siuc - illinois mining institute studies: a tool to project dust control issues and develop...

Wettability Studies: A Tool to Project

Dust Control Issues and Develop

Engineering Controls in Coal Mining

Kanchan Mondal, Yoginder Paul Chugh, Durga Devika Relangi, Vijaya Kumar Kollipara and Bhaskar Bariar

Mechanical Engineering and Energy Processes

Mining and Mineral Resources Engineering

Southern Illinois University, Carbondale, IL

SIUC

8/22/2012 2012 IMI Annual Meeting 1

Dust - small solid particles, conventionally taken as those particles below 75 μm in diameter, which settle out under their own weight but which may remain suspended for some time (ISO 4225)

Particles small enough to stay airborne may be inhaled through the nose (nasal route) or the mouth (oral route)

Respirable Dust – Dust of less than 10 microns which is capable of penetrating deep into the alveoli

MSHA’s definition of respirable dust – Dust with the following size characteristics:

SIUC Definitions - Dust

Aerodynamic diameter Percent

µm passing

2 90

2.5 75

3.5 50

5 25

10 0

8/22/2012 2 2012 IMI Annual Meeting

How is It Generated ?

During cutting, drilling, grinding, shearing and general breakage during mining

operations

During loading, dumping and transferring of mined materials

Re - emission of settled dust due to mine activities

How Does It Affect Us?

Health Hazards – eg Silicosis

Occupational Hazard - explosion

How Can We Control It?

Ventilation

Isolation

Protective Gear

Dust Capture

Dust Collection

Wet Dust Suppression - During handling operations

Wetting with water sprays

SIUC Issues With Dust


Wetting - Air from the air-solid interface is displaced to form a liquid- solid interface

Wettability - Probability of particles being wetted particle size,

surface properties of coal and,

physical and chemical properties of fluid (water).

Wettability Rates - The amount of coal wetted as a function of time

SIUC Definitions - Wetting

8/22/2012 4

Wetting rate is considered to be more important than the wettability due to the short contact times

2012 IMI Annual Meeting

SIUC

8/22/2012 5

Self cleaning of leaves – Lotus Effect Drowning Fleas

Wetting Concepts

Hydrophobic Surface No wetting

Hydrophilic Surface Complete wetting

It can be engineered such that hydrophilic surfaces are made non-wettable and hydrophobic surfaces are wetted

Use Chemicals to Change Solid Surfaces

Use Chemicals to Change Liquid properties

Change Surface Roughness

Beading on Windshields


http://getridofleas.com/wp-content/uploads/2011/10/flea.jpg

SIUC Why Is Size Important?

8/22/2012 6

Area needed to be wetted 6 X Length2

Area needed to be wetted 8 X Length2

More Wetting Agent Required if Material is Identical

The issue is not the same when materials are

different


8/22/2012 7

SIUC Wetting What We Would Like to Happen Dust too small compared to water droplet

When Dust Wetting Occurs When dust is hydrophobic


Wetting depends on

Contact between the dust and the fluid droplets, Relative Particle/Droplet size

Air Velocity

Nozzle Design – Spray Type

Wettability of the particles by the wetting fluid, and Solid Surface Properties

Surface Tension

Surface Roughness

Wettability rate (due to low contact times) Surface Tension

Contact Time

Surface Area

SIUC Key Parameters


9

SIUC Reducing Surface Tension

Methanol Water

Mixtures

Add Surfacatants

2/22/2012 9

Water Temperature

Increase

Temperature


8/22/2012 10

SIUC SIUC Holistic Approach

Physical and Chemical Characterization

XRD, AES, SEM, Petrography, Surface Charge

Wettability Studies Absolute Wettability,

Surface Tension Surfactants

Microscopic Studies Basic Science

Transport and Kinetics Studies Wettability Rate

Fixed Time Wettability Surfactants, Temperature

Macroscopic Analysis Basic Engineering

Design Studies CFD

Dust Control Lab

Engineering Design

Final Controls

Field Application


Mining and Mineral Resources Engineering 11

SIUC Step 1: Sample Collection

8/22/2012

Rock dust Col lected

Newly Exposed Strata

12” above coal seam divided into two segments

12” below coal seam divided into two segments

(~48”) Coal seam divided into three segments

Channel Sample

1”–2 “ thick

3”–4 “ thick



SIUC Step 2 : Sample Preparation

Bulk Sample

Grind to -60 mesh

(50 g)

Is +60 mesh

> 5% ?

Regrind +60 mesh

to -60 mesh

20 g 30 g

Sample

analysis

Sieve 60 mesh

Grind to -400 mesh

Sieve 400 mesh

Is +400 mesh

> 5% ?

-400+500 mesh

-500 mesh Wettability

Wettability

Regrind +400 mesh

to -400 mesh

Un-wetted

fraction

samples

analysis

Yes

No

No

Yes


Absolute Wettability – Whether a particle is wettable

• Altering the surface tension of the wetting fluid – Mixing water with lower surface tension fluid – methanol

– Adding surfactant (may alter solid surface characteristics)

Wetting Kinetics – Detailed kinetics at different residence times

• Methanol water mixture

• Aqueous solution of surfactant

– Fixed time wettability (Chugh et al, 2004) • Methanol water mixture

• Altering temperature of water

SIUC Step 3: Wettability Studies

Mining and Mineral Resources Engineering 13 8/22/2012 8/22/2012 13 2012 IMI Annual Meeting


SIUC AW Procedure

Partitioning of hydrophilic and hydrophobic portions

Addition of sample Wetting

process

Partitioning of wetted

and un-wetted fraction

Collection of wetted

fraction

Same system was also used for the detailed kinetic study Mining and Mineral Resources Engineering 14 8/22/2012 8/22/2012 14 2012 IMI Annual Meeting

SIUC FTW Set-Up


SIUC Wetted and un-wetted fraction

Thin film of un-wetted fraction


The wetted fraction was finer – wetting fluid modifications required for coarser particles

SIUC Absolute Wettability – Size effects

D

A

T

A

F

R

O

M

D

I

F

F

E

R

E

N

T

M

I

N

E

Mining and Mineral Resources Engineering 18 8/22/2012 8/22/2012 18

75

80

85

90

95

100

105

0.1 1 10 100

Pe

rce

nt

of

Fe

ed

re

po

rtin

g t

o W

ett

ed

Po

rtio

n

Particle Size, microns

0

0.5

1

1.5

% Methanol


Quartz concentrated in the unwetted fraction

SIUC Absolute Wettability, contd

90.01 85.99

2.28

9.99 14.01

3.34

0

10

20

30

40

50

60

70

80

90

100

Yield Quartz Recovery Quartz %

Wetted

Unwetted

Middle Bench


Mining and Mineral

Resources Engineering 20

SIUC Effect of Surfactant

80

82

84

86

88

90

92

94

96

98

100

0.0 2.0 4.0 6.0

Cu

mu

lati

ve

We

tta

bilit

y (

%)

Surfactant Concentration (wt % X 103)

Bottom Coal

Top Coal

Middle Coal

Top and bottom coal bench samples - adverse effect of excess surfactant addition


Surfactant affects both the wetting fluid and surface properties

Mining and Mineral


SIUC Effect of Surfactant, contd

Quartz recovery to the wetted fraction decreases with increasing material recovery


SIUC Wettability as a function of contact time

93949495959696979798

10 15 20 25

we

tte

d f

rac

tio

n (

%)

Contact time(Sec)

Mine IL 6-2, -500, C-BB

90

92

94

96

98

100

10 15 20 25

Contact time(Sec)

Mine IL 6-1, -500 C-TB

91

92

93

94

95

96

97

98

10 15 20 25

Contact time(Sec)

Mine IL 6-7, -500 C-BB

40

45

50

55

60

65

70

75

80

10 15 20 25

we

tte

d f

rac

tio

n (

%)

Contact time(Sec)

Mine IL 5-1 , -500 C-TB

75

79

83

87

91

95

99

10 15 20 25

Contact time(Sec)

Mine IN 6-1, -400+500, C-TB

8

13

18

23

28

33

38

43

48

53

10 15 20 25

Contact time(Sec)

Mine IL 5-1 , -400 C-MB


SIUC Wettability Rate Studies, contd

Wetting rates increase with decreasing surface tension, increased amount of surfactant

Mining and Mineral Resources Engineering 23 8/22/2012 8/22/2012 23

% % % %


SIUC Correlation between fixed time and absolute

wettability

Mine IL 5-2, -500 mesh, C-MB Mine IL 5-1, -400 mesh, C-TB

Absolute



Incremental quartz content in the wetted fraction increases initially



Increasing wetting fluid temperature increases degree of wetting and wetting rates

Impact of Temperature on Wettability Rates - FTW


SIUC In Mine Sample Wettability

Finer Size fractions were more wettable

Mesh Size

Wetted fraction

(%)

IN 6-1

-400+500 (25 µm - 37 µm) 94.5

-500+635 (20 µm - 25µm) 95.2

-635 (< 20 µm ) 98.2


Recovery to the wetted fraction is higher for finer fractions.

o Wetting fluid modifications target coarser fractions.

Quartz appears to be more concentrated in the wetted fractions.

Wettability may be suppressed at high surfactant concentrations.

Quartz recovery decreases with initial increase in surfactant concentration

o ??

Surfactant affects both the wetting fluid and the solid surface.

Wettability rates increase with

o Temperature

o Surfactant addition

FTW gives a quick estimate of the degree of wetting and wetting

rates.

Quartz recovery increases at lower contact times and then decreases.

WETTING RATE IS A KEY FACTOR IN MINE CONDITIONS

SIUC Summary

SIUC Information for Engineering controls

Wettability as a function of

surface tension

size distribution

Wettability rates as a function

surface tension

size distribution

Quartz recovery as a function of contact time

8/22/2012 Mining and Mineral




SIUC Quartz control data from field studies

Mine IL 6-8 (% Quartz)

Location Unmodified

Miner

Modified

Miner

Miner Operator 3.5 2.8

Haulage unit Operator 3.7 4.3

Return 3.9 3.3

Full Shift Sample 3.7 3


Location Unmodified

Miner

Modified

Miner

Miner Operator 3.3 2.1

Haulage unit Operator 2.5 2.3

Return 2.7 2.25


Location Unmodified

Miner

Modified

Miner

Miner Operator - 2.5

Haulage unit Operator - 4.2

Return 7 4.8

8/22/2012 Mining and Mineral Resources Engineering 30 8/22/2012 8/22/2012 30 2012 IMI Annual Meeting

Currently, 17 continuous miners are operating on the

developed system with very good results.

We will be performing in-mine sampling studies on

another modified miner (fitted with SIUC Spray System

designed for 9-ft mining height) in middle of September.

SIUC is currently designing spray system for 14-ft mining

heights. That will be tested in the next 6-months.

SIUC SIUC Innovative Spray System- Progress Update

Mining and Mineral Resources Engineering 31 8/22/2012 Mining and Mineral Resources Engineering 31 8/22/2012 8/22/2012 31 2012 IMI Annual Meeting

8/22/2012 Mining and Mineral Resources Engineering 32

SIUC

ICCI/DCEO

CDC/NIOSH

MSHA

All participating mining companies

Joy Mining Technologies

Center for Applied Energy Research,

University of Kentucky

Dr. Punit Kohli, Department of Chemistry and

Biochemistry, SIUC

Acknowledgements

2012 SME Annual Meeting 2/22/2012 32 2012 IMI Annual Meeting

Questions ??

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