Pore-scale Numerical Study On The Self-heating Process Of Packed Coal Stockpile

Spontaneous combustion of coal is one of the major accidents during underground mining, storage and transportation of coal resource. Once this hidden danger occurs, it will cause great harm to both safety and economics. Low-temperature oxidation of coal is the source of spontaneous combustion:Under a suitable ventilation and oxygen condition, accumulated heat prompts coal’s temperature to the ignition temperature, and ultimately leads to burning. In order to prevent spontaneous combustion and achieve the purpose of safe production, it is necessary to deeply analysis the heating process and find out the effect of different external factors microscopically. Considering the mentioned background, this paper aimed at introducing pore-scale numerical simulation among particles into the coal spontaneous combustion research areas and exploring the mechanism in in this way.In the first place, to demonstrate the feasibility of pore-scale simulation, velocity and temperature distribution in pore-scale space constituted by packed bed particles were calculated, and then compared with the experimental data in the literature. The result of comparison showed good conformity.Then the spherical coal particles with heating effect took the place of macroscopic porous medium by forming stacked structure in real law order. After reasonable simplification on the self-heating oxidation of coal, boundary conditions were set to match actual leakage condition. Solutions of these cases solved flow and temperature profiles within the pore in detail, which can explain heat accumulation or dissipation phenomenon due to the flow field.In the stage of actual heating process, research focused on a single coal particle’s oxidation which located within the inflow air background along with solid internal diffusion and heat and mass transfer effect caused by air flow. By accurately analyzing the reaction on particle surface, the exact chemical reaction rate was obtained. Based on above results, a three-dimensional unsteady-state model was established to predict the self-heating evolution of stockpiles including gas consumption and heat source terms. A computational fluid dynamic (CFD) method was applied to solve the equations. The results were compared with the site actual measurements. Judging from the comparison, they were in good agreement with each other:different temperature measuring points have the same trend and the period of coal spontaneous combustion is very close, which show that the numerical model has high credibility and accuracy. Finally, the model was used to simulate the temperature distribution inside the coal pile under different conditions. The influences of inflow velocity, porosity and particle diameter were examined in detail.Based on the above analysis, it is feasible to study the coal spontaneous combustion process by pore-scale simulation. The three-dimensional unsteady model can not only truly reflect the internal changes of temperature distribution or oxidation reaction in the coal pile, but also well predict the period of coal pile spontaneous combustion. The simulation results can provide strong guidance for avoiding self-ignition hazard and ensure safety in production.