Agitator hollow shaft

Mechanical agitator (hollow-shaft turbine) Medium to high 900Wm 2 K, limited exchange area Heat exchange capacity... 

The Dorr agitator (Coulson and Richardson, loc. cit.) consolidates in one unit the principles of the thickener and the Pachuca tank. Resembling a rake-equipped thickener, it differs in that the rake is driven by a hollow shaft through which the solids-liquid suspension is lifted and circulated by an air stream. The rake moves the pulp to the center, where it can be entrained by the air stream. The unit may be operated batchwise or continuously. 

A gas-inducing agitator system is an alternative to a multistirrer system. It contains a hollow shaft with orifices above the liquid level and a hollow impeller. A typical hollow impeller consists of a tube that is, at the centre, connected to the hollow shaft. Both ends of the impeller are cut at 45 so that, at rotation, the open portions of the tube are at the near side of the stirrer. There are several modifications of this design. Obviously, there is a minimum impeller speed at which the onset of gas induction occurs. Loop reactors are also successfully used. 

The third factors to control and keep constant are the gas pressure and superficial gas velocity. This probably will involve gas recirculation with either a small compressor, or through a hollow shaft or some other pumping device. As seen before, the bubble diameter, the mass transfer area, the gas hold-up, and the terminal bubble-rise velocity, all depend on the superficial velocity of the gas and the power input per unit volume. When these are kept constant, the various mass transfer resistances in the pilot plant and in the large unit will be the same, hence the global rate will be conserved. The last factor is the input power to the agitator. As required for mass transfer, the scale-up must be made on the basis of constant power input per unit volume. If turbulent conditions and geometrical similarity prevail, this rule imposes the following relationship ... 

Fig. 8. Inducing type of agitated contactor. I, vessel 2, hollow shaft 3, hollow impeller 4, baffles 5, gland and stuffing box 6, orifice on the impeller 7, gas inlet 8, bearing housing 9, pulley 10, liquid drain. (After Joshi et at., 1985.)...

Fig 6.3. Reactor agitation as provided by a six blade Rushton turbine. Gas dispersion is enhanced by holes in the hollow shaft. (Courtesy Autoclave Engineers.)... 

Agitator Type 54rin. three-blade impeller, glass-covered, hollow shaft for thermometer R.p.m. 90... 

Self inducing agitators have been on the market for many years These communicate the low pressure region behind the blades with the head space Figure 15.4a) or a gas supply source via a hollow shaft and therefore use some of the input shaft energy to draw in the gas. Often they have multiple blades, sometimes curved like a centrifugal pump impeller,... 

An alternative method of agitation of a tubular reactor is the rotation of the reactor itself. Flow of solids is caused by mounting it in a position slightly inclined to the horizontal, and caking upon the sides is sometimes prevented by the presence of, for example, a loose H section beam or similar heavy article along the length of the tube. The powder feed can enter the end of the reactor via the hollow shaft upon which the reactor rotates. Similarly it can leave via a lower hollow shaft, gas being passed in the reverse direction. 

Fig. 14. Reactor of the continuous organomagnesium synthesis of organoethoxysi-lanes 1 - cooling jacket 2 - rake element 3 - choke for loading off the products of the reaction 4 - choke for loading magnesium 5 - agitator shaft 6 - separator 7 -spiral (hollow pipe) 8 - thermocouple pocket 9 - choke for loading the reactive mixture 10 - casing of the reactor...

Dorr Agitator.—This is an ordinary tank in the center of which is a vertical shaft to the bottom of which are attached two arms with rakes, so that when the shaft is revolved they will rake any solids which settle out towards the center. This shaft in the center is hollow and has openings at the bottom and top and it is made into an air lift by a compressed-air pipe leading in at the bottom. To the top of the shaft are attached two perforated launders which revolve with the shaft and any material coming up through the center of the air lift flows into them and will be distributed over the entire surface of the solution in the tank. 

Tlie large-spiral hollow-flight type (Fig. ll-60d) is an adaptation, with external bearings, full fill, and salient construction points as shown, that is highly versatile in application. Heat-transfer coefficients are 34 to 57 W/(m °C) [6 to 10 Btu/(h ft °F)] for poor, 45 to 85 W/(m2 °C) [8 to 15 Btu/(h ft °F)] for fair, and 57 to 114 W/(m= °C) [10 to 20 Btu/(h ft °F)j for wet conductors. A popular version of this employs two such spirals in one material-handhng chamber for a pug-mill agitation of the deep solids bed. The spirals are seldom heated. The shaft and shell are heated. 

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