Pressure filtration dewatering

The same moisture content of the produced cake can be obtained in shorter dewatering times if higher pressures are used. If a path of constant dewatering time is taken, moisture content is reduced at higher pressures with a parallel increase in cake production capacity. This is an advantage of pressure filtration of reasonably incompressible soHds like coal and other minerals. 

Pressure Filtration. High pressure drops have a twofold effect, ie, on capacity and on displacement dewatering which often follows. 

This reduction in permeabiUty due to cake consoHdation or coUapse may be so large that it may nullify or even overtake the advantage of using high pressures in the first place and there is then no reason for using the generally more expensive pressure filtration hardware. While a simple Hquid pump may be cheaper than the vacuum pump needed with vacuum filters, if air displacement dewatering is to foUow filtration in pressure filters, an air compressor has to be used and is expensive. 

D. Blankmeister and Th. Triebert, Dewatering Fltrafme Coal Slurries by Means of Pressure Filtration, Aufbereitungstechnik Nr. 1/1986, pp. 1—5. 

Theoretical studies (30) comparing the abihty to dewater compressible sohds by sedimenting and filtering centrifuges to pressure filters, have shown that at high G levels, scroU decanters produce drier cakes than pressure filtration. 

Soluble impurities can be extracted by washing with deionized or distilled water foUowed by filtration (1,12,26). Powders prepared by wet chemical synthesis are often washed and filtered for purification prior to use. The dewatering (qv) process can be enhanced by pressure filtration. Organic solvents can be used to remove water-insoluble impurities and wash-water sensitive materials. 

Vacuum filtration and screen-bowl centrifuges are the principal unit operations used for mechanical dewatering of fine coal. Pressure filtration (plate and frame filter presses and continuous belt filter presses) is used to a much lesser extent to dewater fine... 

Reduce inlet moisture content X , say, by dewatering by gas blowing, centrifuging, vacuum or pressure filtration, or a predryer. 

Dewatering Pressure filtration in belt filter presses Centrifugation Vacuum filtration... 

A modification to vapor pressure dewatering is the so-called Hi-Bar Steam Pressure Filtration (Bokela GmbH, Karlsruhe, Germany), where pure steam... 

Landman K.A., Sirakoff C. and White L.R., 1991. Dewatering of flocculated suspensions by pressure filtration, Phys. Fluids A, 3(6), 1495-1509. 

Apart from the hyperbar vacuum filtration, the work at Karlsruhe also includes fundamental investigations into cake filtration generally, pressure filtration of coal and ore suspensions, and studies of dewatering of cakes. As an alternative to the small drum filter, they have apparently also used a small belt filter in the same pressure vessel. Some commercial developments, like the KHD pressure filter, are reported to have originated from the work at Karlsruhe. 

Blankmeister, D. and Triebert, Th., Dewatering ultrafine coal slurries by means of pressure filtration , Aji ereirungsfcc/inrk, 1, 1-5 (1986)... 

Cake Dewatering. Dewatering (qv), identified as a separate entity in filtration, is used to reduce the moisture content of filter cakes either by mechanical compression or by air displacement under vacuum pressure or drainage in a gravitational or centrifugal system. Dewatering of cakes is enhanced by addition of dewatering aids to the suspensions in the form of surfactants that reduce surface tension. 

There is an additional pressure drop across the cake, developed by electroosmosis, which leads to increased flow rates through the cake and further dewatering at the end of the filtration cycle. The filtration theory proposed for electrofiltration assumes the simple superposition of electroosmotic pressure on the hydraulic pressure drop. 

Optimization of Cycle Times. In batch filters, one of the important decisions is how much time is allocated to the different operations such as filtration, displacement dewatering, cake washing, and cake discharge, which may involve opening of the pressure vessel. Ah. of this has to happen within a cycle time /. which itself is not fixed, though some of the times involved may be defined, such as the cake discharge time. 

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