Risk Identification of Coal Spontaneous Fire Based on COWA Modified G1 Combination Weighting Cloud Model

To realize the scientific judgment of spontaneous fire risk in the coal mine, the spontaneous fire influence factors were analyzed from the three aspects of coal spontaneous combustion tendency, air leakage, and oxygen supply, heat storage and heat dissipation. And the basis for the evaluation of t spontaneous fire grade was constructed. Combination ordered weighted averaging (COWA) calculation was introduced to optimizes G1 subjective weighting, and a COWA modified G1 combined weighting cloud model was proposed to identify the spontaneous fire risk in the coal mine. Finally, the rationality of the model was verified with actual cases. The research results show that the spontaneous fire risk level in the Lingquan coal mine is relatively safe, which is consistent with the actual situation. And the spontaneous combustion tendency of coal is the leading factor affecting spontaneous fire risk.

Modeling on the Effect of Heat Exchanger Submersion on Controlling Spontaneous Combustion in A Coal Pile

Spontaneous combustion of coal has been well-known as a problem faced by coal industries, especially in storing and trans-shipping processes. The negative impacts of this phenomenon have led to several hazardous incidents and degrading product quality. Several methods have been researched to minimize the impacts; one of the proposed ways is immersing heat exchangers inside the coal stockpile. An experiment was conducted to analyze the cooling effect of an immersed simple heat exchanger made of a copper coil. By varying the number of windings, the experiment showed a significant decrease in pile temperature due to the immersed heat exchanger. This work continues exploring the possibility of applying the method by observing and analyzing the simulation model. COMSOL Multiphysics was used to model the physics phenomena that occur within the coal reactor. The effect of the heat exchanger surface area was studied from the model to observe the heat propagation within the coal reactor. The vast reach of heat propagation from the heat exchanger through the coal pile on the simulation was promisingly showing that this method was useful to limit the occurrence of spontaneous fire in coal piles.

Assessment of Spontaneous Ignition Lability and Gas Evolution of Coal-Bearing Rocks of Dumps and Sludges of the Coal Enterprises

Rock dumps of coal mining and coal processing enterprises contain coal, which is capable to absorbing oxygen to generate heat. Under favorable conditions, the heat generated is sufficient to increase the rock temperature and to form spontaneous fire seats. At the same time, coal-bearing rocks emit combustible and toxic gases generated during the coal decay and the oxidation of combustible elements. To assess the possibility of the development of spontaneous ignition processes in the coal-bearing rock agglomerates that were exposed to air for a long time, the samples were taken, the constant oxygen sorption rate and the duration of the spontaneous ignition incubation period were determined. Sampling was carried out on the surface of two dumps of the open pits, as well as at different depths of the slimepit of the processing plant, which were not in operation for decades. The experiment allowed to determine the concentration and intensity of the evolution of various gases from the coal-bearing rocks at natural ambient temperature. The uneven sorption activity of the rocks on the surface of dumps contributes to forming spontaneous fire seats in the areas that are most liable to this. In addition, rock dumps for decades continue to emit methane and carbon monoxide into the atmosphere at the natural temperature of the rocks, which negatively affects the surrounding nature. In the sludge settling tank, not operated for about 60 years, the sorption activity of the sludge in relation to oxygen changes not only on the surface, but also at different depths of the settling tank. The revealed features of long-term storage of coal-bearing rocks in the dumps and slimepits should be taken into account when choosing the technologies for coal mining and processing, as well as storage of the overburden rocks and processing wastes.

Study of the parameters of spontaneous fire seats in coal pit rock dumps

The presence of coal and coal-bearing rocks in waste rock dumps of open-pit coal mines contributes to the occurrence of spontaneous combustions that negatively affect the environment and people. Measurements of the temperature and the content of hazardous gases in the temperature anomaly that arose in the waste rock dump of the open-pit coal mine were made to assess the parameters of spontaneous fire seats. In the course of the study, the efficiency of detecting spontaneous fire seats in waste rock dumps was assessed by measuring the rock temperature in the wells with a depth of 2.5 m, drilled at a distance of 20 m from each other. The experiment showed the difficulty of drilling control wells in waste rock dumps and the impossibility of drilling them on the slopes of dumps, especially in spontaneous fire seats with a high rock temperature. The necessity of casing control wells with pipes makes it difficult to measure the rock temperature at different depths. It was found that there are sharp drops in the rock temperature in the heated area of the dump, which cannot be detected when the wells are located at the recommended distance. The measurements showed that in all wells the temperature increases with depth, therefore the depth of wells recommended by the regulatory documents does not allow determining the size of the heated area.

Assessment of Heating and Cooling of a Spontaneous Fire Source in Coal Deposits—Effect of Coal Grain Size

Fire hazard assessment in coal mines is performed on the basis of concentrations of particular gases emitted from the heating coal deposit, but more precise criteria and indicators are needed to assess fire hazard properly—both during the temperature rise phase and in the coal bed cooling phase. In the paper the impact of coal grinding on hazard assessment of spontaneous fire development in the coal deposit during heating and cooling the fire source was analyzed. The intensity of desorption of ethane, ethylene, propane, propylene, acetylene, carbon monoxide and hydrogen is the resultant of temperature and grinding of coal samples. The results proved that the ratio of concentrations emitted by standard versus coarsely crushed coal for each of the gases, changed both in the growth phase as well as in the temperature drop phase. It was found that as the temperature rose, the effect of coal grinding on the release of ethane, ethylene, propane, propylene and carbon monoxide decreased. The greatest effect of coal grinding was observed in the case of ethane and propane, while the lowest in the case of hydrogen and carbon monoxide.