Active lime rotary kiln Introduction

Active lime rotary kiln is a special equipment for calcining active lime. Slaked lime with high activity is widely used in the field of metallurgy. Active lime has small volume, low density, large porosity, large specific surface area, and high chemical purity. It can shorten the oxygen blowing time, increase the yield of molten steel, improve the effect of desulfurization and dephosphorization, and significantly improve the efficiency of molten steel quality. During the operation of the active lime 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 lime, 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.

Active lime 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 active lime rotary kiln

Thermal Efficiency: The kiln design should aim for high thermal efficiency to maximize the conversion of limestone into quicklime. Efficient heat transfer mechanisms, such as conduction, convection, and radiation, should be optimized to ensure proper temperature distribution along the length of the kiln.

Counter-Current Flow: Active lime rotary kilns typically operate in a counter-current flow configuration. This means that the limestone feed moves in the opposite direction to the hot combustion gases. This design enhances heat transfer efficiency and minimizes heat losses.

Proper Sizing: The kiln's dimensions, including length and diameter, should be appropriately sized based on factors such as limestone feed rate, desired production capacity, and residence time of the material within the kiln. Proper sizing ensures consistent and thorough calcination.

Refractory Lining: The interior of the kiln should be lined with high-quality refractory materials to withstand the high temperatures and corrosive environment. The refractory lining also helps to reflect heat back into the kiln, improving energy efficiency.

Burner Design: The burner system is responsible for introducing fuel and combustion air into the kiln. An efficient burner design is crucial for maintaining the required temperature profile along the kiln length. It should promote complete combustion while minimizing emissions.

Kiln Inclination and Rotation: The kiln is inclined slightly from the horizontal and rotated slowly. The inclination aids in the movement of limestone material along the length of the kiln by gravity, and the rotation ensures even exposure to heat.

Material Movement and Residence Time: The design should facilitate the smooth movement of limestone through the kiln. The residence time of limestone within the kiln needs to be controlled to ensure thorough calcination without over-burning or under-burning.

Cooling Zone: A cooling zone, often located at the discharge end of the kiln, allows the quicklime to cool before it is handled further downstream. This helps prevent thermal damage to downstream equipment and ensures safe handling of the hot product.

Dust and Gas Handling: Adequate systems for dust collection and gas handling are essential to maintain environmental compliance and protect the health of workers. Particulate matter and emissions should be properly controlled.

Automation and Control: Modern active lime rotary kilns often incorporate advanced automation and control systems to monitor and regulate key parameters such as temperature, feed rate, and fuel consumption. This ensures consistent product quality and efficient operation.

Safety Considerations: Design principles should prioritize the safety of personnel and equipment. Adequate safety features, emergency shutdown systems, and proper ventilation are crucial aspects of the design.

Environmental Impact: Consideration should be given to minimizing the environmental impact of the kiln's operation. This includes optimizing fuel usage, controlling emissions, and adhering to relevant environmental regulations.

Specifications of active lime 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 active lime?

Steel Desulfurization: Active lime is used as a fluxing agent in steelmaking to remove impurities, especially sulfur, from molten iron. It reacts with sulfur to form calcium sulfide, which is then easily removed from the molten metal.

PH Adjustment: Active lime is added to water and wastewater treatment systems to adjust pH levels. It can neutralize acidic or alkaline conditions and help precipitate impurities.

Stabilization of Soil: Active lime can be added to soil to stabilize it and improve its load-bearing capacity, particularly in road construction and embankment projects.

Production of Lime Mortar: Lime mortar, made by mixing active lime with sand, is used for masonry work in historic buildings and restoration projects.

Production of Calcium Hydroxide: Active lime reacts with water to produce calcium hydroxide (slaked lime), which is used in various chemical processes and applications, including in the production of chemicals and as a flocculant in water treatment.

Clarification of Juice: Active lime is used in the sugar industry to clarify sugar cane juice by reacting with impurities and forming insoluble particles that can be separated.

Production of Bleaching Powder: Active lime is used to produce bleaching powder, which is used as a bleaching agent in the paper and pulp industry.

Soil Amendment: Active lime is used to improve soil pH and fertility in agricultural fields. It reduces soil acidity and provides essential calcium to plants.

Gold Ore Processing: Active lime is used in gold ore processing to remove impurities and regulate pH levels during the cyanide leaching process.

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.