Filtration Permeability

To study filtration permeability, the compositions of SPC samples were accepted in accordance with the optimal composition given in Table 3.5. Water was used as a filtration liquid because it did not influence consolidation of the concrete. This allowed determinations about the presence or absence of filtering defects in investigated compositions and estimation of the influence of additives on filtration permeability. For SPC compositions tested with water, a filtration of acids is absent, as the effect of consolidation of the material in this case is shown. 

Zemlyanushnov, Fracture And Crack Resistance of Silicate Polymer Concrete, Journal Scientific Israel Technology Advanced 14, no. 4 (2012) 38—48. With permission. 

Data show that all SPC samples with monomeric additives withstand the pressure of water at 0.6 MPa, whereas samples without the additive (composition 1) began leaking after 1-1.5 hours of testing at an overflow pressure of 0.1 MPa. Thus, it is obvious that the additives TFS and FA eliminate filtering defects in the form of microcracks and conducting channels on a border gel filler.  

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During filtration, as the particulate buildup continues on the filtration medium, the filtration resistance increases, or in other words, the filtration permeability decreases. The capacity of a system, expressed in time, volume of liquid fed, or amount of solids fed, depends on the ability of the system to maintain acceptable permeability. 

Besides the packing density, the pore structures belong to the important properties of particulate structures. They constitute an useful aspect of packed particles, since they control properties such as filtration, permeability, fluid trapping, etc.. Packing structures of powders with continuous size distribution are very complex. The pores in ordered packings of monosized spheres would seem to be the simplest case to study. 

It is assumed that the concentration of the solute in the membrane is related to the concentration of the solute in the bulk phase by the partition coefficient y and it is further assumed that y is the same for both sides of the membrane. The filtration permeability coefficient, P[, in cm/s can be calculated from the experimentally determined and the difference in the concentration of the impermeable solute in the two compartments. 

Permeable intervals can be identified from a number of logging tool measurements, the most basic of which is the caliper tool. The caliper tool is used to measure the borehole diameter which, in a gauge hole, is a function of the bit size and the mudcake thickness. Mudcake will only build up across permeable sections of the borehole where mud filtrate has invaded the formation and mud solids (which are too big to enter the formation pore system) plate out on the borehole wall. Therefore the presence of mudcake implies permeability. 

Membrane filtration Membrane module Membrane permeability Membrane process Membrane processes Membrane reactor Membrane roofing Membranes... 

Addition of Inert Filter Aids. FUtet aids ate rigid, porous, and highly permeable powders added to feed suspensions to extend the appheabUity of surface filtration. Very dilute or very fine and slimy suspensions ate too difficult to filter by cake filtration due to fast pressure build-up and medium blinding addition of filter aids can alleviate such problems. Filter aids can be used in either or both of two modes of operation, ie, to form a precoat which then acts as a filter medium on a coarse support material called a septum, or to be mixed with the feed suspension as body feed to increase the permeabihty of the resulting cake. 

Because gravity is too weak to be used for removal of cakes in a gravity side filter (2), continuously operated gravity side filters are not practicable but an intermittent flow system is feasible in this arrangement the cake is first formed in a conventional way and the feed is then stopped to allow gravity removal of the cake. A system of pressure filtration of particles from 2.5 to 5 p.m in size, in neutralized acid mine drainage water, has been described (21). The filtration was in vertical permeable hoses, and a pressure shock associated with relaxing the hose pressure was used to aid the cake removal. 

The three disadvantages described can be avoided by using soHd elements, instead of permeable ones, which create the shear to prevent or reduce cake formation. Only the stationary surface inside the filter is then available for filtration and this means a reduction in capacity. This is not a problem because the soHd disks can be slimmer and the collection of filtrate does not have to be through a hoUow shaft. 

Filtration Properties. Drilling fluids have a natural tendency to flow into permeable formations because the borehole pressure is generally... 

Membrane-retained components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. It is the objective of ultrafiltration to recover or concentrate particular species in the retentate (eg, latex concentration, pigment recovery, protein recovery from cheese and casein wheys, and concentration of proteins for biopharmaceuticals) or to produce a purified permeate (eg, sewage treatment, production of sterile water or antibiotics, etc). Diafiltration is a specific ultrafiltration process in which the retentate is further purified or the permeable sohds are extracted further by the addition of water or, in the case of proteins, buffer to the retentate. 

Ultra filtration. This process removes macromolecules, microorganisms, particulate matter, and pyrogens using a thin, selectively permeable membrane. Ultrafiltration caimot remove ions from water and is generally employed as a polishing process. 

There are some solids, however, which form a less permeable cake, even in veiy thin layers. With these sohds, the resistance of the deposited cake will be veiy high when compared to that of the precoat bed, and the slope of the filtrate cui ve will be -t-0.5 for all v ues of form time. 

It should be noted also that the intercept is difficult to determine accurately because of large potential experimental error in observing the time of the start of filtration and the time-volume correspondence during the first moments when the filtration rate is high. The value of / calculated from the intercept may vaiy appreciably from test to test, and will almost always be different from the value measured with clean medium in a permeability test. 

The equipment consists of a cvhndrical cell with a permeable bottom and an open top, into which is fitted a close-clearance, hollow, cyhndrical piston with a permeable bottom. Shiny is poured into the cell, and a cake is formed bv applying gentle vacuum to the filtrate discharge line. The cell is then filled with filtrate, and the counter-... 

Use of filter aids is a technique frequently applied for filtrations in which problems of slow filtration rate, rapid medium blinding, or un-satisfactoiy filtrate clarity arise. Filter aids are granular or fibrous solids capable of forming a highly permeable filter cake in which veiy fine solids or slimy, deformable floes may be trapped. Application of filter aids may allow the use of a much more permeable filter medium than the clarification would require to produce filtrate of the same quahty by depth filtration. 

For incompressible cake, the pressure distribution and the rate depend on the resistance of the filter medium and the permeability of the cake. Figure L8-150 shows several possible pressure profiles in the cake with increasing filtration rates through the cake. It is assumed that r /i i = 0.8 and /p//i = 0.6. The pressure at / = ri, corresponds to pressure drop across the filter medium Ap, with the ambient pressure taken to be zero. The filtration rate as well as the pressure distribution depend on the medium resistance and that of the cake. High medium resistance or blinding of the medium results in greater penalty on filtration rate. 

The factors to consider in the selection of cross-flow filtration include the cross-flow velocity, the driving pressure, the separation characteristics of the membrane (permeability and pore size), size of particulates relative to the membrane pore dimensions, and the hydrodynamic conditions within the flow module. Again, since particle-particle and particle-membrane interactions are key, broth conditioning (ionic strength, pH, etc.) may be necessary to optimize performance. 

Filtrates that are acceptable with a low quantity of fines that pass trough the filter cloth in the first few seconds of cake formation. Broadly, and depending on particle size and cloth permeability, the filtrate may contain 1,000 to 5,000 ppm insolubles. 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

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