practical issues of grindingdocuments.epfl.ch/users/s/st/ston/www/7 grinding.pdf · to ball mill,...
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Studies
• B.Sc in Chemistry • B.Tech in Ceramics • M. Tech in Ceramics• MBA in Operation research• PhD area- Electro ceramics
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About myself
Experience
• Assistant general manager (technology management) in TARA from April’2014 onwards
• Senior Design engineer in TDKfrom November’2006 to March’2014.
• Area of experience- R&D, Quality, process, production & environment product quality management (EPQM)
Contents Introduction Objectives Types of comminution Theory of grinding Grinding energy and efficiency Grinding factors Hardness LC3 production in India Conclusions
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Introduction
• Grinding is a part of comminution which involves size reduction of materials by various forces like impact, shear ,abrasion, compaction etc.
• Crushing is normally accomplished by compression/compaction of the materials against rigid surface.
• Grinding involves impact , shear & abrasion of particles by grinding media.
• Intergrinding usually implies to grind together when two or more different materials are present in the system. ( cement blending by ballmill)
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Objectives To prepare the sample by reducing size for further processing
To improve surface area of the particles leading to higher reactivity
To separate impurities from valuable materials ( mineral processing)/ concentration
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Types of Comminution
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Comminution
Crushing
Primary crushing(1m>P80>100mm)
Secondary crushing(100mm>P80>6mm)
Grinding
Coarse grinding(6mm>P80>500µ)
Fine grinding(500µ-> P80> 5µ)
Jaw crusherCone crusher
Hammer crusherGyratory Crusher
Ball mill
Ball millVertical roller mill
Hammer millRod mill
Attrition mill
Theory of grinding Work index
The amount of energy (KWh/t) required to reduce a material from one size to another size. Higher work index indicates more hardness of the material.
Kick’s law (d> 50mm)Wk = cK [ln(dF)-ln(dP)]
Bond’s law (50mm>d>0.05mm)WB = CB(1/√dP - 1/√dF)
Rittenger’s law ( d< 0.05 mm)WR = CR(1/dP - 1/dF)
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• W - work index• C - Grinding coefficient• dP - Product size(d80)• dF - Feed size(d80)• CK - 1.151CB(dBu)-0.5
• CR - 0.5CB(dBu)0.5
Grinding energy & efficiency
Energy required during grinding (Bond’s law)E= 10WB (1/√dP - 1/√dF)
Efficiency of different grinding devices• Beater mills - 17% ÷ 25%• Roller mills - 7% ÷ 15%• Ball mills - 6% ÷ 10%• Jaw crusher - 3%-5%
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Grinding factors
Hardness• Feed material needs to be softer than grinding media• Brittleness coefficient (example)
C3S(4.7)> C3A(2.9)>C2S(2.0)
Ratio of grinding media to charge (by wt.)• Usually grinding media : charge= 3:1
RPM of grinding mill• 75-80 % of critical speed ( Vc= 42.29/√d, d is inner diameter of mill in m) Size ratio • Dia of media: dia of feed = 6:1 (typical grinding)
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Hardness
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• Resistance to permanently indenting the surface.• Large hardness means:
--resistance to plastic deformation or cracking incompression.
--better wear properties.
Conversion of hardness factor
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ASTM E140 - 07 Volume 03.01Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, KnoopHardness etc.
Pilot production of LC3 in India
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• Quantity- 130 Tones• Place - Triranga Cement Industries (Gujarat) • Time- January’2015
Process flow diagramme
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Pilot production in India
Picture of grinding assemblyWeighing &
batching
Ball milling
Separating through classifier
Storage in silo
Bagging
>200 µ
<200 µ
Composition
• Clinker- 50%• Calcined clay- 31%• Lime stone- 15%• Gypsum- 4%
• Weighing sequence of raw materials1. Clinker2.clay3. Lime stone4. Gypsum
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• Capacity of ball mill- 5 T/ h• RPM of ball mill- 24• Throughput time(ball mill)- 25min• Feed size - 6-10mm• Total length of the mill
7.725(2.525+5.2)m• Grinding media- Hardened steel ball• Size of grinding media in chamber 1
50-75 mm (4 ton)• Size of grinding media in chamber2
20-30 mm (10 ton)• Inner dia. of mill 1.8 m• Total electric power 397 HP
Pilot production in India
Existing process parameters
Productivity of LC3
• LC3 production /h: 16 T
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• Color : Reddish grey• Average Blaine value : 495• Size fraction +90µ : 4%
-45µ : 16.52%• LOI : 6.75%• Initial setting time : 110 min• Water consistency : 33.75%• Final setting time : 335 min
Pilot production in India
Product Quality of LC3
Technical Set back
• Limited capacity of pipe lines linked to ball mill, classifier and cement storage silo
• Lower capacity of classifier
• Lack of synchronisation between ball mill and classifier
• Mismatch of grindibility between OPC composition and LC3 blend and hence the productivity
• Restricted flowability of clay due to increased fineness 22
Pilot production in IndiaComparison of grinding energy consumption
0
100
200
300
400
500
Ind.Ave.
ACC(OPC)
ACC(PPC)
T Cem(OPC)
T CemLC3
(20/1)
T CemLC3
(21/1)
T CemLC3
(22/1)
T Cem LC3(24/1)
Ener
gy c
onsu
mpt
ion
(MJ/
t of c
emen
t pro
duce
d)
Indian Industry Average
Legend:Ind. Av. : (Touil et. al)ACC : ACC Ltd. Bhabua grinding unit (Bihar)T Cem : Triranga Cements, RajkotLC3 : Low Carbon Cement
Conclusion
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• Grindibility of LC3 is higher than that of OPC fromsame clinker leading to higher productivity of LC3.
• Grinding energy consumption of LC3 is lower thanthat of OPC.
• Both limestone and calcined clay are softer than clinker which improve grinding efficiency and productivity.
• Blending process of LC3 needs to be modified in an optimised way.
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