Question

b) A 0.1 mm particle of an iron ore, heated in an air stream, takes 0.5 min to react completely to oxide How long would a 0.05 mm particle take if both ash layer diffusion and surface reaction were the rate controlling steps?

Answer 1

Solution Given Data ( Particle 1) Dp, = e 0.1 mm 0.5 min = a complete combustion (Particle 2) Dp2 = 0.05 mm 22 - 1 diffusion we we wen Controlling of particle by Equation ash for layer complete combustion is given as - = SBR² 6b De (Ag ni za R? = (Constant) R² - for particle ① r = (constant) R, 2 - 0 for particle € z = Constant) R ê -

Dividing eqn by ☺ & R = De } putting values = 6.5 min z (6.1)?mm? (0.0572 mm² T2 0.125 min Therefore combustion by of ash layer ous mm controlling particle time of complete is 0.125 min

=> By Surface reaction controlling particle by Equation Surface of complete Combustion of reaction control given as a 7 = Sg B - bli Cag rar ~= (constant JR t for particle for partick ( r 2 = (constant) = ( Constant) R R2 ? - Ri - Opi 22 - Rz - Opz putting all values 0.15 min o.1 mm z 0.05 min 2 = 0.25 min Therefore by Combustion complete surface reaction Controlling of o.o5mm particle is time 0.25 of min