A two-stage preparation process for water-retaining ceramsite from coal gangue

Abstract

This application relates to the field of ceramsite, and specifically discloses a preparation process for two-stage water-retaining ceramsite from coal gangue. The preparation process includes green pellet preparation, drying section, pyrolysis section, decarbonization section, first roasting section, soaking section, second roasting section, and cooling section; the green pellet preparation includes: wetting coal gangue powder with an organic solution, stirring evenly, and kneading with biomass material. The mass ratio of coal gangue powder to biomass material is 1 kg:(3-9) g to obtain green pellets; the soaking section includes: transferring the green pellets after the first roasting section to the soaking section, with the material layer temperature below 900 °C, and evenly spraying nano-silica during the transfer process, spraying 1-2.5 g per 100 g of green pellets; the cooling section includes: using one of sodium bicarbonate solution, ammonium bicarbonate, and ammonia water to form a water mist mixed with air to cool the roasted ceramsite. The prepared ceramsite has a rich and gradient pore structure, can quickly absorb water, and has excellent water-retaining performance.

Description

Technical Field

[0001] This application relates to the field of ceramsite, and more specifically, it relates to a preparation process for two-stage coal gangue water-retaining ceramsite. Background Art

[0002] Coal gangue is a solid waste discharged during coal mining and washing. It is characterized by low calorific value and cannot be used as boiler fuel. For a long time, coal gangue has mainly been stockpiled, which not only occupies a large amount of land resources, but also produces a large amount of sulfur dioxide, carbon dioxide and dust during the spontaneous combustion of coal gangue, polluting the local environment. Currently, producing ceramsite is an important way to recycle coal gangue.

[0003] The current mainstream processes for preparing ceramsite from coal gangue include the rotary kiln process and the sintering process. The rotary kiln process is a dynamic sintering process with the characteristics of low production capacity and high energy consumption. The green balls roll in the rotary kiln to complete drying, pyrolysis, decarbonization, and after cooling, the products are produced through screening. Currently, the maximum single-line processing capacity of the rotary kiln process is about 500,000 tons / year. The sintering machine process is a static sintering process, including the belt-type sintering machine process and the ring-type sintering machine process. The sintering machine process has a large processing capacity, and the single-unit processing capacity can reach 5 million tons / year. This process has the advantage of large processing capacity, but the defects are also very obvious. A large amount of volatile matter released by coal gangue in the pyrolysis section accumulates in the material layer until deflagration occurs. The heat generated by combustion is easily accumulated in the material layer, and the temperature of the material layer continues to rise. When the temperature of the material layer reaches 1000 - 1200 °C, a liquid phase forms on the surface of the green balls, blocking the fine pores on the surface of the green balls and also hindering the oxidation reaction between oxygen and carbon inside the green balls. The decarbonization of coal gangue is incomplete, resulting in black cores. At the same time, the formed ceramsite with a liquid phase adheres and agglomerates to affect the normal production operation, and the unqualified rate of ceramsite is high. Summary of the Invention

[0004] To solve the above technical problems, this application provides a preparation process for two-stage coal gangue water-retaining ceramsite.

[0005] The preparation process for two-stage coal gangue water-retaining ceramsite provided by this application adopts the following technical solutions:

[0006] A preparation process for two-stage coal gangue water-retaining ceramsite, the preparation process includes green ball preparation, drying section, pyrolysis section, decarbonization section, roasting section 1, soaking section, roasting section 2, and cooling section; the thickness of the material layer in the decarbonization section is 200 - 800 mm; the thickness of the material layer in the soaking section is 300 - 600 mm;

[0007] The green pellet preparation includes: wetting the coal gangue powder with an organic solution, stirring evenly, and kneading it with the biomass material. The mass ratio of the coal gangue powder to the biomass material is 1 kg:(3 - 9) g to obtain green pellets. The particle size distribution of the biomass material is as follows: the proportion of particles with a particle size of 80 - 120 μm is 20 - 30%, the proportion of particles with a particle size of 10 - 80 μm is 30 - 50%, and the balance is particles with a particle size less than 10 μm.

[0008] The soaking section includes: transporting the green pellets after the first stage of roasting to the soaking section, where the temperature of the material layer is lower than 900 °C, and evenly spraying nano-silica during the transportation, with 1 - 2.5 g of nano-silica sprayed per 100 g of green pellets.

[0009] The cooling section includes: using one of sodium bicarbonate solution, ammonium bicarbonate, and ammonia water to form a water mist mixed with air to cool the calcined ceramsite.

[0010] By adopting the above technical solutions, in the green pellet preparation process, the biomass material with a specific particle size distribution is combined with the coal gangue powder. The biomass material will decompose and volatilize during the high-temperature process, leaving pores. Biomass materials with different particle size distributions can form pores of different sizes, forming a porous structure inside the ceramsite, which is beneficial to improving the water absorption and water retention performance of the ceramsite. Spraying nano-silica in the soaking section can enhance the strength and pore structure stability of the ceramsite. Using a specific solution to form a water mist in the cooling section and reacting with the surface of the high-temperature ceramsite, and cooling with cold air mixed in, can also prevent cracks caused by too fast cooling, and at the same time contribute to the fixation of the internal pores of the ceramsite and the optimization of the surface performance.

[0011] Strictly control the thickness of the material layer in the decarbonization section and the soaking section, improve the air permeability of the material layer, reduce heat accumulation, accurately release the heat accumulated in the material layer by means of transportation in the soaking section, and cooperate with the two-stage sintering process, which can effectively inhibit the formation of high temperature in the material layer, control the maximum temperature of the material layer < 900 °C, and completely solve the problem of material layer caking.

[0012] Preferably, the organic solution is one of polyethylene glycol, polyvinyl alcohol, and ethylene glycol.

[0013] By adopting the above technical solutions, using one of polyethylene glycol, polyvinyl alcohol, and ethylene glycol as the organic solution, which has good wettability, can reduce the surface tension between the coal gangue powder particles, effectively wet the coal gangue powder, and make the coal gangue powder and the biomass material better kneaded, improving the formability and uniformity of the green pellets.

[0014] Preferably, the biomass material includes at least one of microcrystalline cellulose, rice husk powder, and sawdust powder.

[0015] By adopting the above technical solution, the selection of components of the biomass material is optimized. Microcrystalline cellulose, rice husk powder, and sawdust powder volatilize and decompose at high temperatures, leaving a large number of pores, increasing the specific surface area and porosity of the ceramsite, creating a rich pore structure for the ceramsite, and thus improving the water retention capacity.

[0016] Preferably, the biomass material is a mixture of microcrystalline cellulose and rice husk powder with a mass ratio of 2:(1 - 1.5).

[0017] By adopting the above technical solution, the decomposition characteristics of microcrystalline cellulose and rice husk powder are different. After being mixed in a specific ratio, pores of different sizes and distributions can be formed during the pyrolysis and roasting processes, making the pore structure of the ceramsite more uniform and reasonable, optimizing the water retention performance of the ceramsite. At the same time, the two substances cooperate with each other, which helps to improve the strength of the ceramsite.

[0018] Preferably, the drying section includes: preheating and drying the green balls with flue gas, reducing the moisture content of the green balls to less than 2%, and the flue gas temperature is 250 - 320 °C.

[0019] Select flue gas at a certain temperature to preheat and dry the green balls, slowly remove the moisture, reduce the impact of rapid moisture evaporation on the structure of the ceramsite, and reduce the moisture content of the coal gangue green balls to less than 2%. This is beneficial to avoiding cracks on the surface of the ceramsite or damage to the internal pore structure caused by the rapid evaporation of excessive moisture during the subsequent pyrolysis and roasting processes, and improving the quality of the ceramsite.

[0020] Preferably, the pyrolysis section includes: pyrolyzing at a temperature of 350 - 450 °C for 20 - 30 min.

[0021] Preferably, the decarbonization section includes: under the condition of a temperature of 500 - 700 °C, an oxygen concentration of 11 - 15%, and decarbonizing for 40 - 60 min.

[0022] Optimize the pyrolysis and decarbonization conditions so that the organic matter in the biomass material decomposes and volatilizes to form tiny pores. An appropriate pyrolysis time can ensure the full progress of the decomposition reaction, and at the same time avoid the instability of the ceramsite structure caused by over - decomposition. Under the conditions of appropriate decarbonization temperature and oxygen concentration, carbon can be fully oxidized and decomposed, generating gases such as carbon dioxide and escaping, thereby forming more pores inside the ceramsite. An appropriate decarbonization time can ensure the full removal of carbon, and at the same time avoid damage to other components of the ceramsite caused by over - oxidation.

[0023] Preferably, the first roasting section includes: roasting at a temperature of 700 - 800 °C for 30 - 40 min.

[0024] Preferably, the second roasting section includes: roasting at a temperature of 750 - 900 °C for 20 - 30 min.

[0025] By adopting the above technical solutions, in the first roasting stage, the mineral components in the ceramsite start to undergo sintering reactions, the bonding force between particles is enhanced, and the pore structure is further adjusted and stabilized. An appropriate roasting time can ensure the full progress of the sintering reaction, enabling the ceramsite to have good physical properties. The second roasting stage further optimizes the properties of the ceramsite, making the mineral components in the ceramsite further crystallize and densify, endowing it with better water retention performance, strength, and chemical stability.

[0026] In summary, the present application has the following beneficial effects: Through the synergistic effect of each link, by selecting appropriate organic solutions and biomass materials, and controlling parameters such as temperature, time, and material layer in each stage, the prepared coal gangue ceramsite has a rich and gradient pore structure, can quickly absorb water and has excellent water retention performance, can be widely applied in fields such as horticulture and construction, realizes the effective utilization of coal gangue, and at the same time reduces environmental pollution. Description of the Drawings

[0027] Figure 1 It is the material layer temperature curve of Embodiment 1 of the present application.

[0028] Figure 2 It is the material layer temperature curve of Comparative Example 1 of the present application.

[0029] Figure 3 It is a picture of the ceramsite caking during production in Comparative Example 1 of the present application. Detailed Embodiments

[0030] The following will describe the implementation schemes of the present invention in detail in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For specific conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] Embodiment 1

[0032] The two-stage coal gangue water-retaining ceramsite preparation process includes green ball preparation, drying section, pyrolysis section, decarbonization section, first roasting section, soaking section, second roasting section, and cooling section;

[0033] Green pellet preparation includes: wetting gangue powder with a particle size less than 1 mm (gangue calorific value 700 Kcal, volatile matter 11%, fixed carbon content 6%) with polyethylene glycol, stirring evenly, kneading with biomass material, the mass ratio of gangue powder to biomass material is 1 kg: 7 g, to obtain green pellets with a green pellet size of 15 mm; the biomass material is a mixture of microcrystalline cellulose and rice husk powder with a mass ratio of 2:1; the particle size distribution of the biomass material is: 30% with a particle size of 80 - 100 μm, 40% with a particle size of 10 - 50 μm, and the balance with a particle size less than 10 μm;

[0034] Preheat and dry the green pellets with flue gas at 275 °C, discharge the moisture of the green pellets, reduce the moisture of the green pellets to less than 1.5%, feed the dehydrated green pellets into the pyrolysis section, heat the green pellets with high-temperature flue gas at 380 °C. Under the action of high temperature, the volatile matter in the green pellets begins to be released, the pyrolysis time is 30 min, and the hot air penetrates the material layer and enters the decarburization section through the hot flue gas pipeline; the green pellets enter the decarburization section, the decarburization temperature is 600 °C, the decarburization time is 45 min, the oxygen concentration is 13%, the volatile matter begins to burn to heat the green pellets, continuously raise the temperature of the material layer, the fixed carbon is oxidized and burned, decarburized, and releases heat, and control the material layer thickness to 700 mm, the temperature of the material layer gradually increases, the flue gas temperature in the decarburization section air box < 800 °C, and the generated high-temperature flue gas is fed into the soaking section through the roasting fan and pipeline;

[0035] Feed the green pellets after decarburization into the first roasting section, roast at a temperature of 756 °C for 26 min, and the high-temperature flue gas is used for waste heat recovery through the pipeline and high-temperature flue gas fan. The green pellets enter the soaking section through a transfer device such as a belt. During the transfer, the heat accumulated in the material layer is released, and the high-temperature flue gas is used for waste heat recovery through the pipeline and high-temperature flue gas fan. During the transfer, the green pellets in the upper and lower layers of the material layer are fully mixed, control the material layer thickness to 600 mm, and evenly spray nano-silica on the green pellets after decarburization during the transfer, spraying 2 g per 100 g of green pellets; then feed them into the second roasting section, the roasting temperature is 810 °C, and the roasting time is 25 min; finally, cool the roasted ceramsite with sodium bicarbonate solution mixed with cold air, cool the ceramsite and heat the air at the same time, the flue gas temperature is 150 °C, and the temperature of the cooled ceramsite is 280 °C, and stack them.

[0036] Example 2

[0037] The difference from Example 1 is that the green pellet preparation includes: wetting gangue powder with a particle size less than 1 mm with polyvinyl alcohol, stirring evenly, kneading with biomass material, the mass ratio of gangue powder to biomass material is 1 kg: 3 g, to obtain green pellets with a green pellet size of 15 mm; the biomass material is sawdust powder; the particle size distribution of the biomass material is: 20% with a particle size of 100 - 120 μm, 50% with a particle size of 40 - 80 μm, and the balance with a particle size less than 10 μm;

[0038] The rest is the same as in Example 1.

[0039] Example 3

[0040] The difference from Example 1 is that in the green pellet preparation step, the organic solution is ethylene glycol, the biomass material is rice husk powder, and the mass ratio of coal gangue powder to biomass material is 1 kg: 9 g. The rest is the same as in Example 1.

[0041] Example 4

[0042] The difference from Example 1 is that in the green pellet preparation step, the organic solution is ethanol, the biomass material is a mixture of rice husk powder and sawdust powder with a mass ratio of 1:1, and the particle size distribution of the biomass material is: 25% with a particle size of 80 - 100 μm, 45% with a particle size of 10 - 40 μm, and the balance with a particle size less than 10 μm. The rest is the same as in Example 1.

[0043] Example 5

[0044] The difference from Example 1 is that the green pellets are preheated and dried with flue gas at 320 °C to remove the moisture of the green pellets and reduce the moisture of the green pellets to 1.5%. The dehydrated green pellets are fed into the pyrolysis section and heated with high-temperature flue gas at 450 °C. Under the action of high temperature, the volatile matter in the green pellets begins to be released, and the pyrolysis time is 20 min. The hot air penetrates the material layer and enters the decarbonization section through the hot flue gas pipeline; the green pellets enter the decarbonization section, the decarbonization temperature is 700 °C, the decarbonization time is 40 min, the oxygen concentration is 11%, the volatile matter begins to burn and heat the green pellets, the temperature of the material layer is continuously increased, the fixed carbon is oxidized and burned, decarbonized, and heat is released, and the thickness of the material layer is controlled to be 800 mm. The temperature of the material layer gradually increases, and the flue gas temperature in the decarbonization section air box < 800 °C. The generated high-temperature flue gas is fed into the soaking section through the roasting fan and pipeline;

[0045] The green pellets after decarbonization are sent to the first roasting section and roasted at 720 °C for 40 min. The high-temperature flue gas is used for waste heat recovery through the pipeline and high-temperature flue gas fan. The green pellets enter the soaking section through a transfer device such as a belt. During the transfer, the heat accumulated in the material layer is released, and the high-temperature flue gas is used for waste heat recovery through the pipeline and high-temperature flue gas fan. During the transfer, the green pellets in the upper and lower layers of the material layer are fully mixed, the thickness of the material layer is controlled to be 500 mm, and nano-silica is evenly sprayed on the green pellets after decarbonization during the transfer, 1 g is sprayed per 100 g of green pellets; then it is sent to the second roasting section, the roasting temperature is 900 °C, and the roasting time is 20 min; finally, the roasted ceramsite is cooled with sodium bicarbonate solution mixed with cold air, the temperature of the ceramsite is reduced while the air is heated, the flue gas temperature is 150 °C, and the temperature of the cooled ceramsite is 280 °C, and it is stockpiled;

[0046] The rest is the same as in Example 1.

[0047] Example 6

[0048] The difference from Example 1 is that the green balls after decarbonization are evenly sprayed with nano-silica during transportation, with 3.5 g of nano-silica sprayed per 100 g of green balls; the calcined ceramsite is cooled with ammonia water solution mixed with cold air, and the rest are the same as in Example 1.

[0049] Example 7

[0050] The difference from Example 1 is that the green balls after decarbonization are evenly sprayed with nano-silica during transportation, with 2.5 g of nano-silica sprayed per 100 g of green balls; the calcined ceramsite is cooled with ammonium bicarbonate solution mixed with cold air, and the rest are the same as in Example 1.

[0051] Comparative Example 1

[0052] The preparation process includes green ball preparation, drying section, pyrolysis section, decarbonization section, calcination section and cooling section; among them, the green ball preparation, drying section, pyrolysis section and decarbonization section are the same as those in Example 1. The calcination section includes: directly calcining the green balls after decarbonization at 900 °C for 35 min, with a bed layer thickness of 900 mm. The cooling section includes: cooling the calcined ceramsite with air, and the cooled ceramsite is directly stockpiled.

[0053] Comparative Example 2

[0054] The difference from Example 1 is that the green ball preparation includes: wetting the coal gangue powder with water and mixing and granulating it with activated carbon at a ratio of 1 kg: 5 g to obtain green balls, and the rest of the steps are the same as those in Example 1.

[0055] Comparative Example 3

[0056] The difference from Example 1 is that for the green ball preparation: the coal gangue powder is wetted with sodium chloride solution and kneaded and granulated with rice husk powder. The mass ratio of the coal gangue powder to the biomass material is 1 kg: 15 g, and the particle size of the rice husk powder is 200 - 300 μm. The rest of the steps are the same as those in Example 1.

[0057] The bed layer temperature of Example 1 and Comparative Example 1 was monitored in real time to obtain the corresponding bed layer temperature curves, specifically as Figure 1 and Figure 2 shown.

[0058] The ceramsite products obtained in Examples 1 - 7 and Comparative Examples 1 - 3 were subjected to a 1 h water absorption test according to GB / T 17431 "Lightweight Aggregates and Their Test Methods", and the results were recorded in Table 1.

[0059] The water retention test was carried out on the ceramsite products obtained in Examples 1-7 and Comparative Examples 1-3: The samples were first weighed to measure the dry weight of the ceramsite, and then saturated with water to measure the weight 1 of the ceramsite. The ceramsite was centrifuged at a speed of 1000 rpm for 10 minutes to simulate rapid drainage, and the weight 2 of the ceramsite was measured by weighing. The water loss rate was recorded as = (weight 1 of the ceramsite - weight 2 of the ceramsite) / (weight 1 of the ceramsite - dry weight of the ceramsite), and the results were recorded in Table 1.

[0060] Table 1

[0061] 1h water absorption rate / % Moisture loss rate / % Example 1 17.5 20.5 Example 2 16.3 19.2 Example 3 17 18.6 Example 4 15.7 18.3 Example 5 17.2 19 Example 6 15.1 18.1 Example 7 16.6 19.5 Comparative Example 1 7.7 50.8 Comparative Example 2 13.9 40.7 Comparative Example 3 15 48.5

[0062] It can be seen from Examples 1-7 and in combination with Table 1 that the ceramsite obtained by the specific preparation process of the present application can not only absorb water quickly and has good water absorption, but also effectively reduce the water loss rate and has excellent water retention performance.

[0063] It can be seen from Example 1 and Comparative Example 1 and in combination with Figures 1 - 3 that through the real-time monitoring of the material layer temperature, the preparation process of Example 1 can effectively reduce the heat accumulation in the material layer and avoid the phenomenon of material layer caking through the synergistic effect of each link. In Comparative Example 1, the excessive temperature of the material layer leads to the formation of a liquid phase on the surface of the green balls, blocking the fine pores on the surface of the green balls. At the same time, the ceramsite with the formed liquid phase adheres and cakes to each other (as Figure 3 shown), seriously affecting the water absorption and water retention performance of the ceramsite.

[0064] It can be seen from Example 1 and Comparative Examples 2-3 that in Comparative Example 2, water was used for wetting and granulation was carried out in combination with activated carbon. Although activated carbon also has a good pore structure, the oxidation rate of activated carbon is fast, and there is excessive burn-off of the pore structure under the above process conditions. The ash residue remaining after the oxidation of activated carbon will also cause partial surface closure, reducing the water absorption and water retention performance of the ceramsite. In Comparative Example 3, an inorganic solution of sodium chloride was used for wetting, and at the same time, the dosage of rice husk powder was too much and the particle size was large, so that a rich gradient pore structure could not be formed. Although it can absorb water quickly, its water retention property is poor.

[0065] It can be seen that each step of the preparation process of the present application has an important impact on the performance of the ceramsite. From the preparation of green balls to the final cooling, by selecting appropriate organic solutions and biomass materials and controlling parameters such as temperature, time and material layer in each section, the prepared coal gangue ceramsite has a rich and gradient pore structure, can absorb water quickly and has excellent water retention performance.

[0066] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A two-stage preparation process of water-retaining ceramsite from coal gangue, characterized in that, The preparation process includes green pellet preparation, drying section, pyrolysis section, decarbonization section, first roasting section, soaking section, second roasting section, and cooling section; the thickness of the material layer in the decarbonization section is 200 - 800 mm; the thickness of the material layer in the soaking section is 300 - 600 mm; The green pellet preparation includes: wetting coal gangue powder with an organic solution, stirring evenly, and kneading with biomass material. The mass ratio of coal gangue powder to biomass material is 1 kg:(3 - 9) g to obtain green pellets; the particle size distribution of the biomass material is: the proportion of particles with a particle size of 80 - 120 μm is 20 - 30%, the proportion of particles with a particle size of 10 - 80 μm is 30 - 50%, and the balance is particles with a particle size less than 10 μm; The soaking section includes: transferring the green pellets after the first roasting section to the soaking section, with the temperature of the material layer lower than 900 °C, and evenly spraying nano - silica during the transfer, spraying 1 - 2.5 g per 100 g of green pellets; The cooling section includes: using one of sodium bicarbonate solution, ammonium bicarbonate, and ammonia water to form a water mist mixed with air to cool the calcined ceramsite.

2. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 1, characterized in that: The organic solution is one of polyethylene glycol, polyvinyl alcohol, and ethylene glycol.

3. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 2, characterized in that: The biomass material includes at least one of microcrystalline cellulose, rice husk powder, and sawdust powder.

4. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 3, characterized in that: The biomass material is a mixture of microcrystalline cellulose and rice husk powder with a mass ratio of 2:(1 - 1.5).

5. The two-stage coal gangue water-retaining ceramsite preparation process according to claim 1, characterized in that: The drying section includes: preheating and drying the green pellets with flue gas, reducing the moisture content of the green pellets to less than 2%, and the temperature of the flue gas is 250 - 320 °C.

6. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 1, characterized in that: The pyrolysis section includes: pyrolyzing for 20 - 30 min at a temperature of 350 - 450 °C.

7. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 1, characterized in that: The decarbonization section includes: under the condition of a temperature of 500 - 700 °C and an oxygen concentration of 11 - 15%, decarbonizing for 40 - 60 min.

8. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 1, characterized in that: The first roasting section includes: roasting for 30 - 40 min under the condition of a temperature of 700 - 800 °C.

9. The two-stage water-retaining ceramsite preparation process for coal gangue according to claim 8, characterized in that: The second roasting section includes: roasting for 20 - 30 min under the condition of a temperature of 750 - 900 °C.

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