Spray Granulation Fluid Bed Dryer

The spray fluid bed dryer is a fixed equipment, which is supported by legs. It mainly consists of the following parts.

1.Support Legs: The bottom support legs are made of welded channel steel and support the air chamber, fluidization section and separation section of the fluid bed dryer.

2.Air Inlet Chamber: It is a welded structure composed of plates and reinforcing ribs, which is divided into multiple air inlet chambers. It mainly plays the role of air intake and air equalization to ensure the normal fluidization of the fluid bed dryer and ensure that the cleaning water can be discharged in time during maintenance.

The air chamber is located at the bottom of the fluid bed dryer. Each air chamber is independently separated. The air inlet of the air chamber and the air supply pipes are connected by short pipes. There is an air regulating valve inside to distribute the air volume. During the working process, the drying air is transported to each air chamber by the drying blower through the branch pipes. At the same time, the air volume entering each air chamber can be adjusted by the air valve on each branch pipe, so that the fluid bed dryer can achieve the best working condition under different capacity. 

3.Air Distribution Plate: It adopts advanced air distribution structure, which can not only ensure normal fluidization, but also effectively prevent leakage, and is more conducive to large particle discharge.

The air distribution plate is an important component to ensure a good and stable fluidized state of the fluid bed dryer. In a fluid bed dryer, the performance of the air distribution plate should meet the following points:

• Has the effect of evenly distributing airflow with minimal pressure drop.

• Ensure that the fluid bed dryer has a good fluidized state and create a good gas-solid contact state near the air distribution plate.

• During the long-term operation of the fluid bed dryer, the air distribution plate will not be blocked and abraded, and has the function of discharging large particle material.

• During the operation of the fluid bed dryer, the air distribution plate must be able to withstand the stress caused by thermal expansion without high-temperature deformation.

  
  

  
  

  
  

4.Fluidization Section: It consists of fluidization box and atomizer. This structure mainly completes heat exchange and drying functions. The material exchanges heat with hot air, the steam generated by drying is taken away by the fluidizing air, and the finished product is discharged out of the dryer. This equipment is equipped with a sight glass structure, which can conveniently observe the fluidization state of the material in the fluid bed dryer and facilitate external adjustment. This equipment is equipped with a quick discharge port, which can facilitate the rapid discharge of material when abnormal conditions occur. The atomizer and spray gun adopt a structure that is easy to disassemble and can be quickly and conveniently inspected. The scientific and reasonable frame structure of the entire fluidization section ensures the normal operation of the equipment with load. In addition, this equipment is equipped with several temperature measurement points, which can facilitate temperature measurement and judge the operating status of the equipment.

5.Separation Section: It is a welded structure composed of plates and reinforcing ribs. This structure mainly completes the separation and discharge of the moisture-carrying air after the material is dried; at the same time, most of the dust automatically falls by gravity, reducing the dust content in the outlet air. This equipment is equipped with a manhole to facilitate internal maintenance of the fluid bed dryer.

The fluid bed granulation works on the theoretical basis of the synthetic process of gas-solid two-phase hydrodynamics, liquid spray, droplet evaporation, crystallization or chemical reaction kinetics. During granulation of fluid bed dryer, the particles have two ways for growth: one is coating growth; the other is agglomeration growth. The coating growth method is to repeatedly coat around the master batch by spraying liquid, with crystal nucleus as the center, and the particles growing larger after drying. The final particles use the original particles as the elementary particle, similar to the original particles in shape, solid spherical, with high particle density and mechanical strength. Agglomeration growth occurs because droplets are sprayed onto the surface of particles, and the sensible heat of the hot air and particles themselves is insufficient to enable quick evaporation and drying of moisture in the coating material. At this point, multiple particles are bonded due to the mixing of bed particles, and agglomerated into particles of larger size. According to the agglomeration granulation mechanism, the number of bed particles will be significantly reduced, and these particles often present amorphous, seeing lower particle density and mechanical strength.

The particle growth in fluid bed dryer mainly goes through the following processes:

• Droplets adhered to the surface of larger particles (coating)

• Droplets wrapped on the surface of smaller particles (coating)

• Droplet adhered with agglutination fine powder (agglutination)

• Instantaneous drying of droplets into seed crystals

1.High-efficiency mass and heat transfer characteristics: the gas-solid phases in the fluid bed dryer are intensively mixed to form uniform temperature field and concentration field. There is large contact area between spray droplets and hot gas flow or solid particles, and the heat and mass transfer efficiency is 30% - 50% higher than that of traditional drying equipment (such as box drying);

2.Multi-functional integration: all the process such as spraying - drying - granulation - coating can be accomplished within the same device;

3.Uniform temperature distribution: particularly suitable for drying of heat-sensitive materials.

4.Flexible operation: it can be operated continuously or intermittently. At the same time, the spray pressure/flow rate, fluidization air velocity, inlet temperature and other operating parameters can be adjusted according to the properties of different materials;

5.High controllability of product quality: The particle size and shape are uniform, and the structural density can be adjusted;

6.Adjustable retention time: the moisture content of the product remains stable;

7.Simple equipment: low investment cost, and small maintenance workload.

Applicable material

1.Heat-sensitive materials. The spray fluid bed dryer can achieve low-temperature drying or treatment by controlling the inlet air temperature and the material layer flow rate, thereby reducing the thermal degradation of the materials. For example: biological products, natural extracts (such as microcapsules of plant essential oils), and certain food additives;

2.Materials prone to adhesion or agglomeration. The fluidization movement in the dryer can prevent the material from aggregating. During the spray process, by controlling the droplet volume and the drying rate, wall adhesion can be avoided. For example: high sugar concentration solutions (if in slurry form), certain polymer solution;

3.Materials requiring precise particle size control. The spray fluid bed dryer can regulate parameters such as spray pressure and air velocity of fluid bed dryer to control the growth rate and particle size distribution of the particles. For example: pharmaceutical granules, microspheres for electronic materials (such as particles of lithium battery positive electrodes).

Not Applicable Material

1.High-viscosity non-flowable materials refer to such as pastes with a viscosity greater than 1000 cP, are difficult to be atomized and are prone to clogging the nozzles;

2.Materials with strong hygroscopicity or prone to deliquescence refer to such as ammonium nitrate. After granulation, it must be sealed immediately; otherwise, it is likely to absorb moisture and form lumps in the fluid bed dryer;

3.Materials with excessive particle size refer to when the initial powder particle size is greater than 1 mm, the spray liquid is difficult to evenly cover the particles, resulting in poor granulation effect;

4.Materials prone to thermal decomposition or phase change refer to such as certain organic metal compounds. They requires strict control of the temperature range, otherwise, they may undergo decomposition or crystallization transformation.