Filtration Term Paper Example | Topics and Well Written Essays - 4250 words

Filtration - Term Paper Example There are several methods through which the filtrate induced may flow through the filter medium. This may be by gravity (hydrostatic head), pressure being applied upstream of the filter medium, reduced pressure or vacuum being applied downstream the filter medium or through centrifugal sedimentation. (b) Filtration mechanism This may be through cake or clarifying filtration. Cake filtration is when the solid gets stopped at the surface of the filter medium where it piles upon one another to form a cake. Also known as depth or filter medium filtration, clarifying filtration is when the solids get trapped within the pores of the filter medium. (c) By objective The objective of the filtration process may be either dry solids or clarified liquid or both. The filtration process may be either intermittent or continuous. When classifying filters, they are first divided into either cake or clarifying filters. They are then classified depending on the driving force and then finally into eithe r batch or continuous classes. Continuous filtration testing and scale up In continuous filtration, it is first assumed that the resistance of both the filter cloth and the filter drainage is insignificant as compared to the resistance of the filter cake. It is also assumed that both specific cake resistance and pressure drop remain constant throughout the filtration process. ... Cake discharge A practical filter application is one which produces a cake that is thick enough to discharge. There are minimum acceptable cake thicknesses that are required for discharge for various types of filtration systems and discharge mechanisms. Therefore, when running small scale tests, the experimenter should decide early during the test program the applicable type of discharge then later tailor the data collected in a way that it will fit the physical requirements of that unit type. Feed slurry temperature An increase in the feed slurry temperature decreases the viscosity of the liquid phase. The overall result of this is an increase in the filtration rate and a decrease in the cake moisture content. Cake thickness control At times, the rate of cake formation with bottom feed type filters may be rapid enough in such a way that it creates a cake that is too thick for subsequent operations. The cake thickness can be adjusted by simply adjusting the bridge blocks found in the filter valve so as to decrease the effective submergence, through reduction of the slurry level in the vat, and also by reducing the vacuum level in the portion where the cake forms. Representative samples It is essential for the sample to be used as the representative of the slurry in full scale plants to be tested under the conditions prevailing in the process. If the slurry has a temperature that is different from the ambient temperature, subsequent heating or cooling may change the distribution of the particle size. The age of the sample may also influence the particle size significantly. If an effect is likely, the bench scale testing should be at the laboratory site or at the plant on