Abstract
It was proposed to use CO2/N2 to effectively prevent and control Class A solid spontaneous fires such as coal. The preparation process of CO2/N2 cryogenic slurry pipeline and its pipeline flow characteristics were studied. The temperature field, pressure field and phase change characteristic changed during the transportation of the CO2/N2 mixture in the pipeline are analyzed by numerical simulation. The results showed that: the fluid in the pipeline exchanged heat and started to contact at a position of 0.1m in the pipeline. The temperature first rapidly dropped to the lowest temperature of 103K, and then the fluids in the range of 0.1m to 0.3m were fully mixed, and the temperature rised to 164K. The temperature was consistent with the equilibrium state in the pipe, and the temperature was gentle and stable; the pressure in the pipe was on the whole downward trend, and each position along the main pipe produced a positive pressure difference relative to the end of the pipe. The closer to the mixing place, the greater the corresponding pressure difference; During the mixing process, LN2 was acted as a cold source to sublime CO2 to form dry ice particles. And through the cryogenic fluid mixing experiment, the temperature distribution in the pipeline, range of the dry ice particle generation position, and the dry ice particle generation phenomenon was measured. The results showed that the mixing was completed within 0.8 m of the pipeline, and the temperature in the tube rised to 168K and remain stable. The data were basically consistent. And dry ice particles generated at the temperature of 194.5K, and a diffuse gas cloud formed at the outlet with the momentum of the jet.
Highlights
China is rich in coal resources, but due to the influence of coal seam geological conditions, mining technology, ventilation management and coal's own characteristics, the annual direct burning loss due to spontaneous combustion reaches 10~13.6Mt[1,2]
The solid carbon dioxide particles formed by sublimation are dispersed in liquid nitrogen to form a slurry that is easy to transport, covering the surface and cracks of spontaneous combustion coal
The dry ice particles in the cryogenic slurry are formed by the condensation of low-temperature carbon dioxide gas
Summary
China is rich in coal resources, but due to the influence of coal seam geological conditions, mining technology, ventilation management and coal's own characteristics, the annual direct burning loss due to spontaneous combustion reaches 10~13.6Mt[1,2]. The solid carbon dioxide particles formed by sublimation are dispersed in liquid nitrogen to form a slurry that is easy to transport, covering the surface and cracks of spontaneous combustion coal. Juan et al introduced CO2 into saturated liquid nitrogen through different types of pipelines to form fine and dispersed dry ice particles and a uniform solid-liquid mixture in the pipeline They studied the particle size and pipe blockage during the mixing process and found that capillary tubes were used. The characteristics of state change provide relevant basis and reference for the cryogenic slurry anti-extinguishing technology to realize the solid-liquid two-phase transport into the coal spontaneous combustion high temperature area, so that the CO2 is attached to the surface of the spontaneous combustion coal body in the form of small solid particles and cracks to cool down Oxygen barrier
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