Drying By Makrani Shaharukh

Drying is defined as the removal of small amount of water or other liquids from a material by the application of heat.

1. Drying By S. I Makrani

2. Content Fluidized Bed Dryer ( FBD ) & Freeze Dryer Principle Construction Working Uses Advantages Disadvantages 1

3. Fluidized Bed Dryer ( FBD ) Principle: In fluidized bed dryer, hot air (gas) 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 fluidised state . 2

4. Construction : Figure. Construction of Fluidized Bed Dryer 3

5. 2 types of bed dryer are available, Vertical fluid bed dryer and horizontal fluid bed dryer. The construction of a vertical FBD is shown in figure. The dryer is made up 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 , prefilter and heat exchanger are connected serially to heat the air to the required temperatures. Bag filters are placed above the drying bowl for the recovery 4

6. Working: The wet granules to be dried are placed in the detachable bowl . The bowl is pushed into the dryer. Fresh air is allowed to pass through a prefilter , which subsequently gets heated by passing through a heat exchanger. The hot air flows through the bottom of the bowl. Simultaneously fan is allowed to rotate. The air velocity is gradually increased . When the velocity of the air is greater than settling velocity of granules . The granules rise in the container because of high velocity gas and later fall back in a random boiling motion. This condition is said to be   fludised state. 5

7. Uses: Fluidised bed dryer is popularly used for drying of granules in the production of tablets . Fluidised bed dryer can be used for three operations such as mixing, granulation and drying. Advantages: Fluidised bed dryer requires less time to complete drying . i.e., 20 to 40 minutes compared to 24 hours of tray dryer . It is available in different sizes with the drying capacity ranging from 5 to 200 kg per hour. 6

8. The drying containers are mobile, making handling simple and reducing labour costs. I t can be used either batch type or continues type Disadvantages: Poor fluidization and low flexibility especially if the feed is too wet. Not the best choice of equipment when organic solvents need to be removed during drying. Non-uniform product quality for certain types of fluidized bed dryers. 7

9. Freeze Dryer Freeze drying is also known as Lyophillization . This is a techniques used for preservation of foods etc. Principle: In freeze drying, water is removed from the frozen state by sublimation , i.e., direct change of water from solid into vapour without conversion to a liquid phase. The process of Lyophillization or freezing drying include the conversion of the material directly from the solid phase to the gaseous phase , without going through the liquid phase (sublimation) 8

10. Construction: Figure. Schematic diagram of freeze dryer 9

11. The construction of a freeze dryer is shown in Figure . It consists of: 1. Drying chamber in which trays are loaded. 2. Heat supply in the form of radiation source, heating coils 3. Vapour condensing or adsorption system. 4. Vacuum pump or steam ejector or both. 10

12. Working: A freeze dryer works in three phases 1. Freezing Phase 2. Primary Drying (Sublimation) Phase 3. Secondary Drying (Adsorption) Phase 1. Freezing Phase Freeze dryers use various methods to freeze the product. Freezing can be done in a freezer , a chilled bath (shell freezer), or on a shelf in the freeze dryer. The freeze dryer cools the material below its triple point to ensure that sublimation, rather than melting, will occur. This preserves the material’s physical form. 11

13. 2. Primary Drying (Sublimation) Phase A freeze dryer’s second phase is primary drying (sublimation), in which the pressure is lowered and heat is added to the material in order for the water to sublimate. D irect change of water from solid into vapour without conversion to a liquid phase. About 95% of the water in the material is removed in this phase. Primary drying can be a slow process. Too much heat can alter the structure of the material. 12

14. 3. Secondary Drying (Adsorption) Phase A freeze dryer’s final phase is secondary drying (adsorption), during which the ionically bound water molecules are removed. By raising the temperature higher than in the primary drying phase, the bonds are broken between the material and the water molecules. Freeze dried materials retain a porous structure. After the freeze dryer completes its process, the vacuum can be broken with an inert gas before the material is sealed. Most materials can be dried to 1-5% residual moisture. 13

15. Uses : Freeze dryer is most commonly used in the production of dosage forms, such as injections, solutions and suspensions. It is used for drying of a number of products. Blood plasma and its fractionated products. Bacterial and viral cultures. Antibiotics and plant extracts. Steroids , vitamins and enzymes. Several other products such as food items (mushrooms , meat and poultry products), coffee and tea concentrates and citrus fruit juices are dried. 14

16. Advantages: The entire operation is carried out well below the freezing point Thermolabile materials (heat sensitive materials) can be dried loss of volatile material is less Sterility can be maintained Material can be dried in it final container such as single dose and multiple dose vials 15

17. Disadvantages: Equipment's and running cost are high The period of drying is high 16

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