Results
The most important results of the Project are:
- Development of the fast air pressure monitoring system, the software that controls the system and validation tests performed in large scale methane explosions and in real mining condition.
- Numerical models of methane explosions.
- Experimental data gathered in large scale tests performed at three different test sites: INERIS, GIG and FSB.
Description of the achieved results
WP1 - Project coordination
The general management of technical works was conducted during the whole Project. Five coordination meetings and one internal meeting of the simulation group were organized. The project website was created and updated.
WP2 - Development and calibration of explosion numerical models
A series of large scale methane explosion tests carried out at three different locations (at INERIS, GIG and FSB) provided experimental data necessary for calibration and verification of the numerical models. Apart from this the results provided a new insight into explosions in different geometries, as well as explosion development in inhomogeneous mixtures.
In total, 9 large scale tests were performed in the 400 m underground gallery of Experimental Mine Barbara.
More information can be obtained from Robert Hildebrandt at rhildebrandt@gig.eu or Zdzislaw Dyduch at zdyduch@gig.eu
The numerical model for solving large-scale problems has been verified. Sover b-Xi based on the development of Gülder was implemented and verified. The obtained values of flame propagation velocity in a large scale (400 m gallery) are comparable in size to the order of magnitude with the results obtained in experimental studies. This proves the usefulness of the numerical methods used to conduct a large-scale event case study. Nevertheless, the method used to describe the geometry (domain) - a geometric description directly - provides a sufficient representation of details, but is time-consuming in finding a solution to the problem. There is a large dependence between the representation of geometric details of the analysed space and the time needed to obtain a solution. This is a limitation in the application of the method to the analysis of very large spaces.
Realise of 25 m3 of pure CH4. Methane distribution in the 400 m underground gallery after 45 s
WP3 - Development of a fast air pressure monitoring system
As a result of the works within the WP3 there have been developed modified pressure sensors which met the given requirements. There has also been developed a measuring system consisting of surface devices (a central station of the SP/DTSS system) and underground equipment (NSGP sensors). All devices included in the system have appropriate ATEX certificates which allow us to use the system for operation in underground mines. The system software was developed allowing data communication, data processing and measuring data archiving, as well as locating initial places of a possible explosion based on the recorded pressure measurements. A complete measuring system was tested during experiments of explosions carried out in the EM “Barbara” and under conditions of normal work in a mine in two areas. The trials carried out in the mine allowed us to collect sufficient measuring data enabling us to continue further works on the development of the system software. The trials allowed us also to check the functioning methods of the individual elements of the system in the mine conditions. On the basis of the stored changes in pressure during explosions there were calculated velocities of blast waves and response times of the pressure sensors. The response times of the sensors to rapid pressure jumps are very close to the response times determined in the laboratory.
Software developed within the project allows us to archive the measuring data and allows for on-going assessment and an analysis of pressure levels in a given area of a mine. It allows also for detection with high accuracy a place of a possible explosion on the basis of the indications
of the sensors. The results of the calculations of the initiation place of methane explosion generated by the Program, calculated on the basis of the recorded changes in pressure in comparison with the actual values defined in the experiment, shows that the location of the methane explosion
is characterized by high accuracy - up to 10 m.
The trials in the mine showed that the system for fast measurements of pressure worked, from the technical point of view, correctly. The measuring data from the sensors were transmitted in the absence of any interference at a distance of more than 6 km and were recorded in the system at the surface. The analysis of measurements allowed us to estimate the levels of pressure differences between intake and return air in the base and emergency state. Progressive or short-term stepwise changes in atmospheric pressure caused by the operation of a shearer or a power support kept a comparable level of the pressure difference, while the analysis indicated the possible occurrence of a dangerous change in pressure. In the case of changes in pressure caused by opening/closing the dams, the determined levels of pressure differences showed which of them were contained in the allowable limits of changes in pressure and which of them should be treated as potentially dangerous situations.
Monitoring of the working face area with regard to changes in pressure in selected points and therefore between flowing over air streams and goaf including its significant vicinity, allows a rapid response to changes in the equilibrium state. Due to the continuous monitoring of aerodynamic potentials it is possible to update a potential diagram of a given area in normal conditions, as well as in hazardous situations.
WP4 - Explosion mitigation systems
The Work package consisted of Review of European experiences in the use of triggered barriers In the Review the following general conclusions were formulated. Developing a triggered barrier system capable of stopping methane explosions at an early stage has been a common objective in most coal mining countries across Europe. There has been a significant number of research projects on this field, as well as many validation experiments in controlled conditions. The concept of all the systems developed so far has been very similar, although there are differences in the specific design and the technologies involved.
The results obtained in the different series of experimental tests carried out in the last two decades have been good in general terms, although it has not been possible to assure 100 % reliability in the operation and efficiency of the barriers. The capacity of the triggered barriers to stop an explosion strongly depends on the explosion parameters and the gallery dimensions, and therefore it is not possible to find a general solution for all situations. Each specific explosion scenario requires an individual analysis.
All this, together with the high price of this type of equipment, and other practical constraints, such as their large size, and the difficulties to install, move and maintain the units underground, have probably prevented the general deployment of triggered barriers at a European level. The practical experiences on the efficiency of triggered barriers to stop an explosion in real conditions is therefore very limited, and, according to the review made, is mainly concentrated in the Ukraine. Experience in this country proves that the reliability of the triggered barriers is not as good as it should be.
However, the interest in finding a triggered barrier system that can provide a reasonable level of protection still continues, and in particular a new generation of devices is being developed in the Ukraine. One of the objectives of the EXPRO project was to follow these new developments and in particular to carry out validation tests with these new systems.
WP5 - Integration of the results and dissemination
The Final Report that integrates contributions from all participants has been prepared. The Report was stored in the common disk space of the Project.
Several publications have been prepared and published. Some others will be submitted for the next ISPMIE Conference that will be held in August this year, in Kansas City, USA.
Results of the project were also presented during a meeting organized for directors of the mines and for staff of the mines responsible for safety.