Course title: Industrial Pharmacy-I
Course code: 612-T
Course In-charge: Ms. Sehar Iqtidar
EVAPORATION
• Evaporation is a specific type of vaporization where the liquid to gas transition
occurs at the surface of the liquid and below its boiling point
• It is a thermal separation or thermal concentration process.
• The major requirement is to maintain the quality of the liquid during evaporation
and to avoid damage to the product.
• In almost all evaporators the heating medium is steam, which heats a product on
the other side of a heat transfer surface.
VAPORIZATION EVAPORATION
Vapourization occurs when entire mass of liquid is raised to the It is only a surface phenomenon with only surface molecules
boiling point. escaping at a rate depending upon area of open surface.
It is a much faster process for the production of vapors. It is a relatively slow process and depends mainly on temperature
difference and on difference of vapour pressure between air and
liquid.
Boiling point is related to the pressure above the liquid surface Evaporation occurs at normal room temperature and application
and the amount of solute. of heat is not necessary under normal evaporation process.
Vapourization of liquid is visual in the form of vapor bubbles Evaporation is not usually visual and hence not detected easily
rising and escaping at the surface.
Vapourization can be controlled by variation in pressure. Liquid will evaporate until the pressure of its vapour is equal to
the equilibrium value. It is the vapour pressure of the liquid for
the given temperature of the liquid, for the closed system. In case
of open system, evaporation will continue till there is no more
liquid in the vessel.
EVAPORATORS
• These are most common types of evaporators.
1. Falling Film Evaporators
2. Rising Film Evaporators
3. Forced Circulation Evaporators
4. Plate Evaporators
5. Thermal and Mechanical Vapor Recompression (TVR &
MVR)
EVAPORATING STILL
EVAPORATING STILL
FALLING FILM EVAPORATORS
• Falling film evaporators typically utilize a shell and tube heat exchanger, with the process fluid
(the solution to be concentrated) flowing through the tubes and a heating fluid (e.g., steam)
circulating through the shell.
• The process fluid is fed into the top of the evaporator and distributed evenly across the tubes,
allowing it to flow down the inside walls under the influence of gravity, creating a thin "falling
film".
• As the falling film flows down the heated tubes, the solvent (e.g., water) in the process fluid
evaporates, leaving behind a more concentrated solution.
• The evaporated solvent vapor is separated from the concentrated solution, often through a
vapor-liquid separator.
• Suitable for heat-sensitive products.
• Most frequently used type of evaporator.
FALLING FILM EVAPORATORS
FALLING FILM EVAPORATORS
• Falling film evaporators are highly responsive to alterations of
parameters such as energy supply; vacuum, feed rate,
concentrations, etc.
• When equipped with a well-designed automatic control system they
can produce a very consistent concentrated product.
RISING FILM EVAPORATORS
RISING FILM EVAPORATORS
• These operate on a "thermo-siphon" principle. Feed enters the bottom of the heating tubes and as it heats up, steam begins to
form.
• The ascending force of this steam produced during the boiling causes liquid and vapors to flow upwards in parallel flow.
• At the same time the production of vapor increases and the product is pressed as a thin film on the walls of the tubes, and the
liquid rises upwards.
• This co-current upward movement has the beneficial effect of creating a high degree of turbulence in the liquid.
• This is advantageous during evaporation of highly viscous products.
• Usually there must be a rather high temperature difference between the heating and boiling sides of this type of evaporator.
• Otherwise the energy of the vapor flow is not sufficient to convey the liquid and to produce the rising film.
• The length of the boiling tubes will typically not exceed 23 ft.
• This type of evaporator is often used with product recirculation, where some of the formed concentrate is reintroduced
back to the feed inlet in order to produce sufficient liquid loading inside the boiling tubes.
FORCED CIRCULATION EVAPORATORS
FORCED CIRCULATION EVAPORATORS
FORCED CIRCULATION EVAPORATORS
WIPED FILM EVAPORATORS
WIPED FILM EVAPORATORS
• The Wiped Film Evaporator is used for concentration, distilling, dehydration and deodorization of
products which are heat sensitive or viscous.
• The equipment can handle a very wide range of feed compositions ranging from 1% to over 95%
concentration.
• Feed is introduced at the top of the unit and spread on the shell inner surface by the rotating
distribution plate.
• Specially designed wipers wipe the feed thus creating and renewing the film.
• The operation is continuous with a single pass; the self cleaning continuous contact wipers produce and
renew the thin film. Such an operation improves product yield, avoids residue and color formation.
• It has an internal condenser (optional) that minimizes the pressure drop and maintains vacuum.
WIPED FILM EVAPORATORS
• This thin film enables an efficient heat transfer even for highly
viscous fluids.
• The low boiling component evaporates and passes through an
entrainment separator.
• This minimizes the carry over of liquid droplets along with the
vapors.
• The vapors are removed through the vapor line to an external
condenser (optional) and condensed.
Flash Evaporation
• In flash evaporation, the liquid is preheated at
pressure and then flashed through a restriction into
a vessel at lower pressure where vapor is formed in
the process of restoring the liquid to its saturation
temperature.
Direct Contact Evaporators
• In this type of evaporator, a hot gas is injected into a pool of liquid
and causes it to evaporate, the vapor being carried away with the
efflux gas.
• Such evaporators are relatively cheap and useful for the
concentration of corrosive fluids, viscous liquids and slurries which
may be difficult to handle in more conventional heat exchanger.
• A convenient way of providing the hot gas is to use a submerged
combustion system in which the hot gas is produced in situ by the
combustion of gas or fuel oil in a combustion chamber mounted in
the center of the vessel containing the liquid.
EVAPORATION UNDER REDUCED PRESSURE
• Vacuum evaporation is the process of causing the pressure in a liquid-filled
container to be reduced below the vapor pressure of the liquid, causing the liquid
to evaporate at a lower temperature than normal.
• The vacuum evaporation treatment process consists of reducing the interior
pressure of the evaporation chamber below atmospheric pressure.
• This reduces the boiling point of the liquid to be evaporated, thereby reducing or
eliminating the need for heat in both the boiling and condensation processes.
• There are other advantages, such as the ability to distill liquids with high boiling
points and avoiding decomposition of substances that are heat sensitive.
REFERENCES:
• https://www.thermopedia.com/content/744/
• http://www.pharmacy180.com/article/evaporators-2646/
• Cooper and Gunn’s Tutorial Pharmacy (sixth edition).
• Aulton's Pharmaceutics: The Design and Manufacture of
Medicines.
