Refractory materials are the foundation of all high-temperature industries, with a wide variety of applications. This article summarizes the application of refractory materials in four major downstream industries: steel industry, cement industry, non-ferrous metal smelting industry and glass industry, including the selection of different types of refractory materials for high-temperature equipment such as blast furnaces, converters, electric furnaces, ladle furnaces, LF furnaces, RH vacuum refining equipment, cement kilns, glass kilns, non-ferrous metal smelting furnaces, etc.
1.What are refractory materials?
According to international standards, refractory materials refer to non-metallic (not excluding the presence of a certain proportion of metal) materials and products whose chemical and physical properties are stable and can be used normally in high temperature environments. The US standard definition of refractory materials: non-metallic materials that can be made into structures and devices for use in environments with temperatures exceeding 1000 ℉ based on their chemical and physical properties. According to Japanese standards, refractory materials are defined as shaped refractory materials that can be used at temperatures above 1500℃ and amorphous refractory materials, refractory mud and refractory insulation bricks with a maximum use temperature of more than 800℃. China follows international standards and defines refractory materials as non-metallic materials with physical and chemical properties suitable for use at high temperatures, but does not exclude that some products may contain a certain amount of metal materials.
2.What are refractory materials?
There are many ways to classify refractory materials. According to chemical properties, they can be divided into three categories: acidic refractory materials, alkaline refractory materials and neutral refractory materials.
According to the main mineral chemical components of refractory materials, they can be divided into: siliceous refractory materials, aluminosilicate refractory materials, magnesia refractory materials, magnesia spinel refractory materials, magnesia chromium refractory materials, magnesia dolomite refractory materials, dolomite refractory materials, carbon composite refractory materials, high-aluminum refractory materials, chromium refractory materials, zirconium refractory materials, etc.
According to the supply form, they can be divided into two categories: fixed and unshaped refractory materials.
According to different classifications of refractoriness, they are divided into ordinary/high-grade/special/super refractory materials; ordinary refractory materials are resistant to temperatures of 1580~1770℃, high-grade refractory materials can withstand high temperatures of 1770~2000℃, high-grade refractory materials are resistant to high temperatures of 2000~3000℃, and super refractory materials are resistant to temperatures of 3000℃ or above.
According to the bulk density classification, it can also be divided into light/heavy refractory materials.
According to the different classifications of properties and sizes, it can be divided into standard/general/special/special refractory materials, etc.
Classification according to the chemical composition of refractory materials is the most common way to classify refractory materials.
3.How to choose suitable refractory materials?
Refractory materials are the basic materials for high-temperature industries such as steel, nonferrous metals, petrochemicals, building materials, and electricity, and are important supporting materials for high-temperature industrial thermal equipment. The four major downstream application areas are: steel industry, cement industry, nonferrous metal smelting process, and flat glass industry.
Field 1: Steel Industry
70% of the downstream demand for refractory materials is in the steel industry, which is used in blast furnaces, converters, electric furnaces, ladle furnaces, LF furnaces, RH furnaces, and continuous casting systems.
The steel production process is to smelt iron ore into pig iron in a blast furnace, inject molten iron into a converter or electric furnace to smelt steel, and then cast the molten steel into continuous casting billets or ingots, and process them into steel for various purposes through plastic deformation methods such as rolling. In steel production, since the working environment and use requirements of various furnaces are different, there are also different requirements for refractory materials.
Refractory materials for blast furnaces
The main refractory materials used in blast furnace ironmaking are amorphous refractory materials, carbon refractory materials, clay bricks, high alumina bricks, etc. Among them, carbon refractory materials include graphite bricks, semi-graphite bricks, carbon bricks, and Si3N4 combined with SiC bricks.
Different parts of a blast furnace have different operating environments, and the requirements and selection of refractory materials are also different.
Furnace throat: Mainly built with high-quality clay bricks and high-alumina bricks.
Furnace body: The temperature zone in the middle and upper parts is 400°C~800°C. At present, this part is built with high-quality clay bricks or high-alumina bricks.
Lower part of blast furnace body: After a large number of investigations and studies on blast furnaces, the results show that about 23% of blast furnaces use SiC refractory materials. The Si3N4 combined with SiC bricks developed in my country have significantly improved their anti-corrosion performance and have begun to be used in the masonry of major blast furnaces in my country, which has significantly improved the service life of blast furnaces.
Furnace waist: The temperature during normal operation is 1400℃~1600℃. In response to the erosion and severe scouring of the furnace waist, my country has developed Si3N4 combined with SiC bricks. Practice has proved that this brick has good scouring and erosion resistance.
Bosh: The temperature of the lower furnace charge is about 1600℃~1650℃, and a large amount of intermediate slag begins to drip. In China, silicon carbide bricks made of carbon refractory materials are generally used. In foreign countries, more refractory materials are used in this part. The 3662m3 blast furnace of Hogovin Steel Company in the Netherlands is built with semi-graphite bricks, which has a good effect.
Furnace hearth: The temperature is generally between 1450°C~1500°C. The temperature in the tuyere area can reach 1700°C~2000°C. It is mainly built with carbon bricks. In recent years, many blast furnace bottoms and hearths in China have adopted carbon material-ceramic material composite structures from SAVOIE of France and Japan Electrode Company.
Iron mouth: The main device at the iron mouth is the iron mouth sleeve, which is made of cast steel and welded to the furnace shell. At present, carbon bricks with excellent performance are mainly used in this part.
Converter
Magnesia carbon bricks for converters.
Impact zone repair material (large surface): fused magnesia, sintered magnesia + asphalt + binder.
Trunnion gunning material: magnesia + slaked lime + water, high-pressure air gunning, one repair for several furnaces.
Steel outlet repair material: magnesia + resin.
Furnace mouth magnesia ramming material: magnesia + chrome green.
Electric furnace
Electric furnace cover: high alumina, mullite, corundum, chrome corundum castables.
Electric furnace main wall: direct bonded magnesia chrome brick, pre-reacted magnesia chrome brick, magnesia brick
Slag line and hot spot: oil-immersed magnesia brick, direct bonded magnesia chrome brick, fused cast magnesia chrome brick, magnesia carbon brick
Furnace bottom insulation layer: a layer of asbestos board, covered with diatomaceous earth powder, and flat-laid insulation bricks on it
Furnace bottom permanent layer: staggered masonry of fired magnesia bricks, asphalt-bonded magnesia bricks, etc.
Furnace bottom working layer: knotted furnace bottom: magnesia sand + asphalt, tar, magnesia calcium iron sand; masonry furnace bottom: asphalt-bonded magnesia brick, brine-bonded magnesia brick
Steel outlet: high-strength magnesia carbon brick, Al2O3-SiC-C brick
Ladle furnace
Slag line: magnesia carbon brick, alumina-magnesia carbon brick
Bag wall: low-carbon magnesia carbon brick, alumina-magnesia carbon brick, alumina-magnesia unburned brick (carbon-free brick), alumina-magnesia castable
Bag bottom: alumina-magnesia carbon brick, alumina-magnesia castable, corundum spinel castable
Refractory materials for lag bottom: nozzle seat brick, air-permeable brick, air-permeable seat brick, drainage sand.
Ladle Furnace
LF furnace
The slag line uses refractory materials, high-quality magnesia carbon bricks that are resistant to corrosion and thermal shock, and the antioxidant ZrB2 (1.5%) is added; high-alumina bricks are used for the molten steel line; high-alumina bricks and high-alumina castables are used for the bottom of the ladle.
ASEA-SKF Furnace
Slag line: magnesia carbon bricks, magnesia chrome bricks, magnesia bricks, magnesia dolomite bricks, high alumina bricks with Al2O3>85%;
High alumina bricks and castables with 75% Al2O3 are used for the side walls and the bottom of the ladle;
Alumina carbon bricks are used for the lower part of the waterline.
RH vacuum refining equipment
The main refractory materials: magnesia-chrome bricks, magnesia-spinel bricks, corundum-spinel castables, and corundum-spinel prefabricated materials are developing towards chromium-free.
Continuous casting tundish
Blast furnace bricks, magnesium coatings
Area 2: Cement Industry
Refractory bricks are widely used in various industrial sectors and high-temperature technology fields. They are indispensable production materials for cement companies in the process of clinker calcination. Alkali and silicon-aluminum refractory bricks are widely used in cement companies. Previously, magnesia-chrome bricks were the most widely used in the rotary kiln firing zone, but the pollution risk of water-soluble hexavalent chromium in magnesia-chrome bricks has become an important issue that needs to be urgently solved in the application of refractory bricks. With the improvement of environmental awareness, some industrialized countries (such as Germany and the United States) have passed legislation to restrict the use of magnesia-chrome bricks. my country also has corresponding regulations on this. At present, chromium-free refractory materials have been fully implemented in the cement industry. Magnesia-iron and magnesia-calcium bricks can replace the original magnesia-chrome bricks in the firing zone.
Different parts of the cement enterprise’s clinker calcination and cooling system have different performance requirements for refractory bricks, and the types of refractory bricks used are also different. Commonly used refractory bricks in cement enterprises include: high alumina bricks, Baiyunshan bricks, magnesia chrome bricks, spinel bricks, anti-stripping bricks, silica-molybdenum bricks, etc.
High Alumina Brick
It is mainly suitable for preheaters, decomposition furnaces, tertiary air ducts, decomposition zones of rotary kilns, grate cooler linings, etc.
Dolomite Brick
Dolomite bricks are often used in high-temperature sintering areas of rotary kilns. Due to the inherent hydration of dolomite, it will absorb moisture and hydrate during the kiln shutdown period, causing the brick body to crack and peel off, so dolomite bricks are suitable for use in rotary kilns with long operating cycles. When used in the calcining zone of a rotary kiln, the service life is longer than that of the original magnesia-chrome bricks.
Magnesia Chrome Brick
The appearance of magnesia-chrome bricks in the 1950s has greatly improved the life of the furnace lining, making magnesia-chrome bricks a dominant position in cement rotary kiln refractory materials. In the 1960s, the emergence of large cement rotary kilns made magnesia spinel bricks replace magnesia-chrome bricks in the transition zone.
In order to reduce the pollution of hexavalent chromium to the environment, low-chrome magnesia-chrome bricks and chrome-free alkaline refractory materials have been manufactured to replace magnesia-chrome bricks. If environmental pollution is not considered, magnesia-chrome bricks are a refractory material with a very high cost performance. At present, the cement industry has used ferromagnesia and magnesia-calcium bricks to replace the original magnesia-chrome bricks in the burning zone, and implemented chrome-free refractory materials.
Magnesia Alumina Spinel Brick
Spinel bricks do not contain chromium and are an environmentally friendly product. They are mostly used in the front and rear transition zones of rotary kilns.
Magnesia-iron spinel brick
It does not contain chromium and is suitable for the entire alkaline area of the rotary kiln (firing zone, transition zone), with excellent kiln skin-making ability;
Anti-stripping brick
Anti-stripping bricks are zirconium-containing high-alumina bricks, which are acidic bricks and are ideal materials for transition zones and decomposition zones of rotary kilns in cement enterprises. They can also be used for kiln door covers, coolers and other parts of rotary kilns.
Silicon-molybdenum brick
The “silicon” in silicon-molybdenum brick refers to silicon carbide, and “molybdenum” refers to mullite. In essence, silicon-molybdenum brick is a high-aluminum brick with silicon carbide added. It is suitable for the upper and lower transition zones and safety belts of rotary kilns. Many companies have proved that silicon-molybdenum red bricks or silicon-molybdenum bricks used in the upper transition zone of a 5,000t/d precalciner kiln can achieve a service life of more than 12 months.
Field 3: Nonferrous metal smelting industry
The main equipment for nonferrous metal smelting is nonferrous metal smelting furnaces. The demand and selection of the quality of refractory materials are important factors in improving the life and output of nonferrous metal smelting furnaces. The structural form of the smelting furnace depends on different pyrometallurgical smelting processes. Different types of furnaces are selected according to different smelting process flows.
Aluminum melting furnace
Aluminum smelting furnaces mainly include reverberatory furnaces, rotary furnaces and induction furnaces, and the operating temperature is generally 700-1000℃. The damage to the lining of this type of furnace is mainly caused by the penetration and erosion of aluminum liquid. The lining is generally built with clay bricks, high-aluminum refractory bricks and corundum mullite bricks, and can also be made of high-aluminum refractory castables and refractory plastics.
Blister copper smelting furnace
Magnesia-chrome refractory bricks or chrome-magnesia bricks are commonly used in the lining of copper smelting converters in various countries. Due to the harm of “chromium” to the environment, chromium-containing refractory materials have been gradually developed in recent years, and replaced by new chromium-free environmentally friendly green refractory materials.
The converter tuyere area and slag line are weak links in the converter lining, and high-quality high-grade refractory bricks should be selected.
Lead-zinc industry
Lead-zinc closed blast furnace
The operating temperature is 800-850℃ hot air blast, and the furnace top is kept at a high temperature of 1050-1100℃. The hearth of the lead-zinc closed blast furnace is built with magnesia bricks, the belly is a water jacket, the furnace body is built with high-aluminum bricks, and the hearth is knotted with high-aluminum unshaped refractory materials. At present, the front beds of the two domestic lead-zinc closed blast furnaces are built with chrome slag bricks and aluminum-chrome-titanium bricks.
Zinc concentrate fluidized roasting furnace (fluidized bed furnace)
It is built with clay bricks, and the furnace bottom distribution plate, charging front room, discharge port and other parts are also made of clay refractory concrete. Another development direction is to use all amorphous refractory materials.
Induction zinc melting furnace
Clay bricks are used for masonry, and the melting groove is made of amorphous refractory materials. The temperature of the induction type cannot sinter the refractory materials into a whole, and adhesives are needed to combine them into a whole. At present, water glass clay materials are commonly used.
Area 4: Glass Industry
Kilns are core equipment for glass production. Their technological advancement requires a variety of high-quality refractory materials as a guarantee. The refractory materials must be able to withstand higher temperatures, more rapid temperature changes, stronger chemical corrosion, and more severe stress damage. Only by matching and applying a variety of high-quality refractory materials can the advantages of new kiln technologies such as high efficiency, energy saving, and low pollution be realized.
Fusion Casting Refractory for Glass Furnace
In the fused-cast zirconium corundum refractory, zirconium oxide has the function of improving the corrosion resistance; the process of fused-cast zirconium corundum refractory is to make the primary baddeleyite with suitable particle size and shape evenly distributed in the glass phase with suitable composition and quantity, so that the primary baddeleyite and the glass phase can cooperate with each other and protect each other; this can make the fused-cast corundum refractory have a higher zirconium oxide content, a lower glass phase content and a higher manufacturing qualification rate. With the promotion of the full oxygen combustion process, low-leakage fused-cast refractory materials have been developed, such as ER2001.
Silica refractory for glass furnace
In the 1980s, my country introduced the manufacturing technology of advanced silica bricks for glass kilns from the United States. After adopting the full oxygen combustion technology, the life of silica bricks dropped sharply from 5 to 10 years to 2 to 3 years. Rat holes and melting are the main causes of damage. Rat holes are caused by the condensation of alkali in the leaked gas in the kiln on the brick joints, which corrodes the silica bricks. On the one hand, the dimensional accuracy of the bricks is improved, the brick joints are reduced, and the kiln gas leakage is reduced; on the other hand, the use of low-calcium silica bricks or high-purity silica bricks with better corrosion resistance and the design of the kiln lining structure can move the condensation temperature zone of the alkali to the amorphous refractory layer behind the silica bricks to increase the life of the silica bricks.
Basic refractory materials for glass furnace
Refractory materials for the regenerator of a glass kiln, usually, the top layer of the regenerator grid body uses high-grade magnesia bricks with w(MgO)＞97%; the upper layer uses mid-grade magnesia bricks with w(MgO) of about 95%～96%; the middle layer uses directly bonded magnesia chrome bricks; the lower layer uses low-porosity clay bricks. For this reason, glass companies have expanded the use of M-97 magnesia bricks and directly bonded magnesia chrome bricks in the regenerator, replacing the poor-performing M-95 magnesia bricks, extending the life of the regenerator from the original 1a to 3a, and have achieved initial success. If a longer service life is achieved, composite spinel materials can be used in the middle layer of the glass kiln regenerator. At present, this type of material has achieved good results.