A microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln and its preparation method

Abstract

The present invention discloses a microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln and its preparation method. The microporous magnesia-aluminum-chromium composite brick is composed of 45-60% magnesia-aluminum-chromium spinel sand, 15-30% fused magnesia, 10-25% high-purity magnesia fine powder, 1-5% chrome green powder, 1-5% SiC fine powder, and 1-3% PMMA microspheres. The high-purity magnesia fine powder, chrome green powder, SiC fine powder, and PMMA microspheres are mixed to form a premixed powder. The magnesia-aluminum-chromium spinel sand and fused magnesia are then mixed, followed by the addition of a binder and continued mixing. Finally, the premixed powder is added and mixed to form a mixed slurry. The mixed slurry is then formed into a semi-finished magnesia-aluminum-chromium composite brick. The semi-finished brick is then dried, fired, and cooled to form the microporous magnesia-aluminum-chromium composite brick. The microporous magnesia-aluminum-chromium composite brick prepared by the present invention has the advantages of low thermal conductivity, good thermal shock resistance, excellent high-temperature performance, low density, and light weight, thereby solving the problems of severe spalling and erosion of existing bricks.

Description

1. Technical Field:

[0001] The present invention relates to the technical field of refractory materials, and in particular to a microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln and a preparation method thereof. 2. Background technology:

[0002] The waste incineration rotary kiln is a system where waste is added to the kiln from the feed port and then rotated by a transmission device. During the rotation, the waste is continuously exposed to heat and oxygen in the cylinder, causing a combustion reaction. The high-temperature flue gas generated by the combustion flows within the cylinder, allowing the waste to burn fully. After complete combustion, the waste is converted into ash and flue gas and discharged through a discharge device. Due to the complex composition of the incinerated waste, the kiln lining material must have the following properties, depending on the cause of damage to the kiln lining and production conditions: 1) High strength and good wear resistance to resist wear from solid materials; 2) Good volume stability and corrosion resistance to resist corrosion from various substances in the kiln; 3) Good thermal shock resistance to resist thermal shock damage to the material caused by fluctuations in calorific value and kiln temperature; 4) Good high-temperature corrosion resistance to resist corrosion from high-salt material slag.

[0003] At present, the working layer of the lining of the waste incineration rotary kiln generally uses high-alumina bricks, corundum-mullite or chrome corundum as the kiln lining materials, but they have problems such as poor thermal shock stability or poor resistance to slag corrosion. At the same time, the temperature in the high-temperature zone can reach 1400℃, and some materials melt at high temperature. The wear resistance of refractory materials decreases at high temperatures, and local peeling and severe erosion are prone to occur, resulting in a short service life. 3. Summary of the invention:

[0004] The technical problem addressed by this invention is to address the current issues with refractory materials used in the lining working layer of waste incineration rotary kilns. The present invention provides a novel microporous magnesium-aluminum-chromium composite brick for waste incineration rotary kilns and a method for preparing the same. The resulting microporous magnesium-aluminum-chromium composite brick exhibits low thermal conductivity, good thermal shock resistance, excellent high-temperature performance, low density, and light weight, thereby addressing the severe spalling and erosion issues of existing bricks.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is:

[0006] The present invention provides a microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln. Expressed in percentage by mass, the microporous magnesia-aluminum-chromium composite brick mainly consists of 45-60% of raw material magnesia-aluminum-chromium spinel sand, 15-30% of fused magnesia, 10-25% of high-purity magnesia fine powder, 1-5% of chrome green powder, 1-5% of SiC fine powder and 1-3% of PMMA microspheres.

[0007] According to the above-mentioned microporous magnesia-aluminum-chrome composite bricks for waste incineration rotary kiln, the 45-60% magnesia-aluminum-chrome spinel sand is composed of 15-20% 4-2mm magnesia-aluminum-chrome spinel sand and 30-40% 2-0mm magnesia-aluminum-chrome spinel sand.

[0008] According to the above-mentioned microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, the 15-30% fused magnesia is composed of 5-15% 4-2mm fused magnesia and 10-15% 2-0mm fused magnesia; the mass percentage of magnesium in the fused magnesia is ≥97%.

[0009] According to the above-mentioned microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, the mass percentage of magnesium in the high-purity magnesia fine powder is ≥96.5%, and its particle size is 180 mm.

[0010] According to the above-mentioned microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kiln, the mass percentage of chromium in the chrome green powder is 99%, and its particle size is 325 mesh; the mass percentage of SiC in the SiC fine powder is ≥95%, and its particle size is ≤0.074mm.

[0011] According to the above-mentioned microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, the particle size of the PMMA microspheres is 3 to 5 μm (with good dispersibility).

[0012] According to the above-mentioned microporous magnesia-aluminum-chromium composite brick for waste incineration rotary kiln, the magnesia-aluminum-chromium spinel sand is prepared by the following method:

[0013] a. First, light-burned magnesium powder, magnesite powder, α-Al2O3 powder and chromium concentrate powder are mixed in a mass ratio of 15:35:20:30, and then co-grinded;

[0014] b. Add the mixed material obtained by co-grinding in step a into a mixer, and add a binder to mix thoroughly;

[0015] The binder is pulp waste liquid or yellow dextrin, and the amount of the binder added is 3-5% of the total mass of the mixed material;

[0016] c. After the mixture in step b is fully mixed, the resulting mixture is formed into a blank using a 1000-ton hydraulic press;

[0017] d. Placing the formed material in step c in a high-temperature tunnel kiln for high-temperature sintering at a sintering temperature of 1700-1800° C. and a holding time of 4-6 hours; crushing the resulting material after sintering to obtain magnesium-aluminum-chromium spinel sand with two particle sizes of 4-2 mm and 2-0 mm.

[0018] According to the above-mentioned microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, the mass percentage of magnesium in the light-burned magnesium powder in step a is ≥80%, and its particle size is 180 mesh; the mass percentage of magnesium in the dolomite powder is ≥45%, and its particle size is 180 mesh; the mass percentage of aluminum oxide in the α-Al2O3 powder is ≥99%, and its particle size is 200 mesh; the mass percentage of chromium in the chromium concentrate powder is ≥45%, and its particle size is 180 mesh.

[0019] In addition, a method for preparing microporous magnesium-aluminum-chromium composite bricks for a waste incineration rotary kiln is provided, the preparation method comprising the following steps:

[0020] 1) First, weigh various raw materials according to the ratio of the above-mentioned microporous magnesium-aluminum-chromium composite bricks;

[0021] 2) adding the weighed high-purity magnesia fine powder, chrome green powder, SiC fine powder and PMMA microspheres into a premixer and mixing for 30 to 50 minutes (to ensure that the various materials are evenly dispersed) to obtain a premixed powder;

[0022] 3) adding the weighed magnesium aluminum chromium spinel sand and fused magnesia sand into a mixer and mixing for 3 to 5 minutes, then adding lignin or pulp waste liquid and continuing to mix for 3 to 5 minutes, and finally adding the obtained premixed powder and mixing for 10 to 15 minutes to obtain a mixed slurry;

[0023] 4) The obtained mixed mud material is formed by a hydraulic brick press to obtain a semi-finished magnesium-aluminum-chromium composite brick;

[0024] 5) drying the obtained magnesium-aluminum-chromium composite brick semi-finished product in a tunnel drying kiln at 100-200° C. for 24-28 hours until the residual moisture content is ≤0.5%;

[0025] 6) The dried semi-finished product is placed in a tunnel kiln for firing at a temperature of 1650-1700° C. for 6-8 hours, and then cooled to obtain a microporous magnesium-aluminum-chromium composite brick.

[0026] According to the above-mentioned method for preparing microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, the amount of lignin or pulp waste liquid added in step 3) is 3-4% of the total weight of various materials.

[0027] The positive beneficial effects of the present invention are:

[0028] 1. In the technical solution of the present invention, magnesium-aluminum-chromium spinel sand synthesized from four raw materials, namely, light-burned magnesium powder, dolomite powder, α-Al2O3 powder and chromium concentrate powder, has the advantages of low bulk density, many micropores, low thermal conductivity, good thermal insulation performance and good thermal shock stability, thereby resisting the thermal shock of the waste incineration rotary kiln, reducing the weight of the kiln body, and lowering the temperature of the outer surface of the cylinder. It can not only extend the service life of the product, but also save energy consumption and reduce carbon emissions.

[0029] 2. In the technical solution of the present invention, PMMA microspheres are added. During the firing process, when the temperature reaches about 300°C, the PMMA microspheres begin to gradually decompose, forming tiny pores in the refractory matrix, but without affecting the overall structural strength of the product. This further reduces the density of the product, giving it better low thermal conductivity and thermal insulation properties, while helping to improve thermal shock stability.

[0030] 3. In the technical solution of the present invention, SiC fine powder is added. Because silicon carbide has a relatively high hardness and strong wear resistance, it can improve the wear resistance of the brick. During the firing process, the surface of SiC that is fully in contact with air has a greater chance of reacting, forming a layer of SiO2 protective film on the surface and blocking some open pores. During use, it prevents slag from penetrating into the brick, thereby improving the corrosion resistance. In addition, a protective film is formed on the outside to prevent the internal SiC from continuing to oxidize. SiC has a certain stability and inertness in a high-temperature environment without oxygen, and can resist acid and alkali corrosion, effectively improving the corrosion resistance of the brick. In addition, during the product application process, SiC can generate gaseous SiO in the brick to prevent slag from penetrating and generate SiO2 to protect magnesium oxide from being hydrated by the water in the garbage, thereby improving the product's corrosion resistance and permeability, and increasing its service life. SiC has good thermal shock resistance and can improve the thermal shock resistance of the brick after addition.

[0031] 4. The microporous magnesium-aluminum-chromium composite bricks prepared by the present invention have the advantages of low thermal conductivity, good thermal shock stability, excellent high-temperature performance, low density, and light weight. The relevant performance test data are detailed in Table 1.

[0032] Table 1. Performance test data of the products of the present invention

[0033] 4. Specific implementation methods:

[0034] The following will be combined with some embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] In the following examples, the mass percentage of magnesium in the fused magnesia used is ≥97%; the mass percentage of magnesium in the high-purity magnesia fine powder is ≥96.5%, and its particle size is 180 mm; the mass percentage of chromium in the chrome green powder is 99%, and its particle size is 325 meshes; the mass percentage of SiC in the SiC fine powder is ≥95%, and its particle size is ≤0.074 mm; and the particle size of the PMMA microspheres is 3 to 5 μm (with good dispersibility).

[0036] Example 1:

[0037] The microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln of the present invention consists, expressed in percentage by mass, of 15% of 4-2mm magnesia-aluminum-chromium spinel sand, 30% of 2-0mm magnesia-aluminum-chromium spinel sand, 10% of 4-2mm fused magnesia, 15% of 2-0mm fused magnesia, 25% of high-purity magnesia fine powder, 2% of chrome green powder, 2% of SiC fine powder and 1% of PMMA microspheres.

[0038] The magnesium aluminum chromium spinel sand is prepared by the following method:

[0039] a. First, light-burned magnesium powder, magnesite powder, α-Al2O3 powder and chromium concentrate powder are mixed in a mass ratio of 15:35:20:30, and then co-grinded;

[0040] The mass percentage of magnesium in the light-burned magnesium powder is ≥80%, and its particle size is 180 mesh; the mass percentage of magnesium in the magnesite powder is ≥45%, and its particle size is 180 mesh; the mass percentage of aluminum oxide in the α-Al2O3 powder is ≥99%, and its particle size is 200 mesh; the mass percentage of chromium in the chromium concentrate powder is ≥45%, and its particle size is 180 mesh;

[0041] b. Add the mixed material obtained by co-grinding in step a into a mixer, and add a binder to mix thoroughly;

[0042] The binder is yellow dextrin, and the amount of yellow dextrin added is 5% of the total mass of the mixed material;

[0043] c. After the mixture in step b is fully mixed, the resulting mixture is formed into a blank using a 1000-ton hydraulic press;

[0044] d. The formed material in step c is sintered in a high-temperature tunnel kiln at a high temperature of 1750° C. and a holding time of 5 hours; after sintering, the resulting material is crushed to obtain magnesium-aluminum-chromium spinel sand with two particle sizes of 4-2 mm and 2-0 mm.

[0045] Example 2: basically the same as Example 1, except that:

[0046] The microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln of the present invention consists, expressed in percentage by mass, of 15% of 4-2mm magnesia-aluminum-chromium spinel sand, 35% of 2-0mm magnesia-aluminum-chromium spinel sand, 10% of 4-2mm fused magnesia sand, 10% of 2-0mm fused magnesia sand, 18% of high-purity magnesia fine powder, 5% of chrome green powder, 5% of SiC fine powder and 2% of PMMA microspheres.

[0047] Example 3: basically the same as Example 1, except that:

[0048] The microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln of the present invention consists of 20% of 4-2mm magnesia-aluminum-chromium spinel sand, 35% of 2-0mm magnesia-aluminum-chromium spinel sand, 8% of 4-2mm fused magnesia, 12% of 2-0mm fused magnesia, 15% of high-purity magnesia fine powder, 4% of chrome green powder, 3% of SiC fine powder and 3% of PMMA microspheres, expressed in percentage by mass.

[0049] Example 4: basically the same as Example 1, except that:

[0050] The microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln of the present invention consists, expressed in percentage by mass, of 18% of 4-2mm magnesia-aluminum-chromium spinel sand, 40% of 2-0mm magnesia-aluminum-chromium spinel sand, 11% of 4-2mm fused magnesia sand, 10% of 2-0mm fused magnesia sand, 12% of high-purity magnesia fine powder, 3% of chrome green powder, 3% of SiC fine powder and 3% of PMMA microspheres.

[0051] Example 5: basically the same as Example 1, except that:

[0052] The microporous magnesia-aluminum-chromium composite brick for a waste incineration rotary kiln of the present invention consists, expressed in percentage by mass, of 20% of 4-2mm magnesia-aluminum-chromium spinel sand, 33% of 2-0mm magnesia-aluminum-chromium spinel sand, 10% of 4-2mm fused magnesia, 15% of 2-0mm fused magnesia, 17% of high-purity magnesia fine powder, 2% of chrome green powder, 2% of SiC fine powder and 1% of PMMA microspheres.

[0053] The preparation method of the microporous magnesium-aluminum-chromium composite brick for the waste incineration rotary kiln described in Examples 1 to 5 of the present invention comprises the following detailed steps:

[0054] 1) First, various raw materials are weighed according to the proportions of the microporous magnesium-aluminum-chromium composite bricks described in any one of Examples 1 to 5;

[0055] 2) adding the weighed high-purity magnesia fine powder, chrome green powder, SiC fine powder and PMMA microspheres into a premixer and mixing for 45 minutes (to ensure that the various materials are evenly dispersed) to obtain a premixed powder;

[0056] 3) adding the weighed magnesium aluminum chromium spinel sand and fused magnesia sand to a mixer and mixing for 5 minutes, then adding waste pulping liquid and continuing to mix for 5 minutes, wherein the amount of waste pulping liquid added is 3.5% of the total weight of the various materials, and finally adding the obtained premixed powder and mixing for 15 minutes to obtain a mixed slurry;

[0057] 4) The obtained mixed mud material is formed by a hydraulic brick press to obtain a semi-finished magnesium-aluminum-chromium composite brick;

[0058] 5) drying the obtained magnesium-aluminum-chromium composite brick semi-finished product in a tunnel drying kiln at 100-200° C. for 24 hours until the residual moisture is ≤0.5%;

[0059] 6) The dried semi-finished product is placed in a tunnel kiln for firing at a temperature of 1700° C. for 6 hours, and then cooled to obtain a microporous magnesium-aluminum-chromium composite brick.

[0060] Comparative Example 1:

[0061] A magnesia-aluminum-chrome brick comprises, expressed in percentage by mass, 10% of 4-2mm magnesia-chrome frit, 10% of 2-0mm magnesia-chrome frit, 13% of 4-2mm high-purity magnesia sand, 20% of 2-0mm high-purity magnesia sand, 12% of 4-0mm magnesia-aluminum spinel and 35% of high-purity magnesia sand fine powder.

[0062] The preparation method comprises the following steps: adding 4-2 mm magnesia-chromium frit, 2-0 mm magnesia-chromium frit, 4-2 mm high-purity magnesia sand, 2-0 mm high-purity magnesia sand and 4-0 mm magnesia-aluminum spinel into a mixing mill and mixing for 5 minutes; then adding pulp waste liquid and mixing for 5 minutes (the amount of pulp waste liquid added is 3.5% of the total weight of various raw materials); finally adding high-purity magnesia sand fine powder and mixing for 15 minutes to obtain a mixed mud material; molding the mixed mud material through a hydraulic brick press to obtain a semi-finished magnesia-aluminum-chromium composite brick; placing the semi-finished product into a tunnel drying kiln at 100-200 DEG C for drying; placing the dried semi-finished product into an ultra-high temperature tunnel kiln and sintering it at 1700 DEG C for 6 hours to prepare a magnesia-aluminum-chromium brick.

[0063] The relevant performance test data of the products prepared in Examples 1 to 5 of the present invention and Comparative Example 1 are detailed in Table 1.

Claims

1. A microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln, characterized by: Expressed in percentage by mass, the microporous magnesia-aluminum-chromium composite brick is mainly composed of 45-60% raw material magnesia-aluminum-chromium spinel sand, 15-30% fused magnesia, 10-25% high-purity magnesia fine powder, 1-5% chrome green powder, 1-5% SiC fine powder and 1-3% PMMA microspheres; The magnesium aluminum chromium spinel sand is prepared by the following method: a. First, light-burned magnesium powder, magnesite powder, α-Al2O3 powder and chromium concentrate powder are mixed in a mass ratio of 15:35:20:30, and then co-grinded; b. Add the mixed material obtained by co-grinding in step a into a mixer, and add a binder to mix thoroughly; The binder is pulp waste liquid or yellow dextrin, and the amount of the binder added is 3-5% of the total mass of the mixed material; c. After the mixture in step b is fully mixed, the resulting mixture is formed into a blank using a 1000-ton hydraulic press; d. Sintering the formed material in step c in a high-temperature tunnel kiln at a temperature of 1700-1800° C. for a holding time of 4-6 hours; crushing the resulting material after sintering to obtain magnesium-aluminum-chromium spinel sand with two particle sizes of 4-2 mm and 2-0 mm; The particle size of the SiC fine powder is ≤0.074 mm; the particle size of the PMMA microspheres is 3 to 5 μm.

2. The microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln according to claim 1, characterized in that: The 45-60% magnesium-aluminum-chromium spinel sand is composed of 15-20% magnesium-aluminum-chromium spinel sand of 4-2 mm and 30-40% magnesium-aluminum-chromium spinel sand of 2-0 mm.

3. The microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln according to claim 1, characterized in that: The 15-30% fused magnesia is composed of 5-15% 4-2mm fused magnesia and 10-15% 2-0mm fused magnesia; the mass percentage of magnesium in the fused magnesia is ≥97%.

4. The microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln according to claim 1, characterized in that: The mass percentage of magnesium in the high-purity magnesia fine powder is ≥96.5%, and its particle size is 180 mm.

5. The microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln according to claim 1, characterized in that: The mass percentage of chromium in the chrome green powder is 99%, and its particle size is 325 mesh; the mass percentage of SiC in the SiC fine powder is ≥95%.

6. The microporous magnesium-aluminum-chromium composite brick for a waste incineration rotary kiln according to claim 1, characterized in that: The mass percentage of magnesium in the light-burned magnesium powder described in step a is ≥80%, and its particle size is 180 mesh; the mass percentage of magnesium in the dolomite powder is ≥45%, and its particle size is 180 mesh; the mass percentage of aluminum oxide in the α-Al2O3 powder is ≥99%, and its particle size is 200 mesh; the mass percentage of chromium in the chromium concentrate powder is ≥45%, and its particle size is 180 mesh.

7. A method for preparing microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns, characterized by: The preparation method comprises the following steps: 1) First, various raw materials are weighed according to the proportions of the microporous magnesium-aluminum-chromium composite bricks according to claim 1; 2) Add the weighed high-purity magnesia fine powder, chrome green powder, SiC fine powder and PMMA microspheres into a premixer and mix for 30 to 50 minutes to obtain a premixed powder; 3) Add the weighed magnesia-aluminum-chromium spinel sand and fused magnesia into a mixer and mix for 3-5 minutes, then add lignin or pulp waste liquid and continue mixing for 3-5 minutes, and finally add the obtained premixed powder and mix for 10-15 minutes to obtain a mixed slurry; 4) The obtained mixed mud is formed by a hydraulic brick press to obtain a semi-finished magnesium-aluminum-chromium composite brick; 5) The obtained magnesium-aluminum-chromium composite brick semi-finished product is placed in a tunnel drying kiln at 100-200°C for 24-28 hours until the residual moisture is ≤0.5%; 6) The dried semi-finished product is placed in a tunnel kiln for firing at a temperature of 1650-1700°C for 6-8 hours. After firing, it is cooled to obtain microporous magnesium-aluminum-chromium composite bricks.

8. The method for preparing microporous magnesium-aluminum-chromium composite bricks for waste incineration rotary kilns according to claim 7, characterized in that: The amount of lignin or pulp waste liquid added in step 3) is 3-4% of the total weight of various materials.

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