Filters for Gases

Uses-for ensuring steady plant operation, to minimise deposit of ash on heat transfer surfaces/active catalyst surface etc. 

Maximum and minimum temperature of gases Maximum and minimum pressure of gases Composition on volume percentage basis 

Suspended particles their concentration mgs/nm, size distribution, (minimum and maximum size) attrition loss of fdter media during cleaning must be minimum 

Whether they have acidic or oily or sticky nature of gas mixture whether it contains toxic, inflammable or explosive gases 

Separation efficiency required for the solid particles (especially when they are of 

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In closing, let us mention that successive freeze-drying operations can be done on the same sample to prepare intermingled structures displaying original properties as selective filters for gases and liquids. In this process, aqueous and nonaqueous solvents can be used simultaneously or in successive steps [4]. With the restriction quoted above—relative to the potential toxicity of residual solvents—these techniques can offer wide new possibilities in the chemical field. 

General purpose compact forms of filters for gases and liquids, also limited application in filter presses for facing filter cloth. 

Instrument Designs for Infrared Absorption The simplest instrument for IR absorption spectroscopy is a filter photometer similar to that shown in Figure 10.24 for UV/Vis absorption. These instruments have the advantage of portability and typically are used as dedicated analyzers for gases such as ITCN and CO. 

NOTE These data were obtained when filtering air at ambient conditions. For gases other than atmospheric air, the Api values predicted from Table 17-5 should be multiplied by the actual gas viscosity divided by the viscosity of atmospheric air,... 

Clean Air Machine Corp. Air purifiers - commercial site offers customized filters for specialty applications aimed at removal of microscopic particulates and gases. http //aco.ca/tibbits/index. html... 

Depending on the test method and test result, particle filters are classified as coarse, fine, HEPA, and ULPA filters (Table 9.2). Electrofilters are usually included in the fine filter group. Chemical filters are used for gases. 

Filters for both gases and liquids, including air filters. Their performance should be checked. 

In the Boliden process, developed by Boliden Kemi Company in Sweden, filter beds containing amorphous selenium are used to filter the gases. Mercury in the gas is deposited in the filter as mercury selenide (HgSe). Alternatively, the gases can be scrubbed with a slurry of amorphous selenium, whereupon mercury is precipitated as HgSe. Activated carbon filters are also useful for absorbing mercury vapor from the gas. 

In the course of operation, filtration efficiency will be low until a loose floe builds up on the fabric surface and it is this which provides the effective filter for the removal of fine particles. The cloth will require cleaning from time to time to avoid excessive build-up of solids which gives rise to a high pressure drop. The velocity at which the gases pass through the filter must be kept low, typically 0.005 to 0.03 m/s, in order to avoid compaction of the floe and consequently high pressure drops, or to avoid local breakdown of the filter bed which would allow large particles to pass the filter. 

If possible, media should be sterilized in situ. In-line sterilizing filters for routine addition of gases, media, acids or alkalis, defoaming agents, etc., to fermenters should be used where possible. 

As discussed below with respect to measurement techniques for individual compounds, the filter material is optimized for the compound of interest. For example, nylon has been found to be effective for the adsorption of gaseous HNO-, (Spicer, 1977). However, care must be taken that the filter does not also remove other gases simultaneously that are measured downstream of the filter. For example, SOz has been shown to be taken up by nylon filters, forming sulfate, with the extent of conversion being quite variable (e.g., Chan et... 

The first practical applications of adsorption were based on the selective removal of individual components from then- mixtures using other substances. The first filters for water treatment were installed in Europe and the United States in 1929 and 1930, respectively. Activated carbon was recognized as an efficient purification and separation material for the synthetic chemical industry in the 1940s. By the late 1960s and early 1970s, activated carbon was used in many applications for removing a broad spectrum of synthetic chemicals from water and gases. 

In purification filters for purifying liquids or gases, sometimes a loose bed of grains of an adsorbent material, such as activated carbon, is located between two porous walls which confine the grains. Since there is no cohesion within the granular material, the flow and filter use period are difficult to control. 

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