Fluidized Bed Dryer

SHMT, Chemical Engineering

1. Topic FLUIDIZED BED DRYER Group Members Awais Hafiz (034) Hafiz Luqman (032)

2. What is Drying? Drying is a unit operation in which a liquid is separated from a solid by other than mechanical means. This generally requires supplying heat and resulting in evaporation of liquid. Drying Principle Migration of moisture from the interior of a material to its surface Evaporation of moisture from surface to the surrounding air Basic Mechanism

3. Dryer Feed Dry Solid Heat Moisture Drying Process

4. Purpose of S olid Drying Increasing shelf life Enhancing calorific value of fuel Reduction of transportation cost To improve or keep good properties of materials like flow ability, compressibility To make the material easy and more suitable for handling Preservation

5. Feed Stock for Drying Process Wet Solids Slurry Solution Suspension

6. Types of Dryers on the basis of Heating Mode Convective/Direct Dryers Conductive/Indirect Dryers Dryers by Radiant Energy

7. Continuous Dryers Continuous-Tray Dryers, Continuous Sheeting Dryers , Pneumatic Conveying Dryers, Rotary Dryers, Spray Dryers, Through - Circulation Dryers, Tunnel Dryers, Fluid Bed Dryers Batch Dryers Batch - Through Circulation Dryers, Tray and Compartment Dryers, Fluid Batch Dryers Continuous Dryers Cylinder Dryers, Drum Dryers, Screw-Conveyor Dryers, Steam-Tube Rotary Dryers, Vibrating - Tray Dryers Batch Dryers Agitated Pan Dryers, Freeze Dryers, Vacuum Rotary Dryers, Vacuum Tray Dryers Direct Contact Indirect Contact

8. Types of Dryers on the basis of feed Tray Dryer Screen-Conveyor Dryer Fluid Bed Dryer Rotary Dryer Tower Dryer Screw-Conveyor Dryer Flash Dryer Spray Dryer Thin Film Dryer Drum Dryer Dryers for Solids Dryers for Liquids/slurries

9. Selection of Drying Equipment It depends upon; Physical/Chemical properties of materials Production capacity (Kg/ hr ) Initial moisture content & final moisture content required Particle size distribution Temperature & drying characteristics Explosion & Texicological characteristics

10. General Consideration for Selection of Dryer Dryer must operate reliably, safely & economically Operating & maintenance must not be excessive Pollution must be controlled Energy consumption must be minimized

11. Koncept Learning Center [email protected] Industrial Dryers

12. Fluidized Bed Dryer 13

13. What is Fluidization? Fluidization  (or fluidization ) is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material . Different types of fluidized beds are formed depending upon the velocity of fluid.

14. Status of approach fluid velocity (V ) Type of bed formed V < V mf Fixed Bed V mf ≥ Vo < U t Fluidized Bed V ≥ U t Mobilized Bed Where Vo is approach velocity or superficial velocity, Vmf is the minimized fluidized velocity, Ut is particle terminal velocity.

15. Different Fluidized Bed Formation

16. Fluidized Bed Dryer 1)INTRODUCTION Fluid bed drying is most widely used technique for drying pharmaceutical powders and granulation. The direct contact between particles and air/gas is possible in fluid bed system. Here any type of inert gas or air is used. They can be designed in either batch or continuous type fluid bed dryer. 2)PRINCIPLE In fluidized bed dryer, hot air is passed at high pressure through a perforated bottom of the container containing granules to be dried. The granules are lifted from the bottom and suspended in the stream of air. This condition is called fluidized state .

17. PARAMETERS TO BE CONTROLLED IN FLUIDIZED BED SYSTEMS 1 ) Apparatus Parameters Air distribution plate Position influences the airflow pattern inside the body. 2) Shape of instrument body Annular base gives better product and fluidization 3) Nozzle height in case of coater and granulator. It plays vital role as in coating, the atomized coating solution should not get dried before reaching the tablet surface. 4) Positive and negative pressure operation.

18. 2 )Process Parameters The following inlet air parameters are critical i ) Temperature As the inlet air temperature increases the rate of drying increases and vice versa. This approach to increase the rate of drying can not be used always because some materials are harmed by high temperature, e.g. Ibuprofen liquefies above 60°C temperature of inlet air should be optimized without any impact on product quality. If temperature is high, it leads to blistering. If temperature is low, soft spot can be formed . ii) Humidity Humidity in the inlet air should be as low as possible and ideally dehumidified air should be used for faster drying rate because as the humidity of inlet air decreases the rate of drying increases.

19. iii) Air F low Rate Air flow rate should be controlled properly in order to get efficient use of drying air. Air flow rate should not be too fast or too slow but optimized to have efficient drying. 3 ) Product Parameters : Initial moisture content of material. It should not be high otherwise it increases drying time. Batch size. It should be small and optimized based on feasibility .

20. CONSTRUCTION The construction of a vertical fluidized bed dryer The dryer is made of stainless steel or plastic. A detachable bowl is placed at the bottom of the dryer, which is used for charging and discharging. The bowl has a perforated bottom with a wire mesh support for placing materials to be dried. A fan is mounted in the upper part for circulating hot air . Fresh air inlet, pre-filter and heat exchanger are connected serially to heat the air to the required temperatures. The temperature of hot air and exit are monitored. Bag filters are placed above the drying bowl for recovery of fines.

21. WORKING When the velocity of the air is greater than the settling velocity of granules, the granules remain partially suspended in the gas stream. After some time, a point of pressure is reached at which frictional drag in the particles is equal to the force of gravity. The granules rise in the container because of high velocity gas and fell back in a random boiling motion. This condition is said to be fluidized state. Drying is achieved at constant rate and falling rate period is very short .

22. Solids Drying T, Time dw/dT Drying Rate A B C D AB - Warming up period BC - Constant Rate Period ‘C’ - Critical Moisture Content CD - Falling Rate Period

23. ADVANTAGES It requires less time to complete drying i.e., 20 to 40 minutes compared To 24 hrs of tray dryer. Handling time is also short. It is 15 times faster than tray dryer. Hot spots are not observed in the dryer, because of its excellent mixing and drying capacities. It facilitates the drying of thermo labile substances, since the contact time is short. It can be used either as batch type or continuous type. The free movement of individual particles eliminates the risk of soluble material migrating as may occur in static bed.

24. TYPES OF FLUID BED DRYER A)Batch Type Vertical Fluid Bed Dryer With Granulating Option . I. Reverse Turning Bed Type In this equipment, by turning the gas dispersion plate (the reverse turning bed) in 90° direction with the control motor, all the dried material can be discharged at once. II. Rotating Discharge Type Dried material is discharged by opening the discharge gate equipped at the side of the Dryer. As the perforated plate is used as the gas dispersion plate, the gas inside the equipment whirls and pushes the dried material out from the discharge gate.

25. Batch Type Fluid Bed Dryer

26. Characteristics Of Batch Type Fluidized Bed Dryer The residence period of the dried material can be controlled which results in uniform drying . It is most suitable in case where an accurate control of the residence period is required at the decreasing rate drying zone. Small destruction of particle occurs therefore suitable for granular or crystallized material. Easy operation can be achieved by an automatic control of material feeding, drying discharging etc. When multiple stage system us adopted, the exhaust gas heat can be used efficiently.

27. Continous Fluid Bed Dryer

28. B) Continuous Type Horizontal Vibrating Conveyor Fluid Bed Dryer Residence time in any drying zone is dependent on (1) Length of the zone (2) The frequency and the amplitude of the vibration (3) Use of dams Heat transfer units such as tube or plate, are built inside the equipment. These unit supplies 60-80 % heat necessary for drying.

29. Characteristics Of Continuous Fluidized Bed Dryer The materials with relative high moisture content can also be dried. At and after a second drying chamber, piston flow ability can be achieved by arranging numbers of the partition plates as per the required residence period . The perforated plate at the fixed direction ensures easy discharging. Small destruction of particles, so suitable for granules or crystalline materials. In multiple zones fluid bed dryers, heating and cooling occurs in same unit. Each zone has independent control for temperature, dewpoint and velocity of air/gas. By adjusting the weir height for each zone, residence time can vary up to four fold in the unit.

30. Troubleshooting Problem Cause Solution Material Degrades High Drying Time Reduced particle Size High moisture Contents in dried Solids Material not Fluidizing Surface Shrinkage Very High Temperature Material contains high m oisture contents High residence time Due to internal diffusion of particles Powders develop e lectrostatic charge High temperature Low down the temperature or distribute the particles Prefer using twice drying Reduce resistance time Reduce residence time Use efficient electrical earthing of Drying chamber Optimize temperature

31. Applications Instant Tea/Coffee Milk Powder Ceram Slurry Magnesium Chloride Molasses Poly Aluminium Chloride Enzymes Catalysts Calcium Chloride Pastes Zeolites Resins Fruit Juice Powder Polyvinyl Acetate Dyes Detergent Powder Herbal Products Polymers (PVC, PP)