Drying equipments

Drying equipments

1. Mamta Sahurkar DRYING EQUIPMENTS

2. DRYING AND DRYING EQUIPMENTS

3. DRYING/DEHYDRATION Drying is the simple process of dehydrating foods until there is not enough moisture to support microbial activity.  If adequately dried and properly stored, dehydrated foods are shelf stable (safe for storage at room temperature ).

4. PURPOSE OF DRYING Increase in shelf life/Preservation. Reduction in transportation cost. Easy material handling. Improve or maintain properties (flow ability or compressibility)

5. Dryer is a device that removes moisture by heating the mass to a level where it becomes safe to store. Batch dryers are used for solid throughout (flows) below 50 kg/hr. Continuous dryers is preferred above 1000 kg/hr. DRYER MOISTURE HEAT FEED DRIED PRODUCT DRYING EQUIPMENTS

6. SELECTION OF EQUIPMENT DEPENDS ON GENERAL CONSIDERATIONS Physical/Chemical properties of materials Production capacity Initial and final moisture content required Particle size distribution Temperature and drying characteristics Explosion and toxicological characteristics Dryer must operate reliably, safely and economically. Operating and maintenance must not be excessive Pollution must be controlled Energy consumption must be minimized

7. INDUSTRIAL DRYERS

8. CLASSIFICATION OF DRYERS

9. INDUSTRIAL DRYERS SPRAY DRYER TRAY DRYER FLUIDIZED BED DRYER FLASH DRYER DRUM DRYER VACUUM DRYER TUNNEL DRYER ROTARY DRYER FREEZE DRYER

10. SPRAY DRYER The spray dryer provides a large surface area for heat and mass transfer by atomizing the liquid to small droplets. These are sprayed into a stream of hot air, so that each droplet dries to a solid particle. The drying chamber resembles the cyclone ensuring good circulation of air, to facilitate heat and mass transfer, and that dried particles are separated by the centrifugal action

11. Product quality effectively controlled Product properties effectively controlled Suitable for heat sensitive foods eg: milk High tonnage equipment Corrosion problem minimized Good efficiency ADVANTAGES Product quality effectively controlled Product properties effectively controlled Suitable for heat sensitive foods eg: milk High tonnage equipment Corrosion problem minimized Good efficiency DISADVANTAGES APPLICATIONS Drying of any substance in solution or in suspension form It is most useful for drying thermolabile materials eg: antibiotics Suitable for large quantities solution Suitable for both soluble and insoluble substances It can produce spherical particles in the respiratory range Drying of milk, soap and detergents

12. TRAY DRYER These types of dryers use trays or similar product holders to expose the product to heated air in an enclosed space. The trays holding the product inside a cabinet or similar enclosure are exposed to heated air so that dehydration will proceed. Air movement over the product surface is at relatively high velocities to ensure that heat and mass transfer will proceed in an efficient manner. Operated as batch systems

13. Simple in handling Lesser capital cost ADVANTAGES Non-uniform drying of a product at different locations within the system Time required for drying is more The major disadvantages of this type of dryers are the high labor cost involved during loading and unloading of the drying materials and the low capacities of the units DISADVANTAGES Mainly used for drying agricultural produce Drying foods Eg:( chillies and spices etc) Of potential use in pharmaceuticals,paints,textile and other industries APPLICATIONS

14. FLUIDIZED BED DRYER 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 systems. Here any type of inert gas or air is used. They can be designed in either batch or continuous type fluid bed dryer. 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.

15. The hot gas surrounding every granule to completely dry them. The material or granule are uniformly dried. The hot air/gas used for drying can be generated by either steam coils or a combustion furnace. The angle of repose of gas-solid mixture is zero and it assumes the shape of vessel that contains it. Uniform conditions of temperature, composition and particle size distribution is achieved throughout the bed because of complete mixing between the solids and gas is obtained.

16. Fluidized bed dryer requires less time to complete drying ie: 20 to 40 min. Hot spots are observed in the dryer, because of its excellent mixing and drying capacities. The thermal efficiency is 2 to 6 times greater than tray dryer It facilitates the drying of thermolabile substances, since contact time for drying is short. It can be used 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 Equipment is bulky. Expensive ADVANTAGES DISADVANTAGES APPLICATIONS

17. Flash dryer utilizes superheated steam as the drying medium have some unique quality and energy advantages over air drying systems. Flash dryers consisting of inert media have been employed at pilot scales to dry slurries and suspensions sprayed onto them. The particles are coated thinly by the slurry and dried rapidly as a thin film. Attrition due to inter-particle collisions and shrinkage induced breakage of the dried film allows entrainment of the dry powder into the drying gas for collection in cyclone or baghouse. FLASH DRYER

18. Short contact time and parallel flow make possible to dry thermo liable materials. The dryer needs only a very small area and can be installed outside a building. The dryer is easy to control. The low material content in the dryer enables equilibrium conditions to be reached very quickly. Due to small number of moving parts the maintenance cost is low. The capital cost are low in comparison with other types of dryers. Simultaneous drying and transportation is useful for material handling. ADVANTAGES DISADVANTAGES High efficiency of gas cleaning system is required. Dryer cannot be used for toxic materials. Not suitable for lumped materials. Risk of fire and explosion. Generally, not all the particles have same residence time in the dryer. Drying of heat sensitive products in this type of dryers is very useful. They are successfully used in food, chemical, pharmaceutical, mining, ceramic and wood industries. Widely used in plastic and polymer industries. APPLICATIONS

19. The drum dryer is an indirect type dryer in which the feed to be dried is maintained in a thin film on a rotating steam heated drum. The feed being dried is spread over the outside surface of the dryer. Clinging to it drying continues ad the hot drum rotates. At the end of revolution, the drum comes to a ‘doctor blade’ which scrapes the dried film from the drum,when the product has made about three quarter of a complete rotation on the drum surface. The process is known as roller drying. Drum diameter: 0.5 to 6m and the length from 1m to 6m In operation, steam at temperature to 200 degree celsius heats the inner surface of the drum. The moist material is uniformly applied in a thin layer on to the outer drum surface. DRUM/ROLLER DRYER

20. CLASSIFICATION A)Single drum B)Double drum C)Twin drum A)Atmospheric B)Vacuum A)Nip feed B)Splash feed C)Dip feed D)Roller feed A)Alloy steel B)Stainless steel C)Chrome D)Nickel plate steel

21. Large production capacity Continuous operation Simple structure Easy to operate Less failure Low maintenance costs. ADVANTAGES Large equipment High one time investment Installation and removal are difficult Heat loss is large Thermal efficiency is low Material in dryer stay for long time DISADVANTAGES A P P L I C AT IONS

22. VACUUM DRYER This equipment is a good example of conduction drier. The vacuum oven consists of a jacketed vessel to withstand vacuum within the oven There are supports for the shelves giving a larger area for conduction heat transfer. The oven can be closed by a door. The oven is connected through a condenser and liquid receiver to a vacuum pump. Operating pressure can be as low as 0.03 bar, at which pressures water boils at 25-35 degree Celsius.

23. Drying takes place at low temperature. Maximum retention of nutrition. There is little air present, so there is minimum risk of oxidation. ADVANTAGES DISADVANTAGES Drying takes place at low temperature. Maximum retention of nutrition. There is little air present, so there is minimum risk of oxidation. Mainly used for puffed cereals. APPLICATIONS

24. Freeze drying is a process in which water is removed from a product after it is frozen and placed under a vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase. FREEZE DRYING STAGES Freezing stage a)Shell freezing b)Centrifugal evaporative freezing Vacuum application stage Sublimation stage Primary drying Heat transfer Vapour removal Rate of drying Secondary drying Packaging

25. Drying takes place at low temperature. Product is light and porous The porous form of the product gives ready solubility No concentration of solution prior to drying Nutrition retention. There is little air present, so there is minimum risk of oxidation. ADVANTAGES DISADVANTAGES The porosity, ready solubility and complete dryness yield a very hygroscopic product. Unless the products are dried in their final container and sealed in situ, packing require special conditions. The process is very slow. U ses complicated plant which is very expensive. Limited to certain types of valuable products The method is used for products that cannot be dried by any other heat method. These include biological products,eg:antibiotics,blood products,vaccines,enzyme preparations and microbiological cultures. APPLICATIONS