The determination of the influence degree of mining-geological and mining-technical factors on the safety of the degassing system

. This article presents the results of the calculation of methane emission from the development of coal seam and enclosing rocks in the roof on Mine Management "Sukhodolska-Skhidna". The required degassing efficiency and the degassing method were determined. The degree of influence of mining -technical and mining-geological factors on the safety of the degassing system has established. The determination of the influence degree of mining factors on the safety of the degassing system can be used both at the design stage mine, mining and preparing it, which allow to predict and prevent the formation of an explosive concentration of methane-air mixture.

of the coal seam i 3 1 at level 915 m of the Mine Management "Sukhodolska-Skhidna". The exploitation of the 24th WSW with a regulatory capacity of 1250 ton per day is planned. The ventilation scheme of the workface is direct-flow with a cooling of the outgoing air stream. The direction of the air flow along the workface is upward.
The workface is equipped with a mechanized complex 3KD-90T, combine 2GSH-68B, conveyor SP-326. Shipment of rock mass from a mining site is carried out by belt conveyors 1 LT -1000, 1 L -1000UD, through which coal is transported to a central coal bunker and delivered by skips on the surface.
The enclosing rocks of the immediate roof are composed of siltstone, sometimes overlaid with sandstone with a thickness of 1-4 m . The main roof is represented by sandstone with a thickness up to 25.2 m. The direct and main soil is represented by siltstone with a thickness up to 15 m.The sandstones of the roof and coal seam i 3 1 are outburst and gas-bearing. In accordance with the forecast of the sudden breakthrough of methane from the soil, the 24 WSW is not dangerous.
Sources of methane emission in the mining working are the worked coal seam, the neighboring coal seams (satellites) and containing rocks. In conditions of the 24th WSW gas emission sources are: -the thickness of worked coal seam i 3 1 up to 1.7 -2.5 m; -sandstone, lying in the roof of the seam i 3 1 thickness up to 25.15 m.

Methods
The calculation of the expected methane abundance of 24th WSW by methane emission sources was made in accordance with the guide on coal mine ventilation design [8].The methane emission from the worked coal seam and enclosing rocks in the roof and the necessary degassing coefficient were calculated. The influence of degree of factors, when they increase on the degassing coefficient, as well as the determination of the influence percentage of each factor were obtained by using the statistical methods of results processing.

Methane emission from the worked seam
The calculation of methane emission from the worked seam q s (m 3 where q wm -relative methane emission from the workface of development coals, m 3 /ton; q cm -relative methane release from extracted coal, m 3 /ton; k ol = 0 -the coefficient of the operational loss of coal within the mining site (it was not calculated because of the absence of operational losses); х -the natural methane content of the seam, m 3 /ton; х o -the residual methane content of coal which remains in the worked-out area, m 3 where k ms w wy w ms L b L k 2 − = -the influence of the mining system coefficient on the methane emission from coal seam; n -the parameter, which depends on the rate of the working face advancement, the release of volatile substances from coal and the depth development. , where L w = 345 m -the workface length; b wy WAa g k x x ⋅ = = 14 m -the coefficient, depending on the release of volatile substances [8]; , (4) where x g = 22.5 m 3 /ton of dry ashless mass-the natural methane content of the seam, where k WAa -the coefficient of methane content recalculation on coal seam; W = 3 % -the coal seam humidity; А a where а 1 = 0.152, b 1 = 0.051 -empirical coefficients [8]; H = 1000 m -seam depth; where q' mw -relative methane release from coal extracted workface, m 3 /ton; q'' mc -relative methane release from coal extracted in a belt entry, m 3 [ ] [ ] where b 2 = 0.6, b 3 = 0.4 -empirical coefficients, which take into consideration the proportion of repulsed coal respectively on the conveyor and left on the soil in the workface at one-side coal extraction scheme [8]; k mb , k' mw, k'' c -coefficients, which take into consideration the degassing degree of repulsed coal in the stope entry on the conveyor, on the soil in the workface and on the conveyor in the mining site: where Т w -the spending time of repulsed coal on the conveyor in the workface, min; a = 0.118, b = 0.25 -empirical coefficients, which characterizing gas recovery from repulsed coal [8], where V c = 1 m/s -coal transportation speed in workface. In accordance with the geological and forecasting passport of the mining site of 24th WSW the gas-bearing sandstones are deposited in the roof of the worked seam.
The calculation of methane emission from enclosing rocks in the roof q p (m 3 /ton) was made according to the formula [8], where k r = 0.00106 -the empirical coefficient, taking into consideration the influence of the method of roof control and the lithological composition of rocks [8]; where I c -average expected methane release on the mining site, m 3 /min; I a -average methane rate, which can be diluted with air to a safe level, m 3 where Q c -air flow rate for airing the mining site, m 3 The maximum coefficient of advance degassing without fluid fracturing k ds is equal 0.2 [9]. In order to achieve the required degassing efficiency of 24th WSW its calculation is supposed to be carried out according to the formula /min.
where k os , k dr , k s -the efficiency coefficients of the degassing of the worked-out area, roof and soil, fraction of units; d r , d s Thus, the technological process of gas extraction from the coal deposits development is = 0 -the percentage of methane emissions from the roof and soil in the total gas balance of this area. based on abidance of the safety conditions of miners, located in the mining site.

Results and discussion
The results of the influence of mining-geological and mining-technical factors on the safety of gas extraction in the coal mine are described in Table 1. For the convenience of calculations, the values of all parameters increased by 5%, and the results were entered in Table 1, while their effect on safety conditions was recorded using computer simulation. A graph of the change of the degassing coefficient from the values of mining-geological and mining-technical factors was showed in Figure 1. According to Figure 1, the degassing factor changes with an increase of the following mine factors: k ol (factor 5), Q c (factor 8), H 1 (factor 10), x g (factor 11), A a (factor 13), V w (factor 15). An increase of other factors does not change the degassing coefficient significantly. Therefore, below we will consider only these six factors.
In the tables below the results of calculation of the degassing rate with an increase in mine values by the corresponding percentage (Table 2) and in recalculation by 1 % (Table 3) were presented. With an increase of mine factors by 5 % (such as k ol (factor 5), H 1 (factor 10), x g (factor 11)), the degassing coefficient rises accordingly by 20 %, 25.7 %, 40.4 % and with an increase by 5 % (such as Q c (factor 8), A a (factor 13), V w (factor 15)) degassing coefficient decreases accordingly by 39.6 %, 17.2 %, 7.9 %. The change of the degassing coefficient from the mine factors occurs by linear dependence (Table 2). The change of the degassing coefficient with an increase of the factor value in recalculation by 1 % was showed in Figure 2.
As a result of calculated data analysis the approximation equation (Figure 2) in the form of degree functions and two degree polynomial was obtained by means of mathematical statistics methods, which can represented as: where R 2 -approximation accuracy.

Conclusion
The influence degree of mining-geological and mining-technical on the change of the degassing coefficient was determined. Among the mining factors that have the greatest degree of influence on the safety of the degassing system in the mining coal are: the coefficient of the operational loss of coal within the mining site k ol ; air flow rate for airing the mining site Q c ; workface movement speed V w . Among the mining-geological factors that have the greatest influence on the safety of gas production the mining coal are: the depth development H 1 ; the natural methane content of the seam x g ; the ash content of coal А a The change of degassing coefficient with an increase of mining-technical and mininggeological factors on 1 % occurs by a two-degree polynomial and degree functions with approximation accuracy R² = 0.98 -0.99.
These results can be used both at the design stage mine, mining and preparing it, which allow to predict and prevent the formation of an explosive concentration of methane-air mixture.