Alumina hollow ball bricks
Alumina hollow ball bricks have good thermal insulation performance, high use temperature, high load softening point, high compressive strength and other characteristics. They can not only be used as insulation layers, but also can be in direct contact with flames. Although zirconia hollow ball bricks have better thermal insulation performance and higher use temperature than alumina hollow ball bricks, zirconia hollow ball products are expensive and have limited raw material reserves. They are generally only used in kilns with special requirements; while alumina hollow ball products are currently the most popular high-temperature, high-strength and lightweight insulation materials due to the rich alumina raw materials and high cost performance.
Alumina insulation bricks
Although the use temperature of alumina insulation bricks is lower than that of hollow ball products, their volume density is much lower than that of hollow ball products, so the thermal conductivity is smaller and the thermal insulation performance is better. Alumina insulation bricks are widely used in the insulation of sintering kilns such as metallurgy and ceramics. They cannot bear loads and should be avoided from direct exposure to environments with strong scouring, wear and erosion. According to the difference in the content of alumina, aluminum-silicon lightweight insulation materials are mainly divided into high-aluminum insulation bricks, mullite insulation bricks, clay insulation bricks and silicon insulation bricks. Since these products have good insulation performance and the use temperature can be adjusted in a large range, they are suitable for thermal insulation of various industrial furnaces under general use conditions (no contact with metal solution or slag, no severe thermal shock, no chemical reaction, no erosion, no severe mechanical collision, wear, etc.), can directly contact the flame, and are mostly used as intermediate insulation layers, such as black metallurgy. Thermal insulation of belt sintering machines, pellet roasting furnaces, steelmaking and rolling heating furnaces in the industry, thermal insulation of aluminum electrolytic cells, aluminum smelting furnaces, zinc smelting electric distillation furnaces and distillation equipment in non-ferrous metal smelting, thermal insulation of catalytic cracking units, first-stage, conversion furnaces and second-stage converters of synthetic ammonia units in the building materials industry (ceramics, glass, cement) and petrochemical and chemical industries, as well as thermal insulation of waste heat boilers, waste incinerators, carbon roasting kilns and resistance furnaces for various purposes. Aluminum-silicon thermal insulation materials are currently the most widely used thermal insulation materials in thermal kilns.
Insulation board
Insulation board is a non-fired product composed of refractory fiber materials, refractory raw materials, binders and additives. It is an important variety of thermal insulation refractory materials. Insulation boards are divided into siliceous, magnesian, forsterite, aluminum silicate and floating beads according to the material; this material is characterized by low thermal conductivity, low density and good corrosion resistance. It is mainly used in the ingot cap and continuous casting tundish, so it is called tundish insulation board and mold insulation board respectively. Tundish insulation boards are divided into wall boards, bottom boards and impact boards, and their performance varies depending on the location of use. This board is used in the tundish to reduce the steel tapping temperature, save fuel and speed up the turnover of the tundish. At the same time, the permanent lining of the tundish can be used for a long time, which can reduce the consumption of refractory materials; the insulation board for ingots can increase the steel yield.
In thermal equipment, pipelines and accessories, insulating refractory castable products, such as perlite bricks, are widely used. This type of product can be produced according to the prefabricated block production process according to the mix ratio of the castable; in the past decade, calcium silicate insulation board (also called insulation board) has been developed, with a flexural strength of 0.2~0.6MPa, thermal conductivity of 0.05~0.06W/(m·K), volume density of 0.13~0.23g/cm3, linear shrinkage of ≤2% after burning at 1000℃, and a use temperature of 500~1000℃. This board is widely used in the insulation layer of various kilns and thermal equipment. It is not only convenient to construct, but also has good insulation effect and can reduce the thickness of the lining.
Refractory fiber
Refractory fiber, as a highly efficient thermal insulation refractory material, has the characteristics of softness and high strength of general fibers, and can be processed into various products, such as ceramic fiberboard, ceramic fiber module, ceramic fiber cloth, ceramic fiber blanket, etc., and has properties that ordinary fibers do not have, such as partial anti-oxidation performance, corrosion resistance, high temperature resistance, etc., which makes up for the deficiency of general refractory materials being too brittle. And the volume density of refractory fiber is small, usually 0.1~0.2g/cm3, which is 1/20~1/10 of ordinary clay bricks and 1/10~1/5 of lightweight clay bricks. Therefore, the use of refractory fiber instead of refractory bricks can reduce the weight of the furnace body and the thickness of the furnace wall. For example, the use of fiber lining in a heating furnace can reduce the original heavy lining by 80% and the thickness of the furnace wall by 50%. In addition, the specific heat of refractory fiber is low, which is only 1/72 of ordinary refractory bricks and 1/42 of lightweight clay bricks. Therefore, refractory fiber is often used as the lining of intermittent kilns, which can significantly reduce heat storage loss, save fuel and increase the heating rate. Refractory fiber products are increasingly widely used in industrial kilns, achieving significant energy-saving effects. For continuously operated kilns, the use of refractory fiber products can save 3%~10% of energy. For intermittently operated thermal equipment, the use of fiber refractory materials can save more energy, up to 10%~30%, or even higher. The masonry method of refractory fiber products has a great influence on their thermal insulation effect. When using stacked lining, the fiber direction is perpendicular to the heat flow direction, the radiant heat increases, and the thermal conductivity is 20%~30% higher than that of layered lining under the same conditions; when used as layered lining, the fiber direction is consistent with the heat flow direction, and the thermal conductivity mainly depends on the thermal conductivity of the product.
The application of refractory fibers in industrial furnaces is in the form of fiber-pasted lining structure and full fiber lining. There are three forms of use of refractory fiber-pasted lining, namely internal insulation: the fiber is pasted or pasted on the hot surface of the furnace wall. Whether it is an intermittent or continuously operated furnace, the refractory fiber products are pasted on the hot surface of the lining, which has a good thermal insulation effect. It can not only reduce the heat dissipation loss of the furnace wall, but also significantly reduce the heat storage loss. Therefore, refractory fiber products that can meet the requirements of furnace production process conditions should use this insulation structure as much as possible; external insulation: the fiber is pasted or anchored to the cold surface of the furnace wall. This structure only needs to use low-temperature fiber products or lightweight bricks; intermediate insulation: the fiber is placed in the middle of the furnace wall. Due to the many disadvantages of intermediate insulation, it is rarely used. The inlaid refractory fiber is generally a blanket product with a thickness of 20~50mm. The use of full fiber lining can greatly reduce energy consumption, improve the thermal operation of the furnace, save steel, reduce the weight of the furnace body, extend the life of the furnace, improve the working environment and ensure production safety. However, the one-time cost is high. The full fiber lining has two traditional structural forms: layer laying and stacking. In current applications, the characteristics of these two structural forms are usually combined to adopt a combined lining of layer laying and stacking, and the anchoring splints are used to clamp, staggered, and riveted. This all-fiber furnace lining not only maintains the tightness of the layered type, but also takes advantage of the strong corrosion resistance of the stacked type. After use, it has achieved good energy-saving effects, extended the life of the furnace, and is conducive to strengthening production.
Thermal insulation refractory materials can only play a role in thermal insulation if they do not exceed their maximum allowable use temperature. Therefore, it is necessary to reasonably select thermal insulation refractory materials according to the energy-saving purpose and requirements of the furnace, structural characteristics, working conditions, and service life requirements. For example, in a copper reverberatory furnace, the non-working layer can be constructed with high-strength lightweight refractory clay bricks or refractory fibers, while the lining can only be built with heavy refractory bricks due to the erosion of slag and violent flame scouring, and cannot be built with lightweight porous thermal insulation materials. The thermal insulation refractory material layer is applied to the outer surface or hot surface of the furnace wall, and its thermal insulation effect is also different. Generally, it is more reasonable to use external insulation for continuously operated kilns, that is, dense refractory bricks are used for the working lining, and lightweight bricks are used for the non-working layer, which can significantly reduce heat loss, save more than 10% of energy, and ensure the strength and stability of the furnace wall. For intermittently operated kilns, if external insulation is used, although heat loss is reduced, the increase in heat storage loss sometimes exceeds the heat loss, so internal insulation is often used to reduce heat storage loss. The furnace walls of some non-melting furnaces are even all built with lightweight bricks, which has a significant energy-saving effect.
Precautions for use
According to the performance and characteristics of thermal insulation refractory materials, the following issues should be fully paid attention to during use:
(1) Thermal insulation refractory materials have poor slag resistance and cannot be directly in contact with high-temperature melt or high-speed furnace dust.
(2) Thermal insulation refractory materials have large shrinkage after reburning, and the long-term use temperature should be at least 50~100℃ lower than their firing temperature.
(3) Thermal insulation refractory products have poor wear resistance and cannot be used in areas that are frequently opened or vibrated.
(4) The mechanical strength of thermal insulation products is low and they cannot be used in load-bearing areas.
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