A 1.5-m diameter bed of micro catalyst (s.g.= 2.0, sphericity = 0.9) with size distribution given

below is to be fluidised using a gas (density = 1.2 kg/m3 , viscosity = 1.7x10-5 Pa.s). Initially the

bed is 1.0 m high with a voidage of 0.4.

Volume Diameter dV (m)

from to

Mass

(g)

50 75

20

75 105

77

105 150

150

150 215

53

a. Calculate the minimum gas flow rate necessary to fluidise the bed of catalyst. The bed voidage

at incipient fluidization is not known.

b. What is the highest gas flow rate that can be used to safely fluidise the bed? Determine the

bed voidage, bed height and bed pressure drop under this condition. Assume particulate

fluidisation and verify that it is the case.

c. In actual operation, process requirements may demand a higher gas flow rate than that

calculated in (b). In order to contain all catalyst particles in the bed, the fluidising section needs

to be tapered, i.e. with increasing cross section in the vertical direction. For an operating

fluidising gas rate of 1800 m3 /h, what should the diameter of the upper end of the bed be, if the

base has a diameter of 1.5 m?