Improvement of Ball Mill Improvement of Ball Mill grinding efficiencygrinding efficiency

Presented ByPresented ByRamkrishna Halder Ramkrishna Halder

Under the guidance ofUnder the guidance ofDr. Preeti BajpaiDr. Preeti Bajpai

11

Presentation OutlinePresentation Outline

Introduction of grinding conceptIntroduction of grinding concept

Objectives of the projectObjectives of the project

Experimental Procedure and ObservationExperimental Procedure and Observation

Conclusions and RecommendationsConclusions and Recommendations

22

Introduction

Grinding is used to reduce the size of a particular materialGrinding is used to reduce the size of a particular material

To achieve the required result from grinding process the To achieve the required result from grinding process the grinding efficiency is the most required and important factor grinding efficiency is the most required and important factor

Various factors like hardness, toughness, material structure, Various factors like hardness, toughness, material structure, size, shape and the ratio of feed size to product size etc. size, shape and the ratio of feed size to product size etc. affect the size reductionaffect the size reduction

33

How To Improve Efficiency?How To Improve Efficiency? By monitoring the fill levelBy monitoring the fill level

By controlling operating speedBy controlling operating speed

Feed material to grinding media ratioFeed material to grinding media ratio

By choosing suitable grinding mediaBy choosing suitable grinding media

Size and shape of grinding media Size and shape of grinding media

Mixing ratio of various size of grinding mediaMixing ratio of various size of grinding media

44

Objectives of the ProjectObjectives of the Project

To analyze the existing grinding system

To optimize the factors affecting to efficiency of grinding process

To generate a standard operating procedure on the basis of the evaluated parameters for grinding

55

Experimental ProcedureExperimental Procedure

Where nc = Critical speed (rpm)

R = Radius of the mill (m) r = Radius of the ball (m)

Critical Speed

Observation Radius of the mill = 0.85 m Radius of the ball = 0.025 m

nc = 33 rpm So operating speed = 25 rpm

All basic parameters have been calculated while considering existing experiments in ball mill-3

66

Power Consumption

Power Requirement

W = 10Wi*(1/√P80 - 1/√F80) W = Power (KWh/t)Wi = Working indexP80 = 80% passing size of product (µm)F80 = 80% passing size of feed (µm)

Observation

Wi =13.57P80 = 125 (µm)F80 = 10000 (µm)W = 10.8 KWh/t

77

Maximum Media SizeM = √[(FWi/KCs)/√(S/√D)]

Where M = Diameter of the top size media (inch)F = Feed size (µm)Wi = Work Index, Cs = percent critical speed

K = constant S = Sp. Gravity of feed (g/cc)D = Inside diameter of Mill (ft)

Observation

F = 10000 µm, Wi = 13.57 K = 200 Cs = 75, S = 2.23 g/cc D = 5.58 ftM = (10000*13.57)/(200*75) √(2.23/√5.58) M = 2.9647 inch = 75.30 mm 

88

Observation Total height of ball mill = 67 inch = 5.58 ft Height of Ball + Feed material = 54 inch = 4.5 ft Empty space = 13 inch = 1.08 ft Percentage of Fill level = 54/67*100 = 80.59% Percentage of Empty space = 19.41%

Fill level

The load of the ball is usually a little more than half of the volume of the mill.

Generally 2/3 volume of the mill filled by material and ball.

If the fill level is low, most of the energy of the balls is wasted in impacts between them – leading to low comminution ratio.

If mill is overloaded, the grinding material causes a damping effect that decreases the comminution ratio. So optimization is essential.

99

Comparison between Calculated and Observed parameters

Parameters Experimental Existing

Speed 25 rpm 20 rpmFill level 80.6% 81.9%

Media size 75 mm 50 mmPower Required 10.80 kwh/t 12 kwh/t

1010

Media Quality Calculation

 %AP = (W2 – W1) *100 Where W1 = Dry wt (gm)

(W2 – W3) …. (a) W2 = Soaked wt (gm) W3 = Suspended wt (gm) B.D = W1 (W2 – W3) …. (b)

Observation

Types of Media

Apparent Porosity (%)

Bulk Density (g/cc)

Hardness Moh’s scale

Cumi 0.689 3.61 9Sinoma 0.60 3.66 8-9

Cumi

Dry wt. of the ball = 52.3 g Suspended wt = 37.9 gSoaked wt = 52.4 gA.P = 0.689% B.D = 3.61 g/cc

Sinoma

Dry wt. of the ball = 66.7 gSuspended wt = 48.37 gSoaked wt = 66.75 gA.P = 0.60% B.D = 3.66 g/cc

1111

Apparent Porosity Vs Bulk Density

1212

Hardness

HARDNESS

1313

Types of media

Before shaking wt. of the balls

(g)

After shaking

wt. of the balls (g)

Shaking Time (hrs)

Material loss(g)

Cumi 521.8 521.5 2 0.3

Sinoma 531.8 529.5 2 2.3

Apparatus :

1.Hard Plastic Container2.Sieve shaker

Sinoma:Amount of Grinding media taken = 531.8 gAfter shaking amount of media = 529.5 gMaterial Loss = 2.3 g

Wear Test

Cumi:Amount of Grinding media taken = 521.8 gAfter shaking amount of media = 521.5 gMaterial Loss = 0.3 g

1414

Fresh grinding media

Jar used for shaking

Sieve Shaker

Grinding Media after

shaking

Wear test for Cumi & Sinoma

Cumi

Sinoma

Before Shaking After Shaking

Before Shaking After Shaking

1515

Wear After Two Hours

1616

Experiments performed in Ball mill - 2 (capacity 50 kg)

Dimension

Length = 3ft Diameter = 3 ft.Critical speed = 45.5 rpmOperating speed = 34 rpm

1717

Observation of packing ratio of grinding media

Experiment Number

50 mm balls taken (%)

40 mm balls taken (%)

30 mm balls taken (%)

Before shaking height of the balls (cm)

After shaking height of the balls (cm)

Difference in height

(cm)

1 50 24 26 12 11.6 0.4 2 50 15 35 10.8 10.0 0.8 3 75 12 13 10.5 10.2 0.3

The experiments were started using the combination of various media size mentioned in Exp-2 because of having the best packing ratio

1818

Observation of Grinding Time

Grinding time can be reduced by crushing the feed material before ball milling

Further , the grinding time can be reduced by use of grinding aid

Frit (GF-204, 30 kg) 0.05 % grinding aid (tri-ethanol amine) 0.05 % water

1919

Contd..

Parameters Amount of feed material

(kg)

Amount of grinding

media (kg)

Grinding time (h)

Sieving (240 mesh)

Passing Residue

Without crushing

30 60 10-11 98.5% 1.5%

Using grinding aid

30 60 8 97.5% 2.5%

With crushing

30 60 5 95.8% 4.2%2020

Frit powder after grinding

Sieve from 60 to 240 mesh

Frit powder after sieving

Types of crusher

Amount of feed material

Before crushing max size of feed

After crushing max size of product

Crushing Time

Jaw Crusher 20 kg 50 mm +15 mm 5.50 min

Smooth Roll Crusher

20 kg 50 mm +5 mm 3.45 min

Further Reduction of Grinding Time

Jaw Crusher Smooth Roll CrusherFrit material before crushing

2121

Conclusions and Recommendations The optimized operating speed was 25 rpm while in the existing

system it was observed as 20 rpm

The recommended media size is 75 mm but existing is 50 mm The existing fill level is almost in optimized range

On the basis of the physical and mechanical properties it is recommended to use cumi grinding media

It is recommended to use a suitable grinding aid to reduce further the grinding time

It is recommended to crush (if suitable) the material before grinding

2222

2323