Rotary Kiln

What is a rotary kiln?

Rotary kiln is a kind of thermal processing equipment for drying, calcining, sintering and pyrolyzing raw materials or waste materials to reuse or reduce environmental pollution.

Rotary kilns have been applied in various industrial applications (such as oil shale dry distillation, tar sand coking, incineration, cement production, etc.).

Design and structures of rotary kiln

Main parts of rotary kiln

1.Kiln inlet head  2. Waste gas  3. Rotary kiln shell  4.Thrust roller Hydraulic system

Review of the rotary kiln structures

The structure rotary kiln is mainly composed of kiln shell, driving device, supporting device, catch wheel device, kiln head sealing device, kiln end sealing device, kiln head cover, etc.

Kiln shell

The rotary kiln shell is made of mild steel plates, and the longitudinal and circumferential gaps of the barrel are automatically welded.

As you can see, there are two solid tires on the shell to ensure the rigidity of the cross-section and reduce the force on the supporting devices.

Due to the distortion of the shell caused by thermal expansion, the installation of the two solid tires would solve that distortion problem when the rotary kiln runs.

Kiln shell is installed tilt in a few support wheels and covered several rectangle tires along the shell length direction. These tires bear weights of all rotary parts such as the machine body, material, kiln lining, and pass the weight to the supporting device.

Big ring gears

There are fixed large ring gears fixed on the kiln shell to torque.

Large ring gear connects with kiln shell by the tangential spring plate. The connection generates enough space between the big ring gears for heat dissipation, easing the deformation problem which would affect occlusion accuracy, playing an important role in cushioning shock, and extending the service life of the kiln lining.

Drive device

The Drive system has two types-single drive and dual drive and constituting a set or two sets drive system. Each drive system generally includes a primary drive system and an auxiliary drive system. The primary drive system consists of the main motor, main reducer, small gear, etc. The auxiliary drive system consists of an auxiliary motor, auxiliary speed reducer, etc.

Auxiliary motor electrical power comes from self-equipped power generators to ensure ordinary operation when the city power cuts and makes installation, maintenance, and refractory drying convenient. On the auxiliary motor, there is a brake to prevent the kiln reversal when the main motor accidentally stops.

Supporting device

The supporting device bears almost total weight of the machine, and it is used for positioning kiln and ensuring safe and stable operation. The supporting device consists of a support wheel bearing and welding seat base.

The support wheel sets in the large model generally include support wheel, support wheel axle, axle tile, spherical tile, and bearing seat. Each bearing seat is equipped with two thermal resistances inspecting respectively lubricants oil temperature and axle tile temperature.

Hydraulic catch wheel

According to the force condition and mode of action, the catch wheel can be divided into mechanical and hydraulic catch wheel. The large model of rotary kiln is equipped with a hydraulic catch wheel.

Hydraulic catch wheel mainly consists of catch wheel, catch wheel axle, bearing body, guide axle, ball bearing, catch wheel limit switch.

Hydraulic catch wheel withstands the sliding force of the rotary kiln, moving the kiln body upward, forcing the tire and kiln to make a reciprocating motion along the kiln center direction, and making tire and support wheel can evenly wear at full width.

Working principle of a rotary kiln

1. 1The raw materials are fed into the kiln body from the high end of the feeder.
2. 2Due to the inclined rotary kiln and slow rotation, the raw material rolls in the circumferential direction, moving along the axial direction from the high end to the low end.
3. 3The raw materials are preheated and calcined in the kiln.
4. 4The burned materials are discharged from the lower end of the kiln barrel to enter the next stage.

Rotary kiln works in two ways: direct calcination and indirect calcination.

Direct calcination refers to a single shell vessel with rings added inside to slow the catalytic velocity from the inlet towards the outlet. The oxidation medium reacts with the catalyst and flows countercurrent to catalyst movement.

The zone in the vessel located near the inlet may function as a stripper of volatile components of coke. The kiln is fired by gas burners directly against the outer shell.

By adjusting the burner heat and changing the concentration of O2 in the oxidizing medium, the temperature inside the rotary kiln can be controlled.

The indirect rotary kiln includes a double-shell cylinder vessel. The space in the shell body is heated either by combustion gas or steam. Sometimes the inner cylinder shell is ebullated, allowing hot gases or steam to enter and contact the tumbled catalyst. Monitoring the temperatures of the inlet and outlet gasses can control the catalyst temperatures.

What is a rotary kiln used for?

Calcination

It is the process of heating a material to a specific temperature for chemical dissociation. The method is widely used to calcinating limestone, dolomite for making hydrated lime or cement clinker.

Thermal Desorption

Thermal desorption adopts heat to drive off a volatile component. The most common rotary kiln used in this process is an indirect rotary kiln designed according to physical and chemical properties and calcination curve of raw materials.

The most important feature of the indirect rotary kiln is supplying the heat desorption, and the material has no contact with the flame.

Thermal desorption is the best way to process non-metallic minerals like Kaolin, agricultural waste, mineral coatings, and sewage sediments.

Organic combustion

When the waste material is bulky and difficult to handle, the organic combustion can turn the material into ashes which is much less in mass and volume than before. So, the organic combustion method allows the waste material to be deposited more efficiently in the landfill.

Fote rotary kiln vantages and wear parts design

Advantages of Fote rotary kilns

1. 1The kiln body uses three forms of heating: calcining, sintering, and pyrolyzing to make even heat distribution.
2. 2The equipment runs smoothly, and with a low failure rate and high operating rate.
3. 3Fote rotary kiln can ensure high production efficiency, large output, stable product quality, and excellent performance.
4. 4People can effectively and easily control the roasting process by manipulating the hydraulic push rod of the preheater in the lower part of the silo.
5. 5Fote rotary kiln with the auxiliary devices such as a high-efficiency heat exchanger, dust collector, and world-leading seal system can strictly meet the requirements of environmental protection.

Unique design of rotary kiln wear parts

Refractory lining

Refractory lining is crucial to prolong the longevity of the rotary kiln because the primary function is to prevent the whole body from corroding by the chemical reaction between high-temperature gas and the material.

The refractory as thermal media can absorb part of the heat and transfer the heat to the material by conduction and radiation. So, the refractory material is capable of protecting the whole machine through thermal insulation.

After the repeated tests by Fote experts, they found that:

1. 1Aluminum-silicon refractory bricks are suitable for cylinder, transmitter, and the entire pre-calciner kiln firing system.
2. 2On the upper transition zone near the firing zone, the refractory lining must withstand the flame temperature up to 20000°C and material temperature of 1350~1400°C.
3. 3In addition, the refractory lining also faces the challenge of corrosion caused by sulfur-alkali compounds and clinker liquid. Finally, they found that only alkaline refractory brick can meet the strict requirements.

Insulating refractory

The remarkable characteristics of insulating refractory material are high porosity, large diameter, thermal insulation, low volume density, and lightweight.

In addition, Fote equips a rotary kiln with an infrared scanner to warn of hot spots as early as possible and help to register whether the refractory material has failed.

The complete driving parts

The complete drive parts consist of the main drive and auxiliary drive. The main drive consists of drive reducing gear, open gearing, flexible coupling.

The auxiliary drive includes reducing gear, motor, and brake. It is used for preventing the kiln body from reversing under the weight of materials and kiln skin when the motor accidentally stops.

Fote company makes pinion gear experience a finner process and high-frequency quenching, strengthening the tooth hardness up to HRC(40-50), and finally prolonging the service life of the pinion by nearly five times.

How much is a rotary kiln system?

The final price of a rotary kiln depends on the production requirements. Fote rotary kiln manufacturer provides you with the most reasonable prices based on three different product ranges. Besides, all rotary kilns can also be customized based on customer-specific requirements.

Successful customers' cases

Indonesian customers purchased a cement rotary kilnYes! I'm interested.

Our Indonesia client Mr. Cokorda needs to process limestone with production 650 t/h. After the on-site survey and the customer’s output requirements, we recommend him a cement rotary kiln with a small diameter.

Diameter: Φ3.0×60

Preheater: Grate, Gas-Suspension

Heating types: direct rotary kiln

Heating method: counter current

Temperature range: 1050-1150℃

Pakistani customer purchased a metallurgical chemical rotary kiln

Another client is from Pakistan. He needs to iron ores with output requirement 1000t/h, so he wants to buy a metallurgical chemical kiln. We recommended him the middle-sized model Φ3.2×50.

The working principle of the rotary kiln is removing oxygen from the ore composition through carbon monoxide. Finally, this metallurgical chemical kiln ideally reduced and roasted of hematite-containing materials to produce magnetite.

Diameter: Φ3.2×50

Temperature range: 800-1200℃

Fuel: Crude gas

Coal ash melting point: > 1200°C,

Oxidation degree of crude gas: <15%,

Pressure: 0.1~4MPa

Fote rotary kiln price: Get Latest Price

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