Filter physical size

Fabric filters are limited by physical size and bag-life considerations. Some sacrifices in efficiency might be tolerated if higher air-cloth ratios could be achieved without reducing bag life (improved pulse-jet systems). Improvements in fabric filtration may also be possible by enhancing electrostatic effects that may contribute to rapid formation of a filter cake after cleaning. 

Electrostatic filters have been used in many coal-fired power stations, and they have been used in some biomass combustion facilities. Their use in medium- or large-scale gasification systems is limited. Electrostatic filters are best suited for large-scale operation due to their physical size and cost, and the primary impediment to their use in current gasification systems is an economic one. 

An air inlet area of at least 400 cm2 and a louvered exit of 75 cm2 are recommended for target capacity and physical size of the appliance. The efficient and quiet centrifugal fan unit is popularly used in air conditioners and air purifiers. It costs less than the other fan units of similar size and is easy to install and assemble. A fan with adjustable air deliver rate of 0 to 250 cfm will be used to draw air through the air filter, dehumidifier and purifier units. A smaller fan with air delivery rate of up to 10 cfm is needed for the regeneration... 

Filters can be divided into two types membrane (screen) filters and depth filters. Membrane filters, such as silver membrane filters, physically screen and retain particles on their surfaces. These filters have uniform pore sizes and are rated for absolute retention all particles larger than the pore size are retained. Depth filters, such as glass-fiber filters, consist of a matrix of fibers that form a tortuous maze of flow channels. The particulate fraction becomes entrapped by this matrix. These filters do not have a uniform pore size, and it is not possible to rate them for absolute retention. They are rated according to nominal pore size, which is determined by the particle size that is retained by the filter to a predetermined percentage. This percentage is usually given as 98 retention however, it can be as low as 90. ... 

The principles behind ultrafiltration are sometimes misunderstood. The nomenclature implies that separations are the result of physical trapping of the particles and molecules by the filter. With polycarbonate and fiberglass filters, separations are made primarily on the basis of physical size. Other filters (cellulose nitrate, polyvinylidene fluoride, and to a lesser extent cellulose acetate) trap particles that cannot pass through the pores, but also retain macromolecules by adsorption. In particular, these materials have protein and nucleic acid binding properties. Each type of membrane displays a different affinity for various molecules. For protein, the relative binding affinity is polyvinylidene fluoride > cellulose nitrate > cellulose acetate. We can expect to see many applications of the affinity membranes in the future as the various membrane surface chemistries are altered and made more specific. Some applications are described in the following pages. 

An example of a solid-liquid phase separation - often referred to as a mechanical separation - is filtration. Filters are also used in gas-sohd separation. Filtration may be used to recover liquid or sohd or both. Also, it can be used in waste-treatment processes. Walas [6] describes many solid-hquid separators, but we will only consider the rotary-drum filter. Reliable sizing of rotary-drum filters requires bench and pilot-scale testing with the slurry. Nevertheless, a model of the filtering process will show some of the physical factors that influence filtration and will give a preliminary estimate of the filter size in those cases where data are available. 

The physical size of interference filters is commonly 1 in. diameter by 5 to 10 mm thick, including protective mount. Optical properties important to Raman can usually be specified at the time of purchase, and their relative importance depends on the application. First, the transmission at the laser... 

Filters can be divided into two types membrane (screen) filters and depth filters. Membrane filters, such as silver-membrane filters or cellulose-acetate and cellulose-nitrate filters, physically sieve and retain particles on their surfaces. These filters have uniform pore sizes and are rated for absolute... 

The acid and base values of the surface functional groups of the samples were determined by Boehm s titration method [50]. To determine the acid value, O.lg of the sample was added to 100 ml of 0.1 M NaOH solution and the mixture was shaken for 24 h. The solution was then filtered through a membrane filter (pore size = 0.24 pm, nylon) and titrated with 0.1 M HCl. Likewise, the base value was determined by the reverse titration of the acid value. The specific surface areas (Sbet. [51]) of the samples were determined by gas adsorption. Physical adsorption of gases was used to characterize the CBs support, and the adsorbate used was N2 at 77 K with automated adsorption apparatus (Micromeritics, ASAP 2400). Prior to adsorption measurements, the samples were outgassed at 298 K for 6 h to obtain a residual pressure of less than 10 torr in high vacuum. To analyze the functional groups of CBs, the treated CBs were subjected to infrared (IR) spectroscopy (FTS-165 spectrometer, Bio-Rad Co.). 

Dielectric resonators have gained a position as key elements in microwave components for size reduction in microwave filters and as frequency stabilizing elements in oscillator circuits. Dielectric resonators reduce the physical size of resonant systems because the electromagnetic wavelength is shortened in dielectrics to 1/v of its value in free space, where Sr is the dielectric constant of the resonator. 

The initial advantage (1970s) of the quadrupole mass filter for GC/MS was its faster scan speed than sector-based instrumentation. In addition, the small physical size... 

The simplest physical property that can be exploited in a separation is size. The separation is accomplished using a porous medium through which only the analyte or interferent can pass. Filtration, in which gravity, suction, or pressure is used to pass a sample through a porous filter is the most commonly encountered separation technique based on size. 

The two steps in the removal of a particle from the Hquid phase by the filter medium are the transport of the suspended particle to the surface of the medium and interaction with the surface to form a bond strong enough to withstand the hydraulic stresses imposed on it by the passage of water over the surface. The transport step is influenced by such physical factors as concentration of the suspension, medium particle size, medium particle-size distribution, temperature, flow rate, and flow time. These parameters have been considered in various empirical relationships that help predict filter performance based on physical factors only (8,9). Attention has also been placed on the interaction between the particles and the filter surface. The mechanisms postulated are based on adsorption (qv) or specific chemical interactions (10). 

Example 1 Sizing a Dish Filter Eqiiipmeut physical factors, selected from Table 18-9 Maximum effective siihmergeuce = 28% maximum portion of filter cycle available for dewatering = 45%. (High submergence versions require tninnion seals, and their use is hmited to specific apphcations.)... 

Example 2 Sizing a Drum Belt Filter with Washing Equipment physical factors, selected from Table 18-9 Maximum effective submergence = 30% max. apparent suhm. = 35% max. arc for washing = 29% portion of cycle under vacuum = 75%. 

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