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Granular Matter

, 21:70 | Cite as

Effect of the size distribution of granular top coal on the drawing mechanism in LTCC

  • Jiachen Wang
  • Weijie Wei
  • Jinwang ZhangEmail author
Original Paper

Abstract

The size distribution of granular top coal holds great influence on the drawing mechanism in longwall top coal caving (LTCC) panel. In this paper, based on the data observed from the Ruilong mine in Shanxi province, China, the effect of the size distribution of granular top coal on the drawing mechanism was investigated using theoretical analysis, 3D physical simulation and discrete element numerical calculation. The results show that the volume of the drawing body increases linearly with increasing weighted average size of granular top coal, while the maximum width of the drawing body increases nonlinearly; with increasing length of the opening, the drawing volume also increases nonlinearly at a gradually decreasing rate. With the increasing weighted average size of granular top coal, the top coal recovery ratio of the panel increases first and then decreases, and when the weighted average size of granular top coal is in the range of 150–250 mm, the recovery ratio is higher. A situation in which the size distribution of granular top coal is relatively dispersed and the standard deviation is larger is more conducive to the granular top coal drawing in the working face. When the percent of small particle is larger, the top coal recovery ratio decreases with increasing length of the opening, and it is suggested to use a single opening; in contrast, when the percent of large size particles is larger, the top coal recovery ratio increases first and then remains at a certain level, and it is suggested to use a double opening. Suggested measurements are proposed to improve top coal recovery in LTCC panel based on the research results.

Keywords

LTCC Size distribution of granular top coal Length of opening Drawing body Top coal recovery ratio 

List of symbols

a, b, c

Linear sizes of granular top coal in three directions (mm)

DBn

The nth drawing body in PFC calculation

dc

Size of granular top coal (mm)

dcwav

Weighted average size of granular top coal (mm)

Dp

Diffusion coefficient

k

Constraint coefficient of the boundary of granular top coal

Lo

Length of the support opening (mm)

mc

Initial mass of granular top coal (g)

mcd

Mass of drawn granular top coal of working face (g)

mrd

Mass of drawn rock particles of working face (g)

MKAS

Manual turn knob for advancing support

MKOCO

Manual turn knob for opening and closing support opening

n

Number of supports

N

Number of drawn marked particles

Nn

Number of drawn marked particles on the top of support no. n

N0

Initial number of marked particles on the top of each support before drawing granular top coal

nt

Total number of supports

Q1

Volume of the drawing body at the first drawing (cm3)

Q3

Volume of the drawing body at the third drawing (cm3)

Qav(DB03-12)

Average volume of DBn (n = 3–12) in PFC calculation (m3)

Qc

Initial volume of granular top coal (cm3)

Qcd

Volume of drawn granular top coal of working face (cm3)

QDBn

Volume of DBn in PFC calculation (m3)

Qrd

Volume of drawn rock particles of working face (cm3)

Qt

Volume of drawn particles during period t in theoretical analysis (m3)

R2

Correlation coefficient

SDT

Size distribution of granular top coal

T

Drawing time of working face (s)

Vx

Velocity of particles along the x direction

Vy

Velocity of particles along the y direction

Vz

Velocity of particles along the z direction

w0max

Maximum width of the drawing body in theoretical analysis (m)

w

Mass percentage (%)

wc

Cumulative mass percentage (%)

Wo

Width of the support opening (mm)

z0

Coordinates of particle when t = 0 in kinematic model in theoretical analysis (m)

z0max

Maximum height of the drawing body in theoretical analysis (m)

ηn

Top coal recovery ratio of support no. n (%)

ηnav

Average of ηn (%)

ηw

Top coal recovery ratio of working face (%)

ρb

Bulk density (g/cm3)

μ

Proportionality coefficient

Notes

Acknowledgements

This study was funded by the National Key R&D Plan of China [Grant No. 2018YFC0604501]; the Natural Science Foundation of China [Grant No. 51674264, 51574244]; and China Postdoctoral Science Foundation [Grant No. 2018M631622, 2019T120153].

Compliance with ethical standards

Conflict of interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, this manuscript.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.School of Energy and Mining EngineeringChina University of Mining and Technology (Beijing)BeijingChina
  2. 2.Coal Industry Engineering Research Center of Top-coal Caving MiningBeijingChina

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