Anti-skinned silicon carbide microcrystal blanking pipe for cement kiln and preparation method thereof

Abstract

This invention discloses an anti-scaling silicon carbide microcrystalline feed pipe for cement kilns and its preparation method. The feed pipe includes a metal outer shell cylinder, a nano-insulation board layer and a self-flowing castable lining layer on its inner wall, and an integrally sintered silicon carbide microcrystalline inner tube as the working inner surface, coaxially bonded to the inner side of the lining layer. The preparation method includes batching and mixing, pressing and molding, sintering and crystallization, and composite assembly steps. This invention can significantly inhibit scale adhesion, and also has excellent thermal insulation, wear resistance and corrosion resistance properties. It can effectively reduce the cylinder temperature and extend the service life of the inner lining, and is suitable for feed pipe parts in cement kiln pre-decomposition systems that are prone to scale formation.

Description

Technical Field

[0001] This invention relates to the field of refractory lining technology for cement kilns, and in particular to an anti-scaling silicon carbide microcrystalline feed pipe for cement kilns and its preparation method. Background Technology

[0002] In cement production, the lining surfaces of parts such as the C4, C5, and C6 feed pipes of the cyclone separator, the kiln tail flue, the cyclone umbrella top, and the decomposition furnace cone are coated with powdery materials carried by the airflow, along with sulfur, alkali, and other compounds, forming a crust on the inner wall. This crusting and clogging problem is particularly severe in cement production lines using alternative fuels. Numerous factors contribute to crusting in cement kiln systems, including impurities in the raw materials, harmful components introduced by alternative fuels, the kiln system's air supply matching, temperature control levels, and the performance of the refractory materials at the crusting sites. Traditionally formulated anti-scabbing castables, due to severe crusting and frequent cleaning, are prone to surface wear and roughness, which ironically creates conditions for crust adhesion, further exacerbating the crusting problem.

[0003] In cement precalcination systems, the most severe scaling occurs in two main areas: The first is the C5 and C6 feed pipes and the top of the cyclone separator, where the temperature ranges from 800℃ to 900℃. Scaling is particularly pronounced in production lines using alternative fuels. This area is also highly sensitive to coal combustion characteristics; incomplete combustion makes scaling more likely, potentially causing blockages in the cyclone feed pipes. The second area is the kiln tail flue and rising flue, where the temperature ranges from 1000℃ to 1200℃. The scale formed in this area is typically hard and porous, and scaling is present in most new dry-process cement kilns. If the scale is not cleaned promptly, it will thicken and eventually cause blockages, severely impacting the normal operation of the production line.

[0004] Currently, the main method for cleaning crusts is manual cleaning. On-site operators use air cannons, high-pressure water guns, or manual hammering with steel bars to carry out the cleaning work. This method has problems such as multiple cleaning sessions, long working hours, and high risks of working in high-temperature environments. It not only increases the labor intensity of operators but also poses significant safety hazards and seriously affects the normal production order.

[0005] In existing technologies, cement kiln feed pipes commonly use a traditional lining scheme of calcium silicate board plus castable refractory. This scheme has significant drawbacks in practical applications: firstly, the inner wall of the lining is prone to scaling, which recurs even after cleaning, affecting system ventilation and hindering stable production operation; secondly, traditional calcium silicate boards have limited insulation performance, resulting in high surface temperatures of the feed pipe cylinder, significant system heat loss, and a poor working environment at the production site. Therefore, there is an urgent need to develop a new feed pipe lining structure that can effectively suppress scaling, reduce cylinder temperature, and extend service life. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to solve the technical problems of severe scaling, poor insulation, short wear life, and high maintenance frequency in traditional cement kiln feed pipe linings. It provides a silicon carbide microcrystalline composite feed pipe with high anti-scaling properties, low thermal conductivity, and long life, and also provides its corresponding preparation method.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] This invention provides an anti-scaling silicon carbide microcrystalline feed pipe for cement kilns, comprising a metal outer shell cylinder and an insulation layer and a castable lining layer laid on the inner wall of the metal outer shell cylinder; the insulation layer is a nano-insulation board layer, and the castable lining layer is a structural layer formed by the curing of self-flowing castable; a silicon carbide integral microcrystalline inner tube is coaxially composited on the inner side of the castable lining layer, the silicon carbide integral microcrystalline inner tube is composed of multiple microcrystalline tube units axially spliced ​​together, and the splicing end faces of adjacent microcrystalline tube units are set as mutually cooperating stepped insertion structures to form the inner working surface of the feed pipe.

[0009] As a preferred embodiment of the present invention, the silicon carbide integral microcrystalline inner tube has a silicon carbide mass percentage content ≥80%, a bulk density ≥2.6g / cm³, a room temperature pressure resistance ≥100MPa, and a room temperature wear amount ≤4.5cm³.

[0010] As a preferred embodiment of the present invention, the nano-insulation board layer is formed by at least one layer of nano-microporous insulation board being bonded and laid on the inner wall of the metal outer shell cylinder, and the joint gaps between adjacent insulation boards are filled with fire-resistant insulation sealant.

[0011] As a preferred embodiment of the present invention, the silicon carbide integral microcrystalline inner tube is composed of multiple microcrystalline tube units axially spliced ​​together, and the splicing end faces of adjacent microcrystalline tube units are configured as mutually cooperating stepped insertion structures.

[0012] As a preferred embodiment of the present invention, the feeding pipe is installed at the C4 cyclone feeding pipe, C5 cyclone feeding pipe or C6 cyclone feeding pipe part of the cement kiln pre-decomposition system.

[0013] The present invention also provides a method for preparing the above-mentioned anti-scaling silicon carbide microcrystalline feed pipe for cement kilns, comprising the following steps: (1) Ingredient mixing: Silicon carbide powder is used as the main raw material. Sintering aid and organic molding binder are added according to the proportion and mixed evenly to obtain molding mixture; (2) Press molding: The molding mixture is loaded into a tubular mold of the corresponding specification and pressed to form a single-section tubular green blank after demolding; (3) Sintering and crystallization: The tubular green billet is sent into a high-temperature kiln and cooled with the furnace after solid-state sintering and crystallization treatment to produce multi-segment silicon carbide microcrystalline tube units; the multi-segment microcrystalline tube units are steppedly inserted and spliced ​​to form an integral silicon carbide microcrystalline inner tube, and then coaxially positioned and embedded in the inner side of the self-flowing castable lining. (4) Composite assembly: Nano heat insulation boards are fixedly laid on the inner wall of the metal outer shell cylinder in sequence, and molds are set up to pour self-flowing castable; first, multiple microcrystalline tube units are inserted and spliced ​​to form a silicon carbide integral microcrystalline inner tube, and then the silicon carbide integral microcrystalline inner tube is coaxially positioned and embedded in the inner side of the self-flowing castable. After curing and solidification, the mold is removed to obtain the finished material tube.

[0014] As a preferred technical solution of the present invention, in step (1), the mass of silicon carbide powder accounts for more than 80% of the total mass of the molding mixture; the sintering aid is an oxide sintering aid, and the organic molding binder is at least one of phenolic resin, dextrin or carboxymethyl cellulose.

[0015] As a preferred technical solution of the present invention, step (2) adopts cold isostatic pressing process, the molding pressure is controlled at 150MPa~250MPa, and the holding time is 30s~120s.

[0016] As a preferred technical solution of the present invention, in step (3), the tubular green blank is first subjected to low-temperature drying treatment before sintering. The drying temperature is 100℃~200℃ and the drying time is 6h~12h. The sintering crystallization temperature is 1350℃~1550℃ and the holding time is 2h~6h. The sintering process is carried out in an air atmosphere or an inert protective atmosphere.

[0017] As a preferred technical solution of the present invention, in step (4), the curing time of the self-flowing castable at room temperature is not less than 24 hours, and the relative humidity of the curing environment is not less than 70%.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significantly improved anti-scabbing performance: The integrated sintered silicon carbide microcrystalline inner tube is used as the working surface that directly contacts the material. The material has high density, strong chemical inertness, and a smooth surface that does not easily adhere to sulfur and alkali low-melting substances. This can significantly reduce the rate of scale formation and adhesion strength, and reduce the frequency of cleaning and kiln shutdown losses. 2. Outstanding thermal insulation and energy saving effect: The use of nano-insulation board to replace traditional calcium silicate board significantly reduces the thermal conductivity, effectively blocks the heat conduction path, significantly reduces the outer wall temperature of the feed pipe cylinder, reduces system heat loss, and improves the workshop working environment. 3. Wear-resistant, corrosion-resistant, and long service life: Silicon carbide microcrystalline materials have the characteristics of high strength, high wear resistance, and resistance to alkali corrosion. The integrated sintered structure has no brick joints or weak splicing areas. Its resistance to airflow erosion is far superior to traditional castables, which can significantly extend the service life of the lining and reduce the total life cycle cost. 4. Stable structure and convenient construction: It adopts a three-layer composite structure of "insulation layer + self-flowing castable + microcrystalline inner tube". The self-flowing castable has good fluidity and high lining density; the microcrystalline tube can be prefabricated in the factory and assembled on site, resulting in high construction efficiency and good coaxiality and stability of the overall structure. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the radial cross-sectional structure of the anti-scaling silicon carbide microcrystalline feed pipe for cement kilns according to the present invention; Figure 2 This is a schematic diagram of the axial cross-sectional structure of the segmented spliced ​​silicon carbide integral microcrystalline inner tube of the present invention; Figure 3 is a process flow diagram of the preparation method described in this invention.

[0020] In the figure: 1. Metal outer shell cylinder; 2. Nano-insulation board layer; 3. Self-flowing castable lining; 4. Silicon carbide integral microcrystalline inner tube. Detailed Implementation

[0021] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0022] In the attached diagram, all identical reference numerals refer to the same components.

[0023] Example 1: Segmented Stepped Insertion Type Anti-Skinning Microcrystalline Feed Pipe This embodiment provides an anti-scaling silicon carbide microcrystalline feed pipe for cement kilns, applied to the feed pipe section of the C5 cyclone separator in a 5000t / day cement production line. The feed pipe has a total axial length of 3000mm and operates at a temperature of 800-900℃, which is a high-incidence area for scaling in the kiln system, as shown in Figures 1 and 2. The feed pipe consists of a metal outer shell cylinder 1, a nano-insulation board layer 2, a self-flowing castable lining layer 3, and a silicon carbide integral microcrystalline inner tube 4, arranged coaxially from the outside to the inside. The four layers are bonded and cast together to form a rigid whole.

[0024] The metal outer shell cylinder 1 is made of Q235B carbon steel, rolled and welded, with a nominal inner diameter of 800mm, a wall thickness of 10mm, and an axial length of 3000mm. The outer wall of the metal outer shell cylinder 1 is welded with connecting flanges and lifting lugs for on-site lifting and docking with cyclone components. The inner wall of the metal outer shell cylinder 1 is rust-removed and roughened, achieving a surface rust removal grade of Sa2.5. Connection: The nano-insulation board layer 2 is bonded and fixed to the inner wall of the metal outer shell cylinder 1 using a high-temperature refractory adhesive. The metal outer shell cylinder 1 bears the entire load of the inner lining, providing an installation reference for the inner lining and resisting damage caused by lifting, thermal cycling, and external impacts. Function: As the external load-bearing base of the feed pipe, it provides external protection and bears the entire self-weight and working load of the insulation layer, the castable lining, and the silicon carbide integral microcrystalline inner tube 4.

[0025] Nano-insulation board layer 2 uses nano-microporous silica insulation board with a single layer thickness of 20mm. The board is divided into 4 pieces circumferentially and 3 pieces axially for laying. The outer surface of the board is fully coated with high-temperature refractory adhesive and bonded to the inner wall of the metal outer shell cylinder 1. The bonding area coverage of a single board is not less than 95%. The width of the joint between adjacent insulation boards is controlled within 2mm. The joint is filled with refractory insulation sealant and compacted and smoothed. Connection relationship: The outer side of nano-insulation board layer 2 is bonded and fixed to the metal outer shell cylinder 1, and the inner side is in direct contact with the self-flowing castable lining layer 3. The refractory insulation sealant connects multiple independent insulation boards to form a continuous closed insulation ring, eliminating thermal bridges at the joints. Function: The thermal conductivity of nano-insulation board layer 2 at room temperature is ≤0.03W / (m). K) effectively blocks the conduction of high temperature to the metal outer shell cylinder 1, reduces system heat loss, improves the high-temperature working environment on site, and achieves the heat preservation and energy saving effect of the present invention.

[0026] The self-flowing castable lining 3 is cast and cured using silicon carbide self-flowing castable, with a lining thickness of 80mm, filling the annular cavity between the nano-insulation board layer 2 and the silicon carbide integral microcrystalline inner tube 4. Before casting, a special interface agent is applied to the inner surface of the nano-insulation board layer 2, and the self-flowing castable slurry penetrates into the micropores on the surface of the nano-insulation board layer 2 to form a mechanical interlocking bond; the outer surface of the silicon carbide integral microcrystalline inner tube 4 is pre-roughened, and the self-flowing castable wraps around the roughened surface and cures to form an embedded locking structure, constraining the axial movement and circumferential rotation of the silicon carbide integral microcrystalline inner tube 4; relying on the self-flowing properties of the castable itself, the overall coaxiality deviation after molding is no more than 1mm. Connection Relationship: The outer side of the self-flowing castable lining 3 is mechanically interlocked with the nano-insulation board layer 2, and the inner side is embedded and locked with the silicon carbide integral microcrystalline inner tube 4, serving as an intermediate force transmission structure to transfer the load borne by the silicon carbide integral microcrystalline inner tube 4 to the metal outer shell cylinder 1. Functions: First, as a stress transition layer, it disperses the stress generated by material scouring and thermal shock, avoiding stress concentration that could cause cracking and damage to the lining; second, as a positioning support layer, it ensures the coaxiality of the silicon carbide integral microcrystalline inner tube 4 assembly, ensuring smooth material flow; third, as a secondary seepage barrier layer, it prevents high-temperature flue gas containing sulfur and alkali components from permeating outward, protecting the nano-insulation board layer 2 from alkali corrosion.

[0027] The silicon carbide integral microcrystalline inner tube 4 is composed of three axially spliced ​​microcrystalline tube units, each 1000mm in length, with a wall thickness of 30mm for each unit. Adjacent microcrystalline tube units have mating male and female step faces at their mating surfaces, with a radial clearance of 0.3–0.5mm and an axial insertion depth of 8mm. After uniformly applying high-temperature refractory mortar to the mating surfaces, the units are axially inserted and compacted. The mortar fills the gaps and cures to form a sealed bonding joint. After splicing, the inner surface of the silicon carbide integral microcrystalline inner tube 4 is flush and without misalignment. The material performance indicators of the microcrystalline tube units in this embodiment are shown in Table 1.

[0028]

[0029] Connection Relationship: The integral silicon carbide microcrystalline inner tube 4 is integrally embedded inside the self-flowing castable lining 3, and is fixed by locking with the self-flowing castable lining 3 through the rough surface of its outer surface; the microcrystalline tube units are sealed and connected by stepped interlocking with high-temperature refractory mortar. Function: The integral silicon carbide microcrystalline inner tube 4 constitutes the inner working surface of the feed pipe. The material has high chemical inertness and a dense and smooth surface, which inhibits the adhesion of sulfur and alkali low-melting substances, reduces the adhesion of skin, and achieves an anti-skinning effect; at the same time, it has high wear resistance and alkali corrosion resistance, withstands high-speed material erosion, and extends the service life of the inner lining; the stepped-mortar sealing structure prevents high-temperature flue gas from flowing outward along the splicing gap.

[0030] The feed pipe of this embodiment and the feed pipe of the traditional calcium silicate board + anti-scabbing castable were carried out in parallel at the same position of the C5 cyclone on the same production line for 12 months. The results are shown in Table 2.

[0031]

[0032] As can be seen from the data in Table 2, the outer wall temperature of the cylinder in this embodiment is significantly reduced, and the crust thickness, cleaning frequency, and inner lining wear are all significantly better than the traditional solution. At the same time, the splicing nodes are intact, verifying that this embodiment simultaneously achieves the effects of anti-crusting, heat preservation and energy saving, and wear resistance and long service life.

[0033] Example 2 This embodiment provides an anti-scaling silicon carbide microcrystalline feed pipe for cement kilns, applied to the feed pipe section of the C4 cyclone separator in a 2500t / day cement production line. The total axial length of the feed pipe is 2200mm. From the outside to the inside, the feed pipe is coaxially arranged with a metal outer shell cylinder 1, a nano-insulation board layer 2, a self-flowing castable lining layer 3, and a silicon carbide integral microcrystalline inner tube 4.

[0034] The metal outer shell cylinder 1 is made of Q235B carbon steel, rolled and welded, with a nominal inner diameter of 650mm, a wall thickness of 8mm, and an axial length of 2200mm. Flanges and lifting lugs are installed on the outer wall, and the inner wall is treated to Sa2.5 grade rust removal. Connection: The nano-insulation board layer 2 is bonded and fixed to the inner wall of the metal outer shell cylinder 1. The metal outer shell cylinder 1 bears the entire weight of the inner lining. Function: To bear the overall structural load and provide protection and assembly reference for the inner lining.

[0035] The second layer of nano-insulation board uses a single-layer thickness of 20mm nano-microporous silica insulation board; it is laid in 3 sections circumferentially and 2 sections axially, and the board is bonded to the inner wall of the metal outer shell cylinder 1. The joints are filled with refractory insulation sealant and compacted. Connection relationship: the outer side is bonded to the metal outer shell cylinder 1, and the inner side contacts the self-flowing castable lining layer 3. The sealant makes the insulation board form a complete insulation ring. Function: It inhibits radial heat conduction, reduces the temperature of the outer shell of the cylinder, and reduces heat loss.

[0036] A 70mm thick self-flowing castable lining layer 3 fills the annular cavity between the nano-insulation board layer 2 and the silicon carbide integral microcrystalline inner tube 4. An interface agent is applied to the inner side of the nano-insulation board layer 2, creating a mechanical interlock between the castable lining and the micropores of the insulation board. The outer surface of the silicon carbide integral microcrystalline inner tube 4 has a roughened texture; after the castable lining cures, it forms an embedded interlock, restricting the displacement of the silicon carbide integral microcrystalline inner tube 4, with an assembly coaxiality deviation ≤1mm. Connection relationship: The outer side interlocks with the nano-insulation board layer 2, and the inner side interlocks with the silicon carbide integral microcrystalline inner tube 4, achieving load transfer. Function: Disperses thermal shock and material erosion stress, positions the silicon carbide integral microcrystalline inner tube 4, and prevents sulfur and alkali flue gas from eroding the insulation layer.

[0037] The integral silicon carbide microcrystalline inner tube 4 is composed of two 1100mm long microcrystalline tube units joined together by stepped interlocking. Each unit has a wall thickness of 25mm. The radial gap between the male and female steps of adjacent units is 0.3-0.5mm, the interlocking depth is 8mm, and the mating surfaces are coated with high-temperature refractory mortar. The measured performance of the microcrystalline tube unit is as follows: SiC mass percentage 81.5%, bulk density 2.62g / cm³, room temperature compressive strength 110MPa, and room temperature abrasion loss 4.1cm³, all meeting the performance requirements of the claims. Connection relationship: The integral silicon carbide microcrystalline inner tube 4 is embedded inside the self-flowing castable lining 3, with stepped interlocking and refractory mortar sealing between tube units. Function: Serves as a material scouring surface, inhibiting scale adhesion and resisting scouring and wear; the stepped seal prevents flue gas leakage.

[0038] In this embodiment, the feed pipe was continuously operated in the C4 cyclone for 8 months, and the operating data was collected and summarized in Table 3 with the traditional solution under the same working conditions.

[0039] Table 3 Summary of operational data for different production line examples

[0040] As shown in Table 3, the technical solution of the present invention can be adapted to both long-size C5 feed pipes of large production lines of 5000t / d and C4 feed pipes of small and medium-sized production lines of 2500t / d. The present invention uses factory-prefabricated components and completes splicing and assembly on site, which is convenient for construction and demonstrates the effect of strong structural versatility and convenient assembly. There are no defects such as lining falling off or material leakage and cracking at the splicing points during operation.

[0041] Example 3 This embodiment describes the preparation method of the anti-scaling silicon carbide microcrystalline feed pipe for cement kilns described in Example 1. The method includes all technical features of the claims and the process flow is shown in Figure 3.

[0042] (1) Batching and mixing: By weight, take 85 parts of graded silicon carbide powder (containing 0-1mm coarse particles, 100-325 mesh fine powder, and micro powder below 1μm), 7 parts of alumina micro powder as oxide sintering aid, and 8 parts of phenolic resin as organic molding binder; put them into a high-strength mixer for dry mixing for 5 minutes, add water for wet mixing for 12 minutes, and granulate after mixing to obtain the molding mixture. Silicon carbide powder accounts for 85% of the total mass of the molding mixture. Function: The proportion meets the silicon carbide content requirements, the sintering aid ensures solid-phase sintering, and the organic binder ensures the strength of the molded green body.

[0043] (2) Press molding: The molding mixture is loaded into a single-section tubular mold and cold isostatic pressing is used. The molding pressure is 200MPa and the holding time is 60s. The pressure is slowly released and the mold is demolded to obtain multiple single-section tubular green blanks. Function: Cold isostatic pressing ensures uniform density of the green blank, avoids delamination and crack defects, and obtains the green blank for subsequent sintering and crystallization.

[0044] (3) Sintering and crystallization: The single-section tubular green body is fed into a drying kiln and dried at 150℃ for 8 hours to remove moisture and volatile components; after drying, the green body is transferred to a high-temperature shuttle kiln in an air atmosphere, with a heating rate of 5℃ / min to 1450℃, and held for 4 hours to complete solid-state sintering and crystallization treatment. Then, it is cooled to room temperature with the furnace to obtain silicon carbide microcrystalline tube units with pre-processed male and female step structures at both ends. Function: Low-temperature drying prevents cracking of the green body during sintering; high-temperature sintering and crystallization obtains high-density, high-strength microcrystalline tube units, meeting the performance indicators of wear-resistant and anti-scabbing materials.

[0045] (4) Composite assembly: A nano-insulation board layer 2 is pasted and laid on the inner wall of the metal outer shell cylinder 1. The splicing gap is filled and smoothed with refractory insulation filler. A ring casting mold is set up, and silicon carbide self-flowing castable is poured. The air is vented by slight vibration. High-temperature refractory mortar is applied to the mating surfaces of multiple silicon carbide microcrystalline tube units. The steps are inserted and compacted to form a complete silicon carbide integral microcrystalline inner tube 4. The spliced ​​silicon carbide integral microcrystalline inner tube 4 is coaxially positioned and embedded in the inner side of the castable. The coaxiality deviation is adjusted to ≤1mm. It is placed in an environment with normal temperature and relative humidity of 75% for 30h. After the self-flowing castable is completely cured to form the self-flowing castable lining layer 3, it is demolded to obtain the finished material tube. Connection and process function: Nano-insulation board layer 2 is pre-fixed on the inner wall of the cylinder; self-flowing castable curing achieves a firm bond between the insulation layer, castable and microcrystalline inner tube; prefabricate single-segment microcrystalline tube units and then assemble them on site to solve the problems of sintering and transportation of ultra-long pipe fittings; the curing system ensures that the castable fully acquires strength and that the interfaces of each layer are firmly bonded.

[0046] Three batches of silicon carbide microcrystalline tube units were prepared consecutively, and the sampling and testing results are shown in Table 4.

[0047] Table 4. Sampling and testing results of microcrystalline tube units in 3 batches of samples

[0048] As shown in Table 4, the performance of each batch of products has small fluctuations and all fall within the scope of protection defined by the claims. The process is controllable and suitable for industrial mass production, demonstrating the stable preparation process and convenient factory prefabrication and assembly of the present invention.

[0049] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cement kiln anti-skinned silicon carbide microcrystalline downcomer, comprising a metal shell cylinder (1) and a thermal insulation layer and a castable lining layer laid on the inner wall of the metal shell cylinder (1), characterized in that, The insulation layer is a nano-insulation board layer (2), and the castable lining is a self-flowing castable lining (3); the inner side of the self-flowing castable lining (3) is coaxially composite with a silicon carbide integral microcrystalline inner tube (4); the silicon carbide integral microcrystalline inner tube (4) is composed of multiple microcrystalline tube units axially spliced ​​together, and the splicing end faces of adjacent microcrystalline tube units are set as mutually cooperating stepped insertion structures to form the inner working surface of the feed tube.

2. The anti-skinned, carborundum microcrystalline downcomer tube for cement kiln according to claim 1, characterized in that, The silicon carbide integral microcrystalline inner tube has a silicon carbide mass percentage of ≥80%, a bulk density of ≥2.6g / cm³, a room temperature compressive strength of ≥100MPa, and a room temperature wear of ≤4.5cm³.

3. The anti-skinned, carborundum microcrystalline downcomer tube for cement kiln as claimed in claim 1, wherein, The nano-insulation board layer (2) is formed by at least one layer of nano-microporous insulation board attached to the inner wall of the metal outer shell cylinder (1), and the joint gap between adjacent insulation boards is filled with fire-resistant insulation sealant.

4. The anti-skinned, carborundum microcrystalline downcomer tube for cement kiln as claimed in claim 1, wherein, The radial fit clearance of the step-fitting of adjacent microcrystalline tube units is 0.3-0.5 mm, and the axial fit depth is 8 mm; the step mating surface is coated with high-temperature refractory mortar to achieve bonding and sealing.

5. The anti-skinned, carborundum microcrystalline downcomer tube for cement kilns according to claim 1, characterized in that, The feeding pipe corresponds to the C4 cyclone feeding pipe, C5 cyclone feeding pipe, or C6 cyclone feeding pipe section installed in the cement kiln pre-decomposition system.

6. A method of making the anti-skinned, carborundum microcrystalline downcomer for cement kiln as claimed in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Ingredient mixing: Silicon carbide powder is used as the main raw material. Sintering aid and organic molding binder are added according to the proportion and mixed evenly to obtain molding mixture; (2) Press molding: The molding mixture is loaded into a tubular mold of the corresponding specification and pressed to form a tubular green blank after demolding; (3) Sintering and crystallization: The single-section tubular green billet is sent into a high-temperature kiln, and after solid-state sintering and crystallization treatment, it is cooled with the furnace to produce a multi-section silicon carbide microcrystalline tube unit. (4) Composite assembly: Nano heat insulation board layer (2) is fixedly laid on the inner wall of the metal outer shell cylinder (1) in sequence, and a mold is set up to cast a self-flowing castable lining (3); First, multiple silicon carbide microcrystalline tube units are spliced ​​together through a stepped plug-in structure to form a silicon carbide integral microcrystalline inner tube (4), and then the spliced ​​silicon carbide integral microcrystalline inner tube (4) is coaxially positioned and embedded in the inner side of the self-flowing castable lining (3). After curing and solidification, the tube is demolded to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, In step (1), the mass of silicon carbide powder accounts for more than 80% of the total mass of the molding mixture; the sintering aid is an oxide sintering aid, and the organic molding binder is at least one of phenolic resin, dextrin or carboxymethyl cellulose.

8. The preparation method according to claim 6, characterized in that, Step (2) adopts cold isostatic pressing process, the molding pressure is controlled at 150MPa~250MPa, and the holding time is 30s~120s.

9. The preparation method according to claim 6, characterized in that, In step (3), the tubular green blank is first subjected to low-temperature drying treatment before sintering. The drying temperature is 100℃~200℃ and the drying time is 6h~12h. The crystallization temperature is 1350℃~1550℃ and the holding time is 2h~6h. The sintering process is carried out in an air atmosphere or an inert protective atmosphere.

10. The preparation method according to claim 6, characterized in that, In step (4), the curing time of the self-flowing castable lining (3) at room temperature shall not be less than 24 hours, and the relative humidity of the curing environment shall not be less than 70%.

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