CHE 454A
Unit Operations Involving Particulate Solids for
Chemical Engineers
Dr. Raju Kumar Gupta,
Associate Professor,
Department of Chemical Engineering,
Indian Institute of Technology Kanpur,
Kanpur 208016, India
Cletus ( Lecture l -
2)
-
unit process
unit operation
-
*
upstream process :
-
unit operation :
crushing , grinding ,
washing filtration drying
-
, ,
mining ,
etc .
* Reaction :
chemical Mxn takes place
material
-
raw →
products
Downstream
processes
*
:
unit operation : Distillation ,
evaporation ,
extraction
, settling , centrifugation
etc .
United :
physical / or mechanical
procedure occurring
individually or parallel to chemical
Mxn .
physical steps of preparing reactants
-
separating a
purifying products
-
Recycling unconverted reactants
into
-
controlling energy transfer or
out of the reactor
mechanism .
purely based on
physical or
mechanical forces such as
* Gravitational force
* centrifugal face
* mechanical & kinetic forces
arising from flow
* Final property of product depend
on unit
operation used
⑨ solid
-
-
solid operations :
crushing , gain ding , sieving ,
compaction ,
cutting , storage 4
transport of bulk solids etc .
⑤ solid -
fluid operations :
-
Filtration ,
sedimentation , centrifugation ,
floatation .
cyclone separators
61 Dp
sphericity :
④
-
4S
-
=
setup
-
Dp -
nominal alia .
of particle
SP
surface battle
-
area
of one
Up volume of particle
-
one
For a
sample of uniform particles of dis .
Dp
,
FT m
total
of sample
-
µ up = mass
Pp -
density of particle
Total surface area
of particle ,
A = N
Sp
M 6 up
Msp
A
.
-
-
= =
Ep
-
Up Dp %
Ep up
a-⇐gseT④*
6 m
specific surface area
of mixture
( total surface per mass
of particles)
area
62 , 6am
Ass =
Aw =
+
GRI
t
Ep
+
-4g
-
, Cp Dps & GDI
ki -
mass faction in a
given increment
n - no
of increment
Dpi -
Average particle dia
,
taken as
arithmetic smallest
average of
&
largest particle diameters in
increment
:/ I
opening
mesh Average particle
screen
D#¥m
Y 4699 4.699
÷: : :: :::¥o .
8+10 I O
l 65
-
I } 2.007
-
E¥i:÷ .
dig
Volume
-
mean
, surface
DTs =
qA÷p=E¥
it Bpi
]
Problem 1 :
Pp = O '
00265
81mm
-
As =
O
'
571
For the material b/w 4 -
mesh of 200 mesh
in
particle size calculate specific surface
,
-
in
area mm
1g .
h
6
ki
Ass -
E
E
-
El Dpi
Particle
Understanding of Particle SizeSize Distribution
and
Particle Shape
Particle Size
Particle size or grain size refers to the diameter of a grain of
granular material
Particle
❑ The size of a spherical homogeneous particleSize Distribution
is uniquely
defined by its diameter.
❑ For regular, compact particles such as cubes or regular
tetrahedra, a single dimension can be used to define size.
❑ With some regular particles it may be necessary to specify
more than one dimension: For a cone the base diameter
and height are required whilst for a cuboid three
dimensions are needed.
❑ For irregular particles, it is desirable toParticle Size
quote the Distribution
size of a
particle in terms of a single quantity, and the expression most
often used is the "equivalent diameter".
❑ The assigned equivalent diameter usually depends on the
method of measurement.
❑ Several equivalent diameters are commonly encountered.
For example, the Stokes' diameter is measured by
sedimentation and elutriation techniques; the projected
area diameter is measured microscopically and the sieve-
aperture diameter is measured by means of sieving.
Influences of Particle Size Particle Size Distribution
❑ Particle size influences dissolution
Small particles dissolve more rapidly than large ones, which is important
in various manufacturing processes.
❑ Particle size influences flow properties of powders
The flow properties of powders are strongly dependent on particle size
and, in particular, particle shape. Since most powders are moved from one place to
another by flowing, control of flow behavior is highly important. Generally, coarse,
roughly spherical particles flow much more easily than small or elongated particles.
❑ Particle size influences stability of dispersions
The stability of dispersions, such as suspensions and emulsions,
depends on the size of the dispersed material. The forces between colloidal
particles depend on their dimensions, and the settling.
Particle Size Distribution
Effect of Particle Shape
❑ Particle shape influences such properties as:
➢ Flowability of powders
➢ Packing
➢ Interaction with fluids
❑ The variation between the diameters increases as the particles
diverge more from the spherical shape.
❑ Different results from different techniques can be compared by
applying shape factors and shape coefficients.
Particle Size Distribution
Particle Size Distribution
❑ The particle size distribution (PSD) may be defined as
“Particle size distribution (PSD) of a powder, or granular material,
or particles dispersed in fluid, is a list of values or a mathematical
function that defines the relative amounts of particles present,
sorted according to size.”
Particle Size Distribution
Significance of Particle Size Distribution (PSD)
❑ The PSD of a material can be important in understanding its
physical and chemical properties.
❑ It affects the strength and load-bearing properties of rocks and
soils.
❑ It affects the reactivity of solids participating in chemical
reactions, and needs to be tightly controlled in many industrial
products such as the manufacture of printer toner and cosmetics.
Particle Size Distribution
Sieve Analysis
❑ Sieve analysis is one of the oldest methods of size analysis.
❑ Sieve analysis is accomplished by passing a known weight of
sample material successively through finer sieves and weighing
the amount collected on each sieve to determine the percentage
weight in each size fraction.
❑ Sieving is carried out with wet or dry materials and the sieves
are usually agitated to expose all the particles to the openings.
Particle Size Distribution
Process of Sieving
❑ The process of sieving may be divided into two stages.
❑ First, the elimination of particles considerably smaller than the
screen apertures, which should occur rapidly and, second, the
separation of the so-called "near-size" particles, which is a
gradual process rarely reaching final completion.
❑ The effectiveness of a sieving test depends on the amount of
material put on the sieve (the "charge") and the type of movement
imparted to the sieve.
Particle Size Distribution
❑ The woven sieve is the oldest design, and it is normally made
by weaving fine metal wire into a square pattern, then soldering
the edges securely into a flattish cylindrical Container.
❑ Woven-wire sieves were originally designated by a mesh
number (the number of wires per inch or the number of square
apertures per square inch)
16 Mesh 6 Mesh 3 Mesh
Screen Analysis & Standard Screen Series
❑ Testing sieves are made of woven wire screens, the mesh and
dimensions of which are carefully standardized. The openings are
square. Each screen is identified in meshes per inch.
❑ The actual openings are smaller than those corresponding to mesh
numbers because of thickness of the wires.
Tyler standard screen scale
Tyler standard screen scale
Typical Screen Analysis
The notation 14/20 means ‘through 14 mesh and on 20 mesh’
Dpi means the particle diameter equal to the mesh opening of screen i
Screening equipment
Gyrations at one end,
Gyrations in horizontal plane Gyrations in vertical plane
shaking at other
Shaking Mechanically vibrated Electrically vibrated
