Page 264 - Gas Purification 5E

Mechanical Design and Operation of Alkanolamine Plants 249

Etched disk filter elements in amine service are usually rated for 10 microns absolute.
Each 10 micron rated element has 6 ft2 of external surface and, in amine service, fluxes
range from 0.5 to 5 gpm/ft2 depending on the amine solution particulate loading and size
(Farrell, 1990; Clark, 1996). A typical flux is 4.2 gpm/ft2 or 25 gpm of amine solution per
element (Clark, 1996). An etched disk filter housing can contain as many as seven elements
and can normally filter 175 gpm of amine solution. An etched disk filter element is depicted
in Figure 3-26a. Amine solution flows through the elements, and particles collect on the ele-

Figure 3-26a. Vacco Etched Disc element. Courtesy Pn Techno/ogies, Newbury Pa& CA

ment surface. The etched disk filter elements also trap a substantial fraction of smaller parti-
cles in the cake that forms on the element’s outer surface. As the thickness of the particulate
cake increases, the differential pressure across the filter rises. When the differential pressure
reaches 30 psi, the filter is automatically backflushed. First, the amine is forced out of the
filter housing by a water flush which reduces amine losses in the backflush cycle. After the
water flush, the system is then automatically backflushed with high pressure (150 to 350
psig) nitrogen, steam, or preferably fuel gas. Sludge is collected in a decanter and removed
periodically with a vacuum truck. The decanting drum minimizes amine losses by separating
recoverable amine from the sludge particles. See Figure 3-25. Since particulates are collect-
ed on the surface of the element, the elements are relatively immune to plugging and have a
40-year design life. With element life this long, etched disk filters can be installed in rich
amine service with minimal risk of operator exposure to lethal concentrations of H2S. An
etched disk filter for amine service (known as the Vacco Etched Disc filter) is manufactured
by PTI Technologies, Inc. of Newbury Park, CA.
Sintered metal fiber filters are virtually identical in design and operation to etched disk fil-
ters. See Figure 3-25 and the previous discussion. Sintered metal fiber filter elements con-
sist of layers of metal fibers which have been mechanically compressed and then sintered
together. Typical sintered metal fiber element life in amine service is 18 months (Clark,