Solid Liquid Separations

Solid—liquid separation is concerned with mechanical processes for the separation of liquids and finely divided insoluble solids. 

The unit operations of solid-liquid separation and of drying are closely linked to crystallization. A solid-liquid separation process can best be improved by changes in the habit and particle size distribution obtained in the crystallization step. The same holds for the drying process. Furthermore, both the solid-liquid separation and the drying step can have a pronounced influence on the crop, with respect to chemical purity, crystal size and degree of agglomeration, and solid-state form. Thus, crystallization and the downstream processes have a mutual interference. 

These effects are difficult to model, so a sampling scheme for the suspension from the crystallizer and after solid-liquid separation and drying is advisable. 

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. 

Crystallization Basic Concepts and Industrial ApplicatioiK, First Edition. Edited by Wol ang Bedanann. 

Although there are several ways in which solid/liquid separation may be achieved (e.g. settling, flotation, hydrocyclones, evaporation, magnetic, electrostatic, gravity, centrifuge, vacuum, and pressure), the mechanisms that consume the largest volume of textile filter media, and on which this section will concentrate, are those of pressure and vacuum. 

Media type Approximate minimum particle size retained (pm) 

There are many factors which confront the technologist when choosing or designing a fabric for a particular application. These may conveniently be grouped under the following general headings  

By comparison, polypropylene is generally inert to both strong acids and alkalis and, primarily for this reason, is the most widely used polymer in Uquid filtration. On the down side, this material is limited by its relatively poor resistance to oxidising agents (Fig. 3.11) - nitric acid and heavy metal salts fall into this category - and at temperatures above 90-95 C stabiUty problans may be encountered, especially if the 

Some of the more common fibres (and their general properties) whieh are used in industrial filtration are listed in Table 3.4. Note that the maximum operating temperatures shown in Table 3.4 are somewhat lower than in a previous table and reflect the influence of continuous exposure to aqueous conditions. However, in the absence of official published data, these should only be used as a general comparative guide. 

The first step in downstream processing is the separation of msolubles from the fermentation broth. The selection of a separation technique depends on the characteristics of solids and the liquid medium. 

The solid particles to be separated are mainly cellular mass with the specific gravity of about 1.05 to 1.1, which is not much greater than that of the broth. Shapes of the particles may be spheres, ellipsoids, rods, filaments, or flocculents. Typical sizes for various cells vary widely such as, 

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D. B. Purchas, Solid-Liquid Separation Technology, Uplands Press, 1981. 

Peter Harriott/ Ph.D./ Professor, School of Chemical Engineering, Cornell University Member, American Institute of Chemical Engineering (AlChE), American Chemical Society (ACS). (Selection of a Solids-Liquid Separator)... 

Julian C Smith/ B Chern./ Ch E / Profes.sor Ementus, Chemieal Engineering, Cornell University Member, Ameriean Chemieal Soeiety, (ACS), Ameriean In stitute of Chemieal Engineers (AJChE). (Seleetion of Solids-Liquid Separator)... 

Purchas (ed.), Solid/Liquid Separation Equipment Scale-Up, Uplands Press, Croydon, England, 1977.]... 

Table 18-19 lists the pertinent background information that should be assembled. It is typical of data requested by manufacturers when they are asked to recommend and quote on a solid-liquid separator. The more accurately and thoroughly these questions can be answered, the better the final choice is likely to be. 

TABLE 18-19 Data for Selecting a Solids-Liquid Separator ... 

Modification of Process Conditions Relatively small changes in process conditions often markedly affect the performance of specific solids-liquid separators, makiug possible their application when initial test results indicated otherwise or vice versa. Flocculating... 

L., and Thew M. T., (eds.). Hydrocyclones Analysis and Applications, p. 95, Kliiwer Academic Publishers, Dordrecht, The Netherlands, 1992. Dahlstrom D. A., Fundamental of Solid-Liquid Separation, Mnlar A. L., and Anderson,... 

Joseph D Henry/ Jr./ Ph.D./ P.E./ Senior Fellow, Deportment of Engineering and Public Policy, Carnegie Mellon University Member, American Institute of Chemical Engineers, American Society for Engineering Education. (Section Editor, Alternative Solid/Liquid Separations, Crystallization from the Melt)... 

Surface-Based Solid-Liquid Separations Involving a Second... 

SURFACE-BASED SOLID-LIQUID SEPARATIONS INVOLVING A SECOND LIQUID PHASE... 

Even though surtace-property-based liquid-solid-liquid separation techniques have yet to be widely used in significant industrial applications, several studies which demonstrate their effectiveness have appeared in literature. 

There are several advantages that vacuum filtration has over other solid-liquid separation methods. Some of these advantages include ... 

In this subsection, basic design theory for preliminary sizing and specifying equipment are reviewed. Some sample design calculations are included. References cited at the end of tlie chapter can be consulted for more detailed information and design methods. For solid-liquid separation methods, the reader should refer to Liquid Filtration, 2" edition, by N. P. Cheremisinoff, Butterworth-Heinemarui Publishers (1998). 

Moody, G. M., 1994. In Selection and Scale - Up for Solid/Liquid Separation, The Filtration Society 30th Anniversary Symposium, p.9-29... 

Cheremisinoff, P.N., Pocket Handbook for Solid-Liquid Separations, Gulf Publishing Co., Houston, TX, 1984. 

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