Zaltzman Michail Davidovich, d.t.s., professor (Almaty, KazATK)
Bimagambetova Lalita Nurmanovna, assistant
(Almaty, KazATK)
Intensity of dust spread at
handling operations
Timely goods transportation is a vitally important
factor promoting the development of industrial and agricultural regions. The
railway transport takes first place in the volume of goods transportation among
other means of transport. At the same
time an enormous quantity of transportable bulk solids calls forth a negative
influence of the transport on the environment. Intensive dust spread at
handling operations results in air and soil pollution. Big concentration of
different kinds of dust in the air affects the health of people. While sinking,
dust worsens the contact of the wheel pair with the rails and can cause
operating irregularities of rail chains СЦБ; in that way
it leads to emergency situations. Dustiness of atmosphere has a negative
influence upon operation and working life of different mechanisms and
internal-combustion engines. Even with the effectiveness of the air filter
97-99%, the air coming into the engine which operates on the dock contains 2-6
mg/m3 dust forcing the wear-out of the piston group. It is
ascertained /1/ that every 500 motor-hours of the engine in the dust-laden
environment increase fuel consumption of the motor-vehicle Belaz-540 by 3-4
l/100km, Belaz-548 by 4-5 l/km, and the
increase of oil consumption makes 0,4-0,5 and 1,6-1,7 l/100 km correspondingly.
Therefore the decrease of dust spread at handling operations is not only one of
the major tasks in solving the problems in protection of labour on the
transport, but it is also of great economic importance.
The main sources of intensive dust spread in the
trans-shipping complex are conveyer lines, loading zones of gondola cars,
reloading blocks, car dumpers and receiving bunkers. For the actions to be taken
for highly-effective dust control, it is necessary to precisely assess the
intensity of dust spread in each source of its formation. It is the intensity
of dust spread that causes the complex of anti-dust actions, choice of schemes
of dust control and dedusting systems, equipment capacity and material
consumption which reduce or prevent the formation of dust aerosol.
The intensity of dust spread depends on a number of
interrelated factors which can be conditionally divided into three main groups
(figure 1).
Moisture
Figure
1 – Factors determining the intensity of dust spread
Most researches in this field have been given up to
dust-forming capacity and intensity of dust spread at coal production and
transportation. At that it is established that except of the above mentioned
factors, dust-forming capacity of coal considerably changes depending on basin
location, geological period of its formation, type and depth of rock
occurrence. Decrease of rock dust-forming capacity with increase of its
strength is likely to be bound with geological periods of formation of coal
fields. For instance, there is more dust when old rock fields get broken than
when new fields are developed /2/.
In quarries located in the regions with temperate and
warm climate, the dustiness of atmosphere is considerably lower than the
dustiness of atmosphere in the regions with cold or hot climate /3/. It is
significant that in the regions with cold climate the air dustiness is higher
in a winter period, and in the regions with hot climate – higher in a summer
period. In the first case it depends on winterkilling of moisture, in the
second one – on its evaporation from rock masses. Therefore, most difficult
conditions of work on dust factor are created in winter – at negative
temperatures because the intensity of dust spread increases with the decrease
of air temperature /3/. Especially unfavorable dust conditions are observed in
the regions with continental climate that is characterized with a hot and dry
summer and a cold and low-snow winter.
So, in the open pits of
The intensity of dust spread depends in many respects
on the content of fractions with the size less than 1 mm in the transported
coal. Without this fraction, big coal of the class 100 + 50 mm and small coal
of the class10 + 3mm are approximately equal on the level of dust formation.
Dust spread increases by 3-4 times due to the height
of fall from 1 to
The type of source is of great importance for
assessment of intensity of dust spread, which determines the character and
intensity of raw material income, size of dust-formation zone and height of
material fall /7. The methods approved by Goskomgidromet allow to calculate the
intensity of dust spread at handling
operations take into account only the coal category on the basis of “USSR
Catalog of mine layers on the dust factor”, source productivity and height of
material fall. Therefore, the majority of meteorological and physical-chemical
factors (figure 1) determining in many respects the intensity of dust spread do not consider the current methods of calculation
of intensity of emission of non-organized sources.
At the same time, the same source of dust spread can
have different, very distinct intensity of dust spread depending on a number of
meteorological and physical-chemical factors, especially on speed of air flows.
It is V.S. Nikitin’s generally recognized system of determining of dust spread
intensity /9/ that above all takes into account the wind speed. This system is
based on the experimental determination of dust concentration in a few fixed
points which lay on the flare axis of spreading of dust aerosol with the
simultaneous measuring of air flow speed. The intensity of dust spread is
calculated on the formula:
for
the point source with continuous operation
, mg/s
(1)
for
linear source of continuous operation, to the unit of its length
, mg/s·m (2)
where x is a distance from the source of continuous
operation to the point of spreading of dust aerosol on the flare axis, in which
the dust concentration is measured, m; C – dust concentration measured in the
air at the distance x from the source, mg/m3; v – speed of air flows
at the source of dust spread , m/s; k – empirical coefficient dependant on the source
type of dust formation (figure 2) obtained as a result of mathematical
processing of experimental data; ψ – non-dimensional parameter
characterized by the turbulence of air flow at the source of dust spread ,
which is calculated on the formula:
(3)
figure
2 – Coefficient value k
|
Type of source of dust formation |
Coefficient value k |
|
Point source located on the surface of the
industrial ground (bulldozer) |
5,66 |
|
Point source located above the industrial ground
(excavators, conveyer units for loading into gondola cars and dump
formations) |
3,02 |
|
Linear source, located on the surface of the industrial
ground (moving motor ump-truck) |
2,66 |
|
Linear, located above the surface of the industrial
ground (conveyer) |
2,33 |
It is significant that dependencies 1 – 3 have a
particular character as applied to the equilibrium position of the atmosphere
in summertime. That is why, when they are practically used to determine the
intensity of dust spread in other periods of the year, coefficients k and
ψ need a more precise definition /9/.
Summary
The analysis of the current methods of determination
of intensity of dust spread shows that
they all are based on empirical dependences; their application requires not
only the conducting of experimental investigations but also adjustment of some
coefficients taking into consideration the source type, atmosphere condition,
climate of the region and the year season. It is very problematical to forecast
the intensity of dust spread by means of these methods. There are virtually no
physical models allowing to obtain analytical dependences to determine the
intensity of dust spread in the sources of different types. In this connection,
there is a need to carry out full-scale analytical and experimental
investigations in order to elaborate engineering methods of calculation of the
intensity of dust formation at handling operations on the transport.
Literature:
1. Ивашкин В.С. Борьба с пылью и газами на угольных разрезах. М.: Недра,
1980. – 153 с.
2. Саламатин А.Г., Забурдяев Г.С. Исследование пылеобразующей способности
горных пород основных угольных бассейнов СНГ – Безопасность труда в
промышленности, 1996, № 5, С. 17-20.
3. Лобода А.И., Ребристый Б.Н., Тыщук
В.Ю., Фаермарк А.А. Борьба с пылью на открытых горных работах. Киев, Тэхника,
1989. – 151 с.
4. Радченко Г.А., Ненашев Н.В.,
Уразбаев С.С. Аэрация и обеспыливание карьеров Казахстана. Алма-Ата: Наука,
1975. – 156 с.
5. Клебанов Ф.С.
Борьба с угольной пылью в высокопроизводительных забоях М.: Наука, 1975. – 116
с.
6. Онтин Е.И.,
Лазаренко М.И., Борисенко С.П. Исследование некоторых факторов, определяющих
уровень пылевыделения при транспортировании угля по желобам на углеобогатительных
фабриках и поверхностных комплексах шахт // Борьба с газами, внезапными выбросами и угольной пылью
в угольных шахтах. Тр. ВостНИИ, т. 14, Кемерово, 1972, С. 113-118.
7. Зальцман М.Д.
Анализ условий разрушения пены в источниках пылеобразования различного типа //
Материалы междунар. научн.-техн. конф.
“Достижения науки в области строительной механики и инженерных сооружений”,
Алматы, 2005, Т.1, С. 119-122.
8.
Сборник методик по расчету выбросов в атмосферу загрязняющих веществ различными
производствами. Л: Гидрометеоиздат, 1986.– 183 с.
9.
Никитин В.С. Методика определения
интенсивности пылевыделения различных источников непрерывного действия в
карьерах. М.: Изд. ИГД им. А.А. Скочинского, 1964. – 28 с.