Survey of unit operations

1. Survey of Unit Operations
Nadia Junaid

2. Unit Operations: Introduction
Chemical Engineering is study of a group of industrial processes
in which raw materials are changed or separated
into useful products
RAW MATERIALS >>>>>>>> PRODUCTS
Chemistry:
- to create a new substance
- to study its properties
- to investigate all possible
pathways from one substance to
another
Chemical Engineering:
- to design the most optimal technology
for production of a specified substance
from raw materials
- to develop and discover new
technological applications for materials

3. A raw material can be converted into a
Product by doing such operations that
can cause certain changes/steps,
physical or chemical
Changes
(Steps)
Raw Materials
Product

4. Operations on Raw Materials
The operations may be
Physical operations
or
Chemical Operations.

5. A Physical (Operation) Change
or
A Chemical Change
• Convert Water into Ice (Cooling)
• Is any chemical Change there?
• NO
• Make a sugar solution
• Is any chemical Change there?
• NO
• Convert Water in to Vapours/Steam (Heating)
• This is also a physical Change

6. Differentiate the following as
Physical or Chemical changes
Combustion of Wood
Combustion of Natural Gas
Rusting of Iron
Drying
Heating
Cooling
Crushing of stones
Separation
Distillation
(First 3 steps/operations are
Chemical Changes, and the
remaining are Physical
Operations)

7. History of the term “Unit Operation”
• Historically, the different chemical industries were regarded
as different industrial processes and with different principles.
• Arthur Dehon Little propounded the concept of "unit
operations" to explain industrial chemistry processes in 1916.
• In 1923, William H.Walker, Warren K. Lewis and William H.
McAdams wrote the book The Principles of Chemical
Engineering and explained the variety of chemical industries
have processes which follow the same physical laws.They
summed-up these similar processes into unit operations.
• Each unit operation follows the same physical laws and may
be used in all chemical industries.
• The unit operations form the fundamental principles of
chemical engineering.

8. Define Unit Operation
In chemical engineering and related fields, a unit
operation is a basic step in a process. Unit
operations involve bringing a physical change such
as separation, crystallization, evaporation, filtration
etc. For example, in milk processing,
homogenization, pasteurization, chilling, and
packaging are each unit operations which are
connected to create the overall process. A process
may have many unit operations to obtain the
desired product.

9. Unit Operations are operations that
cause Physical Changes only
Unit Operations is a method of analysis and design of
chemical engineering processes in terms of individual
tasks/operations
-It is a way of organizing chemical engineering
knowledge into groups of individual tasks/operations
-A unit operation: basic step in a chemical
engineering process that can cause physical change
conversions.

10. Examples: Unit Operations
• Heat Transfer
• Evaporation
• Humidification
• Gas absorption
• Solvent Extraction
• Adsorption
• Distillation
• Drying
Mixing
Classification
Fluidization
Filtration
Screening
Crystallization
Centrifugation
Materials Handling
Fluid Dynamics

11. unit operations consist of five classes
• Fluid flow processes, including fluids transportation, filtration, solids
fluidization
• Heat transfer processes, including evaporation, condensation
• Mass transfer processes, including gas absorption, distillation,
extraction, adsorption, drying
• Thermodynamic processes, including gas liquefaction, refrigeration
• Mechanical processes, including solids transportation, crushing and
pulverization, screening and sieving
• Chemical engineering unit operations also fall in the following
categories:
• Combination (mixing)
• Separation (distillation)
• Reaction (chemical reaction)

12. Unit Operations: Classification
Fluid flow processes
- fluid transport
- solids fluidization
- mixing
Heat transfer processes
- heating/cooling
- evaporation/condensation
Mass transfer processes
- absorption
- distillation
- extraction
- adsorption
- drying
Thermodynamic processes
- liquifaction
- refrigeration
Mechanical processes
- crushing
- sieving
- solid transportation

13. Chemical separation processes:
required background
B
V
D
- How do we know that at pressure P
and temperature T, vapour and liquid
phase are present in the system?
- What is the composition of the phases?
Chemical engineering thermodynamics
La,xa
Va,ya
Vb,yb Lb,xb
- How do we know the amount of mass
exchanged by two phases?
- What is the new composition of the
phases?
Mass transfer methods

14. Chemical separation processes
Very Important to know as bio Chemical Engineers
Use
Technology maturity
Distillation
Gas Absorption
Crystallization
Adsortion
Membranes
Chromatography

15. What to Know about Unit operations
• All the unit operations obey simple physical
laws,
• Knowledge of the laws which is governing a
specific unit operation is necessary.
• The information about the Type of equipment
capable of operation/conversion at a large
scale is necessary

16. Heat Transfer
• Laws governing heat transfer
• Modes of heat transfer
• Conducation
• Convection
• Radiation
• (The above has been discussed in class)

17. Heat Transfer Equipment
• In daily life
• Air conditioner
• Heater
• Refrigerator
• Cooking Range
• Fans

18. Daily life examples of Heat transfer
• Car radiator
• Motor Bike engine FINS

19. Heat Transfer In Industry
Normally
• Heating is provided by steam (Boilers)
• Cooling is by
• water / air (Cooling Towers)

20. Heat Transfer Equipment
• Shell & tube type heat exchanger
• Coil type heater

21. DRYING

22. Drying of Clothes

23. Hair drying

24. Drying of food items

25. Open air drying

26. DRYING
• Removal of moisture/water from a substance
is termed as drying.
• Moisture drying from a substance depends on
many factors,
• For example: HUMIDITY,
• During rainy season it is difficult to dry clothes
• And during summer it takes no time is drying

27. Factors affecting rate of drying
• The water which is removed from a wet/damp
material is evaporated in air.
• The more is the temperature diff the more is
the rate of drying
• The more is the humidity, lesser would be rate
of drying
• Area of drying, More is area exposed more
would be rate of drying

28. METHODS OF DRYING
• Application of hot air (convective or direct
drying). Air heating increases the driving force
for heat transfer and accelerates drying. It also
reduces air relative humidity, further
increasing the driving force for drying. In the
falling rate period, as moisture content falls,
the solids heat up and the higher
temperatures speed up diffusion of water
from the interior of the solid to the surface

29. • . Spray drying
• Dielectric drying (radiofrequency or microwaves being
absorbed inside the material) is the focus of intense
research nowadays. It may be used to assist air drying
or vacuum drying.
• Drum drying
• Freeze drying or lyophilization is a drying method
where the solvent is frozen prior to drying and is then
sublimed, i.e., passed to the gas phase directly from
the solid phase, below the melting point of the solvent.
It is increasingly applied to dry foods

32. Application of Drying

35. DRYING vs EVAPORATION

36. Evaporation

40. FACTORS INFLUENCING EVAPORATION
Temperature: Higher the temperature, greater
will be the evaporation (Ex – Alkaloids,
Harmones, Enzymes, antibiotics – heat sensitive)
Vapour pressure: Rate of evaporation is directly
proportional to the vapour pressure of the liquid
Lower the pressure, greater will be the
evaporation
Surface area: Greater the surface area of the
liquid, greater will be the evaporation

41. • Time of evaporation: Exposure time is longer –
more evaporation
• Density: The higher the density, the slower a
liquid evaporates
• Concentration: Low concentration of the
substance – faster evaporation

42. • Moisture Content of Feed: Some drug
constituents undergoes hydrolysis readily in
presence of moisture at high temperature. To
prevent the decomposition, the material is
exposed to low temp. initially, then exposed to
higher temp. Time of evaporation: If time of
exposure is longer, greater will be the
evaporation, provided the constituents are
thermostable. Exposure of a drug to a relatively
high temp. for a short period of time may be less
destructive of active principle than a lower temp.
with long exposure time

43. Theory For molecules of a liquid to
evaporate
They must be located near the surface, be
moving in the proper direction, and have
sufficient kinetic energy Since the kinetic energy
of a molecule is proportional to its temperature,
evaporation proceeds more quickly at higher
temperatures. As the faster-moving molecules
escape, the remaining molecules have lower
average kinetic energy, and the temperature of
the liquid thus decreases. This phenomenon is
also called evaporative cooling

44. Evaporator

45. Examples
• Concentration of milk to produce condensed
milk
• Concentration of juices
• Concentration of NaOH, NaCl from aqueous
solutions to produce salt.
• Ether recovery from fat extraction

46. TYPES OF EVAPORATORS
• Evaporators with heating medium in jacket –
• Steam jacketed kettle (Evaporating pan)
• (II)Vapour heated evaporators with tubular heating surfaces
(A)Evaporators with tubes placed horizontally - Horizontal
tube evaporator (B)Evaporators with tubes placed vertically
(i) Evaporators with short tubes (a) Single effect
evaporators - Short tube vertical evaporator - Basket type
evaporator (b) Multiple effect evaporator - Triple effect
evaporator (ii) Evaporators with long tubes (a)Evaporators
with natural circulation - Climbing film evaporator - Falling
film evaporator (b)Evaporators with forced circulation -
Forced circulation evaporator

48. DISTILLATION

50. Distillation Equipments

54. Types of distillation

57. Application of Distillation
Purification of materials : Natural Products
Flavors Essential Oils Fragrances
Distilled air to separate it’s components like
oxygen, nitrogen, and argon
Solvent Recycling Xylene Solvent Recycling
Alcohol Solvent
Separate crude oil fractions

58. Herbal Distillates