Types of Filtration Equipment

Crossflow filtration membranes are available in a variety of configurations. These are hollow fiber, tubular, flat plate, spiral wound, and rotating. Some key characteristics of each module are given in Table 12.2 reproduced here from [6]. 

Filtration is a separation process which uses pressure differentials through a porous medium to separate suspended or dissolved solids. The two broad categories of filtration are conventional filtration where the fluid flow is perpendicular to the filter medium, and crossflow filtration where it is parallel to the medium. The filter media in conventional filtration are filter cloths, meshes or screens, while in crossflow 

Module type Channel Packing spacing(cm) density (m Energy ) costs Particulate plugging Ease of cleaning 

Spiral wound 0.03-0.1 600 Low Very high Poor-fair 

---

The type of filtration equipment you select for use depends upon which of the two components, the solid or the liquid, you are trying to isolate. In i. general ... 

Various types of filtration equipment are available commercially and can be operated in batch, semicon-tinuous, or continuous modes. Among the commonly used types are the plate and frame filter, rotary drum filter, leaf filter, plate filter, and tray filter. Apart from the plate and tray filters, all other are enclosed and therefore are easy to work with when sterility of the solids is an important issue. Moreover, all these filters are examples of dead-end filters. Cross-flow filtration is mostly used in the purification stage through membranes with very low pore sizes and is discussed later. 

A nonwoven material, for example, would be a felt. They are pads of short nonrandom fibers, made of rigid constmction suitable for many types of filtration equipment. 

In an attempt to organize the almost overwhelming number of different types of filtration equipment, two classification schemes have evolved for continuous operations. The first scheme is based on operating pressure differentials and is provided in Table 1. The second scheme is based on the relative difference between gravity force and filtrate motion. Three orientations are possible forces acting in... 

Classification of filters. There are a number of ways to classify types of filtration equipment, and it is not possible to make a simple classification that includes all types of filters. In one classification filters are classified according to whether the filter cake is the desired product or whether the clarified filtrate or outlet liquid is desired. In either case the slurry can have a relatively large percentage of solids so that a cake is formed, or have just a trace of suspended particles. 

Prior to discussing any specific types of filter media, 1 wish to give a small representation of various types of filtration equipment or hardware, which is the vehicle in which the medium operates. 

Various types of filtration equipment or hardware employ one of four main classes of driving force gravity, vacuum, pressure or centrifugal force. The choice of which type of equipment to use in a specific application depends upon many widely differing factors, which will not be detailed in this chapter. 

The market forces exerted by the imposition of environmental legislation are an important driver for the filtration market. The legislation calls for waste nuni-mization and for the tieatment of unavoidable waste streams to continually higher standards, both of which are well met by available and developing types of filtration equipment. 

Figure 11.6 is of two types of sedimentation equipment, and Figure 12.2(e) of another. They are used for clarifying a valuable liquid or for preparing a concentrated slurry for subsequent filtration. They depend on gravitational sedimentation. Removal is assisted by rake action, or by the conical sides of the vessel of Figure 11.6(b). 

Filtration. Filtration can include filter presses, rotary drum vacuum filters (RDVF), belt filters, and variations on synthetic membrane filtration equipment, such as filter cartridges, pancake filters, or plate and frame filter presses. These processes typically operate in a batch mode when the filter chamber is filled up or the vacuum drum cake is exhausted, a new batch must be started. This type of filtration is also called dead-end filtration because the only fluid flow is through the membrane itself. Due to the small size of cells and their compressible nature, typical cell cakes have low permeability and filter aids, such as diatomaceous earths, perlite, or other mined materials are added to overcome this limitation. Moreover, the presence of high solids and viscous polymeric fermentation byproducts can limit filtration fluxes without the use of filter aids. 

Fitch (1974) discussed the general problem of matching process specifications to SLS equipment and the necessity of considering trade-offs involving such items as filtrate clarity, cake dryness, reliability, maintenance, versatility, and cost. In Table 22.10, a comparative profile of aU major types of SLS equipment is given. It should be emphasized that a wide range of performance occurs because of the endless variation in slurries, and the descriptive terms would undoubtedly vary some if another author were to prepare the same table. 

The types and styles of filtration equipment are legion, but generally fall into one of the four categories viz, gravity, vacuum, centrifuge and pressure. 

Insulating oil plays a vital part in many types of electrical equipment, not only as an insulant but also as a coolant in transformers and as an arc extinguishing medium in circuit breakers. In each case, efficient operation of the equipment depends upon the purity of the insulating oil, which in service can be contaminated by oxidation, condensation and the presence of solids, such as colloidal carbon, formed by arcing in circuit breakers. The electrical and physical properties of the oil may be seriously affected, resulting in reduced operating efficiency or even equipment failure. Frequent replacement of the oil wiU be too costly, and reconditioning by filtration and vacuum dehydration to remove all contaminants is the economic answer. 

Filtration. In many mineral processing operations, filtration follows thickening and it is used primarily to produce a soHd product that is very low in moisture. Filtration equipment can be either continuous or batch type and either constant pressure (vacuum) or constant rate. In the constant pressure type, filtration rate decreases gradually as the cake builds up, whereas in the constant rate type the pressure is increased gradually to maintain a certain filtration rate as the cake resistance builds. The size of the device is specified by the required filter surface area. 

---