This paper presents a method for determining the sensitivity of the main air flow directions in ventilation subnetworks to changes in aerodynamic resistance and air density in mine workings. The authors have developed formulae for determining the sensitivity of the main subnetwork air flows by establishing the degree of dependency of the air volume stream in a given working on the variations in resistance or air density of other workings of the network. They have been implemented in the Ventgraph mine ventilation network simulator. This software, widely used in Polish collieries, provides an extended possibility to predict the process of ventilation, air distribution and, in the case of underground fire, the spread of combustion gasses. The new method facilitates an assessment by mine ventilation services of the stability of ventilation systems in exploitation areas and determines the sensitivity of the main subnetwork air flow directions to changes in aerodynamic resistance and air density. Recently in some Polish collieries new longwalls are developed in seams located deeper than the bottom of the intake shaft. Such a solution is called "exploitation below the level of access" or "sublevel". The new approach may be applied to such developments to assess the potential of changes in direction and air flow rates. In addition, an interpretation of the developed sensitivity indicator is presented. While analyzing air distributions for sublevel exploitation, the application of current numerical models for calculations of the distribution results in tangible benefits, such as the evaluation of the safety or risk levels for such exploitation. Application of the Ventgraph computer program, and particularly the module POŻAR (fire) with the newly developed options, allows for an additional approach to the sensitivity indicator in evaluating air flow safety levels for the risks present during exploitation below the level of the intake shaft. The analyses performed and examples presented enabled useful conclusions for mining practice to be drawn.
In the paper the results of investigations aimed at further identification of the phenomena occurring in abandoned workings and connected with the flow of air-gas (methane, carbon dioxide, nitrogen, oxygen and carbon oxidation products) mixture with taking into consideration the impact of supplied mineral substances on the processes of self-heating of the coal left in goaves were presented. The known and successfully used method for the prevention of fires in abandoned workings is the technology of filling goaf with an ash-air mixture, which also raises the issue of the effective use of that mixture. The computer, i.e. digital simulation methods being developed and intended for the purpose of the process discussed here are a good complement of the use of that technology. A developed mathematical model describing the process of additional sealing of gob with wet slurry supplied with three pipelines is based on the balance of volume of the supplied mixture and contained in the body created in goaves. The form of that body was assessed on the basis of the observation results available in literature and the results of model investigations.The calculation examples carried out for the the longwall area and its goaf ventilated with the "U" system allow to state that the introduced modification of the mathematical model describing the flow of the mixture of air, gases, and wet slurry with consideration of the coal burning process in the fire source area was verified positively. The digital prognostic simulations have confirmed a vital impact of the wet slurry supplied into the goaf on the processes of coal burning and also the change of rate and volume flow rate of the air mixture in goaf. As a complement to the above it should be noted that such elements as the place of the slurry supply in comparison with the longwall inclination or fire source area location is of great importance for the effectiveness of the fire prevention used. The development of computer/ digital simulation methods requires further investigations of the model adopted in this study. Those investigations should be aimed at making credible the theoretical model of the mixture flow through porous medium and the supplied mineral material. Such investigations will allow to verify the body form based on the mixture parameters such as humidity, viscosity, and fluidity and depending on the properties of the porous medium. Further development of the modelling of the phenomena discussed in this paper should be based on the methods of use of the description of the flow of fluids and slurry on the basis of 3D models.Keywords: longwall goaf, digital simulation, fire hazard, inlet mineral substances W artykule przedstawiono wyniki badań prowadzące do dalszego poznania zjawisk zachodzących w zrobach związanych z przepływem mieszaniny powietrzno-gazowej (metan, dwutlenek węgla, azot, tlen i produkty utleniania węgla) z uwzględnieniem wpływu podawanych substancji mineralnych na procesy samozagrzewania pozostawionego w zrobach węgla. Znaną i stosowaną z powodzeniem...
This paper presents a relatively simple method to analyze potential methane hazard and preventive methods based on a computer simulation of the airflow and methane emission on the longwall face and in the goaf. The presented approach considers the operation of a longwall shearer and conveyers and their possible impacts on both direct emissions of methane and migration from adjacent goafs. In this work, an attempt was made to control the advance speed of the virtual mining system based on sample mining data in the longwall 841A area and the abandoned longwall 841B at the Bielszowice Hard Coal Mine. The objective of this study was to verify the suitability of the adopted control algorithm. The results obtained from computer simulations of the mining operation with the developed control algorithm are presented in graphics of methane concentration, shearer advance speed and the speed control system parameters.
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