These are sedimentary, calcium carbonate rocks (CaC03). Most commonly they contain a small amount of magnesium carbonate also.Besides, usual impurities in limestones are those of iron oxides, silica, and alkalies.
The raw materials (limestone and clay) are subjected to such processes as, crushing, drying, grinding, proportioning, and blending or mixing before they are fed to the kilns for calcination or burning process.
The drying stage is typical of the Dry Process. Drying of crushed materials is essential and is achieved by heating these materials (separately) at temperatures sufficiently high to drive out uncombined water.
Each raw material is thus reduced to a required degree of fineness and is stored separately in suitable storage tanks called SILOS or bins where from it can be drawn out conveniently in requisite quantities.
The blended materials are now ready for feeding into the burning kilns. From this stage onwards, there is practically no major difference between the dry and wet processes, except in the design of the rotary kiln.
(c) Compound Formation: Lime and magnesia as formed above are combined in the next stage with silica, alumina and ferric oxide to form the basic compounds of cement, namely, the tri-calcium and di-calcium silicates, tri-calcium aluminates and tetra-calcium-alunino ferrite.
The cement industry is the most important consumer of rubber waste. It uses 236,000 t of scrap tires (26 MJ/kg calorific heat) and 290,000 t of industrial waste (plastic waste, paper, textiles, etc., 22 MJ/kg caloric heat) (VDZ, 1999). Table VI.5.21 shows a comparison of components of traditional fuels and scrap tires.
In 1999, scrap tires supplied about 6% of the total fuels required (VDZ, 1999). They are fed in whole to the primary entering point of rotary kilns. If sufficient air is provided, complete combustion is achieved without increasing emissions. Sulfur dioxide is absorbed in clinker.
The cost of treatment amounts to about 100/t rubber waste. For imported coal, the cost is about 80/t. Therefore, the cement industry charges about 80130/t scrap tire to compensate for the difference (Bilhard, 1997).
The cement industry is one of the main industries necessary for sustainable development. It can be considered the backbone for development. The main pollution source generated from cement industry is the solid waste called cement by-pass dust, which is collected from the bottom of the dust filter. It represents a major pollution problem in Egypt where around 2.4 million tons per year of cement dust is diffused into the atmosphere causing air pollution problems because of its size (1-10 microns) and alkalinity (pH 11.5).
Cement by-pass dust is naturally alkaline with a high pH value and represents a major pollution problem. The safe disposal of cement dust costs a lot of money and still pollutes the environment. The chemical analysis for the by-pass dust is shown in Table 13.7.
Because of the high alkalinity of the cement by-pass dust, it can be used in the treatment of the municipal sewage sludge, which is considered another environmental problem in developing countries since it contains parasites such as Ascaris and heavy metals from industrial waste in the city. Although sludge has a very high nutritional value for land reclamation, it might contaminate the land. The safe disposal of sludge costs a lot of money and direct application of sludge for land reclamation has a lot of negative environmental impacts and is very hazardous to health.
Mixing the hazardous waste of cement by-pass dust with the environmentally unsafe sewage sludge will produce a good quality fertilizer. Cement by-pass dust will enhance the fermentation process of the organic waste and kill all microbes and parasites. The high alkalinity cement bypass dust fixes the heavy metals present in the product and converts them into insoluble metal hydroxide. Hence preventing metal release in the leachate. Agricultural wastes must be added to the mix to adjust the carbon to nitrogen ratio as well as the pH value for better composting (El Haggar 2000). The produced fertilizer from composting is safe for land reclamation and free from any parasites or microbes that might exist in raw sludge.
The U.S. cement industry consists of 39 companies that operate 118 cement plants in 38 states. While its production levels have grown since 1985, the industry's energy intensity declined by 35% between 1985 and 2000 (Figure 10).
The cement manufacturing process involves three components: the mining and preparation of inputs; the chemical reactions that produce clinker; and the grinding of clinker with other additives to produce cement. The feed for older kilns is a slurry of inputs, the wet kiln process, while large new plants mix dry materials for introduction to the kiln. Energy use varies with the process and characteristics of the plant, but in general about 90% of the energy use, and all of the fuel use, occurs in the manufacture of clinker in the kiln. The chemical process that converts limestone to lime, produces roughly the same amount of carbon dioxide gas as that generated by the energy used in its production for coal-fired kilns. Technologies that allow production of cement with a lower per-ton share of clinker thus yield multiple benefits.
Upgrading a kiln from wet to dry, and from a long dry kiln to a preheater, precalciner kiln results in major energy efficiency gains but for a price that requires a payback period of at least ten years. Worrell et al. (2004) conclude that these upgrades are attractive only when an old kiln needs to be replaced. More incremental upgrades could yield commercially attractive benefits including advanced control systems, combustion improvements, indirect firing, and optimization of components such as the heat shell. While opportunities vary with specific plants, the combination of these activities appears to yield an improvement in energy use on the order of 10%. Recovering heat from the cooling stage also yields substantial savings. If the heat is used for power generation, it can save up to half of the electricity used in the clinker process. However, taking full advantage of the heat recovery savings may require other major upgrades (National Academies, 2009).
Changing the chemistry of cement to reduce the need for calcination can decrease the high share of clinker that characterizes U.S. production. Options for blended cements include fly ash and steel slag. Fly ash may be particularly promising as it is a coal combustion byproduct that can be reused in many different contexts, such as construction and pavement. Worrell et al. (2004) identify potential energy savings of up to 20% from deployment of blended cement technologies, and larger carbon dioxide emission reductions. Advanced technologies with potential to further improve energy efficiency and emissions include carbon capture and storage technology, fluidized bed kilns, advanced comminution technologies, and the substitution of mineral polymers for clinker (Worrell et al., 2004; Battelle, 2002).
In the cement industry, coal quality is very important as it affects both the quality of the cement and the operation of the plant. The Indian cement industry uses coal because of its abundant availability and shortage of oil and natural gas. Today the Indian cement industry has to use coal of high ash content with varying characteristics. To resolve this problem, the role of coal on cement making and possible improvements in coal quality and consistency have been explored (Kumar, 1994).
The cement industry is the third largest user of coal after the steel and power industries and it consumes more than 5% of total coal produced in India. This coal requirement will go up further with the rapid expansion of the cement industry (for infrastructure projects). Coal is the principal source of fuel for cement kilns. Its consumption per ton of clinker largely depends on the quality and also on how effectively the cement process technology is being used. Coal consumption varies from 0.2 to 0.3 tons for every ton of clinker. It is known that the indigenous cement plants are consuming at least 20%30% more energy than those of similar plants in other countries. Technology obsolescence has been one of the major reasons accounting for the industrys poor performance. The high moisture and ash content of coal make it difficult for the cement units to maintain the quality and quantity of output. Even today, a good part of the installed capacity is linked to the uneconomical wet process. Both the pace of modernisation and the introduction of the latest precalciner technology have to be prioritised and implemented to make this industry competitive.
Coal in the cement industry is used both as a fuel and as a material in the process of cement manufacture. Therefore, both the supply of proper quality of coal and its effective utilisation are a must in the industry. Deteriorating and inconsistent quality of coal supply in terms of high ash and moisture and low HGI can create the following problems according to a study conducted by National Council for Cement and Building Materials (NCB) (Wheelock and Markuszewski, 1984):
It has been observed from different studies on the clinkerraw-coal interrelationship in some Indian cement plants that an ash content of up to 28%30% can be tolerated for burning Indian raw materials, without appreciably affecting kiln operations and clinker quality. However, in the precalciner system, where available, lower-grade coal (up to 40% ash) can be used for partial calcinations.
The present supply of coal to cement plants usually exceeds the desired limit of 27% ash content. It is not possible to maintain the quality of coal as the superior-quality Indian coal has been almost exhausted and a high degree of mechanisation has been adopted, especially in surface mining. Consistent quality can be ensured only through beneficiation.
One of the applications in the cement industry is as raw material for Portland clinker. Portland clinker is manufactured by cindering a homogeneous mixture of ground lime stone and claylike materials. Fly ash can be used as a substitute for these claylike materials because it has practically the same chemical composition.
An other application of fly ash in cement is as raw material for Portland Fly Ash Cement. The cement industry manufactures class A Portland Fly Ash Cement which has the same characteristic properties as normal class A Portland Cement. This is achieved by using a finer ground, high quality Portland clinker and adding approximately 25% high quality fly ash.
In this and the next section, we will describe waste energy potential in the glass and cement industries, both of which are highly energy intensive. Significant amounts of WH are available at such enterprises. The main problem with attempting to capture these waste heat quantities is the lack of consumers of secondary thermal energy resources at the facilities themselves. Therefore, the waste heat can only be effectively utilized for heating purposes by being transferred to the ultimate end users, which can include city district heating systems. However, if that waste heat is converted into electricity at the plant site, then the electricity can be delivered to distant end users via transmission lines.
Some data on worldwide cement production will set the framework for this discussion. Of all the energy expended in the non-metallic mineral sector (9% of total global energy use), manufacture of cement accounts for 7080%. The weighted average among cement-producing countries for specific energy consumption comes to 4.4GJ per tonne of product. China produces nearly one-half of all cement in the world. With so much energy being expended, there is a comparable high potential for energy savings: 2.5 to 3EJ per year may be saved (2833% of all energy consumed in this sector) by various means, including waste energy recovery. Such savings in primary energy would have corresponding reductions in greenhouse gas emissions, particularly CO2 .
The process of producing cement and its follow-on product concrete are shown schematically in Fig.9.22 . The raw material, mainly limestone, is crushed in ball mills, passed through an electrostatic precipitator, stored, preheated, and reacted in a high-temperature rotary kiln which yields clinker. To make cement, the clinker must first be cooled. Prior to being crushed in the cement mill, the gypsum produced in the kiln is separated from the main product stream. The output from the cement mill may be blended with other constituents to meet certain specifications depending on the end use. The packaged product is then shipped to the consumers. Electricity is one of the main energy inputs; worldwide, the electricity intensity of cement production is about 91kWh per tonne of cement. An international goal has been established to reduce this to 87kWh/t by 2030 .
The main energy consumption (in 109kJ) are for: raw grinding=8.346 (1.88%), kiln heating (fuel combustion)=410.464 (92.68%), and finish milling=24.057 (5.43%) . Although the firing of the kiln consumes the bulk of the energy, there are other places along the production line where waste energy can be recovered. Figure9.23  focuses on the preheater, kiln, and clinker cooler, showing the primary waste heat sources (WHR-I and WHR-II); secondary waste heat may be recovered at the shells of the preheater and the kiln. The primary ones are suitable for power generation while the secondary ones may be appropriate for direct heat applications using hot water . The most commonly used WHR power technologies are steam Rankine cycle with various enhancements and ORC (shown in Fig.9.23), including Kalina, and supercritical CO2 Brayton cycles.
One of the first commercial waste heat power generation plants using ORC technology was implemented by Turboden using the exhaust gas from a cupola furnace in Torbole, Italy . Around the same time, another plant came on-line at Heidelberg Cement in Lengfurt, Germany (1998) by Ormat Technologies.
Figure 9.24 shows the heat balance for a dry ement kiln for the following conditions: exhaust temperature=290390C; cooler exit temperature=250350C. Approximately 35% of the total energy involved can be used for drying the product and for WHR power generation.
Table9.3 provides some information for selected examples of the recovery of waste heat from cement production facilities . The Ait-Baha plant is shown in Fig.9.25 . This plant began with an annual production capacity of 2.2 million tonnes of cement, but currently puts out about 3.6 million tonnes of clinker and 4.9 million tonnes of cement .
Mercury is emitted from a variety of anthropogenic and natural sources. Main anthropogenic sources include coal combustion, the cement industry, chlorine manufacturing plants, and waste incineration. Source strengths will vary within each category depending on the mercury content in the raw material and theextent to which control techniques have been employed. Natural sources include volcanoes and diffuse emissions frommercury-containing mineralizations. Different emission sources emit different fractions of mercury species (see Speciation below). The global anthropogenic emissions of mercury have been estimated to be 1900 t, with Asia contributing more than 50% and Europe and North America less than 25% each.
Natural emissions and reemissions are exceedingly difficult to quantify. Emissions from natural surfaces (soils and water) may also originate from previously deposited anthropogenic mercury as well as from natural sources. The variability in time and with geographical location is also considerable. Most estimates suggest that the natural emissions are of the same order of magnitude as the anthropogenic emissions.
Instant chilling process is a physical method, which modifies the properties of steel-making slag for utilization in the cement industry (Montgomery and Wang, 1991, 1992). It is done in four stages. The first is air cooling where the molten slag is placed on shallow plates to a bed thickness of approximately 100 mm and air cooled for 4 minutes. This is followed by an initial water cooling cycle during which the slag bed is continuously water sprayed for about 20 minutes to produce an end temperature of 500 C. After water cooling the slag is loaded into slag carts and transported to a spraying station for further spraying for 4 minutes to reach an end temperature of 200 C. Finally, the slag is placed in a water pool and cooled to around 60 C to complete the process and it is sent for magnetic screening to separate the iron fraction. The slag is treated in a batch process with a total treatment time of 1.5 to 2.5 hours. This is an environmentally friendly process, producing slag of particle size 30-50 m with <4 % free lime content. Magnesium oxide occurs as mixed crystals in the solid solution phase. The composition is not deleterious to the volume stability (Montgomery and Wang, 1991, 1992). Considerable benefits have been reported from the use of instant chilled slag as coarse aggregates in concrete. They include increased strength of the concrete, an increase in the modulus of elasticity, a reduction in the brittleness and an increase in the fracture toughness (Montgomery and Wang, 1991, 1992).
The paper mill and pulp industry produces enormous quantities of paper and pulp products each year. It is the sixth largest polluting industry after the oil, cement, leather, textile, and steel industries, and many environmental contaminants are associated with the discharge of paper and pulp mill sludge (Ali and Sreekrishnan, 2001). About 6094% of organic content is available in paper mill sludge, which has the potential for use as a soil amendment in disturbed lands (Marko and Polonca, 2012). Sludge rich in organic matter is generated in high content in the paper and pulp industries. Although paper and pulp mill sludge is rich in organic matter, it contains less N and P than biosolids and compost (Park etal., 2011). Hence, paper mill sludge often needs additional nutrient input to be used in mine spoil rehabilitation (Park etal., 2011). Paper and pulp mill sludge is managed through its use in landfills and as landfill capping materials, in land spreading, composting, land reclamation, and in employment in brick, light aggregate, and cement production (Marko and Polonca, 2012).
Precipitated calcium carbonate, commonly called lime sludge or lime mud, is produced when sulphate green liquor is causticized with lime. For many years this lime sludge was considered a waste product and was dumped into rivers or waste ponds, or used for fill around the plants. Large quantities of new lime were purchased from commercial producers to replace that lost in the sludge waste.
A number of paper manufacturers soon became aware of the savings that could be achieved by recovering the lime. Beginning in the 20s, efforts were directed toward lime recovery installations. Today, a proper Rotary Lime Kiln Operation isan integral part of all modern pulp mills.
High quality lime can be produced at a uniform rate only if the kiln is fed at a constant rate with lime sludge of constant composition. In some cases the feed to the kiln consists of a pumpable sludge containing 55 to 65% water. However, in most installations a drum filter or a centrifuge is installed just ahead of the kiln to reduce the moisture content to 35 to 50%. This cake is fed to the kiln through a screw conveyor, which is water-jacketed for that portion extending into the kiln feed end connection.
A ferris wheel slurry feeder and a surge tank located ahead of the filter or centrifuge will insure a constant rate of feed to the kiln. The surge tank should be provided with efficient means of agitation and dilution control to maintain uniform consistency of the feed to the ferris wheel slurry feeder. The overflow from the feeder is returned to the surge tank. The surge tank should have a capacity of 1 to 2 hours kiln feed.
Calcium carbonate begins to dissociate in the kiln at a temperature of about 1500 F. Theoretically, lime sludge could be heated to this temperature and held there until dissociation was complete. However, this dissociation process is accelerated at elevated temperatures. Therefore, to facilitate complete dissociation of various sized pellets with a reasonable retention time, temperatures in excess of 1500 F are necessary. The lime is usually discharged from the kiln at approximately 2200 F, although this will vary somewhat with the size of the kiln and the capacity at which it is operated.
To improve the thermal efficiency of the kiln, a chain system is installed in the feed end. The chains pick up the lime sludge and expose it to the hot gases. The chains also absorb heat from the hot gases, transferring this heat when they again dip into the wet material.
The gases enter the chain system at a temperature of 1200 to 1400 F and leave at approximately 300 to 550 F. In general, the lime sludge leaving the chain system should have a moisture content of 10 to 15%. If the moisture content is permitted to go below this figure, the sludge will no longer protect the chains, with the result that they will be oxidized and disintegrated by the hot gases.
Such samples will also provide the operator with a visual check on whether satisfactory pellets are being produced. To minimize dusting, the lime should travel through the kiln in the form of pellets about inch in diameter. Larger pellets are undesirable since they will be overburned on the outside. The natural rolling action of the sludge on the kiln wall will form good pellets, provided the kiln is fed at a uniform rate with sludge of constant composition.
Excessive impurities, particularly soda, will promote the formation of large balls as well as rings. Experience indicates that the soda content should be maintained below 1% reported as Na2O on a dry basis. Impurities must be controlled by proper liquor clarification, washing and filtering.
Some mills with lime recovery kilns are troubled by ring formation. So many factors influence the ringing characteristics in a given installation that it is difficult to make any definite statements regarding ring control. Varying amounts of moisture, soda, free calcium oxide, iron, alumina and silica will affect ring formation. Increasing the feed rate beyond the normal capacity of the kiln will increase the tendency to ring. In some cases a change in the moisture content has greatly reduced the formation of rings.
The tendency to ring formation is more pronounced in a small diameter kiln than in a large diameter kiln. This is due to the greater arch effect in a small kiln. The smaller arch effect in a large diameter kiln will permit agglomerating material to fall away more readily, thus minimizing ring formation. Sometimes a change in kiln speed or a change in burning conditions will overcome ringing.
The uniformity of the kiln product, as well as kiln operation as a whole, depends first on controlled feed and second on proper combustion control. Good control of both feed and combustion will establish and maintain a definite temperature gradient throughout the length of the kiln. Any fluctuations in combustion or kiln feed will cause corresponding changes in this temperature gradient, with the result that the lime will not be uniformly calcined.
A constant draft at the firing hood is necessary for good combustion control. An automatic draft controller should be installed. This controller will regulate a damper in the exhaust system to maintain a constant draft at the firing hood. The usual draft at the firing hood will range to 0.05 in. water column.
The fuel should be burned with about 5 to 10% excess air to insure complete combustion. Too much air, as well as too little air, wastes fuel. Periodic Orsat analysis of the exhaust gases should be made to determine whether the correct draft is being maintained at the firing hood for proper combustion conditions.
To properly record, interpret and control the kiln performance, there should be available to the operator a record of the exhaust gas temperature, the burning zone temperature, the rate of fuel flow, and the draft at the feed end of the kiln as well as at the firing hood. All of these instruments, together with the necessary gauges, ammeters, voltmeters, and motor starter pushbuttons, should be mounted on a control panel located on the burning floor.
The chain system in a lime sludge kiln is an excellent dust arrester. However, a small amount of dust will be carried out with the exhaust gases, making a dust collecting system desirable. Returning the collected dust to the system will reduce the amount of make-up lime required.
The form in which the collected dust can be handled most conveniently in a particular mill must be decided before selecting the dust collecting equipment. Dust can be collected dry in a simple cyclone or in a commercially manufactured collector, pugged with water and flushed to waste or returned to the system. Pugging is necessary to permit ready transportation and return to the system. Sometimes difficulty is encountered in pugging this fine dust with water. A wet type collector will collect the dust in a form immediately convenient for further use.
CAUTION: Brick lining must be thoroughly dried before kiln is started up for the first time and immediately after extensive lining repairs have been made. Failure to do so may result in disintegration of the lining when kiln is brought to operating temperature.
The exhaust gas temperature in chain equipped kilns ranges from 300 to 550 F, depending on the particular installation. A few days operation will indicate the average temperature for normal operation. Watch the recorder. Any unusual temperature rise may indicate that the kiln feed has stopped. The temperature will change with changes in kiln speed or moisture content of feed.
Use only enough draft to provide air for combustion and to prevent smoke from showing up at the stack. Too much draft chills discharge end and also wastes fuel. The kiln exhaust gas should be checked frequently with an Orsat gas analyzer. The oxygen content should be held to 1.5% or less, under which conditions there should be no combustibles in the exhaust gas.
The moisture content of the sludge to the filter or centrifuge should be maintained constant with a consistency regulator. It is also important to maintain the percent of impurities in the sludge at a constant value.
The ferris wheel slurry feeder is driven by a four-speed motor which is electrically interlocked with the four-speed kiln drive motor to insure a constant rate of feed per kiln revolution. In addition, there is a speed changer which enables the operator to determine the optimum feed rate to the kiln for a given kiln speed.
Steps should be taken in the initial installation to provide a way of determining the rate of solids to kiln. A calibrating tank following the ferris wheel slurry feeder will enable the operator to make periodic checks on the rate of slurry to the filter or centrifuge. If the moisture content of the slurry is known, the rate of solids to the kiln can be readily determined. The rate of solids to the filter must be maintained constant at all times.
While the slurry feeder will insure a constant volume of sludge to the kiln per kiln revolution, it is possible for the rate of solids to the kiln to vary unless the composition of the sludge is maintained constant as pointed out under Sludge Composition, above.
Hourly samples of sludge should be taken from the sample holes located just after the chain system. These samples should be analyzed by the laboratory for moisture, soda and free lime, and the results should be listed on the kiln data sheet. This information is necessary for a proper study of kiln performance.
Hourly samples of lime should be taken from the discharge end of the kiln for determination of available lime (CaO). Good kiln operation should result in a product with an available lime content of 90%.
A ruled form should be printed for the purpose of recording pertinent data in connection with the lime burning operation. The report forms most commonly used provide spaces designated Shift 1, Shift 2, and Shift 3 for the signatures of the three men in charge of these shifts so that the responsibility for irregularities on any shift can easily be placed.
Lime production is a relatively complicated thermal decomposition reaction process of calcium carbonate to calcium oxide. Due to different kiln types, different equipment configurations, different raw material quality and composition, and different fuel types and calorific values, each will appear Various problems and faults The following are the analysis and treatment methods for common problems and faults.
If the top temperature of the calcination belt of the common shaft kiln is increased in the middle of the kiln body, the ash temperature is reduced, the CO2 content is reduced accordingly, the air volume is large, and the excess oxygen increases. The upper part of the kiln burned early. When the charge is lowered to the calcination zone, the fuel has no firepower, the amount of raw lime burning increases naturally, the top temperature control is too high or the fuel entering the kiln is fragmented and burns prematurely. The wind pressure and air volume are too large, or the size of the limestone is too large, the ventilation is smooth, and the unloading amount is unbalanced, which is also the reason for the upward movement of the calcination area. Eventually, a big burn is formed. In this case, you should:
When it is found that the top temperature is low and the ash temperature is increased, the fire and fire are not exhausted when the fuel is serious. Lime also increases the calcination, and the CO2 concentration decreases, which means that the calcination zone has moved down. The main reason for this situation is that the air volume is small, the amount of stone loading is large, and the amount of ash discharge is large, which makes the mixture move down quickly, and the cooling zone is shortened. The air fails to be preheated enough to enter the calcination zone, and the amount of calcium carbonate decomposed Reduced, CO also decreased accordingly. This causes an increase in the amount of lime burned.
In addition, the raw material is fragmented or the particle size deviation is large, and the resistance in the kiln increases. At this time, the air pressure is not low, but the actual air volume is not enough. In this case, the stone loading and ash discharge should be appropriately reduced, and the air volume should be appropriately increased. In this case, if the top pressure is too large, the batch can be appropriately reduced, the raw material can be changed, and the proportion of large particles should be appropriately increased to reduce the particles. The level difference reduces the resistance in the kiln. Adjust the fuel and stone mass to meet the technological requirements.
The extension of the calcination zone will cause the top temperature, the ash temperature will be higher, the CO2 will decrease, and the amount of lime burning will also increase. The formation of nodules or poor local ventilation in the kiln is due to excessive fuel ratio and poor uniformity of limestone, and the formation of nodules or poor ventilation in the kiln. At the same time, there are nodules or kiln wall hanging materials in the kiln, and the ventilation is segregated. The nodules or hanging materials prevent the materials from falling normally and have poor ventilation. Because the nodules fall off under the impact of the material flow, the calcination zone will also be extended for a certain period of time.
When this happens, the production should be properly reduced, the particle size of the raw materials should be adjusted, and the fuel ratio should be reduced to increase the air volume. After temporarily reducing the height of the material layer, the material is restored to the normal material level.
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 RefractoryBatch Rotary Kiln TestingKiln Alignment SoftwareProcessing 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.
(I) LIME: It is main constituent of cement. Calculated amount of lime is added in the manufacturing of Portland cement, If it is excess in amount, it reduces strength of cement, because it makes the cement to expand and disintegrate.
(III) ALUMINA: Tricalcium aluminate is required for setting of cement. If it is an excess quantity, then cement undergoes setting very fastly, because with the reaction of water, there is evolution of large amount of heat.
Raw material is crushed into small pieces -----> Small pieces grind in fine ball mills and stored separately -------> Mixed in proper proportions ------->pulverized in tube mills and homogenized in a mixing mill.
The grinding process can be done in ball or tube mill or even both. Then the slurry is led into collecting basin where composition can be adjusted. The slurry contains around 38-40% water that is stored in storage tanks and kept ready for the rotary kiln.
The burning process is carried out in the rotary kiln while the raw materials are rotated at 1-2rpm at its longitudinal axis. The rotary kiln is made up of steel tubes having the diameter of 2.5-3.0 meter and the length differs from 90-120meter. The inner side of the kiln is lined with refractory bricks.
The kiln is supported on the columns of masonry or concrete and rested on roller bearing in slightly inclined position at the gradient of 1 in 25 to 1 in 30. The raw mix of dry process of corrected slurry of wet process is injected into the kiln from the upper end. The kiln is heated with the help of powdered coal or oil or hot gases from the lower end of the kiln so that the long hot flames is produced.
As the kiln position is inclined and it rotates slowly, the material charged from upper end moves towards lower end at the speed of 15m/hr. In the upper part, water or moisture in the material is evaporated at 400oC temp, so this process is known as Drying Zone.
The central part i.e. calcination zone, the temperature is around 10000C, where decomposition of lime stone takes place. The remaining material is in the form of small lumps known as nodules after the CO2 is released.
The lower part (clinkering zone) have temperature in between 1500-17000C where lime and clay are reacts to yielding calcium aluminates and calcium silicates. This aluminates and silicates of calcium fuse to gather to form small and hard stones are known as clinkers. The size of the clinker is varies from 5-10mm.
The lower part i.e. clinkering zone has the temperature around 1500-1700C. In the region lime and clay reacts to yield calcium aluminates and calcium silicates. This product of aluminates and silicates of calcium fuses together to form hard and small stones known as clinkers. The size of the small and hard clinkers varies from 5 to 10mm.
The clinkers coming from the burning zone are very hot. To bring down the temperature of clinkers, air is admitted in counter current direction at the base of the rotary kiln. The cooled clinkers are collected in small trolleys.
The cooled clinkers are received from the cooling pans and sent into mills. The clinkers are grinded finely into powder in ball mill or tube mill. Powdered gypsum is added around 2-3% as retarding agent during final grinding. The final obtained product is cement that does not settle quickly when comes in contact with water.
After the initial setting time of the cement, the cement becomes stiff and the gypsum retards the dissolution of tri-calcium aluminates by forming tricalcium sulfoaluminate which is insoluble and prevents too early further reactions of setting and hardening.
Rotary Kiln Alignment The continuity of operation of a lime sludge kiln requires strict maintenance control. The rotary kiln is among the largest type of moving machines made and is subjected to extreme temperatures, power failures, atmospheric conditions, varying loads, and other operating conditions which affect its wear and alignment. It should be erected under Read more
Precipitated calcium carbonate, commonly called lime sludge or lime mud, is produced when sulphate green liquor is causticized with lime. For many years this lime sludge was considered a waste product and was dumped into rivers or waste ponds, or used for fill around the plants. Large quantities of new lime were purchased from commercial Read more
The Air-Quenching shaking grate Clinker Cooler was developed more than 20 years ago as an improved heat recuperating cooler for use with rotary kilns. It was designed to air quench and cool large quantities of hot clinker rapidly, and to recover and return to the kiln a major portion of the heat from the clinker. Read more
The integrated model for lime production unit which includes cooler, preheater and rotary kiln is developed.The effect of residence time in each section on efficiency is investigated.Influence of material feed rate and excess air on specific fuel consumption is analyzed.The significant effect of particle size on efficiency and specific fuel consumption is shown.
In this paper, thermal energy analysis of three zones of a lime production process, which are preheater, rotary kiln and cooler, is performed. In order to perform a proper quantitative estimation, the system was modeled using energy balance equations including coupled heat transfer and chemical reaction mechanisms. A mathematical model was developed, and consequently, the thermal and chemical behavior of limestone was investigated. The model was verified using empirical data. After model confirmation, the variation of Specific Fuel Consumption (SFC) versus production rate was predicted and the optimum condition was determined. Subsequently, fuel consumption was calculated regarding to altered residence time inside each zone of lime production process, for a constant output. Results indicate that increasing the residence time inside each zone of lime production process, will enhance thermal efficiency and saves fuel consumption. Relative enhancement will be the same for different sizes of limestone. It was found that a 10-min increase in material residence time inside the preheater or rotary kiln can reduce fuel consumption by around two percent. Whereas, a 5-min increase in material residence time inside the cooler would be enough to obtain a similar result. Finally, the ratio of air-to-fuel and production rate are changed in such a way that the same product is achieved. The model predicts that lowering excess air from 15% to 10% leads to a 2.5% reduction of Specific Fuel Consumption (SFC).
Rotary lime kiln is also called lime rotary kiln or limestone rotary kiln. It is used for the calcination of limestone to make quicklime. And specifically speaking, it is a slightly horizontal device that can rotate continuously to burn down the limestone thoroughly to make quicklime. Lime rotary kiln, along with vertical lime kiln, is the core equipment for lime calcination plant. Daswell provides customized rotary lime kiln with great durability, reliability and great performance. And to improve cost-efficiency and energy-efficiency, Daswell also offers vertical preheater and vertical cooler to work along with our limestone rotary kiln. In fact, Daswell offers tailor-made turnkey solutions for quicklime plant, including designing, planning and supplying the complete set of equipment.
Henan Daswell machinery is a professional supplier of rotary lime kiln. In fact, Daswell offers end-to-end solutions for lime calcination plant, including initial designing, planning, providing complete set of equipment and after-sales services. And Daswell has finished several successful quicklime plants projects worldwide. As for the rotary lime kiln, it is the core equipment for quicklime production plant. Daswell limestone rotary kiln are customized designed and manufactured to meet customers needs. For different production capacity needs, Daswell lime rotary kiln can come in different diameters. Daswell rotary kilns for lime calcination are of robust designs with quality materials so that they can work for long term with great performance. Besides, to ensure the high cost-efficiency of lime calcination plant, Daswell also offers vertical pre-heater and vertical coolers to work with the lime rotary kiln.
Limestone contains mainly of calcium carbonate. And when limestone is strongly heated in rotary kiln, calcium carbonate undergoes thermal decomposition to form calcium oxide, which is quicklime, and carbon dioxide (CO). This reaction takes place at 900, but the temperature in rotary lime kiln is often around 1000 degrees to make the process happen quickly. But excessive temperature is avoided because it produces unreactive, dead-burnedlime. Rotary lime kiln rotates continuously on riding rings for a period of time so that the limestone can be burnt down thoroughly. During the operation of rotary lime kiln, quicklime will be left inside, with carbon dioxide being driven off.
Rotary kiln for lime production is a central equipment for quicklime plant. In fact, it has long been used for making quicklime. And the design of limestone rotary lime has been constantly designed and innovated with the improvement of high technology as well as the great materials. Daswell modern rotary lime kilns are made of high quality materials with high technology. It is a rotating cylindrical vessel. And it is slightly inclined to horizontal, with the higher end being the material inlet and lower end to discharge quicklime. As a result, the processed limestone in the rotary lime kiln will move to lower end to be discharged. Its shell is often made of rolled mild steel plates which are welded to form a cylinder. And the lengths and diameters of the cylinder vary from each other depending on the needs of customers. Daswell provides limestone lime kiln with length ranging 40-72m, while the diameter ranging 2.5-5.24m. Daswell rotary lime kilns tend to shorter because they can work with vertical preheater and vertical cooler.
Except for the rotary lime kiln vessel itself, there are other parts which can be important for the limestone lime kiln. For example, the refractory lining inside the kiln shell, riding rings, rollers, and furnace and so on. As for the refractory lining, it is used to insulate the lime kiln shell from the high temperature in the rotary lime kiln, and also protects the shell from the corrosive property of the processed material. For the riding rings, they are made of quality steel casting and are uniquely designed to fit the shell snugly and allow the smooth movement of the rotary lime kiln. And the rollers are used to support the limestone rotary kiln and allow the smooth rotating of the lime rotary kiln. The furnace is at and the lower end of lime rotary kiln. Through the furnace, fuel, such as oil and gas, will burn the limestone in kiln with high temperature.
How does a rotary lime kiln work? Daswell rotary lime kiln often works with vertical preheater and vertical cooler. So the lime rotary kiln process will include the process of preheater and cooler. Firstly, quarried limestone will be further crushed, sifted and washed to be proper feed material with required sizes. Then the limestone will be transferred to vertical preheater through bucket elevator. In the preheater, the limestone will be preheated by the exhaust hot air from the rotary lime kiln. For the limestone in the rotary lime kiln moves in counter current with the air flow in the kiln. And the preheated limestone will go into the rotary lime kiln for calcination. The rotary lime kiln will rotate constantly for a period of time to burn through the limestone. At the end, the burnt lime will be discharged into the cooler to cool down. Finally, the quicklime then will be stored in product silo. Please fill the form below to get free quotes. We will reply in 24 hours. Product Model: Your Name(required): Your Email(required): Your Tel: Your country: Your Company: Your Message(required):Get in Touch with Mechanic