although the flame is still considered to
have been stopped on the spot.
Tests 1 and 7 were baseline
explosion tests with coal dust placed
outbye of the methane chamber. In
these tests no suppression system was
placed in the tunnel; they were done to
determine flame propagation speeds
and maximum flame travel. In these
tests the coal dust explosion flames
propagated beyond the final
sensor positions at 81 m and
reached maximum speeds of
306.8 – 366.3 m/sec at the 41 m
sensor position.
In the tests with a single
suppression system installed at 5 and
7 m and a double system at 7 m and
12 m respectively, it was clear that the
methane ignition was inhibited to such
an extent that no coal dust participated
outbye of the barrier position.
The average flame speed for the
baseline and for the flame inhibition
by the active barrier system when
installed at 5 m, 7 m and at 7 and 12 m
is shown in Figure 4.
In all the tests, the system was
successful in suppressing flame
propagation. In each case the
performance of the system can be
classified as stopped on the spot, i.e. the
flame was stopped at the position at
which the systemwas placed. The active
barrier successfully suppressed
propagating coal dust flames
approaching the barrier at flame speeds
varying from 24.4 – 62.2 m/sec.
In the unsuppressed explosion, the
flame front reaches a distance of 180 m
within 750 msec, while the flame front,
with the system installed at 30 m from
the end of the tunnel, does not reach
50 m.
The test results in the 200 m
Kloppersbos tunnel were extrapolated
to design the active suppression
protection system for longwall
mining. The 200 m tunnel provides a
means of conducting large-scale
evaluations and assessments of
barrier performance and other
requirements that cannot be done
economically by other means.
Deployment of systems
A total of 17 machine-mounted systems
have been deployed in SouthAfrica at
Sasol mines andAnglo Thermal Coal
operations. The system has successfully
suppressed methane gas ignitions on five
separate occasions.
In China, more than 400 systems have
been deployed. The system is utilised
within longwall operations to protect
against ignitions associated with shearer
frictional events. It is also deployed as a
roadway barrier within 30 m of the
tailgate position. Recent legislative
changes in China have resulted in it
being made mandatory to install
ExploSpot systems on roadheaders and
to install roadway barriers in all returns
in Shanxi Province and
Liaoning Province.
Conclusions
In protecting a mine against methane
and/or coal dust explosions, many
different controls are implemented.
However, many of these controls
remain under the control of man. In
this context, the use of active barrier
systems can assist mine management
in the prevention and control of the
risk associated with mine explosions.
The results obtained in the 10 m,
20 m and 200 m test tunnels at
Kloppersbos still need to be
considered in terms of the constraints
of the different tunnels and different
evaluation protocols. Nevertheless,
from the tests conducted, it can be
concluded that the ExploSpot system
was successful in stopping methane
explosions and the associated flame
propagation when ammonium
phosphate powder was used as the
suppression material.
In all the tests conducted, both
methane explosions and methane and
coal dust hybrid explosions, the
ExploSpot system stopped the flame
spread, thus successfully preventing
coal dust from participating in the
methane ignition.
Note
This article is based on a presentation given
at the Coal Operators’ Conference 2014,
12 – 14 February 2014, Wollongong, Australia.
References
For a complete list of references see:
DU PLESSIS, J.J.L. and SPÄTH, H., “Active
barrier performance preventing methane
explosion propagation”, in AZIZ, N.
et al
(eds.),
Proceedings of the 2014 Coal Operators'
Conference
(University of Wollongong; 2014).
Available at:
.
Figure 3.
Test 2 (baseline) flame and performance of the active barrier.
Figure 4.
Tests 8, 9, 10 and 7 average (baseline) flame speed and active barrier
performance.
46
|
World Coal
|
September 2014
