EVAPORATION-PP

EVAPORATION:

EVAPORATION

MEMBERS:

MEMBERS Debabrata Mandal-1116 Md. Khalequeuzzaman-1124 Dewan Taslima Akhter-1108 Auditi Swarna-1104 Md. Mosaddaque-1120 Shamima Akhter-1106 Md. Raisul Islam-1112 Farhana Afroz-1109 Safinaz Arzu Ara Alam-1103

DEFINATION AND PRINCIPLE OF EVAPORATION :

DEFINATION AND PRINCIPLE OF EVAPORATION Evaporation is nothing but a thermal separation process. Theoretically, evaporation means simply vaporization from the surface of a liquid. Vaporization of a liquid below its boiling point is called evaporation. Thus, no boiling occurs and the rate of vaporization depends on the diffusion of vapour through the boundary layers above the liquid.

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In practice, this would be too slow and can take place even at room temperature. So that the liquid is boiled causing vapour to be liberated in the form of bubbles from the bulk of the liquid Thus a practical definition of evaporation is- ‘The removal of liquid from a solution by boiling the solution in a suitable vessel and withdrawing the vapour, leaving a concentrated liquid residue.

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This means that heat will be necessary to provide the latent heat of vaporization and, in general the rate of evaporation is controlled by the rate of heat transfer. Evaporators are designed, therefore, to give maximum heat transfer to the liquid, with the largest possible area, a suitable temperature gradient.

MECHANISM:

MECHANISM When heat applied in solution the motion of molecules increase and molecules present in the surface overcome the surface tension of the liquid and it evaporates because surface molecules have less cohesive force than others.

Factors Affecting Evaporation :

Factors Affecting Evaporation There are seven factors to affect evaporation. 1) Temperature 2) Surface area 3) Agitation 4) Atmospheric aqueous vapour pressure 5) Atmospheric pressure on the liquid under evaporation 6) Type of product required 7) Economic factors

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1) Temperature The rate of evaporation is directly proportional to the temperature. 2) Surface area The rate of evaporation is directly proportional to the surface area of the vessel exposed to evaporation. 3) Agitation Agitation is necessary for evaporation. 4) Atmospheric aqueous vapour pressure The rate of evaporation is inversely proportional to the atmospheric aqueous vapour pressure.

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5) Atmospheric pressure on the liquid under evaporation The rate of evaporation is inversely proportional to the atmospheric pressure on the liquid under evaporation. 6) Type of product required The selection of the method and apparatus to be used for evaporation depends upon type of product required. 7) Economic factors When selecting the method and apparatus the economic factors are important

TYPES OF EVAPORATOR:

TYPES OF EVAPORATOR Evaporators are divided mainly into three groups. 1.Natural circulation evaporator Examples : #Evaporating pans # Evaporating stills #Short tube evaporator

EVAPORATING PAN:

EVAPORATING PAN

EVAPORATING STILL:

EVAPORATING STILL

SHORT TUBE EVAPORATOR:

SHORT TUBE EVAPORATOR

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2.Forced circulation evaporator 3.Film evaporator Examples #Long Tube Evaporator # Wiped Film evaporator

FORCED CIRCULATION EVAPORATOR:

FORCED CIRCULATION EVAPORATOR

LONG TUBE EVAPORATOR:

LONG TUBE EVAPORATOR

WIPED FILM EVAPORATOR:

WIPED FILM EVAPORATOR

NATURAL CIRCULATION EVAPORATORS:

NATURAL CIRCULATION EVAPORATORS Evaporators in this category are those in which the movement of the liquid results from convection currents set up by the heating process. CONVECTION CURRENTS: The process in which heat moves through a gas or liquid as the hotter parts rises and the cooler, heavier part sinks.

EVAPORATING PANS:

EVAPORATING PANS On a manufacturing scale, liquid extracts containing water are evaporated in open pans called evaporating pans. The evaporating pan consists of- -A hemispherical shallow made of- Copper Stainless steel Alluminium Enameled iron -Steam jacket The hemispherical shape gives the best surface\volume ratio for heating and the largest area for the disengagement of vapour.

EVAPORATING PAN:

EVAPORATING PAN

ADVANTAGES:

1.They are simple, easy and cheap to construct. 2.They are easy to use and clean 3.Stirring of the evaporating liquids can be done easily. ADVANTAGES

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DISADVANTAGES 1.The whole of the liquid is heated all the time which may lead to decomposition of the components. 2.On the evaporating surface scume\foam is rapidly formed which decreases evaporation. Solids may be deposited at the bottom which make the stirring necessary. 3.This pan can only be used for evaporating aqueous and thermostable liquid extracts. They can not be used for evaporating extracts containing organic solvents like alcohol etc.

Forced circulation evaporators:

Forced circulation evaporators Forced circulation evaporators are one type of natural circulation evaporators with some added form of mechanical agitation. Construction Actually it is nothing but an evaporating pan in which the contents are agitated by a stirring rod or pole. Alternatively, a mechanically operated propeller or paddle agitator can be introduced in to an evaporating pan or still, or in to the downtake of a short-tube evaporator.

Working principle:

Working principle Here the liquor is circulated by means of a pump and as it is under pressure in the tubes, the boiling point is elevated and no boiling takes place. As the liquor leaves the tubes and enters the body of the evaporator, there is a drop in pressure and vapour flashes off from the superheated liquor.

FORCED CIRCULATION EVAPORATOR:

FORCED CIRCULATION EVAPORATOR

Advantages :

Advantages 1)These have an great advantage over natural circulation evaporators in that the rapid liquid movement improves heat transfer, especially with viscous liquids or materials that deposit solids or foam readily. 2)The equipment is suitable for operation under reduced pressure due to the capacity of the process to overcome the effect of greater viscosity of liquids. 3)These evaporators possess rapid evaporation rate.

Uses:

Uses 1)These evaporators are mainly used for thermolabile materials. 2)These can also be used in practice for the concentration of insulin and liver extracts

WIPED FILM EVAPORATORS:

WIPED FILM EVAPORATORS A form of film evaporator coming into increasing use is the wiped film evaporator or rotary film evaporator, which contains of a single, short tube of wide diameter, better described as a narrow cylindrical vessel,1 or 2 meters in length. A section across the evaporator is shown here where it will be seen that the vessel is surrounded by a heated jacked. Through the vessel is a bladed rotor, with a clearance of the order of 1mm between the tips of the rotor blades and the wall of the vessel.

MECHANISM:

MECHANISM The liquor is introduced at the top of the vessel and spread as a film over the heated wall by the action of the rotor. Evaporation occurs as the liquor passes down the wall, vapour is taken to a condenser and the concentrated liquor withdrawn at the bottom of the vessel. The evaporator is therefore a form of single tube, falling film evaporator in which the film is formed and agitated mechanically.

WIPED FILM EVAPORATOR:

WIPED FILM EVAPORATOR

ADVANTAGE:

ADVANTAGE Because of obtaining good heat transfer the method being especially useful with liquids that are too viscous to be processed in units in which the film is formed naturally.

APPLICATION OF EVAPORATION :

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.

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4.Used in purification of vitamins. 5.Concentration of proteins. 6.Concentration of biological products. 7.Stripping of solvents from vegetable & plant or herbal extracts. 8.Removal of water & solvents from fermentation broths. 9.Concentration of penicillin & related products

Improvement of Efficiency of Evaporation :

Improvement of Efficiency of Evaporation In theory each part of weight of water vaporized in an evaporator will require an equal weight of steam. In practice more is required because of variation in specific heat and to allow for heat losses. Modification of normal method will allow efficiency to be improved

MULTIPLE EFFECT EVAPORATION:

MULTIPLE EFFECT EVAPORATION The single effect evaporation use steam to supply heat to liquid and provide latent heat of vapourisation. This vapors then taken to a condenser where the latent heat is given up to the cooling water, which commonly then goes to waste. In multiple effects evaporation two evaporators are joined together with piping arrangement so that the calandria of the first effect is heated by steam: the vapor from the first effects used to heat the calandria of second effect. The vapor from the second effect is then taken to a condenser in the ordinary way.

VAPOUR RECOMPRESSION:

VAPOUR RECOMPRESSION When vapor recompression is used on a evaporator some of vapor from the process is returned to the calandria to provide heat to vaporized more of the liquid. Advantage: 1.Evaporation can be carried out at low temperature. 2.Only one evaporator is needed so reduce cost.

EVAPORATION UNDER REDUCEDE PRESSURE :

EVAPORATION UNDER REDUCEDE PRESSURE At reduced pressure evaporation increases. Advantage: 1.Evaporation occurs at low temperature, with less risk of damage to heat sensitive materials. 2.A lower operating temperature gives higher temperature gradients, without the need of excessive steam pressures. 3.The lower the operating, temperature the lower the steam pressure that can be used.

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