Filtering centrifuges selection

Knowledge of the most critical aspect of the process can guide the sometimes difficult selection process. For example, the requirement of a very dry product with strict impurity levels suggests a filtering centrifuge. A product with a feed rate of 150 gpm, without wash requirements, would lead us to a continuous sedimentation centrifuge. 

The selection depends to a great extent on the rate of growth of the cake. This rate has a major effect on the following choices batch versus continuous process pressure or vacuum gravity filters and separation technique (filters, centrifuges, etc.). Table 22.8 (features of slurry), Table 22.9 (selection of filters), and Table 22.10 (comparison of separation processes) aid in this effort. 

In general, the filter centrifuges can be classified into two groups batch and continuous type. Several selected filtering centrifuges are listed in Fig. 18. 

Solid samples are generally treated in one of two ways. If completely soluble, they can be dissolved directly and completely in a suitable solvent. Alternatively, if the samples contain insoluble materials that are of no interest, then they can be extracted with a selected solvent to obtain the relevant compounds in solution. The extract can be subsequently filtered or centrifuged to remove any unwanted substances that make up the sample matrix. The procedure will differ, depending on the amount of the substances present that are germane to the analysis. The preparation of samples for LC analysis from solid... 

In fine chemicals manufacture, batch filtration prevails. This operation is the subject of R D in various steps of process development. The aim of R D on filtration is (1) to establish an effective procedure of filtration and washing providing a filter cake and/or filtrate of desired quality, and (2) to select the most appropriate filter or centrifuge for full-scale operation and determine its productivity. The productivity is defined as ... 

The design, construction and application of thickeners, centrifuges and filters is a specialised subject, and firms who have expertise in these fields should be consulted when selecting and specifying equipment for new applications. Several specialist texts on the subject are available Svarovsky (2001), Ward (2000) and Wakeman and Tarleton (1998). The theory of sedimentation processes is covered in Volume 2, Chapter 5 and filtration in Chapter 7. 

---