Investigation of the influence of the geodynamic position of coal-bearing dumps on their endogenous fire hazard

The paper investigates the hypothesis according to which one of the factors influencing the spontaneous combustion of coal-bearing dumps is its geodynamic position, i.e. its location in the geodynamically dangerous zone (GDZ) at the boundary of the Earth crust blocks. This hypothesis is put forward on the basis of scientific ideas about the block structure of the Earth crust and the available statistical data on the location of burning dumps and is studied using computer modeling. A dump located in the area of Eastern Donbass was chosen as the object of research. The simulation results show that the penetration of air into the dump body from the mine through the GDZ, which crosses the mining zone, is possible at an excess pressure of 1000 Pa created by the main ventilation fans. The fire source appearance in the dump body causes an increase in the temperature of the dump mass and becomes a kind of trigger that "turns on" the aerodynamic connection between the dump and the environment, carried out through the GDZ. It is concluded that the establishment of an aerodynamic connection between the mine workings and the dump through the GDZ can be an important factor contributing to the endogenous fire hazard of coal-bearing dumps. The simulation results can be used in the development of projects for monitoring coal-bearing dumps and measures to combat their spontaneous combustion.

The current state of the problem of predicting spontaneous combustion and explosiveness of sulfide ores and host rocks at a depth of more than 1500 m.

The mining factors of ore fire hazard during mining of the lower horizons of the Oktyabrskiy and Talnakhskiy northern deposits are considered. It is noted that the probability of self-heating of sulfide ores and the sulfide dust’s tendency to spontaneous combustion and explosiveness in certain sections of rich sulfide copper-nickel ores are quite high. The oxidation of sulfide ores occurs continuously due to the absorption of oxygen from the mine atmosphere and is accompanied by the release of heat. The oxidation can be accompanied by intense heating of the ore in mining conditions, with the accumulation of large volumes of broken rock mass for a long time in treatment and preparation workings and with free access of air to the bulk of the ore mass. The processes of ore and rock oxidation are especially intense when their moisture content is 1–4%. When the ore is heated above 35 °C, sulfurous gas (SO2) may be released. The main signs of the above-mentioned oxidative processes’ development and signs of the initial phase of a possible underground endogenous fire are indicated along with a constant increase in the temperature of the air coming from the bottom of the face. It is noted that in case of detecting at least one of the signs of a possible underground endogenous fire’s initial phase, urgent measures are taken to improve the ventilation of this working face, to ensure maximum intensity of shipped ore from the fresh stream and the content of sulfurous gas and hydrogen sulfide and mine air temperature are determined every 4 hours. If after two days on the outgoing stream there is no decrease in the content of sulfur dioxide and air temperature, then it should be considered that an endogenous fire has occurred. Measures for the prevention, localization and elimination of foci of spontaneous combustion are given. As an additional safety measure, it is recommended to moisten the dust, since sulfide dust becomes non-explosive at a moisture content of 9–9,5%, and at a humidity of 10% the dust does not transmit an explosive impulse.

Numerical analysis of inter-panel pillars in the bump prone conditionals of the Alardinskaya mine

The purpose of the paper is to substantiate the width of the barrier and yield pillars for the application of a new seam development scheme in the conditions of the Alardinskaya mine (Russia). The Alardinskaya mine develops gas-bearing coal seams that are prone to spontaneous combustion and are hazardous due to rock bumps, which leads to frequent accidents. The analysis of the world experience of mining seams being hazardous to rock bumps showed that safe mining with longwalls can be provided by a system of inter-panel pillars: very wide barrier pillar and two yield pillars. Numerical modeling using the finite element method was carried out to assess the possibility of reducing the barrier pillar width in order to decrease the volume of coal losses in the subsoil. The model of rock massif was created in Ansys mechanical software. Numerical modeling of the longwall panel development with longwalls was carried out at various widths of broad and yield pillars. The analysis outcomes of the vertical stresses diagrams in the seams are presented for different parts of the longwall panel. The rational parameters of the pillar system, ensuring the minimization of the reference pressure influence from the previously worked-out column and the reference pressure of the operating longwall, are determined as a result of numerical analysis. The conclusion is made about the expediency of the technological scheme application proposed by the authors in the conditions of the Alardinskaya mine to reduce the endogenous fire hazard and the danger of rock bumps.

Design features of coal mines ventilation using a room-and-pillar development system

The safety of mining operations in coal mines for aerological factors depends on the quality of accepted and implemented ventilation design solutions. The current “Design Manual of coal mine ventilation” do not take into account the features of room-and-pillar development systems used in Russia. This increases the risk of explosions, fires, and gassing. The detailed study of foreign experience in designing ventilation for the considered development systems e of coal deposits allowed to formulate recommendations on the ventilation scheme organization for coal mines using a room-and-pillar development system and the procedure for ventilation during multi-entry gateroad development. Observations have shown that the use of the existing Russian procedure for airing mining sites with a room-and-pillar development system complicates the emergency rescue operations conduct. Low speeds and multidirectional air movement, difficult heat outflow, and the abandonment of coal pillars increase the risk of occurrence and late detection of endogenous fire. The results of numerical modeling have shown that the installation (parallel to the drifts) of ventilation structures in inter-chamber pillars will increase the reliability of ventilation by transferring the ventilation scheme from a complex diagonal to a complex parallel. It will also reduce the amount of air required for the mine site and the total aerodynamic drag. The research made it possible to formulate requirements for the design procedure for coal mines ventilation using a room-and-pillar development system, which consist in the order of working out blocks in the panel, and also the additional use of ventilation structures (light brattice clothes or blowing line brattice).

The Method of Combating Coal Spontaneous Combustion Hazard in Goafs—A Case Study

One of the major natural hazards occurring during the process of mining exploitation are endogenous fires. They cause very large material losses and constitute a threat to the health and life of the workers. Such fires usually start and develop in the goafs. The remaining coal and the oxygen-containing air flowing at a certain rate may lead to endogenous fires. The basic element of the assessment of the occurrence of an endogenous fire and the degree of its development is the chemical composition of the air flowing out of the longwall and the goafs. The monitoring of this composition also makes it possible to assess the severity of such a fire. The damage that can be caused by the endogenous fire requires scientific and experimental research being carried out on a wide scale in order to limit its occurrence and development. All papers and research mentioned in the paper aim to find a tool that will help to control the fires. The paper discusses the development of a new and original method of combating the threat of endogenous fires. It is based on the installation designed to feed an ash and water mixture or an ash and water mixture with carbon dioxide to goafs. The foundation of the paper is a method based on a vast depth of expertise and knowledge gained by the authors in the field of combating endogenous fires. The developed installation prepares and transports ash and water mixtures together with carbon dioxide to the zones with high probability of endogenous fires. The mixture is a preparation of the surface of a mine, and later, it is transported underground by pipelines to the goafs where a high level of the fire hazard was identified. The construction of the system and the composition of the mixture used are both original solutions; their practical application limited the process of spontaneous heating of coal. Monitoring the chemical composition of gases in the air of the goafs made it possible to control the effects of applied measures; it proved that carbon dioxide used as an inert gas disturbs the process of carbon oxidation, and the water and ash mixture limits the inflow of the air with oxygen. The advantage of the method is particularly evident in the case of the exploitation of deposits where coal has a short incubation time. This original approach allows for a better and more effective response to endogenous fires.

Influence of the Volumetric Expenditure of Air Supplied to the Longwall Through the “Y” Ventilation System on the Location of an Area at the Risk of an Endogenic Fire

In the case of longwall ventilation, in the underground hard coal mines, a phenomenon related to the migration of a certain amount of the air stream supplied to the longwall deep into goaf zones occurs. One of the wall ventilation systems, in which this phenomenon is quite intense, is the so called “Y” ventilation system. This migration is immensely unfavorable because it can lead to the self-heating process of coal left in a goaf and, consequently, to an endogenous fire. Such a fire is a great threat to both the safety and continuity of operation processes. For this reason, various activities are undertaken to prevent such a fire from occurring in goaf zones. One solution is a method presented in this article. It aims at determining an area in goaf zones, where an endogenous fire may occur. The study focused on the longwall ventilated with the Y system. This area was determined based on two criteria, namely air velocity and oxygen content. The study was carried out for various volumes of air supplied to the longwall. Therefore, the purpose of the study was to develop research methodology and determine the location of an area at the risk of an endogenous fire. The location of this area was determined for three different volume expenditures of air supplied to the longwall ventilated with the Y system.

Influence of the Permeability of the Longwall Goaf Zones on the Location of an Area With Explosive Methane Concentration Levels

One of the basic ventilation hazards and, at the same time most dangerous, in hard coal mines is the methane hazard. During the exploitation process using the longwall system with the breaking down of roof rocks, methane is released into mining excavations from both mined coal and the one left in goaves. Significant amounts of methane also flow from the underworked and overworked seams, through cracks and fissures formed in the rock mass. When accumulated at an explosive concentration level in goves and at an appropriate oxygen concentration level and the occurrence of a trigger (e.g. a spark or endogenous fire), methane may either explode or ignite. These are immensely dangerous phenomena. Therefore, the possibility of their occurrence should be limited. The article presents the results of the research aimed at determining the impact of the permeability of goaf zones on the distribution of methane and oxygen concentration levels in these goaves. The study was carried out for the longwall ventilated with the Y system. The model analysis was conducted, the results of which allowed the authors to determine these distributions. On their basis, both the location and size of the areas in which hazardous methane concentrations could occur were designated. The results are of great practical importance as they indicate areas in goaves where preventive measures should be implemented.

Using pillar-free mining technologies in gently dipping and self-ignitable coal seams

Gently dipping coal seams of the Kuznetsk Coal Basin are cut exclusively by longwalls with preliminary drivage of twin gate ways. At the same time, the source of self-ignition in mines is pillars of coal left in mined-out areas. Endogenous fire hazard grows with higher losses of loose coal in mined-out areas due to a persistent increase in mining depth and in size of longwalls. This research aims at development of an alternative mining technology for gently dipping coal seams to reduce the risk of initiation of self-ignition sources in mined-out areas and at the determination of parameters of the technology elements as functions of coal seam thickness and mining depth. A new concept of preparatory works and actual mining in selfignitable coal seams is described. The study results obtained with numerical modeling of the stress-state behavior of rock mass and the developed technology elements at different stages of longwalling are presented. The studies show that endogenous fire hazard is reduced by means of extraction of coal pillar on the same line with face and due to elimination of aerological connection between the operating longwall and earlier mined-out area owing to construction of a separation belt made of solidifying materials between them. The cross-effect of the widths of the solidifying material belt and coal pillar as the elements of the developed technology is estimated.

ON DETERMINING THE COAL CARBONIZATION INDICATOR FOR ESTABLISHMENT OF MINE FIRE HAZARD GROUPS

The article analyzes the dependence of endogenous fire hazards on the following factors: the degree of coalification, the total sulfur content, the thickness of the developed formations and their structure, the presence of tectonic disturbances. By the genetic propensity of coals to spontaneous combustion, three groups of coal sites are distinguished: І – Vdaf ≥ 41%, Сп ≤ 7, coals of marks D and partially G; ІІ – Vdaf = 40-30%, Сп ≤ 8, coals of marks D and partially F; ІІІ – Vdaf < 36%, Сп >8, coals of marks Zh, K, OS, T. Studies have shown that individual dependences of the decrease in the content of each component (Оo, Нo, No) significantly differ from each other. Decrease in oxygen content, as well as the sum of the main components, occurs with an increase in carbon content. The sum of the content of the main components decreases inversely to the increase in carbon content over the entire range of coal conversion from a small degree of their metamorphism (Со ≈ 70%) to anthracites (Со ≈ 98%). The dependence of decrease in oxygen content with increased carbon is nonlinear. With carbon content of more than 88%, there is a slight decrease in the rate of oxygen reduction in comparison to its decrease at earlier stages of metamorphism. Data analysis showed an almost functional dependence between the sum of the main components of the organic mass (0.995). A significant correlation of carbon with oxygen and hydrogen is observed. A significant scatter of points in experimental data is due to the diversity of composition of the source material, the conditions of its accumulation and transformation for different coal basins and individual coal sites. Studies have shown that the relationships between all the main components of the organic mass of coal during metamorphic transformations change significantly at different stages of these processes. The established dependence of the carbonization index on the carbon content at different stages of coalification allowed us to develop an engineering method for calculating the carbonization index for the entire range of coal metamorphism. The proposed method significantly clarifies the determination of the carbonization index, which is necessary not only for establishing the fire hazard of mine layers, but also for establishing other manifestations of the dangerous properties of coal sites during mining operations. Keywords: carbonization index, endogenous fire hazard, elemental composition, organic mass, metamorphism, coalification.