Surface filters

Surface Filters. In surface filters (Fig. 2), the goal is to achieve separation on the upstream side of a relatively thin filter medium. The particles to be separated must be larger than the pores in the medium, ie, in strainers, membrane filters, etc, or the particles must approach the pores in large numbers and bridge over the pores, as in cake filters. 

Fig. 2. Schematic diagram of a surface filter, ie, the cake filtration mechanism.

Separation Efficiency. Similarly to other unit operations in chemical engineering, filtration is never complete. Some soflds may leave in the hquid stream, and some Hquid will be entrained with the separated soHds. As emphasis on the separation efficiency of soHds or Hquid varies with application, the two are usually measured separately. Separation of solids is measured by total or fractional recovery, ie, how much of the incoming solids is coUected by the filter. Separation of Hquid usually is measured in how much of it has been left in the filtration cake for a surface filter, ie, moisture content, or in the concentrated slurry for a filter-thickener, ie, solids concentration. 

To remove insoluble contaminants, various types of full-flow filters can be used. Two general types are usually selected surface filters and depth filters. Both types of filters are effective for the removal of particulate matter. 

Surface filters, if manufactured from the correct material, will not be affected by water in the oil. Water-resistant pleated-paper elements have much greater surface areas than the depth-type element and yield a much lower differential pressure when used as replacement elements in filters originally equipped with depth-type elements. Pleated-paper elements are available that will remove particle sizes down to a nominal one-half micron. 

At the Lipari Landfill site in New Jersey, the gas venting system installed in 1983 consisted of two underground 4-inch (10-cm) perforated PVC pipes and five vent risers. Two parallel PVC pipes were installed 200 feet apart prior to cap emplacement during the period of wall construction and were placed about 3 feet beneath the finished grade. The vent risers were connected to the buried manifold pipes and consisted of open pipe installed perpendicular to the underground pipes and the ground surface. Filters were not attached to the riser exit points (U.S. EPA, 1987). 

Energy consumption for energy-using devices and systems is typically the same year after year, if heat exchanger surfaces, filters, pipelines, and other plant items are kept clean. 

Bag An extended surface filter in the form of a pocket or bag. A typical example of a bag filter is a mineral fiber bag made up of three layers, in which the first layer acts as a prefilter, the second is for fine filtration, and the third prevents fiber migration from the material used. 

Pocket An extended-surface filter in which the medium is formed into pockets or hags through which the dust-laden gas flows. They may be supported by the air pressure or self-supporting. 

Filter elements may be divided into two classes surface and depth. Surface filters are made of closely woven fabric or treated paper with a uniform pore size. Fluid flows through the pores of the filter material and contaminants are stropped on the filter s surface. This type of filter element is designed to prevent the passage of a high percentage of solids of a specific size. 

Hydroxylamine is a powerful reducant, particularly when anhydrous, and if exposed to air on a fibrous extended surface (filter paper) it rapidly heats by aerobic oxidation. It explodes in contact with air above 70°C [1]. Barium peroxide will ignite aqueous hydroxylamine, while the solid ignites in dry contact with barium oxide, barium peroxide, lead dioxide and potassium permanganate, but with chlorates, bromates and perchlorates only when moistened with sulfuric acid. Contact of the anhydrous base with potassium dichromate or sodium dichromate is violently explosive, but less so with ammonium dichromate or chromium trioxide. Ignition occurs in gaseous chlorine, and vigorous oxidation occurs with hypochlorites. 

Several advanced filtration systems are finding applications in treating refinery wastewaters. Examples include the HydroClear filter (Zimpro, Rothschild, WI) and the Dynasand filter (Parkson Corporation, Fort Lauderdale, FL). The HydroClear filter employs a single sand medium (0.35-0.45 mm) with an air mix (pulsation) for solids suspension and regeneration of the filter surface. Filter operation enables periodic regeneration of the medium... 

Both biotin and strept(avidin) may be covalently attached directly to a variety of surfaces including glass, oxidized silicon, silicon wafers, gold surfaces, filter membranes, and even blood cell membranes using a large variety of methods. Examples of linkers used to immobilize streptavidin or biotin to sulfur-modified silicon surfaces are shown in Fig. 6. Besides direct immobilization, indirect immobilization may occur by binding biotinylated molecules that have been immobilized (Fig. 7). 

Pilz, T. Loeffler, F. (1995) Influence of adhesive and cohesive particle properties in filtration on surface filters. Chemie Ingenieur Technik Vol. 67, Nr. 6, p 745-749... 

Plate Any flat surfaced filter element. Usually found in horizontal plate filters. 

Figure 7. Deposition Velocity vs. Particle Aerodynamic Diameter, Type Surrogate Surface Filter Paper (23-28).

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