Computational fluid dynamics simulation of coal ash filling in underground mine cavity

Abstract

Coal fly ash waste from thermal power plants has recently been considered as a fill material for abandoned coal mine voids in Korea. A volume of fluid method, used in computational fluid dynamics, was adopted to simulate the process of coal ash injection into mine cavities. The difference in the filling efficiency of coal ash versus water using both upper and lower injection points was also investigated. Results show that use of a lower injection point more stably packed the cavity and provided a higher density of fill than use of an upper injection point. Thus, it would be better to place the nozzle of the injection pipe near the bottom of the mine cavity, below the groundwater level. NOMENCLATUREC ε 1 , C ε 2 , C ε 3 , C ε 4 = Coefficients of turbulent dissipation rate E i = Total energy f i = Body force vector (F int ) i = Internal forces (such as solid pressure force between particles) g = Gravity acceleration H i = Total enthalpy h i (T ij ) = Phase i enthalpy evaluated at the interface temperature T ij k = Turbulence kinetic energy k eff,i = Effective thermal conductivity M i = Interphase momentum transfer per unit volume m ij = Mass transfer rate from phase j to phase i (m ij ≥ 0) m ji = Mass transfer rate from phase i to phase j (m ji ≥ 0) p = Pressure, assumed to be equal in both phases Q ij = Interphase heat transfer rate from phase j to phase i Q i ij = Heat transfer rate from phase pair interface (ij) to phase i S u,i = Energy source S i α = Phase mass source term S i v = Phase momentum source term T i = Viscous stress tensor T i = Temperature of phase i u i = Fluctuant fluid velocity of i (i = x) u j = Fluctuant fluid velocity of j (j = y) v i = Velocity of phase i v g = Grid velocityGreek letters α i = Volume fraction of phase i ε = Turbulence dissipation rate µ t = Turbulence viscosity ρ i = Density of phase i ρ a = Density of air ρ w = Density of water ρ c = Density of coal ash σ k = Prandlt number of turbulence kinetic energy σ ε = Prandlt number of turbulence dissipation rate τ i and τ i t = Molecular and turbulent stresses, respectively

Investigation of fill distribution in post-injected longwall overburden with implications for grout take estimation

“…This is particularly necessary in areas of large-scale mine voids (Holz and Batchelor, 2012); without stabilization, unexpected subsidence or sinkholes may occur at the ground surface, posing a risk to public safety (Helm et al, 2013;Ju and Xu, 2015;Turka and Gray, 2005). One such stabilization method is void filling using grout injection, which is applied to remediate sinkhole subsidence associated with voids in abandoned room-and-pillar mines (Greenwood and Hill, 2012;Holmquist et al, 2003;Karfakis and Topuz, 1991;Siriwardane et al, 2003), and surface settlement induced by other abandoned spaces such as drifts (Kipko and Kipko, 1990;Song et al, 2015). Grout injection into bedding separation (GIBS) is another effective method of ground stabilization; this method is used in existing or planned surface construction sites in conjunction with active longwall mining and utilizes the horizontal fractures at the rock layer interfaces associated with underground extraction .…”

The Blocking Mechanism of the Vertical Feeding System of Roadside Support Body Material for Backfilling Gob‐Side Entry Retaining

“…Among them, main forces in the vertical direction include gravity, buoyancy, additional mass force, air resistance, pressure di erential force, and Basset force [11][12][13]. Song et al [14] used CFD for simulation of back lling of an abandoned coal mine with yash and described the dispersion and back lling phenomenon of coal mortar and its movement in the mine clearance. Among them, water and air in the passageway were treated as multiphase ow.…”