Longwall Top Coal Caving (LTCC) Face Gas and Dust Flow Patterns

ENERGY FLAGSHIP

27-28 October 2014

Rao Balusu1, Krishna Tanguturi1 and Mick Kelly2

1 CSIRO 2 BMA

• Introduction

• LTCC method and issues

• Development of CFD models for LTCC face

• Gas flow patterns and control strategies

• LTCC caving dust flow simulations

• Dust and water spray flow patterns and control

• Summary

Presentation Outline

Rao Balusu | Page 2

Introduction

LTCC Method

Rao Balusu | Page 3

Longwall Top Coal Caving – Chock(Rear AFC caving mechanism/door in the ‘Cave’ position)

Rear AFC caving mechanismin the ‘No Cave’ position

• Australian coal industry – Thick Coal Seams

– Roadway development – not able to cope with longwall production rates

• Longwall top coal caving (LTCC)– Enables effective extraction of 6 to 12m thick coal seams (high resource recovery)

– Allows lower cutting height of ~ 3.0m – reducing face slabbing & roof control issues

– Reduced requirement of roadway development rates (& reduced dev cost)

• LTCC applicability and issues– LTCC feasibility and caving assessment critical (geotechnical suitability)

– Equipment design is critical for optimal caving

– Cutting and caving sequences optimisation is critical for success of LTCC

– Gas control near back AFC tailgate motor area is very important

– Dust generation from top coal caving would be high and its control is important

Introduction - LTCC

Rao Balusu | Page 4

CFD Model Development

Rao Balusu | Page 5

CFD model for LTCC face

Rao Balusu | Page 6

CFD Model geometry for LTCC face layout – 3D view

(b) CFD model mesh – cross sectional view

(a) Mesh geometry near Shearer

Air velocity contours – at different sections

Rao Balusu | Page 7

(a) Velocity contours at 20 m from MG

(b) Velocity contours at mid-face area

(c) Velocity contours at shearer area

Effect of ventilation flow rate

Rao Balusu | Page 8

(a) Face ventilation ~ 40 m3/s

Air velocities at the rear AFC tailgate motor area – plan view

(b) Face ventilation ~ 60 m3/s

Model cross-section near TG motor area

Gas Simulations and Control Strategies

Rao Balusu | Page 9

Goaf gas distribution

Methane distribution in the goaf – plan view(for goaf gas emission rate ~ 1,000 l/s)

= 100% CH4

MGTG

Face

Rao Balusu | Page 10

Goaf gas distribution near the rear AFC motor

Rao Balusu | Page 11

Methane distribution at the rear AFC tailgate motor area(for goaf gas emission rate ~ 1,000 l/s)

LW Face

Tailgate

Effect of goaf gas emission rate

Rao Balusu | Page 12

Effect of goaf gas emission rate on methane distribution near the rear AFC motor area

(a) Goaf gas emission rate ~ 400 l/s (b) Goaf gas emission rate ~ 1,000 l/s

Effect of various gas control strategies (1)

(a) Without MG brattice (b) With MG brattice

Effect of MG brattice on gas distribution near the rear AFC motor

MG brattice(more face airflow)

Effect of MG brattice on O2/air ingress into the goaf

Rao Balusu | Page 13

Effect of various gas control strategies (2)

(a) Effect of blower (40 cm dia, 1 m3/s) on air velocities

(c) Methane distribution at TG – with blower (b) Methane distribution at TG – without blower

Blower/Fan near the rear AFC motor (TG)

Rao Balusu | Page 14

Effect of various gas control strategies (3a)

Rao Balusu | Page 15

Curtain near the rear AFC motor

Effect of various gas control strategies (3b)

Rao Balusu | Page 16

Effect of curtain on air velocities near the rear AFC motor (airflow ~ 60 m3/sec)

(a) Without curtain

(b) With curtain

Effect of curtain on gas distribution near the rear AFC motor (airflow ~ 80 m3/sec, goaf gas emissions ~ 1,000 l/s)

(a) Without curtain (b) With curtain

Effect of various gas control strategies (3c)

Rao Balusu | Page 17

Effect of various gas control strategies (4)

Combined effect of goaf gas drainage and curtain on gas distribution near the rear AFC motor

(a) Base case (b) With goaf drainage (c) Goaf drainage & curtain

Goaf gas drainage

Back-return (when feasible)

Rao Balusu | Page 18

Dust and water spray simulations

and control strategies

Rao Balusu | Page 19

Dust distribution patterns – intake dust sources (1)

Air velocity profile near MG corner

(a) Respirable dust concentration at 20 m from MG

(b) Respirable dust concentration at 50 m from MG

Rao Balusu | Page 20

Dust distribution patterns – intake dust sources (2)

Traditional curtains concept

Air velocity profile near MG – with traditional curtains

(a) Respirable dust concentration at 20 m from MG

(i) Without curtains (ii) With traditional curtains

(b) Respirable dust concentration at 50 m from MG

(ii) With traditional curtains(i) Without curtains

Rao Balusu | Page 21

Dust distribution patterns – intake dust sources (3)

Optimum curtains location & orientation

Rao Balusu | Page 22

Dust distribution patterns – intake dust sources (4)

Optimum curtains location

Air velocity profile near MG – with optimum curtains

(a) Respirable dust concentration at 20 m from MG

(i) Without curtains (ii) With optimum curtains

(b) Respirable dust concentration at 50 m from MG

(i) Without curtains (ii) With optimum curtains

Rao Balusu | Page 23

LTCC top coal caving dust

51 52 53 54 55

51

Support number

Caving location

LTCC caving dust flow patterns (Animation on next slide)

• Cutting height and Caving height

• Cutting speed, Cutting method - Uni-di/ Bi-di

• Caving cycles

cutting one full shear and then caving (start-up)

cutting & caving (how far behind shearer/cutting, every shear/every 2nd shear)

caving sequence: 1-2-3-4-5-6; OR- other sequence

caving durations during cutting and flit cycles

LTCC – cutting and caving cycles – various strategies

10 15 20 25 304035

1 2 3 4 5 6

Rao Balusu | Page 24

LTCC caving dust flow patterns – Top view

Rao Balusu | Page 25

Dust flow patterns – LTCC caving dust (Single Shield)

• Caving dust completely covered downstream shield within 5 sec

• Dust migrates to walkway within 5-7 sec (and it travels much faster in walkway area)

LTCC caving dust flow patterns – dust from Single shield

Particle

size (m)

Rao Balusu | Page 26

Caving Shield Nozzle22 l/min @ 30bar (3 Mpa)

LTCC dust control – Rear caving shield water spray

Rao Balusu | Page 27

Water spray flow patterns – Single Shield (caving shield)

• Water spray particle size high compared to dust particle size

• Water spray/droplets settling down and migrating slowly

LTCC caving shield water spray flow patterns – water from Single shield(Water spray nozzle – 1.5 mm, 2.2 MPa (22 bar) pressure, 6 l/min)

Spray size

(m)1 sec 5 sec 9 sec

Rao Balusu | Page 28

Dust and water spray flow patterns – Single shield

• Results indicate water spray pressure is inadequate (higher water droplets size)

• Results also indicate that sprays from single shield won’t be enough

(a) LTCC caving dust – Single shield (b) Water spray – Single shield

Particle

size (m) 10 secSpray size

(m)10 sec

Rao Balusu | Page 29

Dust and water spray flow patterns – Caving sequence

• Results indicate that water spray as per caving sequence won’t be enough

High pressure (60 bar) water spray flow patterns – Animation on next slide

Rao Balusu | Page 30

(a) Caving dust – from multiple shields as per caving sequence

(b) Water spray – from multiple shields as per caving sequence

Particle

size (m) 11 secSpray size

(m)11 sec

High pressure water spray flow patterns

Rao Balusu | Page 31

Water spray flow patterns – effect of pressure

• High pressure water spray creates finer mist and migrates longer distances

(a) Water spray – 2.2 MPa (6 l/min) (b) Water spray – 6 MPa (13 l/min)

Spray size

(m)20 secSpray size

(m) 20 sec

Rao Balusu | Page 32

Dust and high pressure water spray flow patterns (1)

• High pressure water spray improves dust capture efficiency

Rao Balusu | Page 33

(a) Caving dust (b) High pressure water spray

Spray size

(m)8 secParticle

size (m) 8 sec

Flow patterns at 11 sec

Dust and high pressure water spray flow patterns (2)

• Results predicted 30% dust reduction in caving shield

(a) Caving dust - from multiple shields as per caving sequence

(b) Water spray – from multiple shields with modified sequence

Particle

size (m) 24 secSpray size

(m)24 sec

Rao Balusu | Page 34

Summary

• LTCC offers unique advantages in thick seam environment

• Gas control at rear AFC tailgate motor area is critical In medium to highly gassy mines, gas concentration would be > 1%

Blowers create turbulence and not appropriate

Modification of face airflow patterns with appropriate curtains

Goaf gas drainage and back-return systems are also advantageous

• Dust control – a major issue on LTCC faces Intake and MG corner dust control is also critical

Dust generated during top coal caving migrates into walkway area

Requires water spray at high pressure in the caving shields

Water spray only in the caving shields won’t be enough

Water spray sequence and duration needs to be optimised

• Control of dust from other sources is also important

Rao Balusu | Page 35

Thank youDr Rao BalusuSenior Principal Research Engineert +61 7 3327 4614e rao.balusu@csiro.auw www.csiro.au

ENERGY FLAGSHIP