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PPT - Evaporators Notes - Chemical Engineering

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 Page 1


EVAPORATOR
Page 2


EVAPORATOR
Purpose of Evaporation
n To concentrate solution by removing the vapor from a boiling liquid
solution
n In the majority of cases, evaporation refers to the removal of water
from an aqueous solution.
n Example: concentration of aqueous solutions of sugar, sodium chloride,
sodium hydroxide, glycerol, glue, milk, and orange juice.
n In these cases the concentrated solution is the desired product and the
evaporated water is normally discarded.
n In a few cases, water, which contains a small amount of minerals, is
evaporated to give a solids-free water to be used as boiler feed, for
special chemical processes.
n Evaporation processes to evaporate seawater to provide drinking water
have been developed and used.
Page 3


EVAPORATOR
Purpose of Evaporation
n To concentrate solution by removing the vapor from a boiling liquid
solution
n In the majority of cases, evaporation refers to the removal of water
from an aqueous solution.
n Example: concentration of aqueous solutions of sugar, sodium chloride,
sodium hydroxide, glycerol, glue, milk, and orange juice.
n In these cases the concentrated solution is the desired product and the
evaporated water is normally discarded.
n In a few cases, water, which contains a small amount of minerals, is
evaporated to give a solids-free water to be used as boiler feed, for
special chemical processes.
n Evaporation processes to evaporate seawater to provide drinking water
have been developed and used.
Processing Factors
1. Concentration in the liquid
- low viscosity: high mass transfer coefficient
- high viscosity: low mass transfer coefficient
-adequate circulation and/or turbulence must be present to keep
the coeffeicient from becoming too low
2. Solubility
- solubility increases with temperature
- crystallization may occur when a hot concentrated solution is
cooled to room temperature
3. Temperature sensitivity of materials
- food and biological materials may be temperature sensitive and
degrade at higher temperature or after prolonged heating.
Page 4


EVAPORATOR
Purpose of Evaporation
n To concentrate solution by removing the vapor from a boiling liquid
solution
n In the majority of cases, evaporation refers to the removal of water
from an aqueous solution.
n Example: concentration of aqueous solutions of sugar, sodium chloride,
sodium hydroxide, glycerol, glue, milk, and orange juice.
n In these cases the concentrated solution is the desired product and the
evaporated water is normally discarded.
n In a few cases, water, which contains a small amount of minerals, is
evaporated to give a solids-free water to be used as boiler feed, for
special chemical processes.
n Evaporation processes to evaporate seawater to provide drinking water
have been developed and used.
Processing Factors
1. Concentration in the liquid
- low viscosity: high mass transfer coefficient
- high viscosity: low mass transfer coefficient
-adequate circulation and/or turbulence must be present to keep
the coeffeicient from becoming too low
2. Solubility
- solubility increases with temperature
- crystallization may occur when a hot concentrated solution is
cooled to room temperature
3. Temperature sensitivity of materials
- food and biological materials may be temperature sensitive and
degrade at higher temperature or after prolonged heating.
4. Foaming or frothing
- food solution such as skim milk and some fatty-acid solution form a
foam or froth during boiling.
5. Pressure and temperature
- high operating pressure: high boiling point
6. Scale deposition and materials of construction
- Some solutions deposit solid materials called scale on the heating
surfaces.
- results in the overall heat-transfer coefficient decreases and
evaporator must be cleaned.
Page 5


EVAPORATOR
Purpose of Evaporation
n To concentrate solution by removing the vapor from a boiling liquid
solution
n In the majority of cases, evaporation refers to the removal of water
from an aqueous solution.
n Example: concentration of aqueous solutions of sugar, sodium chloride,
sodium hydroxide, glycerol, glue, milk, and orange juice.
n In these cases the concentrated solution is the desired product and the
evaporated water is normally discarded.
n In a few cases, water, which contains a small amount of minerals, is
evaporated to give a solids-free water to be used as boiler feed, for
special chemical processes.
n Evaporation processes to evaporate seawater to provide drinking water
have been developed and used.
Processing Factors
1. Concentration in the liquid
- low viscosity: high mass transfer coefficient
- high viscosity: low mass transfer coefficient
-adequate circulation and/or turbulence must be present to keep
the coeffeicient from becoming too low
2. Solubility
- solubility increases with temperature
- crystallization may occur when a hot concentrated solution is
cooled to room temperature
3. Temperature sensitivity of materials
- food and biological materials may be temperature sensitive and
degrade at higher temperature or after prolonged heating.
4. Foaming or frothing
- food solution such as skim milk and some fatty-acid solution form a
foam or froth during boiling.
5. Pressure and temperature
- high operating pressure: high boiling point
6. Scale deposition and materials of construction
- Some solutions deposit solid materials called scale on the heating
surfaces.
- results in the overall heat-transfer coefficient decreases and
evaporator must be cleaned.
TYPES OF EVAPORATION
EQUIPMENT
1. Open kettle or pan
2. Horizontal-tube natural circulation evaporator
3. Vertical-type natural circulation evaporator
4. Long-tube vertical-type evaporator
5. Falling-film-type evaporator
6. Forced-circulation-type evaporator
7. Agitated-film evaporator
8. Open-pan solar evaporator
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