Fluidized bed dryer

Types of fluidized bed dryers

Fluidized bed dryers are commonly used in various industries, such as food, pharmaceuticals, chemicals, and material processing, for drying granular, powdery, and particulate materials. Here are some popular types of fluidized bed drying machines.

• Regular horizontal fluidized bed dryers

  The standard horizontal fluidized bed dryer consists of a rectangular/ square/ oval horizontal box, an air distributor at the bottom, a cyclone separator, and a bag filter. The air distributor at the base makes the airflow uniform. Materials are impacted and then spread by the upflowing hot air, which makes the particles undergo repeated immersion in the liquid layers and boiling phenomena. Water is removed from the materials through evaporation, and dried products are collected by a cyclone separator or a bag filter.

• Regular vertical fluidized bed dryers

  Regular vertical fluidized bed dryers are like horizontal ones, but the layout is vertical. Both top and bottom air distributors can be used to achieve uniform air distribution around materials. Well-distributed hot air makes materials move up and down in the equipment and fully contact each other, which improves drying efficiency.

• Nozzle fluidized bed dryers

  In nozzle fluidized bed dryers, the nozzles are used as air distributors at the base. They generate additional airflow and make the horizontally/ vertically placed items suitable for the overall equipment.

• Trailing edge slots fluidized bed dryers

  In the trailing edge slot design, a narrow gap forms between the trailing edge of the slot and the rectangular/ square gap. A gap like this provides a wide path for air to go through, which is suitable for bulky and dense material particles.

• Multi-nozzle fluidized bed dryers

  Multi-nozzle fluidized bed dryers employ different spray nozzle types to adapt to solid material classes and shapes. They can achieve uniform air distribution for improved drying efficiency.

• Rotating fluidized bed dryers

  Through the rotation of the beds, some inertia and centrifugal forces are generated. The position of the air distributor at the bottom also makes hot air and raw materials contact and mix, which can improve drying efficiency and make the final products’ qualities uniform.

• Spouted fluidized bed dryers

  In spouted fluidized bed dryers, hot air is spouted into the central tower, where damp solid materials circle and repeatedly rise and fall. The design is suitable for large-size solid material particles and provides a high-throughput processing capacity.

• Pneumatic conveying fluidized bed dryers

  This kind of equipment usually adopts an air-lift system or other means of transporting hot air to uplifts solid materials. It is suitable for handling a vast amount of materials.

Specifications & Maintenance of Fluidized Bed Dryers

Apart from the critical components mentioned above, some specifications affect the working capacity of these machines.

• Airflow Rate

  The air flow rate is the volume of air that moves through the fluidized bed, typically expressed in cubic meters per hour or CFM. This parameter is critical because it directly affects the degree of fluidization of the material. A proper airflow rate helps to achieve the fluidization of the material. Insufficient airflow may lead to poor fluidization, while excess air flow can cause excessive fluidization and even defluidization.

• Bed Height

  The bed height is the vertical distance of the fluidized bed, usually expressed in meters or feet. Bed height affects the residence time of materials and the degree of fluidization. Higher bed tends to extend the residence time, allowing more drying processes to occur. However, excessively high bed heights can result in greater pressure drops and lower operating efficiency.

• Temperature

  The temperature of fluidized bed drying is significant since it affects the drying rate as well as the physical and chemical properties of the materials. The temperature is usually expressed in Celsius or Fahrenheit. Higher temperatures tend to accelerate the evaporation of moisture and drying processes. Nevertheless, it is necessary to control the temperature within an appropriate range to avoid damaging the material and causing safety hazards.

• Pressure Drop

  The pressure drop across the fluidized bed refers to the difference in pressure between the inlet and outlet. It is usually expressed in Pascal or inches of water column. The pressure drop is related to factors and bed height such as the viscosity of the fluid, the particle size and the degree of fluidization. The pressure drop is monitored to ensure that the fluidized bed operates within an appropriate range to maintain its processing power and stability.

• Air Distribution System

  The air distribution system of a fluidized bed dryer plays a crucial role in evenly distributing the injected air. This system consists of components such as air tanks, vents, and distributors. It ensures that the particles receive the same amount of air pressure and flow rate, which contributes to consistent fluidization and drying results. Additionally, this system helps to control the pressure drop across the fluidized bed, thereby optimizing the operational efficiency of the equipment.

Maintaining a fluid bed dryer properly can ensure that it works effectively and has a longer life. Here are some maintenance tips for fluidized bed dryers:

• Regular cleaning

  Clean the dryer surface and interior regularly to prevent the accumulation of dust and debris that might obstruct its normal operation.

• Check for wear and tear

  Regularly inspect and replace damaged or worn parts, such as gaskets, seals, and valves, to prevent air leakage and ensure a stable and safe operation.

• Lubricate components

  Lubricate the adjustable components and transmission parts of the fluidized bed, such as bearings and transmission chains, as per the manufacturer's recommendations, to ensure smooth operation.

• Maintain appropriate bed height

  Fluidized beds have an optimal bed height range. Users should adjust and maintain the bed height according to the processing requirements to ensure a better fluidization effect and drying efficiency.