Production process of color-controllable high-activity metakaolin

Abstract

The invention discloses a production process of color-controllable high-activity metakaolin, which comprises the following steps: crushing kaolin, pulverizing, carrying out magnetic separation to obtain first powder, mixing the first powder with a certain proportion of an iron removal regulator to obtain second powder, and carrying out five-stage cyclone preheating, suspension calcination, three-stage suspension cooling and two-stage fluidized bed treatment to obtain the color-controllable high-activity metakaolin. Further cooling by a sleeve type water-cooling screw conveyor to obtain a finished product of high-activity metakaolin; according to the method, the problem of dispersion of high-humidity raw materials at a high temperature is solved through a multi-stage preheating process and accurate regulation and control of the calcining temperature, efficient activation of kaolin with different activities is realized, and meanwhile, the controllability of the color of a metakaolin finished product is realized by combining cooperation of a multi-step iron removal process and accurate control of a reducing atmosphere; the popularization and application of the metakaolin in various scenes of the building industry are facilitated.

Description

Technical Field

[0001] The invention belongs to the field of metakaolin preparation technology, and more specifically, relates to a color-controllable high-activity metakaolin production technology. Background Art

[0002] my country is rich in kaolin resources, which are clay and clay rock mainly composed of kaolinite clay minerals, mainly white in color. Kaolin has a layered silicate structure, with layers bonded by van der Waals bonds. After high-temperature treatment, the layered structure is destroyed due to dehydration, forming metakaolin with low crystallinity. Since the molecular arrangement of metakaolin is less regular and in a thermodynamic metastable state, it has gelling properties under alkaline excitation and can replace part of the cement as a mineral admixture for the preparation of cement-based materials. In addition, it will also undergo a secondary hydration reaction with calcium carbonate to improve the hardening properties of cement-based materials. It is a mineral admixture with great potential. At the same time, since the CO2 emissions during the preparation of metakaolin are lower than those of clinker, it has great advantages in carbon emission reduction in the cement industry.

[0003] At present, the production methods of metakaolin include fixed bed type (such as tunnel kiln, downdraft kiln, shuttle kiln, push plate kiln and insulation tube), semi-fixed bed type (such as vertical kiln, rotary kiln and multi-layer open hearth), fluidized bed type, etc. Among them, the use of rotary kiln to calcine and activate kaolin is a commonly used method, but when calcining and activating kaolin, the kiln has problems such as high heat consumption, easy overburning and deactivation, and difficult product quality control. Therefore, it is necessary to develop a kaolin activation process with low energy consumption, adaptability to different kaolin mines / tailings, and controllable activity, so as to achieve efficient utilization in cement-based materials.

[0004] In addition, due to the complex composition of kaolin raw materials, it usually contains a certain amount of iron, mainly in the form of goethite, hematite and siderite. Kaolin undergoes oxidation reaction during the calcination process, and the iron phase usually exists in the form of red hematite. When the iron (Fe2O3) content in the kaolin raw material exceeds a certain range, the calcined metakaolin product prepared will show different colors, depending on the existence form of the iron phase in the finished product, among which hematite (Fe2O3) is reddish brown, and magnetite (Fe3O4) and siderite (FeO) are gray-black. When red or pink metakaolin is added to cement, it will be mistaken for inferior material, limiting the large-scale use of metakaolin in the concrete and cement industries. However, some other industries do not have strict requirements on the color of metakaolin. In the existing technology, it is generally achieved by creating a reducing atmosphere during the preparation of metakaolin to reduce Fe 3+ Reduction to Fe 2+ , reduce Fe in kaolin products 3+ concentration to meet the requirements of the cement concrete industry.

[0005] Publication No. CN 111847468 A discloses a method for producing high-whiteness calcined kaolin by multi-stage suspended calcination of coal-based kaolin. The method adopts a "segmented precise control" calcination method to perform segmented treatment on the "dehydration-dehydroxylation-decarbonization" process of the coal-based kaolin, which effectively solves the problem that during the calcination of coal-based kaolin, the partial pressure of oxygen in the system is reduced due to the discharge of water, resulting in incomplete combustion of organic matter, causing carbon deposition in the sample and decreased whiteness, and finally obtains high-whiteness calcined kaolin.

[0006] Publication No. CN112939002A discloses a flexibly adjustable high-activity metakaolin preparation system and preparation method, which controls the color of the metakaolin product by circulating the air in the cooling system after heat exchange in the suspension calcination system. However, no accurate system atmosphere control parameters are proposed.

[0007] Publication No. CN105642433B discloses a decarbonization process for coal-based kaolin, and proposes to utilize crushing, grading, re-selection, crushing of intermediate density products of re-selection, or grinding and flotation operations to remove and recover carbon impurities in coal-based kaolin, and ultimately obtain kaolin with higher purity and whiter color. However, there are problems such as complex process, low efficiency, and poor product quality.

[0008] Publication No. CN113883898A discloses a suspension calcination device and process suitable for high-iron content kaolin raw materials, including a first cyclone separator, an oxidation furnace, a second cyclone separator and a calcination furnace system. The calcination furnace system includes a preheating furnace and a modification furnace. By reasonably controlling the amount of combustion air and fuel entering the calcination furnace system, the fuel in the calcination furnace system is incompletely burned to form a reducing atmosphere, thereby making the calcination furnace system an oxygen-poor combustion zone, thereby reducing the Fe in the raw materials. 3+ Reduction to Fe 2+ , and finally exists in the form of magnetite, making the finished kaolin appear gray-black. However, the system only has a primary preheating furnace, which cannot achieve accurate zoning calcination of kaolin with different activities.

[0009] Publication No. CN117469971A discloses a clay calcination color control system, including a suspended calcination subsystem and a rotary cooling subsystem, wherein the rotary cooling subsystem includes a rotatable cooler, and the cooler is provided with a first water spraying device at least at the inlet or outlet of the material, for spraying cooling water, so that the cooling water vaporizes to generate water vapor and fills the inlet or outlet, isolates the air exchange inside and outside the cooler, and prevents the clay material from being oxidized and discolored during the cooling process, so as to achieve color control of the finished clay. This patent regulates the color of the high-temperature territories in the cooling stage, but the oxidation reaction has already occurred in the calcination stage. Even if an atmosphere with a low O2 content is used in the rapid cooling process, it is difficult to achieve color control of the finished product.

[0010] The calcination temperature, calcination atmosphere, residence time and finished product cooling system in the suspension kiln are all process parameters that must be strictly controlled in the preparation process of kaolin. According to the kaolin raw materials with different components, a kaolin production process is provided which fully considers the requirements of different application fields on the appearance and reaction activity of the finished product, while taking into account low energy consumption and stable product quality. It has important practical significance for the large-scale promotion of its application. Summary of the invention

[0011] The invention provides a color-controllable high-activity metakaolin production process to solve the problems of high heat consumption, easy overburning and deactivation, and difficult product quality control when calcining activated kaolin.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A color-controllable high-activity metakaolin production process comprises the following steps:

[0014] S1, crushing kaolin to a particle size of ≤15 mm, and grinding to form a first powder with a fineness of 80 μm sieve residue ≤15%;

[0015] S2, sent to the silo by a lifting belt conveyor equipped with an electromagnetic iron removal device;

[0016] S3, the first powder after iron removal and the iron removal regulator are mixed into a second powder, which is sent to the first-stage cyclone preheating cylinder, dispersed and suspended in the airflow under the action of the airflow to achieve preheating, and then sent to the second-stage cyclone preheating cylinder from the bottom discharge port, and heat exchange is completed in the same way through the third-stage, fourth-stage, and fifth-stage cyclone preheating cylinders and their connecting pipes;

[0017] S4, the preheated second powder enters the suspension calcining kiln in the suspension calcining system through the discharge port of the fifth stage cyclone preheating cylinder, and the excess air coefficient in the suspension calcining kiln is controlled to be less than 1.0 by controlling the air intake, and the temperature field in the suspension calcining kiln is stable in the range of 500-1100° C., thereby preparing a mixture A;

[0018] S5, the calcined mixture A enters the secondary fluidized bed and the tertiary cyclone cooling cylinder to achieve sufficient cooling and step-by-step separation;

[0019] S6. After the mixture A is cooled in step S5, it is further cooled by a sleeve-type water-cooled screw conveyor and then sent to a finished product warehouse for storage and packaging.

[0020] Through the above technical solution: controlling the oxygen content in the atmosphere in the cooling cylinder to less than 1.0%, a gray-black finished product can be obtained; when a reducing atmosphere is not used, the O2 content at the outlet of the cyclone cooling system should be controlled at 3% to 5%, and the finished product will show different degrees of pink.

[0021] Furthermore, in step S4, the excess air coefficient in the suspension calcining kiln is 0.5 to 1.0.

[0022] Furthermore, in step S3, the internal temperature of each level of cyclone preheating cylinder is controlled by adjusting the air intake volume. The outlet temperatures of the first, second, third, fourth and fifth level preheating cylinders are 50-150°C, 150-250°C, 250-350°C, 350-450°C and 450-550°C respectively, and the residence time of the material in the five-level cyclone preheating cylinder is 5-15 minutes. The O2 content at the outlet of the five-level preheating system is controlled at above 3.5%, and the CO content is controlled below 0.5%.

[0023] Furthermore, in step S5, the outlet temperature of the first-stage cyclone cooling cylinder is controlled at 400-500°C, the outlet temperature of the second-stage cyclone cooling cylinder is controlled at 300-400°C, and the outlet temperature of the third-stage cyclone cooling cylinder is controlled at 100-300°C. The residence time of the material in each stage of the cyclone cooling cylinder is 5-15 minutes respectively.

[0024] Furthermore, the iron removal regulator in step S3 is preferably one or more of NaCl, NH4Cl, and CaCl2, and its mass is 0% to 10% of the mass of the first powder after iron removal.

[0025] Furthermore, the second powder feeding amount in step S3 should be less than 60% of the volume of the preheating cylinder, and the interval between the two feedings should be controlled at 10 to 20 minutes.

[0026] Furthermore, the fuel gas used in the suspension calcining kiln in step S4 is natural gas, and the material stays in the suspension calcining kiln for 30 to 240 minutes.

[0027] Furthermore, in step S4, when the air intake of the suspension calcination system is insufficient, the fluidized bed system is started, and the negative pressure in the fluidized bed system is controlled to be -500 to -700 Pa by adjusting the opening of the air inlet valve. The high-temperature powder flows out from the first, second, third, fourth, and fifth preheaters and gathers in the two-stage fluidized beds. The high-temperature powder gathered in the fluidized bed is fluidized and cooled in the fluidized bed. The variable frequency fan supplies cold air to effectively cool the powder on the fluidized bed. After cooling, the powder returns to the feeding system through the standby conveying system, and can re-enter the suspension kiln for calcination after the suspension calcination system is stabilized.

[0028] Furthermore, in step S5, a reducing atmosphere is formed in the first-stage and second-stage cyclone cooling cylinders, and the reducing gas includes one or more of dry nitrogen, decomposed ammonia, hydrogen, carbon monoxide, formic acid and nitrogen and hydrogen.

[0029] Furthermore, the flue gas formed by the incomplete combustion of the fuel and the decomposition of the second powder in the suspension calcination system carries the decomposed solid materials out of the suspension calcination kiln system and enters the fifth-stage cyclone preheating cylinder, the fourth-stage cyclone preheating cylinder, the third-stage cyclone preheating cylinder, the second-stage cyclone preheating cylinder and the first-stage cyclone preheating cylinder in sequence for gas-solid separation. The separated flue gas then enters the suspension calcination kiln, where the unburned fuel in the flue gas is fully burned, and the separated materials enter the cyclone cooling system.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) A five-stage cyclone preheating system is set up to achieve precise temperature control in stages for different active kaolin raw materials, maximize the activity of the kaolin finished product, and effectively avoid the agglomeration problem caused by rapid temperature rise during the calcination process;

[0032] (2) The core calcination process uses a suspended calcination kiln, which utilizes heat recovery in the kiln to reduce the heat load of the suspended kiln, reduce the unit heat consumption of the finished product, and improve the thermal efficiency of the overall equipment;

[0033] (3) A two-stage fluidized bed system is set up after the suspension calcination system to avoid material collapse and achieve stable production operation;

[0034] (4) Before the raw materials enter the calcination system, a magnetic separation iron removal process is added to adjust the iron content of the raw materials. At the same time, the raw materials are mixed with an iron removal regulator to adjust the iron content during the calcination process. In addition, a reducing atmosphere is introduced during the cyclone cooling stage to achieve color control of the finished product through multi-step coordination and multi-parameter control.

[0035] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The following is a brief description of the contents expressed in each of the drawings in this specification:

[0037] Figure 1 These are product pictures of Examples 1-5 of the present invention.

[0038] Figure 2 It is a production process flow chart of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0040] The kaolin used in the embodiments of the present invention comes from Guangxi Beihai kaolin tailings K1 and Suzhou Yangshan kaolin tailings K2, the 80um sieve residue of K1 is 3.6%, and the 80um sieve residue of K2 is 3.1%. The main chemical compositions of the two kaolin raw materials are listed in Table 1 by weight percentage.

[0041] Table 1 Chemical composition of kaolin tailings (%)

[0042] Kaolin tailings CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[TiO2]]> <![CDATA[Na2O]]> Loss K1 0.9 52.2 34.73 6.35 2.57 0.21 0.18 15.24 K2 1.15 48.25 43.25 2.31 1.69 0.18 0.21 17.05

[0043] Example 1

[0044] K1 kaolin tailings were used to produce high-activity metakaolin. The temperature in the suspension calcination kiln was controlled at 650-700°C, and the calcination time was 90 min. The outlet temperatures of the first, second, third, fourth and fifth preheating cylinders were controlled at (100±10)°C, (200±10)°C, (300±10)°C, (400±10)°C, and (500±10)°C, respectively. The material residence time in the kiln was 10 min. By adjusting the gas flow rate, the O2 content at the outlet of each level of preheating system was controlled at (5±0.5 )%, CO content is controlled below <0.4%; the outlet temperature of the first-stage cyclone cooling cylinder is controlled at (450±10)℃; the outlet temperature of the second-stage cyclone cooling cylinder is controlled at (350±10)℃, and the outlet temperature of the third-stage cyclone cooling cylinder is controlled at (200±10)℃; the residence time of the material in each level of cyclone cooling system is 10min respectively; the outlet O2 content of the three-stage cyclone cooling system is controlled at 4%; finally, it is further cooled to (60±10)℃ by a sleeve-type water-cooled screw conveyor and then sent to the finished product warehouse and bagged.

[0045] The finished metakaolin obtained is pink, with a 45um sieve residue of 3.4% and a specific surface area of ​​3.54m 2 / g, referring to the standard "Mineral admixtures for high-strength and high-performance concrete" GB / T18736, replacing 30% cement clinker, the 28d activity index detected was 67.6%.

[0046] Example 2

[0047] K1 kaolin tailings were used to produce high-activity metakaolin. The temperature in the suspension calcination kiln was controlled at 750-800°C, and the calcination time was 90 minutes. The internal temperatures of the first, second, third, fourth and fifth preheating tubes were controlled at (100±10)°C, (200±10)°C, (300±10)°C, (400±10)°C, (500±10)°C, respectively, and the material residence time in the kiln was 10 minutes. By adjusting the gas flow rate, the O2 content at the outlet of each level of preheating system was controlled at (5±0.5 )%, CO content is controlled below <0.4%; the outlet temperature of the first-stage cyclone cooling cylinder is controlled at (450±10)℃; the outlet temperature of the second-stage cyclone cooling cylinder is controlled at (350±10)℃, and the outlet temperature of the third-stage cyclone cooling cylinder is controlled at (200±10)℃; the residence time of the material in each level of cyclone cooling system is 10min respectively; the outlet O2 content of the three-stage cyclone cooling system is controlled at 4%; finally, it is further cooled to (60±10)℃ by a sleeve-type water-cooled screw conveyor and then sent to the finished product warehouse and bagged.

[0048] The finished metakaolin obtained is pink, with a 45um sieve residue of 2.6% and a specific surface area of ​​4.23m 2 / g, referring to the standard "Mineral admixtures for high-strength and high-performance concrete" GB / T18736, replacing 30% of cement clinker, the 28d activity index obtained by detection is 71.2%.

[0049] Example 3

[0050] K1 kaolin tailings are used to produce high-activity metakaolin. The temperature in the suspended calcination kiln is controlled at 650-700°C, and the calcination time is 90 minutes. The outlet temperatures of the first, second, third, fourth and fifth preheating cylinders are controlled at (100±10)°C, (200±10)°C, (300±10)°C, (400±10)°C, (500±10)°C, respectively, and the material stays in the kiln for 10 minutes. By adjusting the gas flow rate, the O2 content at the outlet of each level of preheating system is controlled at (5±0.5)%, and the CO content is controlled at (5±0.5)%. The temperature of the first-stage cyclone cooling cylinder outlet is controlled at (450±10)℃; the temperature of the second-stage cyclone cooling cylinder outlet is controlled at (350±10)℃, and the temperature of the third-stage cyclone cooling cylinder outlet is controlled at (200±10)℃; the material stays in each cyclone cooling system for 10 minutes; N2 is introduced into the cyclone cooling system to form a reducing atmosphere in the cylinder, and the O2 content is controlled at 0.8%; finally, it is further cooled to (60±10)℃ by a sleeve-type water-cooled screw conveyor and then sent to the finished product warehouse and bagged. The finished metakaolin is gray-green, with a 45μm sieve residue of 2.4% and a specific surface area of ​​4.14m 2 / g, referring to the standard "Mineral admixtures for high-strength and high-performance concrete" GB / T18736, replacing 30% of cement clinker, the 28d activity index obtained by detection is 70.7%.

[0051] Example 4

[0052] K1 kaolin tailings are used to produce high-activity metakaolin, and the mass ratio of iron removal regulator to kaolin is 2.0%; the temperature in the suspension calcination kiln is controlled at 650-700°C, and the calcination time is 90min; the outlet temperatures of the first, second, third, fourth and fifth preheating cylinders are controlled at (100±10)°C, (200±10)°C, (300±10)°C, (400±10)°C, (500±10)°C, respectively, and the material stays in the kiln for 10min. By adjusting the gas flow rate, the O2 content at the outlet of each level of preheating system is controlled at (5±0 .5)%, CO content is controlled below <0.4%; the outlet temperature of the first stage cyclone cooling cylinder is controlled at (450±10)℃; the outlet temperature of the second stage cyclone cooling cylinder is controlled at (350±10)℃, and the outlet temperature of the third stage cyclone cooling cylinder is controlled at (200±10)℃; the residence time of the material in each stage of cyclone cooling system is 10min respectively; N2 is introduced into the cyclone cooling system to form a reducing atmosphere in the cylinder, and the O2 content is controlled at 0.8%; finally, it is further cooled to (60±10)℃ by a sleeve-type water-cooled screw conveyor and then sent to the finished product warehouse and bagged. The finished metakaolin is white, with a 45μm sieve residue of 2.1% and a specific surface area of ​​4.08m 2 / g, referring to the standard "Mineral admixtures for high-strength and high-performance concrete" GB / T18736, replacing 30% cement clinker, the 28d activity index obtained by detection is 67.2%.

[0053] Example 5

[0054] K2 kaolin tailings are used to produce high-activity metakaolin; the temperature in the suspension calcination kiln is controlled at 650-700℃, and the calcination time is 60min; the outlet temperatures of the first, second, third, fourth and fifth preheating cylinders are controlled at (100±10)℃, (200±10)℃, (300±10)℃, (400±10)℃, (500±10)℃, respectively, and the material stays in the kiln for 10min. By adjusting the gas flow rate, the O2 content at the outlet of each level of preheating system is controlled at (5±0.5 )%, CO content is controlled below 0.4%; the outlet temperature of the first stage cyclone cooling cylinder is controlled at (450±10)℃; the outlet temperature of the second stage cyclone cooling cylinder is controlled at (350±10)℃, and the outlet temperature of the third stage cyclone cooling cylinder is controlled at (200±10)℃; the residence time of the material in each stage cyclone cooling system is 10min respectively; the outlet O2 content of the three-stage cyclone cooling system is controlled at 4%; finally, it is further cooled to (60±10)℃ by a sleeve-type water-cooled screw conveyor and then sent to the finished product warehouse and bagged. The finished metakaolin is pink, with a 45μm sieve residue of 3.2% and a specific surface area of ​​8.38m 2 / g, referring to the standard "Mineral admixtures for high-strength and high-performance concrete" GB / T18736, replacing 30% of cement clinker, the 28d activity index obtained by detection is 72.3%.

[0055] For the convenience of comparison, the properties of the metakaolin produced in each embodiment are listed in Table 2.

[0056] Table 2 Properties of the metakaolin produced in each embodiment

[0057]

[0058]

[0059] There is a difference in the activity index of the high-end products obtained by the process parameters of Example 1 and Example 2. When the calcination temperature is in the range of 750-800°C, the activity index is higher, but the color of the finished product is pink. Comparing Example 1 and Example 5, the process parameters are the same, but the activity index of Example 5 is higher than that of Example 1. This is because the kaolin content in the kaolin raw material used in Example 5 is higher and the crystallinity is relatively low. Therefore, at the same calcination temperature, its activity index is higher. Comparing Example 1, Example 3 and Example 4, all are carried out at the same preheating temperature and calcination temperature, but compared with Example 1, Example 3 uses a reducing atmosphere in the calcination kiln and the cooling rate in the cyclone cooling system is faster, resulting in Fe 3+ Reduced to Fe 2+, so that the finished product is gray-black; relative to Example 3, Example 4 further adds an iron removal regulator to the raw material of the kaolin tailings, generates highly volatile gaseous volatiles of FeCl3 in the preheating stage, and discharges the iron element with the waste gas, reducing the influence of iron on the color of the finished product during the subsequent calcination process, and finally still maintaining the original white color of the kaolin. In addition, compared with Example 1 and Example 4, since Example 4 further removes iron by adding an iron removal regulator, the color requirements are met, but the activity of the finished product is slightly reduced, it is necessary to make trade-offs according to the application requirements, and then adjust the specific process flow and parameters.

[0060] Therefore, the color-controllable high-activity kaolin production process proposed in the present invention can not only adjust the process parameters according to the performance of the raw materials to obtain a high-activity finished product, but also combine the synergistic effects of magnetic separation, regulators and reducing atmosphere to regulate the color of the finished product to meet the needs of different application scenarios.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0062] Working principle and method

[0063] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A color-controllable high-activity metakaolin production process, characterized in that: The following steps are involved: S1, crushing kaolin to a particle size of ≤15 mm, and grinding to form a first powder with a fineness of 80 μm sieve residue ≤15%; S2, sent to the silo by a lifting belt conveyor equipped with an electromagnetic iron removal device; S3, the first powder after iron removal and the iron removal regulator are mixed into a second powder, which is sent to the first-stage cyclone preheating cylinder, dispersed and suspended in the airflow under the action of the airflow to achieve preheating, and then sent to the second-stage cyclone preheating cylinder from the bottom discharge port, and heat exchange is completed in the same way through the third-stage, fourth-stage, and fifth-stage cyclone preheating cylinders and their connecting pipes; S4, the preheated second powder enters the suspension calcining kiln in the suspension calcining system through the discharge port of the fifth stage cyclone preheating cylinder, and the excess air coefficient in the suspension calcining kiln is controlled to be less than 1.0 by controlling the air intake, and the temperature field in the suspension calcining kiln is stable in the range of 500-1100° C., thereby preparing a mixture A; S5, the calcined mixture A enters the secondary fluidized bed and the tertiary cyclone cooling cylinder to achieve sufficient cooling and step-by-step separation; S6. After the mixture A is cooled in step S5, it is further cooled by a sleeve-type water-cooled screw conveyor and then sent to a finished product warehouse for storage and packaging.

2. The color-controllable high-activity metakaolin production process according to claim 1, characterized in that: In the step S4, the excess air coefficient in the suspension calcining kiln is 0.5 to 1.

0.

3. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that In step S3, the internal temperature of each level of cyclone preheating cylinder is controlled by adjusting the air intake volume. The outlet temperatures of the first, second, third, fourth and fifth level preheating cylinders are 50-150°C, 150-250°C, 250-350°C, 350-450°C and 450-550°C respectively. The residence time of the material in the five-level cyclone preheating cylinder is 5-15 minutes. The O2 content at the outlet of the five-level preheating system is controlled to be above 3.5%, and the CO content is controlled to be below 0.5%.

4. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that: In the step S5, the outlet temperature of the first-stage cyclone cooling cylinder is controlled at 400-500°C, the outlet temperature of the second-stage cyclone cooling cylinder is controlled at 300-400°C, and the outlet temperature of the third-stage cyclone cooling cylinder is controlled at 100-300°C. The residence time of the material in each stage of the cyclone cooling cylinder is 5-15 minutes respectively.

5. The color-controllable high-activity metakaolin production process according to claim 1, characterized in that: The iron removal regulator in step S3 is preferably one or more of NaCl, NH4Cl, and CaCl2, and its mass is 0% to 10% of the mass of the first powder after iron removal.

6. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that The second powder feeding amount in step S3 should be less than 60% of the volume of the preheating cylinder, and the interval between the two feedings should be controlled within 10 to 20 minutes.

7. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that The fuel gas used in the suspension calcining kiln in step S4 is natural gas, and the material stays in the suspension calcining kiln for 30 to 240 minutes.

8. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that: In the step S4, when the air intake of the suspension calcining system is insufficient, the fluidized bed system is started, and the negative pressure in the fluidized bed system is controlled to be -500 to -700 Pa by adjusting the opening of the air inlet valve. The high-temperature powder flows out from the primary, secondary, tertiary, quaternary and fifth-stage preheaters and gathers in the two-stage fluidized beds. The high-temperature powder gathered in the fluidized bed is fluidized and cooled in the fluidized bed. The variable frequency fan supplies cold air to effectively cool the powder on the fluidized bed. After cooling, the powder returns to the feeding system through the standby conveying system, and can re-enter the suspension kiln for calcination after the suspension calcining system is stable.

9. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that: In step S5, a reducing atmosphere is formed in the first-stage and second-stage cyclone cooling cylinders, and the reducing gas includes one or more of dry nitrogen, decomposed ammonia, hydrogen, carbon monoxide, formic acid and nitrogen and hydrogen.

10. The process for producing color-controllable high-activity metakaolin according to claim 1, characterized in that: The flue gas formed by the incomplete combustion of the fuel and the decomposition of the second powder in the suspension calcining kiln system carries the decomposed solid materials out of the suspension calcining kiln system and enters the fifth-stage cyclone preheating cylinder, the fourth-stage cyclone preheating cylinder, the third-stage cyclone preheating cylinder, the second-stage cyclone preheating cylinder and the first-stage cyclone preheating cylinder in sequence for gas-solid separation. The separated flue gas then enters the suspension calcining kiln, where the unburned fuel in the flue gas is fully burned, and the separated materials enter the cyclone cooling system.

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