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

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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.

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Abbreviations

a, b, c :

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

DBn:

The nth drawing body in PFC calculation

d c :

Size of granular top coal (mm)

d cwav :

Weighted average size of granular top coal (mm)

D p :

Diffusion coefficient

k :

Constraint coefficient of the boundary of granular top coal

L o :

Length of the support opening (mm)

m c :

Initial mass of granular top coal (g)

m cd :

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

m rd :

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

N n :

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

N 0 :

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

n t :

Total number of supports

Q 1 :

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

Q 3 :

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

Q av(DB03-12) :

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

Q c :

Initial volume of granular top coal (cm3)

Q cd :

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

Q DBn :

Volume of DBn in PFC calculation (m3)

Q rd :

Volume of drawn rock particles of working face (cm3)

Q t :

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

R 2 :

Correlation coefficient

SDT:

Size distribution of granular top coal

T :

Drawing time of working face (s)

V x :

Velocity of particles along the x direction

V y :

Velocity of particles along the y direction

V z :

Velocity of particles along the z direction

w 0max :

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

w :

Mass percentage (%)

w c :

Cumulative mass percentage (%)

W o :

Width of the support opening (mm)

z 0 :

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

z 0max :

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

η n :

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

η nav :

Average of ηn (%)

η w :

Top coal recovery ratio of working face (%)

ρ b :

Bulk density (g/cm3)

μ :

Proportionality coefficient

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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].

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Authors and Affiliations

  1. School of Energy and Mining Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China

    Jiachen Wang, Weijie Wei & Jinwang Zhang

  2. Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing, 100083, China

    Jiachen Wang, Weijie Wei & Jinwang Zhang

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  1. Jiachen Wang
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Correspondence to Jinwang Zhang.

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Wang, J., Wei, W. & Zhang, J. Effect of the size distribution of granular top coal on the drawing mechanism in LTCC. Granular Matter 21, 70 (2019). https://doi.org/10.1007/s10035-019-0923-5

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