With the development of large-scale blast furnaces and technologies such as oxygen enrichment and coal injection, the stability of the quality of coke used in blast furnaces has become a key factor restricting the stable operation of blast furnaces. The insulation effect and life of coke oven door bricks directly affect the quality of coke on both sides of the coke oven machine and coke. The mechanization and automation of coke oven operation require the longevity of furnace door bricks. In addition, with increasingly stringent environmental protection standards, the previous phenomenon of fire and smoke from coke oven doors will be eliminated. Therefore, coke oven door bricks must not only have good refractory properties, but also have good insulation effects, corrosion resistance, and overall stable performance.
The refractory materials of coke oven door bricks have developed from traditional clay and lightweight insulation materials to cordierite, mullite and cordierite composite materials with better refractory properties. In addition to the performance of conventional refractory materials, furnace door brick refractory materials must also have better refractory properties than furnace wall bricks. Including thermal shock resistance, lower heat transfer coefficient and density, corrosion resistance, and anti-carbonization performance.
Cordierite Refractory Materials for Coke Oven Doors
Cordierite (2MgO·2Al2O3·5SiO2) is an aluminum magnesium silicate mineral. Cordierite in refractory materials is generally artificially synthesized. Cordierite has a low thermal expansion coefficient, a small thermal conductivity, and a strong compressive resistance. It is currently one of the most commonly used refractory materials for coke oven door bricks.
Early cordierite was generally synthesized from industrial alumina, clay, kaolin, talc, bauxite, coke gemstone, etc. Cordierite has excellent thermal stability, but its high temperature load performance is relatively poor. In order to further improve the high temperature performance of cordierite, cordierite composite materials are currently being studied more. Including cordierite-mullite composite materials, clay-fused quartz, magnesium aluminum spinel-cordierite composite materials, mullite-alumina composite materials, etc. The performance of these refractory materials is significantly better than cordierite materials.
The coke oven door is frequently opened during production, the surface temperature is high, and the coke outlet temperature varies greatly. The lining of the traditional coke oven door in China is mostly made of cordierite bricks and clay bricks, but the service life is not long.
The reason is: the products of the coking process of the coke oven door are complex and the chemical erosion of the products is serious. Diffusion through the pores of the bricks to the inside of the bricks, diffusion destroys the lattice structure of the bricks, reduces the performance of the bricks, and shortens the service life. The temperature of the coke oven door varies greatly, and rapid heating and cooling cause cracks on the surface of the lining bricks, and also damage the corners of the refractory bricks.
Refractory Castables for Coke Oven Doors
If refractory castables are used for coke oven doors, the body density cannot be too large. Because the door is too large and too heavy, the thermal conductivity is high when it is opened frequently. However, lightweight castables have the characteristics of low thermal conductivity, small thermal expansion coefficient and elastic modulus, and good thermal shock resistance. However, the strength is not good, the apparent porosity is large, and it cannot meet the needs. If cordierite material is used as castable, cordierite has high strength and strong resistance to acidic gas erosion, but it is expensive, has high masonry requirements, and is difficult to replace after local damage.
Moreover, during the use of the coke oven, tar will firmly adhere to the surface of the lining, and the thick carbon deposit layer will cause the furnace door to be closed loosely, leaking and emitting fire. If the carbon deposits are cleaned, the mechanical force will accelerate the early damage of the furnace door lining bricks. In recent years, the lining of large-volume coke oven doors has been mostly made of refractory castable prefabricated blocks. The material is clay plus fused quartz composite castable. Because of the combination of this composite property, the refractory castable has strong thermal shock stability. It can withstand the thermal shock and frequent opening of the furnace door during the coke oven production process. In addition, fused quartz has strong resistance to acid gas erosion and carbon deposition.
Clay and fused quartz composite castables are used as prefabricated blocks. Clay materials are cheap and have high strength. When manufacturing molding modules or integral casting, the production process is simple and convenient to use. The introduction of fused quartz with extremely low thermal expansion coefficient into clay plays a dual role of reducing the thermal expansion coefficient and increasing microcracks, and the thermal shock resistance will increase. It is fully adapted to the temperature of frequent opening of the furnace door under acidic high temperature. In addition, the bulk density and thermal conductivity of fused quartz are both low. When fused quartz is introduced into clay materials, the thermal conductivity of the castable is low, and the weight of the furnace door is appropriate, which fully meets the performance of the coke oven door.
While the performance of the composite refractory castable meets the use, it is made into a prefabricated block, which is convenient to construct and has a long service life. Therefore, the use of clay and fused quartz composite refractory castables is most suitable for coke oven doors.
Magnesium refractory materials are alkaline refractory materials, which are widely used in kilns in high-temperature industries such as steel and cement. Magnesium amorphous refractory materials include magnesium castables, magnesium dry vibrating materials (ramming materials), magnesium gunning materials, magnesium refractory mud, etc. Rongsheng Refractory Material Manufacturer, environmentally friendly fully automatic amorphous refractory production line, specializes in providing refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free samples and quotes.
Since calcium aluminate cement can form high melting point CaO·6Al2O3 (CA6) with Al2O3. Therefore, aluminum-magnesium castables combined with calcium aluminate cement are widely used in steel ladle.
If MgO-MA alkaline castable combined with hydrated alumina can be used instead, due to the absence of CaO impurities, hydrated alumina and MgO form magnesium-aluminum spinel self-combination during use, its load softening temperature and slag resistance will be better than Al2O3-MA castable combined with calcium aluminate cement, and it is also beneficial to improve the quality of steel.
Another direction of the development of magnesium castable is to form a cohesive bond between SiO2 fine powder, MgO fine powder and water. The advantages of this combined magnesium castable are: due to the addition of SiO2 fine powder, the castable has good fluidity. The gel contains less structural water, and dehydration is gradual during heating, which will not cause damage to the structure. During use, a magnesium castable combined with forsterite is formed. Adding a small amount of ZrO2 or zircon to this castable can also improve the thermal shock resistance of the castable. In addition, magnesium castables that are combined with TiO2 micropowder, Al2O3 micropowder and magnesia fine powder to form M2T-MA solid solution are also being studied and developed. In order to improve the slag resistance of magnesium castables, the method of adding AlN, AION or MgAlON is also used.
Magnesium carbon-containing castables have been affected by the inability of water to wet graphite and the low density of graphite. Using surfactants to change the hydrophobic surface of graphite to hydrophilic may be an important way to solve the problem of carbon-containing refractory castables. In addition, carbon-containing refractory materials used in steel plants are also good raw materials for making magnesium carbon-containing castables, because the particles or powders made from this kind of residual bricks have a high carbon content, uniform C distribution, and are dense.
Alkaline magnesium dry ramming material is widely used in various induction furnace linings and ultra-high power electric furnace bottoms. In recent years, it has been used on the intermediate ladle of continuous steel casting with good results.
Dry ramming material is an amorphous refractory material without liquid binder and water. It does not need to undergo strict maintenance after construction. It mainly relies on baking or heating of high-temperature melt during use to sinter the hot surface of the dry ramming material into a whole, forming a dense working layer with a certain strength. In use, except for the working layer, the rest of the dry material is still an unsintered dense stacking structure. Therefore, it has good thermal insulation performance, and at the same time avoids cracking and perforation caused by stress caused by expansion and contraction of refractory materials during use. In addition, it is also convenient to dismantle. However, dry ramming material is not suitable for kilns with rotation and high furnace height.
The commonly used sintering agent for magnesium and MgO-CaO dry ramming materials is iron oxide. FeO and calcium ferrite have low melting points and will gradually be absorbed by periclase to form a solid solution, namely magnesium fustenite [(Mg·Fe)O]. The impurities of magnesium and magnesium calcium dry ramming materials are SiO2 and Al2O3 respectively, and their content should be as low as possible and should not exceed 1%.
If MgO-CaO dry ramming materials use low-melting calcium silicate or magnesium silicate as a sintering agent. At this time, iron oxide becomes a harmful impurity and should be limited.
For MgO-MgO·Al2O3 dry materials, iron oxide or magnesium silicate can be used as a sintering agent. For Al2O3-MgO·Al2O3 dry materials, iron oxide or low-melting calcium aluminate can be used as a sintering agent.
Magnesium Coating or Gunning Material
Magnesium and magnesium-calcium materials are good for purifying molten steel, so they are widely used in intermediate ladle for continuous steel casting. However, when this kind of coating or gunning material is used for casting low-phosphorus steel, phosphate binders should be avoided. Secondly, since a lot of water is added to the coating, it is necessary to bake at high temperature to remove the water as much as possible to avoid hydrogenation in the first few barrels of molten steel.
For magnesium-calcium coating, the source of CaO can be lime milk [Ca(OH)2], light calcium carbonate, etc. according to the method of segmented decomposition, and high-calcium magnesium sand can be used less.
Drying and Curing of Magnesite Ramming Mass Before Use
During the drying process of amorphous refractory materials before use, the surface moisture is first evaporated by heat, and the heat is conducted from the surface to the inside, causing the temperature of adjacent parts to gradually increase. Due to the evaporation of surface moisture, the moisture (steam) inside the refractory gradually diffuses to the surface to replenish. If the heat supply is too large and the temperature rises too fast, the amount of steam generated per unit time is too much. Due to the poor air permeability of amorphous refractory materials, the internal moisture (steam) is blocked from diffusing outward. At the same time, due to the vaporization of moisture, the volume increases sharply, and a large tension will be generated inside the refractory. If the tension exceeds the compressive strength of the refractory, it will cause the refractory to expand and crack. When the difference between the two is large, it will peel off or explode. Therefore, conventional heating and drying requirements are high, and the performance of the refractory cannot be guaranteed. The magnesite ramming mass used can be dried naturally at room temperature, avoiding the damage of high temperature to the refractory, and effectively guaranteeing the performance of the refractory.
Unshaped refractory is a kind of refractory that can be used directly without firing. It has the advantages of fast construction, simplified process, energy saving, good integrity, easy replacement, etc. It is widely used in the metallurgical field. Among them, ramming material is an unshaped refractory material that is constructed by ramming (manual or mechanical), made of a high proportion of granular material and a low proportion of binder and other components, and hardened under heating above normal temperature. The use of magnesite ramming mass on the top of the electric furnace and the copper water jacket at the flue gas outlet of the oxygen-enriched side-blown furnace not only meets the process requirements, but also reduces production costs.
To purchase high-quality unshaped refractory materials, please choose Rongsheng Refractory Factory. Rongsheng Factory provides refractory lining material services to the world. Customers who have used our refractory materials are all over South Africa, Chile, Egypt, Colombia, Uzbekistan, Italy, Indonesia, Ukraine, Hungary, Spain, Kenya, Syria, Zambia, Oman, Venezuela, India, Peru, the United States, Ethiopia, Iran, Afghanistan, Iraq, etc. Contact Rongsheng Now!
Fused cast refractory materials are highly valued by experts from all over the world because they are particularly resistant to corrosion by glass liquid, slag, etc. and have a long service life. They have been rapidly developed. The biggest advantage of alumina-based fused cast refractory materials (except fused mullite bricks) is that they contain very little glass phase, so they are widely used in glass melting furnaces. In fact, fused corundum refractory materials should include two varieties, namely fused corundum sand and fused cast products. The former is combined to produce sintered corundum products and amorphous refractory materials, while the latter is a product directly cast into a certain shape after melting.
Composition of Alumina-Based Fused Cast Refractory Materials
Mullite fused cast bricks can be made from ferroalumina and other SiO2-Al2O3 natural raw materials due to their high SiO2 content. There are also re-sintered fused mullite made from fused mullite as aggregate.
The alumina raw material used in fused corundum bricks is chemically treated industrial alumina with a small amount of soda ash introduced. Adding a small amount of sodium carbonate to industrial alumina can make α (alpha)-corundum fused cast bricks. Adding a little more sodium carbonate can make α·β-mixed crystal corundum fused cast bricks. Adding a larger amount of sodium carbonate can make β (beta)-corundum fused cast bricks. Industrial alumina and chromium oxide can be mixed to make aluminum-chromium fused cast bricks.
Alumina fused cast bricks are mainly composed of Al2O3, with good crystal development and dense structure. Al2O3 precipitates α-corundum after melting and solidification, and β-corundum precipitates when a small amount of Na2O coexists. Its chemical formula is Na2O·11Al2O3, in which the weight percentage of Na2O to Al2O3 is 5:95. In addition to a large amount of Al2O3 and a small amount of Na2O, α-corundum bricks, β-corundum bricks and α·β corundum bricks contain very few other oxides. There are only two crystal phases: α corundum and β corundum.
The SiO2 content of mullite electrofused cast bricks is above 15%. Therefore, in addition to the formation of corundum crystals, a considerable amount of mullite crystals are also generated. A small amount of other oxides such as Fe2O3 and TiO2, part of which forms a solid solution with mullite, and the other part forms a glass phase with a small amount of SiO2 and Al2O3. The main crystal phases in the brick are corundum and mullite. The glass phase is filled between the crystal phases, and there are also a small amount of aluminosilicate crystal nuclei in the glass phase.
In aluminum-chromium electro-fused cast bricks, part of Cr2O3 dissolves in the corundum solid solution, and the other part forms composite spinel with Al2O3, MgO, and FeO in a certain proportion. There is very little glass phase, and due to the small amount of SiO2, the glass phase does not contain crystal nuclei.
Characteristics of Alumina Electro-Fused Casting Refractory
General Characteristics
The main crystal phase of Alumina Electro-Fused Casting Refractory is corundum, which belongs to neutral refractory.
The specific gravity of α corundum is 3.99, and the specific gravity of β corundum is 3.2, so the bricks containing more α corundum have a higher specific gravity. Mullite electro-fused casting bricks contain mullite crystals with a lower specific gravity. Therefore, the specific gravity is lower, which is similar to that of β-corundum bricks. Alumina-chrome bricks have a higher specific gravity than α-corundum bricks because the corundum crystals contain Cr2O3 solid solution and the specific gravity of spinel is greater than that of corundum.
α-corundum bricks (rarely used) and αβ-corundum bricks have less pollution to glass liquid
There are almost no metal oxides with strong coloring properties such as Cr2O3, Fe2O3, Ti02 in these two refractory materials. Therefore, when in direct contact with glass, the glass liquid will not be colored at all. The glass phase content in the material is below 1.0%, which is the lowest among all refractory materials in contact with glass. The glass phase is the weak link in the refractory. After the refractory is eroded, the glass phase is softened and lost first. As a result, the main crystal phase loses its binding material and becomes loose, entering the glass to become stones and streaks. Moreover, the glass phase often contains bubbles, and as the glass phase is eroded and lost, the bubbles also enter the glass liquid. Therefore, bricks with less glass phase have better corrosion resistance and less pollution to glass liquid.
The main crystal phase of fused corundum bricks is corundum, and the viscosity of the metamorphic layer generated after being eroded by soda-lime glass at high temperature is lower than that of cast corundum bricks. Therefore, the corrosion resistance is not as good as that of zirconium corundum bricks at high temperatures, and it is generally not used in the melting pool wall and liquid flow hole. It is mainly used on the working pool wall and material channel. The temperature in these parts is relatively low, and the main requirement is that the bricks have less pollution to the glass liquid. When these two refractory materials are used in these low-temperature parts, they have less pollution to the glass liquid than zirconium corundum bricks. Compared with α-corundum bricks and αβ-mixed crystal corundum bricks, α-corundum bricks are more resistant to glass liquid corrosion if the porosity is the same. In fact, due to production reasons, some α-corundum bricks have a higher porosity. The corrosion resistance of α-corundum bricks with higher porosity is worse than that of αβ-corundum bricks with lower porosity. Pay special attention to this point. αβ-corundum bricks are often used for the working pool wall bricks.
β-corundum electric fused cast brick has good stability to alkali vapor
β-corundum brick is pure β-corundum crystal, that is, Na2O·11Al2O3 crystal. The crystal is plate-shaped, large, and cross-bonded. The surface of the brick is soft and light-colored, translucent, brittle and fragile. This brick has two major characteristics. The first is good resistance to alkali vapor erosion. The second is good thermal stability.
Alumina will generate β-corundum after contacting with alkali metal oxides at high temperature. Because β-corundum bricks themselves are composed of corundum crystals, they will not react with alkaline oxides. But another point to pay special attention to is that SiO2 will react with corundum as follows:
2SiO2+Na2O·11Al2O3→Na2O·Al2O3·2SiO2+10Al2O3
That is, nepheline and α-corundum are generated. This will make the structure of β-corundum bricks loose and destroyed. Therefore, β-corundum bricks cannot be in contact with SiO2 at high temperatures. This makes this brick unsuitable for use in areas with large dust content, in the upper space near the charging port in a horizontal flame furnace, and in the upper space of the melting pool in a horseshoe flame furnace.
β-corundum bricks have the best thermal stability among all electro-cast refractory materials due to their well-developed crystals, close bonding and cross-linking between crystals, and high porosity. They are very suitable as refractory materials for the rear section of the melting section of a horizontal flame pool furnace (away from the charging port) and the upper space of the working pool. But one thing to note is that their compressive strength is low. If it is used as a sill brick, the span of the sill cannot exceed 6 meters.
Mullite electro-cast refractory has poor performance
Mullite electro-cast brick is the oldest electro-cast refractory. It is inferior to other electro-cast refractory materials, but better than combined refractory materials. It was used as the lower pool wall brick a long time ago to balance the life of the upper and lower pool wall bricks, so as to reduce the cost.
When electro-cast mullite bricks are manufactured, corundum crystals are first precipitated during the cooling process, followed by mullite crystals. These two crystal phases consume most of the SiO2 and Al2O3 in the brick composition. The remaining small amount of SiO2 and Al2O3 coexists with the remaining components, namely Fe2O3, TiO2, CaO, MgO, and Na2O, and finally becomes a glass phase. The glass phase accounts for a large proportion of the brick, and the glass phase contains so many low-melting-point substances. Therefore, the corrosion resistance is worse than other electro-cast refractory materials. In addition, the glass phase contains bubbles and reducing substances, so the generation of bubbles will pollute the glass liquid. On the other hand, electro-fused mullite bricks have better corrosion resistance than sintered refractory materials with the same composition. This is because the mullite in the refractory material will generate corundum and nepheline liquid phases when it is corroded by alkali. The nepheline liquid phase has low viscosity and is easy to lose. As a result, the brick body is damaged. Due to the high porosity of sintered refractory materials, this reaction can penetrate into the interior of the brick body, so it is very destructive. Due to the high density of mullite electro-fused bricks, this reaction can only occur on the surface of the brick, so it has higher corrosion resistance.
Aluminum-chromium (chrome corundum) electro-cast refractory with particularly good corrosion resistance
The glass phase content of aluminum-chromium electro-cast refractory is very low, below 5%. It is surrounded by two crystal phases with good corrosion resistance. One of the crystal phases is corundum enhanced by the presence of Cr2O3. The second crystal phase is a composite spinel composed of Cr2O3, MgO, Al2O3, etc. Both crystal phases are very stable. Therefore, the corrosion resistance of the entire brick is particularly good, three times higher than the high-temperature corrosion resistance of No. 41 zirconium corundum brick, and it is ideal for use as a flow hole brick.
However, due to the extremely strong coloring of Cr2O3, the coloring ability of trivalent Cr is dozens of times higher than that of trivalent Fe, so it can only be used in glass fiber tank furnaces and dark green bottle glass tank furnaces that have no requirements for color. In addition, the thermal stability of this brick is not good, which also limits its use.
Precautions
Poor thermal shock resistance. Electrofused refractory materials are dense and have low porosity. When subjected to thermal shock and uneven heating, there are no pores for buffering and adjustment, so they are very easy to burst. Since the glass pool furnace is operated continuously for a long time, the temperature does not change much, so this shortcoming does not affect the use. However, near the crater, the temperature will change somewhat due to reversing, so pay attention. In addition, pay attention to temporary cooling and furnace repair. The furnace temperature cannot change too much. This type of brick has poor thermal stability. But there are still differences between different varieties.
The order of thermal stability is as follows (when the porosity is the same):
Corundum Mullite Refractory Bricks for Glass Kilns
Corundum mullite bricks for glass kilns are high-quality refractory products. This product uses corundum as the main raw material and mullite as the auxiliary raw material. By adding an appropriate amount of high-purity alumina, ultrafine silicon oxide powder, and additives, it is strongly pressed and formed by a 630T friction press. It is fired at high temperature in an oxidizing atmosphere and can be used for a long time in a high-temperature environment of 1700 degrees. The characteristics of corundum mullite bricks for glass kilns are as follows:
(1) The Al2O3 of corundum mullite bricks for glass kilns is ≥82%, which has good high-temperature resistance. At the same time, the refractory temperature is high, and the load softening temperature is greater than 1700 degrees.
(2) Resistant to chemical erosion, it has strong resistance to acidic solutions or slag.
(3) The Fe2O3 content in the product is ≤0.3%, which is resistant to oxidation. It is not easy to react chemically with gases such as O2, H2, and CO.
(4) Good thermal stability, high temperature volume stability, not easy to expand or shrink.
(5) Good thermal shock resistance, 1100℃ water cooling ≥30 times, resistant to rapid cooling and heating, not easy to peel off.
(6) High compressive strength at room temperature, ≥100Mpa, not easy to wear during transportation or unloading.
Corundum mullite bricks can directly contact flames, resist peeling, and withstand high temperatures. They can be used as working linings for high-temperature industrial furnaces. They are mainly used in petrochemical industry, large and medium-sized synthetic ammonia gasification furnaces and magnetic material gas furnaces, and supporting facilities for high-temperature industrial kilns. Rongsheng Refractory Material Manufacturercan customize refractory lining solutions according to the working conditions of glass kilns. It can also customize and process various shapes of corundum and mullite refractory bricks and products according to the customer’s high-temperature equipment requirements.
Glass melting pools require high temperature, erosion resistant, long life materials. Typical refractories commonly used in this high temperature application are fused cast zirconium corundum (AZS, 40% ZrO2) and zirconium oxide (>80%), which have low apparent porosity (<0.7%) and high bulk density. The microstructure of refractory bricks made by the fusion casting process varies between the surface and the center, and usually contains shrinkage pores. Sintered AZS refractories with high apparent porosity (~20%) are also used in glass processing. Refractory manufacturers, the performance of sintered high zirconium refractories was compared with fusion cast refractories.
Specific process of preparing zirconia refractory materials: Mix deionized water (11.5%) and alumina in a mixer for 10 min to form a slurry. Then gradually add boron oxide and silica fume, and mix for 10 min before each addition. Add nitric acid (diluted to 50:50 with deionized water) to make the pH value of the slurry about 3.5. Add zirconium oxide to the slurry and stir continuously until the zirconium oxide is evenly distributed. Heat the mixed slurry from room temperature to 40-80℃ (oven) and dry it, then pass it through a 100-mesh sieve. The dried powder is uniaxially pressed into a strip sample, and isostatic pressing and extrusion molding can also be used. Sample firing system: 25-1000℃ heating rate 50℃/h. At 1000-1700℃, the heating rate is 25℃/h. Keep warm at 1700℃ for 6-48h. At 1700-1300℃, the cooling rate was controlled to be 50-200℃/h. The cooling rate from 1300 to 1000℃ was 25℃/h. The cooling rate from 25 to 1000℃ was 50℃/h.
Various properties (specific gravity, apparent porosity, flexural strength, XRD and thermal conductivity) of the sintered sample (BZR) were measured and compared with those of industrial fused-cast zirconia (Scimos CZ). Static erosion tests were conducted on the prepared sintered zirconia refractory and commercial fused-cast zirconia samples (Scimos CZ). The crucible with glass-cullet and the refractory sample were placed in a furnace respectively and preheated to 1660℃. After sufficient insulation for a period of time, the refractory sample was placed in the center of the crucible and kept at this temperature for 3 days. After the test, the corrosion loss of the sample was measured at different points. The resistance of the sintered sample at 1500℃ and 1600℃ was measured by the 4-wire method. The microstructures of BZR and Scimos CZ were observed by scanning electron microscope. The comparative experimental results are as follows:
1) After sintering, the sintered zirconia sample was white or slightly milky due to the presence of impurities. Fusion-cast refractory bricks are usually gray due to the use of graphite electrodes during the melting process.
2) The performance of the sample, its specific gravity, apparent porosity, flexural strength and thermal conductivity test results are comparable to those of commercial fused-cast zirconia refractory materials.
3) Static and dynamic erosion tests show that the corrosion resistance of sintered zirconia refractory materials is comparable to or slightly better than that of commercial fused-cast zirconia Scimos CZ.
4) Sintered zirconia refractory materials exhibit high resistivity at high temperatures (1500-1600 ℃), comparable to commercial fused-cast materials (Scimos CZ).
5) The microstructure of sintered zirconia shows that it is composed of fine zirconia particles with glass phases between the particles. The microstructure of the entire brick body is uniform. The fused-cast zirconia microstructure has large grains that vary in size from the surface (smaller) to the center (larger) of the brick body, which are formed during cooling. During crystallization, voids and/or pores form in the center of the specimen, and the glass phase formed in the center and on the surface may have different compositions.
Performance Characteristics of Sintered High Zirconium Refractory Materials for Glass Industry
By mixing nano-glassy precursors with zirconium oxide particles, high zirconium oxide refractory samples of the required size were prepared by pressing (or isostatic pressing, extrusion, etc.) molding process. Then the sintered zirconium oxide refractory (BZR) was prepared by controlling the sintering process. High zirconium oxide refractory has similar specific gravity and lower apparent porosity, similar flexural strength and thermal conductivity to commercial fused-cast refractory. X-ray diffraction patterns show that the main phases of the sample are zirconium oxide phase and glassy amorphous phase. Static and dynamic erosion tests show that BZR has excellent erosion resistance to different glasses at high temperature (1715°C). BZR also shows high resistivity (measured above 1500°C), which is comparable to fused-cast refractory.
Zirconium-containing refractory bricks are refractory bricks made of zirconium oxide (ZrO2) and zircon (ZrSiO4) as raw materials. Zirconia bricks, zircon bricks, zircon mullite and zirconium corundum bricks all belong to this type of refractory bricks. According to different production processes, zirconium-containing refractory bricks are divided into sintered bricks, fused cast bricks and unfired bricks. Zirconium-containing refractory bricks have the characteristics of high melting point, low thermal conductivity, good chemical stability, especially good corrosion resistance to molten glass.
There are several phases in the Zr-O system that are non-stoichiometric solid solutions of oxygen in zirconium and oxides. The stable compound of zirconium and oxygen is dioxide ZrO2. The ion radius ratio in zirconium dioxide is 0.66, which is close to the boundary between the crystal coordination number 8 and 6. The zirconium cation size is large (0.082nm), and in order to achieve 8 coordination, the oxygen ions are as close as possible in the lattice. Therefore, ZrO2 exhibits abnormal coordination. When its coordination number is equal to 7, one of the oxygen atoms occupies the position between the two nodes of the AB lattice. A lattice -8 coordination and B lattice -6 coordination. At high temperature, the Zr-O bond length increases due to the thermal motion of ions at the lattice nodes. This is the result of the transition of oxygen ions from the unit space to the A or B position. At the same time, the 8-coordination of anion vacancies is achieved.
The properties of zirconium-containing refractory materials depend on the properties of ZrO2. The melting point of dense, stabilized zirconium oxide is 2677℃, and the service temperature reaches 2500℃. The bulk density fluctuates between 4.5 and 5.5g/cm3 due to the purity of the raw materials and the manufacturing method. The bulk density of dense zirconium oxide bricks can reach 5.75g/cm3. Sintered zirconium oxide products react chemically with liquid glass. Caustic solutions, carbonate solutions and acids (except concentrated H2SO4 and HF) do not react chemically with zirconium oxide. ZrO2 has high structural strength and has the ability to work at 2200~2450℃ as a lining hot surface.
Zirconia bricks have high mechanical strength, and the strength is maintained up to 1300~1500℃. The thermal conductivity of ZrO2 is much lower than that of all other oxide materials. This property of ZrO2 can be used as a high-temperature insulation layer, and the physical and chemical properties of zirconium-containing refractory bricks.
Mullite-andalusite-cordierite bricks have excellent thermal shock resistance and are widely used in hot blast furnace ceramic burners. This paper conducts comparative tests on kyanite-mullite-andalusite bricks and mullite-andalusite-cordierite bricks to analyze the effect of kyanite-mullite on the performance of ceramic burner bricks.
Kyanite-Mullite on the Properties of Ceramic Burner Bricks
Kyanite-mullite is an artificially synthesized mullite raw material made of kyanite as raw material. The kyanite concentrate is crushed, wet-milled, filtered, squeezed into mud, and calcined at 1550℃-1600℃. The physical and chemical properties of kyanite-mullite are shown in Table 1, and the X-ray diffraction analysis spectrum is shown in Figure 1.
Table 1 Physical and chemical properties of kyanite-mullite
Items
Kyanite-Mullite
Al2O3 %
46.43
SiO2 %
50.16
Fe2O3 %
0.64
TiO2 %
1.20
CaO %
0.22
MgO %
0.16
K2O %
0.72
Na2O %
0.1
Bulk Density g/cm3
2.29
Apparent Porosity %
1.3
Mullite Phase %
60
Glass Phase %
30-40
Figure 1 X-ray diffraction analysis of kyanite-mullite
From Table 1 and Figure 1, it can be seen that kyanite-mullite is composed of 60% mullite phase, 30-40% glass phase and 3-5% quartz phase.
This experiment designed two sets of process ratios. Process No. 1 uses alumina-based mullite, garnet and cordierite as the main raw materials. Process No. 2 uses kyanite-based mullite and garnet as the main raw materials. A 50kg mixer was used for mixing, a 400 t press was used for molding, and a tunnel kiln was used for sintering. The test sample is shown in Figure 2, and the results of the physical and chemical properties test are shown in Table 2.
Figure 2 Test sample diagram
Table 2 Physical and chemical properties test results
Items
1#
2#
Al2O3 %
61.73
61.22
Fe2O3 %
1.00
0.96
Apparent Porosity %
22.8
19.7
Bulk Density g/cm3
2.32
2.42
Compressive Strength MPa
51.9
81.5
Load Softening Temperature ℃
T0.6/0.2MPa
1482
1548℃
Creep Rate %
0.2MPa
1250℃x50h
-0.622
1350℃x50h
-0.457
Reburning Line Change Rate %
1400℃×2h
+0.1、+0.1
+0.2
+0.1、+0.2
+0.1
Thermal Shock Resistance
1100℃, Water Cooling
＞100
＞100
It can be seen from Table 2 that the chemical compositions of processes No. 1 and No. 2 are similar. The porosity, bulk density, compressive strength and load softening temperature of process No. 2 are significantly better than those of process No. 1. The load softening temperature of process No. 2 is 68°C higher than that of sample No. 1. This is because after the temperature reaches 1460°C, cordierite is completely decomposed into mullite and glass phase. The raw materials of synthetic cordierite used in refractory materials have a high impurity content (in order to expand the temperature range of cordierite formation and promote sintering), so the high-temperature performance is general. Kyanite-based mullite has a low impurity content, a high main crystal phase content, and a good crystal shape. The high-temperature performance (including load softening temperature and creep rate) is much higher than other aluminum-silicon raw materials with the same aluminum content.
The number of thermal shock resistance (1100°C water cooling) of processes No. 1 and No. 2 is greater than 100 times, which meets the requirement of thermal shock performance of ceramic burner bricks > 100 times. The test bricks after 100 thermal shocks are shown in Figure 3. As can be seen from Figure 3, although both can complete 100 thermal shock tests without damage, the number, width and length of cracks in process 1 are significantly smaller than those in process 2. This shows that mullite-andalusite-cordierite bricks have better thermal shock resistance.
Analysis shows that kyanite-based mullite is a mullite-high silica glass composite material. Its well-developed mullite crystals, uniformly distributed network structure and high-viscosity silicon-rich glass phase all have an improving effect on the thermal shock resistance of the material. In particular, the presence of its high-viscosity glass phase can not only reduce the slip between crystals at high temperatures and improve the thermal mechanical properties of the material, but also inhibit crack extension.
Figure 3 Condition of test brick after thermal shock test
The following conclusions were drawn through test data analysis:
The apparent porosity, bulk density, load softening temperature and creep rate of kyanite-mullite-andalusite bricks are better than those of mullite-andalusite-cordierite bricks.
The thermal shock of kyanite-mullite-andalusite bricks is greater than 100 times, which can meet the most demanding thermal shock requirements of hot blast furnace ceramic burners. However, mullite-andalusite-cordierite bricks have better thermal shock resistance.
Semi-cordierite bricks are a type of refractory material with cordierite (2MgO·2Al2O3·5SiO2) as the main component. Pure cordierite contains 13.7% magnesium oxide (MgO) and has the following characteristics: Low thermal expansion coefficient of 3×10-6/℃. Due to the low thermal expansion coefficient, cordierite materials generally have excellent thermal shock resistance.
Pure cordierite is an expensive material, so semi-cordierite materials with lower purity are often used as substitutes. Semi-cordierite materials also exhibit a lower thermal expansion coefficient.
Semi-cordierite materials are often used as kiln furniture, kiln car fixing blocks and ceramic parts for ceramic kilns. In some cases, alumina-silicate materials are also used for the same product applications. Table 7 lists the characteristics of some semi-cordierite products used for kiln furniture/kiln blocks. The maximum service temperature of these products is generally 1200℃ or higher.
Table 7 shows the relationship between magnesium oxide content and thermal expansion coefficient. When magnesium oxide content is very low, the thermal expansion coefficient is close to that of clay brick or mullite [about 6×10-6/℃].
Figures 5 and 6 show the microstructure of typical products of this type.
Figure 5 Microstructure of semi-cordierite extruded into pyrophyllite
Figure 6 Microstructure of clayey semi-clay pressed brick
The microstructure of semi-cordierite material shows “crack-shaped” pores, which are typical of extruded clay products (Figure 5). It is not obvious from this micrograph that the size of the pyrophyllite aggregate particles is large, sometimes approaching 3 to 4 mm. In contrast, the microstructure of the pressed semi-cordierite material shows that the refractory aggregate particles are surrounded by a sintered clay matrix and the pores are mainly round (Figure 6). Many authorities believe that the presence of fine round pores improves thermal shock resistance. Therefore, a pressed product with a magnesium oxide content of about 0.9% (Table 7) may have similar properties to an extruded product with a magnesium oxide content of 3.0%.
The typical impurity in semi-cordierite bricks is cristobalite. When the refractory material is fired at a temperature of at least 1300°C, the “free” silicon dioxide (SiO2) or quartz in the raw material is converted to cristobalite. By reference to the MgO-Al2O3-SiO2 phase equilibrium diagram (not shown), it can be seen that free cristobalite is an equilibrium phase unless the composition of the product is exactly the same as pure cordierite. Too high a cristobalite content will cause “caking” and reduce the life of the kiln furniture/kiln blocks. Cristobalite is conveniently determined by X-ray diffraction (XRD) or thermal analysis (TA) techniques.
Kiln furniture (saggers, shelves, push plates, etc.) is a tool used to space, support, cushion and protect the baked blanks in the industrial kiln during the baking process. The development of high-performance kiln furniture is of great significance for the firing of high-quality products. Since fused mullite has good thermal shock resistance, high-purity fused mullite is the best raw material for preparing high-quality kiln furniture.
Mullite-corundum kiln furniture
Mullite-corundum refractory material is one of the mainstream materials of kiln furniture at present. It has good high temperature strength, thermal shock resistance and chemical stability, and is particularly suitable for supporting soft magnetic (ferrite) materials and electrical insulating ceramics. Using M75 fused mullite and fused corundum as aggregates, aluminum glue, α-Al₂O₃ micropowder and SiO₂ micropowder as bonding matrix, mullite-corundum high temperature push plate with good thermal shock resistance was prepared. After 2 thermal shocks (1100℃⇌water cooling), the flexural strength retention rate was 78%, and no fracture occurred after 23 thermal shocks. The thermal shock resistance of corundum-mullite kiln furniture can be further improved. The mechanism of improved thermal shock resistance is: zircon decomposes into ZrO₂ and SiO₂ during the firing process. On the one hand, SiO₂ migrates outward from the ZrO₂ aggregate, and closed pores are generated at the position of SiO₂. On the other hand, the annular microcracks caused by thermal mismatch between ZrO₂ aggregates and the surrounding mullite matrix can disperse the stress generated during thermal shock cycles.
Cordierite has a low thermal expansion coefficient (2.5×10⁻⁶℃⁻¹ from room temperature to 1000℃) and has excellent thermal shock resistance. The thermal expansion coefficient of cordierite is smaller than that of mullite. Due to the mismatch in the thermal expansion coefficients of the two, microcracks are easily formed at the interface between the two phases, which is beneficial to improve the thermal shock resistance of mullite-cordierite materials. The shelf is a special kiln furniture for supporting porcelain parts, and the material is mostly cordierite-mullite composite material. With M60 mullite and cordierite as the main raw materials and dextrin as a binder, a high-strength cordierite-mullite shelf is prepared, and the high-temperature flexural strength at 1200℃ can reach 17.7MPa. Because the skeleton of the material is composed of mullite and cordierite aggregates, the two are firmly connected by a “connecting bridge” composed of mullite, cordierite and low-aluminum high-silica glass phase, and this structure is conducive to improving the high-temperature mechanical properties of the material.
With the development of new energy vehicles, electronic mobile devices and energy storage fields, the demand for lithium batteries is increasing, and the kiln tools used for firing their positive electrode materials are also increasingly attracting attention.
Mullite-aluminum titanate kiln tools
Compared with cordierite, aluminum titanate has a lower thermal expansion coefficient (room temperature to 1000℃, 1.5×10⁻⁶℃⁻¹) and a higher melting point. It is currently the best material with high temperature resistance among low expansion materials. When mullite and aluminum titanate are used in combination, mullite-aluminum titanate kiln tools with good thermal shock resistance and high operating temperature can be obtained. Studies have shown that when mullite is added to the aluminum titanate matrix, the lattice stability of aluminum titanate can be improved, thereby preventing the decomposition of aluminum titanate. It was found that when mullite exists in aluminum titanate materials, the stability of aluminum titanate can reach 80%.
Mullite-silicon carbide kiln furniture
Silicon carbide has high strength, high thermal conductivity, wear resistance, chemical corrosion resistance and other properties. Therefore, silicon carbide kiln furniture has excellent thermal shock resistance, high wear resistance and strength at room temperature and high temperature. In order to improve the oxidation resistance of silicon carbide kiln furniture, Shi Jinxiong et al. prepared silicon carbide-mullite kiln furniture using silicon carbide, M70 sintered mullite and SiO₂ micropowder as raw materials.
Application of Mullite in Metallurgical Industry
The application of mullite in metallurgical industry is mainly reflected in steel smelting. Mullite bricks made of mullite as the main raw material have the characteristics of small thermal expansion coefficient, low creep rate, high high temperature strength, good thermal shock resistance and strong chemical corrosion resistance. It can be used for blast furnace, continuous casting, the dome of hot blast furnace and the middle and upper parts of the combustion chamber, etc., and can also be used as ceramic burner bricks. Amorphous refractory materials containing mullite also have good thermal shock resistance and mechanical properties, etc., and are used in blast furnaces, permanent linings of ladles, tundishes, ignition and insulation furnaces, hot metal desulfurization spray guns, etc.
Mullite-corundum bricks have high density, low porosity, high strength and good resistance to molten iron and slag erosion. They are ideal refractory materials for blast furnace ceramic linings, furnace walls, tuyere and furnace bottom. Mullite-corundum castables can be used as lining materials for blast furnace hot blast furnaces and heating furnaces.
The purity of mullite raw materials affects the performance of mullite-corundum refractory bricks. Corundum-mullite bricks prepared with high-purity sintered mullite as raw materials have excellent resistance to alkali vapor and CO erosion. Suitable for use in high-temperature reducing atmosphere conditions such as hot blast furnaces. Compared with mullite-corundum castables prepared with fused mullite as aggregate, mullite-corundum castables prepared with microcrystalline mullite as aggregate have higher room temperature compressive strength, room temperature flexural strength, high temperature flexural strength, and better thermal shock resistance.
Introducing other refractory raw materials on the basis of mullite and corundum can further improve the performance of mullite-corundum refractory materials. Adding an appropriate amount of boron carbide to the silica sol combined mullite-corundum castable can further improve the room temperature flexural strength, room temperature compressive strength, high temperature flexural strength and thermal shock resistance of the castable.
Mullite-cordierite refractory materials
In order to meet the requirements of good thermal shock resistance, scouring resistance, high temperature resistance, erosion resistance, high load softening temperature and other requirements of refractory materials for ceramic burners, M70 sintered mullite, M70 fused mullite and cordierite are used as the main raw materials, and the mullite-cordierite ceramic burner composite bricks are prepared through the casting-centrifugal molding process.
The lining bricks of the coke oven door need to have good wear resistance, volume stability, carbon resistance and thermal shock resistance. With M70 sintered mullite and cordierite as the main raw materials and aluminate cement as the binder, a mullite-cordierite precast brick with low linear expansion rate, low porosity and good thermal shock resistance was prepared. The precast brick was applied to the door of a large coke oven. After one year of use, the surface of the precast brick was smooth and crack-free.
Mullite-alumina refractory materials
Casting materials made with mullite and bauxite as the main raw materials use less water and exhibit high mechanical strength over a wide temperature range.
In order to further improve the wear resistance and thermal shock resistance of mullite-alumina-based castables, a mullite-alumina-silicon carbide castable with excellent mechanical properties and wear resistance was prepared with M60 mullite, bauxite and silicon carbide as the main raw materials and calcium aluminate cement as the binder.
Mullite-magnesium aluminum spinel refractory
Magnesium aluminum spinel has excellent thermal shock resistance, corrosion resistance and wear resistance. Studies have found that the introduction of nano-magnesium aluminum spinel into mullite-based castables generates tension ring stress around the spinel and forms microcracks in the matrix due to the mismatch in thermal expansion coefficients between mullite and magnesium aluminum spinel. This is conducive to strengthening the internal structure of the material, thereby limiting the expansion of cracks. Therefore, the prepared mullite-magnesium aluminum spinel castable has good thermal shock resistance.
Mullite-silicon carbide refractory
Silicon carbide has high strength, high thermal conductivity, wear resistance and other properties, and can be combined with mullite to prepare mullite-silicon carbide castables with excellent performance. Mullite-silicon carbide wet jet castable. The wet jetting castable has good rheological properties, showing a pseudoplastic fluid with low yield value and apparent viscosity, suitable for pumping pipeline transportation, and can be used in kilns such as ladles, electric furnaces, blast furnaces, and torpedo tanks. Adding 6% (w) zircon to the mullite-silicon carbide castable can further improve the wear resistance of the mullite-silicon carbide castable, making it suitable for lining parts with strict requirements for thermal shock resistance and wear resistance.
In order to solve the problem of reduced high temperature performance of corundum-silicon carbide castables bonded with ordinary binders (such as calcium aluminate cement), a mullite-bonded corundum-silicon carbide cement-free castable was prepared using corundum and silicon carbide as aggregates, M70 mullite powder, Al₂O₃ micropowder and SiO₂ micropowder as bonding matrix. Because the mullite powder introduced into the matrix can form a network structure of columnar mullite inside the castable after sintering, the room-temperature flexural strength, room-temperature compressive strength, high-temperature flexural strength and thermal shock resistance of the corundum-silicon carbide castable are improved.
Development of the Application of Mullite and Its Composite Refractory Materials
Mullite and its composite refractory materials have been widely used as linings for various kilns in traditional fields such as metallurgy, ceramics, cement and petrochemicals. The future development trend of mullite in refractory materials is mainly reflected in the following aspects:
(1) Expand the application field of mullite refractory materials. In addition to the traditional high-temperature industrial field, mullite refractory materials have emerged in aerospace, military and other fields. However, the application of mullite refractory materials in these fields is quite limited at present, and its application in aerospace, military and other fields will continue to be promoted in the future.
(2) Promote the development of lightweight mullite. With the advancement of energy conservation and emission reduction, the development of lightweight and heat-insulating refractory materials is of great significance to reducing kiln heat loss and improving work efficiency. Refractory materials prepared with lightweight mullite not only have good high-temperature performance, but also have good thermal insulation effect. The use of lightweight heat-insulating refractory materials with good high-temperature performance can thin or even eliminate the working layer. Refractory castables made of lightweight mullite can solve the problem that lightweight refractory castables made of perlite, vermiculite or ceramsite have low use temperature and cannot be used as working linings in direct contact with flames at high temperatures. Therefore, the development of lightweight mullite with large porosity, low bulk density, low thermal conductivity and high strength plays a positive role in the development of lightweight insulating refractory materials with good high-temperature performance that can achieve energy saving and consumption reduction.
(3) Strengthen the application of nano-mullite in refractory materials. In recent years, nanotechnology has been successfully applied in refractory materials and has continuously achieved breakthroughs in material performance. The use of nano-mullite powder can further improve the performance of refractory materials. In the future, nano-mullite will play an increasingly important role in refractory materials.
The energy consumption of cement rotary kiln is very serious, especially when the refractory materials in the transition zone before and after the cement rotary kiln are not protected by the kiln skin, the refractory bricks are directly affected by material erosion, heat load and mechanical stress, and the use conditions are very harsh. At present, the transition zone of large cement rotary kilns generally uses Silicon carbide mullite bricks, silica-molybdenum red bricks or magnesia-alumina spinel bricks, and the service life basically meets the requirements of cement production. However, due to the large thermal conductivity of magnesia-alumina spinel bricks and silica-molybdenum bricks, Silicon carbide mullite red bricks, magnesia-alumina spinel bricks ≥3.0 W/m·K, Silicon carbide mullite bricks ≥2.8 W/m·K. As a result, the outer wall temperature of the cylinder in the transition zone before and after the operation of the cement rotary kiln is too high, averaging about 340℃ and up to 400℃. The higher outer wall temperature of the cylinder brings a series of problems, such as increasing the coal consumption per ton of cement clinker and increasing the emission of polluting gases. Severe cases also cause “red kilns”, affecting the safe operation of cement rotary kilns.
In order to solve the problem of high thermal conductivity of magnesia-alumina spinel bricks, the sintering performance and microstructure of rare earth oxide-doped porous magnesia-alumina spinel refractory aggregates were studied. Porous magnesia-alumina spinel was prepared with industrial α-alumina micropowder and fused magnesia sand as the main raw materials, sodium dodecylbenzene sulfonate (SDBS) as the foaming agent, and dextrin as the binder. In addition, different mass fractions of Y2O3, Yb2O3, La2O3, and Sm2O3 were added respectively, and the samples were kept warm for 3 hours at 1600℃ for sintering. The bulk density and apparent porosity of the sintered samples were measured respectively, and the phase composition and microstructure were analyzed by XRD, SEM, EDS, and other characterization methods to reveal the mechanism of rare earth oxides promoting the sintering reaction process of porous magnesia-alumina spinel.
The introduction of rare earth oxides promotes the sintering of magnesium-aluminum spinel. The sample volume density and compressive strength reach the maximum when the Sm3O2 addition is 1.5wt%, which are 2.28g/cm³ and 50.5Mpa, respectively. A substitution solid solution is formed between the rare earth oxides and magnesium-aluminum spinel, which promotes the sintering densification of magnesium-aluminum spinel. Cation vacancies and lattice defects of magnesium-aluminum spinel are conducive to the development and growth of magnesium-aluminum spinel crystals. The thermal conductivity of the product made from this raw material is significantly lower than that of similar products.
The lightweighting of refractory materials is mainly achieved by introducing a certain amount of pores into the materials, which has a lower thermal conductivity without significantly reducing the strength of the refractory materials. It can save energy and reduce resource consumption in the preparation and service of raw materials, which is a direction of research and development of refractory materials. Therefore, the development of new low thermal conductivity magnesium-aluminum spinel lightweight refractory materials has important practical significance for energy saving and consumption reduction in the cement industry.
When synthesizing magnesium-aluminum spinel lightweight aggregate, adding yttrium oxide, ytterbium oxide, lanthanum oxide and samarium oxide can increase the volume density of the sample, reduce the apparent porosity, increase the compressive strength, and promote the formation of magnesium-aluminum spinel. Among them, the sample with samarium oxide added has better sintering performance. When the addition amount of Sm2O3 reaches 1.5 wt%, the sample has the lowest apparent porosity and the highest volume density of 2.28g/cm³ and 31.72%, respectively.
Rongsheng Magnesia Aluminum Spinel Bricks for Cement Kilns
Application of Low Thermal Conductivity Magnesia-Alumina Spinel Bricks
The low thermal conductivity multi-layer composite magnesia-alumina spinel bricks developed by the above technology are used in 24-32 meters, and the average temperature is 43℃ lower than that of magnesia-alumina spinel bricks, and the service life reaches more than 12 months. Low thermal conductivity magnesia-alumina spinel bricks are not only recognized by domestic customers, but also have been used in many rotary kilns by overseas customers such as Mexican cement and Turkey, and have been highly praised.
In response to the high energy consumption and high carbon emissions in the cement industry, the low thermal conductivity multi-layer composite magnesia-alumina spinel bricks studied by Rongsheng Refractory Material Factory have the following advanced features: through the form of a three-layer composite structure, the working layer is optimized, the thermal conductivity of the working layer is reduced, the thermal shock resistance is improved, and the insulation layer is optimized to improve the strength of the insulation layer. Through the study of different insulation materials, zirconia reinforced alumina fiberboard with excellent high temperature resistance is selected as the insulation layer material. In the preparation process, innovative production processes are used to achieve synchronous molding and synchronous firing, simplify the process, reduce costs, and improve production efficiency. The thermal conductivity of low thermal conductivity magnesium-aluminum spinel brick is 2.4-2.5W/(m·K), which is much lower than the 3.0-3.3W/(m·K) of ordinary magnesium-aluminum spinel brick.
According to the actual application feedback from customers, low thermal conductivity multi-layer composite magnesium-aluminum spinel brick can effectively reduce the temperature of the transition zone cylinder of cement kiln, with significant energy saving and carbon reduction benefits. It provides a new direction for energy saving and emission reduction of cement rotary kiln.
Magnesium-Aluminum Spinel Brick for Lime Kiln
Magnesium-aluminum spinel brick for lime kiln is a high-performance refractory material designed for lime kiln. It is mainly composed of magnesium-aluminum spinel (MgAl2O4) generated by the reaction of magnesium and aluminum oxides at high temperature, and may contain a certain amount of other refractory oxides to enhance its performance. Magnesium-aluminum spinel has excellent high temperature resistance, corrosion resistance, thermal shock resistance and other characteristics, making it an ideal choice for key parts in lime kiln (such as burning zone, preheating zone, etc.).
(1) High temperature resistance: Magnesium-aluminum spinel bricks have extremely high refractoriness and can withstand the high temperature environment in the lime kiln, ensuring the stable operation of the kiln.
(2) Corrosion resistance: In the reducing atmosphere of the lime kiln, magnesium-aluminum spinel bricks can resist the erosion of kiln slag and furnace gas, extending the service life.
(3) Thermal shock resistance: Magnesium-aluminum spinel bricks have good thermal shock resistance and can withstand the thermal stress caused by the rapid change of kiln temperature, preventing the brick body from cracking and falling off.
Magnesium-aluminum spinel bricks are mainly used in key areas such as the firing zone and preheating zone of the lime kiln. These areas have extremely high requirements for the performance of refractory materials. The use of magnesium-aluminum spinel bricks can significantly improve the operating efficiency and product quality of the lime kiln. Contact Rongsheng manufacturers for free samples and quotations.
Mullite polylight bricks are generally marked with JM, where J is the first letter of the pinyin of polylight and M is the first letter of the pinyin of mullite. They are mainly used for heat preservation in the linings of various high-temperature furnaces to improve the heat preservation effect of high-temperature furnaces and reduce energy consumption. Mullite polylight bricks are also used in the heat preservation of equipment in thermal power plants, nuclear power plants, etc.
The Use Temperature of Different Grades of Mullite Polylight Bricks
However, different grades of mullite polylight bricks are used at different temperatures. Insulation mullite bricks are generally divided into different grades of JM-23, JM-26, JM-28, JM-30, and JM-32 according to national standards. JM-32 is not used much. The use ratio of JM-23, 26, and 28 is more.
JM-23 mullite polylight bricks, Al2O3 is 48%, and the use temperature is 1300℃. The volume density ranges from 0.55-1.5, and the most commonly used are 0.8 and 1.0 and body density. Its reburning line changes at 1300℃×24h is ±1.
JM26 mullite polylight bricks, Al2O3≥55%, and the use temperature is 1400℃. The volume density ranges from 0.55-1.5, and the most commonly used are 0.8 and 1.0 and body density. Its reburning line changes at 1400℃×24h to 0.7-0.8.
JM28 mullite poly light brick, Al2O3 at 65%, use temperature at 1500℃. The volume density ranges from 0.55-1.5, and the most commonly used are 0.8 and 1.0 and body density. Its reburning line changes at 1500℃×24h to 0.7.
JM30 Al2O3 at 72%, use temperature at 1600℃. The volume density ranges from 0.55-1.5, and the most commonly used are 0.8 and 1.0 and body density. Its reburning line changes at 1600℃×24h to 0.6.
JM32 is not often used, and is generally customized according to the special requirements of users.
Different grades of mullite poly light bricks can be used at different use temperatures. Different grades of mullite bricks are selected according to the temperature and use conditions of the user’s kiln and different furnace types. Rongsheng Refractory Factory can also customize and produce polylight mullite bricks according to customer’s specifications.
High Temperature Furnace Mullite Insulation Refractory Brick Factory
Mullite insulation brick physical and chemical indicators. Mullite insulation brick, as a material commonly used in building insulation, has excellent insulation performance and mechanical strength. Rongsheng Refractory Factory will elaborate on the physical and chemical indicators of mullite insulation bricks, covering thermal conductivity, compressive strength, water absorption and other aspects.
Heat conductivity is an indicator to measure the thermal conductivity of materials, usually expressed as λ, with the unit of W/(m・K). The thermal conductivity of mullite insulation bricks is mainly affected by factors such as the density, porosity and composition of the material. Generally speaking, the lower the density and the higher the porosity of mullite insulation bricks, the lower its thermal conductivity. According to national standards, the thermal conductivity of mullite insulation bricks should be less than 0.065W/(m・K) to ensure its excellent insulation performance. To achieve this requirement, manufacturers usually take measures such as controlling the raw material ratio and optimizing the process to reduce the thermal conductivity of the brick body.
Compressive strength is an indicator used to measure the compressive performance of materials, usually expressed in MPa. The compressive strength of mullite insulation bricks is directly related to their service life and safety performance in building structures. Generally speaking, the higher the compressive strength of mullite insulation bricks, the more they can withstand external loads. According to national standards, the compressive strength of mullite insulation bricks should be greater than 1.5MPa. In order to improve the compressive strength of mullite insulation bricks, manufacturers usually use methods such as adding reinforcing materials and adjusting the firing process to improve them.
Thermal conductivity is an indicator that describes the thermal conductivity of a material, usually expressed in K, with a unit of W/(m・K). The thermal conductivity of mullite insulation bricks is the ratio of thermal conductivity to material thickness, which is used to calculate heat transfer per unit area. According to national standards, the thermal conductivity of mullite insulation bricks should be less than 0.065W/(m・K). By controlling the thermal conductivity and thickness of the brick body, the thermal conductivity of mullite insulation bricks can be effectively reduced and its insulation performance can be improved.
Density is an indicator that measures the relationship between material mass and volume, usually expressed as ρ, with the unit of kg/m³. The density of mullite insulation brick directly affects its thermal conductivity and compressive strength. Generally speaking, the lower the density of mullite insulation brick, the lower its thermal conductivity, but the compressive strength will also be reduced accordingly. Therefore, when designing, it is necessary to weigh the requirements of thermal insulation performance and structural strength and select an appropriate density.
The physical and chemical indicators of mullite insulation bricks are an important basis for evaluating their insulation performance and performance. By controlling the thermal conductivity, compressive strength, water absorption and other indicators of the brick body, the insulation effect and service life of mullite insulation bricks can be improved.
In actual use, it is necessary to select suitable mullite insulation bricks based on the specific requirements and environmental conditions of the building. At the same time, manufacturers also need to continuously improve the process and material formula to improve the performance and quality of mullite insulation bricks to meet market demand.
The strength of the circulating fluidized bed boiler lining is very important. If the material is not properly selected or the quality control is not done well during the construction process, it is easy to cause large-scale collapse of the castable during operation and even serious wear of the heating surface pipes.
Enhance the Strength of Circulating Fluidized Bed Boiler Lining?
Selection of wear-resistant refractory manufacturers. Since there are many manufacturers of wear-resistant refractory materials on the market, and the quality is uneven, you must pay attention when selecting a manufacturer. It is best to contract the materials, construction and after-sales service to a reputable and qualified manufacturer. In this way, the circulating fluidized bed boiler lining can be guaranteed to the maximum extent. RS Refractory Manufacturer is a powerful refractory manufacturer with rich experience in the production and sales of refractory materials. RS manufacturer has completed many turnkey projects in the design, construction and material supply of circulating fluidized bed boiler refractory lining. If you choose RS manufacturer, RS manufacturer’s products and customer service will not disappoint you.
Circulating Fluidized Bed Boiler Lining Construction
Material selection. Start with the physical and chemical properties of the material (including wear resistance, heat resistance, corrosion resistance, thermal conductivity, stability, thermal expansion, shrinkage, compression and bending resistance and bulk density), while taking into account economy. Combine the characteristics of the lining part, the structure of the components that carry the lining, and the requirements of temperature resistance and wear resistance for comprehensive comparison. Be advanced in technology, reliable in structure and economically reasonable.
CFB lining materials have been developing continuously with the development of boilers towards high parameters, large capacity and new technologies, and many new varieties, new construction methods and technologies have been developed. This has promoted the innovation and improvement of lining structures, continuously improved wear resistance and heat resistance, and promoted the progress of fluidized bed combustion technology. RS manufacturers suggest that accurate design solutions, high-quality material selection, efficient construction quality and maintenance methods can greatly increase the strength of circulating fluidized bed boiler linings.
Why does the Circulating Fluidized Bed Boiler Lining need High-Strength Wear-Resistant Castables?
The main reasons why the circulating fluidized bed boiler lining needs to use high-strength wear-resistant castables are as follows. First of all, the circulating fluidized bed boiler is a high-efficiency, low-pollution boiler with good fuel adaptability, so its operating efficiency and application range have been widely used. However, during the operation of this boiler, due to incomplete combustion of fuel and uneven heat exchange, the temperature and material flow rate in the furnace will be unevenly distributed, causing serious wear and scouring of the boiler lining. Therefore, in order to protect the circulating fluidized bed boiler lining, high-strength wear-resistant castables are needed.
Secondly, high-strength wear-resistant castables are a composite material composed of a variety of polymer materials and wear-resistant materials, with the advantages of high strength, high wear resistance, high temperature resistance, and corrosion resistance. This material can maintain its physical and chemical properties for a long time under a high-temperature environment, and effectively resist high temperature and chemical corrosion in the furnace. In addition, high-strength wear-resistant castables also have good impact resistance and wear resistance, which can effectively resist the high-speed impact and friction of materials and protect the lining from damage.
Finally, the construction of high-strength wear-resistant castables is simple and fast and can be customized according to the shape and size of the boiler, with strong adaptability. This material does not produce harmful gases during the pouring process, which can effectively protect the environment and workers’ health. In addition, the price of high-strength wear-resistant castables is also relatively reasonable, which can effectively reduce the maintenance cost of the boiler.
In summary, the lining of the circulating fluidized bed boiler needs to use high-strength wear-resistant castables to protect it from damage such as incomplete combustion of fuel, material impact and friction, extend its service life, and improve the operating efficiency and application range of the boiler.
Where is the Main Function of Wear-Resistant Castables?
As the name suggests, wear-resistant castables have extremely high wear resistance and can maintain the integrity of the cast body for a long time in harsh working environments. Its wear resistance is better than that of traditional high-aluminum refractory castables, and can extend its service life in key furnace linings. In metallurgy, power and other industries, wear-resistant castables are widely used in rotary kilns, boilers, dust collectors and wear-resistant layers of complex furnace linings, which can effectively resist the erosion of ores, metal materials, high temperatures and chemicals, and improve the operating efficiency of equipment.
Wear-resistant castables have good corrosion resistance due to the addition of silicon carbide components, which play a skeleton support role and can resist the erosion of various acid and alkali chemicals. In the chemical, petrochemical and other industries, wear-resistant castables are suitable for anti-corrosion layers, which effectively prevent corrosive media from eroding the furnace lining and ensure the stability and safety of the production process.
Wear-resistant refractory castables have high compressive strength and can withstand greater pressure and impact. Moreover, it has good thermal shock resistance, which can reduce the wear and failure rate of the furnace lining, thereby reducing energy consumption and production costs. This helps to reduce the operating costs of enterprises and improve their competitiveness. At the same time, wear-resistant castables also have the characteristics of environmental protection and sustainable development. Their production and use processes meet environmental protection requirements and are conducive to reducing the generation of industrial waste.
In summary, wear-resistant castables play an important role in improving wear resistance, enhancing corrosion resistance, improving compressive strength and reducing energy consumption. It is one of the important refractory castables that are indispensable for industrial kiln linings.
Mullite brick is a refractory brick made mainly of mullite, a mineral compound composed of alumina (Al2O3) and silicon dioxide (SiO2). It is famous for its excellent thermal stability, high melting point and thermal shock resistance. Why can mullite brick be used as thermal insulation material? First of all, we need to understand the characteristics of mullite brick.
Features of RS Premium Mullite Bricks
RS premium mullite bricks have some of the following key features:
High-temperature resistance: Mullite bricks can withstand high temperatures, typically ranging from 1600°C (2912°F) to 1800°C (3272°F). Even at high temperatures, it maintains strength and structural integrity, making it suitable for use in high-temperature conditions.
Low thermal conductivity: Mullite bricks have low thermal conductivity, which means it can provide good insulation and reduce heat loss in high-temperature environments. This feature makes it valuable for applications that require insulation or energy efficiency.
Excellent thermal shock resistance: Mullite bricks have excellent thermal shock resistance, which means it can withstand rapid temperature changes without cracking or flaking. This feature is critical for applications involving cyclic heating and cooling, such as furnaces, kilns, and reactors.
Chemical resistance: Mullite bricks have good resistance to chemical attack by acids, alkalis, and molten materials. This makes it suitable for chemical processing, metal refining and other industrial applications that may come into contact with corrosive substances.
Wide application: Mullite bricks are widely used in various industries such as ceramics, glass manufacturing, steel production, petrochemicals, and non-ferrous metals. It is often used in furnace linings, kiln furniture, hot gas pipes, regenerators and other demanding thermal environments.
RS factory mullite bricks are available in different shapes and sizes to meet specific installation requirements. For example, standard bricks, special shapes or custom designs. Contact Rongsheng for detailed information.
Why can Mullite Bricks be Used as Thermal Insulation Materials?
In general, mullite bricks have high-temperature resistance, thermal shock resistance, and chemical durability. This makes it a valuable refractory material in many industrial environments. In these industrial environments, reliable heat conduction and thermal stability are essential.
JM26 Lightweight Mullite Insulation Bricks for Sale
Mullite polylight bricks are a kind of lightweight insulation bricks, also known as mullite insulation bricks. It has good thermal insulation effect, and its small body density and light weight are also one of its characteristics. At present, it is widely used in glass melting furnace upper structure material channel bricks, modification plates, and processing kiln upper structure. Insulation and heat insulation layer of firing kilns, smelting kilns, refining devices, heating devices, and other thermal equipment.
Because mullite polylight insulation bricks have a high porosity, they cannot bear excessive loads when using mullite insulation bricks, and must avoid contact with molten metal, slag and high-temperature furnace dust. When laying mullite insulation bricks, brick joints and expansion joints should be arranged correctly to avoid squeezing the masonry due to expansion. Mullite insulation bricks should not be subjected to strong mechanical vibration, impact and friction.
Layered structure: The molecular structure of mullite has a layered arrangement, which allows it to expand when heated to form an insulating air layer. This structure enables mullite bricks to effectively reduce the conduction of heat. Therefore, it exhibits good thermal insulation performance in high temperature environments.
Lightweight material: Mullite bricks are a lightweight material, so they do not add much weight when used in construction. This makes it suitable for various insulation applications, such as insulation boards, insulation materials, and furnace linings.
Refractory: Mullite bricks have high refractory properties and can withstand high temperatures without decomposing or melting. This makes it an ideal insulation material for high-temperature equipment such as furnaces, stoves, fireplaces, etc.
In general, the reason why mullite polylight bricks can be used as insulation materials is mainly because its density, chemical properties, layered structure, lightweight characteristics and refractory properties make it have good thermal insulation performance in high temperature environments. These characteristics make it one of the important materials in a variety of industrial and construction applications.
Are Lightweight Mullite Bricks Acid-Resistant?
Lightweight mullite bricks usually have a certain degree of acid resistance, but their specific corrosion resistance will be affected by many factors, including the composition of mullite bricks, preparation process, strength of acidic environment and special requirements.
Mullite brick is a refractory material with mullite as the main component. Mullite is a mixture of alumina (Al2O3) and aluminum silicate (Al2Si2O7), which has good high temperature resistance, thermal shock resistance and corrosion resistance. Mullite bricks contain a higher proportion of alumina, which makes it acid-resistant to a certain extent.
However, the strength and type of acidic environment also have an impact on the corrosion resistance of mullite bricks. Generally speaking, mullite bricks may show good corrosion resistance in mildly acidic environments, but corrosion may still occur in harsh strong acidic environments.
If mullite bricks need to be used in special acidic environments, it is recommended to understand their corrosion resistance in detail when selecting materials, and may take additional protective measures. For example, adding anti-corrosion coating or choosing other corrosion-resistant materials that are more suitable for specific acidic environments. It is recommended to conduct relevant experiments and tests before actual use to ensure that lightweight mullite bricks can meet the requirements in specific acidic environments.
