conditions (Table 2). This was
successful, with no flame detected along
the right-hand wall of the tunnel (the
operator’s cab position is on the
right-hand side of the machine). Some
flame was, however, detected at the roof
and along the left-hand wall of the
tunnel.
The pressure rises caused by the
explosion were so small that they were
almost zero. For these tests, the highest
temperature rise at the operator’s
position was approximately 93˚C. The
operator and the rest of the crew
working at the face would be safe under
the worst possible conditions.
Once the full-face tests were
complete, a 4 m shoulder was put in
place against the front right-hand wall
of the tunnel, simulating the second cut.
The machine was moved in adjacent to
this wall for the in-shoulder tests. The
results of these tests are shown in
Table 3.
For the in-shoulder testing, the
system successfully suppressed all the
explosions for the different ignition
(and machine-boom) positions. For this
series of tests, the highest temperature
rise measured at the operator’s cab was
approximately 33˚C, and once again the
pressure sensors detected almost no
pressure variations due to the
explosion. In none of the cases was any
flame detected at the operator’s cab
position.
For the final series of tests, the
machine was pulled out from next to
the shoulder and the boommoved to
simulate cutting the shoulder. The
results of these tests are shown in
Table 4.
The tests were completed
uneventfully for all the given positions
and different concentrations for the
out-shoulder machine conditions. The
maximum length of the flame extension
was 8 m (the operator’s position was
now at 9 m for the out-shoulder tests).
Once again, the pressure sensors
detected almost no pressure changes.
200 m test tunnel
The 200 m test tunnel was used to
conduct various tests. The test tunnel
was instrumented with flame sensors
and a data acquisition system for the
evaluation. The tests were conducted
with and without coal dust present.
The different baseline explosions were:
n
n
Baseline 1: 75 ± 1 m
3
methane/air
mixture without coal dust.
n
n
Baseline 2: 75 ± 1 m
3
methane/air
mixture with coal dust.
For the ExploSpot system evaluation
in the 200 m test tunnel, both
explosions were used to evaluate the
performance of the system. For the
Baseline 2 explosion, coal dust is
distributed on the floor and shelves of
the tunnel (for 60 m after the
membrane position). This results in a
methane-initiated coal dust explosion.
The test sequence included the
placement of the ExploSpot system at
the following positions within the
200 m test tunnel:
n
n
5 m from the closed end (within
the methane chamber).
n
n
7 m from the closed end (within
the methane chamber).
n
n
12 m from the closed end (within
the methane chamber).
The purpose of the tests was to
attempt to simulate explosion scenarios
and to relate the results obtained in the
test tunnel to those likely to be
obtained in a mine. The measure of
success was defined to indicate
whether the flame propagation was:
n
n
Stopped inside the barrier (referred
to as “stopped inside”).
n
n
Stopped at the barrier (referred to as
“stopped on the spot”).
n
n
Stopped.
An explosion is considered to have
been stopped on the spot if the flame
does not exceed a distance of 30 m
beyond the end position of the barrier.
Furthermore, the barrier is considered
to have stopped an explosion if the
flame propagation (i.e. flame distance)
is less than what it would have been
without a barrier installed.
Test 2 was the baseline test in which
no suppression system was placed in
the tunnel. In this test the methane
explosion propagated beyond the 71 m
sensor position with an average
calculated flame speed of 216 m/sec at
the 41 m sensor position, reaching a
maximum calculated flame speed of
249 m/sec. Figure 3 shows the flame
speeds for the baseline methane
explosion and for the tests with the
active system in place for the installation
positions at 5 m, 7 m and 12 m.
The active barrier successfully
suppressed the propagating methane
flames approaching the barrier at flame
speeds varying from 13.4 m/sec during
test 3 to 53.2 m/sec during test 4. In test
5 the flame stop position was at 21 m
and only in this test did the flame
progress beyond the barrier position,
Table 3. In-shoulder active suppression test results
Test
Methane concentration (%) Flame length (m)
Temperature increase (˚C)
92
9
6
33
93
9
3
33
94
9
4
33
95
9
5
33
96
12
5
33
97
9
5
33
Table 4. Out-shoulder active suppression test results
Test
Methane concentration (%) Flame length (m)
Temperature increase (˚C)
85
9
8
100
86
9
7
96
87
9
8
100
88
12
8
81
89
9
8
98
90
12
8
32
91
7.5
6
32
September 2014
|
World Coal
|
45
