5 Kinds Of Refractory Materials For Rotary Kilns
Rotary kiln, commonly known as rotary kiln, is a steel cylinder, lined with refractory material. In the way of rotating production, in the building materials, metallurgy, chemical, environmental protection and other industries, the material is calcined. Cement industry has the largest number of rotary kilns, there are thousands of them in the country, followed by the number of rotary kilns used in black and non-ferrous metallurgy, iron, aluminum, copper, zinc, tin, nickel, tungsten, chromium and other metals with rotary kilns for ore and intermediate calcination. And calcination of active lime as a steelmaking flux and various uses of dolomite (can be used as converter steelmaking slag agent, metal magnesium raw materials, refractory raw materials, etc.), calcined magnesia, aluminum magnesium spinel, bauxite, hard clay and other refractory raw materials. It can also calcination rare earth, ceramic particles, incineration waste and so on. Different calcined materials, rotary kiln firing temperature is also different, some of the highest temperature up to 2000℃, some less than 1000℃.
However, their working principle is the same, the material enters from the kiln tail, the kiln head is discharged, according to the different temperature in the kiln, it is divided into the kiln tail, pre-tropical, burning zone (also known as calcining zone), cooling zone, kiln head (some industry subdivisions and the former transition zone, the post-transition zone) and other segments. The refractories selected for each section are different, but the damage mechanism of refractories is basically the same, that is, the refractory materials of the kiln lining rotate with the shell, are subjected to the stress generated by the rotation of the kiln body, and are subjected to the rolling impact, friction, erosion and other effects of high temperature materials. Due to the different types of materials, the refractory material of the lining is also different.
In order to improve the service life of the lining, in addition to selecting the appropriate refractory materials, it is necessary to improve the kiln building technology, as well as the maintenance and repair technology of the kiln lining. Among the rotary kilns in many industries, the representative cement kilns, dolomite and lime kilns, pellet kilns, zinc oxide kilns and waste incineration kilns are selected in this paper.
Although the calcined materials of rotary kilns in various industries are different, the working principle is the same, so the refractory materials of the lining are also the same and different, such as the lining is divided into different quality refractory materials, and the kiln head and the kiln tail are all made of high aluminum low cement and steel fiber castable. The selection of different refractory materials in different industries is described below.
Cement kiln
In the early 1980s, the refractory technology for cement rotary kiln was basically set. In general, in the cylinder of large SP and PC rotary kilns, the direct bonding magnesium-chrome brick for the firing belt is used, the high aluminum brick for the decomposition belt is used, and the alkali resistant brick or ordinary clay brick is used at the back of the cylinder. At the end of the 20th century and the beginning of the 21st century, Silmo brick appeared, in addition to the firing belt, the front and back of the kiln, the rest of the parts used different grades of Silmo brick. In today's cement industry, the new dry kiln is the mainstream of technology development, the firing temperature is about 1450 ° C, and the combustion gas temperature in the kiln can reach more than 1700 ° C, or even close to 2000 ° C.
In order to meet the technical requirements of the second generation of new dry cement, the selected refractory materials should have various functions such as energy saving, environmental protection, longevity and efficiency, safety and stability. Therefore, the sintered belt uses magnesia ferro aluminum spinel brick instead of magnesia chrome brick (because it is easy to produce hexavalent chromium that is toxic to human body), the transition belt uses magnesia aluminum spinel brick, and tries a new composite brick with three layers (working layer, thermal insulation layer, thermal insulation layer) structure, the working layer is high-strength, wear-resistant, corrosion-resistant mullite, the thermal insulation layer is zirconium alumina fiber board, and the thermal insulation layer has high strength. Low thermal conductivity and as a skeleton to connect the working layer and heat insulation layer, in the kiln 37 ~ 47m than the kiln shell skin temperature of 60℃ lower than the brick, as well as the use of high-performance cement mud, prefabricated parts, so that the large-scale cement rotary kiln from one year overhaul to three years two overhaul development.
Lime, dolomite kiln
The chemical composition and chemical properties of lime and dolomite are similar, and the calcination temperature is roughly the same, and some enterprises use lime and dolomite in rotation in the same kiln. There are roughly three types of refractory materials used in the lining, one is the calcined magnesia-aluminum spinel brick, the transition zone is high aluminum brick, the preheat zone is clay brick, the heat insulation layer is refractory fiber or light brick, the surface temperature of this form of kiln is 300 ~ 350℃, and the lining life is 1 ~ 2 years; The second calcination belt is the spinel light and heavy composite brick, the shell surface temperature is below 250℃, and the lining life is 2 ~ 3 years; The third is the use of prefabricated blocks and castables to form a lining, the surface temperature of the shell is also below 250℃, and the life is also 2 to 3 years.
Baosteel used andalusite brick to replace spinel composite brick in 16.1 ~ 19.55m of calcined zone, the surface temperature of kiln shell was reduced, the weight of kiln was reduced, and the performance of kiln skin was good. After 2 years of use, the kiln skin was removed, and the andalusite brick was well preserved, while the composite spinel brick was seriously spalling. Because the true density of andalusite is lower than that of spinel, if the calcined belt is entirely made of andalusite bricks, the kiln weight can be reduced by 35t and the shell temperature can be reduced by 100℃. The inlet, kiln head and kiln tail are subject to the impact and wear of massive materials, which are easy to be damaged and spalling, and are the parts with the shortest service life. Wisco uses wear-resistant and alkali-resistant castable, which has been used for more than 36 months without repair. The castable is combined with homogenized bauxite clinker aggregate, SIC 1 ~ 0mm and fine powder, SiO2, Al2O3 micro-powder, ultra-low cement.
The calcined belt is made of phosphate combined with non-fired composite brick, the heavy part uses homogenized bauxite clinker as the main aggregate, adds 4% andalusite as the expansion agent, and improves the thermal shock resistance. The thermal insulation layer is made of alumina hollow balls and expanded perlite 2∶1 ingredients.
The use of composite brick and homogeneous brick with heat-insulating brick two kinds of brick lining structure, the service life of more than 3 years, the kiln shell overheating problem has been solved.
In the calcined belt, Angang changed from magnesium-chromium brick to magnesium-aluminum spinel brick in 1992, and later to composite phosphate brick, double-layer structure to composite structure, from dry masonry to wet masonry, from sequential masonry to misplaced masonry, and later to composite masonry with prefabricated blocks and castables. The prefabricated blocks and castables themselves are embedded with metal anchoring parts and are directly consolidated on the steel shell. The prefabricated block and castable are embedded with a layer of thermal insulation material, the kiln shell is reduced from 320℃ to 222℃, and a layer of NJS nanoscale microporous thermal insulation felt is further improved in the cylinder body, so that the shell is reduced from 220℃ to 176℃.
Pellet kiln (grate - rotary kiln)
In recent years, the total production capacity of pellets is more than 60 million tons per year, and the kiln head temperature of the rotary kiln is 1150 ~ 1180 ° C, and the kiln tail is 1050 ~ 1080 ° C. The temperature of the receiving area of the ring cooler reaches 1100 ~ 1300℃. The selection of refractory materials must be based on the use of different parts of the conditions, the grate mainly has wear-resistant high aluminum castable, light mullite castable, some castable using anchor brick. Rotary kilns are generally made of high alumina mullite prefabricated brick with anchor and castable of the same material. The hanging brick of the first cold section of the ring cooler is changed from non-burned phosphate brick to fired high aluminum brick, and the furnace top is changed to low cement castable, and the service life is extended from several months to 2 years.
Zinc oxide kiln
The rotary kiln is the main equipment for the production of zinc oxide by fire method. The reducing agent such as coke powder is added into the charge, and the volatile nature of zinc metal is utilized. The metal zinc vapor enters the flue gas and produces zinc oxide when it meets the oxygen under high temperature conditions. Steel production produces a large amount of dust dust, which contains zinc. With the development of iron and steel, zinc oxide rotary kiln has also been developed. A rotary kiln of a plant used clay bricks for drying pre-heat, while affecting the service life of the reaction zone to the cooling zone.
Using bauxite clinker, fused magnesia, synthetic magnesia alumina spinel, SiO2, Al2O3 micro-powder ingredients, pure calcium aluminate cement bonding, adding water reducing agent and explosion-proof fiber castable and prefabricated brick, fixed with anchoring parts, the effect is good in high temperature zone of zinc oxide rotary kiln. In this way, favorable conditions are obtained for the production of composite products.
Rotary kiln for alumina and other uses
Alumina kiln firing temperature of 1050 ~ 1300℃, the trial of too high aluminum bricks, magnesium bricks are not ideal, and the use of anti-peeling high aluminum bricks hanging kiln skin, the use of better.
Petroleum coke kiln, used to be casting lining, long construction period, large shrinkage, short life. It is better to use prefabricated composite brick with anchor nail and castable composite masonry.
Burning waste kiln, although the use temperature is about 800 ~ 1200℃, but due to the complex composition of waste, the erosion of refractory materials is more serious, some people choose high temperate zone masonry chrome corundum brick. Some people also use clay brick and zirconium chromium corundum brick double composite.
Laterite nickel kiln, rotary kiln direct reduction production of nickel-iron process, its lining has high requirements for refractory materials, the use of microporous magnesia-aluminum-zirconium brick for 1 year, the brick wear is only about 10%.
JIYGO REFRACTORY & ABRASIVE LIMITED
