Filters flow characteristics

Filter Selection. A variety of product- and process-related factors govern filter selection. Considerations include the characteristics of the fluid to be filtered, ie, its chemical composition and compatibiHty with the filtration system (inclusive of the membrane, filter hardware, piping, etc), the level of bioburden present, specifications on effluent quaHty, the volume of product to be filtered, flow rate, and temperature. 

Filtration of viscose is not a straightforward chemical engineering process. The solution of cellulose xanthate contains some easy-to-deal-with undissolved pulp fibers, but also some gel-like material which is retarded rather than removed by the filters. The viscose is unstable and tends to form more gel as it ages. Its flow characteristics make the material close to the walls of any vessel or pipe move more slowly, get older, and gel more than the mainstream viscose. So while filtration can hold back gels arising from incomplete mixing, new gels can form in the pipework after the filters. 

For fine suspended solids with particles that are too small to be separated from the liquid by gravitational or centrifugal methods, a barrier method such as a filter may be used. The liquid is passed through a filter medium (usually a cloth or screen) that provides a support for the solid particles removed from the slurry. In actuality, the pores in the filter medium are frequently larger than the particles, which penetrate some distance into the medium before being trapped. The layer of solids that builds up on the surface of the medium is called the cake, and it is the cake that provides the actual filtration. The pressure-flow characteristics of the porous cake primarily determine the performance of the filter. 

Ultrafiltration (UF) refers to the removal of high molecular weight colloids (10,000 MW) up to particles less than 0.05 pm in diameter [10]. Like MF, UF places a mechanical barrier into the flow stream to separate the solid and liquid phases. The most common UF is a cross-flow hollow fiber type whereby a UF module contains hundreds of hollow microfibers. Whether or not the medium to be filtered flows inside or outside, the microfibers depends on the characteristics of the waste stream. UF is different from MF not only because UF can filter very small particles and some colloids, but also because of the cross-flow dynamics inside the UF module that keeps the surface of the hollow libers clean. Because of the cross flow, UF modules require a reject stream as well as a permeate stream. In other words, 100% of the liquid that enters the UF module does not exit as permeate. Figure 19.1 shows the differences between the UF and microlilters with respect to flow path. 

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... 

Samples should be easily withdrawn for automatic or manual analysis without interrupting the flow characteristics of the liquid. In the latter case, efficient filtering should be achieved. 

This research is being performed in two phases evaluation of pressure drop and flow characteristics of cold flow models of the filter and collection efficiency tests with a pilot-scale filter coupled to a 4.S tonne per day biomass gasifier. In this paper we describe three fluid dynamic design features developed in the cold flow model that improve performance of the Alter. 

Continuous rotary and batch hydrators are used to produce calcium hydroxide (slaked lime) powder. The continuous version uses a slightly inclined, slowly rotating steel cylinder of about 1 m diameter by 6-7 m in length. The calcium oxide is fed into the upper end and the correct proportion of water is sprayed in, followed by tumbling in the cylinder to produce a uniform product. Open trough-type batch hydrators, in which the reacting components are mechanically combined, provide greater control of hydration rate and temperature and some improvements in the quality of the product. An explosion process in which hydration is conducted in a pressure vessel produces a slaked lime with better flow characteristics, and a smaller mean particle size more suitable for uses such as filters [14]. 

A variety of filters with a 0.45 im pore size is available. These filters vary in uniformity of pore size, chemical composition, and flow characteristics. Each of these factors affects the performance of the filter and some filters are better suited for the study of aquatic humic substances than others. The ideal filter would be inert relative to compounds of interest, exhibit good flow characteristics, have a uniform pore size, and be reasonably priced. An evaluation of the suitable filters with respect to pore size, chemical composition, and flow characteristics follows. 

Bulk density and real density Apparent density For estimation of the filter packing volume Important for flow characteristics of the activated ... 

Other methods are based on polymer blends of two immiscible polymers, a water-soluble matrix [e.g., poly(vinyl alcohol)] and an insoluble fiber-forming component [e.g., poly(ethylene terephthalate)]. Upon exfrusion, the streamlined flow characteristics produce a fibrillary morphology. The matrix is extracted after cold drawing. The resulting foamed slurry is then filtered off and spun into microfibers with a diameter of 0.1-10 pm. Using this method, ultrasuperfine fibers with counts of 10 " dtex are obtained for use as filter material [81]. 

In the previous sections the suspending hquid has been assumed to diq>lay Newtonian rheological characteristics, see Appendix B for fiirther details. This section considers the effects of filtering solids firom liquids displaying non-Newtonian flow characteristics. 

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