What is the maximum particle size of powder processed by a vertical fluidized bed tube furnace?

The maximum particle size of powder processed by a vertical fluidized bed tube furnace usually does not exceed 8 millimeters, which needs to be determined comprehensively based on equipment structure, process requirements, and material characteristics. The following is a detailed analysis:

1. Equipment structure and operational limitations
The core structure of a vertical fluidized bed tube furnace, such as gas distribution plates and furnace size, directly affects the maximum particle size that can be processed. Taking a certain type of furnace tube as an example, its furnace diameter is 100 millimeters, and the furnace tube is embedded with microporous ceramic plates as gas distributors. If the particle size of the powder is too large (such as exceeding 8 millimeters), it may cause the following problems:
Gas distribution plate blockage: Large particles are prone to getting stuck in the pores of the ceramic plate, resulting in uneven gas flow field and local fluidization failure;
Decreased fluidization quality: Large particles settle too quickly in the bed, making it difficult to maintain a uniform suspension state and easily forming dead zones or channel flows;
Increased entrainment and wear: The friction between large particles and the inner wall of the furnace tube increases, which may damage the equipment and increase the exhaust gas treatment load.

2. Process requirements and particle size adaptability
Heat treatment process: If high-temperature sintering is required (such as 1600 ℃ silicon carbide preparation), excessive particle size can lead to uneven heat transfer, local overheating or undercooking;
Reaction kinetics: For gas-solid reactions (such as catalyst activation), the particle size needs to match the gas diffusion rate. For example, when the particle size is greater than 5 millimeters, the diffusion resistance of gas inside the particles significantly increases, and the reaction efficiency decreases;
Circulation and separation efficiency: If an external circulation system is used, large particles are prone to deposit in the cyclone separator or return valve, resulting in unstable operation of the system.

3. Material characteristics and particle size selection
Density and sphericity: For high-density particles (such as metal powders) or non spherical particles (such as flake graphite), the maximum particle size should be appropriately reduced. For example, particles with a density exceeding 3 grams per cubic centimeter are recommended to have a maximum particle size of no more than 5 millimeters;
Adhesion and static electricity: Materials that are prone to agglomeration (such as ultrafine nickel powder) need to be pre treated (such as adding anti-static agents) or reduced in particle size (such as controlling below 50 microns) to avoid fluidization failure;
Thermal stability: Materials that are prone to softening at high temperatures (such as biomass) need to have their particle size controlled to prevent melting and clumping. For example, wooden particles may soften above 500 ℃, and it is recommended that the maximum particle size should not exceed 3 millimeters.