D. Wu, E. Van den Bulck

Department of Mechanical Engineering, KU Leuven, Belgium

Numerical Analysis of the Self-Heating Behaviour of Coal

Dust Accumulations

Conclusions and future work

Self-heating behaviour of dust accumulations is a multi-physics field coupled heat and mass transfer in the porous media. A typical

experimental apparatus with a hot storage oven and mesh wire baskets has been taken as the study object. The influence of gas flow velocity,

oxygen concentration and ambient temperature on the self-heating behaviour of the dry coal dust sample has been investigated with

COMSOL Multiphysics®.

Ignition delay time decreases with increasing ambient

temperature and oxygen concentration;

The maximum temperature can be reached after

ignition increases with increasing ambient oxygen

concentration;

The inflow velocity has both positive and negative

affects on self-heating. The critical velocity is

between 0.12 to 2m/s.

The influence of particle size and depletion of coal

should be taken into consideration.

Chemical

Free and Porous Media Flow

2 2Coal O CO 0.1CO heatk

2= Orate k c Aexp( )E

k ART

[ ( ( ) ]Tpt

uI u u

( ) 0 ub b

[ ( ( ) ) ]T pt

uu u I u

Species Transport in Porous Media

b b F, ,( )ii F i i i i

cD c c R

t

u

( ) 0ii i i

cD c c

t

u

p eq p eq( ) ( )T

C C T k T Qt

u

p eq b p p,p b g p( ) (1 )C C C

eq b b b g(1 )k k k

Heat Transfer in Porous Media

p p g( )T

C C T k Tt

u

Table 1: Input parameters

Fig. 1: Domain geometry

2.3h 6.6h

9.4h 11.6h

Fig. 2: Temperature profiles (21 vol.% O2 at 388.15K with

0.059m/s gas flow

References

[1] CEN, Determination of the Spontaneous Ignition Behavior of Dust Accumulations. European Standard EN15188, European Committee for Standardization, Brussels, 2007.

[2] U. Krause, M. Schmidt, C. Lohrer, A Numerical Model to Simulate Fires in Bulk Materials and Dust Deposits, J. Loss Prev. Process Ind. , 19, 218-226 (2006).

[3] L. Yuan, A. C. Smith. CFD modeling of spontaneous heating in a large-scale coal chamber, J. Loss Prev. Process Ind. 22, 426-433 (2009).

[4] H. Zhu, Z. Song, B. Tan, Y. Hao. Numerical investigation and theoretical prediction of self-ignition characteristics of coarse coal stockpiles, J. Loss Prev. Process Ind. 26, 236-244 (2013).

0 5 10 15 20 25

300

400

500

600

700

800

900

Ce

ntr

al p

oin

t te

mp

., K

Time, h

372.15K

374.15K

376.15K

378.15K

380.15K

Fig. 4: Temperature evolution of the central point at 21 vol.%

O2 with 0.059m/s gas flow at various ambient temperatures

Open domain:

Porous domain:

Open domain:

Porous domain:

Porous domain:

Open domain: 0 5 10 15 20 25

400

600

800

1000

1200

Ce

ntr

al p

oin

t te

mp

., K

Time, h

10 vol.% O2

21 vol.% O2

30 vol.% O2

40 vol.% O2

0 5 10 15 20 25

400

600

800

1000

Ce

ntr

al p

oin

t te

mp

., K

Time, h

0.4m/s

0.3m/s

0.2m/s

0.12m/s

0.059m/s

Fig. 5: Temperature evolution of the central point at 380.15K

with 0.059m/s gas flow at various oxygen concentrations

Fig. 6: Temperature evolution of the central point at 380.15K

with 21 vol.% O2 at various inflow velocities

Fig. 3: Temperature profiles of different points on the central line

at 21 vol.% O2 with 0.059m/s gas flow and 380.15K

1 2 3 4 5

12 14 16

360

420

480

Te

mp

., K

Time, h

1 (r=0)

2 (r=0.01)

3 (r=0.02)

4 (r=0.03)

5 (r=0.04)

0 5 10 15 20 25

400

600

800

Te

mp

., K

Time, h

1 (r=0)

2 (r=0.01)

3 (r=0.02)

4 (r=0.03)

5 (r=0.04)

Simplify 3D

2D axisymmetric

Excerpt from the Proceedings of the 2014 COMSOL Conference in Cambridge