Filter cake accumulation

Cake Filters Filters that accumulate appreciable visible quantities of solids on the surface of a filter medium are called cake filters. The slurry feed may have a solids concentration from about 1 percent to greater than 40 percent. The filter medium on which the cake forms is relatively open to minimize flow resistance, since once the cake forms, it becomes the effective filter medium. The initial filtrate therefore may contain unacceptable sohds concentration until the cake is formed. This situation may be made tolerable by recycling the filtrate until acceptable clarity is obtained or by using a downstream polishing filter (clarifying type). 

Both faces of each plate are hollowed to form a chamber for cake accumulation between adjacent plates. This design has the advantage of about half as many joints as a plate-and-frame press, making a tight closure more certain. Figure 18-114 shows some of the features of one type of recessed-plate filter which has a gasket to further minimize leaks. Air can be introduced behind the moth on both sides of each plate to assist cake removal. 

Process Concept The application of a direct elec tric field of appropriate polarity when filtering should cause a net charged-particle migration away from the filter medium. This electrophoretic migration will prevent filter-cake formation and the subsequent reduction of filter performance. An additional benefit derived from the imposed electric field is an electroosmotic flux. The presence of this flux in the membrane and in any particulate accumulation may further enhance the filtration rate. 

One of the basic mechanisms in fluid loss prevention is shown in Figure 2-1. The fluid contains suspended particles. These particles move with the lateral flow out of the drill hole into the porous formation. The porous formation acts like a sieve for the suspended particles. The particles therefore will be captured near the surface and accumulated as a filter-cake. 

Bag filters are composed of woven material that intercepts small particles on the filter surface by impingement and electrostatic attraction. The efficiency of collection increases as the depth of the filter cake increases, making these filters highly efficient for small diameter, even sub-micron, particle size. Filters are periodically shaken or back-flushed to remove particulate accumulation. These filters are usually constructed of woven materials suitable for operation at low temperatures up to about 350°C. 

Once filling is complete, filtration begins [Fig. 22.3(b)]. Treated brine is pumped into the vessel at the desired flow rate through an automatic control valve. The flow of brine is from the outside to inside of the filter candles. Filtrate clarity is achieved immediately no recycling of flow is required. As the filtration proceeds at constant flow, solids accumulate as a filter cake on the outside surface of the filter socks. While... 

The fine structure of the membrane also allows surface filtration to occur. Suspended solid particles are retained on the surface of the membrane and are not allowed to penetrate into or through the supporting felt cloth. In contrast, conventional media depend upon depth filtration in which particles are retained within the medium itself. The results are immediate filtrate clarity without the need to build-up a filter cake, and reduced accumulation of solids within the medium that leads to increasing pressure drop. 

Filter cake. The accumulation of removed matter upstream of the cloth or mesh in a filter drum used to remove solids or sludge from a liquid. 

Starting with the defined amount of solvent delivered, about 29% of the solvent is carried over into water, arriving at a total of about 104% hazardous waste accumulated. So far - notwithstanding the carry over of solvent - more waste was produced than solvents were introduced because also powder lacquer was found in the waste. This does not include the mass of filter cake of the internal waste water recycling. 

After standing in reactor 12, the mixture is cooled there down to 30 °C and filtered in nutsch filter 16 from diethylaminochloride. The filtrate is sent into tank 17 for distillation, and the filter cake is washed with toluene to eliminate amidation products as completely as possible. After the filtrate has been loaded, cooler 18 is filled with water, and the tank agitator is switched on. A residual pressure of 40-55 GPa is created in the system and the tank jacket is filled with a heat carrier or vapour. First, receptacle 20 receives toluene (below 60-65 °C) after separating toluene, amidation products are distilled into fractions. Receptacle 21 receives the intermediate fraction (below 106 °C) the distillation is monitored by the refraction index. At no20 = 1.4210+1.4230 the target fraction, diethylaminomethyl-triethoxysilane, is separated into receptacle 19. The distillation is continued up to 140 °C. As it accumulates, the intermediate fraction from receptacle 21 is sent into apparatus 12 for repeated amidation, and the ready product, diethylaminomethyltriethoxysilane, is sent after additional filtering (in case there is a filter cake) from receptacle 19 into collector 22. 

CM-Sephadex (G-50) in 1.0 M potassium acetate, pH 6.0—Stir 150 g of fresh or used CM-Sephadex (G-50, medium grain size) into 2.5 liters of distilled water and vacuum filter (Buchner funnel) off the excess fluid. Rinse the accumulated filter cake on the filter with 2 volumes of 95% ethanol, followed by 2 volumes of distilled water. Remove and resuspend the filter cake in 4 volumes of 0.1 N HC1 (415 ml concentrated HC1 into 4.6 liters of distilled water), then vacuum filter and rinse with 2 volumes of distilled water as before. Remove and resuspend the filter cake in 2 volumes of 1.0 M potassium acetate, pH 6.0 (i.e., dissolve 490 g of... 

Plate-and-frame press. This press is an alternate assembly of plates covered on both sides with a filter medium, usually a cloth, and hollow frames that provide space for cake accumulation during filtration. The frames have feed and wash manifold ports, while the plates have filtrate drainage ports. The plates and frames usually are... 

Fig. 3 shows a simplified compactible filter cake. Darcy s law and a stress balance involving the accumulated friction drag on the particulate structure (Fig. 3) are used to develop basic theory of flow through compactible porous media. 

Using the transmissions we can calculate the amount that is accumulating as filter cake, if we know the initial feed, Wi, W2, W3. After filtration the filter cake will be found ... 

In the preceding example, the accumulation in the filter cake and in the filtrate of the individual substances with different particle sizes was predicted from the transmission factors and from the amounts initially present. 

Practically another situation is of more interest, i.e., the calculation of the amounts initially present from the measured accumulation in the filter cake. In the previous example the known quantities were the amounts wi,w2, W3 and the unknowns were Wf,WK,Wo. We can easily obtain these amounts as... 

---