can be configured by using water from the product, or it can be a reaction system with water formed during the preparation of the product. Taking the preparation of alumina by hydrothermal method as an example, the slurry here can be a reaction system formed after the hydrothermal reaction, or it can be a slurry formed after the calcination process, after the calcination product is ground with water. Of course, the slurry here can also be a reaction system generated during the preparation of other powder products or a powder slurry to be dispersed and dried.

[0038] The dispersion at least includes water, which can be pure water or a mixed dispersion formed by water and other solvents or dispersions with a volatilization temperature lower than the boiling point of water. The mass ratio of water to the other solvents or dispersions can be any ratio, and water is preferably the main dispersion.

[0039] The solid content in the slurry may be no higher than 50%, and in order to improve the dispersibility of the product, it may preferably be no higher than 30%. Taking alumina as an example, the solid content in the slurry is preferably less than 15%.

[0040] In step (2), the thickness of the filter cake is preferably controlled within the range of 3 to 5 cm. Here, the thickness of the filter cake is preferably within the range of 3 to 5 cm at any point in the vertical direction. The uniformity of the thickness of the filter cake is controlled to facilitate the subsequent crushing to form uniform filter blocks.

[0041] In addition, the solid content (content of the product) in the filter cake is preferably not less than 65%, preferably 65% ​​to 70%. Too low a solid content of the filter cake results in too high a content of the dispersion in the filter cake, and the time required in the subsequent drying process is too long, while too high a solid content of the filter cake easily leads to excessive pressurization pressure on the filter cake, which is not conducive to breaking into filter blocks of relatively uniform size; it is also not conducive to natural explosion into powder after drying. In addition, during the preparation of alumina, since the product is prone to hydration and agglomeration, the control of the solid content here can also control the time of infrared drying, which is conducive to subsequent microwave drying explosion. The inventor unexpectedly discovered that the pulverization of the product provided in the present application is achieved by spontaneous explosion of microwave drying, but the degree of dispersion of the dispersed particles in the slurry, the drying time and drying temperature during the infrared drying process, and the water content of the filter block entering the microwave drying have an impact on the degree of powder crushing and the uniformity of the crushed particles. The reason may be that the infrared drying time is too long, which can easily lead to more obvious agglomeration of particles, resulting in incomplete crushing during the subsequent spontaneous microwave explosion, and some particles will still obviously agglomerate, leading to poor dispersion effect. However, if the water content in the filter block entering the microwave drying is too low or too high, it may affect the instantaneous explosive force of the filter block when it explodes spontaneously, and then affect the degree of powder crushing and the uniformity of the crushed particles. Taking the preparation of alumina as an example, during the process of pressing to form a filter cake, the pressing pressure is preferably not higher than 0.7MPa, and the pressing time is 20 to 50min / time.

[0042] Therefore, in the present application, the filter cake is destroyed into filter blocks with a particle size not higher than 3 mm, so that the size of the filter block is moderate, the surface agglomeration is not obvious after infrared radiation drying, and the water content can be quickly reduced to a suitable range, so that the instantaneous explosive force when the filter block explodes spontaneously can make the powder broken more completely and the uniformity of the particles is better.

[0043] It should be noted that the water content of the filter block can be appropriately adjusted according to the size of the filter block and the physical properties of the material. For example, when the particle size of the filter block is large, the water content of the filter block entering the microwave drying can be appropriately increased; while when the particle size of the filter block is small, the water content of the filter block entering the microwave drying can be appropriately reduced; for another example, when the viscosity of the material in water is high, the water content of the filter block entering the microwave drying can be appropriately increased, and when the viscosity of the material in water is low, the water content of the filter block entering the microwave drying can be appropriately reduced.

[0044] Taking aluminum oxide as an example, the water content of the filter block is not higher than 0.2% and not lower than 0.05%. More preferably, the water content of the filter block is not higher than 0.2% and not lower than 0.1%.

[0045] In addition, during the infrared radiation drying and microwave drying process, the filter block is preferably spread into a material layer with a thickness of no more than 1 cm so that it is heated more evenly.

[0046] The filter cake can be broken by cutting the filter cake with a mesh slice or a splitting net mounted on a roller. Breaking the filter cake into filter blocks with smaller particle sizes can not only achieve rapid drying, but also improve the problem of difficulty in controlling the water content in the filter cake caused by large differences in the size of the filter cake.

[0047] In step (3), the infrared heating of the filter block includes a low-temperature heating stage and a medium-temperature heating stage in sequence;

[0048] In the low-temperature heating stage, the temperature to which the filter block is heated is lower than the temperature to which the filter block is heated in the medium-temperature heating stage;

[0049] The microwave heating causes the filter block to reach a temperature higher than the temperature to which the filter block is heated in the medium temperature heating stage.

[0050] The filter block provided in the present application passes through the low-temperature heating stage and the medium-temperature heating stage in sequence, and then enters the microwave heating stage to achieve segmented drying.

[0051] Wherein, in the low temperature heating stage, the filter block is heated to 70-100°C and maintained for at least 5 minutes, so that at least the moisture on the surface of the filter block is dried;

[0052] In the medium temperature heating stage, the filter block is heated to 110-140° C. and maintained at this temperature for at least 5 minutes, so that the moisture inside the filter block is dried to a certain extent.

[0053] After the medium temperature heating stage, the water content inside the filter block is actually higher than the water content on its surface. Therefore, the water content of the filter block in this application is based on the water content of the entire filter block.

[0054] Preferably, in the low-temperature heating stage, the filter block is heated to 70-100° C. and maintained for 5-20 min; in the medium-temperature heating stage, the filter block is heated to 110-140° C. and maintained for 5-10 min.

[0055] Preferably, the filter block continuously passes through the low-temperature heating stage, the medium-temperature heating stage and the microwave heating stage, so that the filter block can be continuously dried, which is beneficial to a continuous sound field and improves production efficiency.

[0056] During the microwave heating, the filter block is heated to at least 150°C, preferably 150-180°C. The heating temperature should not be too high to avoid cost increase and to avoid excessive volatilization of water. In addition, the microwave heating time is determined based on the time it takes for the filter block to spontaneously explode into powder, which can be appropriately adjusted within a certain range based on the size of the filter block, the water content and the physical properties of the material. Taking aluminum oxide as an example, the microwave heating time is usually preferably 2-8 minutes.

[0057] In the present application, the temperature at which the filter block is heated can be adjusted by the wavelength and power of infrared rays, the wavelength of microwaves, the frequency of microwaves and the power of microwaves. For example, in the microwave heating, the microwave wavelength used is 12.2CM; the frequency is 2450M, and the power is 100KW. In the infrared heating, the wavelength of infrared rays used is 2.5μm-15μm, and the power is 65KW.

[0058] The present application provides a method of segmented drying using infrared and microwaves, which allows filter blocks of the material to spontaneously explode into powder without the need for further grinding after drying, thereby avoiding the defects of introducing impurities and destroying the morphology of particles during the grinding process, so that the impurity content in the obtained powder is lower and the morphology is more complete.

[0059] In order to facilitate those skilled in the art to better understand and implement the drying method provided in the present application, the present application also provides a drying system for drying the slurry into powder, comprising:

[0060] A filter press mechanism, used to filter the slurry into a filter cake;

[0061] A crushing mechanism, disposed downstream of the filter pressing mechanism, for crushing the filter cake into filter blocks;

[0062] An infrared drying mechanism is arranged downstream of the crushing mechanism, and comprises a first infrared drying device and a second infrared drying device arranged in sequence; the first infrared drying device and the second infrared drying device are both used for drying the filter block;

[0063] The microwave drying mechanism is arranged downstream of the infrared drying mechanism and is used for drying the filter block and spontaneously exploding it into powder.

[0064] The system includes a conveying mechanism for transmitting materials, so that the materials are sequentially conveyed from the filter press mechanism to the crushing mechanism, the infrared drying mechanism and the microwave drying mechanism. The conveying structure can be a conveying mechanism capable of realizing material conveying in the prior art, which includes a conveyor belt and a driving device for driving the conveyor belt to move.

[0065] The filter press mechanism can be a device capable of realizing slurry filter press in the prior art, such as a plate and frame filter press, and the filter cloth material is preferably Teflon with less adhesion.

[0066] The crushing mechanism includes a plurality of driving rollers, a mesh knife net arranged on the driving rollers and a driving device for driving the driving rollers to rotate, wherein the driving rollers are located above the conveyor belt; as the driving rollers rotate under the drive of the driving device, the knife nets are driven to rotate, so that the filter cakes on the conveyor belt are cut into filter blocks.

[0067] In some embodiments, a plurality of driving rollers are provided, and the spacing between the plurality of driving rollers and the conveyor belt decreases in sequence along the advancing direction of the conveyor belt, which can not only play the role of cutting the filter cake into pieces, but also gradually spread the filter blocks as they are cut into pieces. In addition, by controlling the vertical spacing between the last driving roller and the conveyor belt, the thickness of the spread filter blocks can be controlled.

[0068] In other embodiments, scrapers are further provided between adjacent driving rollers of the crushing mechanism, and the vertical spacing between the plurality of scrapers and the conveyor belt decreases successively along the advancing direction of the conveyor belt, so that the filter blocks can be gradually spread out as they are shredded.

[0069] The mesh size of the knife net is larger than or equal to the required size of the filter block, preferably larger than the size of the filter block and not higher than twice the size of the filter block.

[0070] The first infrared drying device includes a first infrared generator; the second infrared drying device includes a second infrared generator. The first infrared generator and the second infrared generator can be connected to a controller respectively, or can share a controller. The heating temperature in the first infrared drying device and the heating temperature in the second infrared drying device can be adjusted by controlling the power of the first infrared generator and the second infrared generator by the controller.

[0071] The microwave drying mechanism includes a housing, a microwave generator installed in the housing for emitting microwaves for heating, and a controller for controlling the power and frequency of the microwave generator. An inlet is provided at one end of the housing and an outlet is provided at the other end. In order to prevent dust from scattering, a material extraction port is also provided on the microwave drying mechanism, and the product exploded into powder is pumped to the receiving device through the material extraction port under negative pressure.

[0072] In addition, in the present system, the heating time of the filter block can be adjusted by the forward speed of the conveyor belt in the conveying mechanism and / or the radiation range of the infrared ray and the length along the forward direction of the conveyor belt in the microwave drying mechanism.

[0073] Preferably, the first infrared drying device and the second infrared drying device are also provided with a housing, which can improve energy utilization.

[0074] In some embodiments, the drying system further comprises a first temperature detector, a second temperature detector, and a third temperature detector;

[0075] The first temperature detector is arranged in the first infrared drying device, and is used to detect the temperature in the first infrared drying device; the second temperature detector is arranged in the second infrared drying device, and is used to detect the temperature in the second infrared drying device; the third temperature detector is arranged in the microwave drying mechanism, and is used to detect the temperature in the microwave drying mechanism;

[0076] Also included is a first humidity detector, a second humidity detector, and a third humidity detector;

[0077] The first humidity detector is arranged in the first infrared drying device for detecting the humidity in the first infrared drying device; the second humidity detector is arranged in the second infrared drying device for detecting the humidity in the second infrared drying device; the third humidity detector is arranged in the microwave drying mechanism for detecting the humidity in the microwave drying mechanism.

[0078] These temperature detectors and humidity detectors are respectively connected to the corresponding controllers for constant monitoring of the temperature and humidity therein, providing an effective reference for process parameter adjustment and production maintenance.

[0079] It should be noted that the drive device used in the system provided in the present application can be an electric drive in the prior art, such as a motor, or other drives, such as a hydraulic drive or a pneumatic drive. The controller used can be a controller in the prior art that can realize information collection, information processing, programming, program input and instruction sending, such as a single-chip microcomputer. The detector (temperature detector or humidity detector) used can also be a detector in the prior art that can realize real-time monitoring of environmental information and communication, so it will not be described in detail one by one in this application.

[0080] In order to facilitate those skilled in the art to understand the innovation of the present application, some preferred embodiments are provided below in conjunction with the accompanying drawings to illustrate the above technical solution.

[0081] The slurries provided in the following examples are all alumina monohydrate slurries prepared by a hydrothermal method. After the raw materials are subjected to a hydrothermal reaction, the slurries are diluted and acidified with oxalic acid and pure water to achieve a solid content of 15% and a pH value of 8.0.

[0082] The spray granulation equipment used is a spray granulation tower of model GL-50 purchased from Shengyi Company.

[0083] Example 1

[0084] This embodiment provides an aluminum oxide slurry drying process, comprising the following steps:

[0085] The above-mentioned alumina monohydrate slurry is placed in a plate-frame filter press, and filtered to obtain a filter cake; wherein the feed pressure of the plate-frame filter press is: <0.7 MPa, the purge time is: 30 min, the pressing time is: 30 min; the purge times are 3 times / plate-frame; the pressing times are: 3 times / plate-frame; the feed weight is: 2.6 T / plate-frame; the filter pressing time is: 1.5 H / plate-frame; the purge time is: 1.5 H / plate-frame; the filter cloth material is: Teflon; the filter cloth mesh number is: 1000 mesh;

[0086] The obtained filter cake is moved to a conveyor belt, which feeds the filter cake into a crushing mechanism at a speed of 20 cm / min, and is cut into filter blocks with a size mainly less than 3 mm by a knife net with an aperture of 3.5 mm, and spread into a material layer with a thickness of 0.8 cm;

[0087] The filter block is dried by infrared radiation, the residence time of the filter block in the first infrared drying device is 10 minutes, the temperature in the first infrared drying device is 80° C., the humidity is controlled at 50%, and the power of the first infrared generator is 50%; the residence time of the filter block in the second infrared drying device is 7 minutes, the temperature in the first infrared drying device is 100° C., the humidity is controlled at 5-12%, and the water content of the obtained filter block is less than 0.3%, and the power of the second infrared generator is 100%;

[0088] The filter block is dried by microwaves, and the residence time of the filter block in the microwave drying mechanism is not less than 8 minutes, so that it spontaneously explodes to form powder, thereby obtaining aluminum oxide powder; wherein the power of the microwave generator is 100KW, the frequency is 2450M, and the wavelength of the microwave emitted by the microwave generator is 12.2CM.

[0089] Example 2

[0090] This embodiment provides an aluminum oxide slurry drying process, comprising the following steps:

[0091] The above-mentioned alumina monohydrate slurry is placed in a plate-frame filter press, and filtered to obtain a filter cake; wherein the feed pressure of the plate-frame filter press is: <0.7 MPa, the purge time is: 30 min, the pressing time is: 30 min; the purge times are 3 times / plate-frame; the pressing times are: 3 times / plate-frame; the feed weight is: 2.6 T / plate-frame; the filter pressing time is: 1.5 H / plate-frame; the purge time is: 1.5 H / plate-frame; the filter cloth material is: Teflon; the filter cloth mesh number is: 1000 mesh;

[0092] The obtained filter cake is moved to a conveyor belt, which feeds the filter cake into a crushing mechanism at a speed of 20 cm / min, and is cut into filter blocks with a size mainly less than 3 mm by a knife net with an aperture of 3.0 mm, and spread into a material layer with a thickness of 0.9 cm;

[0093] The filter block is dried by infrared radiation, the residence time of the filter block in the first infrared drying device is 8 minutes, the temperature in the first infrared drying device is 90° C., the humidity is controlled at 45-50%, and the power of the first infrared generator is 55%; the residence time of the filter block in the second infrared drying device is 6 minutes, the temperature in the first infrared drying device is 120° C., the humidity is controlled at 5-10%, and the water content of the obtained filter block is less than 1%, and the power of the second infrared generator is 100%;

[0094] The filter block is dried by microwaves. The residence time of the filter block in the microwave drying mechanism is not less than 8 minutes, so that it spontaneously explodes to form powder, and aluminum oxide powder is obtained. The power of the microwave generator is 100KW and the frequency is 61%.

[0095] Comparative Example 1

[0096] Using the spray granulation equipment provided above, the slurry provided in Example 1 was spray granulated at a conveying pressure of 0.1 MPa, an atomizing disk of 12,000 revolutions, and a temperature of 125°C, and then the alumina particles were crushed into powder by a jet mill, wherein the crushing parameters of the jet mill were: crushing pressure 0.2-0.6 MPa, and a classifying wheel frequency 10-90 Hz.

[0097] Comparative Example 2

[0098] Compared with Example 1, in this comparative example, after the filter cake is obtained by filtering with a plate and frame filter press, the obtained filter cake is moved to a conveyor belt without the step of "the conveyor belt sends the filter cake to the crushing mechanism at a speed of 20 cm / min, and is cut into filter blocks with a size mainly less than 3 mm by a knife net with an aperture of 3.5 mm, and is spread into a material layer with a thickness of 0.8 cm". The filter cake is directly sent to the infrared drying mechanism to dry the filter block by infrared radiation. The remaining steps are the same as those in Example 1 to obtain a comparative sample.

[0099] Comparative Example 3

[0100] Compared with Example 1, in this comparative example, compared with Example 1, the filter block is dried only by the first infrared drying device, the residence time of the filter block in the first infrared drying device is 10 minutes, the temperature in the first infrared drying device is 80°C, the humidity is controlled at 10%, and the power of the first infrared generator; the filter block is not dried by infrared radiation in the second infrared drying device and directly enters the microwave drying mechanism, and the water content of the obtained filter block is>1. The remaining steps are the same as in Example 1, and the comparative sample is obtained.

[0101] Comparative Example 4

[0102] Compared with Example 1, in this comparative example, the filter block is not dried by infrared radiation in the first infrared drying device and directly enters the second infrared drying device, and the filter block is dried only by the second infrared drying device. The residence time of the filter block in the second infrared drying device is 7 minutes, the temperature in the second infrared drying device is 100° C., and the humidity is controlled at 30%. At this time, the water content of the obtained filter block is>1%. The remaining steps are the same as in Example 1 to obtain a comparative sample.

[0103] Comparative Example 5

[0104] Compared with Example 1, the solid content of the filter cake formed by the slurry filter press in this comparative example is 50% compared with Example 1. In the remaining steps, the residence time of the filter block in the first infrared drying device is 20 minutes, the temperature in the first infrared drying device is 80°C, the humidity is controlled at 10%, and the power of the first infrared generator is 80%; the residence time of the filter block in the second infrared drying device is 12 minutes, the temperature in the first infrared drying device is 100°C, the humidity is controlled at 15%, and the water content of the filter block obtained at this time is <0.02%, and the power of the second infrared generator is 80%; the remaining steps are the same as in Example 1, and the comparative sample is obtained.

[0105] Comparative Example 6

[0106] Compared with Example 1, in this comparative example, compared with Example 1, the filter block is dried by the first infrared drying device and the second infrared drying device, the residence time of the filter block in the first infrared drying device and the second infrared drying device is 35 minutes in total, the temperature in the first infrared drying device and the second infrared drying device is set to 80°C, and the power of the first infrared generator and the second infrared drying device is 65kw; the water content of the filter block obtained at this time is 0.3%. The remaining steps are the same as in Example 1, and the comparative sample is obtained.

[0107] The porous alumina powder obtained in the above Examples 1 to 2, the comparative samples and the control samples obtained in Comparative Examples 1 to 6 were respectively subjected to the above tests, and the test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] As can be seen from Table 1, the porous alumina obtained by drying the slurry into powder provided by the present application has a narrow particle size distribution, which is comparable to the particle size of the powder formed by spray drying and grinding, and the particle size of the small particles is smaller. In addition, since the powder formed by the embodiment of the present application does not need to be ground, the crystal morphology of the powder formed is more complete.

[0111] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A process for drying a slurry into powder, characterized in that: The following steps are involved: Providing a slurry, the slurry comprising a dispersion liquid and a powder dispersed in the dispersion liquid; The slurry is filtered into a filter cake, and the filter cake is broken into filter blocks with a particle size not higher than 3 mm; The filter block is heated and dried in sequence by infrared rays and microwaves, so that the filter block spontaneously explodes into powder.

2. The process for drying the slurry into powder according to claim 1, characterized in that: The infrared heating of the filter block includes a low temperature heating stage and a medium temperature heating stage in sequence; In the low-temperature heating stage, the temperature to which the filter block is heated is lower than the temperature to which the filter block is heated in the medium-temperature heating stage; The microwave heating causes the filter block to reach a temperature higher than the temperature to which the filter block is heated in the medium temperature heating stage.

3. The process for drying the slurry into powder according to claim 2, characterized in that: In the low temperature heating stage, the filter block is heated to 70-100° C. and maintained at this temperature for at least 5 minutes; In the medium temperature heating stage, the filter block is heated to 110-140° C. and maintained at this temperature for at least 5 minutes.

4. The process for drying the slurry into powder according to claim 3, characterized in that: In the low temperature heating stage, the filter block is heated to 70-100° C. and maintained for 5-20 minutes; In the medium temperature heating stage, the filter block is heated to 110-140° C. and maintained for 5-10 minutes.

5. The process for drying slurry into powder according to any one of claims 1 to 4, characterized in that: During the microwave heating, the filter block is heated to at least 150°C.

6. The process for drying slurry into powder according to any one of claims 1 to 4, characterized in that: In the microwave heating, the microwave wavelength used is 12.2CM; the frequency is 2450M; and / or In the infrared heating, the wavelength of the infrared rays used is 2.5 μm-15 μm, and the power is 60 KW.

7. The process for drying slurry into powder according to claim 5, characterized in that: After the infrared heating, the water content of the filter block is not higher than 0.2% and not lower than 0.05%.

8. The process for drying slurry into powder according to claim 1, characterized in that: The solid content in the filter cake is not less than 65%.

9. The process for drying slurry into powder according to claim 1, characterized in that: The thickness of the filter cake is 3-5 cm, and the spreading thickness of the filter block is not higher than 1 cm.

10. A drying system for drying slurry into powder, characterized in that: include: A filter press mechanism, used to filter the slurry into a filter cake; A crushing mechanism, disposed downstream of the filter pressing mechanism, for crushing the filter cake into filter blocks; An infrared drying mechanism is arranged downstream of the crushing mechanism, and comprises a first infrared drying device and a second infrared drying device arranged in sequence; the first infrared drying device and the second infrared drying device are both used for drying the filter block; The microwave drying mechanism is arranged downstream of the infrared drying mechanism and is used for drying the filter block and spontaneously exploding it into powder.

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