Mechanical Classifiers

Fig. 6. Schematic of a mechanical classifier with submerged spiral rake where (-) is the pool level and slope = 1 4 to 1 3 (27).

This ring closure is the final step of the reaction of hydrazines with 1,3-difunctional compounds (Section 4.04.3.1.2(ii)), and numerous examples in the literature of pyrazoles have been described. In some cases the N—C ring closure occurs by a concerted mechanism, classified by Huisgen (80AG(E)947) as 1,5-electrocyclizations. 

The Majac jet pulverizer (Ho.sokawa Micron Powder Sy.stems Div.) is an opposed-jet type with a mechanical classifier (Fig. 20-55). Fineness is controlled primarily by the classifier speed and the amount of fan air dehvered to the classifier, but other effects can be achieved by variation of nozzle pressure, distance between the muzzles of the gun barrels, and position of the classifier disk. These pulverizers are available in 30 sizes, operated on quantities of compressed air ranging from approximately 0.6 to 13.0 mVmin (20 to 4500 ftV min). In most apphcations, the economics of the use of this type of jet pulverizer becomes attractive in the range of 98 percent through 200 mesh or finer. 

As representative examples of the various machineries used for classification mention may be made of mechanical classifiers, hydraulic classifiers, and hydrocyclones. Simplified sketches of these have been shown in Figure 2.12 (A-C). 

The mechanical classifier is extensively used where it is necessary to separate a large amount of fines from the oversize material. Arrangement of a number of mechanical... 

For practice in recognizing mechanisms, classify each reaction according to the type of mechanism you expect ... 

Mechanical Classifiers.—These devices consist of a tank into which the material fed flows at one end and what does not settle in the tank overflows at the lower end. Mechanical means are provided for removing the settled material. These devices have attained much use in ore mills of late years but others of similar... 

Mechanical classifiers are used in closed-circuit grinding (see Fig. 29.15), especially in metallurgical operations. Here the relatively coarse particles are called sands and the slurry of fine particles is called slimes. SufScient time is provided to allow the sands to settle to the bottom of the device the slimes leave in the effluent liquid. 

Size separation is a process which often follows size reduction its purpose is to separate and classify the solid particles according to their size. The main methods are screening, magnetic separation, and mechanical classifying. Magnetic separation is limited to iron and similar metals, and is often used to separate iron impurities from other materials to eliminate damage to chemical plant or discoloration of the products. 

Reaction mechanisms classified schematically according to relative impact parameter b (f-wave). Large values of b are classified as peripheral collisions and small values as central collisions... 

Figure 1.47 The typical form of a mechanical classifier with rakes (in the rotating screw version a helical screw replaces the rake mechanism).

Another unusual glycosidase mechanism classified is encountered in family 4, which requires a unique NAD" and Mn " " assisted catalysis. Those enzymes do not follow the classical double-displacement mechanism but act through multiple catalytic steps involving oxidation-elimination-addition and reduction reactions. Other interesting examples can also be found in the case of trans-sialidases and a-glucan lyases. ... 

This is essentially a process to separate the particles according to their sinking rates in water. Wet classifiers are used with grinding and may include rubber-lined or ceramic cyclones (called hydrocyclones) and spiral mechanical classifiers. 

The spiral mechanical classifier is used in pools. The heavier particles are allowed to settle in the pool while the finer particles float and flow out of the pool. The heavier particles are then removed from the bottom of the pool with a spiral or mechanical device. 

A mechanical classifier is a combination of an open channel flow, a weir, and a mechanical device to remove sohds. The trough to which the slurry is directed is inclined with respect to the horizontal. On one side, a weir is constructed opposite to the direction of the flow. The heavier sohds deposit upstream of the weir, whereas the finer solids pass over it. This system operates on the principle of the shding bed described in Chapters 4 and 6. 

Mechanical classifiers are expensive to install but in some apphcations they are selected for high-density valuable minerals as they assist in their immediate recovery without requiring further complicated flotation circuits. In some respects, flotation circuits use some of the principles of mechanical classifiers by using a circular internal weir, a mixer, an underflow pump, and a separate froth pump. 

The reader is directed to three comprehensive reviews and a conference publication, dealing with the reactive-element effects on oxidation Whittle and Stringer (1980), Stott and Wood (1987), Moon and Bennett (1989) and Lang (1989), thus only a broad summary of proposed mechanisms, classified as either chemical, physical or mechanical effects is presented here. These may be further, or even alternatively, sub-divided into effects relating to (i) initial oxidation, (ii) growth-rate, (iii) scale adhesion, or (iv) cracking. 

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