Fluidized bed dryer - it components, Working principle, finger bag , material used in finger bags

 

Fluidized Bed Dryer:-

Fluid bed processing involves drying, mixing, granulation, and coating of particulate materials. Fluid bed drying is suited for powders, granules, agglomerates, and pellets with an average particle size normally between 50 to 5,000 microns. Very fine, light powders or highly elongated particles may require vibration for successful fluid bed drying. Materials with moisture content up to 80% such as some polymers, dye stuffs and molecular sieve catalysts can also be accommodated. Hot air is injected at high pressure through a perforated bed of moist solid particles to get a velocity greater than the settling velocity of the particles in the fluidization process. The moist solids are raised from the bottom of the bucket and suspended in an air stream (fluidized state). the hot air around the solid particles reduces the moisture content of the particles to achieve the desired drying, also refer as a loss on drying (LOD).

 

Principle:-

FBD (fluidized Bed dryer) works on the fluidization principle. A high-pressure Hot air from the supply is passed through the perforated container containing a wet mass of the granules, after some time granules, particles started to suspend in the air to become dry (called (fluidized state), the process is called Fluidization.

 

Components of Fluidized-bed dryer

1.      Main Body

2.      Inlets air handling unit

3.      Expansion chamber

4.      Exhaust unit.

5.      FBD bags( FBD finger bags)

 

 

1.      Main Body:-

 The dryer is made up of stainless steel . It consist of a hollow vertical chamber where dry, heated air enters through the bottom of the chamber and exhaust air exits through the top of the chamber.  A detachable bowl is placed at the bottom of the dryer, which is used for charging and discharging of material.

 

2.      Inlet air unit :-The air handling unit is a rectangular container, from one side fresh air enter and the other end is linked to a fluid bed dryer. It has further components.

1.      Primary filter

The primary filter is also known as the G4 class filter. G4 class filter removes those particles, which we can see with our naked eye. e.g. pollen grain of flower, the power of filtration of a primary filter is up to 10 µm particles.

2.      Post filter:- It’s the second filter mounted just after the primary filter. It deals with very fine dust and may remove particles as small as 1μm.

3.      Dehumidifier:- There are two types of Dehumidifier

Also read :Tablets and its type

   I. Condenser coil Dehumidifier:-The condenser coil dehumidifier is doing the function of cooling the surface.

           II. Wheel type dehumidifier:- It is also named as "Desiccant dehumidification Wheel". It consists of a wheel, and that wheel is made up of corrugated material. The wheel has desiccant material, which attracts water from the air. A desiccant wheel is used mainly in those cases when the air is of low humidity. Mostly silica gel is used as a desiccant material.

Dehumidifier has further parts:-

·         Fan:- It pass air from the surroundings inside the AHU unit past the filters and into the heating chamber.

·         Heating pipes:- The next process after filtering and dehumidifying is heating. Cool incoming air absorbs heat from the surface of heated pipes. Now you may heat the pipes via steam or electricity. AHU comes with both  electric heating coils or steam heating as an optional feature.

·         HEPA filter:- "High efficiency particulate air"

As the air leaves AHU it undergoes the final filtration process. In this, we use a highly efficient HEPA filter, which can remove very small particles ranging in size as small as 0.3µm in diameter. HEPA filter is constructed of borosilicate microfibers in the form of pleated sheet.

 

3.      Expansion Chamber :-

The expansion chamber forms the middle part of the tower. It’s integrated with the filter housing chamber that holds the double structure filter bag. Filter bags resemble sacks suspended over the process chamber. Air flows upwards during fluidization and may carry in it small particles known as fines. The filter bags prevent fines from being exhausted.

The filtering bags become clogged with particles and require mechanical shaking to dislodge this dust layer. Shaking is done by pneumatic cylinders mounted at the top of the main tower.

4.      Exhaust unit:- same as inlet air unit following components:-

·          Fine Filter assembly:- pp Air filter mesh size approx. 3 to 5 microns are used to filter inlet air and arrest the suspended or unwanted solid particles.

·         HEPA filter:- depending on the process requirements the exhaust vapours and hot air streams need to pass through the HEPA filter assembly. HEPA filter due to its highly fine mesh increases the press drop across it and hence the higher capacity suction blower might be needed.

·         SFM sensor:- solid flow monitor is mounted on the exhaust ducting to identify the leakage or damage to the finger bags, which can lead to  powder loss.

·         Finger bag shaking unit:- a pneumatic cylinder is fitted  to shake the finger bags as time  interval or when required.

5.      Finger bags:- the FBD bag dryer finger bag made up of different type of superior quality of fabrics, as per requirements of material involving drying.

·         Anti-static

·         Polypropylene

·         Stain

Finger bags are constructed by a combination of anti- static polymer, nylon fabric and cotton fabric.