Summary The three‐phase foam consisted of solid, liquid and gas is regarded as a highly effective measure for the underground mine fire prevention. In this study, the three‐phase foam technology is introduced and a visualization platform is established to exhibit the foam flow in a physical goaf. The diffusion rule and extinguishing performance for three‐phase foam are researched. Test results show that the three‐phase foam has a superior heat resistance than expansion foam in the top goaf. The coal heating rate is postponed after the three‐phase foam processing and the active functional groups are suppressed effectively. Increasing the foam expansion ratio is adverse to the three‐phase foam stability. The field application of three‐phase foam was evaluated via the practical extinguishment effect. The marked reduction in the sealed zone temperature and CO concentration proved that the proposed three‐phase foam technology was effective on controlling the concealed goaf fire.
The water-sediment two-phase seepage in coarse fractures is one of the major factors to trigger mine water inrush disasters. Based on seepage mechanics theory, a mechanical model of the water-sediment two-phase seepage in coarse fractures was established. An experimental system was also developed to study the seepage characteristics under various conditions. The relationships between the absolute value of the pressure gradient and the seepage velocity were analyzed during the test process. The nonlinear characteristics of the seepage test were revealed. In addition, variation laws of the absolute value of the pressure gradient with the sand volume fraction and the sand particle size were illustrated, which were related to the loss of pressure during the particle movement. The impacts of the sand volume fraction and the sand particle size on the equivalent fluidity and β -factor of non-Darcy flow were discussed and analyzed. It was determined that the local turbulence was the main reason for the change of nonlinear variation characteristics of seepage parameters.
The causes of greater energy loss for throttling in the fan and pump were analyzed, and the principle of frequency control in energy saving were analyzed on the basis of the similarity theory, too. To export the relationship between the power saving rate and flow, the relationship between the energy consumption of throttling regulation and flow were described. Comparison between frequency control and throttling regulation in changing the flow shows that motor frequency control applied in pump and fan is an efficient way to save power. It confirms that under meeting the similarity condition, the power saving rate of theoretical calculation is consistent with the measured data.
Researching the gas’s temperature change trend was important for the system design of spray tower in which the liquid and the gas was mixed and the heat was exchanged. In temperature measurement, it must be concerned that the test data contain impulse noise due to the internal complex environment of spray tower. In order to get the real and accurate data and to acquire temperature change characteristics, the thermocouple sensors were used to do multipoint temperature measurement in different experimental conditions. The method of extremum median filter was used to remove impulse noise of signal. The simulation was made with MATLAB. The analysis result shows that the method can remove impulse noise of temperature signal and get accurate temperature data.
The instability of water-sediment flow in fractures can easily induce water-sediment disasters. Therefore, it is of great significance for the prevention and control of water-sediment inrush to study the water-sediment two-phase flow in fractures. Based on the water-sediment two-phase flow theory, a model of the water-sediment two-phase flow system was established. The Ansys Fluent software was used to study the characteristics of the water-sediment two-phase flow in smooth and rough fractures. The spatial-temporal evolution laws of the water-sediment two-phase flow were studied; the results indicated that they did not change with time in the smooth fractured flow fields, while changing continuously with time in the rough fractured flow fields and in a dynamic steady state. The research results can provide references for the water-sediment two-phase flow in fractures and rock mass.
The water-sediment two-phase flow in the rough fracture is one of the main causes of water-sediment inrush. In this study, numerical simulation models of the water-sediment two-phase flow in the smooth and rough fractures were established by ANSYS Fluent software based on the seepage theory; the mechanical properties of the water-sediment two-phase flow under different conditions were systematically investigated, and the influence laws of the surface morphology of the fracture on sediment volume concentration, sediment particle size, and sediment particle mass density were analyzed. In addition, the influence laws of the sediment volume concentration, sediment particle size, and sediment particle mass density on the absolute value of the pressure gradient, mean velocity of the fluid, and fluid turbulent kinetic energy were also illustrated from the perspective of sediment particle distribution. Research shows that during the water-sediment flow in the smooth fracture, the absolute value of pressure gradient Gp, the sediment volume concentration Ф, the sediment particle size Dp, and the sediment mass density ρp are approximately linear, and the linearity of Gp and Dp is the lowest; during the water-sediment flow in the smooth fracture, the mean velocity v of the continuous-phase fluid rarely changes with Ф, Dp, and ρp. However, during the water-sediment flow in the rough fracture, v is greatly affected by Ф, Dp, and ρp. During the water-sediment flow in the smooth fracture, the fluid turbulent kinetic energy kt decreases with the increase of ρp and Ф and decreases with the decrease of ρp. During the water-sediment flow in the rough fracture, kt is significantly affected by Ф, Dp, and ρp, which was manifested in the changes of curve shapes and deviation of the extreme points.
Summary Mine fire caused by coal spontaneous combustion is one of the main safety problems in mining. For the purpose of developing a more effective inhibitor to suppress the coal spontaneous combustion, a compound deoxidization gel foam inhibitor was proposed by combining sodium dithionite deoxidizer with gel foam. An experimental platform was self‐built to evaluate the suppression characteristic of deoxidization gel foam. Experimental results showed that the deoxidization gel foam reduced the oxygen concentration to below 14% within 180 minutes. STA‐FTIR test indicated that the deoxidization gel foam raised the active temperature from 250.57°C to 275.18°C and reduced CO2 absorption peak from 0.2926 to 0.2201 at the reaction temperature 20°C. The activation energy was also increased from 85.69 to 95.59 kJ·mol−1 in thermal decomposition combustion that exhibited an excellent flame‐retardant efficacy on the coal, especially at the low temperature stage. CH3 and CH2 were reduced by 56.86% and 47.17% processed by deoxidization gel foam. Meanwhile, the significant reduction in the content of reductive functional groups indicated that the new inhibitor had a strong suppression capacity for coal spontaneous combustion. Based on above research, it is believed that this study will lay an important foundation in the widespread application of deoxidization gel foam technology for coal spontaneous combustion prevention in underground mines.
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