Characteristics and main factors of foam flow in broken rock mass in coal mine goaf.

To protect the environment and reduce the occurrence of coal mine fire, foam injection in goafs is an effective measure for preventing and extinguishing mine fires. The flow characteristics of foams injected into goafs have a significant impact on the prevention and extinguishment of such fires. To study the flow characteristics of foam injected into a goaf, we first independently constructed a set of experimental platforms for the visualization of goafs. Next, we performed physical experiments on foam injection using similarity theory. Flow characteristics were simulated under different foam concentrations, flow rates, and goaf porosities. The exponential function was found to provide a good fit to the trajectory of the foam's stacking edge in the goaf. According to the foam injection volume, the trend of the fitting equation parameter a could be divided into two stages. The first stage was the rapidly decreasing stage, and the second stage was the stable stage. It was inferred that the stacking height and diffusion radius of the foam under different conditions were related to the speed of liquid film drainage. The results of this study can provide a valuable reference for the use of fire prevention and extinguishment technology in the goaf.

Changes of physical properties of coal dust with crush degrees and their effects on dust control ability of the surfactant solution spray.

To know about the reasons leading to variations in dust control efficiency of the surfactant solution spray on coal dust (from the same coal source) with different diameters, the changes of coal dust surface features (specific surface area, pore volume, gas adsorption, and surface potential) with crush degrees and their effects on the wettability were investigated. The experimental results indicated that the surface characteristics of coal dust showed remarkably positive correlations with the crush degree. For example, dust size was reduced from 114.96 to 18.71 µm, the pore volume and gas adsorption of coal dust surface was enhanced by 75%, 104.5%, respectively. It made gas film around dust particles more easily been generated, hindering the contact between dust particles and droplets. The adsorption rate of the surfactant molecules on the coal dust surface was significantly reduced with the dust size decreased, increasing the difficulty of capturing coal dust by surfactant solution. Additionally, based on the linear fitting analysis between surface features and the dust control efficiency, it was indicated that the increased gas adsorption and pore structures on the dust surface was the key factors weakening the dust removal efficiency of the surfactant solution from the perspective of the physical features of coal dust. This study was conducive to optimizing the surfactant-aided dust control technology to better capture coal dust with small size.

Recent Progress in Polymer-Containing Soft Matters for Safe Mining of Coal.

Safe mining is the premise and guarantee of sustainable development of coal energy. Due to the combination of excellent properties of polymers and traditional soft matters, polymer-containing soft matters are playing an increasingly important role in mine disaster and hazard control. To summarize the valuable work in recent years and provide reference and inspiration for researchers in this field, this paper reviewed the recent research progress in polymer-containing soft matters with respect to mine dust control, mine fire control, mine gas control and mine roadway support. From the perspective role of polymers in a material system, we classify mine polymer-containing soft matters into two categories. The first is polymer additive materials, in which polymers are used as additives to modify fluid-like soft matters, such as dust-reducing agents (surfactant solution) and dust-suppressing foams. The second is polymer-based materials, in which polymers are used as a main component to form high performance solid-like soft matters, such as fire prevention gels, foam gels, gas hole sealing material and resin anchorage agent. The preparation principle, properties and application of these soft matters are comprehensively reviewed. Furthermore, future research directions are also suggested.

Aqueous clay suspensions stabilized by alginate fluid gels for coal spontaneous combustion prevention and control.

We have developed aqueous clay suspensions stabilized by alginate fluid gels (AFG) for coal spontaneous combustion prevention and control. Specially, this study aimed to characterize the effect of AFG on the microstructure, static and dynamic stability, and coal fire inhibition performances of the prepared AFG-stabilized clay suspensions. Compared with aqueous clay suspensions, the AFG-stabilized clay suspensions manifest high static and dynamic stability, which can be ascribed to the formation of a robust three-dimensional gel network by AFG. The coal acceleration oxidation experimental results show that the prepared AFG-stabilized clay suspensions can improve the coal thermal stability and effectively inhibit the coal spontaneous oxidation process by increasing crossing point temperature (CPT) and reducing CO emission. The prepared low-cost and nontoxic AFG-stabilized clay suspensions, exhibiting excellent coal fire extinguishing performances, indicate great application potentials in coal spontaneous combustion prevention and control.

Novel approach for extinguishing large-scale coal fires using gas-liquid foams in open pit mines.

Coal fires are a serious threat to the workers' security and safe production in open pit mines. The coal fire source is hidden and innumerable, and the large-area cavity is prevalent in the coal seam after the coal burned, causing the conventional extinguishment technology difficult to work. Foams are considered as an efficient means of fire extinguishment in these large-scale workplaces. A noble foam preparation method is introduced, and an original design of cavitation jet device is proposed to add foaming agent stably. The jet cavitation occurs when the water flow rate and pressure ratio reach specified values. Through self-building foaming system, the high performance foams are produced and then infused into the blast drilling holes at a large flow. Without complicated operation, this system is found to be very suitable for extinguishing large-scale coal fires. Field application shows that foam generation adopting the proposed key technology makes a good fire extinguishment effect. The temperature reduction using foams is 6-7 times higher than water, and CO concentration is reduced from 9.43 to 0.092‰ in the drilling hole. The coal fires are controlled successfully in open pit mines, ensuring the normal production as well as the security of personnel and equipment.