Chemical Engineering March 2019 - 61

pressure drop can be regained by
swirl vane inserts, depending on the
cyclone geometry and on the operation
data. Similar results can be
obtained by applying swirl vane inserts
in the vortex finder of uniflow
cyclones. For example, in a uniflow
cyclone with a diameter of 300 mm
(11.8 in.), a pressure-drop reduction
by 43% could be achieved at a gas
volume flow of 1,000 m3/h, and by
40% at 2,500 m3/h [18].
Cyclones in limited space
Often, space avaliable for dedusting
a gas flow within an industrial plant is
limited. If saving space is a high priority,
or if there is a limited space available
for purifying a given gas volume
flow, the question arises whether
under the space restrictions, a uniflow
cyclone system may be preferable
over its standard cyclone counterpart.
This question is addressed
by applying the above-mentioned
calculation programs for standard cyclones
and for uniflow cyclones.
To provide a fair comparison between
both cyclone types, the most
compact representative of a standard
cyclone is considered. This is
a cyclone with an axial inlet (Figure
2c), also called a swirl tube (Figure
14a). This cyclone type is preferably
applied as a multicyclone series (that
is, a system of many parallel cyclone
cells within a common housing, and
having a common solids hopper for
solids discharge). Multicyclones are
generally used to increase the separation
efficiency beyond the level
achievable by a single cyclone. Note
that the minimum particle size that
can be collected by a cyclone generally
decreases with decreasing cyclone
size. Principally, increasing the
number of parallel cyclone cells and
decreasing their size at the same
time improves the efficiency of a multicyclone
without changing the base
area and without affecting its pressure
drop, provided a uniform distribution
of the gas and the solids feed
into each single cyclone cell can be
achieved, and bypass flows through
the solids discharge openings from
one cyclone cell to the other can be
avoided. In many cases, this can
be achieved to a good approximation
by a proper design of the cell
arrangement, the spacing between
them, and the geometry of the housing
inlet and outlet duct.
To compare both cyclone types, a
typical industrial multiclone application
has been considered and investigated
in a systematic way. Various
dedusting problems have been investigated,
specified by the gas-solids
feed, the available volume for the
cyclone and its pressure drop.
In all considered cases, the gas
feed per cyclone cell is 466 m3/h
(15,457 ft3/h) air at ambient conditions
with a gas density of g = 1.2
kg/m3 and a gas viscosity of g = 2
× 10-5 Pa s.
With respect to the particle feed,
only fine powders are taken into consideration
in order to make a meaningful
comparison. Note that the difference
between both cyclone types
becomes most clear when considering
the collection of fine particles.
With increasing particle size of the
feed, the efficiencies of both cyclone
types increase and converge (Figures
9 and 10). Four fine powders
are considered characterized by
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Chemical Engineering March 2019

Table of Contents for the Digital Edition of Chemical Engineering March 2019
