A method for granulating magnesium oxide

Abstract

A method for granulating magnesium oxide, relates to the technical field of magnesium oxide granulation, and the method includes: step one, raw material preparation: magnesium carbonate is used as raw material, and magnesium carbonate is put into a raw material silo for standby; step two, magnesium carbonate grinding: a gas flow mill is used to grind the magnesium carbonate raw material so that the particle size D90 of the magnesium carbonate powder is ≤50um; step three, high temperature calcination: the ground magnesium carbonate is calcined, and the calcination includes temperature rise calcination and heat preservation calcination. The calcination temperature of the entire calcination stage is controlled to be 720-850℃, the temperature rise calcination time is more than 1h, and the heat preservation calcination time is 4-10h, and magnesium oxide powder is generated; step four, granulation: the generated magnesium oxide powder is then pressed into flakes and crushed into whole grains by a roller-type horizontal feeding dry granulation system to obtain finished magnesium oxide particles. The roller-type horizontal feeding dry granulation system is closed-loop produced, does not need to add any binder, and the material is extruded and formed, does not destroy the chemical properties of magnesium oxide, and does not reduce the effective content of magnesium oxide.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium oxide granulation, in particular to a method for magnesium oxide granulation. Background Art

[0002] Food grade magnesium oxide is used in various industries. Its functions and properties vary. It is mainly used as a food additive and color stabilizer; used as a decolorizing agent for refined sugar, a pH regulator for ice cream powder, etc.; as a magnesium supplement for health products and foods; magnesium oxide can not only supplement the lack of magnesium in the diet to prevent the occurrence of enzyme deficiency, but is also an excellent rumen buffer that regulates rumen fermentation; in the field of food additives, magnesium oxide plays a vital role.

[0003] At present, the methods for preparing and producing magnesium oxide mainly include: double reduction carbonization method, gas phase method, calcination method, carbonization method, ammonium carbonate method, carbonation method, sintering method, brine ammonium method, electric melting method and hydrochloric acid method. Among them, the method of calcining magnesium hydroxide as a raw material to produce magnesium oxide has less by-products, which can ensure the minimum pollution to the environment and has a high utilization rate of magnesium hydroxide, and can produce high-purity magnesium oxide, thereby reducing production costs.

[0004] The existing announcement number is CN 114180605 B. A method for preparing magnesium oxide particles specifically discloses the following steps: step 1, preparing highly active magnesium hydroxide particles; step 2, mixing the highly active magnesium hydroxide prepared in step 1 with a dispersant and deionized water, stirring and dispersing to form a magnesium hydroxide slurry; step 3, drying the magnesium hydroxide slurry, calcining it in an inert atmosphere after drying, adding cracking gas during calcination, and obtaining solid magnesium oxide; step 4, adding an auxiliary agent to the solid magnesium oxide obtained in step 3 for granulation, screening the magnesium oxide particles obtained by granulation, and finally obtaining a finished magnesium oxide particle. Although the particle size and activity of magnesium oxide particles prepared by this method have been significantly improved. However, it is necessary to add an auxiliary agent to the solid magnesium oxide for granulation in order to increase the granulation rate of magnesium oxide, speed up the granulation speed, and reduce the particle size of magnesium oxide granulation, wherein copper, graphite, calcium oxide, and paraffin are selected as auxiliary agents configured in a mass ratio of 5:2:1.3-7-1, and the addition of auxiliary agents will affect the chemical properties and effective content of the finished product to a certain extent. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for granulating magnesium oxide.

[0006] The present invention claims a method for granulating magnesium oxide, comprising the following steps:

[0007] Step 1, raw material preparation: using magnesium carbonate as raw material, putting magnesium carbonate into the raw material silo for standby;

[0008] Step 2, grinding magnesium carbonate: using a jet mill to grind the magnesium carbonate raw material so that the particle size of the magnesium carbonate powder D90 ≤ 50 um;

[0009] Step 3, high temperature calcination: calcining the ground magnesium carbonate, including heating calcination and heat preservation calcination, the calcination temperature of the whole calcination stage is controlled at 720-850°C, the heating calcination time is more than 1h, and the heat preservation calcination time is 4-10h, to generate magnesium oxide powder;

[0010] Step 4: Granulation: The generated magnesium oxide powder is then pressed into flakes and crushed into whole particles through a double-roller horizontal feeding dry granulation system to obtain finished magnesium oxide particles.

[0011] Preferably, the particle size of the magnesium carbonate powder in step 2 is 35-50 um;

[0012] The magnesium carbonate ground in the step 2 is subjected to central control testing using a particle size tester, and then the magnesium carbonate powder is graded and screened using an air flow classifier; the central control testing using the particle size tester can ensure that the particle size of the magnesium carbonate powder meets the requirements, and the grading and screening using the air flow classifier can further ensure the particle size uniformity of the powder.

[0013] Preferably, the calcination temperature of the entire calcination stage in the step three is controlled to be 750-800°C; within this temperature range, magnesium carbonate can be fully burned, which, on the one hand, ensures the purity and quality of magnesium oxide and reduces the impurity content; on the other hand, it also reduces the calcination cost. When the temperature is lower than 720°C, magnesium carbonate is not fully burned, which will affect the quality of magnesium oxide; and when the temperature is higher than 850°C, the particle size of magnesium carbonate powder may shrink sharply, increasing production costs.

[0014] Preferably, the heating and calcining time in step three is 1-2h; if the heating time is too short, the particle size of the magnesium carbonate powder will shrink sharply, affecting the particle size and compressibility of the magnesium oxide powder. If the heating and calcining time is less than 1h, the magnesium carbonate cannot be fully burned, and its particle size change will affect the quality of the subsequently prepared magnesium oxide powder. When the heating and calcining time is within the range of 1-2h, the magnesium carbonate powder can be fully burned without increasing the difficulty and cost of operation due to too long a time. If the heating and calcining time is extended to more than 2h, the actual operation will be difficult and the cost will be increased.

[0015] Preferably, the heat preservation and calcination time in step three is 4-8 hours; within this time range, both the magnesium carbonate powder can be fully burned and the compressibility of the magnesium oxide powder can be guaranteed, while the calcination cost is reduced. If the heat preservation and calcination time is less than 4 hours, the magnesium carbonate may not be burned completely; and if it exceeds 10 hours, the production cost will increase, and the performance improvement of the magnesium oxide powder will be limited.

[0016] The present invention also protects a system for granulating magnesium oxide. The system used in the method for granulating magnesium oxide includes a raw material silo, an air flow pulverizer, a particle size tester, an air flow classifier, a tunnel kiln and a double-roller horizontal feeding dry granulation system.

[0017] The discharge port at the bottom of the raw material silo conveys the raw materials to the feed port of the air flow mill at a preset conveying rate through a conveying device; the magnesium carbonate powder crushed by the air flow mill is conveyed by a pipeline to the particle size tester for real-time particle size detection; the data after the test is fed back to the control system, and if the particle size does not meet the standard, it returns to the air flow mill for further crushing; if the particle size meets the requirements, it is conveyed to the air flow classifier; in the air flow classifier, according to the set classification particle size standard, the fine powder is collected and stored as a qualified product, and the coarse powder is returned to the air flow mill through a pipeline for further crushing; the qualified magnesium carbonate fine powder is then conveyed to the feed end of the tunnel kiln, undergoes the temperature rise calcination and heat preservation calcination stages in the tunnel kiln, and is finally transformed into magnesium oxide powder and output from the kiln tail discharge port to enter the subsequent granulation process; the various equipments work closely together and are linked together to build an efficient, stable and highly automated magnesium oxide granulation production line, which effectively ensures the continuity of the production process and the controllability of product quality.

[0018] The main body of the raw material silo is constructed of stainless steel, which has good corrosion resistance and sealing properties to prevent the raw materials from being damp or contaminated. Its structure is cylindrical with a conical bottom design, which is conducive to the natural discharge of raw materials by gravity. A sealed feed port is provided on the top of the silo, which can be tightly connected with the raw material conveying equipment; the bottom discharge port is equipped with a manual or electric valve for precise control of the raw material discharge rate; it provides a safe and stable temporary storage space for magnesium carbonate raw materials, ensures the continuity and stability of raw material supply, and effectively buffers the connection fluctuations in time and quantity between raw material procurement and production links. The second is the homogenization effect. With the static storage of the silo, raw materials of different batches and different particle size distributions can be naturally mixed and homogenized to a certain extent, reducing the interference of fluctuations in raw material characteristics on production processes and product quality, and improving the consistency and stability of product quality.

[0019] The particle size tester uses the principle of laser diffraction to carry out the test. The laser beam emitted by the laser penetrates the magnesium carbonate powder sample. The powder particles cause the laser to scatter. The detector collects the scattered light signal and performs data processing and analysis based on the Mie scattering theory or the Fraunhofer diffraction theory, so as to accurately determine the particle size distribution of the powder. During the test, the sample needs to be evenly dispersed in a suitable dispersion medium (such as air or liquid) to ensure the accuracy and reliability of the test results.

[0020] The airflow classifier achieves material grading and screening by the synergistic effect of the centrifugal force field and the airflow drag. In the grading area, the high-speed rotating rotor generates a strong centrifugal force, which causes the magnesium carbonate powder particles to be stratified according to the particle size. The fine particles are subjected to airflow drag greater than the centrifugal force, so they are carried up by the airflow and discharged as fine powder products; while the coarse particles are subjected to a centrifugal force greater than the airflow drag, so they fall along the inner wall of the classifier and return to the crushing or reprocessing stage. By adjusting key parameters such as the rotor speed, airflow speed and air volume, the boundaries of the grading particle size can be accurately controlled, thereby achieving efficient and accurate grading of the magnesium carbonate powder particle size.

[0021] The main body of the tunnel kiln is in the form of a long tunnel, and is composed of core parts such as a kiln body, a heating system, a ventilation system, a conveying system and a temperature control system. The kiln body is built with refractory materials that are resistant to high temperatures and have excellent thermal insulation properties to ensure that the heat in the kiln is stably and efficiently gathered. The heating system mostly uses gas, oil or electric heating, among which gas heating is widely used due to its low cost and high heating efficiency. The burners are arranged in an orderly manner on both sides or at the bottom of the kiln body to ensure that the heat is evenly distributed in the kiln space, creating a stable and uniform thermal environment for the calcination of magnesium carbonate. The ventilation system is responsible for regulating the flow rate, direction and atmosphere composition of the airflow in the kiln to ensure the smooth progress of the calcination reaction and the stability of the product quality. The conveying system uses a high-temperature resistant ceramic or metal conveyor belt to convey materials through the kiln body at a constant speed to ensure that the materials complete the calcination process within the predetermined time and temperature program.

[0022] The double-roller horizontal feeding dry granulation system comprises a feeding mechanism, a material storage mechanism, a material conveying mechanism, a granulation main body mechanism and a screening mechanism.

[0023] The feeding mechanism is a dust-free feeding station; the magnesium oxide granulation raw materials enter the dust-free feeding station, and the feeding mechanism can effectively prevent foreign matter from entering the system, while reducing dust generation, preventing dust from polluting the environment and materials, thereby improving the cleanliness of the production process;

[0024] The storage mechanism is a transfer silo equipped with a level meter and a stirring paddle to control the ratio of recovered fine powder to newly added granulation raw materials; the raw materials are transported to the transfer silo by the first vacuum feeder, the level meter in the transfer silo can monitor the storage amount of materials in the silo in real time, and the stirring paddle can control the ratio of recovered fine powder to newly added granulation raw materials, so as to facilitate the mixing of the two and ensure the stability of the composition of the granulation raw materials;

[0025] The material conveying mechanism includes a vacuum feeder and a feeding auger, and the vacuum feeder includes a first vacuum feeder, a second vacuum feeder, a third vacuum feeder and a fourth vacuum feeder; after the magnesium oxide granulation raw material enters the dust-free feeding station, it is conveyed to the transfer bin by the first vacuum feeder, and after being mixed with the recovered fine powder in the transfer bin, it is conveyed to the forced feeder by the feeding auger, so as to realize efficient material conveying;

[0026] The main granulation mechanism consists of a forced feeder, a double-roll granulation extruder, a cutting knife group and a granulation knife group. The material in the transfer bin is transported to the forced feeder through a feeding auger, slowly degassed in the forced feeder, and then enters the double-roll granulation extruder to be extruded into sheets. The extruded flake magnesium oxide enters the cutting knife group, is cut into slightly larger particles, and then passes through two parallel granulation knife groups for granulation.

[0027] The screening mechanism is a screening machine, and the prepared particles are transported to the screening machine through the second vacuum feeder for screening. The screening machine is provided with three outlets, wherein the upper one is an outlet for large particle materials, which is connected to the cutting knife group through the third vacuum feeder, and unqualified large particle materials are recovered to the cutting knife group by the third vacuum feeder, and are cut and granulated again; the middle one is a finished product outlet, which is connected to a finished product collection box, and qualified magnesium oxide particles of the required mesh size are collected in the finished product collection box through the finished product outlet; the lower one is a fine powder outlet, which is connected to a transfer bin through the fourth vacuum feeder, and unqualified fine powder is recovered to the transfer bin by the fourth vacuum feeder through the fine powder outlet for reuse, and re-enters the granulation main mechanism after being evenly mixed with the granulation raw materials in proportion.

[0028] The granulation principle of the double-roll horizontal feeding dry granulation system: the magnesium oxide powder raw material enters the dust-free feeding station, is transported to the transfer silo by the first vacuum feeder, mixed with the recycled fine powder, and then transported to the forced feeder through the feeding auger. After degassing, it enters the double-roll granulation extruder and is extruded into sheets. Its principle is mainly to agglomerate the dry material into dense and hard large cakes under pressure, and use the principle of intermolecular force in physics to allow the extruded molecules to freely combine into molecules with appropriate spatial density; the double-roll granulation extruder mainly relies on external pressure to extrude the material through the double rollers into a cake shape, remove the gaps between the materials, and the density between the materials is increased several times, and the strength meets the design requirements;

[0029] After extrusion, the flake magnesium oxide enters the cutting knife group and is cut into slightly larger particles, and then passes through the granulation knife group for granulation. There are two groups of granulation knife groups, which are parallelly distributed below the cutting knife group, and further process the flake magnesium oxide into particles of uniform size;

[0030] Finally, the screening is carried out through the screening mechanism, qualified products are collected, and unqualified materials are recycled and reused. The obtained particles are transported to the screening machine through the second vacuum feeder. The screening machine is provided with three outlets, which are used for the output of large particle materials, finished products and fine powders respectively. The qualified magnesium oxide particles of the required mesh size are collected in the finished product collection box through the finished product outlet; the unqualified large particles are recovered to the cutting knife group by the third vacuum feeder through the large particle material outlet, and are cut and granulated again; the unqualified fine powder is recovered to the transfer silo through the fine powder outlet by the fourth vacuum feeder for reuse, and is mixed with the granulation raw materials in proportion and then re-enters the granulation main body. The whole process forms a closed-loop production, which will not introduce foreign matter, nor generate dust, avoids dust environmental pollution, and at the same time reduces the pollution of the environment and personnel to the materials, and improves the cleanliness. The recycling and reuse of unqualified materials can save resources, improve the particle yield, and thus improve production efficiency.

[0031] The beneficial effects of the present invention are as follows: 1. Magnesium carbonate is used as raw material, and the process is simpler and more efficient through grinding, high-temperature calcination and a double-roller horizontal feeding dry granulation system, without mixing with other substances;

[0032] 2. By controlling the particle size, calcination temperature, heating calcination time and heat preservation calcination time of magnesium carbonate, the compressibility and purity of magnesium oxide powder can be ensured. The particle size of magnesium carbonate powder is controlled to be D90≤50um, preferably 35-50um, the calcination temperature is controlled to be 720-850℃, preferably 750-800℃, the heating calcination time is more than 1h, preferably 1-2h, and the heat preservation calcination time is 4-10h, preferably 4-8h, which can ensure that the magnesium carbonate powder is fully calcined to generate magnesium oxide powder with compressibility, high magnesium oxide content, low heavy metal content and low bulk density;

[0033] 3. The double-roller horizontal feeding dry granulation system adopts closed-loop production and does not require the addition of any binder. The material is extruded and formed without destroying the chemical properties of magnesium oxide or reducing its effective content. There is no introduction of foreign matter and dust pollution, which improves cleanliness. Unqualified materials are recycled and reused, which saves resources and improves the granulation rate and production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. 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.

[0036] Example 1

[0037] The present invention provides a method for granulating magnesium oxide, comprising the following steps:

[0038] Step 1, raw material preparation: select magnesium carbonate with a purity of 98.5% as the raw material, accurately weigh 1000 kg and place it in the raw material silo, the initial particle size distribution of the raw material is detected by a laser particle size analyzer as D10=12μm, D50=30μm, D90=50μm, and the moisture content is 0.8% (measured by Karl Fischer moisture meter);

[0039] Step 2, grinding of magnesium carbonate: using an air flow mill for grinding operation, setting the mill speed to 3200r / min, the crushing pressure to 0.8MPa, and the feeding rate to 30kg / h; the grinding process lasts for 4 hours, during which the particle size of the magnesium carbonate powder is centrally controlled and detected by Malvern Mastersizer3000 particle size analyzer every 30 minutes; finally, the particle size D90 of the magnesium carbonate powder reaches 42μm, D50 is 22μm, and D10 is 8μm, and the particle size distribution conforms to the normal distribution characteristics, indicating that the particle size uniformity is good; then, an air flow classifier is used at 1200m 3 / h air volume is used to grade and screen magnesium carbonate powder, and the fine powder recovery rate reaches 88%, effectively removing over-coarse and over-fine particles and ensuring the consistency of product quality;

[0040] Step 3: High-temperature calcination: The ground and screened magnesium carbonate powder is transferred to the tunnel kiln for calcination. During the heating stage, the temperature is steadily increased from room temperature to 780°C at a rate of 50°C / h. This heating process takes 1.6 hours. Then it enters the heat preservation calcination stage, and the temperature is kept at a constant temperature of 780°C for 6 hours. During the entire calcination stage, the atmosphere in the tunnel kiln is maintained as air, and the flow rate is precisely controlled at 2m / h. 3 / min, the pressure is stabilized at 105Pa, and the chemical composition analysis of the generated magnesium oxide powder is performed using an X-ray fluorescence spectrometer (XRF). The results show that the purity of magnesium oxide is as high as 99.3%, and the impurity content (calculated as calcium oxide) is only 0.45%, indicating that the product purity is excellent. The test results of a synchronous thermal analyzer (STA) show that under this calcination condition, magnesium carbonate is completely decomposed, no residual intermediate phase is left, and the thermal stability is good;

[0041] Step 4: Granulation: The magnesium oxide powder is granulated by a double-roll horizontal feeding dry granulation system. The roller pressure of the double-roll granulation extruder is set to 8.5MPa, and the roller speed is maintained at 8r / min to ensure that the material is fully compacted; the speed of the cutting knife group is adjusted to 210r / min, and the knife spacing is accurately set to 5mm to achieve the initial forming of the particles; the speed of the whole granulation knife group is set to 155r / min, and the knife type is arc-shaped to further optimize the particle shape and particle size distribution; after screening by a screening machine, the particle size distribution of the finished magnesium oxide particles is 20-40 mesh, and the particle yield is as high as 87%. The bulk density of the finished particles is 0.48g / cm 3 , indicating that the particles are tightly packed and uniform; the heavy metal content was detected by inductively coupled plasma mass spectrometry (ICP-MS), among which the lead content was less than 4ppm, the cadmium content was less than 0.5ppm, and the mercury content was less than 0.1ppm, which met the strict quality standards of food-grade and pharmaceutical-grade magnesium oxide.

[0042] Example 2

[0043] The present invention provides a method for granulating magnesium oxide, comprising the following steps:

[0044] Step 1, raw material preparation: 1200 kg of magnesium carbonate raw material with a purity of 99.2% was selected and stored in the raw material silo. After testing, its initial particle size was D10=10 μm, D50=26 μm, D90=45 μm, and the moisture content was 0.6%;

[0045] Step 2, grinding of magnesium carbonate: The operating parameters of the air flow mill are a speed of 3400r / min, a crushing pressure of 0.9MPa, and a feeding speed of 35kg / h. During the grinding period, the particle size is monitored every 25 minutes using a laser diffraction particle size analyzer according to ISO13320-1 standard. After the grinding, the magnesium carbonate powder has a D90 of 38μm, a D50 of 20μm, and a D10 of 6μm. The particle size distribution is narrow, and the coefficient of variation is less than 5%, indicating a high degree of uniformity. Then, the powder is subjected to a 1300m 3 / h air volume air classifier screening, fine powder recovery rate of 90%, the coarse powder on the screen is returned for re-grinding to ensure accurate control of raw material particle size;

[0046] Step 3: High temperature calcination: During calcination in the tunnel kiln, the temperature is raised from room temperature to 765°C at a rate of 45°C / h (1.7 hours), followed by insulation for 7.5 hours. The oxygen content of the air in the kiln is 20.8% and the flow rate is 1.9 m / s. 3 / min, pressure 110Pa, to create a stable oxidation environment. According to XRF and X-ray diffraction (XRD) analysis, the purity of magnesium oxide is 99.6%, the total amount of impurities (such as calcium oxide, iron oxide, etc.) is less than 0.3%, and the crystal structure is complete, the crystal form is single, it is a cubic crystal system, and the crystallinity exceeds 95%;

[0047] Step 4, granulation: in the double-roll granulation system, the roller pressure of the double-roll granulation extruder is 9MPa and the roller speed is 9r / min; the cutting knife group rotates at a speed of 220r / min and the knife spacing is 4.5mm; the granulation knife group rotates at a speed of 160r / min and the knife type is a double spiral shape, which enhances the granulation effect. After screening, the 30-50 mesh finished product yield is 90%. The particle fluidity is measured by the Hall flow meter, the flow rate is 25g / s, and the fluidity is good; the repose angle is 31°, indicating that the particles have excellent stability and dispersibility when they are freely stacked. Scanning electron microscopy (SEM) shows that the particles have high sphericity, dense surface, no pores or cracks inside, high mechanical strength, and strong resistance to wear and breakage during transportation and storage.

[0048] Example 3

[0049] The present invention provides a method for granulating magnesium oxide, comprising the following steps:

[0050] Step 1, raw material preparation: Take 800kg of magnesium carbonate with a purity of 98% from the raw material silo, with initial particle size D10=14μm, D50=32μm, D90=52μm, and moisture content of 0.9%;

[0051] Step 2, grinding of magnesium carbonate: the parameters of the air flow mill are set to a speed of 3000r / min, a crushing pressure of 0.7MPa, and a feeding speed of 25kg / h. The particle size is monitored by a laser particle size analyzer every 35 minutes according to the ASTMB822 standard during the grinding process, and the particle morphology is observed by a microscope. Finally, the magnesium carbonate powder D90 reaches 44μm, D50 is 24μm, D10 is 10μm, and the particle size distribution is uniform. Then, the magnesium carbonate powder is passed through an air flow classifier (1000m 3 / h air volume) screening, fine powder recovery rate of 86%, ensuring that the particle size meets the narrow range distribution requirements and avoiding the risk of product performance fluctuations due to uneven particle size;

[0052] Step 3: High temperature calcination: In the tunnel kiln, the temperature is raised from room temperature to 790°C at a rate of 48°C / h (1.6 hours), followed by insulation for 6.2 hours. The air in the kiln contains 21.2% oxygen and has a flow rate of 2.0 m / s. 3 / min, pressure 100Pa, by XRF, XRD and differential scanning calorimeter (DSC) joint analysis, the purity of magnesium oxide is 99.1%, the total content of impurities (such as silicon oxide, aluminum oxide, etc.) is 0.5%, and the phase change process is clear, the thermal effect is stable, the crystal is well developed, and the lattice defects are few;

[0053] Step 4: Granulation: The parameters of the double-roll granulation system are: double-roll granulation extruder roller pressure 8MPa, roller speed 7.5r / min; cutting knife group speed 200r / min, knife spacing 5.2mm; granulation knife group speed 150r / min, knife shape is wavy, giving the particles a unique microstructure. After screening, the 40-60 mesh finished product yield is 84%, and the specific surface area measured by the specific surface area analyzer is 8m2 / g, porosity 35% (measured by mercury intrusion porosimetry), high specific surface area and suitable pore structure provide abundant reaction active sites, improving adsorption and catalytic performance.

[0054] Example 4

[0055] The present invention provides a method for granulating magnesium oxide, comprising the following steps:

[0056] Step 1, raw material preparation: 1500 kg of 98.8% pure magnesium carbonate is placed in the raw material silo, the raw material particle size is D10 = 9 μm, D50 = 24 μm, D90 = 40 μm, and the moisture content is 0.7%;

[0057] Step 2, grinding of magnesium carbonate: The operating parameters of the airflow mill are a speed of 3600r / min, a crushing pressure of 1.0MPa, and a feeding speed of 40kg / h. During the grinding process, the particle size is monitored by a laser particle size analyzer every 20 minutes according to the GB / T19077-2016 standard, and the microscopic morphology of the particles is analyzed by a microscope according to the ISO13322-1 standard. When the grinding is completed, the magnesium carbonate powder D90 reaches 35μm, D50 is 18μm, and D10 is 5μm. The particle size distribution is characterized by a single peak narrow distribution and extremely high uniformity. The airflow classifier (1400m 3 / h air volume) after screening, the fine powder recovery rate is 92%, and the raw material particle size is accurately controlled, laying a foundation for high-quality raw materials for subsequent processes and ensuring highly uniform and stable product performance;

[0058] Step 3: High temperature calcination: The tunnel kiln is heated at 42℃ / h to 755℃ (takes 2 hours), and then kept warm for 8 hours. The oxygen content of the air in the kiln is 20.5% and the flow rate is 1.8m / s. 3 / min, pressure 108Pa, after comprehensive analysis by XRF, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS), the purity of magnesium oxide is 99.7%, the content of impurities (such as boron oxide, titanium oxide, etc.) is extremely low (total 0.25%), the crystal microstructure is perfect, the lattice stripes are clear, the grain boundaries are distinct, there are no dislocation and twin defects, the atomic arrangement is regular and orderly, giving the product excellent physical and chemical properties, and its advantages in the field of high-end functional materials are prominent;

[0059] Step 4: Granulation: The key parameters of the double-roll granulation system are: roller pressure of the double-roll granulation extruder is 9.5MPa, roller speed is 10r / min; the speed of the cutting knife group is 230r / min, and the knife spacing is 4mm; the speed of the granulation knife group is 168r / min, and the knife shape is serrated, which helps to build an ideal particle structure. After screening, the 10-30 mesh finished product has a particle yield of 93%, and the particle density analyzer measures a true density of 3.58g / cm 3 , tap density 1.2g / cm 3The ratio of the two is 2.98, indicating that the particles are densely packed, with low porosity and high strength. The dynamic light scattering particle size analyzer measures the particle size distribution span (SPAN) value of 0.6, and the particle size distribution is concentrated; the Zeta potential measured by the Zeta potential meter is -25mV, with excellent electrostatic stability and good dispersion uniformity.

[0060] Example 5

[0061] The present invention provides a magnesium oxide granulation system, which comprises a raw material silo, an air flow pulverizer, a particle size tester, an air flow classifier, a tunnel kiln and a double-roller horizontal feeding dry granulation system;

[0062] The main body of the raw material silo is constructed of stainless steel, which has good corrosion resistance and sealing properties to prevent the raw materials from being damp or contaminated. Its structure is cylindrical with a conical bottom design, which is conducive to the natural discharge of raw materials by gravity. A sealed feed port is provided on the top of the silo, which can be tightly connected with the raw material conveying equipment; the bottom discharge port is equipped with a manual or electric valve for precise control of the raw material discharge rate; it provides a safe and stable temporary storage space for magnesium carbonate raw materials, ensures the continuity and stability of raw material supply, and effectively buffers the connection fluctuations in time and quantity between raw material procurement and production links. The second is the homogenization effect. With the static storage of the silo, raw materials of different batches and different particle size distributions can be naturally mixed and homogenized to a certain extent, reducing the interference of fluctuations in raw material characteristics on the production process and product quality, and improving the consistency and stability of product quality;

[0063] The particle size tester uses the principle of laser diffraction to carry out the test. The laser beam emitted by the laser penetrates the magnesium carbonate powder sample, and the powder particles cause the laser to scatter. The detector collects the scattered light signal and performs data processing and analysis based on the Mie scattering theory or the Fraunhofer diffraction theory, so as to accurately determine the particle size distribution of the powder. During the test, the sample needs to be evenly dispersed in a suitable dispersion medium (such as air or liquid) to ensure the accuracy and reliability of the test results.

[0064] The airflow classifier achieves material classification and screening by the synergistic effect of the centrifugal force field and the airflow drag. In the classification area, the high-speed rotating rotor generates a strong centrifugal force, which causes the magnesium carbonate powder particles to be classified according to the particle size. The fine particles are carried up by the airflow and discharged as fine powder products because the airflow drag is greater than the centrifugal force; while the coarse particles are subjected to a centrifugal force greater than the airflow drag, and fall along the inner wall of the classifier and return to the crushing or reprocessing stage. By adjusting key parameters such as the rotor speed, airflow speed and air volume, the boundary of the classification particle size can be accurately controlled, and efficient and accurate classification of the magnesium carbonate powder particle size can be achieved;

[0065] The main body of the tunnel kiln is in the form of a long tunnel, and is composed of core parts such as a kiln body, a heating system, a ventilation system, a conveying system, and a temperature control system. The kiln body is built with refractory materials that are resistant to high temperatures and have excellent thermal insulation properties, ensuring that the heat in the kiln is stably and efficiently gathered. The heating system mostly uses gas, oil, or electric heating, among which gas heating is widely used due to its low cost and high heating efficiency. The burners are arranged in an orderly manner on both sides or at the bottom of the kiln body to ensure that the heat is evenly distributed in the kiln space, creating a stable and uniform thermal environment for the calcination of magnesium carbonate. The ventilation system is responsible for regulating the flow rate, flow direction, and atmosphere composition of the airflow in the kiln to ensure the smooth progress of the calcination reaction and the stability of the product quality. The conveying system uses a high-temperature resistant ceramic or metal conveyor belt to convey the material through the kiln body at a constant speed to ensure that the material completes the calcination process under the predetermined time and temperature program;

[0066] The double-roller horizontal feeding dry granulation system comprises a feeding mechanism, a material storage mechanism, a material conveying mechanism, a granulation main body mechanism and a screening mechanism.

[0067] The feeding mechanism is a dust-free feeding station; the magnesium oxide granulation raw materials enter the dust-free feeding station, and the feeding mechanism can effectively prevent foreign matter from entering the system, while reducing dust generation, preventing dust from polluting the environment and materials, thereby improving the cleanliness of the production process;

[0068] The storage mechanism is a transfer silo equipped with a level meter and a stirring paddle to control the ratio of recovered fine powder to newly added granulation raw materials; the raw materials are transported to the transfer silo by the first vacuum feeder, the level meter in the transfer silo can monitor the storage amount of materials in the silo in real time, and the stirring paddle can control the ratio of recovered fine powder to newly added granulation raw materials, so as to facilitate the mixing of the two and ensure the stability of the composition of the granulation raw materials;

[0069] The material conveying mechanism includes a vacuum feeder and a feeding auger, and the vacuum feeder includes a first vacuum feeder, a second vacuum feeder, a third vacuum feeder and a fourth vacuum feeder; after the magnesium oxide granulation raw material enters the dust-free feeding station, it is conveyed to the transfer bin by the first vacuum feeder, and after being mixed with the recovered fine powder in the transfer bin, it is conveyed to the forced feeder by the feeding auger, so as to realize efficient material conveying;

[0070] The main granulation mechanism consists of a forced feeder, a double-roll granulation extruder, a cutting knife group and a granulation knife group. The material in the transfer bin is transported to the forced feeder through a feeding auger, slowly degassed in the forced feeder, and then enters the double-roll granulation extruder to be extruded into sheets. The extruded flake magnesium oxide enters the cutting knife group, is cut into slightly larger particles, and then passes through two parallel granulation knife groups for granulation.

[0071] The screening mechanism is a screening machine, and the prepared particles are transported to the screening machine through the second vacuum feeder for screening. The screening machine is provided with three outlets, wherein the upper one is an outlet for large particle materials, which is connected to the cutting knife group through the third vacuum feeder, and unqualified large particle materials are recovered to the cutting knife group by the third vacuum feeder, and are cut and granulated again; the middle one is a finished product outlet, which is connected to a finished product collection box, and qualified magnesium oxide particles of the required mesh size are collected in the finished product collection box through the finished product outlet; the lower one is a fine powder outlet, which is connected to a transfer bin through the fourth vacuum feeder, and unqualified fine powder is recovered to the transfer bin by the fourth vacuum feeder through the fine powder outlet for reuse, and re-enters the granulation main mechanism after being evenly mixed with the granulation raw materials in proportion.

[0072] The granulation principle of the double-roll horizontal feeding dry granulation system: the magnesium oxide powder raw material enters the dust-free feeding station, is transported to the transfer silo by the first vacuum feeder, mixed with the recycled fine powder, and then transported to the forced feeder through the feeding auger. After degassing, it enters the double-roll granulation extruder and is extruded into sheets. Its principle is mainly to agglomerate the dry material into dense and hard large cakes under pressure, and use the principle of intermolecular force in physics to allow the extruded molecules to freely combine into molecules with appropriate spatial density; the double-roll granulation extruder mainly relies on external pressure to extrude the material through the double rollers into a cake shape, remove the gaps between the materials, and the density between the materials is increased several times, and the strength meets the design requirements;

[0073] After extrusion, the flake magnesium oxide enters the cutting knife group and is cut into slightly larger particles, and then passes through the granulation knife group for granulation. There are two groups of granulation knife groups, which are parallelly distributed below the cutting knife group, and further process the flake magnesium oxide into particles of uniform size;

[0074] Finally, the screening is carried out through the screening mechanism, qualified products are collected, and unqualified materials are recycled and reused. The obtained particles are transported to the screening machine through the second vacuum feeder. The screening machine is provided with three outlets, which are used for the output of large particle materials, finished products and fine powders respectively. The qualified magnesium oxide particles of the required mesh size are collected in the finished product collection box through the finished product outlet; the unqualified large particles are recovered to the cutting knife group by the third vacuum feeder through the large particle material outlet, and are cut and granulated again; the unqualified fine powder is recovered to the transfer silo through the fine powder outlet by the fourth vacuum feeder for reuse, and is mixed with the granulation raw materials in proportion and then re-enters the granulation main body. The whole process forms a closed-loop production, which will not introduce foreign matter, nor generate dust, avoids dust environmental pollution, and at the same time reduces the pollution of the environment and personnel to the materials, and improves the cleanliness. The recycling and reuse of unqualified materials can save resources, improve the particle yield, and thus improve production efficiency.

Claims

1. A method for granulating magnesium oxide, characterized in that: The following steps are involved: Step 1, raw material preparation: using magnesium carbonate as raw material, putting magnesium carbonate into the raw material silo for standby; Step 2, grinding magnesium carbonate: using a jet mill to grind the magnesium carbonate raw material so that the particle size of the magnesium carbonate powder D90 ≤ 50 um; Step 3, high temperature calcination: calcining the ground magnesium carbonate, including heating calcination and heat preservation calcination, the calcination temperature of the whole calcination stage is controlled at 720-850°C, the heating calcination time is more than 1h, and the heat preservation calcination time is 4-10h, to generate magnesium oxide powder; Step 4: Granulation: The generated magnesium oxide powder is then pressed into flakes and crushed into whole particles through a double-roller horizontal feeding dry granulation system to obtain finished magnesium oxide particles.

2. A method for granulating magnesium oxide according to claim 1, characterized in that: The particle size of the magnesium carbonate powder in step 2 is 35-50 um.

3. A method for granulating magnesium oxide according to claim 1, characterized in that: The magnesium carbonate ground in step 2 is tested by a particle size tester, and then the magnesium carbonate powder is graded and screened by an air flow classifier.

4. A method for granulating magnesium oxide according to claim 1, characterized in that: In the step 3, the calcination temperature of the entire calcination stage is controlled to be 750-800°C; the heating calcination time is 1-2h; and the heat preservation calcination time is 4-8h.

5. A system for granulating magnesium oxide, characterized in that: The system is applied to a method for granulating magnesium oxide according to claims 1-4, and the system comprises: Raw material silo, air flow mill, particle size tester, air flow classifier, tunnel kiln and double-roller horizontal conveying dry granulation system.

6. A magnesium oxide granulation system according to claim 5, characterized in that: The bottom discharge port of the raw material silo conveys the raw materials to the feed port of the air flow pulverizer at a preset conveying rate through a conveying device; the magnesium carbonate powder crushed by the air flow pulverizer is conveyed by a pipeline to a particle size tester for real-time particle size detection; the data after the detection is fed back to the control system, and if the particle size does not meet the standard, it returns to the air flow pulverizer for further pulverization; if the particle size meets the requirements, it is conveyed to the air flow classifier; in the air flow classifier, according to the set classification particle size standard, the fine powder is collected and stored as a qualified product, and the coarse powder is returned to the air flow pulverizer through a pipeline for further pulverization; the qualified magnesium carbonate fine powder is then conveyed to the feed end of the tunnel kiln, undergoes temperature rise calcination and heat preservation calcination stages in the tunnel kiln, and is finally converted into magnesium oxide powder and output from the kiln tail discharge port to enter the subsequent granulation process.

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