Pharmaceutical Eng. 3rd sem Evaporation.pptx

Pharmaceutical Eng 3rd sem Evaporation.pptx

1. EVAPORATION Evaporation is a process of vaporizing large quantities volatile liquid to get a concentrated product. Equipment used for the evaporation are known as evaporators. Heat is supplied to the evaporator, which transmits it to the evaporating liquid so as to provide latent heat of vaporization. Steam is normally used as a source of heat . Evaporation is a surface phenamenon , i.e , mass transfer takes place from the surface.

2. Thus no boiling occurs. In practice , surface evaporation is slow, therefore , the practical definition of evaporation is the removal of solvent from the solution by boiling the liquor in a suitable vessel and withdrawing the vapour, leaving a concentrated liquid residue in the vessel.

3. Evaporation differs from boiling that evaporation takes place at all temperatures where as boiling takes place only at one temperature at a given pressure.

4. Below boiling point, vapour is formed from the surface only. At boiling point, vapour is formed throughout the body of the liquid as well as from surface . Boiling occurs when the vapour pressure of the liquid becomes equal to the atmospheric pressure.

5. Evaporation differs from distillation that in evaporation the solvent which is generally water is not condensed and collected, where as in distillation the solvent vapours are condensed and are collected in a receiver.

6. Purpose of evaporation: To concentrate solution by removing the vapour from a boiling liquid solution . In the majority of cases, evaporation refers to the removal of water from an aqueous solution. Example : concentration of aqueous solutions of sugar, sodium chloride , sodium hydroxide, glycerol, glue, milk , and orange juice .

7. In these cases the concentrated solution is the desired product and the evaporated water is normally discarded.

8. APPLICATION OF EVAPORATION Evaporation is one of the most important processes in the manufacture of pharmaceuticals. It is used in the preparation of 1. Liquid extracts, soft extracts & dry extracts. 2. In the concentration of blood plasma &serum . 3. It is also used in the manufacture of drugs containing, antibiotics, enzymes, hormones & many other substances.

9. 4) Used in purification of vitamins. 5) Concentration of proteins. 6) Concentration of biological products. 7) Stripping(removal of gas or vapour) of solvents from vegetable & plant or herbal extracts. 8) Removal of water & solvents from fermentation broths(A clear liquid made from meat, vegetables etc ). 9) Concentration of penicillin & related products

10. Manufacturing of bulk drugs. Manufacturing of biological products(made for natural source e.g sugar, protein etc ). Manufacturing of food products. Manufacturing of demineralised water. Minimize the chances of chemical reactions . Prepare the product for next operation like drying. Improve product storage life. Decrease the impact of microbial growth.

11. Evaporation and Distillation In evaporation, vaporization takes place below the boiling point. In the distillation method, vaporization takes place at the boiling point Evaporation takes place only from the surface of the liquid Distillation takes place from the whole liquid mass. It takes place below boiling point so there is no bubble formation in evaporation. At the boiling point of the distillation process, the liquid forms bubbles. Evaporation is not necessarily separation or purifying technique. Distillation is a separation or purifying technique Evaporation is a slow process. Distillation happens rapidly. Evaporation is one type of unit operation where the atoms or molecules of the liquid solution acquire sufficient energy(boiling)and gets vaporized that is, enters the gaseous state. Distillation is one of the unit operation which is defined as method of separation and purification of components of a liquid through vaporization and condensation.

12. In evaporation concentrated liquid residue is required as product. In distillation, condensed vapour is required as the product. Evaporating liquid is only one component in most of the cases. Evaporating liquid is a mixture of two or more components. Even if mixtures of vapours are present, it is not necessary to separate them. It is necessary to separate each component. Example: Evaporation process is carried out in the manufacture of bulk drugs, manufacture of biological products(insulin). Biochemical products (Penicillin) and also employ in the preparation of blood products such as blood plasma and serum Distillation process is carried out for the separation of volatile oils, purification of organic solvents, refining of petroleum products etc.

13. Evaporation and Drying The term drying usually refers the removal of relatively small amounts of water from solid or nearly solid material , W hereas Evaporation is usually limited to the removal of relatively large amounts of water from solutions. In most cases drying involves the removal of water at temperatures below its boiling point, whereas , Evaporation means the removal of water by boiling a solution .

14. Evaporation and Drying 1.Evaporation is the unit operations where the atoms or molecules of the liquid solution acquire sufficient energy(by boiling) and gets vaporized(that is enters the gaseous state) 1. Drying is defined as the process of removing relatively small quantity of water or moisture from the material, so as to obtain dry product 2.Evaporation operation is employed when concentrated liquid resolve is required as the product During operation is employed when dried solid residue is required as the product.

15. Factors affecting evaporation The fallowing are the factors which affect the rate of evaporation of a liquid M = ks /P(b-b 1 ) k=Constant M=Mass of vapour formed per unit time S=Surface area of the liquid exposed P=Atmospheric pressure b=Maximum vapour pressure at the temperature of air b1=pressure due to the vapour of the liquid actually present in the air

16. 1.TEMPERATURE The rate of evaporation is directly proportional to the temperature of the liquid. Higher the temperature higher will be the evaporation but evaporation is maximum at the boiling point of the liquid. The evaporation can be accelerated by increasing the temperature but it will cause decomposition of heat sensitive principles of many drugs.

17. Many glycosides and alkaloids are decomposed at a temperature below 100 C. Hormones , vitamins, enzymes and antibiotics being more heat-sensitive materials needs special treatment in order to avoid decomposition e.g , malt extract is concentrated by evaporation under reduced pressure to avoid loss of enzyme and antibiotics are concentrated by freeze drying.

18. 2.Temperature and time of evaporation It has been observed that exposure to a relatively high temperature for short period of time may be less harmful to the active principles of a drug than a lower temperature with exposure for a longer period. On the basis of this fact, liquid is exposed to high temperature for a short period in film evaporator.

19. 3.Temperature and moisture content Some drug constituents decompose more readily in the presence of moisture if heated at a high temperature. This is due to the hydrolysis of the active constituents. To avoid decomposition of the active principles of such materials the evaporation is done at a low temperature and then the final drying is done at a high temperature when only little moisture remains in it . e.g , Dry extract of belladona is prepared in this manner.

20. 4.TYPES OF PRODUCT REQUIRED The type of product required will often decide which method and apparatus should be employed for evaporation. Evaporating pans or stills will produce liquid or dry products. Film evaporators will yield only liquid products. Spray dryer produces dry product with good solubility.

21. Vacuum evaporator gives porous product suitable for conversion to granules , for example , preparation of granular extract of cascara for tablet making.

22. 5.EFFECT OF CONCENTRATION(film and deposit) During evaporation the upper layer of the liquid under evaporation has a tendency to form a film and formation of precipitate in the product may deposit on the heating surface which results in lowering down of the rate of evaporation.

23. Film reduces the evaporating surface and precipitated matter hinders the transfer of heat . Therefore efficient stirring is required in order to prevent degradation of the product at the bottom due to excessive heat and it will also prevent decomposition of solids.

24. 6.SURFACE AREA The rate of evaporation is directly proportional to the surface area of the evaporator, in which the liquid is evaporated. The larger the surface area of the evaporator,the shorter is the time it takes to evaporate the liquid.

25. 7.VAPOUR PRESSURE OF THE LIQUID TO BE EVAPORATED The rate of evaporation is directly proportional to the vapour pressure of the evaporating liquid. The liquid has maximum vapour pressure at its boiling point. As such the rate of evaporation can be increased by raising the temperature of the evaporating liquid. The rate of evaporation of liquid is the maximum at its boiling point.

26. If the atmospheric aqueous vapour pressure or moisture contents in the air are high, the rate of evaporation will be slow. If the outer atmosphere is dry, the rate of evaporation will be greater. Lower the external pressure , the lower the boiling point of the liquid and hence greater will be the rate of evaporation. This condition is achieved by applying vaccum .

27. 8.Vapour pressure The nature of liquid is also important for rate of evaporation , liquid with low boiling points evaporate quickly because of high vapour pressures at low temperatures . Lower the external pressure , the lower the boiling point of the liquid and hence greater will be the rate of evaporation.

28. 9.ECONOMIC FACTORS While selecting the method and apparatus employed for evaporation, due consideration must be given to economy of labour, fuel , floor area and materials. The recovery of solvents and the utilization of ‘waste’ heat are also important factors which contribute significantly in the reduction of over all costs.

29. For evaporation, heat is necessary to provide the latent heat of vapourisation , hence , rate of evaporation is controlled by rate of heat transfer. Therefore , evaporator is designed to give maximum heat transfer to the liquid.

30. EVAPORATING PANS(STEAM JACKETED KETTLE) PRINCIPLE; Steam is supplied to a jacket 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 convection. The temperature rises and the escaping tendency of the solvent molecules into vapour increases. Stirring further enhances the vaporisation of solvent molecules.

31. CONSTRUCTION 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.

32. Copper is an excellent material for the construction of kettle because of its good conductivity . If acidic materials are evaporated some quantity of copper would dissolve . For such preparations , tinned copper(Tinned copper wire is a type of copper wire coated in a thin layer of tin to protect the copper from corrosion) is used . Iron is used for the construction of the jacket because it has minimum conductivity.

33. To prevent rusting of the jacket, the iron is either tinned(Tinning is the process of thinly coating sheets of wrought iron or steel with tin) or enameled (coat or decorate (a metallic or hard object) with enamel(an opaque or semi-transparent glossy substance ) on inner surface.

34. An inlet for the steam and outlet (vent) for non condensed gases are provided near the top of the jacket. Condensate leaves the jacket through one more outlet provided at the bottom. The kettle is provided with one outlet for product discharge at is bottom.

35. WORKING Aqueous extract to be evaporated is placed in the kettle. Steam is supplied through the inlet. Steam gives out its heat to the contents and the condensate leaves through the outlet. The contents must be stirred manually for smaller volumes and mechanically for larger volumes.

36. The rate of evaporation is fast in the initial stages and decreases gradually as the liquid becomes concentrated. Any room where evaporation is carried by this apparatus must have good ventilation to remove the vapour.

37. Otherwise the room is quickly filled with a dense fog of condensed vapour and water falls from the roof and runs down the walls. Fans fitted over the pan not only remove the vapour and prevent condensation in the room, but also accelerate the rate of evaporation by quickly removing saturated air from the surface of the liquid.

38. The kettle may be fixed or made to tilt. A kettle about 90 liters capacity may be made to tilt. But above this capacity the weight of the pan along with its contents becomes to great to tilt . Hence the bottom outlet is used to collect the concentrated product.

39. ADVANTAGES 1.Evaporating pan is constructed both for small scale and large scale operations. 2.It is simple in construction and easy to operate , clean and maintain. 3.Its cost of installation and maintenance is low.

40. 4.Wide variety of materials can be used for construction such as copper , stainless steel and aluminium. 5.Stirring of the contents and removal of the product is easy.

41. DISADVANTAGES 1.In evaporating pans, heat economy is less, hence cost per unit material production is more. 2.It is not suitable for heat sensitive materials due to long time of exposure. 3.The evaporating pan is an open one and the vapours can pass direct to the atmosphere which may lead to saturation of the atmosphere with vapours. This in turn may cause discomfort to the worker. It may also slow down the process of evaporation.

42. 4.Boiling point of water cannot be reduced since reduced pressure cannot be created in open type evaporator . 5.The heating surface is limited and decreases proportionally to increase in size of the pan.

43. USES Evaporating pan is suitable for concentrating aqueous and thermostable liquors for example liquorice extract.

44. FORCED CIRCULATION EVAPORATOR PRINCIPLE: In forced circulation evaporator, liquid is circulated through the tubes as high pressure by means of a pump. Hence, boiling does not takes place, the boiling point is raised.

45. Forced circulation of the liquid also creates some form of agitation[the material is agitated by stirring rod or by mechanical propeller]. When the liquid leaves the tubes and the vapour head. Pressure fall suddenly . This leads to the flashing of super heated liquor and vapour get removed.

46. CONSTRUCTION The steam jacketed tubes are held between two tube sheets. The tube measures 0.1m inside diameter and 2.5m long. The part of the tubes projects into the vapour head(flash chamber). which consists of deflector. The vapour head is connected to a return pipe, which runs downwards and enters in to the inlet of a pump.

47. Working Steam is introduced into calandria . 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 result the vapour and liquid mixtures rushes out of the tubes at a high velocity. This mixture strikes the deflector which throws the liquid downward.

48. Results in effective separation of liquid and vapour . The vapour enters the cyclone separator and leave equipment . The concentrated liquid returns to the pump for further evaporation . Finally the concentrated product is collected.

49. ADVANTAGE The heat transfer coefficient is high due to rapid liquid movement. Salting,scaling( the accumulation and formation of unwanted materials ) are not possible due to forced circulation. The rapid evaporation rate makes this evaporation useful for concentration of thermolabile materials eg.Insulin and liver extract. It Is useful for high viscous preparations because of pumping mechanism is used.

50. DISADVANTAGES It is expensive, because of power(pump)is required for circulation.

51. USE If evaporation is conducted at reduced pressure , its suitable for thermolabile products, Used for concentration of insulin , liver extracts.

52. HORIZONTAL TUBE EVAPORATOR PRINCIPLE Steam is passed through the horizontal tubes. Heat transfer takes place through the tubes gets heated, boiling of the feed occurs leading to vaporization of the solvent, and escapes from the top of the evaporator. The concentrated liquid is collected from the bottom.

53. CONSTRUCTION Large cylindrical body with conical or dome shaped top and bottom. It is made up of cast iron(superior resistance to mode rate corrosion) or plate steel. Size of the body 1.8 to 2.4 m diameter, 2.4 to 3.6 height. Lower part of the body consists of a steam compartment with steam inlet. Steam condensate outlet may be one or two number at the bottom, outlet for non condensed gases,6 to 8 stainless steel horizontal tubes are placed.

54. WORKING Feed is introduced through the feed inlet. The level of feed is slightly taken above the level of the horizontal tubes. Steam is passed through the steam inlet, the horizontal tubes receive heat from the steam and transferred it to the liquid. Hence solvent gets evaporated and escapes through the outlet placed at the top.

55. This process continued until thick concentrated liquid is obtained, is collected from the bottom.

56. ADVANTAGES Cheap, easy to install. Evaporation process is less time consuming when compared to evaporation pan. Suitable for substance which tend to form foam, it has greater capacity to separate vapour from the feed. Cost per square meter of heating surface is less. Ease of tube removals.

57. DISADVANTAGE Liquid circulation is poor , not suitable for viscous substances.

58. USE Suitable for non viscous solutions , do not form scales , cascara extract can be concentrated.

59. LONG TUBE EVAPORATORS(climbing film evaporator) PRINCIPLES In climbing film evaporator, tubes are heated externally by steam cold or preheated liquor is introduced in to the tube(1) 1.Heat is transferred to the liquor from walls and boiling begins(2)Increasing in vigour(3)and (4). Eventually sufficient vapour has been formed for the smaller bubbles to unite to a large bubble(5). As more vapour is formed, the slug of liquid blown up the tube ,the tube is filled with vapour, while the liquid spread as a film over the walls(6).

60. This film of liquid continues to vaporise rapidly , the vapour escaping up the tube and because of friction between the vapour and liquid , the film also dragged up the tube . The liquid film travels up the tube at velocities of the order of 6 or 7 meter/second.

61. Construction In this evaporator , the heating unit consists of steam jacketed tubes , having a length to diameter ratio about 140 to 1. So that a large evaporator may have tubes 50mm in diameter and about 7m in length . Here the tubes (long and narrow) are held between two plates.

62. A separator is placed at the top to the vapour head . The evaporator carries steam inlet , vent outlet and condensate outlet . The liquor to be evaporated is introduced into the bottom of the tube.

63. At the top the mixed vapour and concentrated liquid are ejected at a considerable speed into a separator . The separator allows the vapour to escape from the top and the concentrated liquid is collected at the bottom.

64. Working In these evaporators a large number of vertical tubes about 7 meters in length and 50mm in diameter are enclosed in an outer jacket to which steam is supplied . Thus the tubes are heated externally . The preheated feed liquid is admitted at the base . Here it boils and the vapours formed take the liquid up the tube at a velocity of about 6 to 7 meters/second.

65. At the top the mixed vapour and concentrated liquid are ejected at a considerable speed into a separator . The separator allows the vapour to escape from the top and the concentrated liquid is collected at the bottom .

66. The liquid takes only a few seconds to travel the length of the tube. So the evaporator is very suitable for heat sensitive substances.

67. ADVANTAGES 1.The use of long narrow tubes provide a large area for heat transfer. 2.Since liquid flows at high velocity , the resistance for heat transfer at the boundary layer is reduced. As a result the heat transfer is enhanced . 3.The time of the contact between the liquid and the heating surface is very short , so it is most suitable for the concentration of a liquid containing the thermolabile materials.

68. 4.The evaporation rate is very high in spite of a short heating time. 5.There is no elevation of boiling point although the tubes are very long. 6.The method is suitable for materials which produse foam.

69. DISADVANTAGES 1.Climbing film evaporator is expensive, construction is quite complicated. 2.It is difficult to clean and maintain. 3.It is difficult to maintain at proper feed rate . If is too high , the proper concetration will not be made , If the feed rate is too low , the film cannot be maintained. 4.It is not advisable for very viscous liquids , salting liquids and scaling liquids.

70. USES Using climbing film evaporator , thermolabile substances such as insulin , liver extracts and vitamins can be concentrated . Clear liquids , foaming liquids and corrosive solutions in large quantities can be operated.

71. SHORT TUBE EVAPORATOR(vertical tube evaporator )(Not in syllabus) Principle; In standard vertical tube evaporator, the 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 the tubes gets heated. The solvent evaporates and the vapour escapes from the top. The concentrated liquid is collected from the bottom.

72. CONSTRUCTION It consists of a large cylindrical body made up of cast iron with dome shaped top and bottom. In side the body , calandria is fitted at the bottom. Calandria consists of a number of vertical tubes . These tubes are from 1 to 2m in length and from 0.05 to 0.075m in diameter , with the tubes up to 100 to 1000 in number in a vessel up to 2.5m or more in diameter.

73. In lets are provided for steam and feed . Outlets are provided for vapour , concentrated product , non condensed gases and condensate.

74. WORKING Steam is introduced out side the tubes , The condensate is 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 slightly above the top of the tubes so that the space which is left in the evaporator can be used for the purpose of separation of vapour from the boiling liquid.

75. The liquid in the tube is heated by steam and it begin to boil . The mixture of the liquid and vapour will come out of the tube which sets up a circulation with boiling liquid rising up in the smaller tubes of calandria and returning down the large central down take.

76. 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 the product can be withdrawn from the bottom outlet.

77. ADVANTAGES The heating area is increased by using a tubular calandria . The coefficient of the heat transfer is 3-5 times more as compared to the evaporating pan. The condenser and receiver can be attached to the evaporator in order to recover the costly solvent. A number of units can be joined to obtain more efficient effect[multiple effect of evaporators].

78. DISADVANTAGES The liquid is maintained above the level of the calandria . Hence, the top layers of the liquid need a long time for getting heated . This problem can be minimised by removing concentrated liquid slowly at the bottom. It is quite complicated and hence it is expensive to construct it. It is difficult to clean it. The maintenance of the evaporator is quite costly.

79. USES Vertical tube evaporator is used in the manufacture of cascara extract, sugar, salt , caustic soda.

80. MULTIPLE EFFECT EVAPORATION In single effect evaporators , steam is used to heat the liquid which provides the latent heat of vaporisation . The vapours are condensed in condenser , where the latent heat is given up to the cooling water and it goes to waste.

81. To avoid this wastage , two evaporators are connected together with a piping arrangement so that the vapours from calandria of first effect(which is heated by steam) is used to heat the calandria of the second effect.

82. This means that the calandria of the second effect is used as condenser for the first effect , so that latent heat of vaporisation is used to evaporate more quantity of the liquid instead of its going as waste . The vapour from second effect them taken to a condenser and converted into liquid.

83. In general , not more than two or three effects are combined together to have an economical and efficient evaporation of liquid.

84. P rinciple It is an arrangement of short tube evaporator to achieve economy. In this arrangement, vapours formed in the evaporator are used as the heating medium for the next evaporator. In this way, the energy associated with the vapours produced during evaporation is used many times to achieve economy.

85. Construction The construction of multiple effect of evaporator is using 3 evaporators, i.e triple effect evaporator. Construction of vertical tube evaporator(short tube)remain same. The vapour from first evaporator serves as a heating medium for 2 nd evaporator serves as heating medium for the 3 rd evaporator. Last evaporator is connected to a vaccum pump.

86. Working Parallel feed: In this 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.

87. The parallel feed arrangement is commonly used in the concentration of salt solutions. Where the solute crystallizes on concentration without increasing the viscosity.

88. O perations In the beginning, the equipment is at room temperature 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.

89. 1. the vent valves V 1 ,V 2 and V 3 are kept open and all other valves are closed(To remove non condensed gas) 2. Now high vacuum is created in the liquid chambers of evaporators. 3. The steam valve S 1 and condensate valve C 1 are opened. Steam is supplied. Steam first replaces cold air in the steam space of 1 st evaporator. When all the cold air is removed, the valve V 1 is closed.

90. The supply of steam is continued until the desired pressure P is created in the space of 1 st evaporator. At this pressure the temperature of the steam is t . Steam gives its temperature to the liquid feed in the 1 st evaporator and gets condensed. Condensate is removed through the valve C 1 .

91. Due to heat transfer, the liquid temperature increases and reaches the boiling point. During this process, vapour will be generated from the liquid feed. So formed vapour displaces air in the upper part of 1 st evaporator. Moreover, the vapour also displaces the air in the steam space of 2 nd evaporator.

92. After complete displacement of air vapour in the steam compartment of 2 nd evaporator, the valve V 2 is closed. The vapour of 1 st evaporator transmits its heat to the liquid of 2 nd evaporator and gets condensed. Condensate is removed through the valve C 2 . These steps continue in 3 rd evaporator also.

93. As the liquid in the 1 st evaporator gains temperature, the difference in temperatures between the liquid and steam decreases. As a result, the pressure in the vapour space of 1 st evaporator gradually increases to P 1 by increasing the temperature to t 1 which is the boiling point of the liquid in 1 st evaporator, decreasing the temperature difference(t -t 1 )

94. A similar change takes place in the 2 nd evaporator and the liquid reaches the boiling point. Similarly the process will be repeated in 3 rd evaporator. Finally three evaporators come to a steady state with the liquid boiling in all the three bodies. As boiling proceeds, the liquid level in 1 st evaporator comes down. Feed is introduced through feed valve to maintain liquid level constant.

95. To maintain liquid level constant feed valve F 2 and F 3 are used for 2 nd and 3 rd evaporators. This process continued until the liquid in all the desired viscosity. Now the product valves are opened to collect thick liquid. In this evaporator, there is continuous supply of feed, continuous supply of steam and continuous withdrawal of liquid from all three evaporators. It works continuously.

96. The evaporator can also fed by forward feed method, backward feed method and mixed feed method. In forward feed method the mother liquor is introduced to 1 st then 2 nd and 3 rd . In backward 3 rd to 2ndto 1 st . In mixed feed 2 nd to 3 rd to 1 st evaporator.

97. Advantages Suitable for large scale and continuous operation. Highly economical when compared with single effect. About 5 evaporator can be attached. Wastage of heat is minimized, hence more economical. This is in comparison with single effect which depicts more steam consumption is there and it is less economical . Used in large scale basis. Improved heat transfer.

98. Used in large scale basis. Improved heat transfer.

99. Dis advantages Capacity of triple effect evaporator is reduced when compared to three individual standard vertical tube evaporator.

100. Application Used when feed is costlier and instalment cost in low. T he reverse is seen in case of single effect evaporator.

101. Selection criteria for the evaporation Highest heat transfer coefficient should be reached Heat transfer coefficient even counter balance the power required in including circulation

102. Entrainment losses should be prevented or minimized, it can be prevented by using a deflector. Maximum steam economy should be achieved, this is seen in the case of multiple effect evaporator, where vapour from one effect serve as the heating media for second effect. Care should be taken in the prevention of evaporation so as for minimize the problem of salting,scaling,foaming,corrosive of evaporator etc

103. Appropriate evaporator is to be chosen by considering the aspects of feed supplied and desired product required.