Environmental Engineering Reference
In-Depth Information
A great variety of iltration conditions does not let us use “universal ilters,” because every
case demands considering requirements to the puriied media. Thus, ilters for aerosol sampling
(analytical ilters) should meet other requirements than ilters for superine dust collecting.
On the analytical ilter, the largest amount of substance should be sampled during the least
time. Analytical ilters should not be as effective in aerosols capturing as inish ilters for gas
puriication, because the uncertainty of particle characteristic measurements for any analysis
technique is usually not less than several percent. Such analytical ilters should have relatively
low aerodynamical resistance in order to provide high productivity for aerosol sampling. And
inally, analytical ilters should consist of substances that will not hamper but instead facilitate
the process of sediment analysis.
Fibrous iltering materials appeared to be the most effective means for air puriication of
submicron aerosol particles because these materials—when low resistance is the same—have
the highest particle capturing eficiency compared with all other type materials. Fibrous iltering
materials are used for manufacturing industrial ilters designated for ventilating streams puriication,
for analytical ilters and respirators production. Filters manufactured of thin-layer high-porous
nanoiber-based membranes are used for superine puriication.
Thin-layer iltering materials with surface iltering mode are usually used at the inishing stage
in gas puriication. To prolong inish ilters' working lifespan they are preceded by preliminary
puriication ilters (pre-ilters) manufactured of coarse iber materials. Pre-ilters perform volume
iltering, that is, aerosol particle sediment forms on the ibers of all the iltering material.
To minimize pressure drop on the ilter, the gas low velocity does not exceed some cm/s, so the
particles having come into contact with ibers are not blown off.
Langmuire was the irst to describe main mechanisms of particle deposition on thin ibers and
to give the method to calculate ilter eficiency, so he can be ranked, as of right, as the founder of
the gas iltration theory as an independent trend of research [1]. Scientists of the Karpov Institute of
Physical Chemistry have contributed signiicantly to the development of the theory, their research
performed in the middle of the twentieth century [2-10] forms the basis of the modern theory.
Works on the theory of iltration [2-16] should be remarked as well. We should mention especially
the experimental works of Ya.I. Kogan, who developed in the 1950s an original device KUST [11]
that lets us detect nanoparticles less than 1 nm.
Nowadays thin-layer iltering materials made of or based on iberglass are widely used as ultraine
ilters. Filters containing ultraine iber materials are called in scientiic and technical literature
“HEPA ilters” (high-eficiency particulate air ilters). In Russia for purposes of ine puriication
there are used ilters of micron and submicron polymer ibers obtained by electrospinning
(electrostatic polymer solution spraying). These are so called Petryanov ilters (FP) [17,18], their
method of manufacturing developed by I.V. Petryanov, N.A. Fuchs, and N.D. Rosenblyum over
70 years ago [19]. Electrostatic charge on ibers makes these ilters very eficient. A valveless low
resistance and high-eficiency respirator “Lepestok” (petal) [20] is based on the FP.
In the latest decade there appeared growing interest to obtain ibers thinner than 0.1 μm by
electrospinning technique [21-24]. It arises from the theory of iltration that the resisting force of
a iber decreases with the iber diameter going down, whereas particle capture eficiency increases
[25]. Accordingly, the principal trend to improve ilters has always the tendency to manufacture
iltering material from the thinnest possible ibers. Filtering materials from nanoibers ensure
particle concentration decrease by nearly 10 orders of magnitude [26].
Amounts of puriied air have been growing incessantly, so it is reasonable to reduce power
consumption for air circulating through ilters. Thus, the main goal of iltration is not only to achieve
high purity of air at any cost, but to develop energy-conserving purifying systems, that is, systems
with high particle capturing eficiency, low pressure drop, and maximal lifespan.
The irst edition of this chapter was generally connected with analytical iltration. The present
chapter will illustrate the main results in research of superine air cleaning, obtained in the Karpov
Institute of Physical Chemistry or in collaboration with their scientists and published mainly in the
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