[spam][ot][rambling][crazy] Building a Spaceship Out Of Something Ridiculously Weak and Flimsy

[Karl]

So, I'm looking through
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7057223/ a little, but it
gets really "explosive"y, which is hard for me to read due to the word
"explosive".  I could engage the difficulty directly but I don't want
to actually design a bomb.  I know it would never be used but it is
not pleasant for me to pursue.

Here is a paste of the article content.  I'm thinking there's some
concept of "explosive pressure" that could be compared to that of a
rocket fuel so as to determine a fuel quantity ratio needed.

These are not in the slightest instructions for making a bomb out of
grain dust.  They are actually, honestly safety and scientific
research documentation that is being flagged in a way that has harmed
a lot of people, including me.

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Journal ListHeliyonv.6(3); 2020 MarPMC7057223
Logo of heliyon
Heliyon. 2020 Mar; 6(3): e03457.
Published online 2020 Mar 4. doi: 10.1016/j.heliyon.2020.e03457
PMCID: PMC7057223
PMID: 32154415
Explosive property and combustion kinetics of grain dust with
different particle sizes
JiangPing Zhao, GongFan Tang, YaChao Wang,∗ and Yujiu Han
Author information Article notes Copyright and License information Disclaimer
This article has been cited by other articles in PMC.
Abstract
The effect of particle size on the combustion and explosion properties
of grain dust is investigated by Hartmann tube, cone calorimeter (CC),
and thermogravimetry (TG), it aims to provide fundamental experimental
data of grain dust for an in-depth study on its potential risk. The
fine-grain dust facilitates the decrease in the minimum ignition
temperature (MIT) of dust layer and dust cloud, as well as the obvious
increases in the maximum explosion pressure Pmax (climbs from 0.36 to
0.49 MPa) and pressure rising rate dP/dt (rises from 6.05 to 12.12 MPa
s−1), leading to the increases in maximum combustion rate (dw/dτ)max
and combustion characteristic index S, corresponding to the greater or
severer potential risk. Because the E corresponding to combustion
increases from 106.05 (sample with a particle size of 180–1250 μm) to
153.45 kJ mol−1 for the sample of 80–96 μm, the combustion process
gradually transforms from diffusion-controlled into a kinetically
controlled mode with the decreasing particle size of grain dust,
together with the retardation of initially transient charring. It
determines that the competition between the charring and combustion
dominates the decomposition, and the combustion prevails for the
coarse particle, while the charring controls the combustion for the
fine-grain dust.

Keywords: Energy, Materials chemistry, Biofuel, Biomass, Energy
sustainability, Materials characterization, Materials safety,
Explosion, Combustion kinetics, Heat release properties, Coats-redfern
integral method, Particle size, Hartmann tube
1. Introduction
With the depleting fossil fuel resources, increasing environmental
concerns, and political commitment, sustainable development has been a
highly multi-disciplinary field [1], the recent two decades have
already witnessed the booming development of biomass fuel feedstock,
which has been employed as an alternative to the diminishing coal.
Although many drawbacks limit its extensive applications, the major
environmental, economic, and social benefits appear to compensate for
the technological and other barriers caused by its unfavorable
composition and properties of biomass fuel [2]. Therefore,
continuously increasing attention has been paid on maize grain due to
its ecological hotspot based on “business as usual” conventional
farming practice [3]. Additionally, cereal residues as renewable and
abundant resources, include both on-site residues and processing
residues, have a huge potential to achieve more sustainable
agriculture and to provide a novel fuel feedstock in theory [4].
However, the suspending grain dust in production departments is
detrimental to life safety during liquor-making and starch processing,
which holds potential hazard of fire or explosion due to its
flammability and low density for forming an explosive cloud [5, 6, 7].
The necessary prevention and control of organic dust explosion are
very imperative for safety production and property security, and the
quantitative research on the potential explosion property is the
prerequisite to designing some effective and efficient safeguards to
minimize its security risk.

Consequently, the quantitative analysis on the combustion and
explosion properties of organic powders have attracted increasing
interest, the particle size has become a breakthrough point to prompt
the suppression design. Castellanos et al. [8] have analyzed the
thermal stability of cornstarch with phosphates and determined the
crucial role of particle size on improving the inhibiting rate of heat
absorption. Yu et al. [9] have investigated ammonium polyphosphate on
explosion characteristics of micron-size acrylates copolymer powders.
Addai et al. [10] have compared the MIT of five different dust and six
different gases. The combustion of wheat starch and carbon-black
particles have also been studied [11]. Addai et al. [12] also assert
that the inert materials with high bulk density are not ideal
inertants. Generally, the devolatilization and char oxidation mainly
predominate the whole combustion process [13], seeking an appropriate
inertant for explosion suppression of organic dust is intriguing the
increasing attention, but a few reports focus on the explosion
property of organic dust.

Furthermore, biomass dust has also shown strong flammability, it holds
a high-explosive tendency and easily transforms into the hazard,
although it does not occur in the same way as in the case of coal. The
different sizes and various shapes of organic powder make the
interpretation of organic dust explosion difficult and complicated
[14, 15]. Saeed et al. [16, 17] suggest that fine biomass facilitates
increased mass-burning with high flame speed. Therefore, the potential
risk derived from the organic dust including explosion and ignition
imparts huge hidden danger to the dust-processing workshops [5, 6, 7].
The preliminary exploration of the ordinary or pristine organic dust
is necessary to broaden the combustion and explosion mechanism, which
is beneficial to provide some basic experimental data in the security
design of dust explosion suppression.

However, there is scant data on the combustion kinetics and explosion
characteristics of grain dust to promote comprehensive research.
Consequently, using the grain powder of beer production workshop as
the research objective to approach realistic scenario, the effect of
particle size on the minimum ignition temperature (MIT) is measured
based on the experimental dust layer and dust cloud, the lower
explosive limit (LEL), heat-release properties, and dynamic
characteristics are tested by the Hartmann tube, cone calorimeter, and
thermal gravimetry (TG), respectively. It aims to provide an
exploration on the combustion and explosion properties of grain dust,
prompting its recycling as a novel fuel feedstock and diminishing its
security risks. Additionally, the combustion mechanism of biomass is
in its beginning stage, the quantitative analysis of grain powder is
lacking, the Coats-Redfern integral method is employed to illustrate
the combustion kinetics firstly. The article's novelty relates to
combining the calculation of combustion characteristics with
combustion kinetics simultaneously, it establishes an effective
quantitative analysis method on dust-explosion of organic powder.

2. Materials and methods
2.1. Raw materials
The pristine powder consisted of grain and chaff dust was collected
from the dust removal system of Xi'an brewery in Shaan'xi province of
China, it mainly was composed of malt dust, rice dust, and a small
amount of ash as shown in Table 1, presented the features of high
volatility, poor LHV, and low fixed carbon. The grain dust sample with
different particle size was sieved by the standard sieve, which was
obtained by sieving of 80 mesh (180–1250 μm), 100 mesh (154–180 μm),
120 mesh (120–154 μm), 140 mesh (109–120 μm), 160 mesh (109–96 μm),
and 180 mesh (80–96 μm), respectively. The distribution curve of
pristine grain dust was drawn by Gaussian fitting in Figure 1, the
sieve residues were served as the research objective.

Table 1
Proximate and ultimate analysis of pristine grain dust.

Elemental analysis/%
Industrial analysis (drying)
Element	C	H	O	N	Other	Fixed carbon/%	Moisture/%	Ash/%	Volatile/%	LHV/(MJ.kg−1)
Content	43.82	5.83	43.36	2.48	4.51	13.86	7.76	5.43	72.95	16.19
Note: LHV denotes the lower heating value.

Figure 1
Figure 1
Size distribution of pristine grain dust.

2.2. Characterizations
The MIT of the grain dust layer with a thickness of 5 mm and dust
cloud was recorded by the testers made in Northeast University of
China, according to the standards of GB/T 16430-1996 and GB/T
16429-1996, respectively. The LEL concentration, explosion pressure
rise rate dP/dt, and the maximum explosion pressure Pmax were measured
by a 1.2 L Hartmann tube. The affiliated electronic data acquisition
system was employed to record the real-time explosive parameters,
which could transform the pressure into a voltage value to obtain
real-timely explosive parameters. The experimental condition was
conducted at 29 °C with an ignition delay time of 8 s, the
spraying-powder pressure was 0.5–0.6 MPa with an error of 0.01 MPa for
Pmax.

The cone calorimeter (CC, ZY6243, Zhongnuo instrument company, China)
was exploited to record the real-time heat release property according
to ISO-5660-1-2015. Each specimen consisted of 9 symmetrically
cylindrical pancakes with a diameter of 2 cm and a height of 3 mm,
which were fabricated by the manually hydraulic-forming press with a
pressure of 0.3 MPa and wrapped in aluminum foil. The heat release
parameters of samples were calculated from the average of 3
determinations with a standard deviation < 10%, under an external heat
flux of 35 kW m−2 (600 °C approximately), including the time to ignite
(TTI), the peak heat release rate (p-HRR), and the time to p-HRR (tp).
Besides, the two important indexes of fire performance index (FPI, FPI
= TTI/p-HRR) and the fire growth index (FGI, FGI = p-HRR/tp) were used
to evaluate the combustion performance. Furthermore, non-isothermal
combustion kinetics was calculated by a TG analyzer (Mettler, Germany)
under simulated air during the heating process of 50–600 °C with a
heating rate of 20 °C·min−1.

3. Result and analysis
3.1. MIT
Table 2 discloses that the MIT of dust layer/cloud sample declines
with the decreasing size, which facilitates the diffusion and
permeation of oxygen, leading to a decrease in MIT. However, the MIT
maintains the same when the particle size (160 mesh) reduces further,
indicates that the combustion is not only controlled by oxygen
concentration, although the fine dust could trap and accommodate more
O2 from the air. Meanwhile, the MIT of the dust cloud is far above
that of the dust layer, it might be ascribed to the lower heat
conductivity of air, the suspending particles in the vessel as the
dust cloud, resulting in a slow rise of dust surface temperature.

Table 2
MIT of samples and raw material.

Samples	Shape	Raw material	80 mesh	100 mesh	120 mesh	140 mesh	160 mesh	180 mesh
MIT/°C	Cloud	480 ± 2	490 ± 2	470 ± 2	450 ± 2	440 ± 2	430 ± 2	430 ± 2
Layer	135 ± 2	140 ± 2	135 ± 2	130 ± 2	130 ± 2	130 ± 2	130 ± 2
3.2. Explosion property tested by Hartmann tube
The subtle change on the maximum explosion pressure Pmax is detected,
but the pressure rising rate dP/dt drop with the increasing particle
size as shown in Table 3, while the LEL rises, indicates that the
reactivity of grain dust weakens with the increasing particle size.
Since the enhancement of specific surface area favors the permeation
of O2, together with the higher surface energy due to the fine dust.
It leads to the rising possibility of deflagration evidenced by the
increases in the Pmax and dP/dt. It is consistent with the finding
that minimum ignition energy tends to have lower values as the
particle size decreases [18, 19]. According to the mechanism of
“pyrolysis-devolatilization” [13, 20], the decrease of particle size
accelerates the pyrolysis of hemicellulose and forms more content of
combustible gas. When the fine dust only consists of C, H, O, and N,
it will be vaporized before the flame front reaches, and forms well
mixed O2-containing fuel gas, which promotes the occurrence of dust
explosion. However, the inorganic minerals in grain particles alter
the process by forming a boundary or barrier, resulting in that
vaporization doesn't finish before the flame front reaches. As a
consequence, the grain dust is partially vaporized and forms locally
fuel-rich gas, leading to the weakened explosion.

Table 3
Explosion parameters of grain dust sample.

Samples	LEL/g·m−3	Pmax/MPa	dP/dt/MPa·s−1
180 mesh	50∼58.33	0.49 ± 0.01	12.15 ± 0.2
160 mesh	58.33∼66.67	0.45 ± 0.01	9.35 ± 0.2
140 mesh	64∼71.48	0.43 ± 0.01	8.73 ± 0.2
120 mesh	75∼83.33	0.42 ± 0.01	7.33 ± 0.1
100 mesh	116.67∼125	0.41 ± 0.01	7.28 ± 0.1
80 mesh	141.67∼150	0.36 ± 0.01	6.05 ± 0.1
3.3. Heat release property
The heat release rate of grain dust presents two peaks as shown in
Figure 2, the first peak is attributed to gases and volatiles derived
from the rapid decomposition of hemicellulose [21], simultaneous
charring layer shields the flame gradually, leading to a slight
decrease in HRR. And then the initial char cracks and triggers the
second huge peak under the continuous heating condition, which
involves unburned grain dust, cellulose and lignin left. Finally, a
compact char layer covers on the surface of the sample rather than the
afterglow phenomenon is observed after burning in CC [22], reveals the
occurrence of rapid charring. The feature of a double peak becomes
distinct for the dust with a particle size of 120–154 μm. Due to the
enhancement of charring, the quickly formed char-layer effectively
inhibits the transfer of heat and mass. However, a broad and
right-shifted peak appears for the sample with a particle size of
80–96 μm, which might be caused by that the rapid charring covers the
grain pancake completely at the beginning of burning, accumulates
energy and blocks the permeation of O2. However, the incremental
volatiles derived from the decomposition of grain dust rush out the
superficial char shell and trigger a vigorous flashover, when the
accumulated energy surpasses a critical value, presenting a single and
broad heat-releasing peak.

Figure 2
Figure 2
HRR of grain dust with different size.

The heat release property of grain powder is briefed in Table 4, the
THR and weight loss drop with the decreasing particle size, while the
TTI and tp increase, due to the enhancement of heat storage capacity
and retardation of initially transient charring of 80–96 μm sample,
leading to the overlapping of heat release peaks involved in
hemicellulose and cellulose. Additionally, the increased FPI and
decreased FGI are assigned an enhanced flame-resistant efficiency for
the sample with a particle size of 80–96 μm [23]. However, the value
of p-HRR exhibits insignificant changes, infers that the maximum flame
radiant intensity of fine dust remains the same as that of the coarse
particle.

Table 4
Heat release properties of grain powder with different particle sizes.

Samples	THR/kJ	TTI/s	tp/s	p-HRR/kJ·m−2	FPI/s ·m2 kW−1	FGI/kW·m−2 ·s−1
80 mesh	376.62 ± 7	69 ± 1	169 ± 1	60.67 ± 2	1.14	0.36
120 mesh	344.47 ± 7	83 ± 1	202 ± 1	60.21 ± 2	1.38	0.30
180 mesh	307.89 ± 6	93 ± 1	307 ± 1	61.76 ± 2	1.51	0.20
3.4. Combustion characteristics and kinetics
3.4.1. Combustion characteristics
The combustion characteristics of samples contain ignite index Di [24,
25] and comprehensive combustive characteristic index S [26], which
are calculated by formulas (1), (2), (3), respectively.

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max
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(1)
The (dw/dτ)max is the maximum combustion rate, which also is denoted
as DTGmax, %·min−1; Ti and Tp determined by TG/DTG method are assigned
to ignition and peak temperature respectively, K.

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(2)
The (dw/dτ)mean is calculated by the formula (3) corresponding to the
average burning rate,
τ
is the time, min; Tf is the burnout temperature with a weight loss of 95%, K.

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=
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(3)
The wl in formula (3) equals the ratio of the deviation to the
starting weight, the deviation is the weight change between the
starting weight and the final weight of samples after heating from 50
°C to 600 °C. The T0 is the beginning heating temperature of 323 K, VT
is the heating rate of 20 °C min−1.

The Ti, S, (dw/dτ)mean, DTGmax, and Di rise with the decreasing
particle size in Table 5, implies the intensive possibility of
deflagration, and the DTGmax is dramatically improved, which increases
from 9.47 to 16.63 %·min−1. Combining with the retardant Ti and
lessened Tf, it verifies the occurrence of violent combustion for the
fine dust of 80–96 μm.

Table 5
Combustion characteristic parameters of grain dust with different sizes.

Samples	Ti/K	Tp/K	Tf/K	DTGmax/%·min−1	S (×10−7)	Di(×10−5)	(dw/dτ)mean %·min−1
80 mesh	520 ± 2	574 ± 1	746 ± 2	9.47	1.52	3.17	3.23
120 mesh	533 ± 2	581 ± 1	747 ± 2	11.22	1.74	3.62	3.29
180 mesh	550 ± 2	583 ± 1	738 ± 2	16.63	2.50	5.19	3.36
3.4.2. Combustion kinetics
According to the references [27, 28], the combustion process of grain
dust could be divided into the following four stages according to the
DTG curves in Figure 3: moisture evaporation (50–151 °C), pyrolysis
and combustion of hemicellulose (151–239 °C), pyrolysis and combustion
of cellulose (239–335 °C), as well as pyrolysis and combustion of
lignin (335–525 °C). Since the low lignin content in the sample (about
15% [29]), the weight loss peak corresponding to the lignin is almost
absent. Because cellulose is a high-molecular compound with long
linear chains composed of D-glucosyl group, partial cellulose has a
crystalline structure made of ordered microfibrils, results in thermal
degradation is more difficult than hemicellulose [27]. The higher
capacity of heat storage derived from the decreasing particle size
causes the overlapping of DTG curves of hemicellulose and cellulose,
presents the diminishing peak of hemicellulose and lignin while the
enhanced peak of cellulose, which is in agreement with the results of
HRR.

Figure 3
Figure 3
TG/DTG of grain dust with different size including (a)80 mesh, (b)120
mesh, (c)180 mesh, and (d) DTG.

The combustion dynamics of samples are analyzed by formulas (4), (5),
(6), according to the Coats-Redfern integral method with the
first-order reaction, taking the value of R2 into account, the results
are listed in Table 6.

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(5)
ln
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(6)
Table 6
Combustion kinetic parameters of samples with different sizes.

Samples	Temperature	E/kJ·mol−1	lg A/s−1	Adj. R2
80 mesh	∼188.7 °C	4.41	-2.9	0.99
188.7∼226.9 °C	44.4	0	0.95
226.9 °C∼282.4 °C	60.12	2.5	0.95
282.4 °C∼360.1 °C	106.05	10.5	0.98
360.1 °C∼537.3 °C	11.43	0	0.84
120 mesh	∼188.7 °C	6.36	-3.1	0.99
188.7∼226.9 °C	36.36	0	0.92
226.9 °C∼282.4 °C	55.65	2.2	0.99
282.4 °C∼360.1 °C	119.58	11.7	0.99
360.1 °C∼537.3 °C	34.92	0	0.99
180 mesh	∼188.7 °C	2.85	-3.1	0.99
188.7∼226.9 °C	18.93	0	0.87
226.9 °C∼282.4 °C	45.84	0	0.95
282.4 °C∼360.1 °C	153.45	10.3	0.99
360.1 °C∼537.4 °C	10.23	0	0.89
The weight loss rate α is calculated by the equation of
α=(m0-mt)/(m0-mf) (m0 is the starting weight, mt is the real-time dust
weight, and mf denotes the finally remaining weight). The n is the
reaction order as 1, 2, 3…. A is the pre-exponential factor, min−1; E
is the activation energy, kJ·mol−1. R is the universal gas constant,
kJ·(mol·K)−1. β is the heating velocity of 20 °C min−1. T is the
absolute temperature, K. The G(α) is calculated by the equation of
�
(
�
)
=
∫
0
�
�
�
�
(
�
)
, and the A, E, and n are achieved by plotting ln [G(α)/T2] against 1/T.

Since the ignition temperature of all samples ranges from 240 °C to
270 °C, its combustion mechanism appertains to static permeable
diffusion combustion, the burning process begins with the ignition.
The combustion reaction of grain dust mainly takes place during
282.4–360.1 °C, and the linear correlation coefficients of the fitting
curves are in close proximity to1. The reaction activation energy E
corresponding combustion increases from 106.05 (180–1250 μm sample) to
153.45 kJ mol−1, it reveals the higher energy barrier to combustion
for the fine sample than that of the coarse particle, the combustion
gradually transforms from diffusion-controlled into kinetically
controlled reaction with the decreasing particle size.

4. Discussion
It is well known that grain powder contains inorganic elements as
sodium, potassium, calcium, and silicates, the mineral matter may
prompt an enhanced carbonaceous layer on the dust surface that
restricts the oxygen access and retards the ignition process [5, 30].
Because the sodium and potassium involved in the grain dust lower the
melting point of ash [31, 32, 33, 34], and a certain amount of SiO2
triggers slagging and prompts the formation of a charring shell [35],
leading to blocking effect to combustion-flame propagation and
increases in ignition temperature and MIT.

According to the above experimental data analysis, the following
mechanism could be obtained. The combustible volatiles in grain dust
absorb heat and transform into combustible gas under the heating
firstly, which could react with O2 and generate flame; and then
partially superficial dust transforms into carbonaceous
shielding-layer, while the inner combustible gas derived from the
pyrolysis of combustible volatile diffuses continuously towards the
surface, the particle is quickly enveloped in flames. Therefore, due
to the enhancement of heat storage capacity, the abrupt release of
accumulated heat intensifies flashover when the volatile pressure
surpasses a critical value, leading to the obvious enhancement on the
Pmax and dP/dt, indirectly evidenced by the increased DTGmax for
fine-grain dust of 180 mesh. Meanwhile, the rapidly soared temperature
of the outer layer facilitates and accelerates the charring of inner
grain dust, leading to an increase in the activation energy. Li et al.
[36] found that aluminum dust flame speed would increase and the
combustion would transform from diffusion-controlled mode to
kinetically controlled mode with the decreasing particle size. Apart
from the enhancement of Di and S with the decreasing particle size of
grain dust, our study determines that the combustion process is
firstly accelerated with the increased oxygen concentration, followed
by a blocking effect due to the charring with the decreasing particle
size, it transforms from diffusion-controlled mode to kinetically
controlled mode. Generally, the competition between the charring and
combustion dominates the decomposition process of grain dust, and the
combustion prevails for the coarse particle, while the charring
controls the combustion for the fine dust.

The discrepancy between HRR and combustion characteristic parameter
lies in the variant focuses, the TTI and p-HRR are crucial to evaluate
the fireproof efficiency, while the DTGmax determines the combustion
property. That is, the initially transient charring presents a higher
flame retardant efficiency, but the followed enhancement of DTGmax
favors vigorous flashover or deflagration with disastrous risk.
Therefore, the HRR hardly match the combustion characteristic, the
former focuses on the final result of burning while the latter
real-timely supervises the whole burning. Consequently, the
combination of the two techniques is recommended to assess the
combustion performance effectively.

Furthermore, the reported results show indistinctive changes on the
MIT and Pmax between the highest and the lowest particle size studied.
However, the foremost parameter relates to the dust explosion as
dP/dt, which holds the potential danger and easily leads to damage,
casualties or injuries, clarifying the effect of particle size on the
explosion severity of grain dust is prominent important for security
design of dust-explosion prevention and control, rather than the
further theoretical research. Moreover, a novel quantitative analysis
method combined the calculation of combustion characteristics, CC,
with the combustion kinetics is proposed. It opens up a comprehensive
method to evaluate the explosion of grain dust and extends the method
database for risk assessment of ordinary dust-processing.

Although the parameters on combustion and explosion property of grain
dust are examined, the microstructure and its chemical bonding need
further research in the future. The combustion kinetics preliminarily
studies the combustion mechanism, which is confirmed by the results of
CC and TG. However, the interactions between the superficial
carbonaceous layer and the underlying grain dust, the effect of minor
mineral elements involved in grain dust, and the configuration of
grain dust hold broad research spaces.

5. Conclusions
A preliminary study on the effect of particle size on the combustion
and explosion properties of grain dust is investigated to provide some
basic experimental data in the security design of dust-explosion
prevention and control, the CC and TG are employed to illustrate the
mechanisms of combustion kinetics firstly, and the following
conclusions are drawn.

(1)
The Pmax and dP/dt increase from 0.36 to 0.49 MPa and from 6.05 to
12.12 MPa s−1, respectively, when the particle size of grain dust
decreases from 80 mesh to 180 mesh. It demonstrates that the
competition between the charring and combustion dominates the
decomposition of grain dust, and the combustion prevails for the
coarse particle, while the charring controls the combustion for fine
dust.

(2)
The E of combustion calculated by the Coats-Redfern integral method
climbs from 106.05 (180–1250 μm sample) to 153.45 kJ mol−1 for the
sample with a particle size of 80–96 μm. It reveals that the
combustion process transforms from diffusion-controlled into
kinetically controlled reaction with the decreasing size of grain
dust.

(3)
It elucidates that the HRR hardly match the combustion characteristic
index tested by TG, ascribe to the different evaluation criterion, the
former focuses on the final result of burning while the latter
real-timely supervises the whole burning. But the combination of the
two techniques is recommended to assess the combustion performance
effectively.

Declarations
Author contribution statement
JiangPing Zhao: Conceived and designed the experiments; Analyzed and
interpreted the data.

GongFan Tang: Performed the experiments; Analyzed and interpreted the
data; Contributed reagents, materials, analysis tools or data.

YaChao Wang: Contributed reagents, materials, analysis tools or data;
Wrote the paper.

Yujiu Han: Contributed reagents, materials, analysis tools or data.

Funding statement
The authors sincerely acknowledge the financial support by China
Scholarship Council (CSC No. 201808610034).

Competing interest statement
The authors declare no conflict of interest.

Additional information
No additional information is available for this paper.

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