UFC 3-280-04
17 DEC 2003
5-3.3.4.4 In this way, a x of 1 represents 0% efficiency at size x and a x of 2 repre-
sents 50% efficiency at size x. Therefore, a beta ratio of 10 = 10 means that 90% of
particles 10 microns and larger will be removed by the filter, whereas, a Beta ratio of 10
= 5000 means that 99.98% of particles 10 microns and larger will be removed (Swiez-
bin, 1996).
5-3.3.5 Fluid Viscosity. Filter type, area, and pretreatment needs are all influenced
by pressure drops associated with fluid viscosity. Doubling the viscosity will double the
pressure drop. For coarse filtration and high viscosities above 3000 centipoises (cP)
(7230 lb/hr ft), metal mesh cartridges be used because of their high permeability and
strength. Non-pleated cartridges have been used at viscosities of 20,000 cP (48,400
lb/hr ft) but at low flux rates of <0.2 L/s per cartridge (0.3 gpm). To reduce pressure
drops caused by fluid viscosity, filter area can be increased.
5-3.3.6 Type and Quantity of Contaminant. The type and physical characteristic of
the contaminant influences filter type and area. Hard, irregular, inert type particles are
more easily filtered with cartridge filters than are gelatinous materials. Contaminants of
an organic nature influence cartridge selection, depending on relative concentrations. At
low levels the cartridges may fail on differential pressure before the solvent breaks
down the structural integrity of the filter. At higher organic loadings, the structural integ-
rity may be impaired prior to failure because of solids loading and pressure drop. Ex-
cessive pressure and flow rate may cause the pores of the filter to become misshapen
and widen, possibly resulting in poor filter performance and effluent quality.
5-3.3.7 Maximum Allowable Cartridge Pressure Drop. This is a parameter often
specified by the manufacturer and represents the maximum operating pressure at which
the filter will fail structurally. Often overlooked, pressure drops are those associated with
housing and system hardware that should be considered when selecting a filter for
available pressure drop. Filter selection should minimize the ratio of hardware losses to
total available pressure drop. Typically, the initial clean differential pressure will be <5
psid. Once the filter begins to blind. the differential pressure will begin to increase. Dis-
posable cartridge filters can generally withstand 60 to 80 psid in the forward direction
before structural failure. If higher pressures are present, then metal filters or metal filter
cores should be considered (Swiezbin, 1996).
5-3.3.8 Required Throughput and Flow Rate. Throughput per cartridge is best
determined by laboratory tests, which are relatively easy to do and are specified by the
manufacturer. It is important that the test fluid is representative of the waste stream to
be treated. From pilot or bench scale tests, throughput per cartridge can be determined
and the surface area needed for filtration to maintain pressure drop across the car-
tridges can be optimized without affecting the structural integrity of the filters. Depend-
ing on the waste stream to be treated, throughput per cartridge can range from 0.1 to
1.0 (L/min.)/m2 (0.25 to 4.0 gpm/ft2). The actual throughput is affected by fluid viscosity
and filter media pore size. Generally, all of the factors above influence filter throughput
and they must all be considered when sizing the system. For new facilities, waste
stream parameters need to be estimated and pilot testing is generally not practical.
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