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.

lime kiln - an overview | sciencedirect topics

lime kiln - an overview | sciencedirect topics

Lime kiln dust (LKD) and cement kiln dust (CKD) are by-products of manufacturing and processing of lime and cement, respectively. CKD contains mostly dried raw materials such as limestone, sand, shale, and iron ore. Nearly 4 million tons of CKD is disposed of every year in the United States (Miller and Zaman, 2000). Due to its pozzolanic activator attribute, CKD has been successfully implemented in road soil stabilization (Miller and Azad, 2000). CKD creates a low-ductile asphalt binder, waterproofing, and protection. CKD-treated soils exhibit reduced liquid limit and reduced plasticity indices.

CKD inclusion in soil increases unconfined compressive strength, stiffness, and durability compared to untreated soils (Miller and Azad, 2000). Although LKD and CKD additives are not considered hazardous by environmental regulatory agencies, proper supervision and handling are needed when these additives are used in the field application.

The lime kiln calcines the calcium carbonate in lime mud to produce quicklime. Several modifications are possible to reduce energy consumption in the kiln. High-efficiency filters can be installed to reduce the water content of the kiln inputs, thus reducing evaporation energy. Higher-efficiency refractory insulation brick or chains can be installed to increase heat transfer in the kiln. Heat can also be captured from the lime and from kiln exhaust gases to preheat incoming lime and combustion air. Average savings achieved by these measures is approximately 0.46GJ/t pulp (Elaahi and Lowitt,1988; Grace,1987; Grace etal.,1989; Byrne and Larsen,1997; Lewko,1996; Pearson and Dion,1999). These improvements can also improve the rate of recovery of lime from green liquor. This will reduce the plants requirement for additional purchased lime. Based on an analysis of kiln modifications in cement production, Martin etal. (2000) assumed an investment cost of $2.5/t pulp. One study indicated that newer high-performance refractories can lead to lime kiln energy savings of up to 5%. Heat can also be recovered from the lime and from kiln exhaust gases to preheat incoming lime and combustion air (Kramer etal.,2009).

Materials contributing to air pollution include particulate matter from the boilers, lime kiln, and smelt dissolving tank; gaseous combustion pollutants such as carbon monoxide, NOx, and volatile organics from power boilers, recovery furnaces, and the lime kiln; odor consisting of reduced sulfur compounds in the kraft process arising from the digesters, evaporators, recovery boiler, smelt dissolving tank, and lime kiln; sulfur dioxide from the recovery furnace and boilers using fuel containing sulfur; and volatile organic chemicals from miscellaneous sources. In the sulfite process the primary pollutants are organics, oxides of sulfur, and particulates.

Lime is produced by calcining limestone at 825C in a lime kiln. The cost of this processing is reflected in the cost of the lime produced which is considerably more than that of limestone. The cost of transporting lime is also higher than that of limestone as lime must be protected from moisture. Karlsson and Rosenberg (1980a) estimate the cost ratio of lime to limestone on a molar basis to be between 2 and 4 depending on the transportation distance.

Lime has certain advantages over limestone in FGD applications. Cases of pH instability have been reported for limestone due to its relatively slow rate of dissolution. Limestone has a greater liquid-side resistance to mass transfer. It is also claimed that an unsaturated mode is more readily attained with lime (Karlsson and Rosenberg, 1980a). Despite these relative advantages FGD systems based on lime are becoming less popular than those based on limestone. Recent advances in the reliabilities of both lime and limestone systems have resulted in the cost of reagent being the overriding consideration. Of the plants under construction or contracted in the USA twice as many are based on limestone than on lime. Very few, if any, lime systems are under construction for projected plants (Karlsson and Rosenberg, 1980a).

Whether lime or limestone is employed, efficient utilisation of reagent is important from an economic point of view. Single loop, calcium based FGD systems must operate at pH values of about 6 to 6.5 to obtain adequate removal of SO2. The concentration of reagent, particularly when using limestone, in the solution at these values of pH can be as low as 2 to 4%. At these low solubility values part of the reagent may be discharged with the slurry. When 90% or greater removal of SO2 is required limestone utilisation may be as low as 70% (Braden, 1978) but is typically between 75 and 90% (Karlsson and Rosenberg, 1980a). With double loop operation reagent utilisation approaches 100% because conditions are such that any unused reagent discharged from the absorber loop is dissolved in the quench loop.

As of January 1980 there was a total of 35 680 MW of plant in operation or committed to limestone or lime scrubbing processes in the USA. This represented over 70% of the total FGD capacity in the USA. Operating and maintenance experience is well documented (e.g. Spring, 1980; Hewitt and Saleem, 1980).

From the fuel requirement point of view, rotary kilns are the most flexible of all lime kilns (Oates, 1998). They are successfully fired with natural gas, fuel oil, and pulverized fuels of all types including coal, coke, and sawdust. According to Boynton (1980), the United States is by far the world's leader in rotary kiln lime production with about 88% of its commercial and about 70% of captive plant capacity provided by kilns. The conventional rotary lime kiln has a length-to-diameter (L/D) ratio in the 3040 range with lengths of 75500ft (22.7152.5m) and diameter of 411ft (1.23.3m). Lime kilns are usually inclined at about 35 slope with material charged at the elevated end and discharging at the lower end. The degree of fill is relatively deep, about 1012%. Owing to its low thermal conductivity, limestone with a large diameter of about 2 in (5cm) results in higher effective bed heat conduction than smaller stones. The larger feed material sizes tend to have larger pore volume in the bulk and thereby maximize the particle-to-particle heat transfer, which is usually dominated by radiation at the dissociation temperatures. The smaller feed stones tend to pack themselves upon rotation and render the bed a poor conductor of heat. For many years, most long kilns operated with deplorable fuel efficiencies because of poor or lack of heat recuperation such as coolers and preheaters (Figure10.4) with thermal consumption as high as 1215 millionBtu/ton (33364170kcal/kg) of lime. Thanks to ingenious heat recuperation systems such as coolers, preheaters, and lifters, today, thermal efficiencies of rotary lime kilns are in the 68 millionBtu/ton range (16682224kcal/kg), using fuel at about half the rate of early long kilns.

Some rotary lime kilns operate under reducing conditions by curtailing the combustion air to substoichiometric levels so as to volatilize any sulfur that may be in the limestone in order to meet the stringent sulfur specifications imposed by steel and chemical users. For most operations except for dead burnt dolomite, the burner tip velocities can range between a low of 25m/s and a high of about 60m/s. These are significantly lower than the velocities of cement kilns, which operate around 80100m/s. The momentum ratio and associated CrayaCurtet parameter is usually lower than 2, which means that the burner jet recirculation will have eddies and that fuel/air mixing is moderate and the flame is less intense than that in dead burnt dolomite kilns or cement kilns. A simple heat and mass balance for the kiln section of a lime-making process is shown in Figure10.5.

Borate autocausticizing makes it possible to produce sodium hydroxide directly in the recovery boiler and improves the lime kiln and recausticization operations by reducing causticizing loads and the amount of lime processed through the system. The major function of the recausticizing plant in a pulp mill is to regenerate the caustic. Caustic is typically recovered from the spent pulping chemical in the following stages:

Autocausticizing could be an attractive alternative for kraft mills because it allows higher caustic production without increasing lime demand and can even eliminate lime demand (Kochesfahani and Bair,2002).

The partial borate autocausticizing process occurs when sodium borates are added to the kraft liquor at substoichiometric levels (Bjrk etal.,2005). A portion of the sodium carbonate is causticized in the recovery boiler. The causticization of the remaining sodium carbonate is completed in a conventional recausticizing plant of the pulp mill with a reduced quantity of lime. The technology may appear as an attractive option particularly for kraft pulp mills where incremental causticizing and lime kiln capacity are required. Mill-scale trials have shown that there are no major side effects on the mill operations. The major findings of the studies suggest that borate present in cooking liquor presents several advantages (Table11.19).

Borate autocausticizing technology uses Neobor, a form of sodium borate to replace lime. Each ton of Neobor added to the pulping process replaces 10 to 30 times its weight in lime (RTM,2010). The main autocausticizing reaction that occurs in the recovery boiler is between sodium metaborate and sodium carbonate in the molten smelt, which forms trisodium borate. The trisodium borate reacts with the water in the smelt-dissolving tank to form sodium hydroxide and regenerate sodium metaborate (Bjrk etal.,2005). Sodium metaborate stays in solution and circulates through the chemical recovery cycle to continue forming caustic in the recovery boiler. The borate compounds remain in the liquor cycle, self-regenerating to be used again in producing caustic. Sodium metaborate drives autocausticizing reactions in the recovery boiler and forms sodium hydroxide in the smelt-dissolving tank without the use of lime or additional recovery processes, so this technology reduces energy consumption and increases causticizing and calcining capacities. For kraft and soda pulp mills, reducing the lime kiln load not only translates to lower operating costs, energy consumption, and emissions, but also significantly reduces the amount of lime mud that requires special handling and disposal (ITP,2011b).

The concept of borate autocausticizing was first investigated during the early 1980s in Europe. Rio Tinto Minerals developed partial borate autocausticizing (RTM,2010). They obtained support from the US DOE. This technology is being implemented in pulp mills worldwide to supplement conventional lime causticizing with almost no capital investment (ITP,2011b). A full-scale trial of partial autocausticizing with sodium borate was first conducted at Georgia-Pacific Camas mill, Washington State(United States), from 1999 to 2000 for a period of more than 16months (Hunter etal.,2001). In Europe, a full-scale partial borate autocausticizing trial was conducted in 2002 at the Stora Enso Norrsundet mill in Sweden (Bjrk etal.,2005). In this trial, the total lime requirement has been reduced by about 7%, and the autocausticizing level has typically been 911% during the 15-month period. There is some indication that borates may also improve pulp yield (Bjrk etal.,2005). Partial autocausticizing in the P.H. Gladfelter Co. mill in Spring Grove, Pennsylvania, in the United States increased production by about 5% in 2007 (ITP,2011b). However, full borate autocausticizing, which uses borates to drive all the causticizing reactions instead of just lime causticizing, is still undergoing further research and testing (ITP,2006c).

An air jet laden with particles such as that found in primary air issuing from a pulverized fuel pipe for combustion in cement and lime kilns may be synonymous with a jet of fluid with a density greater than that of air provided the particles are small enough that one can consider the fluid to be homogeneous. Under such conditions, the effect of the solid burden may be accounted for by simply assuming an increase in the gas density and a reduction in the kinematic viscosity. A concomitant result will be an accelerated turbulence and an intensification of mixing and the entrainment phenomena associated with it. Equation (3.32) applies in such situations whereby m0 might be increased by the factor 0/a owing to the presence of suspended solid so that the effective change in air entrained per unit volume of jet fluid might increase by a factor of (0/a)2. When the particles are not small enough to behave like a homogeneous fluid, a relative motion occurs between the particles and the surrounding air as a result of gravity or as a result of inertial forces resulting in the damping of the turbulence since the drag between the dust and the air will extract energy from the turbulent fluctuations. One important estimate is the distance at which a particle in a particle-laden jet will travel before coming to rest. This distance is defined as the range , a product of the initial velocity of the particle and the relaxation time R:

The relaxation time is defined here as the time taken for the relative velocity between particle and gas to fall to 36.8% of its initial value. For a perfect spherical particle, the relaxation time is defined as

where m and rp are the mass and radius of the particle, respectively, and is the dynamic viscosity of the surrounding fluid. With these definitions, one can estimate that coal particles with a diameter of 80m injected at 60m/s will have a range of about 150cm, some 150 nozzle diameters for a 1-cm nozzle pipe, and will have little effect on the jet (Field etal., 1967). However, if the particles were finer, for example, 40m in size, then the range would only be 30cm, which would have a damping effect on the jet due to turbulent energy transfer. The relaxation time is a measure of the shortest timescale of turbulence to which the particle could respond. As mentioned earlier, smaller eddies would have rapid velocity fluctuations and the particles would not have time to accelerate to the velocities within the eddies. However, if the eddies are large, then the particles can follow the streamlines without any appreciable slip and the suspension would tend to behave as a homogeneous fluid. It has been shown that increasing the fluid temperature shortens the relaxation time and thereby reduces the size of the eddy to which particles respond. When it falls within the same range as the timescale of the eddies, some damping of the turbulence can be expected, thereby reducing the eddy viscosity (Field etal., 1967). The concomitant result will be a decrease in the rate of entrainment and the rate of spread of the turbulent jet.

The Paraho Development Corporation developed new vertical shaft kiln hardware and process techniques and confirmed new technology in the 1960s by building three large commercial lime kilns. In the 1970s the company adapted their lime kiln technology to oil shale retorting. Paraho obtained a lease from the US Department of the Interior in May 1972 for the use of the US Bureau of Mines oil shale facility at Anvil Points near Rifle, Colorado, to demonstrate their retorting technology. The indirect combustion mode bums process gas in a separate furnace and hot gases carry heat to the retort. This retort can also be operated in a direct combustion (Section 4.16).

In the indirect mode Paraho retort (Fig.14.5), the portion of the vertical retorting chamber that was used for oil shale combustion in the direct mode is now the region of the retort chamber into which externally heated fuel gas is introduced. No combustion occurs within the retorting chamber. That separate combustion process is typically fueled by commercial fuels (natural gas, diesel, propane, etc.) that are often augmented with a portion of the fuel gas recovered from the retorting operation.

In the process, finely-ground oil shale enters a feed hopper on top of the retort after which, in a continuous moving bed, the oil shale flows downward consecutively through the mist formation, retorting, combustion, and cooling zones. As the shale descends, heat is efficiently exchanged with a countercurrent flow of recycle gas, which is introduced into the retort at different levels by three specific-purpose gas-air and gas distributors. Near the top of the retort the ambient temperature shale is warmed by rising hot oil vapors and gas, which, in turn, are cooled to form an oil mist that is entrained in the gas.

While they are very similar in operation, the direct and indirect mode Paraho retorts offer sufficiently different operating conditions so as to change the composition of the recovered crude shale oils and gases. Oil vapors and mists leave the direct mode retort at approximately 60C (140F), while the vapors and gases in the indirect mode leave the retorting vessel at 135C (280F) and have as much as nine times higher heating values than gases and vapors recovered from the direct mode retort (102 and 885 Btu/ft3) oil vapor and mists recovered from the direct mode are diluted with combustion gases from the combustion of the spent shale at the bottom portion of the retort.

The characteristics of the recovered raw shale oil are somewhat different for the direct and indirect mode retorts, but each has characteristics similar to shale oils recovered from other retorts using similar shale heating mechanisms (direct vs. indirect). In addition, gases from the indirect mode retorts have much lower levels of carbon dioxide but generally higher levels of hydrogen sulfide, ammonia, and hydrogen, which are thought to be the result of the indirect mode retort having much less of an oxidizing environment than the direct mode retort (EPA, 1979).

Smelt is cooled and dissolved in water. Hydroxide sodium is regenerated from sodium carbonate reacting with calcium hydroxide in causticisers. The calcium carbonate produced is regenerated in the lime kiln by heating. Regenerated white liquor, containing sodium hydroxide and sodium sulphide, is then sent back to chip cooking.

Low-pressure steam demand for causticising is approximately 20MJ/ adt. Medium pressure (MP) steam demand for lime-kiln oil burners (atomizing steam) is approximately 20MJ/adt. Kiln fuel demand (heavy fuel oil, natural gas or bio-gas produced in a gasification plant using waste wood and bark) is approximately 2.02.8 GJ/adt. Total power demand, including clarifier, filters and the electrostatic precipitator for lime kiln, is approximately 40 kWh/adt.

how does a lime kiln work - professional manufacturer of mineral processing plants

how does a lime kiln work - professional manufacturer of mineral processing plants

A lime kiln is used for calcination of limestone (calcium carbonate) to produce quicklime also called burnt lime. And the chemical formula is CaCO+ heat = CaO +CO. Usually, the heat is around 900 , but a temperature around 1000 makes the calcination process more quickly. Of course, the temperature can not be too high for it can produce dead lime. Due to the fact that the process is conducted in high temperature, the insides of lime kilns are equipped with refractory materials, while the outer structures are built with sturdy steels. Vertical Lime Kiln Vertical lime kiln is also called vertical kiln lime or vertical shaft kiln for lime. It is a vertical static device for the decomposition of limestone to produce quicklime/burnt lime. Vertical lime kiln is suitable for projects with smaller quicklime ...Get Solutions Rotary Lime Kiln 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 ...Get Solutions

Lime production plant is a whole production line to make quicklime. Lime processing plant is often equipped with either rotary lime kiln or vertical lime kiln. For lime kiln is the core equipment of the plant to produce burnt lime. Of course, except lime kiln, there are also other machines in the lime calcination plant. For example, there are crusher, dust collector, packing machine, transferring systems and so on. With extended experience, Daswell machinery provides advanced lime kiln technology. And we design and manufacture lime kilns according to customersspecific needs.

To produce quicklime in lime kilns, there are mainly three processes. The first stage is preheating. The second stage is calcining. And the third stage is cooling. In the preheating stage. The feed limestone is preheated by the exhaust hot air from the lime kiln, so that partially of the limestone will be calcined. As a result, the preheating process can make sure that the limestone is fully calcined as well as save energy along the process. In the calcining process, the partially burnt limestone will be burnt thoroughly. And usually the temperature in this stage is the highest in the lime kiln. In the cooling stage, the burnt limestone will be cooled down by the air so that it can be handled by conveyors and so on. In fact, except for these three stages, there are also crushing, dust collecting, packing and so on. Firstly, the limestone is crushed in primary or even secondary crusher so that the feed limestone is of required size. Then the fed limestone will be fed into lime kiln, going through preheating, calcining and cooling stages. And then the cooled down quicklime will enter into dust collectors to reduce dust. Finally, the quicklime is directed to product silo through conveyor, waiting for being packed.

Typically, there are two kinds of lime kilns. One is rotary lime kiln and the other is vertical shaft lime kiln. Rotary lime kiln is a horizontal or inclined cylinder which can rotate due to rings and wheels attached. And vertical lime kiln, as the name implies, is vertical.

Limestone rotary kiln is inclined cylinder that can rotate. At the higher end, limestone is fed in. While at the lower end, it is the furnace where a great variety of fuels can be used to burn the limestone, such as coal, gas, oil and so on. For modern lime calcination plant with rotary lime kiln, it is often equipped with vertical preheater and vertical cooler. That is the three stages of the limestone calcination are conducted separately in these three parts: the preheating process in vertical preheater, the calcination process in the rotary lime kiln, and the cooling stage in the vertical cooler. This system can improve quicklime production capacity while reduce energy consumption during the whole lime calcining process. Besides, with advanced system, the rotary lime kiln can come with shorter lengths, which can also reduce heat losses due to long lengths of the rotary lime kiln. Rotary lime kiln with preheater and cooler is advanced lime kiln technology for new lime calcination plant. And it is also good solution for existing quicklime plant upgrade.

As for the vertical lime kiln, it consists all three stages all in one. Usually, the upper side of the vertical shaft lime kiln is the preheating chamber. The central part is calcination chamber and the lower part of the lime kiln is cooling chamber. In light of this design, feed limestone with required sizes will be fed into the lime kiln from top. And after being preheated, the partially burnt limestone will enter into the calcination chamber. In this chamber, the preheated limestone will be fully calcined. And finally in the cooling stage, the burnt limestone is cooled down by the air from outside of the lime kiln. Besides, the furnace of vertical lime kiln is at the bottom. 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):

lime kilns in chemical kraft recovery - convergence pulp & paper training

lime kilns in chemical kraft recovery - convergence pulp & paper training

Get Convergence courses into your current LMS to track and report employee training. Or contact us to learn more about the advantages of licensing our courses with the Convergence LMS.

The full course is 26 minutes long and available in a number of affordable formats.

This course covers the purpose of the lime kiln and the role of lime (CaO) in the chemical recovery process at a kraft pulp mill. Then it describes the components and sections of a rotary lime kiln, and the chemical reaction that takes place inside the kiln. Finally, it lists some common problems experienced in lime kilns.

What kinds of pollutants may be a in the exhaust gas from kiln?Exhaust gas from from kiln typically has high levels of particulate which must be removed. It may also contain sulfur-compounds which need to be removed.

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