Loss of catalyst particles in stack gas 

(a) Estimate the maximum diameter of micro spherical catalyst particles that could be lost in the stack gas of a fluid cracking unit under the following conditions: 

Gas velocity at axis of stack             = 1.0 ft/s (vertically upward) 

Gas viscosity                                       = 0.026 cp 

Gas density                                         = 0.045 lb / ft³ 

Density of a catalyst particle            = 1.2 g/cm³ 

Express the result in microns (1 micron = 10^–6 = 1/μm). 

(b) Is it permissible to use Stokes' law in (a)?