Solid-liquid separation screening

The simplest type of extraction equipment is the stirred tank, coupled with a solid-liquid separation step such as a screen, filter, or centrifuge to separate the marc from the extract. This equipment is readily available in a wide variety of sizes and can be operated as a single-batch extractor or run in series in a countercurrent mode as shown in Figure 11.6. 

If a screen is installed at the bottom of the tank, the solid-liquid separation can take place within the extraction equipment. The extract drains out of the tank, leaving the solids behind. Water can then be added to reslurry the solids, washing solvent from the marc. However, some means of removing the washed marc from a tank equipped with a screen is needed. Where external filtration or centrifuging equipment is used, solvent can be removed from the marc by water washing or conveying to an external dryer. 

When the required particulate removal eflBciency has been determined for each size fraction in the distribution, the technical feasibility of available solids/liquid separation processes must be evaluated. Such a screening procedure will provide the framework for determining the extent of analytical modeling or pilot plant studies needed to develop process design criteria. The solids/liquid separation processes used in water and wastewater treatment exploit the physical-chemical properties of the particulates to achieve rapid and therefore economical separation from the treated water. Microscreening devices remove most particulates with at least one dimension larger than the minimum opening in the... 

In ROM coal, a large portion of both coal and shale is already liberated sufficiently to permit immediate concentration. Because dewatering of coarse coal is much more efficient and cheaper than that of fines, and because many users prefer larger size fractions for their particular processes, the preparation of feed before cleaning has traditionally consisted of as little crushing as possible. Therefore, coal preparation consists mostly of gravity concentration and to some extent flotation, complemented by screening and solid/liquid separation auxiliary processes. 

A schematic flow diagram of a wastewater treatment plant is shown in Figs. 9.9 to 9.12. In primary physical treatment, solid material is separated from the liquid by screens, settling tanks, and skimming devices. This removes about 50 percent of the pollutants. The remaining organic material is subjected to biological treatment. 

The liquid fat or oil coming from the press contains 2% to as much as 15% fat-free solids, which is usually separated out in a two-step procedure. First, the bulky solids are separated in a settling chamber equipped with a drag that collects the solids, passes them over a drainage screen, and then drops them into the conveyor taking fresh material to the screw-presses. The second step is to clarify the liquid in a manual or automatic plate-and-frame filter press. 

Screening (Fig. 1C) is a type of surface filtration to separate solids and liquid by screens with openings smaller than particle size. It is usually employed among the first few steps of a SLS process. Vibrations and other mechanism are often applied to avoid blinding of the screens. 

Filtration Centrifugation Sedimentation Cyclone separator Electrostatic precipitator Demister Magnetic separator Screening Liquid-solid Liquid-solid or liquid-liquid Liquid-solid Gas-solid or Gas-liquid Gas-solid Gas-solid or gas-liquid Solid-solid Solid-liquid Solid-solid Pressure reduction Centrifugal force Gravity Flow Electric field Pressure reduction Magnetic field Size of particles... 

Filtration is the separation of a fluid-solids mixture involving passage of most of the fluidthrough a porous barrier which retains most of the solid particulates contained in the mixture. This subsec tion deals only with the filtration of solids from liquids gas filtration is treated in Sec. 17. Filtration is the term for the unit operation. A filter is a piece of unit-operations equipment by which filtration is performed. The filter medium or septum is the barrier that lets the liquid pass while retaining most of the solids it may be a screen, cloth, paper, or bed of solids. The hquid that passes through the filter medium is called the filtrate. 

The production of aluminum begins with the mining and beneficiation of bauxite. At the mine (usually of the surface type), bauxite ore is removed to a crusher. The crushed ore is then screened and stockpiled, ready for delivery to an alumina plant. In some cases, ore is upgraded by beneficiation (washing, size classification, and separation of liquids and solids) to remove unwanted materials such as clay and silica. 

FUter medium The permeable portion of a filtration system that provides the liquid-solid separation, such as screens, papers, non-wovens, granular beds and other porous media. 

These operations may sometimes be better kno Ti as mist entrainment, decantation, dust collection, filtration, centrifugation, sedimentation, screening, classification, scrubbing, etc. They often involve handling relatively large quantities of one phase in order to collect or separate the other. Therefore the size of the equipment may become very large. For the sake of space and cost it is important that the equipment be specified and rated to Operate as efficiently as possible [9]. This subject will be limited here to the removal or separation of liquid or solid particles from a vapor or gas carrier stream (1. and 3. above) or separation of solid particles from a liquid (item 4j. Reference [56] is a helpful review. 

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