Calculate the time required to burn to complete spherical particles of graphite (radius 12 mm, bulk density 2.4 g/cc) in a 12% oxygen stream at 900°C and 1 atm. Assume gas film resistance to be negligible. Surface reaction rate constant = k” = 25 cm/s.

Solution :

In burning of particle of graphite there is no ash formation. The reacting particle shrinking in size as reaction progresses. As per data k" is only used in Chemical reaction control

Formulae for Chemical reaction control

$$ \tau=\frac{\rho_{\mathrm{B}} \mathrm{R}_{0}}{\mathrm{bk}^{\prime \prime} \mathrm{C}_{\mathrm{Ag}}} $$

Combustion Reaction :

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