Rotary kiln lining refractory and method for producing same

Abstract

The application relates to the technical field of refractory materials, and discloses a rotary kiln lining refractory material and a preparation method thereof, wherein the raw material components include mullite, boron carbide, calcium hexaluminate, silicon carbide, silicon powder, alpha-alumina powder, coated powder, modified refractory fiber and a binding agent. The application selects mullite and boron carbide as the matrix material, the two materials both have excellent acid corrosion resistance, titanium dioxide and alumina are used to treat the refractory fiber, so that a dense enrichment layer is formed, yttrium oxide is added to promote low-temperature sintering, and titanium dioxide is introduced into the refractory fiber to block the micropores on the surface of the fiber, so that the porosity of the refractory material is reduced, and the diffusion path of acid steam is prolonged. The refractory material provided by the application has excellent high-temperature stability and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and more specifically, to a rotary kiln lining refractory material and its preparation method. Background Technology

[0002] A rotary kiln is a steel cylinder lined with refractory material. It calcines materials using a rotating motion and is widely used in building materials, metallurgy, chemicals, and environmental protection industries. During operation, the refractory lining of the kiln is subjected to stresses generated by the kiln's rotation and the rolling impact of high-temperature materials, leading to damage to the refractory material.

[0003] Existing refractory lining materials mainly consist of aggregates, matrix, and binders. Aggregates include high-alumina bauxite clinker, sintered / fused corundum, mullite, etc., and the selection and formulation of aggregates achieve high strength, high-temperature stability, and acid resistance. In addition, a small amount of refractory fiber can be added to the matrix to provide thermal shock resistance, thus preventing lining damage caused by enormous thermal stress during drastic temperature changes due to rotary kiln start-up and shutdown or fluctuations in operating conditions. However, we know that refractory fibers are formed using a melt-blown method. When applied to lining materials, during rotary kiln use, refractory fibers tend to recrystallize into mullite and calcite upon reheating, leading to pulverization and aging of the heated surfaces. Summary of the Invention

[0004] The technical problem solved by this invention:

[0005] This is intended to address the current problem of pulverization and aging of the heated surfaces in rotary kiln linings with added refractory fibers during use.

[0006] The technical solution adopted in this invention is as follows:

[0007] To address the aforementioned technical problems, the present invention aims to provide a refractory material for rotary kiln linings and a method for preparing the same. The specific details are as follows:

[0008] This invention provides a refractory material for rotary kiln lining, the raw materials of which include mullite, boron carbide, calcium hexaaluminate, silicon carbide, silicon micro powder, α-alumina micro powder, coated powder, modified refractory fiber, and binder.

[0009] According to some preferred embodiments, the raw materials, by weight, include 10-30 parts mullite, 5-15 parts boron carbide, 5-15 parts calcium hexaaluminate, 3-8 parts silicon carbide, 5-10 parts silica powder, 10-20 parts α-alumina powder, 5-10 parts coated powder, 2-5 parts modified refractory fiber, and 2-5 parts binder.

[0010] According to some preferred embodiments, the modified refractory fiber is prepared by impregnating the refractory fiber in a slurry, followed by drying and calcination. The refractory fiber includes aluminosilicate fiber and mullite fiber. The slurry contains titanium dioxide, zirconium oxide, α-alumina, yttrium oxide, aluminum phosphate sol, carboxymethyl cellulose, defoamer, and water, with a mass ratio of 25–40:2–6:10–25:2–5:8–12:0.8–1.5:0.1:150–300. Before impregnation, the refractory fiber undergoes plasma activation treatment. Specifically, the refractory fiber is ultrasonically treated with anhydrous ethanol and ultrapure water for 5 minutes, then dried, impregnated in a 68% nitric acid solution for 30 minutes, washed and dried with ultrapure water, and then processed in a plasma device using argon as the reaction gas at a power of 300W for 60 seconds. As described above, impregnation involves ultrasonic impregnation at room temperature for 2–4 hours. Drying involves drying in a 60°C oven. Calcination involves first heating to 600–800°C at a rate of 5°C / min for 1 hour, then heating to 900–1000°C at a rate of 3°C / min for 2 hours, and finally heating to 1100–1150°C at a rate of 5°C / min for 1.5 hours.

[0011] According to some preferred embodiments, the coated powder is porous mullite coated with lanthanum zirconate. Further, the preparation method of porous mullite coated lanthanum zirconate involves spray coating lanthanum zirconate with a precursor sol followed by segmented sintering. The precursor sol is composed of: aluminum isopropoxide, tetraethyl orthosilicate, polyethylene glycol PEG-2000, nitric acid, and ethanol in a ratio of 100:25:8:3:200. Its preparation method involves treating tetraethyl orthosilicate with 2 / 3 parts ethanol and nitric acid at 40°C for 1 hour, then adding aluminum isopropoxide and 1 / 3 parts ethanol and refluxing at 80°C for 3 hours. After this, PEG-2000 is added to obtain the precursor sol. The spray coating process involves an inlet air temperature of 250°C and an outlet air temperature of 100°C. In the aforementioned process, the sintering process involved heating the temperature at 5°C / min to 300°C for 2 hours, then heating it at 3°C / min to 800°C for 2 hours, then heating it at 5°C / min to 1250°C for 2 hours, and finally heating it at 2°C / min to 1350°C for 0.5 hours.

[0012] According to some preferred embodiments, the binder is an organosilicon resin, a phenolic resin, and an aluminum phosphate, with a mass ratio of 1-3:2-6:1-3.

[0013] Second, the present invention provides a method for preparing the aforementioned rotary kiln lining refractory material, comprising the following steps: blending the various raw material components of the refractory material to obtain the refractory material.

[0014] The technical mechanism and beneficial effects of this invention are as follows:

[0015] (1) The refractory material provided by this invention uses mullite and boron carbide as matrix materials. Both of these materials have excellent acid corrosion resistance, and their coefficients of thermal expansion are similar, indicating good compatibility. Therefore, the compounding of the two materials does not cause expansion mismatch. Thus, the refractory material prepared in this way can meet the high-temperature volume stability and acid resistance required in its application. At the same time, silicon carbide and mullite are added to further improve the refractoriness, high-temperature stability, and thermal shock resistance of the refractory material.

[0016] (2) The refractory material provided by this invention modifies the refractory fibers, specifically by treating the refractory fibers with titanium dioxide and alumina to form a dense enriched layer. Yttrium oxide is added to promote low-temperature sintering. The introduction of titanium dioxide into the refractory fibers allows it to seal the micropores on the fiber surface, thereby reducing the porosity of the refractory material and extending the diffusion path of acid vapors. Yttrium oxide promotes the formation of aluminum titanate between titanium dioxide and alumina at high temperatures, thereby enhancing the interfacial bonding strength of the refractory fibers. If the refractory fibers are not treated, when they are distributed in the matrix material, the silica in the refractory fibers will react with acid, leading to pulverization of the refractory fibers and failure of their refractory properties. Furthermore, acid intrusion will cause corrosion and expansion of slag balls in the fibers, resulting in stress cracks and ultimately pulverization and spalling. After modification of the refractory fibers, titanium dioxide transforms into titanium sulfate in a high-temperature acidic atmosphere. This titanium sulfate forms a dense coating, physically blocking the acid diffusion path and thus resisting acid corrosion. Furthermore, the solid solution formed on the surface of the refractory fibers buffers thermal stress, reducing powdering and spalling. The liquid phase generated during sintering penetrates the microcracks in the slag balls, forming a filling phase that matches thermal expansion, thereby inhibiting acid penetration and slag ball expansion, and ultimately slowing down the corrosion rate.

[0017] (3) The refractory material provided by the present invention can effectively improve the high temperature stability and corrosion resistance of the refractory material by adding lanthanum zirconate. However, it has the defect of insufficient toughness. Based on this, by coating lanthanum zirconate, the pores of porous mullite are used to eliminate the brittle cracking of lanthanum zirconate. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] Example 1

[0020] This embodiment provides a rotary kiln lining refractory material. The raw materials, by weight, include 25 parts mullite, 10 parts boron carbide, 10 parts calcium hexaaluminate, 5 parts silicon carbide, 8 parts silica powder, 15 parts α-alumina powder, 8 parts coated powder, 4 parts modified refractory fiber, and 4 parts binder.

[0021] The aforementioned method for preparing modified refractory fibers is as follows:

[0022] (1) Aluminosilicate fiber and mullite fiber were blended at a mass ratio of 1:1. After blending, the fibers were ultrasonically treated with anhydrous ethanol and ultrapure water for 5 min respectively, and then dried. The fibers were then immersed in 68% nitric acid solution for 30 min, washed with ultrapure water, and dried for later use. The fibers were then placed in a plasma device for treatment with argon as the reaction gas, a power of 300W, and a time of 60s to obtain pretreated refractory fibers.

[0023] (2) The pretreated refractory fiber was immersed in the slurry and sonicated for 2 hours. The proportion of each component of the slurry was 35:5:20:3:10:1.2:0.1:200, which is titanium dioxide, zirconium oxide, α-alumina, yttrium oxide, aluminum phosphate sol, carboxymethyl cellulose, organosilicon defoamer, and water.

[0024] (3) After impregnation, the fiber is taken out and dried in an oven. Then, it is heated to 750℃ at a rate of 5℃ / min for 1 hour, then heated to 950℃ at a rate of 3℃ / min for 2 hours, and finally heated to 1100℃ at a rate of 5℃ / min for 1.5 hours. After treatment, it is cooled naturally to obtain the modified refractory fiber.

[0025] The aforementioned method for preparing the coated powder is as follows:

[0026] (1) The components of the precursor sol are: aluminum isopropoxide, tetraethyl orthosilicate, polyethylene glycol PEG-2000, nitric acid, ethanol = 100:25:8:3:200. The precursor sol is prepared by treating tetraethyl orthosilicate with 2 / 3 part ethanol and nitric acid at 40°C for 1 h, then adding aluminum isopropoxide and 1 / 3 part ethanol and refluxing at 80°C for 3 h. After the reaction, PEG-2000 is added to obtain the precursor sol.

[0027] (2) The obtained precursor sol was mixed with lanthanum zirconate at a ratio of 1L:20g and coated in a spray granulation tower with an inlet air temperature of 250℃ and an outlet air temperature of 100℃ to obtain an intermediate.

[0028] (3) The intermediate is sintered, specifically: heated to 300℃ at 5℃ / min for 2h, heated to 800℃ at 3℃ / min for 2h, heated to 1250℃ at 5℃ / min for 2h, and heated to 1350℃ at 2℃ / min for 0.5h to obtain lanthanum zirconate coated with pore mullite.

[0029] In the aforementioned context, the binders are silicone resin, phenolic resin, and aluminum phosphate, in a mass ratio of 2:6:2.

[0030] Example 2

[0031] The difference between this embodiment and Embodiment 1 lies in the different components of the refractory material. Specifically, it consists of: 28 parts mullite, 12 parts boron carbide, 12 parts calcium hexaaluminate, 6 parts silicon carbide, 6 parts silica powder, 12 parts α-alumina powder, 5 parts coated powder, 3 parts modified refractory fiber, and 4 parts binder.

[0032] Comparative Example 1

[0033] The difference between this comparative example and Example 1 is that the modified refractory fiber is replaced with refractory fiber.

[0034] Comparative Example 2

[0035] The difference between this comparative example and Example 1 is that the slurry does not contain α-alumina.

[0036] Comparative Example 3

[0037] The difference between this comparative example and Example 1 is that the slurry does not contain aluminum phosphate sol and yttrium oxide.

[0038] Comparative Example 4

[0039] The difference between this comparative example and Example 1 is that the coated powder is replaced with lanthanum zirconate.

[0040] Test case

[0041] The refractory materials prepared in Examples 1-2 and Comparative Examples 1-4 (the refractory materials were naturally dried at 38℃ for 24 hours, then dried in a 60℃ drying chamber for 48 hours, and then heat-treated at 1400℃ for 4 hours to obtain the finished product) were used as samples for testing. Apparent porosity (GB / T2997-2015), flexural strength retention rate (GB / T 7320-2008), high-temperature thermal expansion coefficient (GB / T-7320-2008), and erosion index (GB / T8931-2007) were measured respectively. The results are shown in Table 1.

[0042] Table 1 Measurement Results

[0043]

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A refractory lining material for a rotary kiln, characterized in that, The raw materials, by weight, include 10-30 parts mullite, 5-15 parts boron carbide, 5-15 parts calcium hexaaluminate, 3-8 parts silicon carbide, 5-10 parts silica powder, 10-20 parts α-alumina powder, 5-10 parts coated powder, 2-5 parts modified refractory fiber, and 2-5 parts binder. The coated powder is porous mullite coated with lanthanum zirconate. The preparation method of the coated powder is to spray lanthanum zirconate and precursor sol and then sinter them in stages. The modified refractory fiber is prepared by impregnating the refractory fiber in a slurry, followed by drying and calcination. The components in the slurry include titanium dioxide, zirconium oxide, α-alumina, yttrium oxide, aluminum phosphate sol, carboxymethyl cellulose, defoamer, and water. The mass ratio of the aforementioned components is 25~40:2~6:10~25:2~5:8~12:0.8~1.5:0.1:150~300.

2. The rotary kiln lining refractory material according to claim 1, characterized in that, The binder is silicone resin, phenolic resin and aluminum phosphate, with a mass ratio of 1~3:2~6:1~3.

3. The rotary kiln lining refractory material according to claim 1, characterized in that, Refractory fibers include aluminosilicate fibers and mullite fibers; the refractory fibers are plasma treated.

4. The rotary kiln lining refractory material according to claim 1, characterized in that, The precursor sol is composed of aluminum isopropoxide, tetraethyl orthosilicate, polyethylene glycol, nitric acid, and ethanol in a ratio of 100:25:8:3:

200. The precursor sol is prepared by treating tetraethyl orthosilicate with 2 / 3 of ethanol and nitric acid at 40°C for 1 hour, then adding aluminum isopropoxide and 1 / 3 of ethanol and refluxing at 80°C for 3 hours. After the reflux is complete, polyethylene glycol is added to obtain the precursor sol.

5. A method for preparing a rotary kiln lining refractory material as described in any one of claims 1 to 4, characterized in that, The refractory material is obtained by blending the various raw material components together.

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