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Similar to EVAPORATION. SlideShare Bpharm Sem -II.
EVAPORATION. SlideShare Bpharm Sem -II.
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- 2. Difference between Evaporationand Sublimation Evaporation • Evaporation is the change of phase from liquid to gas. • The enthalpy gives the amount of energy that is required for evaporation to occur. Sublimation • Sublimation is the change of phase from solid into gas. • The enthalpy gives the amount of energy that is required for sublimation to occur.
- 3. Difference between Evaporationand Boiling Evaporation • It can occur at any temperature. • Takes place only at the surface. • Takes energy from surrounding Boiling • Takes place only at particular temperature at which vapour pressure of liquid becomes equal to the atmospheric pressure. • Involves formation of bubbles of vapour throughout the liquid. • Source of energy needed
- 4. CLASSIFICATION OF EVAPORATORS 1.Evaporatorswith heating medium in jacket Example: Steam jacketed kettle (evaporating pan) 2.Vapour heated evaporators with tubular heating surfaces (A) Evaporators with tubes placed horizontally Examples: Horizontal tube evaporator (B) Evaporators with tubes placed vertically. (i) Evaporators with short tubes (a) Single effect evaporators Examples: Short tube vertical evaporator * Short tube vertical evaporator with propeller * Basket type evaporator (b) Multiple effect evaporator Example: Triple effect evaporator
- 5. (ii) Evaporators withlong tubes (a) Evaporators with natural circulation Examples: Climbing film evaporator (Rising film evaporator) Falling film evaporator (b) Evaporators with forced circulation Example: Forced circulation evaporator
- 6. STEAM JACKETED KETTLE (EVAPORATINGPAN) • Principle: Steam is supplied to a jacketed kettle (evaporating pan) in which aqueous extract is placed. Steam gives out heat to the kettle. The heat is transferred to the aqueous extract by conduction and convention. The temperature raises and the escaping tendency of the solvent molecules into vapour increases. Stirring further enhances the vaporization of solvent molecules
- 8. Construction • The constructionof a steam jacketed kettle is shown in Figure . • It is a hemispherical structure consisting of an inner pan called kettle. • It is enveloped with an outer pan called jacket. • The two pans are joined to enclose a space through which steam is passed. • For smaller quantities, kettle is made up of a single sheet of metal • For larger capacities, several sheets are welded. Though several metals
- 9. • Copper isan excellent material for the kettle, because its good conductivity. • If acidic materials are evaporated, some quantity of copper would dissolve. For such preparations, tinned copper is used. • Iron is used for the construction of the jacket, because it has minimum conductivity. To prevent rusting of the jacket, the iron is either tinned or enamelled on inner surface. • An inlet for the steam and an outlet (vent) for noncondensed gases are provided near the top of the jacket. • Condensate leaves the jacket through the outlet provided at the bottom. The kettle is provided with one outlet for product discharge at its bottom.
- 10. WORKING • Aqueous extractto be evaporated is placed in the Kettle. • Steam is supplied through the inlet. Steam gives out its heat contents and the condensate leaves through the outlet. • The content must be stirred manually for smaller volumes and mechanically larger volumes. • Any room where evaporation is carried by this apparatus must have good ventilation to remove the vapour. Otherwise, the room is quickly filled with a dense fog of condensed vapour and water falls from the and runs down the walls.
- 11. WORKING • Fans fittedover the pan not only remove vapour and prevent condensation in the room, but also accelerate the of evaporation by quickly removing saturated air from the surface of liquid. • The kettle may be fixed or made to tilt. A kettle of capacity upto 90 litres may be made to tilt. But above this capacity, the weight the pan along with its contents becomes too great to tilt. Hence, the outlet is used to collect the concentrated product.
- 12. USES • Evaporating panis suitable for concentrating aqueous and stable liquors, for example, liquorice extract. ADVANTAGES • Evaporating pan is constructed both for small scale and large scale operations • It is simple in construction and easy to operate, clean and maintain. • Its cost of installation and maintenance is low. • Wide variety of materials can be used for construction such as copper, stainless steel and aluminium • Stirring of the contents and removal of the product is easy.
- 13. DISADVANTAGES • In evaporatingpans, heat economy is less. Hence, cost per unit material production is more • It is not suitable for heat sensitive materials due to long time of exposure. • The heating area decreases as the product gets more concentrated. • As it is open type, vapour passes into the atmosphere, which can lead to saturation of the atmosphere, slowing evaporation as well as causing discomfort. • Boiling point of water cannot be reduced, since reduced pressure can not be created in open type evaporator.
- 14. HORIZONTAL TUBE EVAPORATOR PRINCIPLE Inhorizontal tube evaporator, steam is passed through the horizontal tubes, which are immersed in a pool of liquid to be evaporated . Heat transfer takes place through the tubes and the liquid outside the tubes gets heated. The solvent evaporates and escapes from the top of the evaporator. The concentrated liquid is collected from the bottom.
- 16. CONSTRUCTION • The constructionof a horizontal tube evaporator the shown in Figure • It consists of a large cylindrical body with conical or dome-shaped top and bottom. • It is made up of cast iron or plate steel. An average size of the body ranges from 1.8 to 2.4 metres diameter and from 2.4 to 3.6 metres height. • The lower part of the body consists of a steam compartment with inlet for steam at one end and a vent for non condensed gases on the other end. • A condensate outlet is provided at the bottom of the steam compartment.
- 17. CONSTRUCTION • In thesteam compartment, 6-8 stainless steel horizontal tubes are placed. The tubes are cut long enough so that they project about 25.0 millimetres beyond the tube sheet on both ends. • The width of steam compartment is usually half the diameter of the body. • At one convenient point, an inlet for feed is provided . One outlet for vapour is placed at the top of the dome. Another outle for thick liquid is placed at the centre of the conical bottom of the body
- 18. WORKING • The feedis introduced into the evaporator until the steam compartment is satisfactorily immersed. • Steam is introduced into the team compartment. • The horizontal tubes receive heat from the steam and conduct it to the liquid due to temperature gradient. Steam condenate passes through the corresponding outlet. • The feed absorbs heat and solvent gets evaporated. The vapour then escapes through the outlet placed at the top. This process is continued until a thick liquid is formed, which can be collected from the bottom outlet.
- 19. USES • Horizontal tubeevaporator is the best suited for non-viscous solutions that do not deposit scales or crystals on evaporation, for example cascara extract. ADVANTAGE • The cost per square metre of heating surface is usually less in horizontal tube evaporator
- 20. HORIZONTAL TUBE EVAPORATORVERTICAL TUBE EVAPORATOR
- 21. VERTICAL TUBE EVAPORATOR(Short Tube Evaporator) • Principle: In standard vertical tube evaporator, liquid is passed through the vertical tubes and the steam is supplied from outside the tubes. Heat transfer takes place through the tubes and the liquid inside tubes gets heated. The solvent evaporates and the vapour escapes m the top. The concentrated liquid is collected from the bottom
- 22. Construction: • The constructionof a standard vertical tube evaporators shown in Figure . • It consists of a large cylindrical body made of cast iron with dome shaped top and bottom . • In side body, calandria is fitted at the bottom. Calandria consists of a number of vertical tubes, whose diameter ranges from 0.05 to 175 metres and length of 1-2 metres. • About 100 such tubes are fitted body measuring 2.5 metres or more diameter. • Inlets are provided steam and feed. Outlets are provided for vapour, concentrated duct, non-condensed gases and condensate.
- 23. Working • Steam isintroduced outside the tubes. The condensate passed through the corresponding outlet and non-condensed gases escape through the vent • The feed is introduced in such a way as to maintain the liquid level slightly above the top of the tubes. • The liquid inside tubes is heated by the steam and begins to boil. As the liquid boil, spouts up through the tubes and returns through the central down-take . • It sets up a circulation of hot liquid, which enhances the rate of heat transfer. The vapour escapes through the top outlet. Steam is supplied until required concentration of the product is obtained. Finally, product can be withdrawn from the bottom outlet.
- 24. Uses: Vertical tubeevaporator is used in the manufacture of sugar, salt, caustic soda. Advantages 1) In vertical tube evaporator, tubes increase the heating surface nearly 10 to 15 times when compared with steamjacketed kettle. 2) Vigorous circulation enhances the rate of heat transfer. 3) It can be connected to a condenser and receiver, which further increases rate of evaporation. Such attachment is also suitablefor volatile solvents. 4) A number of units can be joined to obtain more efficient effect (multiple effect evaporators are discussed later).
- 25. Disadvantages: 1) Theliquid is maintained above the level of the Calandria. Hence, the upper layers of the liquid need a long time for getting heated. This problem can be minimised by removing concentrated liquid slowly at the bottom. 2) The evaporator is complicated, hence, installation cost increases 3) Cleaning and maintenance is difficult when compared with steam jacketed kettle.
- 26. CLIMBING FILM EVAPORATOR (RisingFilm Evaporator) Principle: In climbing film evaporator, Tubes are heated externally by steam. The preheated liquid enters from the bottom and liquid flows up through the heated tubes. Liquid near walls becomes vapor and forms small bubbles. Larger bubbles flow up with slag and strikes deflector. Deflector throws the concentrate, down to the bottom.
- 27. Construction: • The constructionof a climbing film evaporator is shown in Figure • In this evaporator, the heating unit consists of steam jacketed tubes. Here, the tubes (long and narrow) are held between two plates. • An entrainment separator(deflector) is placed at the top to the vapour head. • The evaporator carries steam inlet, vent outlet and condensate outlet. The feed inlet is from the bottom of the steam compartment.
- 28. Working: • The preheatedliquid feed is introduced from the bottom of the unit. • Steam enters into the spaces outside the tubes through the inlet. • Heat transferred to the liquor walls of the tubes. • Liquid and vapor moves upward at high velocity. • Vapor and liquid is separated from upper part having cyclone separator. • The vapor leaves from the top while concentrate is collected from the bottom.
- 29. Uses: 1. Using climbingfilm evaporator, thermolabile substances such as insulin, liver extracts and vitamins can be concentrated. 2. Clear liquids, foaming liquids and corrosive solutions in large quantities can be operated. 3. Deposit of scales can be removed quickly by increasing the feed rate or reducing the steam rate so that the product is unsaturated for a short time.
- 30. Advantages: • Long andnarrow tubes provide large surface area • Very high film velocity reduces boundary layers to a minimum giving improved heat transfer. • The contact time between the liquid and the heating surface is very short. So, it suitable for heat sensitive materials. • It is suitable for foam-forming liquids, because foam can be broken by an entrainment separator.
- 31. Disadvantages 1. Climbing filmevaporator is expensive. 2. Construction is quite complicated. 3. It is difficult to clean and maintain. 4. It is not advisable for very viscous liquids.
- 32. FORCED CIRCULATION EVAPORATOR Principle: • Inforced circulation evaporator, liquid is circulated through the tubes at high pressures by means of a pump. Hence, boiling does not takes place because boiling point is elevated. • Forced circulation of the liquid also creates some form of agitation. • When the liquid leaves the tubes and enters the vapour head, pressure falls suddenly. • This leads to the flashing of super heated liquor. Thus evaporation is effected.
- 34. Construction • The constructionof a forced circulation evaporator is shown in Figure • The steam jacketed tubes are held between two tube sheets. • The tube measures 0.1 metres inside diameter and 2.5 metres long. • The part of the tubes projects into the vapour head (flash chamber), which consists of a deflector. • The vapour head is connected to a return downwards and enters into the inlet of a pump.
- 35. Working • Steam isintroduced into calendria. • Pump sends the liquid to the tubes with a positive velocity. • As the liquid moves up through the tubes, it gets heated and begins to boil. • As a result, the vapour and liquid mixture rushes out of the tubes at a high velocity. • This mixture strikes the deflector, which throws the liquid downward. This results in an effective separation of liquid and vapour. • The vapour enters the cyclone separator and leaves the equipment. The liquid returns to the pump for further evaporation. Finally the concentrated product is collected.
- 36. Uses 1. If evaporationis conducted under reduced pressure, forced circulation evaporator is suitable for thermo labile substances. 2. This method is used for the concentration of insulin and liver extracts. 3. It is well suited for crystallizing operation where crystals are to be suspended at all times.
- 37. Advantages 1 In forcedcirculation evaporator, there is a rapid liquid movement due to high heat transfer coefficient 2 Salting, scaling and fouling are not possible due to forced circulation. 3 This evaporator is suitable for themo labile substances because of rapid evaporation. 4 It is suitable for the viscous preparation because pumping mechanism is used.
- 38. Disadvantages 1. In forcedcirculation evaporator the hold up of liquids is high. 2. The equipments is expensive because the power is required for the circulating of the liquids.
- 39. MULTIPLE EFFECT EVAPORATOR Verticaltube evaporator discussed earlier is a single effect evaporators. Such evaporators are connected in several ways so achieve large scale evaporation as well as greater economy. A multiple effect evaporators are not used in the pharmaceutical industry. • Advantages 1. It is suitable for large scale and for continuous operation. 2. It is highly economical when compared with single effect. 3. About 5 evaporators can be attached.
- 40. Construction •The construction ofa multiple effect evaporator is shown in Figure using 3 evaporators, i.e., triple effect evaporator .The other aspects of construction of vertical tube evaporator remain same as mentioned earlier. •A Figure indicates that the vapour from first evaporator serves as a heating medium for the 2nd evaporator. Similarly, vapour from 2nd evaporator serves as a heating medium for the 3rd evaporator. • Last evaporator is connected to vacuum pump.
- 41.
- 42. Working Parallel feed • Inthis method, a hot saturated solution of the feed is directly fed to each of the three effects (evaporation) in parallel without transferring the material from one effect to the other. •The parallel feed arrangement is commonly used in the concentration of salt solutions.
- 43. Operations In the beginning, •The equipment is at room temp and atmospheric pressure. • The liquid feed is introduced to all the three evaporators up to the level of the upper tube sheets • The following operations are attempted to achieve the effects as specified below. 1. The vent valves V1, V2 and Vs are kept open and all other valves are closed 2. Now a high vacuum is created in the liquid chambers of evaporators.
- 44. 3 The steamvalve S1, and condensate valve C are opened ₁ . Steam is supplied. Steam first replaces cold air in the steam space of 1st evaporator. When all the cold air is removed, the valve, V1 is closed. 4 The supply of steam is continued until the desired pressure Po is created in the steam space of 1st evaporator. At this pressure, the temperature of the steam is t0 5 Steam gives its temperature to the liquid feed in the 1 evaporator and gets condensed. Condensate is removed through the valve C1. 6 Due to heat transfer, the liquid temperature increases and reaches the boiling point. During this process, vapour will be generated from the liquid feed.
- 45. Operations 7 So formedvapour displaces air in the upper part of 1st evaporator. Moreover, the vapour also displaces the air in the steam space of the 2nd evaporator. 8 After complete displacement of air by vapour in the steam compartment of 2nd evaporator, the valve V is ₂ closed. 9 The vapour of 1st evaporator transmits its heat to the liquid and evaporator and gets condensed. Condensate is remove through the valve C2. These steps continue in the 3rd evaporator also.
- 46. Heating the Liquid •The liquid in the 1st evaporator gains temperature as steam is supplied. • The temperature difference between the steam and liquid decreases over time. Pressure Increase • Due to heating, the pressure inside the 1st evaporator increases gradually. • The temperature of the liquid also rises to its boiling point.
- 47. Evaporation Process inOther Evaporators •A similar process happens in the 2nd and 3rd evaporators. •The liquid in each evaporator starts boiling one after another. •Eventually, all three evaporators reach a steady state, meaning boiling continues smoothly in all. Maintaining Liquid Levels •As boiling continues, the liquid levels in the evaporators decrease. •To maintain the levels, feed valves (F , F , and F ) ₁ ₂ ₃ are used to add fresh liquid.
- 48. Continuous Operation •Once theliquid thickens (concentrated), product valves are opened to collect the final product. •The system runs continuously, with steam supply, liquid feed, and product withdrawal all happening at the same time. Different Feeding Methods •Forward Feed: Liquid moves from the 1st → 2nd → 3rd evaporator. •Backward Feed: Liquid moves from the 3rd → 2nd → 1st evaporator. •Mixed Feed: Liquid enters the 2nd evaporator first, then moves to the 3rd and finally the 1st evaporator.
- 49. Economy of MultipleEffect Evaporator • One unit of steam produces one unit of vapor. • Therefore, the economy of a single-effect evaporator is 1. Assumptions for Economy Calculation • Feed enters at boiling point, so it does not require extra heat for preheating. • Supplied steam condenses completely, transferring all its latent heat to the liquid. • No heat loss occurs due to radiation or conduction.
- 50. • Economy ofthe evaporators = Total steam supplied Total vapour produced • In single effect evaporator, steam produces vapour only once. Hence, Economy of a single = N units of vapour produced effect evaporator N units of steam supplied = 1 • In multiple effect evaporator, one unit of steam produces vapour many times, depending on the number of evaporators connected. Hence, • Economy of multiple = N units of vapour produced effect evaporators 1 unit of steam supplied =1
- 51. Factors Affecting theEconomy • The actual economy is slightly less than N because of: • Feed temperature: If feed is cold, extra heat is required. • Temperature range: A high temperature drop across evaporators improves economy. • Feed-to-product ratio: More concentrated products may require additional heat. • Pressure differences: Affects boiling efficiency and vapor reuse.