Mullite unshaped material for waste incinerator and production process thereof

Abstract

The present application relates to the technical field of refractory materials, in particular to a mullite unshaped material for waste incinerator and a production process thereof; the unshaped material comprises the following components in parts by weight: lightweight porous mullite 60-75 parts, calcium aluminate cement 10-20 parts, aluminum oxide fine powder 4-10 parts, silicon powder 6-12 parts, hydroxymethyl cellulose 1-3 parts, kaolin 2-5 parts, and sodium hexametaphosphate 0.5-1 part. The unshaped material is prepared by using lightweight porous mullite as aggregate and other auxiliary materials, and the solidified unshaped material has excellent corrosion resistance, and uniform pores exist in the unshaped material, which can effectively reduce the thermal conductivity of the unshaped material, reduce heat loss, and improve energy utilization.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, specifically to a mullite unshaped material for waste incinerators and its production process. Background Technology

[0002] A waste incinerator is a device used to process waste. The operating temperature of a waste incinerator is 1200℃~1700℃, therefore a good refractory material is required as the inner lining.

[0003] Refractory materials are divided into unshaped refractories and shaped refractories. Shaped refractories are usually refractory bricks, with standard and regular shapes, but they can also be machined to specific dimensions. However, shaped refractories must be processed according to the specific application environment, making them inconvenient to use and limiting their applicability. Unshaped refractories, on the other hand, are mixed powdery granules composed of various aggregates and binders. They can be used directly or mixed with appropriate liquids before casting.

[0004] Most existing unshaped refractory materials use mullite as aggregate. However, mullite refractory materials have a high thermal conductivity, which causes heat to be lost quickly in the waste incinerator, resulting in a large amount of energy waste. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a mullite unshaped material for waste incinerators and its production process.

[0006] The technical solution of the present invention is: a mullite amorphous material for waste incinerators, comprising the following components by weight: 60-75 parts of lightweight porous mullite, 10-20 parts of calcium aluminate cement, 4-10 parts of fine alumina powder, 6-12 parts of silica powder, 1-3 parts of hydroxymethyl cellulose, 2-5 parts of kaolin, and 0.5-1 parts of sodium hexametaphosphate.

[0007] Note: The above-mentioned lightweight porous mullite is used as aggregate and combined with other auxiliary materials to make amorphous material. The cured amorphous material has excellent corrosion resistance and uniform pores inside, which can effectively reduce the thermal conductivity of the amorphous material, reduce heat loss, and improve energy utilization.

[0008] Furthermore, the preparation method of the lightweight porous mullite includes the following steps: S1. Add aluminum nitrate and zinc nitrate to anhydrous ethanol and stir until completely dissolved to obtain a mixed solution; the mass ratio of aluminum nitrate, zinc nitrate and anhydrous ethanol is 2~3:1~1.5:7~9. S2. Adjust the pH of the mixed solution to 2-3 using 15-20% hydrochloric acid. Then, while stirring, continuously add tetraethyl orthosilicate to the mixed solution at a rate of 2-3% of the initial mass of the mixed solution per minute until the precursor is obtained after 10-12 minutes. During the addition of tetraethyl orthosilicate, add a binder to the mixed solution every 3-4 minutes; the amount of binder added at one time is 0.1-0.2% of the initial mass of the mixed solution. S3. Stir the precursor at 60~70℃ for 0.5~1h, then let it stand for 1~1.5h to obtain a mixed gel; S4. Dry the mixed gel, and then sinter the dried mixed gel at 1200~1300℃ for 2~3h to obtain lightweight porous mullite.

[0009] Explanation: In the above process, tetraethyl orthosilicate hydrolyzes to produce silicic acid. The silicic acid molecules condense to form a three-dimensional silicon-oxygen network. At the same time, aluminum and zinc ions react with silicic acid to generate aluminum silicate and zinc silicate, which enter the silicon-oxygen network under the action of a binder to form a silicate mixed gel. Then, through sintering, a mullite structure appears in the mixed gel. The zinc silicate in the mixed gel decomposes at high temperature, resulting in uniform pores in the mullite structure, thereby reducing the thermal conductivity of mullite. After the zinc silicate decomposes, a zinc oxide layer is formed in the pores, which improves the corrosion resistance of the pores.

[0010] Further, in step S2, the binder is a mixture of butyl acrylate and dioctyl phthalate in a ratio of 1:1.2~1.6.

[0011] Note: The above binder can effectively bind silicates to form a mixed gel, and zinc silicate can be evenly distributed within the mixed gel.

[0012] Furthermore, in step S2, the initial temperature of the mixed solution is 15~25℃, and the temperature of the mixed solution is increased by 3~5℃ after each addition of the binder.

[0013] Note: Gradually increasing the temperature of the mixed solution allows the tetraethyl orthosilicate to react fully and form a mixed gel under the action of the binder, thereby improving the conversion rate of the mixed gel.

[0014] Furthermore, in step S4, the drying temperature is 130~150℃ and the drying time is 30~40min.

[0015] Note: The above drying parameters ensure that the moisture in the mixed gel is fully removed, forming a dry gel.

[0016] Further, in step S4, the heating curve during sintering is as follows: heating to 280-320℃ at a heating rate of 3-5℃ / min, holding for 15-20min; then heating to 760-800℃ at a heating rate of 6-8℃ / min, holding for 30-40min; then heating to 1000-1100℃ at a heating rate of 10-12℃ / min, holding for 50-60min; and then heating to 1200-1300℃ at a heating rate of 6-8℃ / min.

[0017] Note: The above heating curve can form a stable mullite structure, ensuring that the mullite grains are fine and uniform, and that zinc silicate can be fully decomposed to form uniform pores inside the mullite.

[0018] Furthermore, the average particle size of the alumina fine powder is 1.0 μm to 3.0 μm.

[0019] Note: Alumina powder with the above particle size can adjust the flowability and wear resistance of amorphous materials.

[0020] Furthermore, the average particle size of the silicon micropowder is ≤1.0μm.

[0021] Note: The above-mentioned particle size of silica powder can improve the mechanical strength and structural uniformity of amorphous materials.

[0022] On the other hand, the present invention provides a production process for mullite unshaped material for waste incinerators, which is used to prepare the above-mentioned mullite unshaped material for waste incinerators, including the following steps: Step 1: Put lightweight porous mullite, calcium aluminate cement, alumina fine powder, silica powder, and kaolin into a mixer and mix for 10-15 minutes to obtain a mixture. Step 2: Add water (10-15% of the total mass) to the mixture, then add sodium hexametaphosphate and hydroxymethyl cellulose to the mixture, and continue stirring for 20-30 minutes to obtain mullite amorphous material.

[0023] Note: The mullite amorphous material prepared by the above process has a uniform internal composition, fine grains after curing, high internal porosity, low thermal conductivity, and excellent corrosion resistance.

[0024] The beneficial effects of this invention are: (1) The present invention uses lightweight porous mullite as aggregate and other auxiliary materials to make amorphous material. The cured amorphous material has excellent corrosion resistance and uniform pores inside, which can effectively reduce the thermal conductivity of the amorphous material, reduce heat loss and improve energy utilization.

[0025] (2) In this invention, tetraethyl orthosilicate hydrolyzes to produce silicic acid, which condenses to form a three-dimensional silicon-oxygen network. At the same time, aluminum ions and zinc ions react with silicic acid to generate aluminum silicate and zinc silicate, which form a silicate mixed gel under the action of the binder. Then, through sintering, a mullite structure appears in the mixed gel. After the zinc silicate in the mixed gel decomposes, it forms a zinc oxide layer in the pores, which improves the corrosion resistance in the pores.

[0026] (3) The mullite amorphous material prepared by the process of the present invention has uniform internal composition, fine grains after solidification and molding, high internal porosity, low thermal conductivity and excellent corrosion resistance. Detailed Implementation

[0027] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0028] Example 1: A mullite amorphous material for waste incinerators, comprising the following components by weight: 68 parts lightweight porous mullite, 15 parts calcium aluminate cement, 7 parts fine alumina powder, 8 parts silica powder, 2 parts hydroxymethyl cellulose, 3 parts kaolin, and 0.75 parts sodium hexametaphosphate. The preparation method of lightweight porous mullite includes the following steps: S1. Add aluminum nitrate and zinc nitrate to anhydrous ethanol and stir until completely dissolved to obtain a mixed solution; the mass ratio of aluminum nitrate, zinc nitrate and anhydrous ethanol is 2.5:1.25:8. S2. Adjust the pH of the mixed solution to 2.5 using 18% hydrochloric acid. Then, while stirring, continuously add tetraethyl orthosilicate to the mixed solution at a rate of 2.5% of the initial mass of the mixed solution per minute until the precursor is obtained after 11 minutes. During the addition of tetraethyl orthosilicate, add a binder to the mixed solution every 3.5 minutes; the amount of binder added at one time is 0.15% of the initial mass of the mixed solution. The binder is a mixture of butyl acrylate and dioctyl phthalate in a ratio of 1:1.4; The initial temperature of the mixed solution is 20℃. After each addition of binder, the temperature of the mixed solution is increased by 4℃. S3. Stir the precursor at 65°C for 0.75 h, then let it stand for 1.25 h to obtain a mixed gel; S4. The mixed gel was dried, and then the dried mixed gel was sintered at 1250℃ for 2.5h to obtain lightweight porous mullite; the drying temperature was 140℃ and the drying time was 35min. The heating curve during sintering is as follows: heat up to 300℃ at a heating rate of 4℃ / min and hold for 18min; then heat up to 780℃ at a heating rate of 7℃ / min and hold for 35min; then heat up to 1050℃ at a heating rate of 11℃ / min and hold for 55min; then heat up to 1250℃ at a heating rate of 7℃ / min. The average particle size of fine alumina powder is 1.0 μm to 3.0 μm, and the average particle size of silica powder is ≤1.0 μm. The production process of the above-mentioned mullite unshaped material for waste incinerators includes the following steps: Step 1: Put lightweight porous mullite, calcium aluminate cement, alumina fine powder, silica powder, and kaolin into a mixer and mix for 13 minutes to obtain a mixture. Step 2: Add water (12% of the total mass) to the mixture, then add sodium hexametaphosphate and hydroxymethyl cellulose to the mixture, and continue stirring for 25 minutes to obtain mullite amorphous material.

[0029] Example 2: This example is basically the same as Example 1, except that the mullite amorphous material used in the waste incinerator includes the following components by weight: 60 parts of lightweight porous mullite, 10 parts of calcium aluminate cement, 4 parts of fine alumina powder, 6 parts of silica powder, 1 part of hydroxymethyl cellulose, 2 parts of kaolin, and 0.5 parts of sodium hexametaphosphate.

[0030] Example 3: This example is basically the same as Example 1, except that the unshaped mullite material used in the waste incinerator includes the following components by weight: 75 parts of lightweight porous mullite, 20 parts of calcium aluminate cement, 10 parts of fine alumina powder, 12 parts of silica powder, 3 parts of hydroxymethyl cellulose, 5 parts of kaolin, and 1 part of sodium hexametaphosphate.

[0031] Example 4: This example is basically the same as Example 1, except that the mass ratio of aluminum nitrate, zinc nitrate and anhydrous ethanol is 2:1:7.

[0032] Example 5: This example is basically the same as Example 1, except that the mass ratio of aluminum nitrate, zinc nitrate and anhydrous ethanol is 3:1.5:9.

[0033] Example 6: This example is basically the same as Example 1, except that the pH value of the mixed solution is adjusted to 2 using dilute hydrochloric acid with a mass concentration of 18%.

[0034] Example 7: This example is basically the same as Example 1, except that the pH value of the mixed solution is adjusted to 3 using dilute hydrochloric acid with a mass concentration of 18%.

[0035] Example 8: This example is basically the same as Example 1, except that the amount of tetraethyl orthosilicate added per minute accounts for 2% of the initial mass of the mixed solution.

[0036] Example 9: This example is basically the same as Example 1, except that the amount of tetraethyl orthosilicate added per minute accounts for 3% of the initial mass of the mixed solution.

[0037] Example 10: This example is basically the same as Example 1, except that the amount of binder added at one time accounts for 0.1% of the initial mass of the mixed solution.

[0038] Example 11: This example is basically the same as Example 1, except that the amount of binder added at one time accounts for 0.2% of the initial mass of the mixed solution.

[0039] Example 12: This example is basically the same as Example 1, except that the binder is a mixture of butyl acrylate and dioctyl phthalate in a ratio of 1:1.2.

[0040] Example 13: This example is basically the same as Example 1, except that the binder is a mixture of butyl acrylate and dioctyl phthalate in a ratio of 1:1.6.

[0041] Example 14: This example is basically the same as Example 1, except that the temperature of the mixed solution is increased by 3°C after each addition of the binder.

[0042] Example 15: This example is basically the same as Example 1, except that the temperature of the mixed solution is increased by 5°C after each addition of the binder.

[0043] Example 16: This example is basically the same as Example 1, except that the heating curve during sintering is as follows: the temperature is increased to 280°C at a heating rate of 3°C / min and held for 15 min; then the temperature is increased to 760°C at a heating rate of 6°C / min and held for 30 min; then the temperature is increased to 1000°C at a heating rate of 10°C / min and held for 50 min; then the temperature is increased to 1200°C at a heating rate of 6°C / min.

[0044] Example 17: This example is basically the same as Example 1, except that the heating curve during sintering is as follows: the temperature is increased to 320°C at a heating rate of 5°C / min and held for 20 min; then the temperature is increased to 800°C at a heating rate of 8°C / min and held for 40 min; then the temperature is increased to 1100°C at a heating rate of 12°C / min and held for 60 min; then the temperature is increased to 1300°C at a heating rate of 8°C / min.

[0045] Example 18: This example is basically the same as Example 1, except that the mixed gel is sintered at 1200°C for 2 hours.

[0046] Example 19: This example is basically the same as Example 1, except that the mixed gel is sintered at 1300°C for 3 hours.

[0047] Comparative Example 1: Commercially available mullite particles were used to replace lightweight porous mullite.

[0048] Comparative Example 2: Both tetraethyl orthosilicate and the binder were added all at once.

[0049] Comparative Example 3: The temperature of the mixed solution was kept constant at 20℃ and did not change.

[0050] Comparative Example 4: During sintering, the temperature was increased to 1250℃ at a heating rate of 11℃ / min.

[0051] Experimental Example: To investigate the influence of parameters in each embodiment on the performance of the amorphous material, the amorphous materials prepared in each embodiment were placed in a mold, vibrated, and baked at 120°C for 28 hours. After demolding, samples were obtained, and the thermal conductivity of each sample was tested to obtain the thermal conductivity at 1200°C. The samples were then immersed in a 10% sodium hydroxide solution for 24 hours to obtain the mass loss rate of each sample, as detailed below: Experiment Example 1: Investigating the Influence of Composition on the Properties of Amorphous Materials Using Examples 1-3 and Comparative Example 1 as experimental comparisons, the properties of the amorphous materials with different compositions are shown in Table 1 below: Table 1 Properties of Amorphous Materials with Different Compositions

[0052] As shown in Table 1, compared with Examples 1, 2, and 3, the composition of the amorphous material affects its performance. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate, indicating that the sample of Example 1 has the best thermal insulation and corrosion resistance. This may be because the sample of Example 1 has uniform pores and fewer defects. Therefore, the amorphous material composition selected in Example 1 is the best. Compared with Comparative Example 1, in Example 1, the thermal insulation and corrosion resistance of the sample decreased after using commercially available mullite particles to replace lightweight porous mullite. This may be because after using lightweight porous mullite, there are uniform pores inside the amorphous material, and there is a zinc oxide coating inside the pores, which reduces corrosion inside the pores.

[0053] Experiment Example 2: Investigating the effects of mixed solution ratio and pH value on the properties of amorphous materials. Using Examples 1 and 4-7 as experimental comparisons, the properties of the amorphous material under different proportions and pH values ​​of the mixed solution are shown in Table 2 below: Table 2. Properties of amorphous materials under different proportions and pH values ​​of the mixed solution.

[0054] As shown in Table 2, compared with Examples 1, 4, 5, 6, and 7, excessively high or low mixed solution ratios and pH values ​​can lead to a decrease in the performance of the amorphous material. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate. Therefore, the mixed solution ratio and pH value selected in Example 1 are optimal. Experiment Example 3: Investigating the effect of tetraethyl orthosilicate addition on the properties of amorphous materials. Using Examples 1, 8-9, and Comparative Example 2 as experimental comparisons, the properties of the amorphous materials with different amounts of tetraethyl orthosilicate added are shown in Table 3 below: Table 3. Properties of amorphous materials with different amounts of tetraethyl orthosilicate added.

[0055] As shown in Table 3, compared with Examples 1, 8, and 9, both excessive and insufficient addition of tetraethyl orthosilicate will lead to a decrease in the performance of the amorphous material. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate. Therefore, the amount of tetraethyl orthosilicate added in Example 1 is optimal. Compared with Comparative Example 2, after the addition of tetraethyl orthosilicate in Example 1, both the thermal conductivity and mass loss rate of the sample increased. This may be because after the addition of tetraethyl orthosilicate in one go, zinc ions cannot be evenly distributed in the mixed gel, resulting in uneven pore size in the mullite.

[0056] Experiment Example 4: Investigating the effects of binder dosage and composition on the properties of unshaped materials. Using Examples 1 and 10-13 as experimental comparisons, the properties of the amorphous materials with different amounts and compositions of binder are shown in Table 4 below: Table 4. Properties of amorphous materials with different binder addition amounts and compositions.

[0057] As shown in Table 4, compared with Examples 1, 10, 11, 12 and 13, the amount and composition of the binder will affect the performance of the amorphous material. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate. Therefore, the amount and composition of the binder selected in Example 1 are the best.

[0058] Experiment Example 5: Investigating the effect of mixed solution temperature on the properties of amorphous materials. Using Examples 1, 14-15, and Comparative Example 3 as experimental comparisons, the properties of the amorphous material at different temperatures of the mixed solution are shown in Table 5 below: Table 5. Properties of amorphous materials from mixed solutions at different temperatures

[0059] As shown in Table 5, compared with Examples 1, 14, and 15, both excessively high and low temperatures of the mixed solution will affect the properties of the amorphous material. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate. Therefore, the mixed solution temperature selected in Example 1 is optimal. Compared with Comparative Example 3, in Example 1, the thermal conductivity and mass loss rate of the sample increased when the temperature of the mixed solution remained unchanged. This may be because the conversion rate of the mixed gel was low and the internal pores of the mullite were uneven when the temperature of the mixed solution remained unchanged.

[0060] Experiment Example 6: Investigating the Influence of Sintering Parameters on the Properties of Amorphous Materials Using Examples 1, 16-19, and Comparative Example 4 as experimental comparisons, the properties of the amorphous material under different sintering parameters are shown in Table 6 below: Table 6 Properties of Amorphous Materials under Different Sintering Parameters

[0061] As shown in Table 6, compared with Examples 1, 16, 17, 18, and 19, the heating curve and sintering parameters during sintering all affect the properties of the amorphous material. Among them, the sample of Example 1 has the lowest thermal conductivity and the smallest mass loss rate. Therefore, the sintering parameters selected in Example 1 are optimal. Compared with Comparative Example 4, in Example 1, after the heating rate was kept constant during sintering, the thermal conductivity and mass loss rate of the sample both increased. This may be because the constant heating rate during sintering prevented zinc silicate from fully decomposing and thus prevented the formation of pores inside the mullite.

Claims

1. A mullite unshaped material for waste incinerators, characterized in that, The composition by weight is as follows: 60-75 parts of lightweight porous mullite, 10-20 parts of calcium aluminate cement, 4-10 parts of fine alumina powder, 6-12 parts of silica powder, 1-3 parts of hydroxymethyl cellulose, 2-5 parts of kaolin, and 0.5-1 parts of sodium hexametaphosphate. The preparation method of the lightweight porous mullite includes the following steps: S1. Add aluminum nitrate and zinc nitrate to anhydrous ethanol and stir until completely dissolved to obtain a mixed solution; the mass ratio of aluminum nitrate, zinc nitrate and anhydrous ethanol is 2~3:1~1.5:7~9. S2. Adjust the pH of the mixed solution to 2-3 using dilute hydrochloric acid with a mass concentration of 15-20%. Then, while stirring, continuously add tetraethyl orthosilicate to the mixed solution at a rate of 2-3% of the initial mass of the mixed solution per minute until the precursor is obtained after 10-12 minutes. During the addition of tetraethyl orthosilicate, add a binder to the mixed solution every 3-4 minutes. The amount of binder added at one time is 0.1-0.2% of the initial mass of the mixed solution. The initial temperature of the mixed solution is 15-25℃. After each addition of binder, increase the temperature of the mixed solution by 3-5℃. S3. Stir the precursor at 60~70℃ for 0.5~1h, then let it stand for 1~1.5h to obtain a mixed gel; S4. Dry the mixed gel, and then sinter the dried mixed gel at 1200~1300℃ for 2~3h to obtain lightweight porous mullite; the heating curve during sintering is as follows: heat up to 280~320℃ at a heating rate of 3~5℃ / min, hold for 15~20min; then heat up to 760~800℃ at a heating rate of 6~8℃ / min, hold for 30~40min; then heat up to 1000~1100℃ at a heating rate of 10~12℃ / min, hold for 50~60min; then heat up to 1200~1300℃ at a heating rate of 6~8℃ / min.

2. The mullite unshaped material for a waste incinerator according to claim 1, characterized in that, In step S2, the binder is a mixture of butyl acrylate and dioctyl phthalate in a ratio of 1:1.2~1.

6.

3. The mullite unshaped material for a waste incinerator according to claim 1, characterized in that, In step S4, the drying temperature is 130~150℃ and the drying time is 30~40min.

4. The mullite unshaped material for a waste incinerator according to claim 1, characterized in that, The average particle size of the alumina fine powder is 1.0 μm to 3.0 μm.

5. The mullite unshaped material for a waste incinerator according to claim 1, characterized in that, The average particle size of the silicon micropowder is ≤1.0μm.

6. A production process for mullite unshaped material for waste incinerators, used to produce the mullite unshaped material for waste incinerators as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Put lightweight porous mullite, calcium aluminate cement, alumina fine powder, silica powder, and kaolin into a mixer and mix for 10-15 minutes to obtain a mixture. Step 2: Add water (10-15% of the total mass) to the mixture, then add sodium hexametaphosphate and hydroxymethyl cellulose to the mixture, and continue stirring for 20-30 minutes to obtain mullite amorphous material.

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