Woodchip rotary dryer Introduction

Woodchip rotary dryer also known as sawdust rotary dryer is a special equipment designed and manufactured for drying wood chips, sawdust, wood powder and other materials. It has the characteristics of large drying output, remarkable energy saving effect and low maintenance. The main working principle is: the woodchip enters the woodchip rotary dryer and heated in the cylinder, through rotational motion and the hot air, the woodchip fully contacts with the material to complete the drying. Tongli dryer is manufactured with our patented inner structure design, which is more efficient than the traditional three-channel dryers.

Woodchip rotary dryer structure

A wood rotary dryer is a specialized industrial machine used to dry wood chips, sawdust, or other types of wood materials through the process of evaporation. It's commonly used in the wood processing industry to reduce the moisture content of wood products before they are further processed or used for various applications.The basic principle of a wood rotary dryer involves exposing the wood material to a stream of hot air while it is constantly tumbled or rotated within a drum or cylinder. The rotation helps to ensure even drying and prevents the wood from sticking together. As the wood material comes into contact with the hot air, the moisture within the wood evaporates and is carried away by the air, leaving behind dried wood with a lower moisture content.The sawdust 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 sawdust rotary dryer

The design principles of a sawdust rotary dryer involve various factors to ensure efficient and effective drying of sawdust while maintaining the overall safety and functionality of the equipment. 

Energy Efficiency: Aim to design a dryer that maximizes energy efficiency. This includes insulation to reduce heat loss, using waste heat when possible, and optimizing heat recovery systems.

Drum Design: The drum is a key component in the rotary dryer. Its shape, size, and material play a critical role in the drying process. A larger drum provides more residence time for sawdust, but it may also require more energy. The drum should be designed to facilitate uniform drying and minimize heat loss.

Airflow and Ventilation: Proper airflow distribution is essential to ensure even drying. The design of the air distribution system, including fans and ductwork, should consider factors such as air velocity, direction, and control to maintain consistent drying conditions throughout the drum.

Lifting Flights: Inside the drum, lifting flights or fins are used to lift and cascade the sawdust through the hot air stream. The design of these flights impacts the efficiency of the drying process. Properly designed flights enhance heat and mass transfer by creating a tumbling motion that exposes more surface area of the sawdust to the hot air.

Heat Source: The choice of heat source is crucial. Common options include direct combustion (using gas, oil, or biomass), indirect heat transfer through steam or thermal fluid, or waste heat utilization. The heat source needs to provide sufficient heat energy for drying while minimizing environmental impact.

Moisture Control: Implementing moisture sensors and control systems can help regulate the drying process. These systems monitor the moisture content of the sawdust and adjust drying parameters (such as temperature and airflow) accordingly to achieve the desired moisture level.

Safety Considerations: Safety should be a priority in the design. Implement mechanisms to prevent overheating, fire hazards, and dust explosions. Adequate ventilation and dust collection systems are essential to maintain a safe working environment.

Specifications of wood 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.

HIGH-TECH ENTERPRISES

Modern intelligent processing base integrating R&D, production and sales.

Zhejiang Tongli Heavy Machinery Manufacturing Co., Ltd (Formerly known as Tongxiang Coal&Mining Machinery Factory) established in year 1958 is a member of the Chinese National Building Material Machinery Association. Tongli is on the vendor list of designated production enterprise of the Ministry of Coal Industry. ISO9001、ISO14001、ISO45001 certified, accredited as High-tech & new technology enterprise of Zhejiang Province. With 65+ years of experience, Tongli has earned first class R&D and manufacturing capabilities, dedicated to provide satisfactory manufacturing equipments for global customers.   

Industry Knowledge extension

What is the application of dried woodchip/sawdust? 

Dried sawdust has a variety of applications across different industries and domains due to its unique properties. Here are some common applications:

Fuel: Dried sawdust can be used as a biomass fuel for heating purposes. It can be burned in furnaces, stoves, or biomass boilers to generate heat and energy.

Animal Bedding: Sawdust can be used as bedding material for animals in agricultural settings. It provides a comfortable and absorbent surface for animals to rest on and helps control odor and moisture.

Composting: Sawdust can be added to compost piles to enhance the composting process. It helps maintain proper aeration and moisture levels, which are crucial for efficient decomposition.

Mulching: Sawdust can be used as a mulching material in gardening and landscaping. It helps retain soil moisture, suppress weed growth, and regulate soil temperature.

Woodworking Filler: Sawdust can be mixed with adhesive to create wood fillers. These fillers are used to repair small gaps, cracks, or imperfections in wooden surfaces.

Art and Craft: Sawdust can be used in various art and craft projects. It can be mixed with glue to create papier-mâché-like materials or used as texture in paintings.

Packaging Material: Sawdust can be used as a packaging material for fragile items. It provides cushioning and protection during shipping.

Wood Pellets: Dried and compressed sawdust can be used to create wood pellets, which are a form of biomass fuel. Wood pellets are commonly used in pellet stoves and boilers for heating.

Soil Amendment: In certain cases, sawdust can be used as a soil amendment to improve soil structure and drainage. However, it's important to consider the carbon-to-nitrogen ratio and potential nutrient deficiencies when using sawdust in this way.

Industrial Absorbent: Sawdust can be used as an absorbent material in industrial settings to clean up spills, particularly those involving liquids like oil, grease, or chemicals.

Particleboard and MDF: Sawdust is a common component in the manufacturing of particleboard and medium-density fiberboard (MDF). These engineered wood products use sawdust as a raw material mixed with adhesive to create panels and boards.

Incense Production: Sawdust can be used as a base material for making incense sticks, especially when mixed with aromatic resins and essential oils.

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.