Filter applications

In many applications of filters for roads, railways, levees, dikes and other embankments, the filter is placed more or less horizontally and then covered by fill. Significant loads for this type of installation are overburden and traffic, especially during construction. The latter is discussed in Section 12.10 (installation impacts). 

Any vertically installed geotextUe, besides the mentioned trench drain, eg, filter and drain sheets adjacent to walls, edge drains or others, are to a lesser extent exposed to traffic, compaction or overburden loads, because the lateral earth pressure is much less than the vertical load. In these cases damage may occur as a result of compaction of the fill because the differential settlement of the fill and the adjacent soil will create shear stress in the geotextile, which might exceed its strength. 

In ponds, lakes, canals and rivers, bank protection with hard armour is needed when the hydraulic load is prone to creating scour and erosion. Because the interaction of 

Care must be taken with the installation under water because the filter sheet will float and will not sink into the desired position under its own weight. Even when the fabric is polyester, a material with a density higher than water, it will float owing to air bubbles trapped between the fibres. Placement can be eased with a so-called sandmat , two geotextile layers with a sand fill of 5—9 kg/m kept between. The two sheets are needlepunched or sewn in short distances to reach a good shear resistance and to keep the sand fill in place during the placement procedure and on slopes under working loads. 

The filter sheet must be submerged carefully to avoid folds and wrinkles. In greater depths the correct placement of a geotextile filter requires special equipment. The simplest equipment to place a single roll would be a spreader bar, preferably with a hydraulic drive. Care must be taken that the necessary overlap of the sheets is guaranteed. Further equipment is discussed by Heibaum (2008). 

---

Parquet, The E/ectroscrubber Filter Applications and Particulate Collection Performance, EPA-600/9-82-005c, p. 363,1982. 

Because of their inherently high efficiency on dusts in all particle-size ranges, fabric filters have been used for collection of fine dusts and fumes for over 100 years. The greatest limitation on filter application has been imposed by the temperature limits of available fabric materials. The upper limit for natural fibers is about 90°C (200°F). The major new developments in filter technology that have been made since 1945 have followed the development of fabrics made from glass and synthetic fibers, which has extended the temperature limits to about 230 to 260°C (450 to 500°F). The capabihties of available fibers to resist high temperatures are still among the most severe limitations on the possible applications of fabric filters. 

The filter press has the advantage of simplicity, low capital cost, flexibility, and ability to operate at high pressure in either a cake-filter or a clarifying-filter application. Floor-space and headroom needs per unit of filter area are small, and capacity can be adjusted by adding or removing plates and frames. Filter presses are cleaned easily, and the filter medium is easily replaced. With proper operation a denser, drier cake compared with that of most other filters is obtained. 

Table 1 lists typical filtering applications and operating ranges. The simplest and oldest types of designs include a series of thin metal disks that are 3-10 inches in diameter and set in a vertical stack with very narrow uniform spaces between them. The disks are supported on a vertical hollow shaft and fit into a closed cylindrical... 

The filter application is typically applied to handling streams containing less than 100 to 200 mg/Liter suspended solids, depending on the required effluent level. Increased-suspended solids loading reduces the need for frequent backwashing. The suspended solids concentration of the filtered liquid depends on the particle size distribution, but typically, granular media filters are capable of producing a... 

Reference [55] provides additional details beyond the bag filter applications, and Reference [60] provides a technical and analytical review of flowing gas-solids suspensions. 

Filter application Continuous vacuum filters Multicompartment drum Single compartment drum Top feed drum Scroll discharge drum Tilting pan Belt Disc... 

Having recently won the 1999 Product Achievement Award for Filter Applications from Filtration + Separation magazine, the SRS has become the state-of-the-art technology for sulphate removal. Development of the SRS enhances Kvaerner Chemetics record as a provider of cost-effective and environmentally friendly solutions for the chlor-alkali and sodium chlorate industries. 

Fibers for filter applications can be produced with diameters smaller than it is practical to obtain with granules. Consequently, most concern with filtration of fine particles has been focused on fibrous-... 

Table 7.3. Operating data for some vacuum filter applications... 

TABLE 11.17. Operating Data of Some Vacuum Filter Applications... 

Potential applications of photorefractive materials are manifold. To date, demonstrated effects include real time holography, correlation filtering, and various "novelty filter applications, one of which is the development of a microscope which distinguishes moving objects (such as living cells) from a stationary background.(149) The latter application employed BaTiC>3 as the active material. 

As the reflected radiation is emitted from the sample in a random direction, diffusely reflected radiation can be separated from, potentially sensor-blinding, specular reflections. Common techniques are off-angle positioning of the sensor with respect to the position(s) of the illumination source(s) and the use of polarisation filters. Application restrictions apply to optically clear samples with little to no scattering centres, thin samples on an absorbing background and dark samples. In either of these cases, the intensity of radiation diffusely reflected off such samples is frequently insufficient for spectral analysis. While dark objectives remain a problem, thin and/or transparent samples can be measured in transmission or in transflectance. 

Dielectric resonators are extensively used in mobile communications technology. As far as selectivity and temperature drift are concerned the requirements for hand-held units are far less demanding than for those used in the base stations, and for the more general filter applications. For example, for... 

Other nonfluorinated /3-diketonates such as Ba(dpm)2 have been used in conjunction with HF, in one case by sequential reaction using atomic layer deposition (ALD).311 This method also gave high-quality fluoride films and enabled deposition of multilayer stacks for optical filtering applications. 

Applications that have received attention, and the material properties that enable them, are shown in Figure 27.1. These applications are reviewed in detail in Waser and Ramesh. Decoupling capacitors and filters on semiconductor chips, packages, and polymer substrates (e.g., embedded passives ) utilize planar or low aspect ratio oxide films. These films, with thicknesses of 0.1 to 1 J,m, are readily prepared by CSD. Because capacitance density is a key consideration, high-permittivity materials are of interest. These needs may be met by morpho-tropic phase boundary PZT materials, BST, and BTZ (BaTi03-BaZr03) solid solutions. Phase shifters (for phase array antennas) and tunable resonator and filter applications are also enabled by these materials because their effective permittivity exhibits a dependence on the direct current (DC) bias voltage, an effect called tunability. 

Hugon O, Sauvan M, Benech P, Pijolat C, and Lefebvre F. Gas separation with a zeolite filter, application to the selectivity enhancement ot chemical sensors. Sens Actuators B 2000 67(3) 235-243. 

Hayashi, K. et al., Membrane filter applications for cmd separation from radioactive waste water generated in LWR power plants. In proceedings of Symposium on On-site Management of Power Plant Wastes, Zurich, 1979, OECD/NEA, Paris, 229, 1979. 

---