2. 4th
Stage Lect. 1 Unit Operations
2
Introduction to Unit Operations
Combination of basic concepts from mass transfer, heat transfer and
momentum.
What is chemical engineering?
Chemical engineering is a branch of engineering that applies sciences
(e.g. chemistry and physics) and life sciences (e.g. biology, microbiology and biochemistry)
together with mathematics and economics to produce properly useful chemicals, materials and
energy. Modern chemical engineers are concerned with processes that convert raw materials
or chemicals into more useful or valuable forms.
What are unit operations?
Every industrial chemical process is based on Unit Operations (physical treatment) and
Unit Process (chemical treatment) to produce economically a desired product from specific
raw materials. The raw materials are treated through physical steps to make it suitable for
chemical reaction. So, knowledge of unit operations like ‘Mixing and agitation of liquid’
and’ heat flow’ is very much necessary. The subject Unit Operations is based on fundamental
laws, physicochemical principles. Unit Operations gives idea about science related to specific
physical operation; different equipments design, material of construction and operation; and
Raw Materials
Processes
Products
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Stage Lect. 1 Unit Operations
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calculation of various physical parameters (mass flow, heat flow, mass balance, power and
force etc.).
Unit operations in chemical engineering consist of five classes:
1. Fluid flow processes, including fluids transportation, filtration, and solids fluidization.
2. Heat transfer processes, including evaporation and heat exchange.
3. Mass transfer processes, including gas absorption, distillation, extraction, adsorption,
and drying.
4. Thermodynamic processes, including gas liquefaction, and refrigeration.
5. Mechanical processes, including solids transportation, crushing and pulverization,
and screening and sieving.
Examples of unit operations in chemical engineering
No. Unit operation No. Unit operation
1. Heat flow, Fluid flow, momentum 8. Fluidization
2. Drying 9. Liquid Filteration
3. Reynolds Analogloy 10. Membrane separation
4. Boundary layer 11. Centerfugal separation
5. Friction Fcator 12. Mixing process
6. Heat transfer for laminar flow 13. Sedimentation
7. Extraction 14. Crushing
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Stage Lect. 1 Unit Operations
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Following are some examples of physical processes which are considered
unit operations:
1. Sugar Manufacture:
Sugar cane crushing → sugar extraction → thickening of syrup → evaporation of
water → sugar crystallization → filtration → drying → screening → packing.
2. Salt Manufacture:
Brine transportation → evaporation → crystallization → drying → screening →
conveying → packaging.
3. Pharmaceutical Manufacture:
Formulation of chemicals, mixing, granulation → drying of granules → screening →
pressing tablet → packaging.
Some Important Quantities in Unit Operations
( )
( )
Heat capacity: amount of heat required to increase the temperature of a material 1 degree.
[ ] [ ]
Where:
is the enthalpy.
is the internal energy.
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Stage Lect. 1 Unit Operations
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For ideal gases,
g where Rg is the constant of gas Rg = where R is universal gas constant,
Mwt is molecular weight in kg/kmol
harles's Boyle's law
Other important laws
: ,
Basic Principle of Unit Operations
All unit operations are rate processes, based on a transfer rate of mass or energy:
( )
( )
Process Driving force Resistance
Fluid Flow Pressure Viscosity and density of fluid
Heat transfer Temperature Conductivity of solid
Mass Transfer Concentration Diffusivity
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Stage Lect. 1 Unit Operations
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Unit Systems
We have three main unit systems as incorporated in the table
Temperature
Power
Time
energy
pressure
Force
volume
length
Mass
Properties
System
K
W
s
J
Pa
N
m3
m
Kg
SI
unit
o
C
erg/s
s
erg
cal
barye
(Ba)
dyne/cm2
atm
dyne
cm3
cm
g
CGS unit
o
F
o
R
F
hp
s
lbf.ft
pdl
lbf
ft3
ft
lbm
FPS unit
Ex. For discussion
Convert the following amount into corresponding units
1. A body of 120 lb is hanging by rob of 15 ft, find the potential energy in lbf.ft; and
then in Joule
2. 100 Pascal to psi
3. 20 hp to W
4. 20 kJ/(kg.o
C) to Btu/ (lb. o
F)
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Stage Lect. 1 Unit Operations
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H.W. ( required as a homework)
1. Convert 100 N to pound force.
2. A fluid of 100 lb is flowing through a pipe with 15 ft/s, what is its kinetic energy in lbf.ft
and J.
3. convert 1 hp to W
4. As shown below, determine
Gas mixture
=25 %
yair= 75 %
Q gas= 1500
m3
/hr (dry)
At 15.6 o
C and 1
atm
Gas mixture
=0.5 %
T=21.1 o
C
T= 37.8 oC
P= 1.02 atm
=10 %
a. The percentage of NH3 entering the tower and is not absorbed by the water?
b. The volumetric flowrate of water in (ft3
/s) pumped to the top of the tower?
