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Drying

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Yogeshwary Bhongade
Yogeshwary Bhongade

Drying Objectives, applications & mechanism of drying process, measurements & applications of Equilibrium Moisture content, rate of drying curve. principles, construction, working, uses, merits and demerits of – Tray dryer, Drum dryer spray dryer, Fluidized bed dryer, Vacuum dryer, Freeze dryer.

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Drying Yogeshwary Bhongade Assistant Professor Gondia college of Pharmacy, Gondia
UNIT- III 1- Drying • Objectives, applications & mechanism of drying process, measurements & applications of Equilibrium Moisture content, rate of drying curve. • principles, construction, working, uses, merits and demerits of – Tray dryer, Drum dryer spray dryer, Fluidized bed dryer, Vacuum dryer, Freeze dryer.
Drying
Introduction Material Water Dry Material
Defination • Removal of small amount of water or other liquid from material application of heat is called as drying. Mechanism of drying Thermal process Non- thermal process By Heating By squeezing By absorption By extraction
Application of drying 1. In preparation of bulk drug 2. Preservation of drug product 3.Improved Handling 4.Improved characteristics 5. Weight reduction 6. Help in Transportation 7. Microbilogy- prvent growth of microbs 8. Stability
Mechanism of Drying Process Vapor Solid Material Heating Medium
Theory of Drying • Diffusion Theory • Capillary Theory • Pressure Gradient Theory • Gravity Flow Theory • Vaporization & Condensation Theory
Diffusion Theory
Capillary Theory
Pressure Gradient Theory Radiation
Measurement and application of EMC • EMC- Amount of water present in the solid which exert vapour pressure is equal to the vapour pressure of the atmosphere surrounding it. Desorption- Transfer of moisture from solid to air Absorption- Transfer of moisture from air to solid
FMC • Removal of water to attained equilibrium is called free moisture content • Humidity- Amount of water present in air is called as humidity • Relative Humidity- total moisture content in normal air / total moisture content in saturated air ×100
Drying Equipment • On the basis of mechanism Try Dryer Freeze Dryer • Moving Bed Dryer Drum Dryer • Fluidized Bed Dryer Pneumatic Dryer • Spry Dryer
On the basis of contact of material Direct Dryer • Batch Dryer- Tray Dryer • Continuous Dryer- FBD Indirect Dryer • Batch Dryer- Freeze Dryer, Vacuum Dryer • Continuous Dryer- Spray Dryer
Tray dryer
Principle: In tray dryer hot air is continuously passed over wet mass. Heat transfer takes place by forced convection. Construction: It consist of rectangular chamber whose wall is insulated. Trays are placed in the chamber according to need Working: Wet solid is loaded into trays. Trays are placed in the chamber. Fresh air is introduced through inlet which passes through the heaters and heated up. The hot air is circulated by means of fans at 2 to 5 meter per second. The water is picked up by air and moist air is removed from outlet. During the cycle of drying only 10 to 20 % of fresh air is introduced and 80 to 90% air is circulated back.
Drum Dryer
Principle • Heated hollow metal drum rotates on its longitudinal axis, the drum is dipped in the solution to be dried. • The solution is carried as a film on the surface of the dryer and dried to form a layer. • A suitable knife scraps the dried material whle drum is rotating
Construction • Consist of horizontally mounted hollow steel drum dryer of 0.6- 1.5 meters in diameter and 2-4 meter in lenght, whose external surface is smoothly polished. • Below the drum, feed plan is placed in such a way that the drum dips partially into feed. • on one side of drum the a speader is placed and on other side doctor knife is placed to scrap the dried material. • A storage bin (or a conveyor) is placed connecting the knife to collect the material. • The drying rate can be controlled by adjusting rotation speed and temperature of drum
Working • The liquid material is placed in the feed pan and then drum is deep into the pan. • Allow the drum to rotate, the liquid material present in the feed pan adhers as a thin layer to the external surface of the drum during its rotation. • The material is dried which is scrapped by the doctor knife, which is then falls into the storage bin. • The time od contact of material with hot metal is 6- 15 second only. so that the processing condition such as the film thickness, steam temperature are closely controlled.
Advantages • less drying time. hence heat sensative material can be dried. • Quick method • less space occupy • Temperature can be contros as equipment can be enclosed in vaccum chember. • High rate of heat and mass transfer.
Disadvantages • High maintainance cost • Skilled operator needed to control speed of drum.
Uses • For drying of solutions, slurries and suspention.
Spray Dryer
Principle • Fluid to be dried is automized into fine droplets which are thrown radiallyinto moving steam of hot gas. • The temperature of droplets are immediately increased and from droplets are dried instantaneously in the form of spherical particles. • This process is completes in a few second before droplets reach the wall of dryer.
Construction • It consist of the drying chamber with a short conical bottom which is made up of stainless steel. • Inlet for hot air • Inlet carrying spary disk atomizer. • Cyclone separator.
Working 1. Atomization of feed into a spray 2. Drying of the liquid droplets 3. Separation and recovery and dried product.
Advantages • continuous operation • can be used for heat sensitive and heat resistant material • high evaporation rate • spray dried powder can be easily compressed in the form of tablet
Disadvantages • High installation cost • poor thermal efficiency
Fluidized bed dryer
Introduction • Fluidized bed dryer (also called fluid bed dryer) is a kind of equipment used extensively in the pharmaceutical industries to reduce the moisture content of pharmaceutical powder and granules. • The equipment works on a principle of fluidization of the feed materials. • In fluidization process, hot air is introduced at high pressure through a perforated bed of moist solid particulate. • The wet solids are lifted from the bottom and suspended in a stream of air (fluidized state). • Heat transfer is accomplished by direct contact between the wet solid and hot gases. • The vaporized liquid is carried away by the drying gasses. Sometimes to save energy, the exit gas is partially recycled.
Principle • Hot air is passed at high pressure through a perforated bottom of container containing granules to be dried. • The granules are lifted from bottom and suspended in stream of air. • This condition is known as fluidised state. • The hot gas surrounds every granule to completely dry them. • thus material oranules are uniformly dried.
Construction typical fluidized bed dryer consists of the following components a. Air preparatory unit. b. Product container.c. Exhaust filter. d. Exhaust blower. e. Control panel. f. Air distribution plate. g. Spray nozzle. h. Solution deliver.
• dryer made up of stainless steel. • Detachable bowl is placed at the bottom of the dryer which is used for charging and discharging. • The bowl has perforated bottom wh a wire mesh support for placing material to be dried. • A fan is mounted in the upper part of circulating hot air. • Fresh air inelet, pre-filter and exchanger are connected serially to heat the to the required temperature. • the temperature of hot air and exist is monitored. • Bag filters are placed above the drying bowl for the recovery of the fine.
Working • Granules to be dried are placed in the detachable bowl and then bowl is pushed into the dryer. • Fresh air allow to pass through the prefilter, which subsequently get heated by passing rough a heat exchanger. • The hot air if flow through the bottom of bowl. • Simultaneously fan is allow to rotate. • The air velocity is gradually increased • When the velocity of air is greater than settling velocity of granules. • The granulremains partially suspended in the gas stream.
• Due to increase in pressure the granules risen in container due to high velocity and latter fall back in a random boiling motion. this condition is said to be fluidised state. • The gas surrounds the granules completelty dry them.
Advantages of Fluidized-bed Dryers 1. High rates of moisture removal due to excellent gas-particle constant which results in high heat and mass transfer rates. 2. High thermal efficiency is usually achieved if part of the thermal energy for drying is supplied by the internal heat exchanger 3. Lower capital and maintenance cost 4. Reduced contact time for drying. 5. Ease of control.
Disadvantages of Fluidized Dryers 1. High pressure drops results as a result of the need to suspend the entire bed in gas which equally leads to high energy consumption. 2. Requires increased gas handling due to extensive recirculation of exhaust gas for high thermal efficiency operation. 3. Poor fluidization and low flexibility especially if the feed is too wet. 4. Not the best choice of equipment when organic solvents need to be removed during drying. 5. Non-uniform product quality for certain types of fluidized bed dryers. 6. Entertainment of fine particles. 7. High potential for attrition; and in some cases agglomeration of fine particles. 8. The conventional hot air fluidized bed dryers are not a good choice of dryer when handling toxic or flammable solids since there is danger of fire or explosion of flammability limits are exceeded.
Vacuum Dryer
Principal: by application of vacuum. Construction: • Iron heavy jacketed vessel. • Hallow shelves. • Metal trays. • Oven to vacuum pump.
Working: • Material of trays- placed on shelves. • Pressure decreased by vacuum pump. • Steam/hot hair- into jacket of shelves. • Drying will takes place. Application: • Drying of heat sensitive material, dusty hygroscopic material, • Drugs containing toxic solvents.
Advantages : • Easy operating • Easy for batch process of different compounds. • Various modes can be used for heating. Disadvantages: • Low heat transfer efficiency. • Limited capacity. • More expensive.
Freeze dryer
Principle • Drying by sublimation-triple point- temp. & pressure below triple point.
Construction • Drying chamber in trays. • Heating coils. • Vapor condensing or adsorption system with refrigerator. • Vacuum pump. • Door Heating System Refrigerator Condenser Vacuum pump Shelves Fig. Industrial freeze dryer Drying chamber
Working • Preparation & pretreatment: vacuum ay vacuum tray dryers • Pre-freezing for solidifying water: cold (-50oC) • Primary drying (Sublimation of ice under vacuum): at 0.0098oC & 0.533 kilopasals. temperature is increased to 300C within 2 hours. • Then temperature kept constant around 98 to 99% water is removed. • Secondary drying (Removal of moisture at high vacuum): temp as 50 to 60oC & low vacuum. • Packing: air replace with gas and seal.
Application • For production of dosage forms as injections, solutions, suspensions. • For drying of Blood plasma and its fractionated products, Bacterial & viral cultures, Human tissue, Antibiotics, Steroids, Food items (Prawns etc)
Advantages • Suitable for thermo-labile material. • Loss of volatile is less. • No migration occurs. • Suitable for moisture sensitive material. • Sterility maintain Disadvantages • High costs. • Time consuming. • Oxidation may occurs.
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Drying

  • 2. UNIT- III 1- Drying • Objectives, applications & mechanism of drying process, measurements & applications of Equilibrium Moisture content, rate of drying curve. • principles, construction, working, uses, merits and demerits of – Tray dryer, Drum dryer spray dryer, Fluidized bed dryer, Vacuum dryer, Freeze dryer.
  • 5. Defination • Removal of small amount of water or other liquid from material application of heat is called as drying. Mechanism of drying Thermal process Non- thermal process By Heating By squeezing By absorption By extraction
  • 6. Application of drying 1. In preparation of bulk drug 2. Preservation of drug product 3.Improved Handling 4.Improved characteristics 5. Weight reduction 6. Help in Transportation 7. Microbilogy- prvent growth of microbs 8. Stability
  • 7. Mechanism of Drying Process Vapor Solid Material Heating Medium
  • 8. Theory of Drying • Diffusion Theory • Capillary Theory • Pressure Gradient Theory • Gravity Flow Theory • Vaporization & Condensation Theory
  • 12. Measurement and application of EMC • EMC- Amount of water present in the solid which exert vapour pressure is equal to the vapour pressure of the atmosphere surrounding it. Desorption- Transfer of moisture from solid to air Absorption- Transfer of moisture from air to solid
  • 13. FMC • Removal of water to attained equilibrium is called free moisture content • Humidity- Amount of water present in air is called as humidity • Relative Humidity- total moisture content in normal air / total moisture content in saturated air ×100
  • 14. Drying Equipment • On the basis of mechanism Try Dryer Freeze Dryer • Moving Bed Dryer Drum Dryer • Fluidized Bed Dryer Pneumatic Dryer • Spry Dryer
  • 15. On the basis of contact of material Direct Dryer • Batch Dryer- Tray Dryer • Continuous Dryer- FBD Indirect Dryer • Batch Dryer- Freeze Dryer, Vacuum Dryer • Continuous Dryer- Spray Dryer
  • 17. Principle: In tray dryer hot air is continuously passed over wet mass. Heat transfer takes place by forced convection. Construction: It consist of rectangular chamber whose wall is insulated. Trays are placed in the chamber according to need Working: Wet solid is loaded into trays. Trays are placed in the chamber. Fresh air is introduced through inlet which passes through the heaters and heated up. The hot air is circulated by means of fans at 2 to 5 meter per second. The water is picked up by air and moist air is removed from outlet. During the cycle of drying only 10 to 20 % of fresh air is introduced and 80 to 90% air is circulated back.
  • 19. Principle • Heated hollow metal drum rotates on its longitudinal axis, the drum is dipped in the solution to be dried. • The solution is carried as a film on the surface of the dryer and dried to form a layer. • A suitable knife scraps the dried material whle drum is rotating
  • 20. Construction • Consist of horizontally mounted hollow steel drum dryer of 0.6- 1.5 meters in diameter and 2-4 meter in lenght, whose external surface is smoothly polished. • Below the drum, feed plan is placed in such a way that the drum dips partially into feed. • on one side of drum the a speader is placed and on other side doctor knife is placed to scrap the dried material. • A storage bin (or a conveyor) is placed connecting the knife to collect the material. • The drying rate can be controlled by adjusting rotation speed and temperature of drum
  • 21. Working • The liquid material is placed in the feed pan and then drum is deep into the pan. • Allow the drum to rotate, the liquid material present in the feed pan adhers as a thin layer to the external surface of the drum during its rotation. • The material is dried which is scrapped by the doctor knife, which is then falls into the storage bin. • The time od contact of material with hot metal is 6- 15 second only. so that the processing condition such as the film thickness, steam temperature are closely controlled.
  • 22. Advantages • less drying time. hence heat sensative material can be dried. • Quick method • less space occupy • Temperature can be contros as equipment can be enclosed in vaccum chember. • High rate of heat and mass transfer.
  • 23. Disadvantages • High maintainance cost • Skilled operator needed to control speed of drum.
  • 24. Uses • For drying of solutions, slurries and suspention.
  • 26. Principle • Fluid to be dried is automized into fine droplets which are thrown radiallyinto moving steam of hot gas. • The temperature of droplets are immediately increased and from droplets are dried instantaneously in the form of spherical particles. • This process is completes in a few second before droplets reach the wall of dryer.
  • 27. Construction • It consist of the drying chamber with a short conical bottom which is made up of stainless steel. • Inlet for hot air • Inlet carrying spary disk atomizer. • Cyclone separator.
  • 28. Working 1. Atomization of feed into a spray 2. Drying of the liquid droplets 3. Separation and recovery and dried product.
  • 29. Advantages • continuous operation • can be used for heat sensitive and heat resistant material • high evaporation rate • spray dried powder can be easily compressed in the form of tablet
  • 30. Disadvantages • High installation cost • poor thermal efficiency
  • 32. Introduction • Fluidized bed dryer (also called fluid bed dryer) is a kind of equipment used extensively in the pharmaceutical industries to reduce the moisture content of pharmaceutical powder and granules. • The equipment works on a principle of fluidization of the feed materials. • In fluidization process, hot air is introduced at high pressure through a perforated bed of moist solid particulate. • The wet solids are lifted from the bottom and suspended in a stream of air (fluidized state). • Heat transfer is accomplished by direct contact between the wet solid and hot gases. • The vaporized liquid is carried away by the drying gasses. Sometimes to save energy, the exit gas is partially recycled.
  • 33. Principle • Hot air is passed at high pressure through a perforated bottom of container containing granules to be dried. • The granules are lifted from bottom and suspended in stream of air. • This condition is known as fluidised state. • The hot gas surrounds every granule to completely dry them. • thus material oranules are uniformly dried.
  • 34. Construction typical fluidized bed dryer consists of the following components a. Air preparatory unit. b. Product container.c. Exhaust filter. d. Exhaust blower. e. Control panel. f. Air distribution plate. g. Spray nozzle. h. Solution deliver.
  • 35. • dryer made up of stainless steel. • Detachable bowl is placed at the bottom of the dryer which is used for charging and discharging. • The bowl has perforated bottom wh a wire mesh support for placing material to be dried. • A fan is mounted in the upper part of circulating hot air. • Fresh air inelet, pre-filter and exchanger are connected serially to heat the to the required temperature. • the temperature of hot air and exist is monitored. • Bag filters are placed above the drying bowl for the recovery of the fine.
  • 36. Working • Granules to be dried are placed in the detachable bowl and then bowl is pushed into the dryer. • Fresh air allow to pass through the prefilter, which subsequently get heated by passing rough a heat exchanger. • The hot air if flow through the bottom of bowl. • Simultaneously fan is allow to rotate. • The air velocity is gradually increased • When the velocity of air is greater than settling velocity of granules. • The granulremains partially suspended in the gas stream.
  • 37. • Due to increase in pressure the granules risen in container due to high velocity and latter fall back in a random boiling motion. this condition is said to be fluidised state. • The gas surrounds the granules completelty dry them.
  • 38. Advantages of Fluidized-bed Dryers 1. High rates of moisture removal due to excellent gas-particle constant which results in high heat and mass transfer rates. 2. High thermal efficiency is usually achieved if part of the thermal energy for drying is supplied by the internal heat exchanger 3. Lower capital and maintenance cost 4. Reduced contact time for drying. 5. Ease of control.
  • 39. Disadvantages of Fluidized Dryers 1. High pressure drops results as a result of the need to suspend the entire bed in gas which equally leads to high energy consumption. 2. Requires increased gas handling due to extensive recirculation of exhaust gas for high thermal efficiency operation. 3. Poor fluidization and low flexibility especially if the feed is too wet. 4. Not the best choice of equipment when organic solvents need to be removed during drying. 5. Non-uniform product quality for certain types of fluidized bed dryers. 6. Entertainment of fine particles. 7. High potential for attrition; and in some cases agglomeration of fine particles. 8. The conventional hot air fluidized bed dryers are not a good choice of dryer when handling toxic or flammable solids since there is danger of fire or explosion of flammability limits are exceeded.
  • 41. Principal: by application of vacuum. Construction: • Iron heavy jacketed vessel. • Hallow shelves. • Metal trays. • Oven to vacuum pump.
  • 42. Working: • Material of trays- placed on shelves. • Pressure decreased by vacuum pump. • Steam/hot hair- into jacket of shelves. • Drying will takes place. Application: • Drying of heat sensitive material, dusty hygroscopic material, • Drugs containing toxic solvents.
  • 43. Advantages : • Easy operating • Easy for batch process of different compounds. • Various modes can be used for heating. Disadvantages: • Low heat transfer efficiency. • Limited capacity. • More expensive.
  • 45. Principle • Drying by sublimation-triple point- temp. & pressure below triple point.
  • 46. Construction • Drying chamber in trays. • Heating coils. • Vapor condensing or adsorption system with refrigerator. • Vacuum pump. • Door Heating System Refrigerator Condenser Vacuum pump Shelves Fig. Industrial freeze dryer Drying chamber
  • 47. Working • Preparation & pretreatment: vacuum ay vacuum tray dryers • Pre-freezing for solidifying water: cold (-50oC) • Primary drying (Sublimation of ice under vacuum): at 0.0098oC & 0.533 kilopasals. temperature is increased to 300C within 2 hours. • Then temperature kept constant around 98 to 99% water is removed. • Secondary drying (Removal of moisture at high vacuum): temp as 50 to 60oC & low vacuum. • Packing: air replace with gas and seal.
  • 48. Application • For production of dosage forms as injections, solutions, suspensions. • For drying of Blood plasma and its fractionated products, Bacterial & viral cultures, Human tissue, Antibiotics, Steroids, Food items (Prawns etc)
  • 49. Advantages • Suitable for thermo-labile material. • Loss of volatile is less. • No migration occurs. • Suitable for moisture sensitive material. • Sterility maintain Disadvantages • High costs. • Time consuming. • Oxidation may occurs.