Filters classification

To save energy, the filter is dimensioned in normal ventilation plants, often with a lower final pressure loss than indicated by the classification, and the filter does not achieve the intended filter classification. For reasons of hygiene, the filter is replaced after a certain period of time, rather than a specific final pressure loss. 

Note The filter classifications referred to above relate to the EN1822 and EN779 test standards (EN 779 relates to filter classes G1 to F9 and EN 1822 relates to filter classes H10 to U16). 

Where the powders are not highly potent, final filters on a dust exhaust system should be fine dust filters with a filter classification of F9 according to EN779 filter standards. 

Filter classifications are marked on the filter or filter package. These classifications are N-Series Not Oil Resistant (approved for non-oil particulate contaminants such as dust, fumes, or mists not containing oil) R-Series Oil Resistant (approved for all particulate contaminants, including those containing oil such as dusts, mists, or fumes—time restriction of 8 hours when oils are present) and P-Series Oil Proof (approved for all particulate contaminants including those containing oil such as dust, fumes, or mists). (See manufacturer s time use restrictions on packaging.)... 

Figure 3 Classification of detection for various orientation - analysis of the influence of the use of filters (figure 4) ...

Insofar as they are used to purify other products, several processes used in the refinery fall under the classification of dewaxing processes however, such processes must also be classified as wax production processes (2). Most commercial dewaxing processes utilize solvent dilution, chilling to crystallize the wax, and filtration (28). The MEK process (methyl ethyl ketone—toluene solvent) is widely used. Wax crystals are formed by chilling through the walls of scraped surface chillers, and wax is separated from the resultant wax—oil—solvent slurry by using fliUy enclosed rotary vacuum filters. 

In a batch process, NaOH is chlorinated in the presence of recycled neutral Ca(OCl)2 mother Hquor. After separation of salt, lime slurry is added and chlorinated (205). The Ca(OCl)2 2H20 crystals are recovered by filtration. In another version, classification of the Ca(OCl)2—NaCl slurry gives a Ca(OCl)2-rich fraction that is filtered and the filtrate recycled along with the NaCl-rich fraction to the first chlorinator (206). Also, 50% NaOH and soHd slaked lime are used in the second chlorination. 

These methods of classification are not mutually exclusive. Thus filters usually are divided first into the two groups of cake and clarifying equipment, then into groups of machines using the same land of driving force, then further into batch and continuous classes. This is the scheme of classification underlying the discussion of filters of this subsection. Within it, the other aspects of operating cycle, the nature of the sohds, and additional factors (e.g., types and classification of filter media) will be treated explicitly or implicitly. 

Various types of filter media and the materials oi which they are constructed are surveyed extensively by Purchas Industrial Filtration of Liquids, CRC Press, Cleveland, 1967, chap. 3), and characterizing measurements (e.g., pore size, permeabihty) are reviewed in detail by Rushton and Griffiths (in Orr, op. cit., chap. 3). Briefer summaries of classification of media and of practical criteria for the selec tion of a filter medium are presented by Shoemaker (op. cit., p. 26) and Purchas [Filtr Sep., 17, 253, 372 (1980)]. 

TABLE 18-11 Classification of Filters According to Duty and Slurry-Separation Characteristics ... 

The collection technique involves the removal of particles from the air stream. The two principal methods are filtration and impaction. Filtrahon consists of collecting particles on a filter surface by three processes—direct interception, inertial impaction, and diffusion (5). Filtration attempts to remove a very high percentage of the mass and number of particles by these three processes. Any size classification is done by a preclassifier, such as an impactor, before the particle stream reaches the surface of the filter. 

Mass concentration units for ambient measurements are mass (/xg) per unit volume (m ). Size classification involves the use of specially designed inlet configurations, e.g., PMjq sampling. To determine mass concentration, all the particles are removed from a known volume of air and their total mass is measured. This removal is accomplished by two techniques, filtration and impaction, described in Chapter 13. Mass measurements are made by pre-and postweighing of filters or impaction surfaces. To account for the absorption of water vapor, the filters are generally equilibrated at standard conditions T = 20°C and 50% relative humidity). 

Filter aids should have a narrow fractional composition. Fine particles increase the hydraulic resistance of the filter aid, whereas coarse particles exhibit poor separation. Desired particle-size distributions are normally prepared by air classification, in which the finer size fractions are removed. 

Develop a general classification system for dry bulk chemical additives and filter aids based on ease of feeding to a filtering machine. 

EN 779 1993 in principle contains two different test methods. The filter is tested both with untreated outdoor air and with the addition of synthetic dust. In the first case, the filter s dust spot efficiency is determined, i.e., its capacity to clean normal outdoor air. In the second case, the filter s arrestance is measured, i.e., its capacity to separate synthetic dust. The average value for dust spot efficiency or arrestance during the course of the test is used for classification of the filter. 

In EUROVENT 4/9 the dust spot efficiency has been replaced by measurement of the degree of separation of particles within the 0.2-3 pm range, with a particle size of 0.4 pm used for classification of the filter. 

Classification is based on laboratory tests with synthetic dust and does not provide a basis for calculation of the life of air filters or assessment of the filter s performance in actual application. Moreover, the dust-holding capacity and average efficiency for each classification vary with final pressure loss and... 

Efficiency, minimum The minimum efficiency obtained during the performance classification of a filter. 

Minimum filter efficiency The value of a filter s efficiency relating to its performance classification under specified operating conditions. See also Maximum penetrating particle size. 

Cascading effects Check valve Clogged (of filter) Consensus standard Conservation vent Dike, berm Discharge valve Division (in electrical area classification) Downspout Expansion joint Explosion proof Faucet... 

Absolute-fault limits are typically based on industrial standards for specific classifications of machinery. Generally, these standards are based on a filtered broadband limit and are not adjusted for variables such as speed, load or mounting configuration. However, vibration amplitude and its severity depend on speed and load. Therefore, alert/alarm limits must be adjusted for variations in both of these critical factors. 

Do NOT wash away into sewer. Sweep spilled substance into containers if appropriate, moisten first to prevent dusting. Carefully collect remainder, then remove to safe place. Personal protection P3 filter respirator for toxic particles. Unbreakable packaging put breakable packaging into closed unbreakable container. Do not transport with food and feedstuffs. EU Classification Symbol T, N R 21-25-36/38-48/23/25-50/53 S 1/2-35-36/37/39-45-60-61 Note A, 1 UN Classification UN Hazard Class 6.1 ... 

In summary, such simple classification schemes for drug-likeness can, in a very fast and robust manner, help to enrich compound selections with drug-like molecules. These filters are very general and cannot be interpreted any further. Thus, they are seen rather as a complement to the more in-depth profiling of leads and drugs by using molecular properties and identifying trends in compound series. 

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