Lignite rotary dryer Introduction

Lignite rotary dryer is one of the dryer series produced by Zhejiang Tongli Heavy Machinery. This equipment is suitable for drying lignite, bituminous coal, briquette coal, anthracite, blue coal and other granular or paste-like materials. It has a unique drying effect especially for fly ash, blue coal, and lignite. This equipment is also called coal dryer or lignite dryer. This lignite drying equipment has advanced technology and unique performance. After the wet material is added to the dryer, it is evenly distributed and dispersed in the dryer under the agitation of the flights or lifting plates, and fully contacts with the hot air in parallel (countercurrent) flow, which accelerates the drying heat transfer and mass transfer. It is widely used in building materials, metallurgy, chemical industry, cement industry and so on.

Lignite rotary dryer structure

A lignite rotary dryer is a type of industrial dryer used to reduce the moisture content of lignite, a type of low-grade coal. Lignite, also known as brown coal, has a high moisture content and is considered one of the lowest quality coal types in terms of energy content and combustion efficiency. It is often used as a fuel in power plants, but its high moisture content makes it less efficient to burn directly.The lignite rotary dryer is designed to remove a significant portion of the moisture from lignite before it is used as a fuel. The process involves feeding the wet lignite into the rotary dryer, where it comes into contact with hot air or other heat sources. As the lignite tumbles through the dryer, the moisture in the coal evaporates, and the dried lignite is then collected at the discharge end of the dryer.The lignite rotary dryer is composed of, dryer shell, dryer riding ring, dryer girth gear, dryer transmission unit, dryer hood cover and so on.

Dryer Shell: The rotary dryer shell is the main body of the dryer, where the material is loaded and rotated. It has a cylindrical shape and is equipped with lifting plates or flights to lift and disperse the material. The drum is heated by hot air or gas that flows through it, either in parallel or countercurrent direction. The drum transfers heat to the material and evaporates the moisture.

Dryer Flights: Rotary dryer flights, also known as "flights" or "lifters," are the inclined, curved structures that are attached to the internal shell of a rotary dryer. A rotary dryer is a device used to remove moisture from materials like powders, granules, and bulk solids through the process of drying. It consists of a large cylindrical drum that rotates while the material is fed into one end and is discharged from the other end after being dried.

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

Dryer pinion: The pinion is an essential part of the rotary dryer drive system, responsible for transmitting rotational motion and torque from the driving mechanism to the rotary dryer 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 dryer. When the pinion is rotated by the drive system, it drives the girth gear, causing the rotary dryer to rotate.

Dryer bearing housing: The bearing housing serves as the support structure for the dryer's rotating motion and is responsible for holding and guiding the dryer's trunnion bearings. Trunnion bearings are large, heavy-duty bearings that support the weight of the dryer 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 dryer. The bearing housing provides a stable mounting point for the trunnion bearings and ensures proper alignment of the dryer's rotation. It is typically designed to accommodate the axial and radial forces generated during the rotation of the dryer.

Dryer Hood Cover: The rotary dryer hood is located at the discharge end of the kiln and provides sealing to retain heat and gases. The rotary dryer 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 dryer Transmission device: The transmission device of the rotary dryer 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 dryer, 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 dryer and the quality of the products being processed. Usually, the rotary dryer 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 lignite rotary dryer

The design principles of a lignite rotary dryer involve various considerations to ensure efficient and effective drying of lignite (a type of low-grade coal) while minimizing energy consumption and maximizing product quality.

Energy Efficiency: Lignite drying can be energy-intensive, so the design should focus on energy-efficient mechanisms such as heat recovery systems, insulation, and optimized burner designs.

Heat Transfer Efficiency: The primary purpose of a rotary dryer is to remove moisture from the lignite through heat transfer. Efficient heat transfer is achieved by maintaining good contact between the lignite particles and the hot drying medium (usually air or combustion gases). The design should ensure optimal mixing and dispersion of lignite within the dryer to maximize heat transfer efficiency.

Drying Medium Flow: Proper flow of the drying medium is crucial. The design should facilitate a consistent and controlled flow of hot air or combustion gases through the dryer to evenly distribute heat and moisture removal throughout the lignite bed.

Temperature Control: Careful temperature control is necessary to prevent over-drying or under-drying of lignite. The design should include mechanisms to monitor and adjust the drying temperature based on the moisture content of the lignite.

Retention Time: The time lignite spends in the rotary dryer, known as retention time, impacts the drying efficiency. Design considerations should ensure that the retention time is sufficient for moisture removal while avoiding overexposure that could lead to degradation of lignite quality.

Lignite Particle Size and Distribution: The size and distribution of lignite particles affect the drying process. The design should account for proper particle sizing to promote efficient heat transfer and prevent blockages or uneven drying.

Drying Drum Configuration: The drum's shape, size, and internal lifting arrangements influence the movement and behavior of lignite within the dryer. These factors impact drying uniformity and efficiency. The drum design should promote tumbling and cascading of lignite particles to expose them to the drying medium effectively.

Combustion System: The dryer uses combustion gases for heating, the combustion system design is crucial. Efficient combustion with proper air-to-fuel ratio and exhaust gas circulation helps maintain consistent drying temperatures and minimize emissions.

Moisture Control: Designing moisture monitoring and control systems allows for adjustments in the drying process based on real-time moisture content measurements. This helps optimize drying efficiency and lignite quality.

Safety Measures: Safety features should be incorporated into the design to prevent issues such as fires, explosions, or overheating. Proper ventilation, fire detection, and emergency shutdown systems are examples of safety measures.

Product Quality Preservation: The design should minimize the potential for lignite degradation or quality deterioration during the drying process, ensuring the resulting dried lignite meets the desired specifications.

Specifications of lignite rotary dryer

Note: *The initial moisture is assumed to be 2~6% and final moisture is 1~4%; Inlet temperature of hot air is 150~250 Celsius and outlet temperature is 70~90 Celsius; Production Capacity will vary according to the composition and moisture of the material.

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Industry Knowledge extension

What is the application of dried lignite? 

Dried lignite, also known as dried brown coal, has a variety of applications due to its relatively low moisture content compared to raw lignite. While lignite is generally considered to be a lower quality and less energy-dense coal compared to other coal types like bituminous or anthracite, the drying process can enhance its usability in certain contexts. Here are some potential applications of dried lignite:

Power Generation: Dried lignite can be used as a fuel for power generation in coal-fired power plants. The reduced moisture content improves its combustion efficiency and reduces greenhouse gas emissions compared to burning raw lignite. However, it's important to note that even dried lignite still has relatively high emissions compared to other, cleaner energy sources.

Industrial Processes: Dried lignite can be used in various industrial processes as a heat source. Its lower moisture content makes it more suitable for applications such as drying processes, cement manufacturing, and other heat-intensive operations.

Gasification: Dried lignite can be used as a feedstock in gasification processes, where it is converted into synthesis gas (syngas) that can be further processed to produce chemicals, fertilizers, and even liquid fuels like synthetic natural gas (SNG) or synthetic liquid fuels.

Domestic Heating: In regions where lignite is abundant, dried lignite can be used for residential heating purposes, although its use for this purpose is less common due to concerns about air pollution and emissions.

Activated Carbon Production: Lignite can also be converted into activated carbon through a series of processes. Activated carbon has numerous applications in water purification, air filtration, and even in some industrial processes.

Soil Amendment: Lignite can be used as a soil amendment or conditioner due to its organic content. When added to soil, it can improve soil structure, water retention, and nutrient-holding capacity.

Briquette Production: Dried lignite can be compressed into briquettes or pellets for more efficient storage, transportation, and combustion. These briquettes can be used for heating and power generation.

Chemical Industry: Certain chemical processes require coal as a feedstock, and dried lignite might find applications in these processes, particularly when other coal types are not readily available or economical.

What is the difference between rotary dryer and rotary kiln?

Rotary dryer: A rotary dryer is used to remove moisture from materials, such as minerals, ores, chemicals, food products, and biomass. The primary purpose of a rotary dryer is to reduce the moisture content of the material through the application of heat and the movement of the material within the drum. In a rotary dryer, materials are fed into the rotating drum, and hot gases or air are introduced to evaporate the moisture. The material is tumbled and agitated as it moves through the drum, allowing for efficient drying. Rotary dryers operate at elevated temperatures to facilitate drying, the temperatures used are generally lower compared to those in rotary kilns. Rotary dryers are used in industries such as agriculture, mining, chemicals, and food processing to remove moisture from bulk solids, powders, and other materials.

Rotary Kiln: A rotary kiln is designed for high-temperature processes, such as calcination, sintering, pyrolysis, and other thermal treatments. It's used to process raw materials or products at elevated temperatures, often in a controlled atmosphere, to bring about physical or chemical changes in the material. In a rotary kiln, materials are typically fed into one end of the kiln and gradually move towards the other end. The kiln is heated to very high temperatures, and the material undergoes chemical reactions, phase changes, or thermal treatments as it progresses through the kiln. Rotary kilns operate at much higher temperatures, often reaching well over 1000 degrees Celsius (1800 degrees Fahrenheit), depending on the specific process. These high temperatures are necessary to achieve the desired chemical or physical transformations in the material. Rotary kilns are used in industries such as cement production, lime calcination, metallurgy, and waste incineration. They are designed for processes that require high-temperature reactions, phase changes, or material transformation.