Thickness of filter cake

L Thickness of filter cake with same resistance as cloth m L... 

Thickness of filter cake at the transition between filtration and consolidation stages of expression, m... 

Hence, the thickness of the cake, uniformly distributed over the filter plate, is... 

For solution by digital simulation, the depth of filter cake is divided into nine segments, each of which has an equivalent dimensionless thickness Ax. For any element n, the form of the resulting difference differential equation is given by... 

A slurry containing 100 kg of whiting/m3 of water, is filtered in a plate and frame press, which takes 900 s to dismantle, clean and re-assemble. If the filter cake is incompressible and has a voidage of 0.4, what is the optimum thickness of cake for a filtration pressure of 1000 kN/m2 The density of the whiting is 3000 kg/m3. If the cake is washed at 500 kN/m2 and the total volume of wash water employed is 25 per cent of that of the filtrate, how is the optimum thickness of cake affected The resistance of the filter medium may be neglected and the viscosity of water is 1 mN s/m2. In an experiment, a pressure of 165 kN/m2 produced a flow of water of 0.02 cm3/s though a centimetre cube of filter cake. 

In practice, it is sometimes possible to incorporate moving blades in the filter equipment so that the thickness of the cake is limited to the clearance between the filter medium and the blades. Filtrate then flows through the cake at an approximately constant rate and the solids are retained in suspension. Thus the solids concentration in the feed vessel increases until the particles are in permanent physical contact with one another. At this stage the boundary between the slurry and the cake becomes ill-defined, and a significant resistance to the flow of liquid develops within the slurry itself with a consequent reduction in the flowrate of filtrate. 

The recessed type of press is similar to the plate and frame type except that the use of frames is obviated by recessing the ribbed surface of the plates so that the individual filter chambers are formed between successive plates. In this type of press therefore the thickness of the cake cannot be varied and it is equal to twice the depth of the recess on individual plates. 

If the cake is noncompressible, / must be equal to the thickness of the cake leaving the filtering zone. Therefore, by Eq. (41) and using the same procedure as was followed in the development of Eq. (34),... 

On-line measurements of cake thickness during filter-system operation have not been feasible in most systems. However, when the pressure drop across the filter system, the gas flow rate, and the particle concentration in the incoming gases are measured, these data can be used to calculate the mass of filter cake on each filter. The overall pressure drop can be modeled as ... 

COMPRESSIBLE AND INCOMPRESSIBLE FILTER CAKES. In the filtration under low pressure drops of slurries containing rigid uniform particles, all factors on the right-hand side of Eq. (30.13) except m are independent of L, and the equation is integrable directly, over the thickness of the cake. If is the total mass of solids in the cake, the result is... 

Figure 42. Dependence of (a) limiting dynamic filtration rate (Q/d) and (b) inverse of filter cake thickness (l/hc) on shear rate of drilling fluid. (Muds 2 and 3 from reference 139 with Fordham and Ladva s data from reference 135.) Lines show least squares fit to data from muds 2 and 3.

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