Methane is accompanied by most of the coal deposits. The methane hazard is excessive content of this gas in the mining excavations. This is a source of high risk security and continuity of the mine. The Piast–Ziemowit is the only non-methane mine in the Polish Mining Group. In 2015, 66,4% of the coal mined in Kompania Węglowa S.A. mines comes from methane coal seams. Methane drainage is the most effective but very costly method of combating methane hazard.The costs of prevention and eradication of methane hazard is charged to the costs of coal mining. Therefore, performance of methane drainage in the mines of the Polish Mining Group is adapted to the scale of the methane hazard. The article presents an analysis of the costs of prevention of methane hazard for mines with different absolute methane and its impact on the level of these costs.
This paper describes the concept of controlling the advancement speed of the shearer, the objective
of which is to eliminate switching the devices off to the devices in the longwall and in the adjacent
galleries. This is connected with the threshold limit value of 2% for the methane concentration in the
air stream flowing out from the longwall heading, or 1% methane in the air flowing to the longwall.
Equations were formulated which represent the emission of methane from the mined body of coal in the
longwall and from the winnings on the conveyors in order to develop the numerical procedures enabling
a computer simulation of the mining process with a longwall shearer and haulage of the winnings. The
distribution model of air, methane and firedamp, and the model of the goaf and a methanometry method
which already exist in the Ventgraph-Plus programme, and the model of the methane emission from the
mined longwall body of coal, together with the model of the methane emission from the winnings on
conveyors and the model of the logic circuit to calculate the required advancement speed of the shearer
together all form a set that enables simulations of the control used for a longwall shearer in the mining
process. This simulation provides a means for making a comparison of the output of the mining in the
case of work using a control system for the speed advancement of the shearer and the mining performance
without this circuit in a situation when switching the devices off occurs as a consequence of exceeding
the 2% threshold limit value of the methane concentration. The algorithm to control a shearer developed
for a computer simulation considers a simpler case, where the logic circuit only employs the methane
concentration signal from a methane detector situated in the longwall gallery close to the longwall outlet.
This paper presents mathematical models enabling the calculation of the distribution and patterns of methane inflow to the air stream in a longwall seam being exploited and spoil on a longwall conveyor, taking into account the variability of shearer and conveyor operation and simulation results of the mining team using the Ventgraph-Plus software. In the research, an experiment was employed to observe changes in air parameters, in particular air velocity and methane concentration in the Cw-4 longwall area in seam 364/2 at KWK Budryk, during different phases of shearer operation in the area of the mining wall in methane hazard conditions. Presented is the method of data recording during the experiment which included records from the mine’s system for automatic gasometry, records from a wireless system of eight methane sensors installed in the end part of the longwall and additionally from nine methane anemometers located across the longwall on a grid. Synchronous data records obtained from these three independent sources were compared against the recording the operating condition of the shearer and haulage machines at the longwall in various phases of their operation (cleaning, cutting). The results of the multipoint system measurements made it possible to determine the volume of air and methane flow across the longwall working, and, consequently, to calculate the correction coefficients for determining the volume of air and methane from measurements of local air velocity and methane concentration. An attempt was made to determine the methane inflow from a unit of the longwall body area and the unit of spoil length on conveyors depending on the mining rate. The Cw-4 longwall ventilation was simulated using the data measured and calculated from measurements and the simulation results were discussed.
In longwall absolute methane emission rate forecasting, the range of the destressing zone is determined empirically and is not considered to be dependent on the geomechanical parameters of the rock strata. This simplification regarding destressing zone determination may result in significant differences between the forecast and the actual methane emission rates. During the extraction of coal seams using a system involving longwalls with caving under the conditions of low rock mass geomechanical parameters, the absolute methane emission rate forecasts are typically underestimated in comparison to the actual methane emission rates.
In order to examine the influence of the destressing zones on the final forecasting result and to assess the influence of the rock mass geomechanical parameters on the increased accuracy of forecast values, destressing zones were determined for three longwalls with lengths ranging from 186 to 250 m, based on numerical modelling using the finite difference method (FDM). The modelling results confirmed the assumptions concerning the upper destressing zone range adopted for absolute methane emission rate forecasting. As for the remaining parameters, the destressing zones yielded great differences, particularly for floor strata. To inspect the accuracy of the FDM calculation result, an absolute methane emission rate forecasting algorithm was supplemented with the obtained zones. The prepared forecasts, both for longwall methane emission rates as well as the inflow of methane to the longwalls from strata within the destressing zone, were verified via underground methane emission tests. A comparative analysis found that including geomechanical parameters in methane emission rate forecasting can significantly reduce the errors in forecast values.