Filter cakes resistivity

Filter cake resistance (Rq) is the resistance to filtrate flow per unit area of filtration. R increases with increasing cake thickness during filtration. At any instant, Rc depends on the mass of solids deposited on the filter plate as a result of the passage of V (m ) filtrate. Rf may be assumed a constant. To determine the relationship between volume and residence time t. Equation 5 must be integrated, which means that Rc must be expressed in terms of V. 

Assume laminar flow of filtrate of liquid through the filter cake. Rate of filtration is usually measured as the rate at which liquid filtrate is collected. The filtration rate depends on the area of the filter cloth, the viscosity of the liquid, the pressure drop across the filter and filter cake resistance. At any instant during filtration, the rate of filtration is given by the equation ... 

Filter aids can be added to the slurry to reduce the filter cake resistance. These are materials that have high porosity. Their application is normally restricted to cases where the filtrate is valuable and the solid cake is a waste. In cases where the solid is valuable, the filter aid should... 

The resistance has two components the resistance of the support medium, Rm, and the filter cake resistance, Rc> If R,n remains constant and all particles are removed to give a uniform filter cake, then ... 

It is anticipated that the equilibrium filter cake mass would depend strongly on the axial velocity through the cross-flow filter assembly. The shear rate at the filter surface will increase the entrainment of the catalyst solids for a given permeate flow rate. Therefore, for each differential pressure condition, the axial velocity will be varied in order to quantify the effect of the wall shear on the filter cake resistance term. 

The very nature of process development necessitates the contributions of all members of a typical development team. Thus, reaction engineers determine reaction kinetics and select the best reactor type, while filtration experts measure the filter cake resistance and washing efficiency. To reduce development time, it is crucial that all of these activities be performed in a coordinated manner. Proper workflow automates such a development process, in whole or part, during which documents, information, or tasks are passed from one participant to another for action, according to a set of procedural rules. 

The specific filter cake resistance, a [L-2], is defined with the equation describing the pressure loss, Ap, of the liquid in the porous filter cake at laminar flow ... 

Here, Tc is the filter cake resistance, is the cake height and is the resistance of the filter cloth, h is calculated from the following equation ... 

Where successful cake filtration is obtained, the medium resistance will generally be a low percentage (< 10%) of the mean filter cake resistance. Another way of eTqiressing this principle is that the medium should represent an extra equivalent cake thickness in the range 0.02 < I. < 0.15. 

The filter cake resistance a may depend on the operational eed of the machine and the... 

Improvement in filtration efficiency of gypsum upon flocculation is determined to be due to reduction in the blockage of filter media pores and in the filter cake resistance. An optimum in polymer dosage is explained in terms of stabilization of fines and deformability of the floes formed. Anionic polyacrylamides were found to be more effective filter aids than cationic polymers. 

Rushton, A., Hosseini, M. and Hassan, I., The effects of velocity and concentration on filter cake resistance , pp. 78-91, Proc. Symp. on Solid-liquid Separation Practice, Leeds, UK, Yorkshire Branch of the I. Chem. E., 27-29 March (1978)... 

The filter cake resistance typically ranges from 10 ° < a < 10 "m . For... 

The slope of the tjV versus t plot indicates the filter cake resistance. Note, however, that in practice the tjV versus t plots do not pass through the origin, due to the resistance of the filter cloth and any associated particles entrapped within it (Figure 4.8). 

The permeability characteristics of a filter cake deposited on a highly permeable filter cloth were determined by passing plain water at 20 C and an applied pressure difference of 0.95 atmosphere. The filter cloth was 5.08 cm in diameter the water flux was found to be 36 cm /min. The filter cake thickness was measured to be 1.5 cm. Determine the value of the filter-cake resistance, R and the value of water permeability, Q , through the cake. Neglect the filter cloth resistance. (Ans.R = 0.32 x 10t cm Q , =4.73 x 10 cm -cp/s-atm.)... 

Examination of Figs. 6 and 7 reveals that the filter cake resistance starts at a much higher level for HPAM polymers (sohd symbols) than for xanthan polymers (open symbols). As mentioned earlier (and as will be discussed in detail in the Rheology in Porous Media and Mechanical Degradation section), much of this effect is attributed to viscoelasticity of HPAM (Jennings et al. 1971 Hirasaki and Pope 1974). 

Fig. 15—Fracture extensicn vs. filter-cake resistance in a vertical well.

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