OCR Text |
Show Equation (3) can be transformed by choice of r as an independent variable, with d/dt = Vr (d/dr). Hence a solution for Vr can be obtained as a function of r, with the time varying d defined below. The change in particle diameter due to diffusion controlled burning is given by a diameter square law: p p,o » g s c [H (t - th)] . (t - th) where d ,o, particle diameter at t = o (5) PC V D , V density of char free stream concentration of reacting gas which can be 0^, C0~, etc. stoichiometric consumption of reacting gas per unit mass of char diffusion coefficient time to heat up the particle to diffusion controlled reaction temperature H (t - t.) , Heavy side function n = 0;t < t. = l;t > th For Eq. (5) it is assumed that the mineral matter is concentrated at the center and as such is small compared to the diameter of the original coal particle. The burning time can be calculated from Eq. (5) by setting d = 0 W o (Vc/8Y-pgD) + h (5a) -12- ^AVCO EVERETT |