the efficiency of capturing methane using a drainage ...€¦ · •methane drainage using...

The efficiency of capturing methane using a drainage system

in Polish conditions

Marek BOROWSKI

Faculty of Mining & Geo-engineeringDepartment of Underground Mining30 Mickiewicz Av.30-059 Cracow, POLAND

Kraków, 28/02/2018

Introduction

Methane hazard remains one of the most serious natural hazard occurring in underground coal mining.

Introduction

Methane emissions are obtained for:

• underlying seams

• underlying sandstone

• mined seams

• overlying seams

• overlying sandstone

To ensure the safety of the working crew and obtain a high levels of extraction, it is necessary to evaluate

properly possible release to combat methane hazard.

Introduction

CH4

CH4

The risk assessment is done by

forecasting release of methane into

longwall workings based on the study

of the gas properties of the

rock masses.

Methane emissions to the working faces

• Because of heterogeneity of rock strata and

disruptions of the geologic structure as well as

tectonic conditions, the methane emissions to the

working faces will vary during the mining

operations.

The gas conditions of the hard coal deposit in Silesia basin

Geological map of Carboniferous deposits

For the methane content in the seams, an hole method for determining natural methane in coal is used.

Box-and-whisker plot of changes in methane content (measured in coal seams)

depending on particular coal deposit

The box-and-whisker plot presents the central trend of methane content median (middle value - point).

Methane contentspread is shown in the graph by quartiles (25 and 75 percentiles) as well as by minimum and maximum values.

Introduction

Methane content with depth Coal Mine Z

-800

-775

-750

-725

-700

-675

-650

-625

-600

-575

-550

-525

-500

-475

-450

-425

-400

-375

-350

-325

-300

0 1 2 3 4 5 6 7 8 9 10 11 12

głę

bo

iko

ść, m

np

mMetanonośność, m3/Mg csw

Poziom 1080m

Poziom 900m

Poziom 830m

Poziom 705m

Methane content with depth Coal Mine R

-1000

-900

-800

-700

-600

-500

-400

-300

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

głę

bo

ko

ść,

m

metanonośność, m3 CH4/ Mg

Dependence of methane content with depth Coal Mine B

Z = -280,9891-12,8447*M

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

M - metanonośność, m3/Mg csw

-700

-600

-500

-400

-300

-200

-100

0

100Z

- g

łęb

oko

ść, m

A frame chart of the dependence of methane content from the depth, coal mine B

-600 -500 -400 -300 -200 -100 0

Z - głębokość, m

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

M -

meta

nonośność, m

3/M

g c

sw

Mediana 25%-75% Min.-Maks.

Generally, methane contentincreaseswith increasing depth

Introduction

• Methane present in coal seams has a bad influence on safety in underground mines as it is emitted during mining works.

• In order to conduct mining in gaseous mines it is necessary to take special technical measures not to allow methane concentrations in mine air to be exceeded.

• The main method is using ventilation systems which aim at ensuring the required air stream

• Ventilation systems are frequently not sufficient enough and it is necessary to drain methane from coal seams and surrounding rocks

The main preventive actions in underground coal mines are:

• effective ventilation that prevents forming of methane fuses or placed methane accumulation in roadways and in headings with auxiliary ventilation,

• methane drainage using boreholes that are drilled from underground excavations or from the surface,

• methanometry control of methane concentration in the air;

• additional ventilation equipment used in places of lower intensity of ventilation and places where methane is concentrated.

LONGWALL VENTILATION SYSTEMS

The most popular panel ventilation systems in Polish hard coal mines

a) U ventilation system, b) Y - return side ventilation system with parallel return gateroad c) Y - return side ventilation system, d) Y - return side ventilation system (bleeder system),

a)

c)

b)

d)

GO

AF

- intake air - return air

Parallel return gateroad

- sttoping

GO

AF

Headgate road

Tailgate road

Headgate roadHeadgate road

Headgate road

Tailgate road Tailgate road

Tailgate road

GO

AF

GO

AF

Methods for methane drainage in Polish coal mines

Methods for methane drainage in Polish coal mines:

• methane drainage in development headings,

• pre-mining drainage,

• mining methane drainage,

• post-mining methane drainage.

very low effectiveness

low effectiveness

satisfied effectiveness

good effectiveness

Geological conditions of coal seams(porosity, permeability, reservoirpressure, diffusivity), seam methanecontent and low desorption of Polishcoal seams result in low gas emissionnot disturbing the structure ofrock-mass. The direction of methane flow

Methane drainage with increased permeability

• Methane drainage methods used in Poland are based first of all on a seam relaxation by mining and an increase in permeability.

• In order to increase permeability it is necessary to take some steps regarding fractures of rock mass and reduction in stress states.

• Both when current and pre-mining methane drainage is used it is necessary to affect a rock mass in order to increase permeability.

• The amount of methane drained due to methane desorption depends on rock crushing (fractured rock mass) and its permeability.

• Changes in stress states caused by mining result in an increase in rock strength

• In favorable conditions self-destruction processes are likely to happen and they lead to an increase in permeability in fractured rocks.

Methane drainage in Polish coal minesis carried out taking into account the following conditions:

• location of a drilling rig – methanedrainage with in-seam boreholes(underground)

• time of methane drainage – methanedrainage can take place prior to and during coal production,

• way of increasing the gaspermeability of coal – methanedrainage without fracturing,

• length of the boreholes – methanedrainage using short borehols up to 200m.

THE LONGWALL DRAINAGE SYSTEMS

The longwall from the field is ventilated with the U system

The Longwall from the field is ventilated with the Y system from parallel return gateroad

Systems for drain gas exploitation longwalls -using the overlying excavation

The effectiveness of the methane intake depending on total methane emissionU system

0 10 20 30 40 50 60 70

metanowość całkowita, m3/min

0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

The effectiveness of the methane intake depending on total methane emissionU system

0 10 20 30 40 50 60 70


0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

Średnia

Min-Maks

The effectiveness of the methane intake depending on total methane emissionY system

0 5 10 15 20 25 30 35 40


0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

The effectiveness of the methane intake depending on total methane emissionY system

0 10 20 30 40

Metanowość całkowita, m3/min

0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

Średnia

Min-Maks

The effectiveness of the methane intake depending on total methane emissionU system with parallel excavation

20 30 40 50 60 70 80 90 100

metanowość bezwględna, m3/min

0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

The effectiveness of the methane intake depending on total methaneU system with parallel excavation

20 30 40 50 60 70 80 90 100


0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

Średnia

Min-Maks

The effectiveness of the methane intake depending on total methane emissionU system with overlying excavation

0 10 20 30 40 50 60 70 80


0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

The effectiveness of the methane intake depending on total methane emissionU system with overlying excavation

0 10 20 30 40 50 60 70 80 90


0

10

20

30

40

50

60

70

80

90

100efe

kty

wność o

dm

eta

now

ania

, %

Średnia

Min-Maks

The relations between the efficiency of methane drainage in longwalls and the type of the ventilation and drainage systems in Polish coal mines in the last 10 years

Breakdown Efficiency of methane drainage Average

drainage

efficiency,

%

Total methane

emission, m3/min

<10 10-

20

20-

30

30-

40

40-

50

50-

60

60-

70

70-

80

>80

Longwalls with a U

ventilation system

38.5 39.0 40.6 38.3 48.8 64.0 x x x 41.2

Longwalls with a Y

ventilation system

33.8 43.7 52.4 56.1 49.9 46.2 57.9 x x 48.7

Longwalls with a

parallel gateroad

and U ventilation

system

x x 58.0 60.1 62.2 64.2 64.5 68.3 71.5 63.9

Longwalls with

overlying drainage

gallery and U

ventilation system

49.0 58.6 60.2 62.6 68.4 64.7 68.6 68.8 76.0 63.4

INFLUENCE OF THE DRAINAGE HOLES LENGTH ON THE AMOUNT OF CAPTURED METHANE

The influence of the distance of the drainage drainage hole from the longwall side - on the

amount of methane captured

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 [m]

[m3/min]

mieszanka metan Wielom. (mieszanka) Wielom. (metan)

Longwall ventilated to "U" - from 60m long holes




0

2

4

6

8

0 10 20 30 40 50 60 70 [m]

[m3/min]

mieszanka metan Wielom. (metan) Wielom. (mieszanka)




0

2

4

6

8

0 10 20 30 40 50 60 70 80 [m]

[m3/min]

mieszanka metan Wielom. (metan) Wielom. (mieszanka)

Conclusion

• Methane drainage of rock-mass is themost effective method of preventingmethane hazard as it reduces thefrequency of methane inflows into workingareas and prevents or reducesoccurrences such as outflows, suddenoutbursts of methane and rocks, etc.

• In Polish coal mines, the effectivness ofused methane drainage system is limitedby low permeability of coal seams.

Conclusions

• On the basis of the results from the simulations it can be concluded that there are two groups of parameters responsible for methane emission in a borehole:

o The first group is technical parameters which we can influence when we plan methane drainage

o The second group is parameters connected with rock mass properties responsible for gas filtration

• Using a proper methane drainage system is strictly connected with time that can be found until mining is started.

Conclusions

The concept presented and the method allowing for increasing the effectiveness of methane drainage

consists of:

• Determining places (relevant to specific geotechnical conditions) where the zones of breaking stresses will be located during the influence of the longwall face (both in a seam and in the surrounding rocks).

• Taking some actions aiming at “weakening” rocks (e.g. by means of blasting) in the zones of breaking stresses.

• Locating methane drainage boreholes in “weakened” zones.

THANK YOUFOR YOUR ATTENTION

2

the efficiency of capturing methane using a drainage ...€¦ · •methane drainage using...

Documents