Preparation process of high-activity metakaolin

Abstract

The invention discloses a high-activity metakaolin preparation process which comprises the following steps: S1, carrying out an oxide content analysis test on coal series kaolin, and controlling the alumina content of the coal series kaolin to be greater than 30%; s2, grinding and screening the coal series kaolinite meeting the standard until the particle size of the coal series kaolinite is 20-60 [mu] m, and preparing the coal series kaolinite into powder; s3, the powder is heated to 150-200 DEG C through a first-stage cyclone preheating cylinder and enters a first-stage suspension calcining kiln, the temperature in the kiln is controlled to be 250-300 DEG C, the powder stays for 5-10 minutes, and free water in the powder is fully removed; s4, the powder is heated to 350-400 DEG C through a second-stage cyclone preheating cylinder and enters a second-stage suspension calcining kiln, the temperature in the kiln is controlled to be 450-500 DEG C, the powder stays for 5-10 minutes, and structural water of the powder is rapidly separated. According to the method, accurate control over the calcining process of the coal series kaolinite is achieved, the quality of the metakaolin is kept stable, the carbon content of the metakaolin is stabilized to be 1.2-2.0%, and the coal series kaolinite can be recycled. The activity index of the calcined kaolin is greater than or equal to 100%, and the requirements of cement products can be well met.

Description

Technical Field

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

[0002] Since kaolin can be converted into metakaolin with poor crystallinity at a certain temperature, it can react with Ca(OH) 2 It reacts with water to generate hydration products similar to cement, and has high pozzolanic activity. Adding it to cement can greatly improve the performance of concrete. The energy consumption and carbon dioxide produced in its preparation process are also much lower than cement clinker, so it has great potential in replacing clinker.

[0003] However, due to the large differences in the composition of coal-based kaolin and the high impurity content, the prepared products have poor uniformity and unstable activity, which has many disadvantages in actual use. Therefore, processing low-grade coal-based kaolin into metakaolin with higher activity and stable and uniform quality is of great significance for the large-scale use of coal-based kaolin in the cement and construction industries.

[0004] Patent CN113045227B discloses a method for activating coal-based kaolin, which involves mixing coal-based kaolin with calcium-containing substances and grinding them for activation and calcination, which can generate substances with gelling activity and improve the overall activity of the product. However, the calcination temperature must reach a maximum of 1150°C, which consumes a lot of energy. Summary of the invention

[0005] In view of the problems of unstable activity, uneven quality, and more impurities in the existing calcination process for treating low-grade coal-based kaolin products, the present invention provides a high-activity metakaolin preparation process with high product activity and stable quality.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A process for preparing high-activity metakaolin comprises the following steps:

[0008] S1. Analyze and test the oxide content of coal-based kaolin to control its alumina content to be greater than 30%;

[0009] S2, grinding and screening the coal-based kaolin that meets the standards to make its particle size between 20 μm and 60 μm to prepare powder;

[0010] S3, the powder is heated to 150-200℃ by the first-level cyclone preheating cylinder, and enters the first-level suspension calcining kiln. The temperature in the kiln is controlled at 250-300℃, and the powder stays for 5-10 minutes to fully remove free water from the powder;

[0011] S4, the powder is heated to 350-400℃ by the secondary cyclone preheating cylinder, and then enters the secondary suspension calcining kiln. The temperature in the kiln is controlled at 450-500℃, and the powder stays for 5-10 minutes to quickly separate its structural water;

[0012] S5, the powder is heated to 650-700℃ by three-stage and four-stage cyclone preheating cylinders, and fed into a three-stage suspension calcining kiln. The temperature in the suspension calcining kiln is controlled at 850-900℃, and the powder residence time is 30-50 minutes, so that the powder is fully dehydroxylated and decarbonized to obtain the material;

[0013] S6. The calcined material enters the five-stage cyclone preheating cylinder with the air flow, and after separation, enters the three-stage suspension cooling cylinder and the two-stage fluidized bed.

[0014] Through the above technical solution, the carbon content of the material after calcination is 1.2%-2.0%.

[0015] Furthermore, in steps 3, 4 and 5, the first, second and third stage suspension calcining kilns use oxygen-enriched air, and the oxygen volume concentration is controlled at 30-35%; the first, second and third stage suspension calcining kilns are provided with four combustion systems.

[0016] Furthermore, the initial material feeding rate in steps 3, 4 and 5 is 10% of the design capacity of the suspension calcining kiln. To ensure that the conditions in the suspension calcining kiln are normal, the feeding amount is gradually increased by 5% / h of the design capacity until it reaches 60% of the design capacity.

[0017] Furthermore, in step 6, the material is cooled to below 400° C. in a primary fluidized bed, and the cooling rate is ≥40° C. / min.

[0018] Furthermore, in step 5, the three-stage suspension kiln is equipped with two combustion systems, and the temperature field in the three-stage suspension calcining kiln is controlled by controlling the number of open burners of the combustion system and the corresponding gas flow rate.

[0019] Furthermore, temperature detectors are provided at the inlet and outlet of the five-stage cyclone preheating cylinder, the inlet and outlet of the three-stage suspension calcining kiln, the burner nozzles of the four combustion systems, the inlet and outlet of the three-stage cyclone cooling cylinder, and the inlet and outlet of the two-stage fluidized bed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention reasonably sets the fineness to ensure that the powder can be fully heated and decomposed in the suspension calcining kiln; optimizes the components of the powder to ensure that its effective ingredients are in a reasonable range, so that highly active metakaolin can be obtained, and its alumina and silica dissolution rates are relatively fast, which is particularly suitable for the cement industry, and the activity index is above 100%.

[0022] 2. The present invention performs graded treatment on the calcination process of coal-based kaolin, which is divided into three stages of calcination: free water removal calcination, structural water removal calcination, and hydroxyl and decarbonization calcination, and preheating treatment is performed before each stage of calcination, thereby achieving precise control of the calcination process of coal-based kaolin.

[0023] 3. Two combustion systems are installed in the three-stage calcining kiln to ensure uniform temperature distribution in the kiln, and oxygen-rich air is introduced to ensure that the material can be fully decarbonized, so that the quality of the obtained kaolin remains stable, and its carbon content is stable at 1.2% to 2.0%, which can better meet the needs of cement products.

[0024] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following is a brief description of the contents expressed in the drawings of this specification:

[0026] Figure 1 It is a production process flow chart of the present invention. DETAILED DESCRIPTION

[0027] 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.

[0028] The coal-based kaolin in the embodiment of the present invention contains SiO 2 :42%~46%,Al 2 O 3 :31%~36%,Fe 2 O 3 :8%~13%, CaO:1%~2.5%, TiO 2 :0.3%~1.4%, MgO:0.5%~1%, K 2 O: 0.5%~2.4%, Na 2 O: 0.3% to 0.75%, C: 9% to 13%.

[0029] Example 1

[0030] The powder is ground to 40μm~47μm, then heated to 200℃ by a first-stage cyclone preheater, and enters a first-stage suspension calcining kiln. The temperature in the kiln is controlled at 300℃, and the powder residence time is 8 minutes to fully remove free water from the powder.

[0031] The powder is then heated to 400°C in a secondary cyclone preheater and enters a secondary suspension calcining kiln. The temperature in the kiln is controlled at 480°C and the powder stays for 8 minutes to quickly separate its structural water.

[0032] The powder is then heated to 700°C by three-stage and four-stage cyclone preheating cylinders and fed into a three-stage suspension calcining kiln. The three-stage suspension kiln's combustion system has an air oxygen volume concentration of 35%, the kiln temperature is controlled at 890°C, and the powder residence time is 40 minutes to dehydroxylate and decarbonize the material.

[0033] The material is then cooled to 400°C through a primary fluidized bed, and then cooled to 48°C through a secondary fluidized bed and a sleeve-type water-cooled screw conveyor to form the final product.

[0034] The carbon content of the calcined coal-based kaolin is 1.87%, the active alumina dissolution rate of the calcined coal-based kaolin is 78.2%, the active silica dissolution rate is 49.3%, and the 28d volcanic ash activity index of the calcined coal-based kaolin is 102%.

[0035] Example 2

[0036] The powder is ground to 30μm~35μm, then heated to 180℃ by a first-stage cyclone preheater, and enters a first-stage suspension calcining kiln. The temperature in the kiln is controlled at 280℃, and the powder residence time is 6 minutes to fully remove free water from the powder.

[0037] The powder is then heated to 400°C in a secondary cyclone preheater and enters a secondary suspension calcining kiln. The temperature in the kiln is controlled at 470°C and the powder stays for 7 minutes to quickly separate its structural water.

[0038] The powder is then heated to 700°C by three-stage and four-stage cyclone preheating cylinders and fed into a three-stage suspension calcining kiln. The three-stage suspension kiln's combustion system has an air oxygen volume concentration of 33%, the kiln temperature is controlled at 880°C, and the powder residence time is 35 minutes to dehydroxylate and decarbonize the material.

[0039] The material is then cooled to 390°C in a primary fluidized bed, and then cooled to 46°C in a secondary fluidized bed and a sleeve-type water-cooled screw conveyor to form the final product.

[0040] The carbon content of the calcined coal-based kaolin is 1.54%, the active alumina dissolution rate of the calcined coal-based kaolin is 79.4%, the active silica dissolution rate is 51%, and the 28d volcanic ash activity index of the calcined coal-based kaolin is 108.1%.

[0041] Example 3

[0042] The powder is ground to 20μm~25μm, then heated to 160℃ by a first-stage cyclone preheater, and enters a first-stage suspension calcining kiln. The temperature in the kiln is controlled at 250℃, and the powder residence time is 5 minutes to fully remove free water from the powder.

[0043] The powder is then heated to 400°C in a secondary cyclone preheater and enters a secondary suspension calcining kiln. The temperature in the kiln is controlled at 450°C and the powder stays for 6 minutes to quickly separate its structural water.

[0044] The powder is then heated to 700°C by three-stage and four-stage cyclone preheating cylinders and fed into a three-stage suspension calcining kiln. The air oxygen volume concentration of the three-stage suspension kiln's combustion system is 31%, the temperature in the kiln is controlled at 870°C, and the powder residence time is 35 minutes to dehydroxylate and decarbonize the material.

[0045] The material is then cooled to 380°C in a primary fluidized bed, and then cooled to 43°C in a secondary fluidized bed and a sleeve-type water-cooled screw conveyor to form the final product.

[0046] The carbon content of the calcined coal-based kaolin is 1.56%, the active alumina dissolution rate of the calcined coal-based kaolin is 77.9%, the active silica dissolution rate is 48.5%, and the 28d volcanic ash activity index of the calcined coal-based kaolin is 101.7%.

[0047] It can be seen from the above Examples 1 to 3 that when the raw material components meet the requirements, the temperature and time of each calcination stage are adjusted according to the powder particle size, and the prepared metakaolin mineral has a high dissolution rate and a volcanic ash activity index of >100%, indicating that the method can effectively improve the activity of metakaolin. The carbon content of the prepared metakaolin mineral can be stably controlled at 1.2% to 2.0% by adjusting the decarbonization calcination gas atmosphere according to the powder particle size, thereby improving the stability and uniformity of the metakaolin quality.

[0048] 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 process for preparing high-activity metakaolin, characterized in that: The following steps are involved: S1. Analyze and test the oxide content of coal-based kaolin to control its alumina content to be greater than 30%; S2, grinding and screening the coal-based kaolin that meets the standards to make its particle size between 20 μm and 60 μm to prepare powder; S3, the powder is heated to 150-200℃ by the first-level cyclone preheating cylinder, and enters the first-level suspension calcining kiln. The temperature in the kiln is controlled at 250-300℃, and the powder stays for 5-10 minutes to fully remove free water from the powder; S4, the powder is heated to 350-400℃ by the secondary cyclone preheating cylinder, and then enters the secondary suspension calcining kiln. The temperature in the kiln is controlled at 450-500℃, and the powder stays for 5-10 minutes to quickly separate its structural water; S5, the powder is heated to 650-700℃ by three-stage and four-stage cyclone preheating cylinders, and fed into a three-stage suspension calcining kiln. The temperature in the suspension calcining kiln is controlled at 850-900℃, and the powder residence time is 30-50 minutes, so that the powder is fully dehydroxylated and decarbonized to obtain the material; S6. The calcined material enters the five-stage cyclone preheating cylinder with the air flow, and after separation, enters the three-stage suspension cooling cylinder and the two-stage fluidized bed.

2. A process for preparing high-activity metakaolin according to claim 1, characterized in that: In the steps 3, 4 and 5, the first, second and third stage suspension calcining kilns use oxygen-enriched air, and the oxygen volume concentration is controlled at 30-35%; the first, second and third stage suspension calcining kilns are provided with four combustion systems.

3. A process for preparing high-activity metakaolin according to claim 1, characterized in that: The initial material feeding speed in steps 3, 4 and 5 is 10% of the design capacity of the suspension calcining kiln. To ensure that the conditions in the suspension calcining kiln are normal, the feeding amount is gradually increased by 5% / h of the design capacity until it reaches 60% of the design capacity.

4. A process for preparing high-activity metakaolin according to claim 1, characterized in that: In step 6, the material is cooled to below 400° C. in a primary fluidized bed, with a cooling rate of ≥40° C. / min.

5. The process for preparing high-activity metakaolin according to claim 1, characterized in that: In step 5, the three-stage suspension kiln is equipped with two combustion systems, and the temperature field in the three-stage suspension calcining kiln is controlled by controlling the number of open burners of the combustion system burners and the corresponding gas flow rate.

6. A process for preparing high-activity metakaolin according to claims 1 and 2, characterized in that: Temperature detectors are provided at the inlet and outlet of the five-stage cyclone preheating cylinder, the inlet and outlet of the three-stage suspension calcining kiln, the burner nozzles of the four combustion systems, the inlet and outlet of the three-stage cyclone cooling cylinder, and the inlet and outlet of the two-stage fluidized bed.

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