Backflushing filters

M. Backflushing filters for field processing of water samples prior to trace-element analyses. U. S. Geol. Survey VJater Resour. 

Cleanable Granular-Bed Filters The principal objective in the development of cleanable granular-bed filters is to produce a device that can operate at temperatures above the range that can be tolerated with fabric filters. In some of the devices, the granules are circulated continuously through the unit, then are cleaned of the collected dust and returned to the filter bed. In others, the granular bed remains in place but is periodically taken out of service and cleaned by some means, such as backflushing with air. 

Cake-discharge methods are the chief distinguishing feature among the various designs. That of the Industrial Filter Pump Hydro-Shoe, for example, removes cake from the tubes by filtrate backflushing assisted by the shocking action of a compressed-gas pocket formed... 

Air Backflush A configuration unique to microfiltration feeds the process stream on the shell side of a capillaiw module with the permeate exiting the tube side. The device is rim as an intermittent deadend filter. Eveiw few minutes, the permeate side is pressurized with air. First displacing the liquid permeate, a blast of air pushed back-... 

A common cause of unusually high pressure is a plugged in-line filter. In-line filters are found at the very beginning of the flow line in the mobile phase reservoir, immediately before and/or after the injector, and just ahead of the column. With time, they can become plugged due to particles that are filtered out (particles can appear in the mobile phase and sample even if they were filtered ahead of time), and thus the pressure required to sustain a given flow rate can become quite high. The solution to this problem is to backflush the filters with solvent or clean them with a nitric acid solution in an ultrasonic bath. 

Plugged in-line filter is a typical cause of unusually high pressure. The solution is to backflush the filter or otherwise clean it. 

SPEC was essentially able to market their Zr02-based ultrafiltration membranes to an already existing market in the sense that these membranes replaced polymeric UF membranes in a number of applications. They also developed a certain number of new applications. For Ceraver, the situation was different. When the Membralox membranes were first developed, microfiltration was performed exclusively with dead-end polymeric cartridge filters. In parallel to the development of inorganic MF membranes, Ceraver initiated the development of cross-flow MF with backflushing as a new industrial process. 

Filtration Size of filter bed Length of time before backflushing... 

The particulate matter (sand and silt) is removed by flowing upward through a gravel-and-sand filter bed. The coarser gravel is in the lower part of the bed. The filter beds are backflushed periodically with clear water to clean off the accumulated mud. 

In the last few years, a third type of microfiltration operating system called semi-dead-end filtration has emerged. In these systems, the membrane unit is operated as a dead-end filter until the pressure required to maintain a useful flow across the filter reaches its maximum level. At this point, the filter is operated in cross-flow mode, while concurrently backflushing with air or permeate solution. After a short period of backflushing in cross-flow mode to remove material deposited on the membrane, the system is switched back to dead-end operation. This procedure is particularly applicable in microfiltration units used as final bacterial and virus filters for municipal water treatment plants. The feed water has a very low loading of material to be removed, so in-line operation can be used for a prolonged time before backflushing and cross-flow to remove the deposited solids is needed. 

Backflushing A method for cleaning filters involving reverse flow throngh the membrane (or Back occasionally nsed for cleaning large-scale chromatographic columns. See... 

Plugged frit, pre-filter, guard column plugged inlet frit Backflush column/cartridge. Replace frit, pre-filter, guard column replace endfitting or frit assembly. 

A solution of cyclonona-1,2-diene (180 mg, 1.48 mol, prepared from cyclooctene ) and benzene (260 mg, 3.33 mmol) was placed into a 3.7-LVycor tube, the bottom portion of the tube was cooled to — 78 C, and the system was degassed by evacuating to ca. 0.15 Torr and backflushing with Nj several times. After evacuation to 0.15 Torr, the tube was allowed to warm to rt and was irradiated for 4.5 d in a Rayonet photoreactor fitted with 2537-A lamps. The reaction vessel was then cooled to — 78 °C and vented to N, and the product was collected with pentane. The pentane solution was filtered through neutral alumina and was concentrated under reduced pressure at 0"C to give 165 mg (92%) of a clear oil. Capillary GC analysis indicated 97% conversion to four major products. These were isolated on a preparative scale and identified as follows bicyclo[4.3.0]non-l(9)-ene (11 4%, / = 3.41 min) c -bicyclo(4.3.0]non-2-ene (9, 2%, / = 3.67 min) bicyclo[4.3.0]non-l-ene (10, 5%, = 3.90 min) and the product 3 yield 160 mg... 

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