THEORETICAL STADY OF MULTISTAGE COAL PARTICLE BURNING
Keywords:
coal, heating, burn out, drying, inflammation, coke residue, mathematical modelAbstract
Nonlinear mathematical modelling of coal particle thermal preparation and further burn-out is considered as a multi-stage process. Analysis of this process on sequential stages of heating, drying, ignition and coal burnout is done with semi-analytical approach. On a heating stage with convection and radiation the solution for temperature is found by asymptotic expansions at low and high dimensionless time. Calculations using obtained expressions show that thermal stress inside smaller than 100 mkm Kansk-Achinsk coal particles at 1500 °K are lower then limiting and particle remains solid. 10 mm and bigger particles at 1000 °K are thermally destructed (destruction starts very early at low Fo numbers). Drying process is formulated as nonlinear Stephan task with moving boundary of "liquid-vapor" phase transfer. Drying rate and timing is calculated with approximate analytical formulation using two zones: dry fuel zone and residual moist zone. At particular case of small evaporation values the solutions are matching exactly solutions of L.S. Leybenzon. Ignition characteristics are found using adiabatic method of V.N. Vilunov. Ignition point, ignition temperature and induction time are found. Time to burnout of coke residue was found using quasi-stationery approximation with assumptions common for Shvaab-Zel’dovich formulation. Influence of ash compound, coal dryness, porous reactions and oxygen concentrations is studied. Parametrical analysis for physical and operational parameters of burning Kansk-Achinsk coal particle is done. Optimal conditions for burning of coal particle are defined.
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