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Abstract

The safety of mining operations in hard coal mines must be constantly developed and improved. There is ongoing multi-directional research focused at best recognition of the phenomenon associated with the properties of the coal-gas system and its connections with mining and geological conditions. This article presents the results of sorption experiments on coals from the Upper Silesian Coal Basin, which are characterized by varying degrees of coalification. One of the parameters that describes the kinetics of methane sorption, determining and providing valuable information about gas hazard and in particular the risk of gas and rock outbursts, is the effective diffusion coefficient De. It is derived from the solution of Fick’s second law using many simplifying assumptions. Among them is the assumption that the carbon matrix consists of only one type of pore – micropores. In fact, there are quite often at least two different mechanisms, which are connected to each other, related to the diffusion of methane from the microporous matrix and flows occurring in voids and macropores. This article presents both the unipore and bidisperse models and a set of comparisons which fit them to experimental curves for selected coals. For some samples the more complex bidisperse model gave much better results than the classic unipore one. The supremacy of the bidisperse model could be associated with the differences in the coal structure related to the coalification degree. Initial results justify further analyses on a wider set of coals using the methodology developed in this paper.

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Authors and Affiliations

Marcin Karbownik
Jerzy Krawczyk
ORCID: ORCID
Tomasz Schlieter
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Abstract

The mining in seams with a high methane content by means of a longwall system, under conditions of high extraction concentration, results in exceeding methane concentrations allowed by the regulations at workings of the longwall environment, with the effect of mining machines’ standstill periods. The paper is a part of a study supporting the development of a system for shearing cutting speed control at the longwall, which should substantially reduce the production standstills due to exceeded limits and switching off the supply of electric equipment. Such a control system may be appropriate for longwalls ventilated using “Y” and “short Y” methods. Efficient Computer simulations of the 3D airflow and methane propagation may assist the design and initial evaluation of the control system performance. First chapters present studies that are necessary for a proper formulation of the properties of the longwall model. Synthetic analysis of production during the period of longwall operation allowed one to choose the input assumptions to carry out ventilation-methane computations in a CFD numerical model of longwall Z-11. This study is followed by a description of the model that is used for a case study, considering three variants of the shearer position. Finally, initial simulation results and directions of further studies are discussed.
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Bibliography

[1] S. Prusek, E. Krause, J. Skiba, Designing coal panels in the conditions of associated methane and spontaneous fire hazards 30 ( 4), 525-531 (2020). DOI: https://doi.org/10.1016/j.ijmst.2020.05.015
[2] W. Dziurzyński, A. Krach, T. Pałka, Shearer control algorithm and identification of control parameters. Arch. Min. Sci. 63 (3), 537-552 (2018).
[3] W. Dziurzyński, A. Krach, J. Krawczyk, T. Pałka, Numerical Simulation of Shearer Operation in a Longwall District. Numerical Simulation of Shearer Operation in a Longwall District. Energies 13, 5559 (2020). DOI: https://doi.org/10.3390/en13215559
[4] E. Krause, A. Przystolik, B. Jura, Warunki bezpieczeństwa wentylacyjno-metanowego w ścianach o wysokiej koncentracji wydobycia. XXI Międzynarodowa Konferencja Naukowo-techniczna Górnicze Zagrożenia Naturalne. 6-8.11.2019 r., Jawor k. Bielska Białej.
[5] A. Walentek, T. Janoszek, S. Prusek, A. Wrana, Influence of longwall gateroad convergence on the process of mine ventilation network-model tests. International Journal of Mining Science and Technology 29, (4), 585-590 (2019).
[6] A. Juganda, J. Brune, G. Bogin, J. Grubb, S. Lolon, CFD modeling of longwall tailgate ventilation conditions. In: Proceedings of the 16th North American mine ventilation. Golden, CO; 2017.
[7] E. Krause, Z. Lubosik, Wpływ koncentracji wydobycia podczas eksploatacji pokładów silnie metanowych na wydzielanie się metanu do środowiska ścian. 9th International Symposium on Occupational Heat and Safety Petrosani Rumunia. October 3rd 2019 r.
[8] E. Krause, J. Skiba, B. Jura, Overview of Ventilation Characteristic, Practices and regulations in Poland. XXVIII Szkoła Eksploatacji Podziemnej, Kraków, 25-27.02.2019 r. https://unece.org/fileadmin/DAM/energy/images/CMM/CMM_CE/12._Krause_Skiba_Jura.pdf
[9] E. Krause, B. Jura, J. Skiba, Mining speed control in the coal panel with high coal output concentration. Kontrola prędkości urabiania w ścianach o wysokiej koncentracji wydobycia. Spotkanie Grupy Roboczej Ekspertów ds. metanu z kopalń Europejskiej Komisji Gospodarczej ONZ. Genewa 7-8.11.2019 r.
[10] J. Qin, Q. Qingdong, H. Guo, CFD simulations for longwall gas drainage design optimization. International Journal of Mining Science and Technology 27 (5), 777-782 (2017). DOI: https://doi.org/10.1016/j.ijmst.2017.07.012
[11] E. Krause, Ocena i zwalczanie zagrożenia metanowego w kopalniach węgla kamiennego. Prace Naukowe GIG nr 878. Katowice 2009.
[12] K .M. Tanguturi, R.S. Balusu, Computational fluid dynamics simulations for investigation of parameters affecting goaf gas distribution. Journal of Mining and Environment 9, 3, 547-557 (2018). DOI: https://doi.org/10.22044/jme.2018.5960.1410
[13] G . Xu, K.D. Luxbacher, S. Ragab, J. Xu, X. Ding, Computational fluid dynamics applied to mining engineering: a review. International Journal of Mining, Reclamation and Environment 31 (4), 251-275 (2017).
[14] Z . Wang, T. Ren, L. Ma, J. Zhang, Investigations of ventilation airflow characteristics on a longwall face – a computational approach. Energies 11, 1564 (2018). DOI: https://doi.org/10.3390/en11061564
[15] Z . Wang, T. Ren, Y. Cheng, Numerical investigations of methane flow characteristics on a longwall face Part I: Methane emission and base model results, Journal of Natural Gas Science and Engineering 43, 242-253 (2017).
[16] Z . Wang, T. Ren, Y. Cheng, Numerical investigations of methane flow characteristics on a longwall face Part II: Parametric studies. Journal of Natural Gas Science and Engineering 43, 242-253 (2017).
[17] SolidWorks Flow Simulation 2012 Technical Reference. https://d2t1xqejof9utc.cloudfront.net/files/18565/SW_CFD_technical_reference.pdf?1361897013
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Authors and Affiliations

Tomasz Janoszek
1
ORCID: ORCID
Jerzy Krawczyk
2
ORCID: ORCID

  1. Central Mining Institute (GIG), 1 Gwarków Sq., 40-166 Katowice, Poland
  2. Strata Mechanics Research Institute, Polish Academy of Science, 27 Reymonta Str., 30-059 Kraków, Poland
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Abstract

For underground mine workings, the shape of the computational domain may be difficult to define. Historically, the geometry models of mine drifts were not accurate representations of the object but rather a simplified approximation. To fully understand a phenomenon and save time on computations, simplification is often required. Nevertheless, in some situations, a detailed depiction of the geometry of the object may be necessary to obtain adequate simulation results. Laser Scanning enables the generation of 3D digital models with precision beyond the needs of applicable CFD models. Images composed of millions of points must be processed to obtain geometry suitable for computational mesh generation. A section of an underground mine excavation has been selected as an example of such transformation. Defining appropriate boundary conditions, especially the inlet velocity profile, is a challenging issue. Difficult environmental conditions in underground workings exclude the application of the most efficient and precise methods of velocity field measurements. Two attempts to define the inlet velocity profile have been compared. The first one used a sequence of simulations starting from a flat profile of a magnitude equal to the average velocity. The second one was based on the sixteen-point simultaneous velocity measurement, which gave consistency with measurement results within the range of applied velocity measurement method uncertainty. The article introduces a novel methodology that allows for more accurate replication of the mine excavation under study and the attainment of an appropriate inlet velocity profile, validated by a satisfactory correspondence between simulation outcomes and field measurements. The method involves analysing laser-scanned data of a mine excavation, conducting multi-point velocity measurements at specific cross-sections of the excavation that are unique to mining conditions, and utilising the k-ω SST turbulence model that has been validated for similar ventilation problems in mines.
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Authors and Affiliations

Jakub Janus
1
ORCID: ORCID
Jerzy Krawczyk
1
ORCID: ORCID

  1. Strata Mechanics Research Institutes of Polish Academy of Science, 27 Reymonta Str., 30-059 Kraków, Poland
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Abstract

The closure of deep mines, featuring multi level seam extraction, lasts many years. During this time period, the ventilation system must ensure adequate working conditions, and ensure the safety and stability of fan operation in gas and fire hazards conditions. The analysis of air flows and methane inflows during the progress of mining mine excavations closure, is the primary object of the article. Execution of such analysis requires knowledge of the mining mine excavations’ closure schedule, the structure of the ventilation system under consideration, the values of the parameters describing the air flows delivered to the mine excavations, and the current characteristics of operating fans and predicted methane exhalation. A computer database, currently being updated by a mine ventilation department for the VentGraph-Plus computer software, has been used simulate the various ventilation scenarios experienced, during the final stage of closure, including the shutdown of the main fans and the backfilling of shafts. The results of case study, containing 2 variants of simulated examples, are presented in the form of diagrams of methane concentration changes in time at characteristic places of the mine. The completed simulations of ventilation processes during the closure of mine excavations and transfer of inflowing methane, indicate useful possibilities of the computational tool used.
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Authors and Affiliations

Wacław Dziurzyński
1
ORCID: ORCID
Jerzy Krawczyk
1
ORCID: ORCID
Teresa Pałka
1
ORCID: ORCID
Andrzej Krach
1
ORCID: ORCID
Przemysław Skotniczny
1
ORCID: ORCID

  1. Strata Mechanics Research Institutes of Polish Academy of Science, 27 Reymonta Str., 30-059 Kraków, Poland

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