Numerical Estimation of Fuel Loss Caused by Self-ignition and Application to Coal Fire Propagation in Inclined Seam

All the headings should be uppercase, bold Arial size 10 font. In order to comprehensively understand the serious disaster of underground mineral self-ignition and source loss in practice, dynamical and thermo-chemical phenomena of coal spontaneous combustion were investigated. A coupled conductive, convective and radiative heat transfer model for inclined outcrop seam in porous coal-bearing stratum with transient exothermic source term was established. Combined with models of coal oxidation, oxygen supplement and fuel consumption, the large-scale and long-term history of coal fire was simulated. Recorded data indicate that spontaneous combustion firstly occurs under lean oxygen condition and fire development is mainly controlled by reaction heat release during early oxidation process but by oxygen restriction after coal self-ignition. Considering the variation of influence factors, comparative analyses illustrate that the propagation rate and fuel loss, that reduce when the stratum porosity decreases, are significantly and positively related to the leakage intensity. The presented method and results could provide a useful reference to loss estimation and efficient treatment of nature hazardous. NOMENCLATURE A Frequency factor, Hz Co Local oxygen concentration, kg/m 3 CP Specific heat, kJ/(kg·K) Ea Activation energy, kJ/mol ?̅? Gravitational vector, m/s k Permeability, m Or Theoretical oxygen requirement for combustion, kg/kg coal p Hydrostatic pressure, Pa S Compressibility, 1/Pa q Heat release rate, W/g qr Heat flux of radiation, W/m Q Reaction heat, J/g Qnet Net calorific value of coal, MJ/kg R Gas constant t Time, s T Absolute temperature, K v Seepage velocity, m/s w Quantity of local oxygen consumption. Kg/(m·s) Greek symbols β Attenuation coefficient, m σ Stephan-Boltzmann constant λ Thermal conductivity, W/(m·K) μ Air dynamic viscosity, Pa·s ρ Density, kg/m φ Porosity Subscripts s Solid material f Leakage air INTRODUCTION Coal fire, referring to large-area spontaneous combustion of underground coal oxidation caused by natural condition or human activities, is a serious disaster associated with coal mining in a long history. Uncontrolled coal fires are widespread in China [1], India [2], Indonesia [3], the United States [4,5], South Africa [6] and distribute throughout the world. Because of special geographical location, climate condition and artificial factor, some worst disasters of coal fire occur in China with an annual coal loss of 13.6 million tons [7]. Among all the fire areas, Xinjiang region where has the most abundant coal in China suffers the most severe coal fires. According to the latest report issued by Xinjiang Coal Fire Fighting Bureau [8], by the end of 2010, there were 49 coal fire areas in Xinjiang region. About 8,126 kilotons of coal were burned out each year with a burning area of 9.06 × 10 m and the direct economic loss was nearly one billion yuan every year.