Filter media entry

The blocking of the pores of the filter medium by particles is a complex phenomenon, partly because of the complicated nature of the surface structure of the usual types of filter media, and partly because the lines of movement of the particles are not well defined. At the start of filtration, the manner in which the cake forms will lie between two extremes — the penetration of the pores by particles and the shielding of the entry to the pores by the particles forming bridges. Heertjes(11) considered a number of idealised cases in which suspensions of specified pore size distributions were filtered on a cloth with a regular pore distribution. First, it was assumed that an individual particle was capable on its own of blocking a single pore, then, as filtration proceeded, successive pores would be blocked, so that the apparent value of the specific resistance of the filter cake would depend on the amount of solids deposited. 

Figure 6. Block drawing of the pilot installation for the production of trichloromethyl chloroformate by exhaustive photochlorination [39] 1 Dryer for gaseous Cl2 (H2S04 cone.). 2 Safety tank. 3 Thermoregulated immersion-type photochemical reactor. 4 Raschig column. 5 Cl2 detection system (1,2,4-trichlorobenzene). 6 Neutralization tank (20% NaOH). 7 Reservoir of 20% NaOH. 8 Buffer to atmospheric pressure (20% NaOH). 9 Active carbon filter. 10 Reservoir of crude trichloromethyl chloroformate. 11 Buffer to normal atmosphere via CaCl2 filter and direct entry for trichloromethyl chloroformate to be distilled. 12 Distillation flask with Vigreux column. 13 Exit to vacuum pump. 14 Solid NaOH filter before pump. 15 Cooling water alarm linked to power supply of the light source. 16 Medium pressure mercury arc. 17 Heater for distillation apparatus. 18 Magnetic stirrers. /T thermometer /P manometer.

It has been inferred by Tessier Campbell (1987) that a strong dependence of trace metal accumulation upon sediment characteristics does not imply that the main route of entry of trace metals is necessarily via ingestion of particulate metals it can be explained by a control through adsorption reactions of the dissolved trace metal concentrations in the solution to which the organisms are exposed, such as in the case of filter-feeders where high levels of trace metals were found associated with the gills and mantle (Tessier et al., 1984), For the latter pathway the study of the intermediate water phase - e.g., pore water - and the different forms and availabilities of metals in this medium seems to be particularly promising (Kersten Forstner, 1988). 

Modem developm ts aimed at avoiding such effects involve the use of high-porority, smaD-pore ceramic filters wdiich use the inherently high capillary pressure of such materials to avoid gas entry into the medium. This materially reduces the cost of con ression power in filters dewatered by conqiressed air. 

Filter tab Process parameters specific to the type of filter being simulated. Entries typically include filter area (or entries that allow its calculation), medium resistance and in the case of continuous filters, rotational or linear speed of the cloth. 

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