Static filtration

A static leaf filter is used for cleaning machine tool coolants. These are used on the suction side of a pump circulating system, with the same pump employed for withdrawal of the filtrate as for backdushing the filter elements. SoHds in this case are removed from the sump by a scraper conveyor. 

The scale-up of filtration centrifuges is usually done on an area basis, based on small-scale tests. Buchner funnel-type tests are not of much value here because the driving force for filtration is not only due to the static head but also due to the centrifugal forces on the Hquid in the cake. A test procedure has been described with a specially designed filter beaker to measure the intrinsic permeabiHty of the cake (7). The best test is, of course, with a small-scale model, using the actual suspension. Many manufacturers offer small laboratory models for such tests. The scale-up is most reHable if the basket diameter does not increase by a factor of more than 2.5 from the small scale. 

Belt Presses Belt presses were fiiUy described in the section on filtration. The description here is intended to cover only the parts and designs that apply expression pressure by a mechanism in adchtion to the normal compression obtained from tensioning the belts and pulling them over rollers of smaller and smaller diameters. The tension on the belt produces a squeezing pressure on the filter cake proportional to the diameter of the rollers. Normally, that static pressure is calculated as P = 2T/D, where P is the pressure (psi), T is the tension on the belts (Ib/hnear in), and D is the roller diameter. This calculation results in values about one-half as great as the measured values because it ignores pressure created by drive torque and some other forces [Laros, Advances in Filtration and Separation Technology, 7 (System Approach to Separation and Filtration Process Equipment), pp. 505-510 (1993)]. 

If the solvent is nonconductive, additional precautions are needed. These are (1) continuous draining to prevent build-up of charged liquid in the tank and (2) measures to avoid accumulation of solids if the solvent is recirculated. Measures to separate solids before recirculation, such as filtration, may increase static generation (5-3.5). 

Vansteenkistle, P. Prevention of Static Charges in Dust Filter Fabrics with Stairdcss Steel Fibers. Filtration Separation (Mar./Apr. 1981), pp. 13.5-139. 

The invasion of particles can be eliminated either by using solids-free systems or by formation of a competent filter cake on the rock surface. If the components forming the filter cake are correctly chosen and blended, they will form a very effective downhole filter element. This ensures that colloidal sized clays or polymeric materials are retained within the filter cake and do not enter the formation. Further protection is provided by ensuring that a thin filter cake is formed due to low dynamic and static filtrate losses. Thus, the cake may be easily removed when the well is brought into production. Additionally, the filter cake can be soluble in acid or oil. 

In the work reported here (in the 150 m3 room) it was found that if an ion generator was operated without the assistance of a filtration device an effect could be detected only if the generator was of the open field type, i.e. if the generator not only produces ions but also exposes the surrounding air to a static field. Typical values for a 150 m3 room were for both ERF and DRF 0.8-0.9. If the ion generators were operated simultaneously with a filtering device the performance of the filters were always increased typically by 5-10 %. 

One could go on with examples such as the use of a shirt rather than sand reduce the silt content of drinking water or the use of a net to separate fish from their native waters. Rather than that perhaps we should rely on the definition of a chemical equilibrium and its presence or absence. Chemical equilibria are dynamic with only the illusion of static state. Acetic acid dissociates in water to acetate-ion and hydrated hydrogen ion. At any instant, however, there is an acid molecule formed by recombination of acid anion and a proton cation while another acid molecule dissociates. The equilibrium constant is based on a dynamic process. Ordinary filtration is not an equilibrium process nor is it the case of crystals plucked from under a microscope into a waiting vial. 

The SpinTek system does not destroy the wastes but rather separates and concentrates them. Thus, additional treatment technologies may be required. In addition, the vendor points out that the system is not for every application in that it is designed for tough applications where normal static membrane filtration works poorly or not at all. 

A suspension of methyl p-lactoside 13 (S.O g, 14 mmol) in benzene (130 mL) was refluxed for 17 h in the presence of BujSnO (4.18 g, 16.6 mmol) in a flask equipped with a Dean-Static separator. Then allyl bromide (20 mL) and tetrabutylammonium bromide (2 g, 6.2 mmol) were added, the solution was refluxed for 3 h, and the volatiles were evaporated. The residue was dissolved in water and washed twice with ethyl acetate. The aqueous phase was evaporated to dryness, benzene (ISO mL) and BujSnO (3.83 g) were added to the residue and the mixture was refluxed as before for 17 h. Then allyl bromide (IS mL) and tetrabutylammonium bromide (1.5 g) were added, and the solution was again refluxed for SO min. The volatiles were evaporated, and the residue was taken over in methanol. The crystalline precipitate of BrBi SnOSnBu OH), mp 80-81°C, was removed by filtration and the mother liquor was evaporated. Addition of ethyl acetate to the residue gave the allyl ether 14 as a crystalline compound (3.88 g, 70%) mp 107-112°C [a]D + 20° (c 1.0 in water). 

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