Bauxite rotary kiln Introduction

The bauxite rotary kiln is a non-metallic mineral calcination equipment. The principle of bauxite plus limestone plus coal calcination is a relatively common aluminum extraction process. Its main advantage is that aluminum can be extracted from the ore, and the reaction is completed in a short time. In addition, this process can also calcinate impurities such as magnesium and iron in limestone together with bauxite to convert them into different compounds, so as to achieve the purpose of purification. During the operation of the bauxite rotary kiln, the slurry that has been homogenized to meet the is fed requirements into the kiln by the feeder at the kiln head to calcine the bauxite, and the fuel is injected from the kiln head and burned in the kiln, and the heat emitted is heated to the raw material. The raw material is calcined and finish product is discharged from the bottom of the kiln shell, enters the cooling machine, and is collected after cooling.

Bauxite rotary kiln structure

Rotary kiln thrust roller：The thrust roller is a critical part of the rotary kiln system. It serves the purpose of supporting the kiln's weight and maintaining its axial position, ensuring that the kiln remains properly aligned along its axis. The thrust roller is typically positioned on the downhill side of the kiln and is attached to the kiln shell, it consists of a central shaft or journal and a roller assembly.

Rotary kiln pinion: The pinion is an essential part of the rotary kiln drive system, responsible for transmitting rotational motion and torque from the driving mechanism to the rotary kiln itself. It consists of a gear wheel with teeth that mesh with the teeth of a larger gear, often referred to as the "girth gear" or "ring gear." The girth gear is attached to the outer shell of the rotary kiln. When the pinion is rotated by the drive system, it drives the girth gear, causing the rotary kiln to rotate.

Rotary kiln bearing housing: The bearing housing serves as the support structure for the kiln's rotating motion and is responsible for holding and guiding the kiln's trunnion bearings. Trunnion bearings are large, heavy-duty bearings that support the weight of the kiln and allow it to rotate smoothly. These bearings are subject to high loads, extreme temperatures, and potentially harsh environments due to the nature of the processes occurring inside the rotary kiln. The bearing housing provides a stable mounting point for the trunnion bearings and ensures proper alignment of the kiln's rotation. It is typically designed to accommodate the axial and radial forces generated during the rotation of the kiln.

Kiln Shell: The rotary kiln shell is a thick, steel cylindrical structure that provides the necessary strength and rigidity to withstand the high-temperature environment inside the kiln. It also serves as a containment vessel for the materials and gases during the manufacturing process. Inside the kiln shell is the refractory lining usually refractory bricks or sometimes refractory castable. Tongli kiln shell has good sealing performance, the edge of each shell is machined smoothly, enhance the sealing and service life of the rotary drum.

Kiln Hood Cover: The rotary kiln hood is located at the discharge end of the kiln and provides sealing to retain heat and gases. The rotary kiln operates under the negative pressure, therefore Tongli implied SS304 lining plate and ceramic felt both in the front and back end to prevent heat leakage.

Rotary Kiln Transmission device: The transmission device of the rotary kiln is mainly composed of main transmission, auxiliary transmission, mechanical thrust roller/hydraulic thrust roller, motor, gearbox and other components. The unique design of tongli transmission can greatly improve the service life and safety performance of the equipment.

PLC control system: A PLC is a digital computer-based system that is designed to control various industrial processes automatically. In the context of a rotary kiln, a PLC is used to monitor and control parameters such as temperature, rotation speed, air flow, fuel flow, and other critical variables that affect the performance of the kiln and the quality of the products being processed. Usually, the rotary kiln control system is integrated in the whole factory’s plc system, therefore we will provide the on-site cabin and a signal cable to the central plc.

Design principles of bauxite rotary kiln

The design principles of a bauxite rotary kiln involve various factors that ensure efficient and reliable operation while maximizing the production of alumina from bauxite ore. A rotary kiln is a large, cylindrical device used in various industrial processes like calcination, roasting, and sintering. When it comes to the design of a bauxite rotary kiln, several key principles should be considered:

Material Flow and Bed Movement: The bauxite ore is fed into the rotary kiln from one end, and it gradually moves along the length of the kiln due to the rotation. The design should ensure proper material flow and bed movement to facilitate even heat distribution and complete chemical reactions.

Heat Transfer: Efficient heat transfer is crucial for the chemical reactions that take place within the kiln. The kiln's design should optimize heat transfer mechanisms, including conduction, convection, and radiation, to ensure uniform heating of the bauxite and effective removal of moisture and volatile components.

Temperature Control: Precise temperature control is essential for the various stages of bauxite processing. The kiln design should incorporate mechanisms to monitor and control the temperature along the kiln's length, ensuring that the desired reactions occur at the appropriate temperatures.

Refractory Lining: The inside of the rotary kiln is lined with refractory materials that can withstand high temperatures and chemical reactions. The design should consider the selection of suitable refractory materials, their arrangement, and installation techniques to ensure a durable and efficient lining.

Gas Flow and Combustion: In some cases, rotary kilns are used in conjunction with combustion systems to provide the necessary heat for the processes. The design should ensure proper gas flow patterns and combustion control to achieve the desired temperature profiles and avoid hotspots.

Waste Gas Management: The design should incorporate systems for treating and managing waste gases generated during the process. This could involve dust collection, gas cleaning, and potential heat recovery to enhance energy efficiency.

Mechanical Integrity: The rotary kiln's structural design should account for mechanical stresses, thermal expansion, and other operational factors to ensure its long-term integrity and prevent deformations or failures.

Instrumentation and Monitoring: The kiln design should include provisions for instrumentation and monitoring devices to gather real-time data on temperature, gas composition, pressure, and other relevant parameters. This data can be used for process optimization and troubleshooting.

Specifications of bauxite rotary kiln

Note: *The diameter is the inner diameter, Weight excludes refractory material.

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Industry Knowledge extension

What is the application of calcined bauxite?

Calcined bauxite, also known as rotary kiln bauxite or refractory bauxite, is a high-temperature processed form of bauxite ore. It is used in various industries due to its excellent refractory and abrasive properties.

Refractory Bricks: Calcined bauxite is a key component in the production of refractory bricks used in the lining of high-temperature industrial furnaces, such as those used in steel, cement, glass, and non-ferrous metal industries. Its high heat resistance and ability to withstand thermal shock make it suitable for these applications.

High-Alumina Refractory Cement: Calcined bauxite is used as a raw material in the production of high-alumina cement, which is used for various refractory applications, including in the construction of refractory linings and repair materials.

Abrasive Materials: Calcined bauxite is used as an abrasive material in the production of sandpapers, grinding wheels, and polishing compounds. Its hardness and durability make it effective for surface finishing and material removal.

Insulating Firebricks: Calcined bauxite is incorporated into insulating firebricks used in applications requiring high-temperature insulation, such as in kiln linings and industrial furnaces.

Ceramic Products: Calcined bauxite is used as an ingredient in the production of ceramic and pottery products, where its high alumina content contributes to the strength and durability of the final products.

Welding Fluxes: Calcined bauxite can be used in welding fluxes to improve the performance of the flux and the quality of the weld.

Foundry Sand: Calcined bauxite is used as a molding sand in foundry applications, particularly in metal casting.

Highway and Road Surfacing: In some cases, calcined bauxite aggregates are used in road construction to create high-friction, skid-resistant road surfaces, especially on roadways with steep grades or in wet conditions.

Sports Courts and Tracks: Calcined bauxite is used as an aggregate in the construction of sports surfaces, such as tennis courts and running tracks, to provide good traction and durability.

Anti-Skid Coatings: Calcined bauxite is used in anti-skid coatings for walkways, ramps, and industrial flooring to improve traction and safety.

What is the difference between rotary kiln and vertical roller mill?

The rotary kiln and vertical roller mill are both essential pieces of equipment in the cement manufacturing process, but they serve different purposes and are used at different stages of the process.

The rotary kiln is a large cylindrical vessel used for calcining raw materials at high temperatures. It's a core component of the cement manufacturing process and is responsible for transforming raw materials, particularly limestone and clay, into clinker. In the rotary kiln, the raw materials are heated to temperatures exceeding 1400°C (2552°F), where chemical reactions occur that result in the formation of clinker nodules. And they need to be ground into a fine powder to produce cement. This final grinding process is often performed using a vertical roller mill. The clinker is mixed with gypsum and possibly other additives to create the final cement product.

Vertical Roller Mill (VRM): The vertical roller mill is a grinding machine that grinds materials into fine powders, after the raw material is crushed by the crusher, it enters the vertical roller mill. It is typically used for grinding raw materials, clinker, and additives in the cement manufacturing process. The VRM operates by applying hydraulic pressure and vertical force to the grinding rollers, which then grind the materials between the rollers and the grinding table. This grinding process results in a fine powder that is later used as a key ingredient in the production of cement which is important for the subsequent chemical reactions in the rotary kiln.