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?