Tower Packing (structured and random)
Tower packing is used in lots of
applications. Packed columns are most frequently used to
remove contaminants from a gas
stream (absorption). However, packed columns can
also be used to remove volatile components from a liquid
stream by contacting it with an inert gas (stripping). We will restrict ourselves here to these
two applications (gas scrubbers and
stripper-absorber combination), both in the field of air
pollution and odour control and industrial waste water
treatment.
Tower packing is a mass of inert, solid
shapes to be inserted in a mainly cylindrical column. The
purpose of tower packing is to create a bigger surface
area for the gas and liquid transfert in a packed column (whether it is a gas scrubber or a
stripper-absorber combination). A maximised surface area
increases the exchange surface where gaseous components
can be absorbed in the liquid (mass transfer). Tower packing materials
combine a high surface area (maximum absorption area) with a low bulk
density (to reduce obstruction risk of the packing).
Types of tower packingThere are many different types of tower packing and
tower fill materials. In general and depending on the
application, this packing may be random or structured.
Structured packing are honeycomb (waffle,
herringbone) block structures made of plastic or metal. The
advantages of structured packings are the higher efficiency
(lower Height of Transfert Units ), the efficient use made
of available surface
and lower pressure-drop they provide, compared to either
random packings or trays.
Structured packing are readily cut to measure to fit in
the scrubber/absorber column (in several layers). Can also
be built into cassettes for easy removal and cleaning.
Random packings (Pall rings, Rashig
rings, saddle rings, etc.) are made of metal, plastic,
ceramic. They are in general relatively inexpensive. The
advantages are : high strenght, low weight, fouling
resistance, easily interchangeable and
cleanable. Metal or plastic random packing is most
suitable for applications where the efficiency and pressure
drop is not extremely important and in cases where the
fouling risk is higher. Ceramic random packing
is designed for applications demanding for a high
temperature and/or high chemical resistance.
Other internals
A gas scrubber or air scrubber mainly
consists of following components : scrubber body or tower
(packed column), tower packing (structured or random),
droplet separator, spray nozzle(s) or liquid distributor,
pump, chemical dosing system and a ventilator. Part from the
tower packing, we also supply droplet separators,
demisters, spray nozzles, liquid distributors, liquid
collectors, liquid redistributors, support plates, hold-down
grids, etc.
Packed Column Design
Correct packed column design, correct
dimensioning and correct selection of internals, as
described above, is a matter of know-how and experience.
Part from determining the colum diameter and colum height,
it includes the art and knowledge of selecting a type and
size of column packing. This is probably one of those areas
of engineering where past experience with specific
applications is the best guide. Consult us for a
proposal, whether it's for a new gas scrubber or
stripper-absorber installation or for the optimization of an
existing installation in this area.
|