Coal is an important strategic resource in the world; coal production safety has always been widely concerned. In coal mine production, inert dust can effectively reduce coal dust explosion accidents in mine tunnels. To reveal the suppression effect of inert dust on lignite dust explosion, CaCO3, SiO2, and NH4H2PO4 are selected for suppression experiments. It is found that the lignite dust explosion pressure decreases continuously as the mass percentages of inert dust mixed into lignite dust increase. By calculating the molar mass, the suppression effects of CaCO3 and SiO2 on lignite dust explosion are compared. The lignite dust no longer explodes when the mass percentage of NH4H2PO4 dust mixed into lignite dust is 70%, indicating that NH4H2PO4 is more effective than that of CaCO3 and SiO2. The smaller the particle size of NH4H2PO4, the better the suppression effect on explosion. The lignite dust does not explode when the mass percentage of NH4H2PO4 is 60% and the particle size of NH4H2PO4 is 25-38 μm, which proves that decreasing the particle size of NH4H2PO4 is important to suppress explosion. The research results are of great significance for grasping the explosion suppression effect of inert dust on lignite dust.
Coal is an important strategic resource in the world; coal production safety has always been widely concerned. In coal mine production, inert dust can effectively reduce coal dust explosion accidents in mine tunnels. To reveal the suppression effect of inert dust on lignite dust explosion, CaCO3, SiO2, and NH4H2PO4 are selected for suppression experiments. It is found that the lignite dust explosion pressure decreases continuously as the mass percentages of inert dust mixed into lignite dust increase. By calculating the molar mass, the suppression effects of CaCO3 and SiO2 on lignite dust explosion are compared. The lignite dust no longer explodes when the mass percentage of NH4H2PO4 dust mixed into lignite dust is 70%, indicating that NH4H2PO4 is more effective than that of CaCO3 and SiO2. The smaller the particle size of NH4H2PO4, the better the suppression effect on explosion. The lignite dust does not explode when the mass percentage of NH4H2PO4 is 60% and the particle size of NH4H2PO4 is 25-38 μm, which proves that decreasing the particle size of NH4H2PO4 is important to suppress explosion. The research results are of great significance for grasping the explosion suppression effect of inert dust on lignite dust.
Coal dust explosion is
one of the major accidents affecting the
safety production of coal mines, which usually causes huge casualties
and property losses.[1] In the process of
coal dust explosion, high-temperature flame and high-speed propagating
pressure shock wave will be generated. The propagation speed of the
pressure shock wave is much greater than the propagation speed of
the flame; theoretical research shows that the flame propagation speed
of the coal dust explosion can reach more than 1120 m/s and the propagation
speed of the pressure shock wave can reach more than 2340 m/s, both
of which are extremely destructive.[2,3] At the same
time, the average theoretical pressure of the coal dust explosion
in coal mine tunnels is 736 kPa, and the explosion pressure increases
rapidly with the increase of the distance from the explosion source.[4,5] Nowadays, with the development of dust explosion test methods, it
is of great significance for coal mine safety production to master
the variation law of coal dust explosion pressure characteristics
and the suppression effect of different types of inert dust on coal
dust explosion.[6,7]Fundamentally, coal dust
explosion is a combustion chemical reaction
with an extremely fast reaction rate, in which rapidly propagating
pressure shock waves are generated. Previous studies have found that
the mechanism of combustible gas explosion is different from that
of coal dust explosion.[8−15] In the process of coal dust explosion, volatile matter and moisture
of coal dust are first released from coal dust particles under the
action of an ignition source, which can make the explosion intensity
far greater than the explosion intensity of the combustible gas.[16−18] Based on the experimental testing and analysis methods of dust explosion,
different types of dust are used as samples; Eckhoff[19] researched on the effects of particle dispersion and dust
cloud concentration on explosion characteristics and the effects of
dust cloud turbulence and particle aggregation on explosion intensity.
Oran[20] studied the flame propagation speed
and flame structure of dust explosion caused by gas explosion in the
duct space. Kosinski and Hoffmann[21] revealed
the propagation process of primary dust explosion by using the connected
vessels and carried out the simulation research on explosion characteristics
by establishing numerical models.In the field of coal dust
explosion, the method of suppressing
coal dust explosion by inert dust is mainly used in coal mine tunnels,[22−26] because in the coal mine tunnels, due to the coal mine production
and transportation, a large amount of suspended coal dust and deposited
coal dust will be generated in the tunnel. If there is an ignition
source, the coal dust will explode, and the consequences will be very
serious. Therefore, the use of inert dust can effectively suppress
the intensity of the explosion, prevent the spread of the explosion,
and even completely suppress the occurrence of the explosion.[27,28] Even if a large amount of explosion-suppressing dust is required,
it is also a safe and effective method to control explosion accidents,
which is very important to ensure the safe production of coal mines.
In addition, when suppressing coal dust explosion, if a smaller amount
of inert dust can be used to effectively suppress the explosion, such
inert dust should be selected. However, at present, new types of inert
dust are still under continuous research and development, and developing
an inert dust that can more effectively suppress coal dust explosion
is an important research direction for coal dust explosion in the
future.In previous research, the author of this paper revealed
the ignition
characteristics and flame propagation process of different types of
coal dust cloud under different conditions[29−32] and also discovered the explosion
characteristics of deposited coal dust driven by airflow carrying
coal dust and the suppression effect of inert dust CaCO3 on explosion.[33] Using inert dust is a
very economical and effective method to control coal dust explosion.
The particle size and type of inert dust used in related research
at home and abroad are relatively simple; in most previous research,
a single particle size of CaCO3 was selected as the inert
dust; the comparative research results on the explosion suppression
effects of different types of inert dust are insufficient. Therefore,
this paper selects different types and particle sizes of inert dust
to suppress coal dust explosion, which is innovative in the research
content. To further study the suppression effect of different types
of inert dust on the coal dust explosion pressure, in this paper,
the 20 L spherical dust explosion experimental device was used to
test the explosion pressure, and the micron-sized explosive lignite
dust was used as the sample. CaCO3, SiO2, and
NH4H2PO4 were selected as three different
types of inert dust to conduct an experiment on the suppression effect
of lignite dust explosion pressure, by which the suppression mechanism
of inert dust on coal dust explosion can be better understood. Meanwhile,
the research results are of great significance for guiding the use
of inert dust for coal dust explosion suppression.
Experimental Section
Experimental Apparatus
There are
mainly two parameters that can be used to describe the coal dust explosion
pressure characteristics; they are the maximum explosion pressure Pmax and the maximum pressure rise rate (dP/dt)max. The 20 L spherical
explosive experimental apparatus is shown in Figure , which is used to test the coal dust explosion
pressure characteristics in this study. The test process of the experiment
refers to the Chinese national standard “GB/T 16426-1996 Determination
for maximum explosion pressure and maximum rate of pressure rise of
dust cloud”. The experimental apparatus is used internationally,
which is mainly composed of an automatic dust spraying system, an
ignition data acquisition system, a data transmission system, and
an automatic water circulation system. It can be got that the volume
of this spherical experimental apparatus is 20 L and the volume of
the dust storage tank is 0.6 L. The experimental test range of the
explosion pressure is from −0.1 to 2 MPa, and the test accuracy
is 0.001 MPa. The interval time of the pressure sensors to collect
the explosion pressure data is 0.2 ms, and the maximum acquisition
time of the experimental data can be up to 12 s, which can meet the
requirements of collecting pressure data in the whole explosion process.
Figure 1
Experimental
apparatus.
Experimental
apparatus.The structure of the 20 L spherical explosive experimental
apparatus
is shown in Figure . Before the experiment, put the dust sample in the dust storage
tank. During the experiment, the dust particles are driven into the
spherical space by high-pressure airflow under the action of the dispersion
valve and then explode under the action of ignition; in addition,
the pressure sensors would collect the pressure data in real time.
After the experiment, the temperature inside the experimental apparatus
can be quickly lowered by using the automatic water circulation system
in a few minutes.
Figure 2
Structure of the experimental apparatus. 1 sealing cap;
2 outer
side of mezzanine; 3 inside of mezzanine; 4 vacuum gauge; 5 outlet
of circulating water; 6 mechanical two-way valve; 7 base; 8 observation
window; 9 vacuum hole; 10 dispersion valve; 11 dust storage tank;
12 pressure gauge; 13 pressure sensor; 14 inlet of circulating water;
15 safety limit switch; 16 ignition rod.
Structure of the experimental apparatus. 1 sealing cap;
2 outer
side of mezzanine; 3 inside of mezzanine; 4 vacuum gauge; 5 outlet
of circulating water; 6 mechanical two-way valve; 7 base; 8 observation
window; 9 vacuum hole; 10 dispersion valve; 11 dust storage tank;
12 pressure gauge; 13 pressure sensor; 14 inlet of circulating water;
15 safety limit switch; 16 ignition rod.The parameters of the explosion experiment are
set as follows.
When testing the explosion pressure of the coal dust, the coal dust
injection pressure is set to 2 MPa, and the ignition delay time is
set to 100 ms; the setting of the ignition delay time is determined
under the premise of continuous testing so that the explosion pressure
can reach the maximum, which can make the coal dust particles fully
diffuse in the spherical space and achieve a uniform suspension state
before being ignited. Experiments were carried out according to the
Chinese national standard “GB/T 16426-1996 Determination for
maximum explosion pressure and maximum rate of pressure rise of dust
cloud”; when the coal dust particles enter the interior of
the 20 L sphere under the action of a dust injection pressure of 2
MPa, after a period of an ignition delay time of 0.6 s, two chemical
ignition heads with an ignition energy of 10 kJ are ignited at the
same time; the suspended coal dust cloud will be instantly ignited
and exploded, which can also be observed through the circular quartz
glass window with a diameter of 20 mm. Ten experiments are carried
out in each pressure experiment, and the mean value is calculated.
If the relative error between the measured Pmax result and the mean value is less than 4%, then the experimental
result is reliable. Otherwise, the experiment needs to be repeated.
Experimental Materials
Coal Dust Sample
In this experiment,
the selected experimental sample is lignite with a low degree of metamorphism.
The data of the proximate and ultimate analyses of lignite dust are
shown in Table . It
can be seen that the lignite dust sample is a type of highly volatile
coal dust and the main components of the sample are carbon and oxygen
elements. Generally, the volatile matter is the combustible gas, which
is first released from the coal dust particles after the coal dust
cloud is heated. So the greater the volatile content of the coal dust,
the greater the corresponding explosion risk. The air-dried volatile
content of the sample is 43.31%, which is greater than 40%; this indicates
that the experimental dust samples have a great explosion hazard.
Meanwhile, the particle size analyzer is used to observe the distribution
of coal dust particles; the results are shown in Figures and 4. It is found that the particle size of the lignite dust sample is
greater than 58 μm and less than 75 μm; under such conditions,
the risk of dust sample explosion is great. In addition, within the
observation range, the particle size of all coal dust particles conforms
to a normal distribution, indicating that the distribution of coal
dust particles is relatively uniform.
Table 1
Proximate and Ultimate Analyses of
the Coal Dust Samplea
In coal mine
tunnels, inert dust can effectively suppress coal dust ignition and
explosion. In this paper, the suppression effect of different types
of inert dust on the coal dust explosion pressure is studied by mixing
inert dust into coal dust. Three types of inert dust selected are
CaCO3, SiO2, and NH4H2PO4, which are shown in Figure . It is found that three types of inert dust
are all white inorganic particles under normal temperature, among
which the melting points of CaCO3 and SiO2 dust
are greater than 1500 K, indicating that CaCO3 and SiO2 dust are difficult to be involved in the chemical reaction
of coal dust explosion and can effectively reduce the explosion intensity.
However, the melting point of NH4H2PO4 is only 453.15 K. After mixing NH4H2PO4 into the coal sample, it will undergo a decomposition reaction
under the action of high temperature generated by explosion.
Figure 5
Inert dust
samples: (a) CaCO3, (b) SiO2,
and (c) NH4H2PO4.
Inert dust
samples: (a) CaCO3, (b) SiO2,
and (c) NH4H2PO4.
Results and Discussion
Explosion Pressure of Micron-Sized Lignite
Dust in a Confined Space
The micron-sized lignite dust is
used to test the explosion pressure in the spherical explosive apparatus.
During the experiment, 6 g of coal dust is placed in the dust storage
tank, so that the coal dust cloud mass concentration inside the 20
L spherical space could reach 300 g/m3, which can ensure
that the coal dust cloud can be ignited. By using the data transmission
system, the explosion pressure curve is obtained, and the result is
shown in Figure .
It can be found that as the time after ignition increases, the explosion
pressure increases continuously in a short period of time. At a time
of 0.8 s after ignition, the coal dust explosion pressure increases
to the maximum value, indicating that the Pmax in this explosion experiment is 0.71 MPa, which is seven times the
standard atmospheric pressure and can cause huge harm to the human
skin and vital organs. Meanwhile, within a time of 0–0.8 s
after ignition, (dP/dt)max in this coal dust explosion reaches 65.69 MPa/s, indicating that
a violent explosion occurred in the interior of the spherical space.
Figure 6
Coal dust
explosion pressure curve.
Coal dust
explosion pressure curve.However, although the lignite dust cloud with a
mass concentration
of 300 g/m3 has exploded, it does not mean that the coal
dust explosion intensity has been already at its most violent state.
Therefore, to study the influence of the coal dust cloud mass concentration
on the coal dust explosion pressure characteristics and to obtain
the coal dust cloud mass concentration under the condition of maximum
explosion intensity, in the course of subsequent research, the explosion
pressure characteristics experiments under the condition of different
coal dust cloud mass concentrations are carried out.
Explosion Pressure under the Condition of
Different Lignite Dust Cloud Mass Concentrations
According
to the Chinese national standard “GB/T 16426-1996 Determination
for maximum explosion pressure and maximum rate of pressure rise of
dust cloud”, experiments can be carried out with different
dust concentrations to obtain the relationship between explosion pressure
and dust concentration. Therefore, under the condition that the particle
size of the lignite dust sample is still greater than 58 μm
and less than 75 μm, in subsequent experiments, the mass of
lignite dust put into the dust storage tank each time has been increased
from 6 to 6.5, 7, 7.5, 8, 8.5, 9, 9.5, and 10 g, which means that
the mass concentration of the lignite dust cloud in the 20 L spherical
space has been increased from 300 to 325, 350, 375, 400, 425, 450,
475, and 500 g/m3, respectively. To study the effect of
increasing the mass concentration of the lignite dust cloud on the
explosion pressure, the mass concentration of the lignite dust cloud
is set to increase continuously with 25 g/m3 as the step
size.The lignite dust explosion pressure characteristics obtained
from the experimental tests are shown in Table , and the variation trend of explosion pressure
characteristics with the lignite dust cloud mass concentration is
shown in Figure .
The experimental data in this paper are the average value of the data
obtained after multiple tests. The average value is calculated by
multiple tests, which can effectively reduce the experimental error.
It can be seen that as the lignite dust cloud mass concentration increases
in the range of 300 to 500 g/m3, both Pmax and (dP/dt)max increase first and then decrease. When the lignite dust
cloud mass concentration is 400 g/m3, Pmax and (dP/dt)max increase to the local maximum values of 0.82 MPa and 76.19
MPa/s, respectively, which indicates that there are local maximum
points in the curve of lignite dust explosion pressure characteristics
with the lignite dust cloud mass concentration. Based on the current
experimental results, the lignite dust cloud mass concentration corresponding
to this local maximum point is 400 g/m3, which means that
when the lignite dust cloud mass concentration is 400 g/m3, the lignite dust explosion pressure characteristics in the 20 L
spherical space are at the most violent state.
Table 2
Explosion Pressure under the Condition
of Different Lignite Dust Cloud Mass Concentrationsa
explosion pressure
characteristics
c (g·m–3)
m (g)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
325
6.5
0.75
68.21
350
7
0.79
71.55
375
7.5
0.80
73.80
400
8
0.82
76.19
425
8.5
0.77
73.54
450
9
0.73
71.68
475
9.5
0.71
69.61
500
10
0.70
68.08
c, lignite dust
cloud mass concentration; m, the mass of lignite
dust put into the dust storage tank.
Figure 7
Explosion pressure under
the condition of different lignite dust
cloud mass concentrations.
Explosion pressure under
the condition of different lignite dust
cloud mass concentrations.c, lignite dust
cloud mass concentration; m, the mass of lignite
dust put into the dust storage tank.According to the lignite dust explosion mechanism,
when the lignite
dust cloud mass concentration is greater than 300 g/m3 and
less than 400 g/m3, the lignite dust particles will fully
undergo a redox reaction with oxygen after being ignited. Under such
conditions, there is sufficient and surplus oxygen in the explosion
space, so that there is still a tendency for the explosion to be more
violent. When the lignite dust cloud mass concentration is greater
than 400 g/m3 and less than 500 g/m3, after
the lignite dust cloud is ignited, the volatile release rate of the
lignite dust particles becomes larger; it means that the volume of
the volatile gas released from lignite dust particles increases due
to the increase in the number of lignite dust particles. Meanwhile,
compared with the explosion pressure characteristics when the mass
concentration of the lignite dust cloud is 400 g/m3, more
oxygen is consumed per unit time, resulting in insufficient oxygen
concentration among lignite dust particles, which decreases the combustion
rate of lignite dust particles in a short period of time. The insufficient
explosion reaction of lignite dust interrupts the chain reaction of
explosion, and at the same time, the explosion intensity is greatly
reduced.
Suppression Effect of Different Types of Inert
Dust on the Lignite Dust Explosion Pressure
Three types of
inert dust are selected for lignite dust explosion suppression experiments
in the 20 L spherical explosion space; they are CaCO3 dust,
SiO2 dust, and NH4H2PO4 dust. In the explosion suppression experiment, the particle size
of the lignite dust sample is greater than 58 μm and less than
75 μm, and the mass concentration of the lignite dust cloud
is 400 g/m3; it means that the mass of lignite dust put
into the dust storage tank is 8 g, because the explosion intensity
of the lignite dust cloud is in the most violent state under this
experimental condition, which is more conducive to analyzing the suppression
effect of inert dust on lignite dust explosion. The particle size
of three types of inert dust is also greater than 58 μm and
less than 75 μm, which is the same as the particle size of lignite
dust. During the explosion suppression experiment, different types
of inert dust will be mixed into the lignite dust sample in different
mass percentages. The test results of the explosion suppression experiment
are shown in Table ; to analyze the explosion suppression effect more intuitively, the
experimental data are drawn as Figures and 9. It can be found that
the Pmax and (dP/dt)max of lignite dust explosion decrease continuously
as the mass percentages of three types of inert dust mixed into lignite
dust increase from 0 to 70%, indicating that the inert dust of CaCO3, SiO2, and NH4H2PO4 have a significant suppression effect on the lignite dust explosion.
Table 3
Suppression Effect of Three Types
of Inert Dust on the Lignite Dust Explosion Pressure Characteristicsa
CaCO3
SiO2
NH4H2PO4
p (%)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
0
0.82
76.19
0.82
76.19
0.82
76.19
10
0.76
70.63
0.75
69.15
0.71
62.78
20
0.68
65.73
0.63
64.48
0.62
55.26
30
0.61
60.19
0.57
56.03
0.55
48.09
40
0.56
50.31
0.53
46.62
0.47
39.72
50
0.50
44.15
0.45
37.17
0.35
30.64
60
0.44
35.49
0.40
32.27
0.16
16.78
70
0.39
29.16
0.35
26.42
0
0
p, mass percentage
of inert dust mixed into lignite dust.
Figure 8
Suppression
effect of inert dust on Pmax.
Figure 9
Suppression effect of inert dust on (dP/dt)max.
Suppression
effect of inert dust on Pmax.Suppression effect of inert dust on (dP/dt)max.p, mass percentage
of inert dust mixed into lignite dust.Some previous studies also have related results on
the suppression
effect of inert dust on coal dust explosion;[25−28] to compare with the previous
research results, in Table , it shows the comparison between the results of this paper
and the previous research results of explosion suppression on Pmax. It is found that when the mass percentage
of inert dust mixed into coal dust is 50%, the percentage reduction
of Pmax by mixing CaCO3 into
coal dust in this study is 39.0%, while the percentage reduction of Pmax in previous research is 42.9%, indicating
that the results obtained in this study are very close to the results
obtained in previous studies. When the inert dust SiO2 or
NH4H2PO4 is mixed into coal dust,
the percentage reduction of Pmax in this
paper is also close to the result of previous research. Although the
research results show that the effect of NH4H2PO4 on the explosion suppression of coal dust is relatively
better, in previous studies, the influence of the particle size of
NH4H2PO4 on the explosion suppression
effect of coal dust is seldom considered, and this content will be
discussed later in this article.
Table 4
Comparison between This Paper and
the Previous Research Results of Coal Dust Explosion Suppression on Pmaxa
CaCO3
SiO2
NH4H2PO4
p (%)
ε1%
ε2%
ε1%
ε2%
ε1%
ε2%
50
39.0
42.9
45.1
46.5
57.3
55.2
p, mass percentage
of inert dust mixed into coal dust; ε1, percentage
reduction of Pmax under explosion-suppressed
conditions obtained in this study; ε2, percentage
reduction of Pmax under explosion-suppressed
conditions obtained in previous research.
p, mass percentage
of inert dust mixed into coal dust; ε1, percentage
reduction of Pmax under explosion-suppressed
conditions obtained in this study; ε2, percentage
reduction of Pmax under explosion-suppressed
conditions obtained in previous research.As shown in Figures and 9, although three types
of inert dust
have a suppression effect on coal dust explosion, different types
of inert dust have different suppression effects on the coal dust
explosion pressure characteristics. When the mass percentages of different
types of inert dust mixed into coal dust are the same, the inert dust
of NH4H2PO4 is relatively more effective
in suppressing the coal dust explosion. When the mass percentage of
NH4H2PO4 dust mixed into coal dust
is 70%, the coal dust explosion no longer occurs, indicating that
the lignite dust has completely lost its explosiveness under the explosion
suppression effect of NH4H2PO4 dust.
In terms of the explosion suppression effect, compared with the inert
dust of NH4H2PO4, the inert dust
of CaCO3 and SiO2 have a relatively poor suppression
effect on coal dust explosion. Considering that the particle size
of inert dust has a significant impact on the explosion suppression
effect, therefore, it is necessary to further study the suppression
effect of NH4H2PO4 dust with different
particle sizes on coal dust explosion.
Suppression Effect of the Inert Dust NH4H2PO4 with Different Particle Sizes
on Lignite Dust Explosion
To discuss the suppression effect
of the particle size of NH4H2PO4 on
lignite dust explosion, on the basis that the particle size of NH4H2PO4 is greater than 58 μm and
less than 75 μm, NH4H2PO4 with
particle sizes of 0–25, 25–38, 38–48, and 48–58
μm are selected for further explosion suppression experiments.
The parameters of lignite dust are as follows; the mass concentration
of the lignite dust cloud is 400 g/m3, and the particle
size of lignite dust is greater than 58 μm and less than 75
μm. The experimental results of lignite dust explosion suppression
by NH4H2PO4 with different particle
sizes are shown in Table , and the experimental data are plotted in Figures and 11. It can be found that in the particle size range of 0–75
μm, the smaller the particle size of the NH4H2PO4, the better the suppression effect on the explosion
pressure of micron-sized lignite dust.
Table 5
Suppression Effect of the Particle
Size of the Inert Dust NH4H2PO4 on
the Lignite Dust Explosion Pressurea
0–25 μm
25–38 μm
38–48 μm
48–58 μm
58–75 μm
p (%)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
Pmax (MPa)
(dP/dt)max (MPa·s–1)
0
0.82
76.19
0.82
76.19
0.82
76.19
0.82
76.19
0.82
76.19
10
0.58
50.39
0.63
52.61
0.66
56.42
0.68
59.20
0.71
62.78
20
0.47
41.28
0.54
44.05
0.57
47.98
0.59
51.72
0.62
55.26
30
0.39
36.55
0.45
39.57
0.49
43.14
0.52
45.36
0.55
48.09
40
0.30
25.86
0.33
29.04
0.41
32.50
0.44
35.88
0.47
39.72
50
0.17
12.84
0.22
16.72
0.28
22.87
0.31
26.79
0.35
30.64
60
0
0
0
0
0.12
9.60
0.13
11.52
0.16
16.78
70
0
0
0
0
0
0
0
0
0
0
p, mass percentage
of NH4H2PO4 mixed into lignite dust.
Figure 10
Suppression effect of
NH4H2PO4 on Pmax.
Figure 11
Suppression effect of NH4H2PO4 on (dP/dt)max.
Suppression effect of
NH4H2PO4 on Pmax.Suppression effect of NH4H2PO4 on (dP/dt)max.p, mass percentage
of NH4H2PO4 mixed into lignite dust.In Figure , it
is found that when p is less than 10%, the suppression
effect of NH4H2PO4 dust on Pmax is very obvious, and the downward trend
of the explosion suppression curve is very large. However, when p is greater than 10% and less than 40%, the downward trend
of the explosion suppression curve is smaller than that when p is less than 10%, which indicates that the suppression
effect of NH4H2PO4 on Pmax is not linear. When p is greater
than 10% and less than 40%, the suppression effect of the inert dust
particles on Pmax becomes smaller. When p is greater than 40%, since the concentration of the NH4H2PO4 dust particles increases, so that
the heat transfer between lignite dust particles and the surrounding
space can be better controlled. Therefore, the suppression effect
of the inert dust particles on Pmax increases
again; the downward trend of the explosion suppression curve also
becomes larger again.By comparing the explosion suppression
effects of NH4H2PO4 dust with different
particle sizes on
the explosion pressure characteristics of lignite dust, it can be
seen that under the condition that the particle size of the inert
dust NH4H2PO4 is 25–38 μm,
when the mass percentage of NH4H2PO4 dust mixed into lignite dust is 60%, the lignite dust no longer
explodes, which further verifies that the NH4H2PO4 dust has a good suppression effect on the lignite
dust explosion. When the particle size of the NH4H2PO4 dust mixed into the lignite dust is 0–25
μm, the explosion intensity is relatively minimal. Under the
condition that the mass percentage of NH4H2PO4 dust mixed into lignite dust is 50%, when the particle size
of the NH4H2PO4 dust is reduced from
58–75 to 0–25 μm, the Pmax under the explosion suppression condition is reduced from 0.35 to
0.17 MPa; at the same time, the (dP/dt)max under the explosion suppression condition is reduced
from 30.64 to 12.84 MPa/s, indicating that decreasing the particle
size of the NH4H2PO4 dust plays an
important role in reducing the explosion intensity of lignite dust.
Analysis on the Suppression Effect Mechanism
of Different Types of Inert Dust on Lignite Dust Explosion
In the experimental part of this paper, the reason for selecting
NH4H2PO4 dust for explosion suppression
research is that the inorganic compound NH4H2PO4 is the main component of fire extinguishing agents
in many industrial fire extinguishers. Based on the experimental results,
the explosion suppression effects of CaCO3 and SiO2 can be compared. It is known that the relative molecular
masses of CaCO3 and SiO2 are 100 and 60, respectively,
so the molar masses of CaCO3 and SiO2 are 100
and 60 g/mol, respectively, and the ratio of their molar masses is
5:3. To compare the explosion suppression effects of CaCO3 and SiO2 under the same molar conditions, the explosion
suppression analysis should be carried out under the condition that
the ratio of p of CaCO3 and SiO2 is also 5:3. In Table , according to the explosion suppression data of CaCO3 under the condition of p = 50% and the explosion
suppression data of SiO2 under the condition of p = 30%, it can be obtained that the Pmax values under the inhibition of two types of inert dust
are 0.5 and 0.57 MPa, respectively, and the (dP/dt)max values are 44.15 and 56.03 MPa/s, respectively.
This shows that under the same mole of inert dust, CaCO3 has a more significant suppression effect on the lignite dust explosion
than SiO2. However, the explosion suppression effect of
both is not as effective as that of NH4H2PO4 dust.Compared with the suppression effect of CaCO3 dust and SiO2 dust on lignite dust explosion,
NH4H2PO4 dust has a more effective
explosion suppression effect; it is mainly because the explosion suppression
process of NH4H2PO4 dust includes
chemical explosion suppression. The physical suppression effect of
CaCO3 dust and SiO2 dust in the process of lignite
dust explosion is mainly reflected in that when they are mixed into
lignite dust particles, the heat transfer among lignite dust particles
is reduced. However, NH4H2PO4 dust
not only plays the role of diluting oxygen concentration and reducing
temperature but also can be decomposed to generate NH3,
H2O, and P2O5 under heating conditions,
as shown in Figure . As a solid product, P2O5 can be mixed with
lignite dust particles, which will physically suppress the explosion
by isolating oxygen. As two gas products, NH3 and H2O can dilute the concentration of oxygen. In addition, the
thermal decomposition reaction of NH4H2PO4 is endothermic, which can reduce the ambient temperature,
making the lignite dust particles unfavorable for ignition, so that
the combustion chain reaction is interrupted.
Figure 12
Suppression effect of
NH4H2PO4 dust on coal dust explosion.
Suppression effect of
NH4H2PO4 dust on coal dust explosion.
Conclusions
The aim of this study is
to get better understanding of the suppression
effect of different types of inert dust on the lignite dust explosion
pressure characteristics. The following results are obtained.The lignite dust cloud mass concentration has an obvious effect
on the lignite dust explosion pressure characteristics. As the lignite
dust cloud mass concentration increases in the range of 300 to 500
g/m3, both Pmax and (dP/dt)max increase first and
then decrease. When the lignite dust cloud mass concentration is 400
g/m3, the lignite dust explosion in the spherical space
is at the most violent state.By carrying out the explosion
suppression experiment of inert dust
on lignite dust, it is found that the Pmax and (dP/dt)max of lignite
dust explosion decrease continuously as the mass percentages of inert
dust mixed into lignite dust increase from 0 to 70%, indicating that
the inert dust of CaCO3, SiO2, and NH4H2PO4 have a significant suppression effect
on the lignite dust explosion. When the mass percentage of NH4H2PO4 dust mixed into lignite dust is
70%, the lignite dust explosion no longer occurs, indicating that
the explosion suppression effect of NH4H2PO4 dust is more effective than that of CaCO3 and
SiO2.The smaller the particle size of the inert
dust NH4H2PO4 in the particle size
range of 0–75 μm,
the more obvious the suppression effect on the lignite dust explosion
pressure characteristics. Under the condition that the particle size
of the inert dust NH4H2PO4 is 25–38
μm, the lignite dust no longer explodes when the mass percentage
of NH4H2PO4 dust mixed into lignite
dust is 60%, which verifies that decreasing the particle size of the
NH4H2PO4 dust is important to reduce
the lignite dust explosion intensity.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12