Page 310 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

280 Applied Process Design for Chemical and Petrochemical Plants

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l'lA .. 011 IQUAH
DUTCH TWIU
Equivalent DUTCH WIAVE
Standard
Nominal Rating Absolute Rating
Microns Microns
2 20
5 25
10 40
20 55
40 90
Figure 4-778. Porous sintered metal filter elements. By permission,
Figure 4-77A. Woven wire mesh filter cartridges. By permission,
AMF Corp., Cuno Div., Catalog MP-20.1. Pall Process Filtration Co.

Metals usually used are stainless steel, nickel, monel, lie unit; therefore, the economics involving the life
inconel, high nickel alloys, and special designs for unique span of each unit should be examined.
services.
Electrical Precipitators
The pressure drops for these units are typically low,
ranging from 0.2 to 10-15 psi. The woven wire mesh The electrical precipitator is a dry dust or liquid mist
runs even lower in pressure drops for the same or larg- removal unit which utilizes the ionization of the process
er flow rates. Consult the manufacturers for specific gas (usually air) to impart electrical charges on the sus-
application data. pended entrained particles and effect particle collection
by attraction to an oppositely charged plate or pipe. This
With some types of particles the porous metal tends type of unit is in use in services which are difficult for
to plug, but they can usually be backwashed or washed other types of entrainment removal equipment. Figures 4-
with a solvent or acid/alkali to remove the particles 79, 4-80, and 4-81 illustrate the usual fundamental action
from within the metal pores. This is one reason why of these units.
manufacturer's testing or plant testing can be impor- For these units the usual particle size for removal is
tant to the proper selection. Once the internal plug- greater than 2 microns with a loading rate of greater
gage has reached a point of reduction in flow-through than 0.1 grains/ cu ft, with a collection efficiency of
capacity, it must be discarded. The actual cost of this 99%±. The pressure drop is very low for a range of gas
type of cartridge is several times that of the non-metal- velocity through the unit of 100-600 ft/min [ 40].