Coal spontaneous combustion (the term is hereafter abbreviated as CSC) is an important problem facing by China to achieve carbon peak and carbon neutrality. CSC affects the mining process of mining for a long time, not only causing a large amount of waste of coal resources, but also severely destroying the ecological environment. At present, filling & plugging materials (the term is hereafter abbreviated as F&P materials) is widely welcomed and developed rapidly because of its advantages of wide application, obvious performance and low price. Based on the research of the prevention and control of CSC and the materials applying for it, this paper creatively puts forward an application system of materials used for the prevention and control of CSC. The types of F&P materials are systematically summarized. According to the form of materials, the F&P materials are divided into slurry, colloid and foam. The performance and effect of three kinds of F&P materials are analyzed in detail. On this basis, the cost and environmental protection characteristics of F&P materials in China were compared and evaluated. Finally, this paper predicts the development of F&P materials. This paper provides an effective reference for Chinese coal mining enterprises to select suitable F&P materials, which is of great significance for the prevention and control of CSC and environmental protection.

Coal spontaneous combustion is a major threat for safe production. In order to achieve the application of sound wave technology to the monitoring and early warning of coal spontaneous combustion, clarify the propagation characteristics of sound waves in loose coal heating process, and illustrate the temperature sensing mechanism of the sound wave detection and early warning of coal spontaneous combustion, the present study built a test system of sound wave kinematic parameter for loose coals to survey the attenuation characteristics of sound wave propagation during loose coal heating. The elastic wave CT algorithm was used to reconstruct the sound wave velocity field, clarify the propagation path, and identify the temperature anomaly area. The results show that with the increase of temperature, the time for sound wave propagation reduces rapidly and then slowly, the velocity increases gradually, and the internal structure and pores of coals become enlarged. In the sound velocity field reconstructed on the basis of SIRT algorithm, the area with high value corresponds to the high temperature area of the coal, which better reflects the changes of the temperature anomaly area during coal heating.

With the increasing amount of resources required by the society development, mining operations go deeper, which raises the requirements of studying the effects of temperature on the physical and mechanical properties of coal and adjacent rock. For now, these effects are yet to be fully revealed. In this paper, a mechanical-electromagnetic radiation (EMR) test system was established to understand the mechanical deterioration characteristics of coal by the effect of thermal treatment and its deformation and fracture characteristics under thermo-mechanical coupling conditions. The mechanical properties of high -temperature-treated coal were analyzed and recorded, based on which, reasons of coal mechanical deterioration as well as the damage parameters were obtained. Changes of the EMR time series under unconstrained conditions were further analyzed before characteristics of EMR signals under different damage conditions were obtained. The evolution process of thermal damage and deformation of coal was then analyzed through the frequency spectrum of EMR. In the end, based on the time -frequency variation characteristics of EMR, a method of determining combustion zones within the underground gasification area and combustion zones' stability level was proposed.

Inhibitors play an important role in preventing and controlling coal spontaneous combustion (CSC). In this study, the effect of DL-malic acid, an environment-friendly inhibitor, on the CSC characteristics of lignite and bituminous coal was studied. A contrastive analysis was conducted on the inhibitory effects of malic acid solution with different concentrations on CSC. Moreover, the inhibition characteristics of malic acid on coal samples with different soaking times were analyzed. In so doing, the inhibition mechanism of malic acid on CSC was revealed. It was found that malic acid can obviously inhibit CSC of lignite and bituminous coal. After the treatment of malic acid, the concentrations of CO released by coal samples during oxidation fall, and the crossing-point temperatures increase. Compared with the raw coal, the acid-treated coal corresponds to lower concentrations of free radicals and functional groups -CH2- and -CH3 and boasts better thermal stability before 150 degrees C. A contrastive analysis on the inhibitory effects on coal samples with different soaking times disclose that the water-soaked coal sample is inhibited better in CSC by malic acid than the unsoaked coal sample. The malic acid solution can effectively weaken the catalytic effect of metal ions in coal and inhibit the generation of free radicals, thus inhibiting CSC well.

Flow instability is a key question which needs to be solved for the development of dense-phase pneumatic conveying. Flow patterns are closely related with flow instability. There is a gap in our knowledge of gas–solid flow patterns in the dense-phase pneumatic conveying due to the lack of advanced measure technology and analysis methods. Electrical Capacitance Tomography (ECT) is an effective and advanced measure method which was used to research flow patterns in pulverized coal dense-phase pneumatic conveying with solid–gas ration of 60–560 kg/kg. With stack of ECT images in order of time, different flow patterns were defined and classified in the horizontal and vertical pneumatic conveying systems. Plug flow, fluidized flow, slug flow and stratified flow were observed in the horizontal pneumatic conveying; there were plug flow, fluidized flow, slug flow and annular flow in the vertical pneumatic conveying. The relationship between Reynolds number and Archimedes number was used to predict transition of these flow patterns. The prediction is in good agreement with experimental results in the experimental range. In addition, some analysis methods were introduced to research the flow patterns, such as the Standard Deviation (SD), Power Spectrum Density (PSD) and wavelet analysis. We found that flow stability can be represented with SD and PSD. PSD is preferred to SD for its higher resolution ratio and noise immunity. The wavelet analysis can reflect flow characteristics and energy distributions in the different scales for different flow patterns.