Separation of solids from gases

Introduction.—This subdivision will fall into the following sub-heads Separation of solids from solids separation of solids from liquids liquids from liquids and the separation of solids from gases. The separation of liquids from liquids is also covered under Distillation. ... 

SEPARATION OF SOLIDS FROM GASES CYCLONES. Most centrifugal separators for removing particles from gas streams contain no moving parts. They are typified by the cyclone separator shown in Fig, 30.38, It consists of a vertical cylinder with a conical bottom, a tangential inlet near the top, and an outlet for dust at the bottom of the cone. The inlet is usually rectangular. The outlet pipe is extended into the cylinder to prevent short-circuiting of air from inlet to outlet. 

The field of filtration in its widest sense covers the capture of particles ranging in size from several millimetres down to the molecular scale. Table 71 provides an indication of the various particle size ranges, and where textile filter media fit into this picture. The industrial filtration processes on which the chapter will concentrate are separated into two broad sections, namely, the separation of solids from gases, more commonly referred to as dust collection, and the separation of solids from liquids, usually referred to as liquid filtration. 

Separation of solids from gases (dust removal)... 

Figure 3.4.19 Technologies involved in the separation of solids from liquids and gases.

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

In this section, the general design of the hydrocyclone and its application in the grading of solid particles, or their separation from a liquid, is considered and then the special features required in hydrocyclones required for the separation of immiscible liquids will be addressed. The use of cyclones for separating suspended particles from gases is discussed in Section 1.6.2. 

Instead of filtration or centrifuging as a means of separating the crystallized wax from oil, an electrical precipitation method has been proposed, similar to that employed in desalting of crude or removal of entrained solids from gases. 

There are a number of different forms of cyclone but the reverse flow cyclone represented in Fig. 1 is the most common design used in the industry. The cyclone consists of four main parts the inlet, the separation chamber, the dust chamber and the vortex finder. Tangential inlets are preferred for the separation of solid particles from gases [1]. In this study, the numerical simulation deals with the standard case of reverse flow cyclone with a tangential rectangular inlet. Cyclone dimension used in this simulation are as shown in Table 1. 

During the separation of solid, liquid and gaseous pollutants from exhalates, different processes may be used. Solid and liquid particles (dust, fly ash, aerosols) are retained in different types of separators. In the capture and destruction of gaseous pollutants, many chemical and physico-chemical principles are used. Separation equipment for solid and liquid particles are characterized by a higher degree of development than those for the separation of gases and vapours, which are still in the course of development. 

Drying is used to separate volatile eomponents called moisture from a carrier. In many cases this implies the separation of water. The carrier may be solid, hquid, or gas. In this chapter only the drying of solid materials shall be discussed. The presented methods are also applicable to paste-like materials. Drying of fluids denotes the removal of small amount of water from gases or organic liquids. Adsorption as well as absorption and rectification processes are used for this. Thus, the drying of liquids and gases has been dealt with in other chapters. 

Recovery techniques exist for the separation of solvents from solids, residues, liquids, including water, and from gases. These are achieved by such technologies as decanting, distillation, liquid-liquid extraction, condensation, adsorption and absorption. In many instances several processes are used in series to achieve the most efficient recovery, or desired quality, from the recovered solvent. A summary of the principal technologies used in solvent recovery is discussed below. 

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