rotary kiln blog archive rotary kiln construction

scheme of kiln construction about rotary kiln installation

scheme of kiln construction about rotary kiln installation

The weight of a single unit of rotary kiln is 262390kg(not includes the linings weight). It has 17 components which are combustion chamber, mixing chamber, kiln head hood, stealing, dumping device, supporting device, cylinder, temperature measuring device, gearing, the hydraulic catch wheel, retaining wheel hydraulics, balance device, kiln tail hood and stealing, lubricating device, oil cylinder device, the door hydraulic device meter. The 1/5 part of the cylinder among them is sent one at a time, which needs to be installed after. Because the rotary kiln has mass volume and heavyweight, heavy installation tasks, strong relativity among components and it needs to be installed inside a plant, to guarantee the success of the installation, we especially make this construction scheme to describe the installation methods in detail. To increase working efficiency meanwhile decrease the probability of high-place operations danger and inconvenient and to guarantee to reach the radial runout value which rotary kiln be required, firstly combine number one shell ring with number two of the inner side kiln, then number 3 with number 4 and number five, then number one rolling ring with number one, two shell ring in the outside of kiln, then rolling ring two with shell ring three and four, then rolling ring three with shell ring five. Interface is not welding, using code plate and the vertical plate and bolt connection, after initial adjustment, tighten bolts, code plate matter, then USES the 1.2.2 hoisting transportation method will be the inside of the kiln described in two transport in place, then the lateral kiln has installed a hoop of paragraphs directly hoisting in place, the cylinder hoisting in place to supporting wheel, the bolt, and plate welded cylinder into the overall, barring is measured with a dial indicator at five-cylinder radial runout until the whole adjustment to allow the radial runout of weld deviation within the scope of the rear; The welding deformation control method is adopted to better ensure the concentricity of the cylinder.

rotary kiln maintenance

rotary kiln maintenance

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 the supervision of an experienced erecting engineer.

Even though great care has been taken in the design and the construction of the concrete piers, in some cases settling or tipping of the foundation can occur, throwing the carrying mechanisms, bases, and rollers out of alignment. If this condition is not corrected, it will lead to continual trouble with the kiln shell and the riding rings and rollers. It is advisable when making the original installation of the kiln to establish bench marks away from the kiln foundation. The kiln alignment should then be checked from the bench marks within six months after initial installation, and annually thereafter.

The thrust rollers are designed to carry the full downhill thrust of the kiln, with the riding ring and roller faces lined up for full bearing across the width. Carrying rollers should be set parallel to the axis of the kiln or cut slightly to avoid excessive downhill thrust, which might be detrimental to the thrust roller.

In aligning the kiln by adjusting or cutting the rollers, it is necessary to cut all rollers equally rather than taking all of the cut on one set of rollers. If only one set of rollers is cut to move the kiln in a given direction, and another set of rollers cut to move the kiln in the opposite direction, such action, if continued, would cause various sets of mechanism rollers to work against each other. If this action is carried to extremes, misalignment could occur between any one set of rollers and the corresponding riding ring, resulting in unequal and aggravated wear between the riding ring and roller surfaces. Operators should be discouraged from adjusting only the most easily accessible rollers, which would be on the discharge end mechanisms. A record of all roller adjustments should be kept as an aid to maintaining proper alignment.

When a kiln with a hot charge is stopped for any reason, such as a power failure, it is imperative to keep the kiln rotating with the auxiliary drive. Failure to do so may result in a warped or distorted kiln shell. It is difficult to return a warped shell to its original condition, and operating a kiln with a bowed or warped condition will place an excessive load on various mechanism piers. This is particularly troublesome in multiple support kilns.

Sometimes a warped kiln can be returned to somewhat its original alignment by carefully re-heating the kiln on the side opposite from the warp to draw it back in line. Even at best, though, constant attention must then be given to the carrying mechanisms to provide an alignment which will not cause additional damage or excessive wear.

Sometimes the only way in which to correct a warped or bowed condition or misaligned shell is to cut out a portion of the shell, realign the ridng rings and carrying rollers, and weld the shell section back in. This might result in a slightly disjointed shell, but the items of major importance, namely the riding rings and rollers, are then realigned.

Some kilns are installed without auxiliary drives. This is false economy, since the small additional cost of the auxiliary drive in the initial installation provides good insurance against much more serious difficulties.

The main gear, usually a spur gear, is made in halves with full machined teeth to permit reversing of the gear to obtain a double life. This gear is bolted to a gear flange which is welded to the kiln shell. The driving pinion is mounted on a jackshaft which is coupled to the low speed shaft of an enclosed gear reducer. The gear reducer and jackshaft assembly is fixed to the foundation on the same slope as the kiln, and is provided with adjusting bolts and lugs on the base plate to provide for alignment of the drive. The driving motor is usually connected to the high speed shaft of the gear reducer through a multiple V-belt drive. The motor is also mounted on the same slope as the kiln. Ball bearing motors should always be used, since oil will run out of the bearings on a sleeve bearing motor.

The main gear and pinion should be maintained in proper mesh. Improper meshing of the teeth results in a jerky or vibrating motion of the kiln. Too small a clearance will cause bottoming of the main gear on the base of the pinion teeth. Proper adjustment of the carrying rollers to compensate for the wear on the tires and rollers should prevent this condition.

If a minimum adverse clearance is allowed to continue with a resulting scoring of gear teeth and peening of pinion teeth, it will be necessary to reverse the gear and pinion before such action is normally necessary and then reset the drive accordingly.

Large, slow moving equipment such as rotary kilns will have a low natural frequency of vibration which in some cases could coincide with a kiln speed. Were this to occur, there would be a pronounced vibration of the kiln on the supporting rollers, and knocking and pounding in the main gear and the gear reducer. If such a condition were allowed to continue, the foundations and the kiln could be severely damaged.

The design of the kiln installation insures a natural frequency of vibration well out of the range of recommended operating speeds. Consequently, the kiln speed should never be changed without first investigating the effect which the increased speed might have on the vibrational characteristics of the kiln.

Confirm the original centerline of carrying mechanism bases. To do this, establish an offset centerline, preferably with piano wire, along the side of the kiln from the first to the last support where visibility is unobstructed, as shown in Figure 1. This offset centerline should be equidistant from the centerline marks on the carrying mechanism bases at the two extreme supports of the kiln. By tramming from this offset centerline, determine if the centerline marks on the carrying mechanism bases are all in line.

If the intermediate piers are not in line, determine whether they or the end piers have settled before proceeding with the alignment work. Some changes may be required in order to bring either the bases or piers into line, depending on whether or not the settling has reached its final stages. If no further settling is anticipated, or in cases where no settling has taken place, the offset centerline should be permanently located by setting lead or brass markers into the piers or floor. The true centerline should be clearly marked on each carrying mechanism base by tramming from the offset centerline.

Check the setting of the kiln shell in relation to the true centerline of the bases. This can be done by stringing a cord with a plumb bob attached to each end over the top of the shell as near the riding rings as possible. In cases where there are irregularities in the shell, the cord should be strung over the wearing faces of the riding rings. This cord must be long enough to permit the plumb bobs to hang free beneath the kiln, as shown in Figure 1. The midpoint of the distance between these plumb bobs is the center of the kiln shell at that position. Mark this point on the bases and proceed with the same operation at the next support. Rotate the shell 90 degrees and repeat the markings at each support. The mean of the four marks at each quarter point through a complete revolution will then indicate the path from support to support of the true centerline of the kiln shell.

If condition (2) applies, the carrying rollers must be adjusted so that the true centerline of the kiln shell is made to coincide with the true centerline of the bases. The carrying rollers must be kept parallel to the centerline of the kiln shell and carrying mechanism bases, as shown in Figure 1. In making these adjustments care must be taken to maintain the proper clearance at the feed end and discharge end air seals and at the main drive gear and pinion.

This check should be made when the kiln is shut down and at a time when the shell is not distorted by either radiant heat from adjacent kilns or the sun. Tape the circumference of each riding ring so the distance from the outside diameter of the riding ring to the center of the kiln can be determined for each ring. Set up a transit or level on top of the kiln over the feed end riding ring. Adjust transit so the line of sight is parallel to centerline of the kiln at the feed end and discharge end riding rings. Check the distance from the riding ring to line of sight for each intermediate ring, repeating this check at quarter points around the circumference. Knowing the radius of each riding ring, the average misalignment at each mechanism can now be determined. Correct this misalignment by making the necessary adjustments to the carrying rollers. The slope of the kiln can be checked with the transit at this time.

With the kiln now in correct vertical alignment, a simple gauge can be constructed to check vertical alignment at each mechanism without having to shut down the kiln and go through the elaborate measurements outlined above. This consists of a gauge pin or tram just long enough to reach from the mark of the true centerline on the carrying mechanism frame to kiln shell. A pin should be made for each mechanism frame. Gauging the distance between the frames and the shell will indicate the extent of wear on the rollers and riding rings. The carrying rollers can then be moved in to return the kiln to its original elevation.

Since the shell may not be perfectly round at the planes where the measurements are taken, reference points should be established on the shell so that the vertical distances between the mechanism bases and the shell will always be gauged at the same points on the circumference of the shell. Reference points can be made by welding four -in. nuts to the shell in each plane where measurements are to be taken. These nuts should be spaced 90 degrees apart. A bolt can then be turned into each nut to a point where the head of the bolt will just touch the gauge pin. The bolt is then welded to the nut. Four of these bolts are used at each mechanism to provide an average reading.

The floating type riding rings should not wobble as the kiln rotates, since it is impossible to obtain full contact between the carrying rollers and riding ring under such conditions. Figure 2 shows a method for determining the amount of runout in a ring.

Two pointers are constructed of angle iron and placed as shown. By using two pointers the effect of any kiln float is eliminated. These pointers should be mounted on the kiln pier away from the carrying mechanism and should extend to the centerline of the kiln. The edge of each pointer should be approximately one inch from the machined outer edge of the riding ring.

Measurements are taken from reference marks on the pointers to the machined sides of the riding ring. A set of readings taken at 16 equally spaced points around the circumference of the ring will indicate the location and magnitude of maximum runout. If the runout at any location exceeds it must be corrected by relocating the retaining bands and riding rings.

When rollers are set parallel to the centerline of the kiln, the roller shafts should bear against the downhill bearing caps. This can be checked by tapping the bearing caps with a hammer. The loaded caps will emit a solid sound.

Check each downhill bearing cap to make certain there is no excessive downhill thrust on any cap. This is done by cutting the roller to just relieve the pressure of the roller shaft against the cap. Note how much the adjusting screw was turned. Then return the roller to a setting which will just produce a light roller shaft force against the downhill bearing cap. After all the rollers are adjusted the kiln will bear against the lower thrust roller. Care must be taken to avoid excessive thrust roller loading.

Sometimes, when starting up a new kiln with the carrying rollers set parallel to the axis of the kiln, the carrying rollers and riding rings will not make 100% contact throughout the complete revolution of the kiln. In such cases it is better to let the rolling surfaces wear in to obtain full contact rather than to adjust the rollers to obtain full contact immediately.

The thrust mechanisms on modern kilns are designed to carry the full thrust of the kiln. On many older kilns, however, it is necessary to carry much of the thrust by adjusting the carrying rollers, since the thrust mechanisms were not designed to take the full thrust load. To float the shell of such a kiln, thus reducing or even eliminatingcompletely the thrust on the downhill thrust roller, the carrying rollers are set at an angle as shown in Figure 3. The illustrations exaggerate the amount of adjustment to show the principle involved more clearly. Any such adjustments must be performed carefully with each roller to avoid excessive pressure with resultant wear from developing on any one roller.

The main gear is equipped with adjusting screws to facilitate centering of the gear on the shell. This gear must run true. Several points around the circumference of the gear should be checked with a feeler gauge for uniform contact across the full face of the teeth. Flange bolts should be inspected periodically to be sure they are tight at all times. A tight fit can be achieved by pulling each bolt up tightly, then heating the bolt to about 350 F and advancing the nut an additional 20 degrees.

The pinion and gear must mesh properly, as shown in Figure 5. Pitch lines are scribed on both sides of the gear and pinion at the factory. The pinion should be set so the pitch lines on the gear and pinion are 1/16 in. apart when the shell is cold. When the shell is hot the pitch lines should be from 0 to 1/16 in. apart. In no case should the pitch lines overlap, since this would cause excessive wear and overloading of the pinionshaft and bearings.

The mesh of the gear and pinion should be checked at regular intervals. Any wear or adjustment on the carrying rollers will change the mesh. If the pinion is meshing too deeply, the kiln should be raised to its original position by moving the carrying rollers in toward the centerline of the kiln. It should not be necessary to back the drive out to obtain the correct mesh. While the drive is equipped with adjusting screws, these are mainly for use in the initial alignment of the drive. Sometimes it becomes necessary to back the drive away from the kiln to relieve a serious condition which, if permitted to continue, would result in damage to the gear and pinion. This must be considered only a temporary expedient, and the drive should be returned to its correct location immediately upon returning the shell to its true centerline in the recommended manner.

Sometimes it becomes necessary to reface riding rings or rollers. A grinding rig, shown in Figure 6, can be constructed on the job and used to reface the riding rings while the kiln is in operation. The coil springs and adjusting bolts serve as a stop so that the high spots on the ring will be ground off first. In operating this refacing tool, a reference mark should be established on the side of the riding ring being ground, and the adjusting screw on the tool turned one revolution per revolution of the kiln to assure even grinding across the face of the ring. Any circumferential ridges on the ring must be ground off first.

If it is not feasible to operate the tool throughout a full 24-hour period, it is a simple matter to lower the grinding table on the adjusting bolts, thereby removing the carborundum blocks from contact with the riding ring. This tool can also be adapted for refacing the carrying roller by tipping the rig up on its side and setting it against the face of the roller. This can be more easily accomplished on the outer side of the carrying mechanism due to space limitations, especially at the thrust mechanism. These rollers can also be refaced by using a lathe and cutting tool arrangement, or it may be more expedient and economical to put the kiln on cribbing and reface the rollers in the machine shop. In either case, whether the ring and roller are to wear in over a period of time or whether they are to be refaced, it is essential to watch the following:

Use high grade lubricant with specifications shown in Figure 7. After a new kiln has been in service for one month, drain oil and clean reservoir. Refill with new oil. Thereafter change oil every six months.

Use high grade lubricant with specifications shown in Figure 8. The oil level should be checked at frequent intervals and maintained at the proper level. When starting a new kiln the level should be checked daily. The oil should be changed after the first month of operation and at six-month intervals thereafter.

Floating type riding rings should be lubricated between riding rings and filler bars with a graphited grease. Initially, apply lubricant to the inner surface of the riding ring at all spaces between filler bars. Subsequent applications of lubricant need be made only at four evenly spaced points around the circumference of the ring. The lubricant can be most easily applied with a hand gun with extended nozzle.

rotary lime kiln operation

rotary lime kiln operation

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.

huachen refractory

huachen refractory

Zhengzhou Huachen Refractory Co.,ltd was founded in 2003, Headquarter is located in Zhengzhou city, which is the capital of Henan Province. Henan province is located in the center of China. Zhengzhou is the center of politics and economy and traffic center in middle of China. Zhengzhou as the staring port of One Belt and One Road,plays an increasingly important role in the international trade.

Since established of the company, we are focusing on producing research and development of refractory bricks and raw materials, especial the fused cast block and the Magnesite series bricks and materials. Now we have two plant, one produce the fused cast blocks, like AZS 33#.36#,41#. the other plant produce the MgO2 series bricks and Al2O3 series bricks, like Magnesite brick, Magnesite-chrome brick, Mg-Al spinel brick, high alumina brick and fire clay bricks ...

Huachen Refractory expands his sale market during these years with our hard working, Now we have export out products to America, Australian, Vietnam, Russia, Kazakhstan,Turkey etc, increased with our sale amount, our service is improving greatly day by day, we believe that our high quality products and excellent service will fulfill any requirements from you.

Huchen Refractory governed by its commitment to protecting the environment, creating genuine customer value, promoting life-long learning, and assuring a reasonable profit. Huachen refractory is dedicated to helping its customers succeed in thecompetitive marketing and rapidly changing global market by offering uniquely differentiated products.

rotary kiln archives | mineral processing & metallurgy

rotary kiln archives | mineral processing & metallurgy

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

rotary kilns: frequently asked questions (faqs)

rotary kilns: frequently asked questions (faqs)

As a cornerstone technique in engineering the raw materials and products our constantly evolving society depends on, the advanced thermal processing carried out in rotary kilns is an integral component of modern industrial processing.

The diverse nature of rotary kilns makes them a vessel for accomplishing just about any objective associated with thermal processing. Most commonly, rotary kilns are used to carry out the following reactions:

Its important to note that each process listed above is a broad thermal processing technique, covering an array of applications. These specific applications often have their own name within the industry, or may facilitate a subset of reactions. For example, in the extraction of lithium ore from spodumene, calcination is used to cause decrepitation, or the shattering of the crystal structure, in order to convert alpha spodumene to beta spodumene.

More specifically, rotary kilns process material at a predetermined temperature for a predetermined amount of time (referred to as residence or retention time) based on the unique temperature profile of the material to be processed. By controlling temperature and retention time, rotary kilns can initiate and carry out chemical reactions or phase changes in a controlled setting.

Rotary kilns are a large, rotating drum that can be either of the direct or indirect configuration. In the direct configuration, the kiln can be designed for either co-current (parallel) or counter-current air flow. As solids pass through the drum, the heating medium increases their temperature. The constant rotation of the drum creates a tumbling action that redistributes the bed of material for even heat transfer throughout the bed. Tumbling flights and other internals can be added to further optimize processing.

In a direct-fired kiln, the material is in direct contact with the products of combustion, with the heat passing through the kilns interior. Conversely, in an indirect-fired rotary kiln, the processing environment is sealed off, and the rotating drum is externally heated in order to prevent contact between the material and any products of combustion. Instead, the material is heated through contact with the drum shell.

As a result, there are some differences in design between these two types of rotary kilns, such as the use of a heating shroud/furnace (for indirect), refractory (in the direct kiln), and the materials of construction, among other things. Indirect kilns are also commonly referred to as calciners, though the term is not always technically correct.

Rotary kiln design is a complex undertaking, as advanced thermal processing techniques and chemical engineering principles come into play. This is especially true considering that many kiln applications are new, and must be developed from scratch.

The design process may differ depending on how much is known about the material and its physical and chemical behavior under heat. Most often, the design process begins with a thermal and chemical analysis of the material, followed by batch rotary kiln testing.

Material is tested in either a batch indirect or direct kiln to gather initial process data points. Testing continues, advancing to a pilot-scale test kiln to scale up the process and refine process and material variables to produce a product with the desired characteristics.

Rotary kilns can be designed for handling a broad range of capacities, from small, batch-scale units processing anywhere from 50 to 200 lb/hr, to commercial-scale units processing material in the range of 200 lb/hr to 20 TPH.

While there is some overlap between rotary drum dryers and kilns, the key difference lies in the intent: is the processing intended to simply dry the material, or is some sort of chemical reaction or phase change required?

Selection of the proper material is based on the material characteristics (i.e., abrasiveness and corrosiveness), as well as the temperatures employed and whether the unit will be of the direct or indirect design. Since direct kilns employ refractory, they are typically constructed of carbon steel. Indirect kilns, however, which cannot use refractory as it would add another layer for heat to pass through, do not use refractory and therefore must be able to withstand greater temperatures and hence, are constructed from a more heat-resistant alloy.

The temperature(s) at which a rotary kiln operates is specific to the reaction requirements of the material being processed and therefore differs in every setting. In general, however, rotary kilns can process material at temperatures ranging from 800 to 3000F (430 to 1650C).

Programmable logic controllers (PLCs), motor control centers (MCCs), and data collection systems can all be integrated into the rotary kiln system for improved data collection, process control, and advanced reporting.

Residence time, also known as retention time, is the amount of time in which the material is processed in the kiln. As with temperature, the residence time is determined solely on the requirements of the intended reaction.

The rotary kiln is an essential thermal processing device. As its use continues to spread to an increasing number of applications and industries, questions around everything from the rotary kilns capabilities to its operation arise. As the leading provider of custom rotary kilns, FEECO can answer all of your rotary kiln questions.

FEECO rotary kilns are robust and engineered around their precise application for optimal processing. Batch and pilot kiln testing is available in our Innovation Center to assist in commercial-scale kiln design and process scale-up, and we also offer a comprehensive line of parts and service support to keep your kiln running reliably for years to come. For more information on our rotary kilns, contact us today!

Related Equipments