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Fire protection is an important part of the industry where flammable and explosive dusts are found. Production, storage and transport of food powders such as flour can be very dangerous in terms of explosiveness. The article deals with the measurement of explosion characteristics of wheat flour dust. The measurements were carried out according to EN 14034-1+A1:2011 Determination of explosion characteristics of dust clouds. Part 1: Determination of the maximum explosion pressure p max of dust clouds and the maximum rate of explosion pressure rise according to EN 14034-2+A1:2012 Determination of explosion characteristics of dust clouds - Part 2: Determination of the maximum rate of explosion pressure rise (dp/dt) max of dust clouds. A sample of wheat flour with a median particle size 84 μm exhibits the maximum explosion pressure 7.00 bar at the concentration of 600 g.m ⁻³ and then explosion constant is 16.9 bar.s ⁻¹ .m. A sample of wheat flour with a median particle size 50 μm exhibits the maximum explosion pressure 7.97 bar at the concentration of 1000 g.m ⁻³ and the explosion constant 54.9 bar.s ⁻¹ .m.Based on the results of the measurements, we found that the particle size distribution has a significant influence on the explosion parameters of the wheat flour samples.
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DOI 10.2478/rput-2019-0007 65
RESEARCH PAPERS
FACULTY OF MATERIALS SCIENCE AND TECHNOLOGY IN TRNAVA
SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA
2019 Volume 27, Number 44
STUDY OF EXPLOSION CHARACTERISTICS
OF THE WHEAT FLOUR DUST CLOUDS
IN DEPENDENCE OF THE PARTICLE SIZE DISTRIBUTION
Richard KURACINA1, Zuzana SZABOVÁ1, Eva BURANSKÁ1
1SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA,
FACULTY OF MATERIALS SCIENCE AND TECHNOLOGY IN TRNAVA,
INSTITUTE OF INTEGRAL SAFETY
ULICA JÁNA BOTTU 2781/25, 917 24 TRNAVA, SLOVAKIA
e-mail: richard.kuracina@stuba.sk, zuzana.szabova@stuba.sk, eva.buranska@stuba.sk
Received: 30.14.2019, Accepted: 05.06.2019, Published: 25.07.2019
Abstract
Fire protection is an important part of the industry where flammable and explosive dusts
are found. Production, storage and transport of food powders such as flour can be very
dangerous in terms of explosiveness. The article deals with the measurement of explosion
characteristics of wheat flour dust. The measurements were carried out according to EN 14034-
1+A1:2011 Determination of explosion characteristics of dust clouds. Part 1: Determination
of the maximum explosion pressure pmax of dust clouds and the maximum rate of explosion
pressure rise according to EN 14034-2+A1:2012 Determination of explosion characteristics
of dust clouds - Part 2: Determination of the maximum rate of explosion pressure rise (dp/dt)max
of dust clouds. A sample of wheat flour with a median particle size 84
m exhibits the maximum
explosion pressure 7.00 bar at the concentration of 600 g.m-3 and then explosion constant is
16.9 bar.s-1.m. A sample of wheat flour with a median particle size 50
m exhibits the maximum
explosion pressure 7.97 bar at the concentration of 1000 g.m-3 and the explosion constant 54.9
bar.s-1.m.Based on the results of the measurements, we found that the particle size distribution
has a significant influence on the explosion parameters of the wheat flour samples.
Key words
Wheat flour dust clouds, explosion characteristic, maximum explosion pressure, maximum rate
of explosion pressure rise
INTRODUCTION
A dust explosion needs to be triggered by an ignition source of sufficient energy and
simultaneously requires the presence of dust clouds of appropriate concentration and an
atmosphere containing enough oxygen to permit combustion. The combustion process leads to
a rapid and significant increase in pressure, typically up to 7001000 kPa within a confined
DOI 10.2478/rput-2019-0007 66
space; such pressures could lead to the fracture and collapse of a silo or to a burst of the silo
roof and upper walls with resultant flying projectiles [1].
The highest risk of explosion poses primary threat in the production processes, where dust
is handled in some way. Such processes are used, for example, in the food, pharmaceutical or
chemical industries. Technologies that companies use for milling, drying, pneumatic or
mechanical transport, storage and filtration are highly susceptible to self-ignition, occurrence
of fire and explosion. A series of accidents, fires and explosions, which happened in the past,
turned attention of experts to the development of the systems and devices that could protect
industrial technologies from these events [2].
A dust explosion could be triggered when flammable particulates suspended in the air
encounter ignition sources with sufficient energy. Combustible dust can be found in the form
of a by-product in various industries such as drilled-charcoal powder in coal mining and wood
powder in the wood industry, or in the form of raw materials or intermediate products such as
sugar powder in the food processing plants. Aside from high temperatures and overpressures
caused by dust explosions, toxic gases can also be produced in the violent chemical reactions.
Thus, dust explosions pose significant threats to people, assets, and the environment. Dust
explosions have caused numerous losses in industry [3].
According to the previous research of Eckhoff [4], fuel, oxidant, ignition source,
confinement, and suspension are the essential factors for a dust explosion [2].
Properties of dust clouds and settled dust are characterized by the Lower Explosive Limit
(LEL), the maximum explosion characteristics (maximum explosion pressure pmax, maximum
rate of explosion pressure rise (dp/dt)max), minimum ignition energy Emin, minimum ignition
temperature of dust clouds troz, induction period for ignition τi and Limiting oxygen
concentration (LOC) [5].
The article presents the practical measurement of the maximum explosion pressure and the
maximum rate of explosion pressure rise of the wheat flour dust clouds in dependence of the
particle size distribution. Research on the dependence of the explosion parameters on the
granulometry of the samples has also been dealt in [6, 7 and 8].
The measurements were carried out in accordance with EN 14034-1+A1:2011
Determination of explosion characteristics of dust clouds. Part 1: Determination of the
maximum explosion pressure pmax of dust clouds and the maximum rate of explosion pressure
rise according to EN 14034-2+A1:2012 Determination of explosion characteristics of dust
clouds - Part 2: Determination of the maximum rate of explosion pressure rise (dp/dt)max of dust
clouds [9].
MATERIALS AND METHODOLOGY OF EXPERIMENT
For the measurement of monitored characteristics, we used a modified chamber of KV 150-
M2. Scheme of the chamber is shown in Figure 2. Dust clouds in this unit is carried out
mechanically. From the tank with volume 5.5 liters, the compressed air is transmitted by a fast
opening electromagnetic valve to inner space of the chamber which a volume of 291 liters. The
sample is located on a plate and spread by the compressed air at the pressure of 9.5 bar. The
compressed air is directed to the sample through the metal profiled sheeting. The sample is
ignited by a nitrocellulose igniter after spreading the sample. The igniter works on a resistive
principle. Immediate ignition of nitrocellulose is achieved by the power source with parameters
of 60 V DC and 5.5 A, which is supplied to the resistance wire and results in an immediate burn
and interruption of the wire. Ignition energy of the nitrocellulose used in initiator is 10 kJ.
DOI 10.2478/rput-2019-0007 67
Fig. 1 Scheme of a modified KV 150-M2 chamber (1- lid, 2- disperser, 3- desk, 4- base, 5-
nitrocellulose igniter, 6- vessel, 7- manometer, 8- compressed air inlet valve, 9- fast opening
electromagnetic valve, 10- window
Ignition of dust and dispersion of the dust is timed by a solid state timing relay. The relay
has a fixed time interval set between the opening of the fast opening valve and with the
connecting power to the initiator clamps. Time delay was set on 260 ms. The pressure changes
inside the chamber were recorded by the pressure transducer with mA output and the maximum
measurable overpressure value of 20 bar. The pressure transducer is powered by a stabilized 24
V DC source. Response time of pressure transducer is 0.5 ms and the current value is recorded
through the datalogger. The measured samples were two different wheat flour dusts. Particle
size of samples is shown in Table 1.
Table 1 Particle size of wheat flour dust samples
Particle size
Sample 1 %wg.
Sample 2 %wg.
> 500 m
0.00
0.25
250 500 m
0.13
0.56
200 - 250 m
5.76
5.83
150 - 200 m
33.94
19.48
90 - 150 m
24.18
17.04
56 - 90 m
22.53
17.75
0 - 56 m
9.05
39.09
median value:
84 m
50 m
moisture
15.0 %
7.2 %
Measurement of the parameters was carried out on the apparatus described above. The
igniter was nitrocellulose of a weight from 1.25 g. As mentioned above, the weight of the
nitrocellulose corresponded to the energy of the initiator with the value of 2 x 5 kJ.
The current in the circuit was measured by the 269.3 resistor with a data logger. The
values were recorded at the rate of 2000 values/second. Recording of the pressure changes
during the explosion of dust clouds was measured in the concentrations range 150 - 1000 g/m3.
DOI 10.2478/rput-2019-0007 68
RESULTS AND DISCUSSION ON RESULTS
The values of pressure depending on the time obtained by the measurement are shown in
Figures 3 and 5. The results suggest that the increasing concentration of the dust leads to the
increase of the pressure value and the pressure rise value in the chamber. Tab. 2 shows the
explosion characteristics of the wheat flour dust clouds samples at various concentrations.
By comparing the measurement results with the Gestis-Dust-Ex database [10], we
determined that the measurement results of both samples correspond to the measurements in
the database. The Gestis database for Sample 1 lists the maximum explosion pressure of 7.2 bar
and the explosion constant of Kst of 41 bar.s-1.m. For Sample 2, the Gestis database lists the
maximum pressure of 7.3 bar and the explosion constant of 59 bar.s-1.m.
Table 2 Explosion characteristics of the wheat flour dust samples
Concentration
(g/m3)
Sample 2
Pmax (bar)
dP/dt (bar.s-1)
Pmax (bar)
dP/dt (bar.s-1)
150
2.58
6.79
2.32
250
3.54
11.54
4.87
24.23
500
5.71
18.90
7.28
68.47
600
7.00
25.49
7.31
82.81
750
6.25
23.35
7.59
73.84
1000
7.97
82.21
  
 
   (1)
  
 
   (2)
Fig. 2 Explosion pressure of sample 1 with various concentrations
DOI 10.2478/rput-2019-0007 69
Fig. 3 Explosion pressure P and pressure rise dP/dt of sample 1 with the concentration
of 600 g/m3
Fig. 4 Explosion pressure of sample 2 with various concentrations
DOI 10.2478/rput-2019-0007 70
Fig. 5 Explosion pressure P and pressure rise dP/dt of sample 2 with the concentration
of 600 g/m3
CONCLUSIONS
The tests of the explosion of the wheat flour dust clouds by the device which parameters
were described above proved that the maximum value of the pressure of Sample 1 (median
value of particle size 84 m) was reached at concentration of 600 g / m3 and its value is 7.00
bar.
The maximum value of the pressure of Sample 2 (median value of particle size 50 m) was
reached at the concentration of 1000 g/m3 and its value is 7.97 bar. The explosion constant Kst
of Sample 1 was calculated for the concentration of 600 g/m3 and its value is 16.9 bar.s-1.m.
The explosion constant Kst of Sample 2 was calculated for the concentration of 600 g/m3 and
its value is 54.9 bar.s-1.m.
On the basis of measurement, we found that the distribution of the particles has a significant
impact on the parameters of the wheat flour dust samples. It can be concluded that the sample
with smaller particles exhibits higher explosion parameters.
Acknowledgements
This research output was supported by the Slovak Research and Development Agency
under the contract No. APVV-16-0223 and by the VEGA Project 1/1010/16.
References
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[2] ŠTROCH, P. 2016. Do not underestimate danger of explosion; Even dust can destroy equipment
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[4] ECKHOFF, R.,K. 2003. Dust Explosions in the Process Industries, 3rd ed. Gulf Professional
Publishing. 719 p. ISBN 978 075 067 6021
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[5] DAMEC, J., 1993, Risk of industrial dust explosions (Part 4). In 150 Fire, No. 6, ISSN 0682-
8467
[6] CASTELLANOS, D., CARRETO-VAZQUEZ, V.A., MASHGUA, C.V., TROTTIER, R., MEIJA
A. F., MANNAN, M.S. 2014. The effect of particle size polydispersity on the explosibility
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Effects of particle size on flame structures through corn starch dust explosions. Journal of Loss
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Behaviour Affected by the Change of Particle Size. Procedia Engineering, 148, 1156 - 1161, ISSN
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[9] STN EN 14034-3+A1:2012 Determination of explosion characteristics of dust clouds. Part
3:Determination of the lower explosion limit LEL of dust clouds
[10] GESTIS-DUST-EX, Database Combustion and explosion characteristics of dusts, IFA, online
[2019-6-21]: http://staubex.ifa.dguv.de/exploergebnis.aspx?lang=e
ORCID
Richard Kuracina 0000-0003-1468-0820
Zuzana Szabová 0000-0002-7886-1623
Eva Buranská 0000-0002-2382-7508
DOI 10.2478/rput-2019-0007 72
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Risk of industrial dust explosions (Part 4)
  • J Damec
DAMEC, J., 1993, Risk of industrial dust explosions (Part 4). In 150 Fire, No. 6, ISSN 0682-8467
Database Combustion and explosion characteristics of dusts, IFA, online
  • Gestis-Dust-Ex
GESTIS-DUST-EX, Database Combustion and explosion characteristics of dusts, IFA, online [2019-6-21]: http://staubex.ifa.dguv.de/exploergebnis.aspx?lang=e ORCID Richard Kuracina 0000-0003-1468-0820