The balance of methane and ventilation as a tool for methane hazard assessment in the areas of longwalls exploited in hard coal mines

Purpose
This article presents an algorithm for the current assessment of methane hazards during the exploitation of longwalls in conditions where there are methane hazards. The algorithm has been developed within the framework of the international AVENTO project (Advanced Tools For Ventilation and Methane Emissions Control), carried out in Poland, inter alia, by the Central Mining Institute in cooperation with Kompania Weglowa SA (KW SA). The algorithm was developed based on the analysis of the ventilation-methane balances for longwall areas, based on the data registered by automatic methane sensors and the velocity of ventilating air.
Methods
Multiple research methods were used, such as: observation, a questionnaire and statistical methods. The questionnaire was used for the preliminary determination of methane hazards in the longwalls belonging to the industrial partner (KW SA). The polls were used to obtain relevant information about the hazards and means of prevention taken, such as: the methane content in the seam, the emissions of methane into the exploitation workings, the volume of methane drainage, the ventilation system used, and the amount of ventilation air used to combat the methane hazard.
Based on the poll’s data, the longwalls with methane emissions in their environment were selected for testing, based on long-term observations of changes in the concentrations of methane in the ventilation air and in the methane drainage net. Methane concentration measurements were based on the values recorded by the methane sensors located in the workings which were considered to be most dangerous. For data processing a statistical method was used.  In the research, the average results of the indicated concentrations of methane from the methane sensors were used for the correlation between the average values of methane emission in the region of the longwall or methane drainage, with other parameters, such as absolute pressure changes on the surface, technological processes or cycles in the longwall. For the evaluation of the methane hazard, an indicator was proposed, these being the ratio of the ventilation methane bearing capacity to the criteria methane bearing capacity. An increase of this indicator indicates an increase in the level of methane hazard.
Results
On the basis of the average daily value of the methane hazard status indicator, an algorithm for the assessment and visualization of methane hazard in the areas of the active longwalls was developed. The algorithm contains a list of technical and organizational actions which should be taken in the event of unfavourable risk assessment of methane hazard, reflecting very high risk or unsafe conditions for conducting further work.
Practical implications
The proposed algorithm can be used for the ongoing assessment of methane hazard in areas of exploited longwalls in order to support staff in surface control rooms and in ventilation departments.
Originality/ value
The current assessment of methane hazard in the areas of longwalls which are under methane conditions by means of the developed algorithm will improve the safety of exploitation.