Evaporators

What is an evaporator? What are its

applications?
• An evaporator is used to vaporize a volatile solvent, usually water, from a
solution. Its purpose is to concentrate nonvolatile solutes such as organic
compounds, inorganic salts, acids, or bases. Typical solutes include
phosphoric acid, sulfuric acid, acid sulfate liquor, Kraft liquor, caustic soda,
sodium chloride, sodium sulfate, sugars, gelatin, radioactive wastes,
syrups, urea, etc.
• In many applications, evaporation results in the precipitation of solutes in
the form of crystals, which are usually separated from the solution with
settlers, cyclones, wash columns, elutriating legs, filters, or centrifuges.
Examples of precipitates are sodium chloride, sodium sulfate, sodium
carbonate, and calcium sulfate. The desired product can be the
concentrated solution, precipitated solids or both.
• In some applications, the evaporator is used primarily to recover a solvent,
such as potable water from saline water (desalination). In any case, the
relatively pure condensate from many evaporators is recovered for boiler
feed makeup, salt washing, salt dissolving, pump seals, instrument purges
equipment and line washing, and other uses.
 Name different types of evaporators.
• Short Tube/Calandria Type Evaporators: Generally used in sugar industry. Short tube evaporators can be of vertical
or horizontal tube types. These are less popular for present day applications. The calandria can handle both salting
and scaling applications as well as those where no precipitates are formed.
• Most Popular Types Are Long Tube Vertical with Natural or Forced Circulation:
• ➢ High capacities and for low viscosity solutions.
• ➢ Forced circulation type, usually with a submerged inlet, are advantageous for fouling or crystallizing solutions.
• Falling Film and Rising Film Evaporators: Less holdup and boiling takes place from a film of liquid. Shorter
residence times. Suitable for viscous and heat-sensitive liquids. Long tube vertical rising film evaporators are
commonly used to concentrate many nonsalting liquors and falling type are preferred for liquors requiring
evaporation at extremely low DT and for critically heat-sensitive liquors. Both types provide maximum evaporative
performance for the least capital investment.
• Agitated Film/Wiped Film Evaporators: For very high viscosity solutions.
• Plate and spiral type evaporators.
• Scraped surface evaporators.
• Direct-Heated Evaporators: Solar pans, submerged combustion type, etc.
• Jacketed and coiled vessels for small-scale evaporation applications. Jacketed evaporators are used when the
product is very viscous, the batches are small, good mixing is required, ease of cleaning is important, or glass-lined
equipment is required.
• Coils for evaporator heating surfaces come in an almost unlimited variety of shapes and sizes. The most common
application is to provide coils inside a tank with the evaporation process outside the coils. Evaporation can also
occur inside coils with the heating medium outside the coil.
 What are the ways by which energy
efficiency of an evaporation system can be
improved?
• There are three basic possibilities to save energy:
• ➢ Multiple effect evaporation.
• ➢ Thermal vapor recompression.
• ➢ Mechanical vapor recompression.
• & Application of one of these techniques will
considerably decrease the energy consumption. Often
it is feasible to combine two of these possibilities to
minimize capital and operating costs. In highly
sophisticated evaporation plants all three techniques
may be applied.
What are the ways by which energy
efficiency of an evaporation system
can be improved?
 What are the important problems
arising in an evaporation
process?
• High viscosity.
• Heat-sensitivity.
• Scaling.
• Entrainment problems.
• Problems involved with vacuum-generating equipment.
• Handling crystallized solids.
• Formation on heat transfer surfaces an insulating
blanket of air through which steam must diffuse before
it can condense. This is due to accumulation of
noncondensables on the surface.
 Illustrate with a diagram short vertical
tube calandria-type evaporator and
describe its characteristic features.
• The short tube vertical calandria-type evaporator is a type of industrial evaporator used in
various industries for concentrating solutions by removing the solvent or water. It consists of
a vertical shell (the calandria) with short tube bundles immersed in the liquid to be
evaporated. The liquid is fed into the evaporator and flows over the tubes, while steam or a
heating medium is passed through the tubes.
• The working principle of a short tube vertical calandria-type evaporator can be described as
follows:
• Feed Entry: The liquid solution to be concentrated is introduced into the evaporator through
an inlet at the top of the calandria. It is usually a preheated solution to improve the efficiency
of the evaporation process.
• Film Formation: The liquid forms a thin film as it flows down the vertical tubes in the
calandria. This film increases the surface area available for heat transfer and facilitates the
evaporation process.
• Heat Transfer: Steam or a heating medium, such as hot water or thermal oil, is circulated
through the tubes in the calandria. The heat from the heating medium is transferred through
the tube walls to the liquid film on the outside of the tubes. This heat causes the solvent or
water in the liquid to vaporize.
• Vapor Generation: As the heat is transferred to the liquid film, the solvent or water molecules
gain enough energy to overcome their binding forces and change into vapor (steam).
 Illustrate with a diagram short vertical
tube calandria-type evaporator and
•
describe its characteristic features.
Vapor Separation: The generated vapor rises due to its lower density compared to the liquid.
The vapor-liquid mixture enters a vapor-liquid separator at the top of the calandria. In the
separator, the vapor is separated from the remaining liquid. The separated liquid, which is
now more concentrated, is collected and removed from the evaporator.
• Condensation: The separated vapor, which contains the solvent or water vapor, is condensed
back into liquid form by cooling it down using a condenser. The condensation releases latent
heat, which is typically removed by a cooling medium, such as water.
• Product Collection: The condensed solvent or water, now in liquid form, is collected as the
concentrated product. If required, additional downstream processes may be employed to
further purify or process the concentrated product.
• Steam Generation: The non-condensable gases and any uncondensed vapor from the
separator may be directed to a vacuum system or vapor recompressor to create a pressure
differential that assists in continuous vapor generation.
• The process described above continues in a continuous or batch mode, depending on the
design and operation of the specific short tube vertical calandria-type evaporator. This type
of evaporator is favored for its compact design, efficient heat transfer, and suitability for
handling heat-sensitive products. It is commonly used in the food, pharmaceutical, chemical,
and other process industries for concentrating various liquid solutions.
Calandria-type evaporator
 Describe the working Principle of
Swenson rising film evaporator unit.
• The Swenson rising film evaporator is a type of industrial evaporator used for the
concentration of liquid solutions by removing the solvent or water. It is designed to handle
heat-sensitive materials and is commonly used in the food, dairy, and chemical industries.
The evaporator operates on the principle of a rising film of liquid and involves the following
working steps:
• Feed Entry: The liquid solution to be concentrated is fed into the top of the evaporator,
where it is evenly distributed to the tubes.
• Film Formation: The liquid forms a thin film on the inner surface of vertical tubes. The tubes
are heated using steam or a heating medium, which causes the liquid to start boiling and
form a rising film along the tubes' walls.
• Vapor Generation: As the liquid film moves downward due to gravity, the heat from the tubes
causes the solvent or water in the liquid to vaporize. The vapor generated flows in the
opposite direction to the liquid film and moves upward through the center of the tubes.
• Separation of Vapor and Liquid: As the vapor rises, it carries the vaporized components with
it. Near the top of the tubes, the vapor and liquid are separated. The vapor exits the top of
the tubes, while the concentrated liquid continues to flow downward.
• Condensation: The vapor containing the solvent or water vapor is directed to a condenser
where it is cooled and condensed back into liquid form. The condensation releases latent
heat, which is typically removed by a cooling medium, such as water.
 Describe the working Principle of
Swenson rising film evaporator unit.
• Product Collection: The condensed solvent or water is collected separately
from the concentrated liquid product.
• Recirculation: In some designs, a portion of the concentrated liquid may
be recirculated back to the feed to assist in maintaining a uniform liquid
film on the tubes and to control the concentration of the product.
• Heat Efficiency: The design of the Swenson rising film evaporator allows
for efficient heat transfer and minimizes the residence time of the liquid at
high temperatures, making it suitable for heat-sensitive products.
• The process is continuous, and the concentrated product is continuously
removed from the bottom of the evaporator while fresh feed is
continuously introduced at the top. This ensures a steady-state operation
and high efficiency in concentrating the liquid solution.
• The Swenson rising film evaporator is favored for its ability to handle
delicate and heat-sensitive materials, as well as its relatively compact
design and high evaporation rates. It is widely used in the processing of
heat-sensitive products such as milk, fruit juices, pharmaceuticals, and
various chemicals.
 Describe the working Principle of
Swenson rising film evaporator unit.
 Describe the working principle of
Swenson falling film evaporation unit
• The Swenson falling film evaporator is another type of industrial evaporator used for the
concentration of liquid solutions by removing the solvent or water. It is particularly suitable
for heat-sensitive materials and is commonly used in the food, beverage, and chemical
industries. The evaporator operates on the principle of a falling film of liquid and involves the
following working steps:
• Feed Entry: The liquid solution to be concentrated is fed into the top of the evaporator and
enters the heating section.
• Film Formation: The liquid is evenly distributed to the top of vertical heating tubes. The tubes
are designed to promote the formation of a thin and uniform film of liquid along their inner
walls. The feed liquid flows downward due to gravity.
• Vapor Generation: The tubes are heated using steam or a heating medium, which causes the
liquid film to start boiling and vaporize the solvent or water present in the solution. As the
liquid film moves downward, the vapor generated flows in the opposite direction (upward)
through the center of the tubes.
• Separation of Vapor and Liquid: Near the bottom of the tubes, the vapor and liquid are
separated. The vapor exits the top of the tubes, while the concentrated liquid continues to
flow downward.
• Condensation: The vapor containing the solvent or water vapor is directed to a condenser
where it is cooled and condensed back into liquid form. The condensation releases latent
heat, which is typically removed by a cooling medium, such as water.
 Describe the working principle of
Swenson falling film evaporation unit
• Product Collection: The condensed solvent or water is collected separately
from the concentrated liquid product.
• Recirculation: In some designs, a portion of the concentrated liquid may
be recirculated back to the feed to assist in maintaining a uniform liquid
film on the tubes and to control the concentration of the product.
• Heat Efficiency: The design of the Swenson falling film evaporator ensures
efficient heat transfer and minimizes the residence time of the liquid at
high temperatures, making it suitable for heat-sensitive products.
• The process is continuous, and the concentrated product is continuously
removed from the bottom of the evaporator while fresh feed is
continuously introduced at the top. This ensures a steady-state operation
and high efficiency in concentrating the liquid solution.
• The Swenson falling film evaporator is favored for its ability to handle
heat-sensitive materials, its relatively compact design, and its high
evaporation rates. It is widely used in the processing of heat-sensitive
products such as fruit juices, dairy products, pharmaceuticals, and various
chemicals.
 Describe the working principle of
Swenson falling film evaporation unit
 Describe the working principle of
Vertical forced circulation evaporator
• The Vertical Forced Circulation Evaporator (VFCE) is a type of industrial evaporator used for the
concentration of liquid solutions by removing the solvent or water. It is designed to handle viscous
or fouling materials and is commonly used in industries such as sugar, pulp and paper, chemical,
and wastewater treatment. The VFCE operates on the principle of forced circulation and involves
the following working steps:
• Feed Entry: The liquid solution to be concentrated is fed into the evaporator through an inlet at the
top or side of the vessel.
• Preheating: The feed liquid is preheated before entering the evaporator to reduce the temperature
difference between the feed and the boiling liquid inside the evaporator.
• Forced Circulation: The VFCE uses a pump or a recirculation system to force the liquid solution
through external heat exchangers, where it is heated by steam or a heating medium. This forced
circulation helps in maintaining a high velocity of the liquid, which prevents the formation of a thick
film on the heat transfer surfaces and minimizes fouling.
• Concentration and Vaporization: The heated liquid is then directed to the vertical tubes or channels
of the evaporator. Inside the tubes, the liquid starts boiling and vaporizing due to the applied heat.
The boiling liquid forms a rising film along the inner walls of the tubes, and the vapor flows in the
opposite direction (upward) through the center of the tubes.
• Vapor Separation: Near the top of the tubes, the vapor and liquid are separated. The vapor exits the
top of the tubes, while the concentrated liquid continues to flow downward.
 Describe the working principle of
Vertical forced circulation evaporator
• Recirculation: A portion of the concentrated liquid may be recirculated back to the feed to maintain
a steady flow and ensure uniform concentration distribution throughout the evaporator.
• Condensation: The vapor containing the solvent or water vapor is directed to a condenser where it
is cooled and condensed back into liquid form. The condensation releases latent heat, which is
typically removed by a cooling medium, such as water.
• Product Collection: The condensed solvent or water is collected separately from the concentrated
liquid product.
• Heat Efficiency: The forced circulation design of the VFCE ensures efficient heat transfer and
minimizes the residence time of the liquid at high temperatures, which is beneficial for heat-
sensitive materials and prevents fouling on heat transfer surfaces.
• The process is continuous, and the concentrated product is continuously removed from the bottom
of the evaporator while fresh feed is continuously introduced at the top. This ensures a steady-state
operation and high efficiency in concentrating the liquid solution.
• The Vertical Forced Circulation Evaporator is favored for its ability to handle viscous and fouling
materials, its high evaporation rates, and its effective heat transfer capabilities. It is widely used in
industries where conventional evaporators may face challenges related to fouling and scaling.
 Describe the working principle of
Vertical forced circulation evaporator
 Describe the working principle of
Mechanical vapor recompression
evaporation system
• The Mechanical Vapor Recompression (MVR) Evaporation System is a type of industrial evaporation
process used for the concentration of liquid solutions by removing the solvent or water. It operates on the
principle of utilizing mechanical energy to compress and recycle the vapor generated during evaporation,
thereby saving energy and improving overall efficiency. The MVR evaporation system involves the
following working steps:
• Feed Entry: The liquid solution to be concentrated is fed into the evaporator through an inlet.
• Preheating: The feed liquid is preheated using steam or a heating medium before entering the evaporator.
Preheating helps reduce the temperature difference between the feed and the boiling liquid inside the
evaporator, improving overall energy efficiency.
• Vapor Generation: The preheated liquid is directed to the evaporation chamber, where it is heated by
steam or another heating medium. As the liquid is heated, it starts to boil and generate vapor, separating
the solvent or water from the concentrated solution.
• Vapor Compression: Unlike traditional evaporators where the vapor is condensed separately, in an MVR
evaporator, the vapor is directed to a mechanical compressor. The mechanical compressor compresses the
vapor, increasing its temperature and pressure.
• Vapor Recycling: The compressed and high-temperature vapor is then recycled back to the evaporation
chamber. This recycled vapor is mixed with the incoming feed liquid or directly introduced into the
evaporation chamber to provide additional heat to the liquid. This process is called vapor recompression.
• Secondary Vapor Generation: The recycled and recompressed vapor continues to provide heat to the
liquid solution, facilitating further vapor generation. As a result, the need for external heating using steam
or other heating mediums is reduced, leading to significant energy savings.
 Describe the working principle of
Mechanical vapor recompression
•
evaporation system
Concentration: The evaporation process continues, and the concentrated liquid continues to
flow through the evaporation chamber.
• Vapor Separation: Near the top of the evaporation chamber, the vapor and liquid are
separated. The vapor, now enriched with the solvent or water vapor, is directed to a
condenser.
• Condensation: In the condenser, the vapor is cooled and condensed back into liquid form,
releasing latent heat. This heat can be recovered and used to preheat the incoming feed
liquid, further improving energy efficiency.
• Product Collection: The condensed solvent or water is collected separately from the
concentrated liquid product.
• Recirculation: In some designs, a portion of the concentrated liquid may be recirculated back
to the feed to maintain a steady flow and ensure uniform concentration distribution
throughout the evaporator.
• The MVR evaporation system offers significant advantages in terms of energy efficiency and
operational cost savings compared to traditional evaporators. It is widely used in industries
where energy consumption is a critical factor, such as the chemical, pharmaceutical, and
wastewater treatment industries. The ability to recycle and reuse the vapor generated during
the evaporation process makes the MVR system an environmentally friendly and sustainable
solution for concentrating liquid solutions.
Describe the working principle of
Mechanical vapor recompression
evaporation system