Solid bowl systems

If a cylindrical bowl holding a slurry is left to stand, the solids will settle out under the force of 1 g or gravity. By spinning the bowl the solids will settle under the influence of the centrifugal force generated as well as the force of gravity which is now negligible. Solids will collect at the wall with a liquid layer on top. This is an example of a sedimentation in a solid bowl system. 

Sedimentation centrifuges are commonly known as solid bowl systems, i.e., perforated bowls that are used to separate materials such as cream from milk, sludges from water in waste water treatment plants, and, of course, the biotechnology materials. 

Centrifugation is performed in a closed system and is therefore an excellent choice for treating volatile fluids. The liquid and solid are mechanically separated by centrifugal force. The removal of most of the liquid increases the solid concentration in, and reduces the volume of, the waste stream. The collected solid waste may then be treated and disposed of or recovered. Three types of units are available for centrifugation the solid bowl, the disk, and the basket. The first two are used in large plants, the third in smaller plants. 

The first two illustrations are of typical pilot plant-size centrifuges. Figure I is a continuous, solid bowl centrifuge especially suitable for studying the recovery and concentration of polymer solids from hydrocarbon mother liquor. It is of the standard model that has been widely used for this purpose in the past. A similar size centrifuge is also available for operation under pressures up to 1 atm. gage and higher if required, for continuous operation in a pressurized system. 

Experience has shown that this system is now in satisfactory condition for further separation and purification on perforated basket centrifuges. These, on systems with which they are compatible, have the advantages of more completely separating the solid and liquid phases, recovering the solids at lower residual volatile content, and greatly improved rinsing of the solids for reduction of their mother liquor impurity content, than is possible on the solid bowl type of centrifuge. 

A final mixing system worthy of mention is that used by the Canadian Armament Research and Development Establishment and Bristol-Aerojet, which is a horizontal ribbon mixer. In this case, the blades carry the material from the center to the ends of the mixer and return it by internal spirals along the center shaft. This mixer is noted for its rapid incorporation of solids and the ease by which material is discharged as compared with the other fixed bowl, batch mixers. A comparison of typical batch mixers is shown in Table II. 

Solids and liquids are discharged continuously in this type of design which can process coarse particles that would blind the discharge system and disks of disk bowl machines. The principle of operation is shown in Fig. 1. 

In a manual design, the bowl is one piece and the system must be stopped and opened up to discharge the collected solids. In a continuous operation, such as a wall-valve-discharge centrifuge, the bowl is made of two cones, a top and a bottom, which periodically separate to release the solids at full rotational speed. 

Original 1,2,4,5-tetrazines disubstituted by heterocyclic rings have been prepared and their electrochemical and spectroscopic properties studied <04NJC387>. A bowl-shaped neutral radical with a core annulene system bearing a verdazyl radical 47 has been synthesized in two steps from aldehyde 44 and carbazide derivative 45, as a stable solid in air <04OL1397>. 

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