The main heat source in a rotary kiln is the high-temperature smoke produced by braize calcination. The heat transfers to the inner wall and materials, also the inner wall transfers heat to materials in all kinds of ways. The inner wall transmits the heat to the shell through conducting heat. The shell emission to the outer environment by convection and radiation.
The transition zone is around 60-26 meters from the kiln head. Smoke and refractory lining s temperature continually rises. The caloric receptivity of materials sharply rises. So, the temperature of materials on this zone rises.
Cement kiln is a mechanism to calcinate clinker cement. It consists of a cylinder, transmission gear, support device, kiln head, and fuel device. When calcinating, clinker cement in virtue of rotation of cylinder to make itself sufficiently mix up and full contact. Coal Ejection Pipe calcinates and releases much heating. The heat in kiln is transferred to clinker cement by flame radiation, heat convection, and bricks transmission. Clinker cement moves forward-leaning on cylinders inclination and rotation of kiln. The max temperature of cement kiln can be 1600.
Lime rotary kiln is a professional device for processing limestone, which is mainly focused on calcinating lime. It consists of a shell, operation panel, control system, heating `parts, kiln head, kiln tail, sealing device and protective circuit. Lime rotary kiln is different from other rotary kilns because it has a preheat bin. Before limestone even come in a rotary kiln, the temperature of the preheating bin has arrived at 1150. Meanwhile, limestone will be put into the preheat bin through a bucket elevator and be heated to 900. Then be put into the kiln to process calcinating by the hydraulic push rod. Be ejected until calcination craft is over. The temperature in the lime rotary kiln can be 1350.
After coal is fully calcinated, massive heat covers the whole kiln from kiln tail to kiln head. Ceramsite keeps being calcinated the whole time. Rotary kiln for ceramists highest temperature can be 1050.
It is important to monitor the temperature in the kiln during the entire operation to keep optimal performance, minimize downtime, ensure the safety and durability of the kiln-shell and to optimize its efficiency.
FEECO is a leading manufacturer of highly engineered, custom rotary kilns for processing solids. Our high temperature kilns have earned a reputation for their durability, efficiency, and longevity. We offer both direct- and indirect-fired units.
Rotary kilns work by processing material in a rotating drum at high temperatures for a specified retention time to cause a physical change or chemical reaction in the material being processed. The kiln is set at a slight slope to assist in moving material through the drum.
Direct-fired kilns utilize direct contact between the material and process gas to efficiently process the material. Combustion can occur in a combustion chamber to avoid direct flame radiation, or the flame can be directed down the length of the kiln.
All FEECO equipment and process systems can be outfitted with the latest in automation controls from Rockwell Automation. The unique combination of proprietary Rockwell Automation controls and software, combined with our extensive experience in process design and enhancements with hundreds of materials provides an unparalleled experience for customers seeking innovative process solutions and equipment.
Indirect-fired kilns are used for various processing applications, such as when processing must occur in an inert environment, when working with finely divided solids, or when the processing environment must be tightly controlled.
Calcination refers to the process of heating a material to a temperature that will cause chemical dissociation (chemical separation). This process is used frequently in the creation of inorganic materials, for example, the dissociation of calcium carbonate to create calcium oxide and carbon dioxide.
Thermal desorption is also a separation process. This process uses heat to drive off a volatile component, such as a pesticide, from an inorganic mineral, such as sand. The component is vaporized at the increased temperature, causing a separation without combustion. In some cases, an indirect rotary kiln would be best for this application, because the volatile chemicals may be combustible. The indirect kiln will supply the heat for desorption, without the material coming into direct contact with the flame.
Organic combustion refers to the treatment of organic wastes with the intent of reducing mass and volume. Organic waste is treated in the kiln, leaving behind an ash with considerably less mass and volume. This allows for more efficient and effective deposit of waste materials into landfills.
Sintering is the process of heating a raw material to the point just before melting. This increases the strength of the material, and is commonly used in the proppant industry, where sand or ceramic materials are made stronger.
Heat setting involves bonding a heat resistant core mineral with another, less heat resistant coating material. Unlike an unheated coating process, here, a rotary kiln heats the coating material to just below liquefaction point, allowing it to coat the heat resistant core more evenly and more securely. This process is commonly seen in the manufacture of roofing granules, where a mineral such as granite is coated with a colored pigment, producing a product that is both durable and aesthetically pleasing.
Reduction roasting is the removal of oxygen from a component of an ore usually by using carbon monoxide (CO). The CO is typically supplied by mixing a carbonaceous material such as coal or coke with the ore or by feeding it separately. Examples are the reduction roasting of a hematite containing material to produce magnetite that can be magnetically separated. In the Waelz process, zinc oxide in steel mill wastes is reduced to metallic zinc and volatilized for recovery in the off-gas system.
Thermal Desorption for Spent CatalystsRotary Kiln3D Indirect Kiln for Activated CarbonPyrolysis Kiln Seal3D FEECO Pyrolysis KilnPyrolysis KilnWorn Rotary Kiln RefractoryKiln Alignment SoftwareBatch Rotary Kiln TestingProcessing Challenges When Working with Rotary KilnsFEECO Batch Kiln BrochureIndustry Focus COVID-19 Demands Medical Waste Incineration CapacityIndirect Fired Rotary Kiln ReplacementRotary Kiln IncineratorsResource of the Week: Thermal Testing with Kilns3D Model of a FEECO Carbon Activation KilnRotary Kiln Testing ThumbnailRotary Kiln TestingIndirect Batch Rotary Kiln Testing, Batch Calciner Testing, Thermal Process DevelopmentKnowing When its Time to Replace Your Rotary Drum Seal, Leaf SealRotary Drum Drive ComponentsRotary Drum BreechingReplacement Rotary Drum BearingsBoomin Catalyst Market Drives Demand for Rotary Kiln Repair Services, Rotary KilnsReplacement Dryer (Drier) and Kiln BurnersCombustion ChambersReplacement Rotary Drum ShellRotary Drum Laser Alignment Process, Rotary Drum AlignmentWhy Post Maintenance Alignment is Critical to Rotary DrumsCauses of Tire (Tyre) and Trunnion Wear, Rotary Drum TireFEECO Tire (Tyre) Grinding Machine, Tire and Trunnion Grinding in ProgressRotary Drum Tire (Tyre) Wear Pattern from Excessive Wheel Skewing, Rotary Drum Tire in Need of Tire GrindingRotary Drum Tire (Tyre) Wear Pattern from Poor Housekeeping Practices, Rotary Drum Tire in Need of Tire GrindingRotary Drum Tire (Tyre) Wear Pattern from Misalignment, Rotary Drum Tire in Need of Tire GrindingRotary Drum Tire (Tyre) Wear Pattern from Using Improper Tire Lubricant, Rotary Drum Tire in Need of Tire GrindingTire (Tyre) and Trunnion Wheel GrindingTire (Tyre) and Trunnion GrindingIndirect Rotary Kiln (Calciner) for Plastics PyrolysisPlastic to Fuel Conversion via Pyrolysis Replacement Rotary Drum PartsRotary Drum Thrust RollersRotary Drum Trunnion Wheels (Rollers)Rotary Drum Riding Ring (Tire/Tyre)Resource of the Week: Girth Gears PageRotary Kiln System Optimization, Rotary Kiln Process AuditSpring-Mounted Replacement Rotary Drum Girth GearRotary Kiln Gains Traction as E-Waste Crisis Looms, Metal Recovery from E-WasteIndirect Batch Rotary Kiln Testing, Batch Calciner Testing, Thermal Process Development, Metal RecoveryDirect-Fired Rotary KilnRotary Kiln Chain and Sprocket Drive AssemblyRotary Kiln Gear and Pinion Drive AssemblyRotary Kiln Friction Drive AssemblyRotary Kiln Direct Drive AssemblyRotary Kiln Trunnion BaseRotary kiln end dam for increasing loading, retention time, and bed depthResource of the Week: Rotary Kiln Customization Slideshare PresentationKaolin Clay CalcinationLithium-ion Battery Recycling OpportunitiesRotary Kilns in Expanded Clay Aggregate ProductionBatch Kiln for Testing Expanded Clay AggregatesRotary Kiln Refractory Failure Illustration, Rotary Kiln Shell Hot SpotRotary Kiln Refractory InspectionDirect-Fired Rotary Kiln for SpodumeneCalciner (Indirect Kiln) for Lithium Recovery from SpodumeneRotary Kiln Complete SystemFEECO Batch Kiln for Testing CalcinationRotary Drum Drive BaseRotary Kilns for Advanced Thermal Processing in SustainabilityResource of the Week: Project Profile on a Rotary Kiln (Calciner) Resource Recovery SystemResource of the Week: Tire Grinding BrochureResource of the Week: Slideshare Presentation on Rotary Kiln Sizing and DesignResource of the Week: Unitized Drive Base BrochureDiagram Showing a Rotary Kiln with Co-current AirflowDiagram Showing a Rotary Kiln with Counter Current AirflowDiagram Showing Co-current Airflow View All >
The advantages to a FEECO rotary kiln are that it is built to the highest quality standards and is backed by over 60 years of process design experience. The FEECO Innovation Center offers batch and pilot scale kilns that can simulate conditions in continuous commercial rotary kilns, allowing our customers to test small samples of material under various process conditions, as well as part of a continuous process. With options in both co-current and counter-current flow, and direct or indirect configurations, the FEECO test kilns offer a variety of options to suit your thermal testing needs. We also offer support equipment such as a combustion chamber, afterburner, baghouse, and wet scrubber for testing.
The insiders of mining industry are clear that the kiln will dissipate a lot of heat in a long period of operation. And the temperature of the flame is closely related to the quality of the finished product. When the flame is strong, the kiln shell will naturally form, and it can better maintain the firing cycle of refractory bricks. Based on many years' experience, the method of how to maintain the flame temperature in rotary kiln is summarized as follows.
i. Strictly control the swirling air around the rotary kiln. Transport the swirling air from the inner pipe conveying coal powder and the air to the outer pipe. The inner side of the pulverized coal tube forms a small portion of the swirling flow, and the outer tube of the pulverized coal tube forms a uniformly strong swirling flow. The volatilization of fuel in rotary kiln and the peak difference temperature will be constant and uniform.
ii. Increase the flow velocity of the rotary kiln and install the smoke gathering hood. If the wind is too large, the flame will naturally lengthen. The main function of the smoke gathering hood is to speed up the flame diffusion in the kiln, and to ensure uniform flame intensity.
iv. Adjustment of burner in rotary kiln. There are two kinds of burner jet form whose purpose is to assemble air currents and produce large quantities of airflow outside the flame. Its reflux mode is that the air in the central part is jetted in parallel. The reflux of air flow will promote the volatilization of coal powder in the rotary kiln, and reduce the steep peak temperature.
Yuhong Heavy Machinery Co., Ltd., Zhengzhou City, Chinais a professional calcination rotary kiln equipment manufacturer integrating production, research and development, sales and export of products.For further inquiry, please visit our website.
Rotary kilns are synonymous with cement making, being the workhorses of this industry. There are many types of rotary kiln arrangements for producing cement clinker with each incremental design goal aimed at improving energy efficiency, ease of operation, and product quality and minimizing environmental pollutants. Rotary cement kilns can be classified into wet-process kilns, semidry kilns, dry kilns, preheater kilns, and precalciner kilns. All of these are described in the book by Peray (1986) and many others, hence we will not dwell upon them here. Rather, we will briefly show the pertinent process chemistry and the heat requirements that drive them, so as to be consistent with the transport phenomena theme.
Rotary kilns have been used in various industrial applications (e.g., oil shale retorting, tar sands coking, incineration, cement production, etc.). The rotation of a cylinder-shaped vessel positioned longitudinally approximately 30 of the horizontal position ensures a continuous motion of catalyst between the entrance and exit of the kiln. With regard to the spent catalyst regeneration, the description of rotary kilns was given by Ellingham and Garrett . There are two types of rotary kilns, i.e., direct fire and indirect fire.
The direct fire is a single shell vessel with rings added inside to slow the catalyst as it tumbles from the inlet (elevated part) towards outlet (lower part). The oxidation medium flows countercurrent to catalyst movement. The O2 concentration in the medium will decrease in the same direction because of its consumption. Therefore, the zone in the vessel located near the inlet may function as a stripper of volatile components of coke. The kiln is fired by gas burners directly against the outer shell of the vessel. The temperature inside the kiln is controlled by adjusting the burner heat, varying concentration of O2 in the oxidizing medium and its flow. The indirect fire kiln comprises a double-shell cylinder vessel. The inner shell is similar as that of the direct fire kiln. The space between the shells is heated either by combustion gas or steam. In some cases, the inner cylinder shell is ebullated allowing hot gases or steam to enter and contact the tumbled catalyst. The catalyst temperatures are controlled by monitoring the temperatures of the inlet and outlet gases. It is believed that Eurocat process evolved from a rotary kiln process by be improving the control of operating parameters such as temperature, gas flow, speed of rotation, etc.
The rotary kiln is used to process the lead-containing components resulting from the breaking and separation of waste batteries. The main components of a rotary kiln are an inclined cylindrical, refractory-lined reaction shaft equipped to rotate over rollers and a burner. Process heat is generated by burning fine coke or coal contained in the charge and by the exothermic heat of the PbO reduction by CO. This process produces molten lead and a slag with 35% Pb. A drawback of this technology is the short life of refractory liners.
The rotary kiln is a long tube that is positioned at an angle near horizontal and is rotated. The angle and the rotation allow solid reactants to work their way down the tube. Speed and angle dictate the retention time in the kiln. Gas is passed through the tube countercurrent to the solid reactant. The kiln is operated at high temperatures with three or four heating zones depending on whether a wet or dry feed is used. These zones are drying, heating, reaction, and soaking. Bed depth is controlled at any location in the tube with the use of a ring dam.
The most common reactor of this type is the lime kiln. This is a noncatalytic reaction where gas reacts with calcium carbonate moving down the kiln. Other reactions performed in the rotary kiln include calcination, oxidation, and chloridization.
Use of rotary kilns for hazardous waste incineration is becoming more common for disposal of chlorinated hydrocarbons such as polychlorinated biphenyls (PCBs). Flow in these kilns is cocurrent. Major advantages include high temperature, long residence time, and flexibility to process gas, liquid, solid, or drummed wastes.
The rotary kilns used in the first half of the twentieth century were wet process kilns which were fed with raw mix in the form of a slurry. Moisture contents were typically 40% by mass and although the wet process enabled the raw mix to be homogenized easily, it carried a very heavy fuel penalty as the water present had to be driven off in the kiln.
In the second half of the twentieth century significant advances were made which have culminated in the development of the precalciner dry process kiln. In this type of kiln, the energy-consuming stage of decarbonating the limestone present in the raw mix is completed before the feed enters the rotary kiln. The precalcination of the feed brings many advantages, the most important of which is high kiln output from a relatively short and small-diameter rotary kiln. Almost all new kilns installed since 1980 have been of this type. Figure1.4 illustrates the main features of a precalciner kiln.
The raw materials are ground to a fineness, which will enable satisfactory combination to be achieved under normal operating conditions. The required fineness depends on the nature of the raw materials but is typically in the range 1030% retained on a 90 micron sieve. The homogenized raw meal is introduced into the top of the preheater tower and passes downwards through a series of cyclones to the precalciner vessel. The raw meal is suspended in the gas stream and heat exchange is rapid. In the precalciner vessel the meal is flash heated to ~900C and although the material residence time in the vessel is only a few seconds, approximately 90% of the limestone in the meal is decarbonated before entering the rotary kiln. In the rotary kiln the feed is heated to ~ 1500C and as a result of the tumbling action and the partial melting it is converted into the granular material known as clinker. Material residence time in the rotary kiln of a precalciner process is typically 30 minutes. The clinker exits the rotary kiln at ~ 1200C and is cooled to ~60C in the cooler before going to storage and then being ground with gypsum (calcium sulfate) to produce cement. The air which cools the clinker is used as preheated combustion air thus improving the thermal efficiency of the process. As will be discussed in section1.5, the calcium sulfate is added to control the initial hydration reactions of the cement and prevent rapid, or flash, setting.
If coal is the sole fuel in use then a modem kiln will consume approximately 12 tonnes of coal for every 100 tonnes of clinker produced. Approximately 60% of the fuel input will be burned in the precalciner vessel. The high fuel loading in the static precalciner vessel reduces the size of rotary kiln required for a given output and also reduces the consumption of refractories. A wider range of fuel types (for example, tyre chips) can be burnt in the precalciner vessel than is possible in the rotary kiln.
Although kilns with daily clinker outputs of ~9000tonnes are in production in Asia most modem precalciner kilns in operation in Europe have a production capability of between 3000 and 5000 tonnes per day.
A rotary kiln is a physically large process unit used in cement production where limestone is decomposed into calcium oxide which forms the basis of cement clinker particles under high temperatures. The modelling of rotary kilns are well documented in literature. Mujumdar et al. 2007 developed an iteration based rotary kiln simulator (RoCKS), which integrates models for a pre-heater, calciner, kiln and clinker cooling that agreed well with observations in industry. The model takes complexities in reactions and heat transfers with different sections into account by coupling multiple models with common boundaries regarding heat and mass communications. Other work (Ngadi and Lahlaouti, 2017) neatly demonstrates an experimentally proven kiln model being applied for screening of combustion fuel used for kilns, and how it may impact the production. This contribution coupled modelling of reactions and heat transfer in the bed region and another model for combustion and heat transfer in the freeboard region.
While modelling of these processes with varying degree of complexity has been performed, proper uncertainty and sensitivity analysis of these models have not been given due importance/consideration. As the use of computer aided process engineering tools increases, the need for robust uncertainty and sensitivity analysis frameworks becomes more important. There are several frameworks of uncertainty and sensitivity analysis applied for different problems, from good modelling practice (Sin et al., 2009) to process design and product design (Frutiger et al. 2016). These frameworks typically include the following steps (0) problem statement, (i) identification of input sources of uncertainties, (ii) sampling (iii) Monte Carlo simulations and (vi) sensitivity analysis. The purpose of this work is to perform a systematic uncertainty and sensitivity analysis of rotary kiln process design in order to address the following: (1) Given a certain base case design, what is the impact of uncertainties in the model and measurements on the key process design metrics (minimum required reactor length and degree of conversion), and, (2) given a certain source of uncertainties, what is the robust design to ensure process performance with 95 % confidence.
The rotary kiln is often used in solid/liquid waste incineration because of its versatility in processing solid, liquid, and containerized wastes. The kiln is refractory lined. The shell is mounted at a 5 degree incline from the horizontal plane to facilitate mixing the waste materials. A conveyor system or a ram usually feeds solid wastes and drummed wastes. Liquid hazardous wastes are injected through a nozzle(s). Non-combustible metal and other residues are discharged as ash at the end of the kiln. Rotary kilns are also frequently used to burn hazardous wastes.
Rotary kiln incinerators are cylindrical, refractory-lined steel shells supported by two or more steel trundles that ride on rollers, allowing the kiln to rotate on its horizontal axis. The refractory lining is resistant to corrosion from the acid gases generated during the incineration process. Rotary kiln incinerators usually have a length-to-diameter (L/D) ratio between 2 and 8. Rotational speeds range between 0.5 and 2.5 cm/s, depending on the kiln periphery. High L/D ratios and slower rotational speeds are used for wastes requiring longer residence times. The kilns range from 2 to 5 meters in diameter and 8 to 40 meters in length. Rotation rate of the kiln and residence time for solids are inversely related; as the rotation rate increases, residence time for solids decreases. Residence time for the waste feeds varied from 30 to 80 minutes, and the kiln rotation rate ranges from 30 to 120 revolutions per hour. Another factor that has an effect on residence time is the orientation of the kiln. Kilns are oriented on a slight incline, a position referred to as the rake. The rake typically is inclined 5 from the horizontal.
Hazardous or non-hazardous wastes are fed directly into the rotary kiln, either continuously or semi-continuously through arm feeders, auger screw feeders, or belt feeders to feed solid wastes. Hazardous liquid wastes can also be injected by a waste lance or mixed with solid wastes. Rotary kiln systems typically include secondary combustion chambers of afterburners to ensure complete destruction of the hazardous waste. Operating kiln temperatures range from 800C to 1,300C in the secondary combustion chamber or afterburner depending on the type of wastes. Liquid wastes are often injected into the kiln combustion chamber.
The advantages of the rotary kiln include the ability to handle a variety of wastes, high operating temperature, and continuous mixing of incoming wastes. The disadvantages are high capital and operating costs and the need for trained personnel. Maintenance costs can also be high because of the abrasive characteristics of the waste and exposure of moving parts to high incineration temperatures.
A cement kiln incinerator is an option that can be used to incinerate most hazardous and non-hazardous wastes. The rotary kiln type is the typical furnace used in all cement factories. Rotary kilns used in the cement industry are much larger in diameter and longer in length than the previously discussed incinerator.
The manufacture of cement from limestone requires high kiln temperatures (1,400C) and long residence times, creating an excellent opportunity for hazardous waste destruction. Further, the lime can neutralize the hydrogen chloride generated from chlorinated wastes without adversely affecting the properties of the cement. Liquid hazardous wastes with high heat contents are an ideal supplemental fuel for cement kilns and promote the concept of recycling and recovery. As much as 40% of the fuel requirement of a well-operated cement kiln can be supplied by hazardous wastes such as solvents, paint thinners, and dry cleaning fluids. The selection of hazardous wastes to be used in cement kiln incinerators is very important not only to treat the hazardous wastes but also to reap some benefits as alternative fuel and alternative raw material without affecting both the product properties and gas emissions. However, if hazardous waste is burned in a cement kiln, attention has to be given to the compounds that may be released as air emissions because of the combustion of the hazardous waste. The savings in fuel cost due to use of hazardous waste as a fuel may offset the cost of additional air emission control systems in a cement kiln. Therefore with proper emission control systems, cement kilns may be an economical option for incineration of hazardous waste.
The rotary kiln gasifier is used in several applications, varying from industrial waste to cement production and the reactor accomplishes two objectives simultaneously: (1) moving solids into and out of a high temperature reaction zone and (2) assuring thorough mixing of the solids during reaction. The kiln is typically comprised of a steel cylindrical shell lined with abrasion-resistant refractory to prevent overheating of the metal and is usually inclined slightly toward the discharge port. The movement of the solids being processed is controlled by the speed of rotation of the kiln.
The moving grate gasifier is based on the system used for waste combustion in a waste-to-energy process. The constant-flow grate feeds the waste feedstock continuously to the incinerator furnace and provides movement of the waste bed and ash residue toward the discharge end of the grate. During the operation stoking and mixing of the burning material enhances distribution of the feedstocks and, hence, equalization of the feedstock composition in the gasifier. The thermal conversion takes place in two stages: (1) the primary chamber for gasification of the waste (typically at an equivalence ratio of 0.5) and (2) the secondary chamber for high temperature oxidation of the synthesis gas produced in the primary chamber (Grimshaw and Lago, 2010; Hankalin et al., 2011).
The rotary kiln ICM/Phoenix Bioenergy demonstration gasifier was operated at a transfer station in Newton, Kansas from 2009 to 2012 for more than 3200h, testing various types of biomass, RDF, tire-derived fuel or automobile shredded residue mixed with RDF. The 150-t-per-day facility reported to have tested more than 16 types of feedstock listed in Table 3.2 .
The gasification process consists of a horizontal cylinder with an internal auger which slowly rotates  allowing feedstock to move through the reactor, whereas air is injected at multiple points. Only small portion of the syngas was used to produce steam, whereas the rest was flared (Fig. 3.2).
Unfortunately, ICM had to take down the demonstration gasifier at the transfer station, upon completion of the project and financing grant, declaring that the facility did not prove to be a viable solution for the county. Some of the problems that ICM mention  were related to the availability of feedstock of only 90t per day, whereas the prototype was designed for 150t per day, but also insufficient investment from financial partners due to the lower projected returns. ICM announced that through a contract with the City of San Jose, CA they will have the ICM demonstration gasifier at the San Jos-Santa Clara Regional Wastewater Facility . The facility will process 10 short tons per day of woody biomass, yard waste or construction and demolition materials mixed with biosolids from the WWT.
Pyroprocessing is a process in which materials are subjected to high temperatures (typically over 800 C) in order to bring about a chemical or physical change. It consists of three stages: Preheater, Kiln & Cooler.
Preheaters are used in industrial dry kiln cement production plants to heat the raw mix and drive off carbon dioxide and water before it is fed into the kiln. Temperature typically used from 100C to 300C
The Kiln is the heart of the plant what an entire cement plant is dimensioned around, and where most of the final chemical reactions take place. The kilns play a key role in ensuring optimal quality clinker. The rotary kiln consists of a tube made from a mild steel plate and slowly rotates on its axis. Rawmix is fed in at the upper end, and the rotation of the kiln causes it to gradually move downhill to the other end of the kiln. Kiln size & Dia is dependent on the capacity of the production of the plant.
There are many different types of refractory brick and they have to withstand not only the high temperatures in the kiln but reactions with the meal and gases in the kiln, abrasion and mechanical stresses induced by deformation of the kiln shell as it rotates. The range of kiln temperature is between 700C to 1800C.
The burning zones are in a more aggressive environment and So, different parts of the kiln are lined with different types of bricks in the refractory. Severe changes in the temperature may damage the refractory lining. The cost of refractories is a major expense in operating a cement plant, kiln stoppages are avoided as far as possible.
AST A450C Two color pyrometer is most recommended for cement industry environments like dusty which measure accurate temperature of the KILN BURNING ZONE. 2 color pyrometers overcome the obstacles like dust & fumes and focus on the target for reading.
The Pyrometer measures the temperature of an object by calculating the ratio of the energies at two different wavelength bands. A wide band detector with spectral range from 0.7 to 1.15 m is used in A450C+
A 450C+ has real time color video for data monitoring in a burning zone measuring temperature and emissivity is displayed on the television screen. Pyrometer offers RS 485 interface, Analog output 0..20mA & 4..20 mA
The Clinker Cooler is used to cool the clinker. After cement is dried by being put through a rotary kiln and converted to a clinker, it needs to be cooled. The rate of cooling tunnels are used to reduce the temperature of the clinker from over 1250C to a workable 100C. These tunnels typically use forced draft fans to push the cooled air through the clinker. It is essential to monitor the clinker for rogue hot inclusions before it reaches the conveyor belt and causes damage.
EL50 is an economic digital IR Pyrometer from E series with extended sensing head in 4 wire technology for non-contact temperature measurement between 0C to 800C. The pyrometer comes with wide angle optics to cover more area, fast response time within milliseconds and PC software for remote parameterization.
Refractory, or the lining utilized on the interior of rotary kilns, is a critical component in ensuring process efficiency and prolonging the life of a rotary kiln. Here, well discuss everything you need to know about refractory, including how it works, the different types, and best practices for preventative care.
Rotary kilns employ high temperatures to cause a chemical reaction or physical change in a material. In most cases, these high operating temperatures would immediately destroy an unprotected carbon steel shell. For this reason, refractory is used.
Only direct-fired rotary kilns employ refractory; in an indirect-kiln, heat transfer occurs primarily through the kiln shell wall. Refractory would be another barrier for heat to pass through before it is in contact with material, reducing the efficiency of the process. Because of this, instead of using refractory, indirect-fired kilns typically rely on a more heat resistant shell.
Further necessitating the need for refractory, direct-fired kilns typically do not utilize combustion chambers, so the flame is in constant direct contact with the internals. Flame temperature can typically range anywhere between 1600 3200 (depending on excess air) a harsh processing environment that carbon steel is not capable of withstanding.
As the skeleton of the system, protecting the shell is paramount to prolonging the life of the equipment; a major repair or total replacement of the shell is a substantial undertaking, requiring significant downtime and repair costs. For this reason, choosing the right refractory configuration and taking measures to protect that refractory once operational is critical.
While the main objective of refractory is to protect the kiln shell, refractory also serves to minimize heat loss. A kiln with sub-par refractory may protect the kiln shell, but allow significant heat loss, reducing overall process efficiency and increasing operational costs.
Castable refractory comes in a powder form and is mixed with water on-site. Before the mixture can be put in place, anchors are installed. These y-shaped anchors are similar to rebar in cement; they help give the castable lining its strength. Once these anchors are in place, the cement-like mixture is pumped into the lining of the rotary kiln, and allowed to cure for several days.
Castable refractory has a similar material cost to brick. However, brick installation is much more labor intensive, as each brick is individually installed. This makes the overall cost of a brick lining more expensive than castable.
Besides lower overall cost, the advantage to using castable refractory in a rotary kiln is that it is usually easily patched when a problem is encountered. Down time is typically minimal, because the problem area can be cut out and new refractory poured into the cavity.
The disadvantage to using castable refractory in a rotary kiln is that it is very susceptible to installation problems. When castable refractory is expertly installed, it can nearly match the quality of brick. But if installed incorrectly, there can be a considerable difference in quality, and the life of the refractory can be severely compromised.
Although slightly more expensive than castable, brick does not require anchors, and its quality is superior, but as mentioned, incurs greater install costs. When processing a highly abrasive material, brick refractory is advisable most of the time, as castable does not have the durability to stand up against abrasive materials as well as brick.
The disadvantage to brick refractory is that it is kept in place much like a roman arch: bricks are held in place by the pressure of the other bricks pushing against each other. When a problem is encountered, typically the failed brick needs to be replaced, but when one brick is relying on the bricks around it to hold it in place, often one cannot replace just one brick, and whole sections of the refractory must be replaced. Unlike castable refractory, the repair of a fail in brick refractory is much more involved.
There is more to refractory than just the choice of material; refractory is a customizable part of rotary kiln design and can be tailored with multiple layers to meet the demands of a given application.
When efficiency is of great concern, or when extreme temperatures are involved, it is common to employ both a working layer, and an insulating layer. Layer thickness can also vary, with total refractory thickness generally falling between 4.5 12, pending process temperatures..
The working layer is the layer of refractory that is in direct contact with the material being processed. This layer is a dense, durable lining designed to withstand the high temperatures within the rotary kiln, as well as the constant abrasion from the material.
When it comes to refractory, the more dense it is, the less insulating capabilities it has. This means that even though there may be a working layer in place, the heat can easily pass through it to the shell of the rotary kiln. For this reason, an insulating layer is needed beneath the working layer. The insulating layer serves as insulation to protect the shell of the rotary kiln so the high temperatures within cannot reach the shell and damage it.
Typically the working layer and the insulating layer are made of the same material (ie. brick or castable), with varying chemistries. The working layer tends to be a higher density, strongermaterial that is more conductive. The insulating layer does not need these qualities, and tends to be softer, lighter, and less conductive, therefore more insulating. These two layers often vary in thicknesses, determined by the needs of the rotary kiln and what material is being processed. In some cases, such as when temperatures are fairly low, or when efficiency is not a concern, a single working layer may be all that is needed.
In contrast, when insulation is extremely critical, an optional third layer of ceramic fiber backing may be used. This thin, but very efficient layer is similar to fiberglass insulation found in a house, but it is much more compressed. The decision to employ this layer comes with some responsibility. Should a crack in the refractory occur and go unnoticed, it is possible for the high heat inside the rotary kiln to reach this backing and burn it up. This would create a gap between the refractory and the shell of the rotary kiln, which would cause disastrous problems. Due to this potential of increased risk, this third layer is not always appropriate.
The processing environment within a direct-fired rotary kiln can be harsh. The combination of constant rotation, extreme temperatures, heavy loads, and abrasive and corrosive environments, has the potential to cause significant damage or catastrophic failure to a kilns shell. Once your rotary kiln refractory is installed and in use, it is important to take the extra steps to ensure it is properly maintained.
A well-installed, high quality refractory can have a lifespan of many years, but there are factors that can cut refractory life short. While early signs of refractory failure can be hard to spot, the good news is, many of the things that can cause refractory failure are preventable. The two primary causes of refractory failure are cycling and chemical incompatibility.
The biggest source of refractory failure is what is called cycling. Cycling is simply the heating up and cooling down of the rotary kiln. Each time the rotary kiln is heated, the refractory expands with the drum, and as the kiln is cooled, the refractory retracts. If a kiln is constantly being turned on and shut down, the refractory can easily become stressed, resulting in cracks.
Similarly, cracks can also occur from heating or cooling the kiln too quickly. To maximize refractory life, it is important to try to reduce cycling as much as possible, keeping shut downs to a minimum.
Chlorides can aggressively attack refractory, causing excessive wear because of their corrosive nature. When these chemicals are identified up front, refractory can be designed with this in mind to help reduce the potential for excessive wear. Similarly, unknown components in a material or a change in feedstock can also result in excessive wear on refractory.
Operators should be well-versed in the proper operation of the kiln and what to look for to spot potential problems. Operators and maintenance personnel should always follow the guidelines for safety and maintenance set forth by the original equipment manufacturer.
Regularly observing the kiln to check for any visual, auditory, or other abnormalities can mean the difference between a small repair and a catastrophic failure. As part of routine observations on the unit, the kiln shell should be regularly measured with a temperature gun to check for hot spots.
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 read the same temperature for the entire circumference of the shell. For example, a temperature reading of 400, 400, 700, 400 would likely indicate a failure in refractory. Left untreated, this could lead to severe damage to the rotary kiln shell.
In addition to circumference temperature being the same in a given location, there should be a gradual shift in temperatures from one end of the kiln to the other, not a drastic change. Catching these problems early is important to minimizing the potential for damage.
Additionally, having a service technician visit the site to observe and inspect the kiln every so often is also considered best practice in preventative maintenance. Depending on what the original equipment manufacturer recommends, this is generally on an annual basis, but may be more frequent for especially demanding settings.
Refractory failure can have disastrous results. Even a small crack can allow heat to reach the rotary kiln shell. It is important to routinely temp gun the exterior of the rotary kiln shell, ensuring that the temperature is consistent for the entire circumference of the drum.
Refractory is a critical component in the design of a direct-fired rotary kiln, helping to protect the kiln shell from the harsh processing environment within. A customizable part of kiln design, refractory can be engineered to suit the unique needs of an application, with factors such as material and multiple layers coming into play.
As the only barrier between the shell and the kiln interior, protecting and maintaining refractory is of the utmost importance in order to prolong the life of the equipment and avoid potential catastrophic failures.