circumgyrate kiln indirect fired rotary kiln lime rotary kiln clay rotary

indirect-fired rotary kiln in your rotary kiln business

indirect-fired rotary kiln in your rotary kiln business

Indirect-fired rotary kiln has a combustion chamber on the peripheral barrel. The heat generated by the combustion of flue gas is transferred to the material through the cylinder. The material is calcined at high temperatures, and the calcined product is discharged from the discharge valve. The exhaust gas is treated or emptied or utilized. The indirect-fired rotary kiln is suitable for the production of various materials requiring indirect continuous heating.

Our indirect-fired rotary kiln can use different fuels for heating, in addition to traditional coal, oil, gas, it can also use electricity for heating. Among them, the electric heating rotary kiln is in huge demand and is highly praised by the market. One is because the heat source is clean and does not cause environmental pollution, and the other is because the power supply is more convenient and efficient.

When the indirect-fired rotary kiln is used to calcine the catalyst and molecular sieve. It can make s sure that the purity of the product. This is because the multi-zone temperature can be set coordinatedly in order to complete the reaction such as dehydration or unit cell shrinkage.

The indirect-fired rotary kiln can recycle the condensed water, combustible gas and biochar left by the calcined sludge. The indirect rotary kiln chemically reacts sludge in a closed, anaerobic, non-combustible and high-temperature state. Under the reaction of dry distillation and thermal decomposition, sludge goes through pyrolysis, dehydrogenation, thermal condensation, gasification and carbonization, so that the water in the sludge becomes condensed water, and the organic matter in the sludge is converted into a combustible gas, which is then recycled.

Indirect-fired rotary kiln equipment has been widely recognized as the most suitable solid bulk material handling the machine in the past 100 years. The common type of rotary kiln equipment is the direct-fired rotary kiln. The direct-fired rotary kilns character is that the combusted materials are directly in contact with the raw material being processed. In traditional rotary kilns, pulverized coal is generally fed into the kiln and ignited by a burner, so that the mixed coal materials are burned and heated to the required temperature. Traditional rotary kilns can also use fuel gas, heavy oil, and other fuels as heat sources. But its shortcoming is also obvious, that is, it cannot handle flammable and explosive materials that cannot be heated by an open flame.

Indirect combustion has received widespread attention in recent years. Indirect rotary kiln has become a more common commercial option in the past 25 years. Indirect rotary kiln differs from direct combustion in that all heat transferred to the processing material is radiated through the casing meanwhile the construction material can withstand higher temperatures.

The indirect rotary kiln is horizontal. You can preheat the surface of the rotary kiln by burning natural gas or fuel. Heat is transferred to many burners outside the barrel to avoid local overheating of the enclosure. The indirect heating rotary kiln is mainly used to process flammable, explosive or chemically active substances, and it is not recommended to be applied to the production line of quicklime or cement.

Indirect-fired rotary kiln treatment of waste is a popular method of treating waste in recent years, but it is still rarely used in China. In fact, the use of indirect rotary kiln incineration to treat waste has been successfully practiced in worldwide, showing great advantages in economics, prevention of secondary pollution, and thoroughness of waste innocuous treatment. Indirect-fired rotary kiln has so many advantages.

rotary kiln for sale - sale rotary kiln by qualified manufactures

rotary kiln for sale - sale rotary kiln by qualified manufactures

Rotary kiln refers to rotary calcination kiln (commonly known as rotary kiln) and belongs to the category of building materials equipment. Rotary kilns can be divided into cement kilns, metallurgical chemical kilns, and lime kilns according to different materials processed. Cement kilns are mainly used for calcining cement clinker, which divided into two categories: dry process cement kilns and wet process cement kilns. Metallurgical and chemical kilns are mainly used for magnetizing roasting of iron ore-depleted ore in iron and steel plants in the metallurgical industry; oxidizing roasting of chromium and nickel-iron ore; refractory plant roasting high alumina vanadium ore and aluminum plant roasting clinker and aluminum hydroxide; And chrome ore powder and other minerals. Limekiln (ie active lime kiln) is used for roasting active lime and light-burning dolomite used in iron and steel plants and ferroalloy plants.

Cement rotary kiln belongs to the category of building materials and equipment, it is a kind of lime kiln. 0.5mm tolerance cement rotary kiln means that the allowable error of rotary kiln shell is within plus or minus 0.5mm.

Lime rotary kiln is also called roller rotary kiln. To make sure its air leakage coefficient is less than 10 percent, lime rotary kiln adopts advanced structure and reliable combined scale-like seal in both ends. It also uses composite refractory to reduce the loss of heat radiation.

Shaft kiln, just as its name implies, is a kiln with erected shape. Shaft kiln with modern new technology has environmental protection function, energy-saving function, high mechanization, and high automaticity. It also has the ability to turn waste into wealth.

The rank of countries alumina bauxite storage is Australia, The Republic of Guinea, Jamaica, China, and India. Rich reserves provinces in China are Shanxi, Guizhou, Guangxi, and Henan province. Generally, alumina bauxite is used to produce alumina or aluminum.

The data survey found that the price of AGICO groups rotary kiln will be about 600-1000 cheaper than the prices offered by the merchants in other cities. The reasons for the analysis are as follows:

It is the main body of the rotary kiln (rotary kiln), usually 30 to 150 meters long, cylindrical, with 3 to 5 rolling circles in the middle. Most of the barrels are processed into 3-10 sections by the factory, and then welded by large trucks to the destination.

On the contrary, the cooler and the preheater are devices that rapidly reduce the temperature of the rotary kiln after firing. It looks like a small rotary kiln, but the diameter is smaller and shorter.

It is also called preheater, which is a device for preliminary heating of materials by the waste heat of exhaust gas discharged from the rotary kiln before the materials enter the rotary kiln. Most of them are vertical structures.

everything you need to know on rotary kiln refractory

everything you need to know on rotary kiln refractory

Refractory, or the lining utilized on the interior of rotary kilns, is a critical component in ensuring process efficiency and prolonging the life of a rotary kiln. Here, well discuss everything you need to know about refractory, including how it works, the different types, and best practices for preventative care.

Rotary kilns employ high temperatures to cause a chemical reaction or physical change in a material. In most cases, these high operating temperatures would immediately destroy an unprotected carbon steel shell. For this reason, refractory is used.

Only direct-fired rotary kilns employ refractory; in an indirect-kiln, heat transfer occurs primarily through the kiln shell wall. Refractory would be another barrier for heat to pass through before it is in contact with material, reducing the efficiency of the process. Because of this, instead of using refractory, indirect-fired kilns typically rely on a more heat resistant shell.

Further necessitating the need for refractory, direct-fired kilns typically do not utilize combustion chambers, so the flame is in constant direct contact with the internals. Flame temperature can typically range anywhere between 1600 3200 (depending on excess air) a harsh processing environment that carbon steel is not capable of withstanding.

As the skeleton of the system, protecting the shell is paramount to prolonging the life of the equipment; a major repair or total replacement of the shell is a substantial undertaking, requiring significant downtime and repair costs. For this reason, choosing the right refractory configuration and taking measures to protect that refractory once operational is critical.

While the main objective of refractory is to protect the kiln shell, refractory also serves to minimize heat loss. A kiln with sub-par refractory may protect the kiln shell, but allow significant heat loss, reducing overall process efficiency and increasing operational costs.

Castable refractory comes in a powder form and is mixed with water on-site. Before the mixture can be put in place, anchors are installed. These y-shaped anchors are similar to rebar in cement; they help give the castable lining its strength. Once these anchors are in place, the cement-like mixture is pumped into the lining of the rotary kiln, and allowed to cure for several days.

Castable refractory has a similar material cost to brick. However, brick installation is much more labor intensive, as each brick is individually installed. This makes the overall cost of a brick lining more expensive than castable.

Besides lower overall cost, the advantage to using castable refractory in a rotary kiln is that it is usually easily patched when a problem is encountered. Down time is typically minimal, because the problem area can be cut out and new refractory poured into the cavity.

The disadvantage to using castable refractory in a rotary kiln is that it is very susceptible to installation problems. When castable refractory is expertly installed, it can nearly match the quality of brick. But if installed incorrectly, there can be a considerable difference in quality, and the life of the refractory can be severely compromised.

Although slightly more expensive than castable, brick does not require anchors, and its quality is superior, but as mentioned, incurs greater install costs. When processing a highly abrasive material, brick refractory is advisable most of the time, as castable does not have the durability to stand up against abrasive materials as well as brick.

The disadvantage to brick refractory is that it is kept in place much like a roman arch: bricks are held in place by the pressure of the other bricks pushing against each other. When a problem is encountered, typically the failed brick needs to be replaced, but when one brick is relying on the bricks around it to hold it in place, often one cannot replace just one brick, and whole sections of the refractory must be replaced. Unlike castable refractory, the repair of a fail in brick refractory is much more involved.

There is more to refractory than just the choice of material; refractory is a customizable part of rotary kiln design and can be tailored with multiple layers to meet the demands of a given application.

When efficiency is of great concern, or when extreme temperatures are involved, it is common to employ both a working layer, and an insulating layer. Layer thickness can also vary, with total refractory thickness generally falling between 4.5 12, pending process temperatures..

The working layer is the layer of refractory that is in direct contact with the material being processed. This layer is a dense, durable lining designed to withstand the high temperatures within the rotary kiln, as well as the constant abrasion from the material.

When it comes to refractory, the more dense it is, the less insulating capabilities it has. This means that even though there may be a working layer in place, the heat can easily pass through it to the shell of the rotary kiln. For this reason, an insulating layer is needed beneath the working layer. The insulating layer serves as insulation to protect the shell of the rotary kiln so the high temperatures within cannot reach the shell and damage it.

Typically the working layer and the insulating layer are made of the same material (ie. brick or castable), with varying chemistries. The working layer tends to be a higher density, strongermaterial that is more conductive. The insulating layer does not need these qualities, and tends to be softer, lighter, and less conductive, therefore more insulating. These two layers often vary in thicknesses, determined by the needs of the rotary kiln and what material is being processed. In some cases, such as when temperatures are fairly low, or when efficiency is not a concern, a single working layer may be all that is needed.

In contrast, when insulation is extremely critical, an optional third layer of ceramic fiber backing may be used. This thin, but very efficient layer is similar to fiberglass insulation found in a house, but it is much more compressed. The decision to employ this layer comes with some responsibility. Should a crack in the refractory occur and go unnoticed, it is possible for the high heat inside the rotary kiln to reach this backing and burn it up. This would create a gap between the refractory and the shell of the rotary kiln, which would cause disastrous problems. Due to this potential of increased risk, this third layer is not always appropriate.

The processing environment within a direct-fired rotary kiln can be harsh. The combination of constant rotation, extreme temperatures, heavy loads, and abrasive and corrosive environments, has the potential to cause significant damage or catastrophic failure to a kilns shell. Once your rotary kiln refractory is installed and in use, it is important to take the extra steps to ensure it is properly maintained.

A well-installed, high quality refractory can have a lifespan of many years, but there are factors that can cut refractory life short. While early signs of refractory failure can be hard to spot, the good news is, many of the things that can cause refractory failure are preventable. The two primary causes of refractory failure are cycling and chemical incompatibility.

The biggest source of refractory failure is what is called cycling. Cycling is simply the heating up and cooling down of the rotary kiln. Each time the rotary kiln is heated, the refractory expands with the drum, and as the kiln is cooled, the refractory retracts. If a kiln is constantly being turned on and shut down, the refractory can easily become stressed, resulting in cracks.

Similarly, cracks can also occur from heating or cooling the kiln too quickly. To maximize refractory life, it is important to try to reduce cycling as much as possible, keeping shut downs to a minimum.

Chlorides can aggressively attack refractory, causing excessive wear because of their corrosive nature. When these chemicals are identified up front, refractory can be designed with this in mind to help reduce the potential for excessive wear. Similarly, unknown components in a material or a change in feedstock can also result in excessive wear on refractory.

Operators should be well-versed in the proper operation of the kiln and what to look for to spot potential problems. Operators and maintenance personnel should always follow the guidelines for safety and maintenance set forth by the original equipment manufacturer.

Regularly observing the kiln to check for any visual, auditory, or other abnormalities can mean the difference between a small repair and a catastrophic failure. As part of routine observations on the unit, the kiln shell should be regularly measured with a temperature gun to check for hot spots.

This can be done by picking a spot on the rotary kiln shell, and holding a temperature gun in place. As the rotary kiln rotates, that spot should read the same temperature for the entire circumference of the shell. For example, a temperature reading of 400, 400, 700, 400 would likely indicate a failure in refractory. Left untreated, this could lead to severe damage to the rotary kiln shell.

In addition to circumference temperature being the same in a given location, there should be a gradual shift in temperatures from one end of the kiln to the other, not a drastic change. Catching these problems early is important to minimizing the potential for damage.

Additionally, having a service technician visit the site to observe and inspect the kiln every so often is also considered best practice in preventative maintenance. Depending on what the original equipment manufacturer recommends, this is generally on an annual basis, but may be more frequent for especially demanding settings.

Refractory failure can have disastrous results. Even a small crack can allow heat to reach the rotary kiln shell. It is important to routinely temp gun the exterior of the rotary kiln shell, ensuring that the temperature is consistent for the entire circumference of the drum.

Refractory is a critical component in the design of a direct-fired rotary kiln, helping to protect the kiln shell from the harsh processing environment within. A customizable part of kiln design, refractory can be engineered to suit the unique needs of an application, with factors such as material and multiple layers coming into play.

As the only barrier between the shell and the kiln interior, protecting and maintaining refractory is of the utmost importance in order to prolong the life of the equipment and avoid potential catastrophic failures.

kiln vs flash calciner

kiln vs flash calciner

TK: The ability to recover lithium from spodumene concentrate begins with the process of converting alpha spodumene to beta spodumene in the calcining equipment. This process unlocks the lithium contained within the spodumene concentrate, making it available for extraction after the subsequent acid roasting process (which produces water soluble lithium sulfate). Without proper conversion, the lithium remains entrapped within the structure of the spodumene.

The alpha to beta conversion generally takes place around 1075 C with minor variation depending on the raw material. This conversion temperature can be achieved both in a rotary kiln system and in a gas suspension calciner but the key in either case is the finite control of that temperature in the calcining system and control of the time at the conversion temperature.

The other key is to apply the correct technology based on the particle size distribution of the spodumene concentrate. Both technologies will work when properly designed and controlled, and in that case, we have demonstrated consistently high conversions typically 95% to 99%.

TK: Both the rotary kiln approach and the suspension calciner effectively convert spodumene. The primary consideration of which approach is best is the concentrate particle size distribution (PSD). Concentrate produced via dense media separation (DMS) often results in feed size from 3mm to as large as 12mm or sometimes larger. This PSD is too large for a suspension calciner and so the rotary kiln system is better suited for these concentrates. Although it is possible that, even with the appropriate PSD, some concentrates may contain contaminant minerals or have other properties that result in flowability issues or that otherwise prevent full alpha to beta conversion, in which case, a kiln can still be used. The kiln system provides the gradual heating and extended retention time (normally ~30 minutes) needed to effect the conversion on large particles.

Conversely, a gas suspension calciner (GSC) is best suited for spodumene concentrate that has a PSD less than 1mm, which is common for concentrates produced via the floatation process. As the feed size is very small, it takes very little time to heat the sub 1mm particles to conversion temperature and once temperature is reached, the conversion happens almost immediately. Therefore, unlike the rotary kiln process, the retention time of the material in the GSC is only a matter of seconds and yet the conversion is achieved just the same.

TK: For those concentrates with significant fraction less than 1mm and also a significant fraction above 1mm, we can look at several different approaches. One approach is to screen the concentrate and then grind the +1mm fraction to less than 1mm and utilise a gas suspension calciner. This involves a grinding step at the beginning of the process but allows for the most efficient thermal conversion.

Alternatively, we can design a rotary kiln type system without any pregrinding in a configuration suitable for processing the feed containing both coarse and fine particles. This is done by altering kiln size to lower gas velocities, altering preheater cyclones for increased efficiency and other steps to prevent excessive dust losses and recirculating loads. It then becomes a matter of determining which approach is the most efficient in terms of CAPEX and OPEX, and reaching a consensus with the customer.

TK: For customers dealing specifically with fine ores, we designed the Gas Suspension Calciner (GSC) technology something we have supplied since the beginning of the 1970s. It consists of a series of preheating cyclones, a calciner vessel and a series of cooling cyclones.

Hot air is introduced into the system via an external air heater. The raw feed is introduced at the top stage preheat cyclone, entrained in the hot gases, and carried through subsequent preheat cyclones after which it enters the calciner vessel for final conversion. Additional fuel is directly injected in the calciner vessel to complete the conversion in seconds.

The turbulent swirling mixture of combustion gases, fuel and material produces a highly uniform temperature profile throughout the calciner. Processed ore and gas continues on to several cooling cyclones after which the ore reports to a fluid bed cooler for final temperature control and dust reports to the main baghouse after which it is recovered and put back in the process.

The number of stages in the system is custom designed based on the materials being processed by the customer, as well as process requirements, thermal and system efficiency optimisation and capacity. The key advantages of the GSC (relative to a rotary kiln) are very low specific energy consumption due to full heat recovery, limited maintenance due to no moving parts, small footprint, and low energy consumption.

TK: Having provided well over 6,000 rotary kilns in our history, FLSmidth has a solid claim to be the world leader and for spodumene conversion, our tried and tested approach is one where we integrate two to three stages of preheat cyclones ahead of the rotary kiln inlet, a rotary kiln, followed by a rotary cooler.

The wet spodumene concentrate (normally ~6% moisture) is fed into the top stage cyclone where it is dried after which it passes through the other cyclone(s) and is preheated prior to entering the rotary kiln. In this way, we recover the heat from the hot kiln gas and reduce the size of the kiln. The preheated spodumene then enters the kiln where the temperature gradually increases to the conversion temperature.

Once converted, the hot beta spodumene then discharges into a rotary cooler where the temperature is reduced via a combination of direct and indirect water cooling. It is then discharged and sent to the next step in the process. The rotary kiln system is well suited for converting larger particle sizes and the integration of the cyclone preheater greatly improves specific energy consumption over just a straight kiln. It also reduces the size of the kiln and makes treatment of off gases very simple because the heat is removed prior to treatment.

TK: While there can be some variation, the most common subsequent step in the process is a step called acid roasting, in which the beta spodumene is mixed with concentrated sulfuric acid, roasted in an indirect fired kiln and converted into water soluble lithium sulfate.

Following acid roasting, FLSmidth Hydromet take over the process, which involves impurity removal and extraction. FLSmidth Pyromet offers the complete pyroprocessing system. Downstream of the calcined spodumene cooling equipment, we can provide a ball mill system to prepare the beta spodumene for acid roasting, Pneumatic Transport systems to transfer the beta spodumene, mixing equipment to combine it with the acid and the indirect fired acid roaster unit for the conversion to lithium sulfate, the rotary cooler and all necessary gas treatment equipment.

FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.

rotary kiln design: direct fired vs. indirect fired

rotary kiln design: direct fired vs. indirect fired

When designing a thermal processing operation, confusion often results on whether a direct-fired or indirect-fired kiln is the better option. And while there can be some overlap in applications, in general, each type of kiln is better suited for different processes. Below is a brief overview on these two types of kilns.

Direct-fired rotary kilns rely on direct contact between the process gas and the material in order to heat the material to the specified temperature. Direct-fired kilns can be either of the co-current design, or counter current design, referring to the direction that the process gas flows through the drum in relation to the material.

Direct-fired rotary kilns are most often the equipment of choice in thermal processing, because they are more efficient than their indirect counterparts. There can be disadvantages to a direct-fired kiln, however. For example, because a process gas is used to treat the material, direct-fired kilns subsequently produce more off-gases that will require treatment.

Additionally, some materials must be processed in an inert environment, so as not to be exposed to oxygen or nitrogen. In applications such as this, a direct-fired kiln would not be an option. Materials that are commonly processed in a direct-fired kiln include:

Conversely, indirect-fired kilns, sometimes called calciners, can process material in an inert environment, where the material never comes into contact with the process gas. Here, the kiln is heated from the outside, using a heat shroud, and the material is heated via contact with the hot kiln shell. While this method is significantly less efficient than a direct-fired kiln, it is necessary in some processes that require a more tightly controlled environment. This might include instances where an undesirable oxide compound will form in the presence of oxygen at high temperatures. Similarly, some materials may form an undesirable compound with nitrogen at high temperatures. In situations such as these, the use of an indirect-fired kiln provides the necessary inert environment for effective processing.

Indirect kilns also allow for precise temperature control along the length of the kiln. This is advantageous in settings where a material will need to be brought up to temperature, and then held there for a specific amount of time as it moves through the kiln.

Indirect-fired rotary kilns can also be beneficial when the material to be processed consists of finely divided solids. In a direct-fired rotary kiln, the heat source is hot gas (products of combustion and air), which flows with an inherent velocity. These gases can carry particles through form drag. The degree of entrainment depends on a variety of factors, such as gas velocity, gas density, particle density, and shape. Due to entrainment potential, direct-fired rotary kilns processing fine materials require the design to be centered on permissible gas velocities as opposed to heat transfer requirements. Examples of materials commonly processed in an indirect-fired kiln include filter cakes, carbon black, chemical precipitates, and other finely ground solids.

Because the heat is being transferred through the shell, an indirect rotary kiln is not lined, in order to maximize the heat transfer through the shell. Therefore, an indirect rotary kiln is usually made out of a more temperature-resistant alloy, instead of carbon steel.

While direct-fired kilns offer maximum efficiency, they are not always appropriate for the intended process. In settings such as these, an indirect-fired kiln would offer the best processing solution. In some process situations, a combination of a direct and indirect rotary kiln is required; the direct-fired rotary kiln is used to burn off the organic fraction of the material being processed, and further polishing of the resultant ash material is conducted in a specialty indirect kiln.

FEECO is a leading provider of both direct- and indirect-fired rotary kilns. Our rotary kilns are engineered around the material to be processed in order to produce the optimal thermal processing environment for the objective. For more information on our custom rotary kilns, contact us today!

rotary kiln,lime rotary kiln,clinker rotary kiln,indirect fired rotary kiln,limestone rotary kiln - hongxing crusher machinery

rotary kiln,lime rotary kiln,clinker rotary kiln,indirect fired rotary kiln,limestone rotary kiln - hongxing crusher machinery

A rotary kiln is a device that supplies tremendous amounts of heat in order to change the chemical composition of an object. It is made up of a strong reinforced steel outer shell that is coated with a heat-resistant inner lining, support rollers and a drive gear to keep the contents in a continuous rotating motion and internal heat exchangers capable of producing temperatures well over 2732 degrees Fahrenheit (1500 degrees Celsius).

Perhaps one of the most common uses for this technology is the creation of a rotary cement kiln, which grinds limestone, clay, and shale down to small bits of rock and transforms them into a usable cement mixture that is ready to be either packaged or immediately used.

Our rotary kiln system is developed with the most advanced hydraulic gear wheel device, the metering piston pump of high precision, the high precision control valve and contact graphite block sealing devices and other advanced technologies. Compared with the equipment with the same specification, Hongxing rotary kiln can stabilize the thermal system program and improve the equipment operation rate, with the operation rate increased by 10%, the yield increased by 5% -10% and heat consumption reduced by 15%.

a lime rotary kiln to build your lime calcinating plant

a lime rotary kiln to build your lime calcinating plant

Lime rotary kiln is also called roller rotary kiln. To make sure its air leakage coefficient is less than 10 percent, lime rotary kiln adopts advanced structure and reliable combined scale-like seal in both ends. It also uses composite refractory to reduce the loss of heat radiation.

Lime rotary kilns whole process is well-regulated. The limestone is stored in a silo. Then be carried in preheaters top silo by hoist. There are two-level gauges in silo to control the feed amount. They distribute limestone evenly into different preheaters rooms through feed pipe.

Limestone is decomposed 30% when it is heated to 900 by hot smoke at 1150 . After being pushed into the kiln by a hydraulic push rod, lime is resolved into CaO and CO2. Then be cooled down to 100 by cold air in cooler and then be discharged.

After successively through vibrating feeder, chain bucket conveyor, bucket elevator and tape conveyor, lime eventually is sent into lime finished product library. Then the clients decide whether screening is needed.

Lime rotary kiln has a reliable combined scale-like seal. The scale-like seal in both ends guarantees its air leakage coefficient is less than 10 percent. It also uses composite refractory to reduce the loss of heat radiation.

Lime rotary kiln has a vertical cooler. The filled cooler with dividable ventilation cools down the lime into 80 making it easier to be transported and stored. And it can preheat the secondary kiln air up to more than 700, which reduces the need for moving parts and special materials.

3. Pay attention to the details of the lime rotary kiln below. The gradient of preheater and precalciner should be 3.5%-4%. Precalciners maximum speed should be 3.0-3.5r/min while preheaters should be 2.0-2.5r/min. The speed range should be 1:10.

indirect fired rotary kiln applications part 1

indirect fired rotary kiln applications part 1

In the thermal processing industry, rotary kilns are used to cause chemical reactions or state changes in varying materials. As discussed previously in Direct Fired Rotary Kilns vs. Indirect Fired Rotary Kilns: Whats the Difference, while direct fired rotary kilns and indirect fired rotary kilns use similar thermal processing principles, they are each beneficial in different applications. In this three part mini-series, we will look at some of the situations in which an indirect fired rotary kiln is a more efficient choice.

There is an array of applications in which a hazardous component may be absorbed on an inert solid substrate. An example of this is spent activated carbons, used to absorb an undesirable waste component from a liquid or gaseous stream. In such cases, the spent, or used up carbon can be activated for reuse through means of an indirect fired rotary kiln. The used up carbon can be held at high temperatures and the absorbed component will volatilize and effectively be desorbed from the carbon, making the carbon again ready to absorb a hazardous component.

Following desorption, the volatilized waste is then evacuated from the system via an imposed draft. This off-gas from the indirect fired rotary kiln would be laden with a hazardous waste component that could then be either condensed in high purity, or incinerated as a concentrated vapor stream. This operation of reactivating a solid substrate could be performed in a direct fired rotary kiln, but the off-gas burden would be significantly increased. Depending on the regulations placed on the volatilized compounds, the treatment of this off-gas could be quite costly.

Conversely, the goal of some processes is to recover a high value volatile component from a somewhat valueless solid carrier. As an example, consider the thermal separation of oil from oil shale. Such an application is likely best suited in an indirect fired rotary kiln. As in the case of combustible materials, a direct fired rotary kiln can be carefully designed to perform the separation, but the load on separation equipment, such as a condenser, becomes greatly increased by undesired tramp air. The cost associated with these ancillary separation devices can far exceed the cost of the heat transfer vessel. By processing such a material in an indirect fired rotary kiln, the desired volatile product is highly concentrated and does not burden the recovery equipment with needless tramp air.

Another highly promising application is in using an indirect fired rotary kiln to effectively distill valuable oils from low value wastes such as scrap tires, oil saturated soils, and oil drilling wastes (cuttings).

Other typical indirect fired rotary kiln applications include chemical laden soils, absorbents, tank wastes, and other inert substrates. As these examples indicate, there are countless applications wherein an indirect fired rotary kiln may result in a more cost effective system overall. The developer of a thermal process must take into account the cost of all required ancillaries, operating cost, product quality requirements, and several other variables as opposed to merely the cost of the primary heat transfer device. When evaluating an overall system approach, the designer must also take into account operating cost factors such as the cost of fuel, cooling water, power, instrument air, the air quality restrictions, and the cost of off-spec product.

indirect-fired rotary kiln design alpha thermal process

indirect-fired rotary kiln design alpha thermal process

Indirect-fired kilns are unusually important where direct-fired operation cannot be employed due to controlled heating, product contamination, etc. These challenges respond to niche applications of unusually high value.

In the forefront of the indirect-fired kiln offering is Harper International, a reliable AlphaThermal collaborator. We have been privileged in having a cordial working relationship with Harper in the area of indirect kiln design for several applications including Ni-Co processing in China, design of a nickel briquette in South Africa, reduction of copper oxide to elemental copper in Germany, molybdenum ore reduction kilns, and metal-alloy kilns in the US. A typical design approach for a recent job may be summarized as including the following:

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