Solid/liquid separation cake filtration

Staff profile page - the Engineering Faculty at Loughborough. .. Broad Interests and Expertise. Compressible cake filtration Selection, scale-up and process simulation of solid/liquid separation equipment Washing and. .. http //WWW. Iboro. ac. uk/departments/eng/research/staff/html/tarleton. html [More Results From www.lboro.ac.uk]... 

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

The solids-liquid separation of slurries containing particles below 10 xm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as a concentrated slurry. Such filters use filter cloths as the filtration medium... 

Crystal morphology (i.e., both form and shape) affects crystal appearance solid-liquid separations such as filtration and centrifugation product-handling characteristics such as dust formation, agglomeration, breakage, and washing and product properties such as bulk density, dissolution kinetics, catalytic activity, dispersability, and caking. 

Svarovsky, Ladislav. 1990. Solid-liquid separation. 3rd ed. London, Boston Butterworth Co., 29-30. Tiller, F.M. 1978. Characteristics of staged, delayed-cake filters. Filtration and Separation May/June XXX. Tiller, F.M. 1974. Continuous processes for cake filtration. Chemical Engineering April 29. 

This chapter summarizes the solid-liquid separation operations commonly used for the pretreatment of drying operations. We focus on the practical aspects of cake filtration, centrifngal filtration, and mechanical expression. The choice of equipment depends on the objective of the separation, the properties of the slurry, and the scale of prodnction. The details of solid-liquid separation theories are omitted. The reader is referred to the references for further information. 

One of the most commonly used solid-liquid separation methods in crystallization processes is centrifugal filtration, such as continuous pusher and batchwise peeler centrifuges shown schematically in Figure 64.10. A manufacturer of centrifuges used in crystallization processes is KMPT AG [52]. In addition, Nutsche filters, frame pressure filters, and belt filters have also been used. Most of these filters have a possibility of cake washing which is important for the final purity as discussed earlier. 

The term post-treatment refers to processes vdiich are used after the principal solid-liquid separation has been achieved. The final step in the latter operation is usually some type of cake filtration which will leave a cake that may be fully saturated with liquid or partially drained and it is extremely unlikely that the solids are in an acceptable condition for any subsequent operation such as thermal drying. Thus the post treatment processes are washing and deliquoring which are concerned req>ectively with removing the soluble solids from the liquid remaining in the cake and then purging the major proportion of the liquid fi om the cake pores. 

We are concerned primarily here with the process filter - its selection and design, and calculations for simulation and scale-up. During preparation of the current text a conscious decision was taken to largely limit the contents to cake filtration. However, although most chapters concentrate on cake filtration, it is not possible to give a balanced account of the practical aspects of filtration without some presentation of other separation techniques. To present information to a similar depth about all of these other processes would have made the book encyclopaedic. While there is certainly a technical need for such a book, or series of books, the authors did not set out to include all solid/liquid separation techniques in the current volume. This should not be seen as an attempt to diminish the importance of depth filtration, crossflow filtration or other solid/liquid separation techniques it is... 

This is an area of solid-liquid separation which has enjoyed considerable interest recently, although the basic concept is an old one. In conventional cake filtration, a cake is allowed to form on the filter medium and this gradually increases resistance to flow, leading to increasing time or pressure requirement for filtration of a given volume of slurry. 

Thirdly, there are those chapters which only needed minor updating and amendments. These include Characterization of Particles Suspended in Liquids, Efficiency of Separation of Particles from Fluids, Hydrocyclones, Separation by Centrifugal Sedimentation, Filtration Fundamentals, Methods for Limiting Cake Growth, Pressure Filtration, Particle-Huid Interaction, Thermodynamics of Solid-Liquid Separation. 

Depending on the task of the separation process, a large number of different types of equipment for the solid-liquid separation are available. Criteria for the selection are, inter alia, the filtration properties of the crop and the size of the particles, the suspension density, and the mode of operation, batchwise or continuous. Two main types of solid-liquid separations can be distinguished, cake forming filtration under pressure and centrifugation. In both cases, the crystals form a filter cake on a medium through which the mother liquor has to pass. The resistance is the rate-limiting step for the filtration and the characteristic property of the suspension. 

The vast majority of polymeric flocculants are used to aid solid-liquid separation in aqueous systems where the benefits are many and varied. In sedimentation, flocculants and coagulants provide a significant increase in settlement rate and improvement in supernatant clarity. In filtration applications, the rate of filtration is significantly increased and this is usually accompanied by improvement in cake solids and filtrate clarity. In the case of centrifugation, often the whole process is reliant upon the use of high molecular weight synthetic flocculants to give the separation required. 

This chapter summarizes the solid liquid separation operations commonly used for the pretreatment of drying operations. We focus on the practical aspects of cake filtration, centrifugal filtration, and mechanical... 

Wells, S. A. and Dick, R. I. (1993) "Permeability, Solid and Liquid Velocity, and Effective Stress Variations in Compressible Cake Filtration," Proceedings, American Filtration Society Conference on System Approach to Separation and Filtration Process Equipment, Chicago, Illinois, May 3-6, pp. 9-12... 

Expression is the separation of liquid from a two-phase solid-liquid system by compression of the system under conditions that permit the liquid to escape, while the solid is retained between the compressing surfaces. Expression serves the same purposes as filtration but is distinguished from the latter in that the pressure is applied by movement of the retaining walls instead of pumping the material into a fixed space. Expression is usually employed to separate systems that are not easily pumped. It is also used instead of filtration when a more thorough removal of liquid from the cake is desired. The usual equipment for expression is a hydraulic press. Most of the common vegetable oils are produced by expression, In the expl in-... 

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