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Mechanical Design and Operation of Alkanolamine Plants 245

able, it is difficult to compare and select filters for amine service. However, most filters used
in amine service have a nominal or absolute rating between 5 and 10 mimns. Also, mechani-
cal filtration of a 10 to 20% amhe solution slipstream is usually provided both upstream and
downstream of an activated carbon filter. The large mechanical filter upstream of the activat-
ed carbon filter is usually designed to remove smaller particles (e.g., 5 micron), and the small-
er downstream filter is rated for larger particles, (e.g., 10 micron) (Calgon, 1986; Keaton and
Bourke, 1983). Rating the downstream filter for a larger particle size ensures that particles
bypassing the upstream filter will not plug the smaller downstream filter.
When the lack of an industry-wide filtration standard is coupled with a tendency to pur-
chase filters on the basis of price, it is not surprising that there is a general tendency to
undersize amine filters (Ballard and von Phul, 1991). A severely undersized filter that
requires frequent filter element change out can seriously impact operator acceptance and lead
to long-term operability and maintenance problems. Therefore, the designer is urged to size
amine filters conservatively, as a filter that is too large is far superior to one that is too small.
Table 3-7 summarizes recommendations from various sources. The relative merits of vari-
ous filter selections follow.

String- Wound Cotton Catiridge Filters

String-wound cotton cartridge filters are probably the most common filter used for amine
solution filtration since they have lowest replacement cost. However, string-wound cotton
cartridge filter changeouts may require considerable operating labor when these filters are

Table 3-7
Amine Mechanical Filter Sizing Criteria from Various Sources for Several Filter Types
Rating, Slipstream Max. Flux FilterLife, Source I
Filter Type micron(4) YO AP,psi gpdft2(1) months
String-wound cotton - 17% - 0.65 0.25-2.0 Scheinnan, 1973A
String-wound cotton - - - 1 -3 - Fabio, 1992
String-wound
polypropylene 5pN 5-100 30 1-3 - Clark, 1996
boat, pressure
leaf type <1pN 12% - ~1.0 0.25-0.50 Scheirman, 1973A
Precoat, vertical
tubular <1pN - - 4.0 0.5-1.0 Scheirman, 1973A
Sintered metal fiber lop4 10-15 30 4.2 2-8 hrs (3) Clark, 1996
Etched disk lop4 8-16 30 4.2 (2) 2-8 hrs (3) Farrell, 1990;
Clark, 1996
Notes:
I. Based on external surface.
2. Each element has 63.2 of external surface. There are a maximum of 7 elements (42ft2) per housing. Each
housing typically filters I75 gum (4.2 x 42).
3. Typical time beiween automatic backwash cycles.
4. ‘*A*’ denotes absolute rating. “N denotes nominal rating.