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278 Lawrence K. Wang et al.

current packing (to allow for the increased throughput) and the new packing would also have
to have an increased transfer efficiency to be able to meet the effluent specifications at the
higher flow rate.
In addition to the capacity issue, the stripper (or packed tower, shown in Fig.1b), having a
diameter of 18 in. and packing height of 28.5 ft, performs the function of stripping ele-
mental chlorine (Cl ) from hydrochloric (muriatic) acid (HCl). The existing packing
2
(media) in the stripper tower is 2-in. Pall rings. Originally developed in the 1920s, Pall
rings have traditionally been used for scrubbing applications. However, as needs dictated
over the years, the Pall rings (and other similar packings) have found their way into
stripping process applications.

Solution
For the plant in Louisiana, in this process situation the target contaminated liquid stream
is hydrochloric acid from which elemental chlorine must be stripped. The gas stream is
simply the air driven by an air blower (fan). The new packing material, in addition to the
requirements stated above, also needed to have adequate acid and chlorine resistances to
ensure a service lifetime of longer than 10 yr.
When approached by the Louisiana plant with this problem, the environmental engineer in
charge considered several possible packing materials. Previous discussion has indicated
that Q-PAC (supplied by Lantec Products) can be used to optimize a scrubber process sys-
tem. However, in this instance, being a stripping process system, a different packing was
found to be the solution to the needs of the Louisiana chemical plant.
The packing material recommended by the environmental engineer was #2 NUPAC in
polyethylene. Although slightly more expensive than polypropylene, polyethylene offers
better resistance to oxidative attack than polyethylene. This packing material also offers both
improved mass transfer properties as well as reduced pressure drop compared to Pall rings.
In February 1999, the 28.5-ft bed of the packed tower was packed with #2 NUPAC. The
performance of the tower after repack was excellent, so plant personnel were relieved that
no new capital project would be required. Stripping of elemental chlorine remained at
99% efficiency in the hydrochloric acid liquid system at the increased flow of 75 gpm in
the existing air stripping system. The upgraded stripping process system is summarized
as follows:
Reactor design = packed tower (Fig. 1b)
Packing material = #2 NUPAC (Lantec Products)
Tower diameter = 18 in.
Packing height = 28.5 ft.
Target pollutant liquid stream = hydrochloric acid containing elemental chlorine
Liquid design flow = 75 gpm
Liquid maximum flow = 85 gpm
Gas stream = clean air
Service life of packing = 10+ yr
Design stripping efficiency = 99+%
Flow pattern = liquid flows downward, air flows upward in a countercurrent flow pattern

Example 24

Discuss the past problem and the recent developments in packing materials for scrubbers
and stripper absorption systems.