Filter system

Ensurance of the cleanliness of the end product is very important. Every batch therefore has to be filtered at least one before or during filling. 

Sieves. To clean, paint must be screened. The simplest method containing undesirably coarse particles is to sieve it through metal (steel) or plastic fabrics of specific mesh size. Polyamide screen bags are employed to facilitate handling. Metal fabric is fastened or soldered onto cylindrical metal frames. 

Vibrating screens are used for products (e.g., metallic effect paints) that are difficult to screen. The screens are vibrated horizontally or vertically and the material flows rapidly through the sieve. 

Filters. In the production of paints inpurities sometimes occur which have to be eliminated by filtration. The simplest method is filtration through bag filters made of sintered synthetic micro fibres (Fig. 7.13). The bag filters can be installed in metal filter housings with closable, sealable covers. A perforated sheet-metal basket protects the filter bag against overloading. 

If impurities cannot be removed with bag filters, filter cartridges or candles are used (Fig. 7.14). The filter cartridges are inserted in individual housings or, in large-scale equipment, up to 24 cartridges are inserted side by side or one above the other and held in place with quick-release mechanisms. Resin-bonded, sintered synthetic micro fibres and metals are used as filter material. The fineness of the filter fabric (5-100 pm) determines the filtration effect. 

Whilst entering the vacuum conveyor, the conveyed material is decelerated by the increased diameter of the receiver vessel and therefore the main bulk material is collected at the bottom section of the conveyor. 

According to the particle size distribution a more-or-less small fine dust is moved towards the filter unit which is located at the top, below the vacuum source. The filter unit should achieve a high separation rate (dustless conveying) whilst maintaining the pressure difference low. With modern filters the exhaust air from the vacuum pump can be blown in the environment whereas with toxic, potent or cancerous powders further treatment is necessary. Precise demands are given by filter classes, for example from BIA [5] (German employer s liability insurance association) or other authorities (Table 17.1). 

The extraordinary variety of applications for vacuum conveyors made it necessary to maintain the modular and flexible design even for the filter system. A filter change should be possible in a very short time without any tools. This is only possible in combination with the modular receiver vessels. 

In chemical processes filter out of sintered polyethylene, polyester, PTFE, stainless steel and cellulose are used. With the standard cyclic operation the discharging time is used for an efficient filter cleaning with backblowing air shocks. Filter blockages can be avoided as well as maintenance. 

VOLKMANN GmbH - VakuumtechnIk - 59494 Soest - www.volkmann.lnfo 

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Pollutants. The problems posed by ak pollutants are very serious. Within a museum, measures can be taken to remove harmful substances as efficiently as possible by means of the installation of appropriate filter systems in the ventilation equipment. Proposed specification values for museum climate-control systems requke filtering systems having an efficiency for particulate removal in the dioctyl phthalate test of 60—80%. Systems must be able to limit both sulfur dioxide and nitrogen dioxide concentrations <10 /ig/m, and ozone to <2 /ig/m. ... 

A computer-controlled bandpass filter system controls the size of the acquired spectral window. Typically, this is set to about 120% of the desired sweep width. Only frequencies within these limits are allowed to reach the ADC. Those frequencies outside the limits would only contribute to the noise in the final spectmm. The need for this system is dictated by the nonselective nature of the excitation rf pulse. 

Cleaning is frequently aided mechanically. Foam balls scour the center of tubes, and hoUow-filter systems can be back-flushed. HoUow fibers and membranes attached to rigid supports can be back-pressured, thereby eliminating the pressure drop that holds redispersed films on the membrane surface. 

TABLE 25-17 Advantages and Disadvantages of Fabric-Filter Systems... 

A differential pressure switch set to alarm when the pressure drop reaches a predetermined point protects against the loss of oil flow. In addition to the differential pressure switch, a two-way, three-port valve with a pressure gauge is piped in parallel with the differential pressure switch for accurate indication of inlet and outlet oil filter pressure. When a single transflow valve is used with a cooler-filter installation, the differential pressure switch and pressure gauge assembly should span the cooler-filter system. 

The prime design objeetive of the filter system is to proteet the gas turbine. The performanee of the gas turbine inlet-air filter system has important and far-reaehing influenees on overall maintenanee eosts, reliability, and availability of gas turbines. There are three major results of improper air filtration (1) erosion, (2) fouling of the axial-flow eompressor, and (3) eorrosion of the gas turbine hot-gas path inlets. The importanee of the inlet-air filter, as it relates to eaeh of these three phenomena, ean be appreeiated if... 

All the energy-filter systems referred to above are incorporated into the electron-microscopic column, usually between the diffraction lens and the following intermedium lens. They are, therefore, known as in-column filters, which are also commer-... 

Cartridge collectors perform very effectively in many different applications. Common applications of cartridge filter systems with pulse jet cleaning are comparable to baghouses described earlier. In addition to these applications, cartridge collectors can be used in any process where dust is generated and can be collected and ducted to a central location. 

Pressure filters are worth noting. These are usually set up in the form of steel cylinders positioned vertically. Another variation consists of using horizontal filtration groups. This has the drawback that the surface loading is variable in the different layers of the filter bed moreover, it increases with greater penetration in the filter bed (the infiltration velocity is lowest at the level of the horizontal diameter of the cylinder). The filter bottom usually consists of a number of screens or mesh sieves that decrease in size from top to bottom or, as an alternative, perforated plates supporting gravel similar to that used in the filter bottoms of an open filter system. 

Downstream side The side of a product stream that has already passed through a given filter system portion located after the filtration unit. 

Electrostatic precipitator A filtering system for the removal of particles from an air stream by giving them an electrical charge. The charged particles are attracted to plates of opposite polarity onto which they adhere. The precipitators are classified as... 

Figure 9.8 Crystallizer-filter system optimization (Rajagopal etal., 1988)...

Effective inlet air filtration is required to ensure satisfactory operation of the engine. The location of the unit determines the most appropriate filter system to use. Desert environments where a large amount of sand particles could be expected in the ambient air may use an automatic roll type of filter that allows new filter material to be rolled in front of the inlet without frequent shut-downs to change filters. Arctic or extremely cold locations may use pad type filters, snow hoods to prevent blockage, and exhaust recirculation to prevent icing. Filter assemblies for offshore marine environments may include weather louvers, demister pads, and barrier elements for salt and dirt removal. Screens may be u.sed for insect removal prior to filtration in areas with bug problems. 

This three-dimensional cutaway drawing illustrates the filtering operation of the QAF9 filter-bag pressure filter system, showing the flow patterns of unflltered liquid through a preselected micronrated felt filter bag which renders the desired quality of filtered product. 

Figure 4-73. Flow scheme for GAF filter-bag pressure filter system for liquids. Courtesy of GAF Corporation, Chemicetl Group, Greenwich, Conn.

Figure 4-78. Tubular in-line pressure filter with reusable elements. The flow unfiltered liquid enters the inlet port, flows upward, around, and through the media, which is a stainless steel or fabric screen reinforced by a perforated stainless steel backing. Filtered liquid disch lrges through the outlet (top) port. Because of outside-to-lnside flow path, solids collect on the outside of the element so screens are easy to clean. By permission, Ronningen-Petter Engineered Filter Systems, Bulletin RP-2.

Filter systems designed by acoustical principles. Figure 13-lD and 13-lE. 

The first consideration for establishing a filter system is to determine what frequencies will exit for a given compressor unit ... 

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