A SIMPLIFIED DESCRIPTION OF CHAR COMBUSTION

A simplified analysis of carbonaceous particle combustion is presented that includes the effects of pore diffusion and growth as well as gas-phase heat and mass transfer. The combustion dynamics are described by time-dependent equations for particle temperature, radius and a number of intraparticle conversion variables. These are coupled to pseudosteady equations for gas-phase transport and internal reaction and diffusion. The differential equations for gas-phase transport are reduced by quadrature to a nonlinear boundary condition to the intraparticle boundary value problem. Numerical calculations are performed for conditions relevant to pulverized coal combustion. An analytical solution of the intraparticle problem, pertinent to the regime of strong diffusional limitations, reduces the intraparticle solution into a set of two quadratures which drastically simplifies the numerical calculations. The simplified intraparticle solution is in excellent agreement with the full solution at 1800 K free stream temperature and fair agreement at 1500 K.