Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

Experiment study on the propagation laws of gas and coal dust explosion in coal mine

The experiment of gas and coal dust explosion propagation in a single lanewaywas carried out in a large experimental roadway that is nearly the same with actual environmentand geometry conditions.In the experiment,the time when the gas and coal dustexplosion flame reaches test points has a logarithmic function relation with the test pointdistances.The explosion flame propagation velocity rises rapidly in the foreside of the coaldust segment and comes down after that.The length of the flame area is about 2 timesthat of the original coal dust accumulation area.Shock wave pressure comes down to therock bottom in the coal dust segment,then reaches the maximum peak rapidly and comesdown.The theoretical basis of the research and assemble of across or explosion is suppliedby the experiment conclusion.Compared with gas explosion,the force and destructiondegree of gas and coal dust explosion is much larger.

Mechanism research of gas and coal dust explosion

Combined with the experimental results from the large tunnel of the ChongqingResearch Institute,the mechanism of gas and coal dust explosion was studied.Someconcepts about gas and coal dust explosion were introduced such as the form conditionand influential factors.Gas and coal dust explosion propagation was researched and thelifting process of coal dust was simulated.When an explosion occurred due to great mixtureof gas and air,the maximum explosion pressure appeared in the neighborhood of theexplosion source point.Before it propagated to the tunnel of the deposited coal dust,themaximum explosion pressure appeared to be in declining trend.Part of the energy waslost in the process of raising the deposited coal dust through a shock wave,so the maximumexplosion pressure was smallest on the foreside of the deposited coal dust sector.On the deposited coal dust sector,the explosion pressure rapidly increased and droppedoff after achieving the largest peak value.Because of coal dust participation in the explosion,the flame velocity rose rapidly on the deposited coal dust and achieved a basic stablevalue;coal dust was ignited to explode by initial laminar flame,and the laminar flametransformed into turbulent flame.The turbulence transformed the flame fold into a funnelshape and the shock wave interacted with the flame,so the combustion rate rose and thepressure wave was further enhanced.The regeneration mechanism between the flamecombustion rate and the aerodynamic flowing structure achieved the final critical state forforming the detonation.

Explosion limits for combustible gases

Combustible gases in coal mines are composed of methane, hydrogen, some multi-carbon alkane gases and other gases. Based on a numerical calculation, the explosion limits of combustible gases were studied, showing that these limits are related to the concentrations of different components in the mixture. With an increase of C4H10 and C6H14, the Lower ExplosionLimit （LEL） and Upper Explosion-Limit （UEL） of a combustible gas mixture will decrease clearly. For every 0.1% increase in C4H10 and C6H14, the LEL decreases by about 0.19% and the UEL by about 0.3%. The results also prove that, by increasing the amount of H2, the UEL of a combustible gas mixture will increase considerably. If the level of HE increases by 0.1%, the UEL will increase by about 0.3%. However, H2 has only a small effect on the LEL of the combustible gas mixture. Our study provides a theoretical foundation for judging the explosion risk of an explosive gas mixture in mines.

Safety research in the gasification process of novel multi-thermal-source coal gasifier

In order to collect the gas safely produced in the gasification process of the novel multi-thermal-source coal gasifier,based on its gasification skill and the characteristics of the products,this paper analyzes the possible dangers in the gasification process,devises the gasifier eruption and explosion experiments,explores the conditions of gasifier eruption and gas explosion,studies their effects on the gasification process and establishes safe operation measures.Gasifier eruption hazard occurs easily in the gasification process of one-thermal-source coal gasifier when MSiO2 is far higher than that in the normal adjuvant.The gas permeability in the gasifier is not the same and the power supply is too large.However,similar conditions in the gasification of multi-thermal-source coal gasifier do not produce a gasifier eruption accident so easily.When it erupts,the gasifier should be stopped and then cooled down naturally or inert gas can be sprayed on the gasifier to cool it off,and thus gas explosion can be avoided.There is a possibility of direct gas explosion,but it can be avoided when the gas in the gas collecting space is replaced slowly by supplying a small amount of power or the inert gas fills the space in the previous gasification.The time a fire is lit is strictly controlled,the gas is drawn in by using the aspirator pump,and the gasifier pressure is kept in the state of micro-positive pressure in the middle and later gasification process.The conclusion is that the gasification process of the novel multi-thermalsource coal gasifier is safe according to normal operation rules.

Influence of obstacle disturbance in a duct on explosion characteristics of coal gas

In combination with experimental research,numerical simulation is performed to investigate the influence law of the obstacles in a duct on the explosion flame of premixed coal gas and air. The numerical method uses upwind WENO scheme and two-step chemical reaction model. The interaction mechanism is addressed between the compression wave from reflection on the right end of the duct and flame propagation. The reflected wave is found to result in the decrease of flame velocity. On this basis,we analyze the mechanism of the obstacles on flame as well as the law of flow field variation thus caused. The results suggest that,due to the obstacles,deflagration wave is repeatedly reflected,combustible gas mixture is fully compressed,temperature and pressure rise,chemical reaction speed increases,and hence flame intensity is strengthened. At the same time,a tripe point forms as a result of wall reflection of the deflagration wave from the obstacles and furthermore local flame speed increases. As the triple point propagates forward,the flame speed gradually decreases due to dissipation of energy. These conclusions provide a valuable theoretical foundation for the prediction of explosion field,prevention of fire and explosion and effective control of the com-bustion speed and flame propagation speed in detonation propulsion.

Disasters of gas-coal spontaneous combustion in goaf of steeply inclined extra-thick coal seams

In light of the escalating global energy imperatives,mining of challenging-to-access resources,such as steeply inclined extra-thick coal seams(SIEC),has emerged as one of the future trends within the domain of energy advancement.However,there is a risk of gas and coal spontaneous combustion coupling disasters(GCC)within the goaf of SIEC due to the complex goaf structure engendered by the unique mining methodologies of SIEC.To ensure that SIEC is mined safely and efficiently,this study conducts research on the GCC within the goaf of SIEC using field observation,theoretical analysis,and numerical modeling.The results demonstrate that the dip angle,the structural dimensions in terms of width-to-length ratio,and compressive strength of the overlying rock are the key factors contributing to the goaf instability of SIEC.The gangue was asymmetrically filled,primarily accumulating within the central and lower portions of the goaf,and the filling height increased proportionally with the advancing caving height,the expansion coefficient,and the thickness of the surrounding rock formation.The GCC occurs in the goaf of SIEC,with an air-return side range of 41 m and an air-intake side range of 14 m,at the intersection area of the“<”-shaped oxygen concentration distribution(coal spontaneous combustion)and the“>”-shaped gas concentration distribution(gas explosion).The optimal nitrogen flow rate is 1000 m3/h with an injection port situated 25 m away from the working face for the highest nitrogen diffusion efficacy and lowest risk of gas explosion,coal spontaneous combustion,and GCC.It has significant engineering applications for ensuring the safe mining of SIEC threatened by the GCC.

ANALYSIS OF ABILITY FOR IGNITING METHANE OF WATER-CARRYING EXPLOSIVES

In this paper, the ability to ignite methane of water-carrying explosives is discussed in detail. The difference of the safety towards methane of water- carrying explosives and ammonite is analysed comparatively. lt is shown that the process of detonation reaction, the duration of fIame by combustible residues of detonation and the fineness of cooling salt in detonation products are important factors of the safety of explosive towards methane. Water-carrying explosives are safer than ammonite used in coal mines.

Analysis of coal mine safety accident features in China,2017–2022

Coal-related accidents are prevalent in China, often attributed to the intricate geology and challenging workingconditions of mines. This study seeks to determine the patterns of these accidents by examining the characteristicsof an accidents database, considering regional, temporal, mining method, and classification distribution characteristics. The analysis centers on all significant coal accidents (involving three or more fatalities) that occurredin China from 2017 to 2022, as documented in China’s (excluding Hong Kong, Macao, and Taiwan) national coalmining safety accident report. Over the most recent six years, roof falls and gas explosions have emerged as themost common types of accident. Case studies were conducted to comprehensively investigate the histories andunderlying causes of these incidents. Countermeasures are proposed from three perspectives: prospective measures, optimization strategies, and enterprise management.

Study on Lignite-Blended Burning Technology in the 1025t/h Bituminous Boiler

Due to a serious shortage of the coal in Tonghua, a retrofit solution of mixing warm flue gas extracted from reversing chamber into the coal pulverizing system and cold air into the hot air coal pulverizing system is proposed so as to reduce oxygen content. At the end of the pulverizing system and medium temperature of the conveying system, dual-channel combustion burner is transformed into horizontal bias combustion burner. The measurement results show that 50% ratio of lignite blended in the 1025t/h bituminous boiler is feasibility. It is also an important technology to reduce NOx pollutant emission.

Risk field assessment of longwall working face by the double-sided roof cutting along the gob

In order to study the mechanism of the dual side roof cutting technology on the composite disaster of gas and coal spontaneous combustion in goaf,a model for the evolution of porosity and permeability in the dual side roof cutting working face was constructed.The location of the occurrence of the compound disaster of gas explosion and coal spontaneous combustion under the double-sided roof cutting mode was studied,and the sensitivity of the evolution pattern of the compound disaster area to the amount of air supply and gas gush was summarized.The results indicate that the top cutting pressure relief technology significantly reduces the permeability of porous media,and the sensitivity of the goaf on the intake side to airflow disturbances is significantly reduced.As the volume of air supply increases,the distance between the gas explosion risk area and the coal spontaneous combustion risk area gradually decreases,and the probability of composite disaster areas is 0.The increase of air supply and gas emission makes the gas concentration in the middle and deep goaf increase in an exponential function,and the width of the gas explosion risk area increases gradually.When the outflow reaches 40 m^(3)/min,there is no composite disaster zone,indicating that the rapid increase in outflow inhibits the occurrence of composite disasters.