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[Display omitted] Ignition of coal dust caused by hot particles (ICDHP) will lead to serious combustion or explosion. In this work, the coupling details of multi–physical fields of the ICDHP were established. Two different chemical reactions of flaming combustion of volatiles and smoldering of coal dust were established to understand the mechanism and process of the ICDHP. The evolution of temperature, volatiles molar concentration and heat release characteristics under different particle temperatures and contact conditions between the hot particle and coal dust were investigated. Results show that there are two ways of the ICDHP, which are volatiles ignition and coal smoldering ignition. The ignition delay time (IDT) increases exponentially with the decrease of the hot particle temperature. The temperature of the hot particle is 1100 K, and thermal runaway occurs in the way of coal smoldering ignition. When the temperature of the hot particle is higher than 1100 K, thermal runaway occurs in the way of volatiles ignition. In addition, it is found that the IDT decreases exponentially with the increase of the buried depth (l p) of the hot particle in coal dust for the hot particle temperature of 1186 K. The IDT shows a trend of decreasing – increasing – decreasing with the increase of l p for the hot particle temperatures of 1271 K and 1369 K. If the hot particle is completely embedded in the coal dust, the smoldering combustion of the coal dust is found. In addition, the volatiles first react on the side of the hot particle, and the thermal runaway occurs at the position where the concentration and temperature of volatiles are high enough. [ABSTRACT FROM AUTHOR]

In many actual industrial scenes, the coal body and coal dust are not always in the tiled state, but in the inclined situation. A two – dimensional transient numerical model of coal oxidation reaction was established to study the self–ignition and smoldering characteristics of coal dust layers in the presence of inclination angle. The effects of gravity and thermal buoyancy were considered to solve the coupling problem of coal oxidation reaction and air flow. The results show that the growth coefficients of minimum ignition temperature of coal dust with thicknesses of 6.4 mm, 12.7 mm, 19.1 mm and 25.4 mm are 0.117 °C/°, 0.0467 °C/°, 0.033 °C/° and 0.033 °C/°, respectively. With the increase of hot plate temperature, the inclination of coal dust can greatly shorten the ignition delay time (IDT). The ΔIDT of coal dust inclination of 60° is 128 s/°C greater than that of 0°. The movement of high temperature point of coal dust in self–heating development stage is from the inside to the outside, and that in decaying stage is from the outside to the inside. In addition, some interesting phenomena in the process of coal self–ignition and smoldering have also been found. The influence of coal dust inclination on its self–heating is mainly reflected in the location of high temperature points and the spread of smoldering. This study is helpful to understand the characteristics of coal dust self–ignition and smoldering spread in inclined situation, and can guide the prevention of coal dust self–ignition. [ABSTRACT FROM AUTHOR]

In industries related to fossil energy, coal dust is often deposited at an angled position. A two–step parallel coal dust oxidation reaction mechanism is used to study the self–ignition and combustion characteristics of coal dust under inclination conditions. The consumption and transfer of multiple substances are considered. In addition, the gravity direction is used to simulate the influence of the inclination conditions on ignition characteristics of coal dust. Firstly, the reliability of the numerical model is verified, and the time series characteristics of the self–ignition and combustion of coal dust are studied. Then the characteristic parameters and evolution of self–ignition and combustion under different inclination are analyzed. The results show that under hot plate conditions, the ignition and combustion process of coal dust can be divided into five stages. The minimum ignition temperature of the coal dust layer (MITL) changes sinusoidally with the inclination angle. Coal dust deposited under the ceiling is easier to be ignited. As the temperature of the hot plate increases, the ignition delay time (IDT) is shortened. It is necessary to adjust the fire safety management according to the inclination conditions of the coal dust, especially in the area with an inclination angle of 150°–180°. [Display omitted] • Self-ignition and combustion characteristics of coal dust at different inclined angles are revealed. • MITLs change sinusoidally with the inclination angle. • Coal dust deposited under the ceiling is easier to be ignited. • Increasing of hot plate temperature leads to the advance of coal dust thermal runaway. • Hot spot moves from the inside to the surface, spreads on the surface, and moves from the surface to the inside. [ABSTRACT FROM AUTHOR]

The multi-field coupling of coal dust ignited by hot particles of different shapes and materials has not been studied in detail, which is an important basis for understanding the multiphase ignition characteristics in the energy industry. The multi-physics coupling method is used to study the solid-gas coupling ignition characteristics. The influence of particles material and shape in a wide temperature range on the ignition characteristics of coal dust is studied. The results show that as the temperature of the hot particles decreases from 1400 K to 1100 K, the ignition delay time increases exponentially in the range of 0 s–1.8 s. The thermal energy and thermal conductivity of hot particles have a positive impact on coal dust ignition. The minimum ignition temperature is 1150 K for metallic particles and 1250 K for non-metallic particles. For the same thermal conductivity, the minimum ignition temperature is positively correlated with the thermal energy of the hot particles. In addition, as the hot particles temperature decreases, the hot spots move from the side to the top of the hot particles. The characteristics of multiphase coupling ignition under different hot particles conditions discussed have certain significance for energy security utilization. • Detailed numerical model of coal dust being ignited by hot particles. • Material and shape of the hot particles on the ignition of coal dust. • Ignition delay time and the minimum ignition temperature vary with hot particles properties. • The location of the hot spot changes with hot particles temperature. [ABSTRACT FROM AUTHOR]