Filter cake characteristics

Filter Cake Characteristics. Ease of handling and disposing of the waste as well as economic considerations dictate the need for a reasonably dry waste material from which most of the sodium value has been recovered. In general, both of these goals were not achieved at Scholz. 

Lee., S. J., Chu, C. P. and Lee, D. J., Effects of polyelectrol34e flocculation on filter cake characteristics . Proceedings Volume 11, World Filtration Congress 8, European Federation of Chemical Engineering Event No. 607, organised by The Filtration Society and Elsevier Science, The Brighton Centre, Brighton, UK, 3-7 April 2000, 1236-1239 (2000)... 

The softened seawater is fed with dry or slaked lime (dolime) to a reactor. After precipitation in the reactor, a flocculating agent is added and the slurry is pumped to a thickener where the precipitate settles. The spent seawater overflows the thickener and is returned to the sea. A portion of the thickener underflow is recirculated to the reactor to seed crystal growth and improve settling and filtering characteristics of the precipitate. The remainder of the thickener underflow is pumped to a countercurrent washing system. In this system the slurry is washed with freshwater to remove the soluble salts. The washed slurry is vacuum-filtered to produce a filter cake that contains about 50% Mg(OH)2. Typical dimensions for equipment used in the seawater process may be found in the Hterature (75). 

Drum filters commonly are classified according to the feeding arrangement and the cake-discharge technique. They are so treated in this subsection. The characteristics of the shiny and the filter cake usually dictate the cake-discharge method. 

Filter aids may be applied in one of two ways. The first method involves the use of a precoat filter aid, which can be applied as a thin layer over the filter before the suspension is pumped to the apparatus. A precoat prevents fine suspension particles from becoming so entangled in the filter medium that its resistance becomes exces-sive. In addition it facilitates the removal of filter cake at the end of the filtration cycle. The second application method involves incorporation of a certain amount of the material with the suspension before introducing it to the filter. The addition of filter aids increases the porosity of the sludge, decreases its compressibility, and reduces the resistance of the cake. In some cases the filter aid displays an adsorption action, which results in particle separation of sizes down to 0.1 /i. The adsorption ability of certain filter aids, such as bleached earth and activated charcoals, is manifest by a decoloring of the suspension s liquid phase. This practice is widely used for treating fats and oils. The properties of these additives are determined by the characteristics... 

The characteristics of the pump relate the applied pressure on the cake to the flowrate at the exit face of the filter medium. The cake resistance determines the pressure drop. During filtration, liquid flows through the porous filter cake in the direction of decreasing hydraulic pressure gradient. The porosity (e) is at a minimum at the point of contact between the cake and filter plate (i.e., where x = 0) and at a maximum at the cake surface (x = L) where sludge enters. A schematic definition of this system is illustrated in Figure 2. 

Polyethercyclicpolyols possess enhanced molecular properties and characteristics and permit the preparation of enhanced drilling fluids that inhibit the formation of gas hydrates prevent shale dispersion and reduce the swelling of the formation to enhance wellbore stability, reduce fluid loss, and reduce filter-cake thickness. Drilling muds incorporating the polyethercyclicpolyols are substitutes for oil-based muds in many applications [195-197,1906,1907]. Polyethercyclicpolyols are prepared by thermally condensing a polyol, for example, glycerol to oligomers and cyclic ethers. 

A filter press is used to determine the wall-building characteristics of a mud. This press consists of a cylindrical chamber, which may withstand alkaline milieu. A filter paper is placed on the bottom of the chamber. The mud is placed into the chamber and a pressure of 0.7 MPa is applied. After 30 minutes the volume of filtrate is reported. The filter-cake is inspected visually and the consistency is noted as hard, soft, tough, rubbery, or firm. 

Static leak-off experiments with borate-crosslinked and zirconate-cross-Unked hydroxypropylguar fluids showed practically the same leak-off coefficients [1883]. An investigation of the stress-sensitive properties showed that zirconate filter-cakes have viscoelastic properties, but borate filter-cakes are merely elastic. Noncrosslinked fluids show no filter-cake-type behavior for a large range of core permeabilities, but rather a viscous flow dependent on porous medium characteristics. 

Whilst it may be possible to predict qualitatively the effect of the physical properties of the fluid and the solid on the filtration characteristics of a suspension, it is necessary in all cases to carry out a test on a sample before the large-scale plant can be designed. A simple vacuum filter with a filter area of 0.0065 m2 is used to obtain laboratory data, as illustrated in Figure 7.5. The information on filtration rates and specific resistance obtained in this way can be directly applied to industrial filters provided due account is taken of the compressibility of the filter cake. It cannot be stressed too... 

Dewatered sludge, or filter cake, is a highly viscous material in which the remaining water is mechanically trapped within the cake. For further drying, the cake must be broken up before heating to expose as much surface area as possible. This is difficult, because semisolid filter cake often takes on the characteristics of a heavy, sticky paste when efforts are made to break it up (PACE 1986). 

Recovery economics depend upon the characteristics of the filter cake, sludge generation rates, and present disposal costs. Small generators will best be served by central recovery plants. Larger generators will find it more economical to install their own recovery systems. 

Data collected for each run included acid analysis using inductively coupled plasma (ICF) to determine cation concentration and titration to determine H concentration. Filtering characteristics were determined using solid and filtrate yield rates, as well as back pressures during the filtration cycle. The filter cake was characterized by moisture content and composition. Solid samples were analyzed with scanning electron microscopy (SEM) to determine changes in particle shape and size under various process conditions, and X-ray diffraction (XRD) was used to determine the solids composition. 

Characteristics of the performance of the main types of commercial SLS equipment are summarized in Table 11.3. The completeness of the removal of liquid from the solid and of solid from the liquid may be important factors. In some kinds of equipment residual liquid can be removed by blowing air or other gas through the cake. When the liquid contains dissolved substances that are undesirable in the filter cake, the slurry may be followed by... 

In this equation, p and Vs influence directly the flow characteristics of the filtering water. Since S determines the value of Vs, it also influences directly the flow characteristics of the fluid. All the other factors in the equation are inherent characteristics of the cake. AU these cake characteristics may be lumped up into a single term. Call this term as the specific cake resistance a. Hence, in terms of the specific cake resistance, dp is... 

Factors Affecting Expression Operations Based on fundamental theory, variables affecting expression include characteristics of suspending particles, properties of liquid, properties of filter cake, and expression operation conditions as summarized in Fig. 18-187. Expression efficiency is determined by the properties of the filter cake, which very much depend on characteristics of the suspending particle, properties of liquid, and operation conditions. Interrelationships of the above parameters are described by empirical equations covering restrictive ranges. 

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