Degassing Systems Rational Parameters Selection at Coal Mines

In coal industry there is an acute problem of occupational safety provision. Special attention is paid to mines with high gas inflow where high methane concentration repeatedly leads to blow-ups that become the reason of large-scale accidents. The basic requirement for their prevention is safety rules observation during mining operations. But with increase of working depth and methane-inflow of coal seams it is impossible to ensure permissible gas concentration in the air. Under such conditions degassing of gas-bearing coal seams, bearing rocks and worked-out areas is an important technological process contributing to mining operations safety increase and face output increase.

The aim of the work is to consider and substantiate questions connected with coal deposits degassing efficiency increase, development of new and improving of already existing calculation methods and optimization of basic parameters of degassing systems:

  • to perform natural researches of degassing systems defining dynamics of methane capture value and methane-air mix consumption that come into degassing network;
  • to establish correlation dependences of degassing parameters and equation of regression based on natural observations and statistic materials depending on mining-technical conditions;
  • to improve calculation methodology and boreholes number optimization, and distance between them providing maximal total methane debit captured at production, unit taking into account permissible methane concentration in gas pipeline;
  • to develop methodology focused on pipeline diameter optimization based on economic indices for all parts of the pipeline that are included in the degassing network.

Research Object

The “Almaznaya” mine of a production complex “Dopropol’eugol’” has become the object of experimental researches of coal seams degassing pa rameters. The field of mentioned mine is located in northwestern part of Krasnoarmeysk coal region of Donbass at the territory of Donetsk oblast in Ukraine. Based on gas-inflow volume, the mine is considered to be extra-dangerous having relative methanebearing capacity equal to 32 m3/ t of a daily output, by coal dust explosiveness - dangerous. At present, the mine has been developing l3 and m5 seams with thickness 1.45-2.5 and 1.0-1.1 respectively. The seams are not inclined to self-ignition, and they are not dangerous by bursts of coal and gas. Bedding of the seams is flat having dip angle of 8-12°. Biggest part of the host rocks is clay and sand shales with middle strength and stability values. Continuous prediction of outburst hazard is carried out during development of l3 seam at depth of 600 m.

Development method of the mine field is panelwise, mining method – by long pillars along the strike. Ventilation scheme of the mine is centralflank, ventilation method – exhaustive. Degassing of underworked coal seams and worked-out area is implemented during development of l3 seam at “Almaznaya” mine. Natural observations are carried out at the extraction area of the 5th north longwall face of southern stone incline (SSI) of l3 seam at horizon of 550 m. In order to decrease methane release at this area the degassing of underworked coal seams is provided by means of boreholes drilling into the lн4 seam. The boreholes are drilled from the filled ventilation drift after the longwall advance and with turning toward longwall face. Length of the degassing boreholes makes up 34 m. Distance between the boreholes is 8 m.

Methane-air mixture coming into the degassing boreholes is pumped out with help of surface vacuum-pump station equipped with four pumps of VVN-150/2 type. As the boreholes collars are underworked by the longwall face they get disconnected from gas pipeline and shut by chump plugs. Area gas pipeline consists of pipes with diameter of 325 mm except for the adjoining to the longwall area having length of 100 m, where gas pipeline diameter is equal to 100 mm. Parallel to this area a pipeline with diameter of 100 mm is laid and it is designed for gas suction from the worked out area thanks to degassing column left in the caved ventilation working. There is a perforated vertical pipe outgrowth (“candle”) with diameter of 250 mm and height – 2 m installed at the end of the pipeline for gas suction from the worked-out area. “Candles” are installed every 16-24 m.

Together with underworked coal seam degassing, isolated capture of methane from the ventilation drift dead-end is implemented. Capture of methaneair mixture is carried out along metallic pipeline with 800 mm diameter. From the worked-out area isolated from the working by chump plug, methane is sucked out by gas-suction unit equipped with VMCG-7 fan. The fan is located in special chamber located at the 4th northern conveyor drift SSI (southern rock incline) of 550 m horizon of l3 seam between an incline and northern foot-way. Methane-air mixture is supplied from the fan into the mixing chamber located at northern foot-way of southern rock incline above the 4th conveyor drift.

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