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Mechanical Design and Operation of Alkanolamine Plants 247

chemical resistance, dirt holding capacity, the optimum flow rate through the cartridge, the
maximum allowable operating temperature, and the maximum allowable pressure differen-
tial before changeout is required.

Precoat Filters
Precoat filters in amine filtration service use a diatomaceous earth or perlite filteraid pre-
coat (typically about 10 pounds of filteraid per 100 square feet of filter surface area) and a
body feed of 1 pound of filteraid per pound of solids removed. They usually filter a 10%
slipstream, and depending on the type of filter aid, can remove particles as small as 1
micron. Precoat filters were widely used in large amine systems (greater than 1000 gpm cir-
culation) in the 1970s. However, precoat filters require significant operator attention, and
amine losses can be substantial unless they are carefully operated. For these reasons, precoat
filters are no longer widely used for amine filtration.
Two types of precoat filters (tubular and filter lea0 have been used for amine filtration. Typ-
ical sizing criteria and performance data are summarized in Table 3-7. A review of experience
with several precoat filters in DEA plants located in Canada and the United States has been
presented by Scheirman (1973A, B). Combined use of filter aid and activated carbon in a pre-
coat filter of the pressure leaf type has been reported by Dailey (1970). Such a system removes
suspended solids and undesirable dissolved compounds in one operation. However, Smith and
Younger (1972) report that precoat filters using both activated carbon and filteraid are not as
effective as a precoat filter combined with a dedicated activated carbon filter.

Bag Filters
Fabio (1992) discusses some of the advantages of bag filters for amine mechanical filtra-
tion. Figure 3-24 depicts a proprietary bag filter. This filter has 35 separate filtration layers

Figure 3-24. Proprietary polypropylene bag filter for amine service. Each bag has
multiple layers with internal bypasses which provide 32 ft2 of filtration surface per bag.
Courtesy 3M Filter Products