Американский Научный Журнал INVESTIGATION OF COAL DUST FORMATION UNDER CYCLIC CRYOGENIC INFLUENCES

Abstract. Analysis of the need to consider the fractional composition of coal dust in the calculation of the dust load is carried out. The impact of cycles of freezing and thawing on the fractional composition of the dust generated during mechanical destruction of coal marks D are found. To achieve this goal, in vitro experiments were carried out with coal mark D of the Tugnuisky deposit. The collected sample was split into smaller samples and, with the help of mechanical crushing followed by classifying, the following fractions were obtained: 1 mm, 1 + 0.63 mm, 0.4 mm -0.63, -0.4 +0 25 mm, -0.25 mm + 0.2, 0.2 + 0.14 mm, -0.14 mm. For determining the fractional composition of the coal, depending on the degree of hydration was used Camsizer XT installation, which allows obtaining a density distribution of particles in a sample. Altogether were conducted 80 trials, of which 40 - in the natural moisture and 40 - with artificial moisture (full saturation). The experimental results showed that there is a relationship between the fractional composition of the sample, its moisture content and the number of cycles of freezing and thawing. It is shown that the level of dust, depending on the number of cycles at increasing humidity is substantially reduced: by the degree of destruction of 7-fold effect of the dry coal is 1-fold to humidified coal. Also was found the effect size fractions on the degree of destruction. In particular, the processing of the experimental data showed that the initial fraction of less than 0.14 mm output of fine dust does not change, and further research may be excluded from the analysis. The maximum degree of destruction observed dust sample fractions 1 + 0.63 mm, which should be used in determining the impact of man-made laws of moisture on the fractional composition of the dust in the cyclic cryogenic effects. The established regularities will continue to develop the best plan of experimental work to achieve this goal for different marks of coal. Скачать в формате PDF
American Scientific Journal № ( 32) / 2019 35

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INVESTIGATION OF COA L DUST FORMATION UND ER CYCLIC CRYOGENIC INFLUENCES

Obozhina Elena
Cand. of Science (Engineering),
modeling laboratory of the Scientific center of geomechanics and mining issues,
Saint -Petersburg mining university,
Saint -Petersburg

Abstract. Analysis of the need to consider the fractional compositio n of coal dust in the calculation of the
dust load is carried out. The impact of cycles of freezing and thawing on the fractional composition of the dust
generated during mechanical destruction of coal marks D are found. T o achieve this goal, in vitro expe riments
were carried out with coal mark D of the Tugnuisky deposit. The collected sample was split into smaller samples
and, with the help of mechanical crushing followed by classifying, the following fractions were obtain ed: 1 mm,
1 + 0.63 mm, 0.4 mm -0.6 3, -0.4 +0 25 mm, -0.25 mm + 0.2, 0.2 + 0.14 mm, -0.14 mm. For determining the
fractional composition of the coal, depending on the degree of hydration was used Camsizer XT installation, which
allows obtaining a density di stribution of particles in a sampl e. Altogether were conducted 80 trials, of which 40 -
in the natural moisture and 40 - with artificial moisture (full saturation).
The experimental results showed that there is a relationship between the fractional composi tion of the sample,
its moisture c ontent and the number of cycles of freezing and thawing. It is shown that the level of dust, depending
on the number of cycles at increasing humidity is substantially reduced: by the degree of destruction of 7 -fold
effect of the dry coal is 1 -fold to humid ified coal.
Also was found the effect size fractions on the degree of destruction. In particular, the processing of the
experimental data showed that the initial fraction of less than 0.14 mm output of fine dust does not change, and
further research may b e excluded from the analysis. The maximum degree of destruction observed dust sample
fractions 1 + 0.63 mm, which should be used in determining the impact of man -made laws of moisture on the
fractional composition of the d ust in the cyclic cryogenic effect s. The established regularities will continue to
develop the best plan of experimental work to achieve this goal for different marks of coal.
Keywords: dust concentration, fractional composition, coal, pneumoconiosis, cyc les of freezing and thawing,
dusti ng, respirable fraction.

Introduction. Currently, there is no unified
system for measuring the dust content in the working
area. Each country adheres to its own way of
normalizing the dust content in the air of the workin g
area and, accordingly, its dust suppression measures.
The only thing that is similar in all countries is the
rationing of coal dust depending on the content of
silicon dioxide in it, because this compound has a
negative impact on the early appearance of
pneumoconiosis in workers. Table 1 shows the
maximum permissible concentrations of coal dust in
different countries. The table shows that Russia is the
most" loyal " to dust: the content of silicon dioxide can
reach up to 70%, which is unacceptable in most
developed countries [1, 19].
Tab le 1
Indicative data on the measurement and assessment of dust concentration in the coal industry in
Germany, France, the UK, the USA and Russia.
Indicator Germany France The UK The USA Russia
Maximum permissible dust
concentration, mg/m 3 10 13,5 7 2 10
Assessment of quartz content
q>5% with a
coefficient К=1;
0,7 и 0,3
Fixed
q>7%
At the
testing
stage
Fixed
q>7%
q>10%, 2
mg/m 3,
q<10% -
10 mg/m 3

Over the past 10 years, it has been revealed that
the incidence of workers is affected not only by the
content of free silicon dioxide, but also by the fractional
composition of dust (the most dangerous is the dust
fraction from 2 to 5 microns, since it is retained in the
alveoli of the lungs and remains there in 50 -90% of

36 American Scientific Journal № ( 32) / 20 19
cases). A number of countries have already
implemented a transition to the regulation of dust
content in the air depending on the fractional
composition. Some countries draw such a border up to
2.5 microns, others - up to 10 microns. In Russia, this
rationing is not carried out, which negatively affects the
whole situation: if in the world there is a tendency to
reduce the level of pneumoconiosis, in Russia – on the
contrary, lung diseases in workers are among the three
most frequent occupational diseases. All this indicates
the urgency of the problem of dust control at coal
enterprises in Russia [2 , 62].
In the work of Kudryashov V.V. [3, 112], the fact
of increasing the dust yield during the destruction of
rocks subjected to a cyclic process of freezing -thawing
was established and experimentally confirmed. At the
same time, the author did not consi der the influence of
freezing -thawing cycles on the fractional composition
of dust and also t he number of cycles.
Similar studies using modern analytical base were
given by Romanchenko S.B. and Rudenko Yu.F. in [4,
30], where it was found that with a decre ase in air
temperature (the range was studied to -25 oC), the
intensity of dust formation in t he development of rocks
increases. The fractional composition of dust was also
studied, but the influence of humidity and cyclicality on
the amount and fractional composition of dust was not
considered.
Methods. The aim of the work was to establish the
dependence of the yield of fine dust fraction on the
freezing -thawing cycles. At the Scientific center of
Geomechanics were conducted laboratory studies of
dust -prod ucing capacity of the Tugnuisky open -pit,
with a coal mark D. Method of measurement was as
follows: was initially selected a representative sample
of coal that represents the pieces with a mass of 1 kg.
Single piece was pre -moistened during the day. By
pre liminary crushing, grinding and subsequent sieve
analysis, the following size classes were di stinguished:
+1, -1 + 0.63 mm, -0.63+0.4 mm, etc.
Each sample was divided into equal parts and was
frozen once and seven times, before and after freezing,
control measurements were carried out. Figure 1
presents the results of studies of the effect of free zing -
thawing cycles on the dust formation of coal samples
with a size of +1 mm, from which it can be seen that
the main effect of one freeze on the dust formation of
coal occurs at a fraction of 100 microns. 7 cycles of
freezing -thawing affect the formatio n of a smaller
fraction in the entire sample under consideration.
Evaluation of the results of dust formation was assessed
by the presence of a fraction of up to 2 5 microns.

Figure 1. Results of measurements of dust for mation of coal samples more than 1 mm

For a pre -moistened coal sample, there is a
different situation (Fig. 2): at the interval from 15 to 25
microns, the number of small particles prevails in the
coal, not subject to single and 7 -fold freezing. This
effec t is explained by the ability of coal particles to
stick together, forming larger particles. However, with
a fraction of 75 microns, the percentage of fine particles
begins to prevail samples without freezing and with one
freeze to 250 microns.

American Scientific Journal № ( 32) / 2019 37

Figure 2. Results of measurements of dust formation of coal samples more than 1 mm saturated with water

For coal sample fractions: -1+0,63; -0,63+0,4; -
0,4+0,25 mm occur the same changes, that and under
fract ion +1 mm. Although, u nder fractional the
composition of the -0,14 mm cycles freezing -thawing
affect dusting marginally, i.e. in further experiments
cannot be viewed. This may be due to the difficulty of
trapping particles by the Camsizer XT unit on which
the studies were condu cted.
Conclusion. There is a dependence of the state of
the coal on the cycles of freezing -thawing. Whether it
is dry or saturated with water, its fractional composition
increases in the direction of fine particles that adversely
aff ect workers. This effe ct is significant and should be
taken into account when choosing methods and means
of dust suppression of coals subjected to cryogenic
effects.

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