At present, due to the raw materials, most of the production processes of alumina in China use the sintering method and the combined method. Rotary kiln is mostly used in the drying and calcination of bauxite and the roasting of aluminum hydroxide. In recent years, the introduction of fluidized roasting equipment has been widely used, but in some old factories, rotary kiln still accounts for a large proportion.
The rotary kiln is a sintering kiln of alumina clinker. In the preparation of alumina, the bauxite and soda ash and lime are proportioned into the rotary kiln, calcined at 1200 ~ 1300 C, and then discharged into the kiln, and then processed to prepare aluminum hydroxide and mother liquor to prepare aluminum hydroxide. It can be produced by calcining at a high temperature of 1200 C in a rotary kiln. The calcination process in the rotary kiln is a high temperature flame and the heated material is reversely moved in the furnace. Alkali lime bauxite raw slurry (40% water) or aluminum hydroxide (12%-18% water) is added from the kiln tail, dehydrated by low temperature drying, heating, high temperature calcination, discharging from the kiln head, and the high temperature gas is The kiln head flows to the kiln tail. Therefore, the kiln is divided into pre-tropical and high-temperature calcined zones. In order to prevent the slurry from bonding to the kiln lining during the heating and calcining process and strengthening the heat transfer process, a chain is arranged between the refractory masonry, and the kiln lining is continuously struck during the rotary motion of the kiln body. The service life has a certain impact.
The rotary kiln body for alumina production is a simplified steel plate welded with refractory material. Refractory materials work in harsh conditions and harsh conditions. It should have the following characteristics: strong resistance to alkali corrosion, long-term operation at high temperature of 1200 ~ 1300 C, without damage; can withstand the impact of dynamic load; can resist the erosion of the charge; can withstand the erosion of high temperature airflow. The refractory materials used in the rotary kiln are mainly high-aluminum bricks and magnesia-chrome bricks, while the low-temperature drying kiln is lined with clay bricks.
At present, the amorphous refractory material has been widely used in the aluminum industry. Due to the high temperature wear and thermal shock stress of the material in the kiln mouth of the rotary kiln, the kiln mouth is easily deformed and damaged in the transition zone of the alumina clinker kiln. The ambient temperature is 400-1000 C, which is severely damaged by alkali and mechanical damage (vibration, distortion), and the liner often falls off.
The main function of the rotary kiln refractory lining is to protect the barrel of the rotary kiln from high-temperature gas and high-temperature materials and to ensure normal production. According to the different types of calcined materials, the use conditions of kiln linings are also different. For cement rotary kiln, dolomite rotary kiln, active lime rotary kiln, alumina rotary kiln, chemical waste rotary kiln, a layer of stable kiln crust should be hung on the burning zone of rotary kiln to protect the rotary kiln bricks. However, there is no need to hang the kiln crust on the rotary kiln refractory lining which calcined metalized pellet and oxidized pellet. In addition, to use refractory bricks made of wear-resistant refractory materials, measures such as preventing ring formation and repairing should be considered to protect the inner rotary kiln brick lining.
Cement rotary kiln is a typical type of rotary kiln that needs to hang kiln crust. Kiln crust refers to the protective layer that materials adhere to the surface of the lining bricks of the rotary kiln. It can prevent chemical erosion and mechanical wear of high-temperature materials, and play the role of heat insulation and heat preservation, which is an important factor to improve the rotary kiln refractory linings service life.
The formation of a kiln crust is a complicated physical and chemical process. When the material is close to the burning zone, the flame will gradually shorten, appropriately increase the exhaust and burning volume, control the high-temperature flame, and burn the refractory bricks into a semi-melted state so that the chemical components in the bricks and the chemical components in the clinker react and bond with each other. When the temperature decreases, the product after reaction forms a block with the brick and forms kiln crust.
This process requires that the grain size of the kiln crust should be small and uniform, with good integrity and firmness without falling off. If the kiln crust of the rotary kiln refractory lining cannot be hung, the semi-melted material will corrode the inner lining very seriously. If the kiln crust is not hung firmly and falls off frequently, the inner rotary kiln brick lining will be subjected to rapid cold and heat, which will be severely damaged.
In industrial production, the use cycle of refractory bricks installed on the burning zone of the rotary kiln is very short. The damage of rotary kiln brick often leads to planned out of kiln maintenance, which is the key factor affecting the good, high yield, low consumption, and annual operation rate of sponge iron kiln, carbon kiln, and other rotary kilns.
The refractory in a direct-fired rotary kiln is a crucial component, serving to both protect the shell of the drum and combustion chamber from the high interior temperatures, and to minimize heat loss. As a result, protecting refractory is not only critical to promoting optimal efficiency, but also to maintaining and prolonging the life of a rotary kiln.
Refractory failure has the potential to cause catastrophic consequences if left unaddressed. Significant downtime, extensive maintenance or even total kiln replacement, as well as lost production, can all result from refractory that has been allowed to degrade.
A well-installed, high-quality refractory can have a lifespan of many years. There are several factors, however, that have the potential to cut refractory life short if not properly monitored and managed the most common of which, are summarized below.
Each time the rotary kiln is heated, the refractory expands with the drum. As the kiln cools down, the refractory retracts. If a kiln is constantly being heated up and shut down, the refractory can easily become stressed, causing cracks. Similarly, cracks can also occur from heating or cooling the kiln too quickly, which also stresses the refractory.
Chlorides can aggressively attack refractory, causing excessive wear because of their corrosive nature. When these chemicals are identified up front, refractory can be designed to handle such aggressive corrosion as best as possible. However, if not prepared for in the initial design, chlorides or other corrosive materials can quickly degrade refractory.
Like corrosion, refractory can be designed to combat an abrasive material, but if not prepared for in the initial design, can have devastating effects. For example, when compared to castable, brick refractory wears less in the presence of an abrasive material and may be the refractory of choice when working with an especially abrasive material.
Signs of refractory damage or failure can be difficult to recognize. And since damage can accelerate quickly, regular monitoring is critical to catching problems early. Any potential signs of damage should be addressed immediately to avoid escalation of an issue to a more severe situation.
Refractory should be regularly inspected as part of the overall preventative maintenance program. When permissible, operators or a customer service engineer from the original equipment manufacturer should inspect the refractory from the inside of the drum to check for the start of any potential cracks or wear while the unit is shut down.
Castable refractory can exhibit hairline cracks over time. If anchors are not properly installed, these cracks can get bigger and allow portions of refractory to fall out. Similarly, these hairline cracks can become bigger, trapping material and creating hot spots.
While not a guaranteed method of detection, refractory problems can also be detected through regular monitoring of the drum shell temperature. This can be done by picking a spot on the rotary kiln shell and holding a temperature gun in place. As the rotary kiln rotates, that spot should be the same temperature for the entire circumference of the shell. For example, a reading of 400, 400, 700, 400 reveals a hotspot on the shell, indicating a failure in refractory. Left unnoticed, this could lead to severe damage to the rotary kiln shell.
In addition to circumference temperature being the same in a given location, the kiln should also exhibit a gradual shift in temperature from one end of the kiln to the other, rather than a drastic or sudden change.
Refractory failure can have disastrous results. Even a small crack can allow heat to reach the rotary kiln shell. It is important to routinely check the exterior temperature of the rotary kiln shell, ensuring that the temperature is consistent for the entire circumference of the drum.
Regularly monitoring and maintaining the refractory in a direct-fired rotary kiln is essential in achieving maximum efficiency and prolonging the overall life of the rotary kiln. Various factors can cause failure and early detection is critical to avoiding excessive downtime, maintenance or replacement costs, and lost production.
FEECO is a leading manufacturer of custom rotary kilns. We also provide a comprehensive range of parts and service support, including annual inspections, to help keep rotary kilns running optimally. For more information on preventative care for rotary kilns, contact us today!
Industrial Rotary Kilns are primarily used in cement, lime, and iron ore processing. These furnaces use direct flame-fired heating methods to remove volatile compounds, instigate chemical reactions, and fuse powder into pellets. The material is rotated as it moves through the kiln, in order to evenly heat said material without relying on conduction.
There are six relevant temperature measurements throughout the Rotary Kiln. These six measurement areas are the Shell & Under Tyre, Product Entry, Mid-Zone, Flame Temperature, Product Discharge, and Conveyor Belt Protection.
Inaccurate heat measurements in any one of these areas can result in major equipment damage, product irregularities, production lags, and toxic fume build-up. Rotary Kilns present several temperature measurement challenges including harsh optical obstructions, varying measurement sizes, and hostile operating conditions.
Using carefully selected narrowband wavelengths to view through smoke, flames, dust, and moisture, Williamson pyrometers provide unequalled accuracy and repeatably across all crucial Rotary Kiln temperature measurements.
If the refractory material lining the Rotary Kiln overheats or is damaged in any way, then hot spots appear on the kilns outer shell. Detecting these hot spots is crucial in maintaining the kilns structural integrity, protecting human health & safety, and preventing costly downtime. Infrared pyrometers are often used to monitor shell temperature and identify hot spots before they become a problem. Rotary Kilns also have cylindrical steel castings, known as tyres, attached to the shell, which obstruct the shell monitoring system. If a hot spot forms under a tyre, then the instrument will not detect it. Consequently, a local hot spot monitor should be installed at each tyre.
Williamson short-wavelength pyrometers are optimized to identify hot spots by providing positional information while viewing a relatively large area. Pyrometers installed for local hot spot detection at each tyre, compensate for the hard to reach measurement area. This infrared system has proven to be a highly effective lower-cost alternative to line scanning systems.
Aggregate Materials are preheated using hot process gases that flow through the kiln and into the preheat zone. Aggregate material temperature at the Product Entry is used as a critical process parameter for overall heat balance throughout the Rotary Kiln. This important measurement often presents heavy dust and fluctuating air pressure. Williamsons Short-Wavelength pyrometers provide unequalled accuracy and repeatability at the Rotary Kiln Product Entry.
Peak aggregate material temperature is reached at the end of the kiln, known as product discharge. Peak temperature or peak product temperature is the primary Rotary Kiln process control parameter. Inaccurate or widely varying peak temperatures at product discharge can lead to production inefficiencies, lowered product quality & yield, fuel waste, and equipment damage. There are, however, several challenges associated with this temperature measurement area including heavy dust, flames, and sight path obstructions.These challenges combined with hostile operating conditions demand the use of Williamsons infrared technology and protective cooling system.
Williamsons Short-Wavelength (SW) and Two-Color (TC) pyrometers use carefully selected narrowband wavelength set(s) to view through severe optical obstructions, while the protective cooling jacket prevents pyrometer damage. Williamson pyrometers make continuous peak temperature measurements with unequalled accuracy and repeatability at product discharge.
Aggregate Material temperature in the middle of the Rotary Kiln provides important process efficiency and heat supply feedback. Underheated materials can compromise product quality, while overheated materials indicate fuel waste and potential equipment damage. Precise temperature control in the mid-zone improves production efficiency, increases consistent product quality, and decreases input costs by minimizing fuel waste.
Because Rotary Kilns are extremely long, it is often difficult to obtain accurate mid-zone temperature measurements from the ends of the kiln. Instead, measurements are taken from the side of the kiln using a closed-ended viewing tube. This measurement should also be made once per rotation. Williamsons Short-Wavelength (SW) pyrometers use high resolution optics and temperature-based peak hold settings to produce highly accurate mid-zone temperature measurements with each rotation.
Flame-fired processes inside the Rotary Kiln are fueled primarily by natural gas that is frequently combined with oxygen, oil, pulverized coal, or CO2 gas. Precise control over the fuel-to-air ratio within the kiln reduces fuel waste, heat loss, and dangerous nitrogen oxide accumulation. Flame or combustion temperature is a key indicator of the fuel-to-air ratio, and as a result, accurate and continuous flame temperature measurement is essential in optimizing Rotary Kiln operations. Traditional thermocouples used for this measurement must be frequently replaced, resulting in increased maintenance costs and production lags.
Williamsons Specialty-Wavelength (SP) pyrometers use a unique wavelength selection to accurately monitor Rotary Kiln Flame temperature from difficult angles and through severe interferences. While the protective cooling jacket enables the pyrometer to withstand hostile operating conditions.
As the material exits the kiln, it is pushed onto a conveyor where it finishes cooling. Some products tend to form heat retaining clumps that can easily exceed the rubber conveyor belts upper temperature limits. When this occurs, the material can cause significant equipment damage and even present thermal safety hazards.
Temperature measurement along the conveyor belt presents several challenges. The measurement area is relatively large (the entire conveyor belt,) temperature across said measurement area can vary significantly, and steam, water, and dust are common optical interferences.
Williamsons Short-Wavelength conveyor belt pyrometer monitors a large measurement area, uses a rate of change algorithm to identify hot spots regardless of bulk temperature, views through heavy obstructions without interference, and triggers an alarm when hot spots are detected.
The majority of coke calcining plants process petroleum coke which is then used in the primary aluminum, steel, and chemical production industries. Calcining coke involves heating the material to remove moisture and volatiles which increases the coke density and electrical conductivity. Many coke calcining plants are located next door to oil refineries for easy and constant access to petroleum coke.
Typically, petroleum coke is fed into the backend of the rotary kiln. Rotary kilns are lined with refractory monolithics or brick. As the coke travels down the rotary kiln, it passes through numerous sections, some containing refractory lifters and refractory lined air injection nozzles. Rotary kilns are heated via the firing hood at the discharge end of the kiln. Abrasion, thermal shock, and temperature resistance up to 2900F are the most important refractory property considerations.
For the rotary kiln lining, RSS Dixie supplies our pumpable, self-flowing, Dixie Crete LC-6001. The firing hood, where thermal shock is a main consideration is routinely lined with our Thermogen 85 Plastic and Dixie Crete ULC 85.
After passing through the rotary kiln, the calcined coke is discharged via a feed shoot into a rotary cooler. Thermal shock of the refractory is common as the cooler often contains a water quench to decrease the coke temperature. We routinely supply our coarse grained Dixie Crete LC 65 C for this area which provides excellent resistance to thermal shock.
The settling chamber and stack are upstream from the green coke feed. The stack in many plants is typically gunned or shotcreted. RSS Dixie can supply numerous materials for this area such as our fireclay gun mix- Dixie Gun 28 T. The settling chamber is often gunned with a 2500-2600F, lightweight gun mix such as our Dixie Mono Kast 28 G.
Refractory bricks are built inside the hazardous waste incineration rotary kiln to protect the rotary kiln from direct hazards due to high temperature and corrosion during hazardous waste incineration. The properties of Refractory Materials for Hazardous Waste Rotary Kilns depend on the composition and distribution of their phases and the chemical characteristics of each phase. In other words, it depends on the chemical mineral composition and chemical composition in the hazardous waste rotary kiln.
The main chemical components of refractory bricks used in general hazardous waste incineration rotary kilns include high alumina bricks, magnesia bricks, magnesia alumina bricks, and silica bricks. The content of AlO in high alumina bricks is relatively high, generally around 70%. Magnesia bricks are mainly minerals composed of MgO and other metal oxides. Silicon bricks are mainly stable amorphous substances formed by SiO and other metal oxides. Therefore, refractory materials for hazardous waste rotary kilns should have the following characteristics at the same time.
The materials entering the hazardous waste rotary kiln are mainly organic wastes such as industrial residues and chemical wastes. In the incineration process, the organic sulfur in hazardous waste undergoes high-temperature oxidation, mainly in the form of SO and SO. The temperature of hazardous waste in the rotary kiln can reach 800~1300. In a high-temperature environment, SO and SO in the flue gas can easily react with minerals on the surface of refractory bricks to produce low-melting copolymers. The reaction equation of sulfur is as follows:
The corrosion of these low melting point polymers leads to serious loss of the bonding strength of the refractory bricks, forming a new low eutectic substance without bonding strength. This leads to the formation of low-melting polymers and low-melting substances on the surface of the refractory bricks. Driven by the movement and friction of the material, the surface will eventually fall off, resulting in the thinning of the refractory bricks.
Since the main components of silicon-alumina refractories are mullite and corundum, the main components are SiO and AlO. The alkali metals contained in the hazardous waste can react with refractory bricks to generate nepheline-like substances and cause the volume expansion of refractory bricks. It may also cause the melting point to decrease, which in turn increases the corrosion effect on the refractory bricks, and accelerates the thinning rate of the refractory bricks, and shortens the service life.
Pure magnesia refractories have very poor resistance to alkaline residues. However, when magnesia-alumina spinel is added to magnesia materials, it can well prevent the permeability of alkaline residues to refractory materials. And as the amount of magnesia-alumina spinel added increases, the penetration resistance will gradually become stronger, but the additional amount should not exceed 20%.
After studying the reaction characteristics of alkali metals and refractory materials, the results show that changes in temperature, excess air coefficient, Cl content, and S content will all affect the migration of alkali metals. Therefore, it is recommended to choose composite components according to the actual situation when selecting molded refractories. The properties of refractory materials can resist the combined action of multiple corrosive factors.
Taking sodium carbonate as the research object, the corrosion mechanism of refractory materials is studied from the aspects of corrosion thermodynamics and kinetics. The results show that magnesia-containing refractories have better thermal stability than chrome-containing refractories.
Rongsheng is an experienced refractory material manufacturer. We also have rich experience in the production and sales of refractory materials for hazardous waste rotary kilns and cement rotary kilns. And every year, we can receive customer return orders. If you need to replace the refractory lining of your rotary kiln, or you need to build a new rotary kiln, please contact us. Our companys refractory lining materials not only have the price advantage of the factory but also we provide high-quality customer service. Look forward to working with you.
Rongsheng Refractory Supplier provides kinds of refractory bricks and monolithic refractories. Exclusive customer service and refractory lining material solutions for metallurgy, nonferrous metals, building materials, electric power, petrochemical and other industries. Save production costs and improve economic efficiency.
With the continuous progress of the cement industry, rotary kiln, as the core cement equipment of cement production line, is developing towards a large scale. Compared with the traditional rotary kiln, its technology is more complex, and the requirements for rotary kiln design and accessories are higher. The rotary kiln refractory lining is a layer of refractory material installed inside the kiln cylinder, which plays a protective role in many aspects, and is an important part of cement rotary kiln.
Refractory brick is a kind of rotary kiln lining. At the early time, due to the small size of the kiln body and low calcination temperature, we mainly used high-alumina brick and clay brick as the lining. In the 1960s, the kiln lining at high-temperature zone was replaced by alkaline bricks. With the large-scale of rotary kiln, its sintering temperature increases, meanwhile, the cylinder rotating speed and the diameter also increase, all of which cause certain damage to the rotary kiln refractory brick. Besides, the corrosion of alkali, sulfur, chlorine, and other volatile substances, as well as some erosive wear, aggravate the wear degree of refractory bricks inside the kiln body. After a summary, they can be respectively classified as chemical damage, mechanical stress damage, and thermal stress damage. In most cases, they act on the refractory lining in combination.
Therefore, if we want to ensure the smooth running of cement rotary kiln and prolong its service life, we should select the right kind of refractory bricks according to their damage mechanism in different parts of the rotary kiln body.
In addition, we should combine the structure of cement rotary kiln to choose the refractory brick. The cement rotary kiln can be generally divided into preheating zone, lower transition zone, upper transition zone, sintering zone, and cooling zone. The length, temperature, and function of each zone are different, so the selection of refractory lining brick should meet the requirements of each area.
Lower Transition Zone: the temperature in this area is relatively low, so the thermal conductivity of the refractory brick is required to be low. Both anti-stripping alumina brick and silicon mullite brick are frequently used in this zone. Of the two bricks, the performance of silica mullite brick is superior, its service life is about 1 time longer than the anti-spalling high alumina brick, but the price is about 1.5 times higher.
Upper Transition Zone: the coating formation in this zone is unstable, the kiln lining is required to has good thermal shock resistance, low thermal conductivity, and strong wear resistance. Magnesia alumina spinel brick is a good choice, but its thermal conductivity is relatively high. By contrast, the wear resistance and overall performance of the silica-alumina brick are equivalent to the magnesia alumina spinel brick, and its thermal conductivity is low.
Sintering Zone: the sintering zone has a high calcining temperature and intense chemical reaction, the lining brick in this area should have a strong ability to resist the erosion of clinker, SO3, and CO2. Magnesia-chrome brick has a poor performance and is easy to react with clinker to produce Cro3, resulting in short service life. The commonly used magnesia iron spinel brick has a great effect but a high cost. Therefore, comprehensive consideration, we had better choose periclase spinel compound brick in this area.
Cooling Zone: the temperature fluctuates greatly in this zone and the coating formation is unstable. The rotary kiln refractory lining should be wear-resisting and has excellent thermal shock resistance and low thermal conductivity. In recent years, we usually use silicon mullite bricks and anti-stripping abrasive brick.
According to the above analysis, we can select suitable refractory bricks for the cement rotary kiln, but the raw materials and fuels of each cement kiln may be different, we should make appropriate adjustments according to the characteristics of our rotary kiln.
AGICO Group is an integrative enterprise group. It is a Chinese company that specialized in manufacturing and exporting cement plants and cement equipment, providing the turnkey project from project design, equipment installation and equipment commissioning to equipment maintenance.
Kiln Refractory Bricksare shaped refractory bricks materials for application in all kinds of kilns such as cement rotary kiln, limekiln, electric ceramickilnand so on. There are all kinds of kiln refractory bricks for sale available cheap in Rongsheng Refractory Factory. Welcome to Contact Us for Detailed Products List and Price!
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