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PRACTICAL ISSUES OF GRINDING

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PALAS KUMAR HALDAR

30th June2015

LC3 Doctoral school

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

Jaw crusher

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Ball mill

Jaw crushing

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Ball milling

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

Average work index

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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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Energy consumption vs surface area of a typicalcement grinding

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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.

Various hardness testers

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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

Weighing

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Pilot production in India

Ball milling

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.

Thank you

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