Limestone rotary kiln Introduction

Limestone rotary kiln is a kind of calcination equipment for processing limestone. The most common use of limestone is the production of Portland cement. Limestone, as a main raw material in a cement plant, after being crushed by the crusher, it is mixed with clay and calcined in a limestone rotary kiln to produce cement clinker. Limestone is widely used in the building materials industry, and it can also be used as a raw material for calcium fertilizer to cover the performance of the soil. During the operation of the limestone rotary kiln, the material that has been homogenized to meet the is fed requirements into the kiln by the feeder at the kiln head to calcine the limestone, 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.

Limestone 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 limestone rotary kiln

Material Selection and Preprocessing: Choose high-quality refractory materials for the kiln lining to withstand the high temperatures and chemical reactions. Limestone is usually calcined (heated to drive off carbon dioxide) in the kiln, so it's essential to ensure that the kiln can handle the abrasive and reactive nature of limestone.

Kiln Length and Diameter: The dimensions of the kiln affect the retention time, heat transfer efficiency, and overall performance. Longer kilns provide more residence time for material processing, but they also require more energy to operate. The diameter of the kiln influences the heat distribution and material movement inside the kiln.

Kiln Inclination: The kiln is slightly inclined from the horizontal to allow material to move gradually from the feed end to the discharge end due to the rotation of the kiln. This inclination aids in maintaining a consistent residence time and optimizing the material flow.

Rotational Speed: The kiln's rotation speed affects the conveying of the material through the kiln and the heat transfer rate. Optimal rotational speed helps achieve efficient heat exchange and avoids material buildup along the kiln walls.

Heating Method: Limestone is calcined by raising its temperature to a specific range. The heating method can be direct or indirect. In direct heating, flames and hot gases pass through the kiln, while in indirect heating, the kiln is heated from the outside, and heat is transferred through the kiln's shell.

Airflow and Combustion: Proper airflow and combustion control are crucial for efficient heat transfer and calcination. Adequate oxygen supply and control of combustion gases help ensure complete calcination while minimizing energy waste.

Kiln Shell Design: The kiln shell should be designed to withstand thermal stresses and minimize heat loss. Insulation and refractory materials are used to prevent heat from escaping the system.

Cooling Zone: A cooling zone at the discharge end of the kiln helps to gradually cool down the processed material before it is removed from the kiln. This prevents thermal shock and preserves the quality of the calcined limestone.

Automation and Control: Incorporate advanced control systems to monitor and adjust the operating parameters of the kiln. This helps in maintaining consistent calcination and energy efficiency.

Environmental Considerations: Implement emission control systems to manage the release of pollutants and ensure compliance with environmental regulations. Limestone calcination can produce emissions like carbon dioxide and particulate matter, so designing with emission reduction in mind is important.

Maintenance Access: Design the kiln with adequate access points for maintenance and cleaning. Regular maintenance helps extend the kiln's lifespan and ensures continuous operation.

Safety Measures: Implement safety features to protect personnel and equipment from potential hazards associated with high temperatures, rotating machinery, and gas emissions.

Specifications of limestone 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 limstone powder? 

Limestone powder,also known as calcium carbonate powder, is a versatile material with various applications across different industries due to its unique properties.

Concrete Production: Limestone powder is often used as a partial replacement for cement in concrete. It contributes to improved workability, durability, and sulfate resistance. It can also reduce the heat of hydration and enhance long-term strength.

Mortar and Plaster: Limestone powder is used in mortar and plaster formulations to improve workability, adhesion, and setting time.

Tile Adhesives: It is added to tile adhesives to enhance their bonding strength and workability.

Stabilization of Soil: Limestone powder can be added to soil to stabilize it, improve load-bearing capacity, and reduce soil erosion.

Soil Amendment: Limestone powder is used as a soil conditioner to adjust pH levels in acidic soils. It improves soil structure, enhances nutrient availability, and promotes healthy plant growth.

Flue Gas Desulfurization (FGD): Limestone powder is used in FGD systems to remove sulfur dioxide (SO2) from flue gases generated by industrial processes and power plants. It reacts with SO2 to produce calcium sulfate, which can be further processed into gypsum.

Iron and Steel Production: Limestone powder is used as a flux in iron and steel production to remove impurities and facilitate the melting process.

Glass Manufacturing: It is used in glass manufacturing to control the melting temperature and improve the optical properties of glass.

Filler in Paints: Limestone powder is used as a filler in paints and coatings to improve opacity, gloss, and impact resistance.

Filler in Plastics and Rubber: Limestone powder can be used as a filler in plastics and rubber products to enhance strength, stiffness, and dimensional stability.

PH Adjustment: Limestone powder is used in water treatment to adjust pH levels and neutralize acidic water.

Calcium Supplement: Limestone powder is added to animal feed as a calcium supplement for livestock and poultry. It helps improve bone health and eggshell quality.

Filling Agent: Limestone powder is used as a filler in the paper and pulp industry to improve paper properties, such as brightness and opacity.

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.