Vladimir Artamonov, Yevgeny Nikolayev
The solution of scientific and technical task on improving of dust and gas formation after blasting operation in the final sections of faces is given. The solution implies prevention of harmful and dangerous dust and explosive gases appearance at the expense of dust forming ability change of coal layer and adsorptive coal dust ability decrease by means of change of physical and mechanical properties of coal by hydro effect.
Introduction
Mining operations imply a wide use of blasting operations while developing preparatory excavations and forming of niches in breakage face in the final sections of faces. More than a half of breakage faces of “Donetskugol” prepare niches using DBO (drilling and blasting operations).
Dust which is formed in the result of coal deformation is of high dispersive quality and consequently the danger of pneumoconiosis is very high, it is difficult to be watered and neutralized. Aggressive influence of such kind of dust on respiratory system of a human being is intensified by ads option of poisonous gaseous blast products on its surface. This leads to high fibrohenic activity and causes pheumoconiosis among mining workers. The consequent poisonous gases outlet can cause intoxication among miners [1].
The real state of the question
Analysis of applied methods has shown that in sprite of hydro blasting technologies improvement, effeciency of a single method of dust and gas suppression does not allow to descrease residual dust contents of air and gas release from cut coal according to demanded standards.
To fight against coal dust formation and adsorption of poisonous gases is necessary to carry out some efficient measures on prevention of harmful effects of poisonous gases and dust appearance which occur while carrying out blasting operations. It is simpler, cheaper and more efficient to prevent dangerous and harmful phenomena than to elliminate its results.
One of the methods of dust and gas formation can be hydroprocessing of edge parts of coal layers by water solution of active surface substances (ASS). Moisturized zones of the layer are formed in these substances changing physical and mechanical coal properties. Being combined with applied method and measures on dust and gas forming decrease while carrying out blast operations it will allow to create local zones on workplaces of face final sections in which concentration level of dust and gas contents is not higher than the maximum possible concentration [2].
Both coal destruction mechanism and processes of dust formation are changed while carrying out blasting operations in a moisturized zone of a coal layer.
The theoretical basis of the researches
It is known that energy contents (capacity) of destruction depends on both a kind of load application and physical and mechanical properties of the surroundings. Changing these properties leads to certain changes of energy indicators of destruction. When coal porosity is increased, steady increase of specific dust release is observed.
Functional dependence of specific dust formation on energy destruction has been calculated [3,4]:
P=[1-exp (-βHW)], ( 1 )
where β – an indicator that features coal massif according its ability to crush;
Hw – specific energy of destruction.
ai – arithmetic mean of release of particles with size less than d1, %
di – size of holes of sieve i , mm; n – the amount of sieves,( items ).
Researches [5] show that summarized release of dust particles is proportional to work spent on coal destruction. Meanwhile the layer’s properties effect dust contents in destroyed coal more than its destruction regime.
The change of properties of a layer by hydro effect leads to change of coal crush degree, i.e. it leads to change of its surface destruction. Area of dust surface F specific, which is formed when coal destruction occurs, is one of the main indicator of sorbing quantity of poisonous gases. These gases come into excavation atmosphere later. Specific energy of destruction Hw of both dry and moisturized coal is changed proportionally to the area of surface of their destruction depending on the degree of moisturizing.
The results of the theoretical researches
The graph of area change of destruction surface depending on coal particles size is built on the bases of idea physical and mechanical model. (pic.1). The dependence of this area change is calculating using the following formula:
Ssurf. i. = 0,0007d2 - 0,0957d + 2,398 , (3)
where d – particles size of destroyed coal, mm.
Specific energy of destruction Hw depends on change of surface destruction area and coal particles size:
Strengthening properties and structural peculiarities of coal massif alongwith energetic parameters of destruction influence significantly the amount of forming dust [3]:
where α – efficiency coefficient of blast (EC); G – mass of charge, kg; Q – specific heat of blast ( J/kg ); E – module of coal flexibility; KT – mechanical equivalent of heat; τ – extent of strength of coal shift,(Pa); μ – Puasson’s coefficient; dp – diameter of dust particles, m; Kf – coefficient, including form of dust particles, Kf= 20….26; Fsp – area of dust surface, m2
The parameters included into the formula (5) can be divided into two groups: the first group includes variable parameters which feature properties of surroundings where blast occurs (E, τ , μ , dp , Kf , Fsp); the second group includes constant energetic parameters of blast – aB, G, Q, KT.
This allows to put down equation with constant parameters of blast and variable parameters of properties of coal layer before and after moisturizing:
where
= const
where E1, E2 – modules of flexibility; τ1,τ2 – modules of shift; μ1, μ2 – Passion’s coefficient and Fsp 1, Fsp2 – area of dust surface of coal layer before and after moisturizing.
The change of dust formation using blasting method of coal cutting with account of the change of layer humidity can be calculated by the following formula:
If we mark ratio of layer features before and after moisturizing as in formula (7)
as k1, k2 , k3 , k4 ,
where
in this case the change of dust formation while carrying out blasting operations at the expense of the changes of physical and mechanical properties of a coal layer being effected by the process of moisturizing can be calculated by the following equation:
∆Р= k1· k2 · k3 · k4 (9)
The experiments in real conditions
The whole range of laboratory and real researches were held. In order to establish effect of low pressure of moisturizing on deformation coal features, its destructive and dust formation abilities. Coal of KB layer of ‘Lidiyevka’ mine SE ‘Donetskugol’ was chosen to be tested because of coal high hardness (f=1,5) and its destruction energy capacity require use of DBO while preparing niches.
The moisturized zone of the layer has been formed on section 7 of western face from the side of haulage drift in the distance of 25-50mm. from the lower niche. From this niche sampling cut coal was done in order to establish granulometric contents of cut coal. The same kind of sampling has been done in the zone of upper niche which wasn’t moisturized.
The results of the experiments in real conditions
The results of granulometric contents of destroyed coal from different zones of moisturizing showed that outcome of large fractions is increased from (30 mm) 38,2 to 60% and outcome of small fractions decreased from 39,05% to 23,25%.
Consequently the areas of surface of destroyed dry and moisturized coal are changed depending on fractions outcome with different degrees of coal moisturizing (pic. 1).
These changes have polynominal dependence and they are calculated by:
– unfinished coal:
Ssurf. 1= 0,0031d2 - 0,1294d + 1,2213 , (10)
– coal treated with ASS water solution:
Ssurf. 2 = 0,0015d2 - 0,0694d + 0,7865 , (11)
Dependence of change of specific energy destruction Hw
unfinished coal:
– coal treated with ASS water solution
The results of the researches
Total area of destroyed coal after analyzing of granulometric contents was 2,15m2 for coal which wasn’t moisturized by sintanol solution (is 1,3 times reduced). The surface of small fractions of destroyed coal (1,5 mm) is decreased from 1.49m2 to 0,896m2 (in 1,67 times). Thus decrease of total area of moisturized coal surface and area of small coal fractions surface leads to reduction of adsorbing capacity of poisonous gases and their release into atmosphere.
According to sieve analysis average value (according to number of samples) was calculated as summing outcome of sublattice product and indicator featured coal massif as for its crushing ability was calculated as well.
For coal from moisturized zone β = 0,57. For coal from the zone moisturized by syntanol (solution: β=0,66). Specific energy of destruction of dry coal is Hw=1,58J/kg. The coefficient of specific dust formation from coal destruction energy for different degrees of moisturizing: Pdry = 0.70 kg/t; Pmoist = 0.59 kg/t.
Calculating average coefficients included in the equation (7) of variable quantities: Puasson coefficient (μ), module of flexibility (E, Pa), module of shift, (τ, Pa), dust surface area, (Fsp m2) for sorts of coal with different degrees of moisturizing made it possible to calculate coefficients included in the dependence (9).
Conclusion
As a result, the amount of coal dust formed while carrying out blasting operations in the final sections of a face with physical and mechanical properties change of a coal layer under the moisturizing effect decreases dramatically (in 3 times).
The effect of extra preliminary hydro treatment of a coal layer in the potential drilling and blasting operations (DBO) zone gives the opportunity to reduce dust and harmful gas release from the cut coal into the mine atmosphere. It helps to create safe conditions of blasting operations.
Literature
1) Professional illnesses of coal mine workers guide / Edited by G. A. Kobets – K.: Zdorovye , 1992- 232p.
2) V. N. Artamonov, E. B. Nikolayev. Preliminary moisturizing as a complex method of more effective and safe mining // Geotechnologies in the 21st centure – Donetsk.. DUNPGO.- 2001-t.1,-p124-129
3) Ishchuck I. G., Pozdnyakov G. A. Methods of complex dedust formation in mines. Reference book – M: Nyedra, 1991, 253p.
4) Dust control in coal mines guide: the 2nd ed. M: Nyedra, 1979 – C 29 – 33p.
5) Rodyn A. V., Usov O. A., Medvyedev E. N., Bandyrin V. I. The problems and prospects of preliminary moisturizing of coal layers as a method of dust pollution reduction in the mine atmosphere. Pit and mine ventilation. Atmosphere comfort and safety. Scientific work collection. – Leningrad: L. M. I. 1988 p. 51-54