Comminution Theory
The Siam Cement Industry Co.,Ltd.
Content
Principle of Size Reduction
Reduction Ratio
Law of Comminution
The Siam Cement Industry Co.,Ltd.
Process to break solid particle into
small pieces
Need many kind of equipment
e.g.crusher for coarse particle and
grinding mill for fine particle
The Siam Cement Industry Co.,Ltd.
Tensile
Stress
Compressive
Stress
The Siam Cement Industry Co.,Ltd.
Stress
Stress - Strain Curve according to Hookes Law
Yield Point
Fracture
(Ultimate Tensile Strength)
Elastic Limit
dl
Deformation
(Plastic Material)
d stress
Strain (or elongation)
The Siam Cement Industry Co.,Ltd.
Comminution Process
Crushing: rock (1-1.5 m) to raw material (<100 mm)
Grinding : raw mat to raw meal (<2% R200um)
Grinding (and mixing) : clinker and gypsum (<25 mm)
to cement (fineness defined by standard or customer
requirement)
Grinding : raw coal (20 mm) to coal powder
The Siam Cement Industry Co.,Ltd.
Comminution Process
Specific Power Consumption
Raw material crushing
Raw material grinding
Coal grinding
Cement Grinding
Cement plant total
7
1-2
5 - 15
2-4
30 - 60
90 -130
kWh/t clinker
kWh/t clinker
kWh/t clinker
kWh/t clinker
kWh/t clinker
The Siam Cement Industry Co.,Ltd.
Breaking Forces
Impact Forces
Compressive Forces
Shear/Friction Forces
Interparticle contact Forces
The Siam Cement Industry Co.,Ltd.
The Siam Cement Industry Co.,Ltd.
Particle
Size
Before
Reduction
Red. Ratio =
Particle Size After Reduction
10
The Siam Cement Industry Co.,Ltd.
1. Limiting Reduction Ratio
=
11
Top Size of Feed
Top Size of Product
Size of Screen which Feed passes
Size of Screen which Product passes
The Siam Cement Industry Co.,Ltd.
2. Apparent Reduction Ratio
=
Size of Feed Opening
Size of Product Opening
Gap
Set
12
The Siam Cement Industry Co.,Ltd.
3. Working Reduction Ratio
13
Feed Thickness
Set
The Siam Cement Industry Co.,Ltd.
4. Medium Reduction Ratio
d50 of Feed
d50 of Product
50
14
Fe
ed
Pro
du
ct
Cumulative % Passing
100
Log Size
The Siam Cement Industry Co.,Ltd.
5. 80% Passing Reduction Ratio
d80 of Feed
d80 of Product
Fe
ed
80
Pro
du
ct
Cumulative % Passing
100
15
b
Log Size
The Siam Cement Industry Co.,Ltd.
1. Rittinger (1867) First Law of Comminution
The energy consumed in the size reduction of
solid is proportional to the surface produced.
16
The Siam Cement Industry Co.,Ltd.
1. Rittinger (1867) First Law of Comminution
1
1
ER = KR [ Xp - Xf ]
Kr = Rittingers Constant
Xf = initial size of the particle
Xp = final size of the particle
Energy input ,ER , is inversely proposional to
the decrease in particle size
17
The Siam Cement Industry Co.,Ltd.
2. Kick (1885) Second Law of Comminution
Deformation energy of a body or work
required for size reduction is
proportional to its volume.
18
The Siam Cement Industry Co.,Ltd.
2. Kick (1885) Second Law of Comminution
Xf
EK = KK log [ Xp ]
Kk = Kicks Constant
Xf = original avg. particle size in unit volume
Xp = final size in unit volume
Energy input is proportional to particle volume reduction
19
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
The energy consumed in size reduction is
proportional to square root of particle
size to be reduced.
20
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
1 1
EB = KB[ X - X ]
P
F
KB = Bonds Constant
XF = particle size of feed
XP = particle size of product
21
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
1 1
EB = KB[ P - F ]
80
80
KB = Bonds Constant
F80 = particle size of feed at 80% pass (in micron)
P80 = particle size of product at 80% pass (in micron)
22
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
1 1
EB = KB[ P - F ]
80
80
KB = 10 Wi
10 10
EB = Wi[ P - F ]
80
80
23
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
Wi is called WORK INDEX
and unit of energy is kWh/ton
24
The Siam Cement Industry Co.,Ltd.
3. Bond (1952) Third Law of Comminution
Wi means energy consumed for size
reduction from very large particle size
down to 100 micron.
25
The Siam Cement Industry Co.,Ltd.
(n = 4)
1010
Grinding Practice
106
n=
er (
ting
Rit
104
Bond
102
1
10-2
10-4
26
(n =
2)
Energy Input, kWh/t
10
1.5)
Crushing Practice
Kick (n = 1)
Possible Plastic
Deformation
Unit Crystal (Quarts)
10-2
102
104
106
Particle Size(10-6 m.)
The Siam Cement Industry Co.,Ltd.
Energy Utilization
EU
S
=
W s 3.6
[cm/J]
S = SSB Pr od SSB Feed [cm 2 / g ]
Ws = specific energy used [kWh/t]
SSB = Specific Surface according to Blaine
27
The Siam Cement Industry Co.,Ltd.
Energy Efficiency
c = Ei / EP
Ei = theoretical energy input
EP = actual energy input
Energy efficiency is relation between theoritical energy input
and actual process input energy
28
The Siam Cement Industry Co.,Ltd.
