Blade agitators

FIG. 18-41 Agitator blades for double-arm kneaders a) sigma (h) dispersion (c) miiltiwiping overlap (d) single-curve (e) doiible-naben. (APV Baker Ferkins, Inc.)... 

E = height of the agitator from the bottom of the tank J = baffle width L = agitator blade length W = agitator blade width... 

Peters, D. C. and Smith, J. M. Trans. Inst. Chem. Eng. 45 (1967) 360. Fluid flow in the region of anchor agitator blades. 

The streamlines of this flow are shown by Peters and Smith (12). In this case, the effective thickness of this layer appears to be about equal to the gap with the wall, indicating a pressure flow about equal to the drag flow. It can be calculated that this would increase the maximum shear rate on the fluid passing under the agitator blade by a factor of seven. 

Todd [64] applied heat transfer technology from hatch mixer tanks using close-fitting agitator blades [65] to model heat transfer data from twin-screw extruders. The model that best fit his data is as follows ... 

Figure 13.3 A schematic diagram of agitation fluidized bed granulator (NQ-i60, Fuji Paudal). i Agitation fluidized bed. 2 Bag filter. 3 Spray nozzle. 4 Blower. 5 Heater. 6 Motor. 7 Agitator blade. 8 Slit plate. 9 Image probe. 10 Image processing system. II Host computer. 12 Controller. 13 Pump. 14 Binder. Reprinted from Watano et al. (2001) with permission from Elsevier Science.

The lower flammability limit for fine mists (<0.01 mm diameter) of hydrocarbons below their flash point, plus accompanying vapor, is about 48 g of mist/m3 of air at 0°C and 1 atm. Mist can occur in agitated vessels under some conditions, especially when an agitator blade is at or near the liquid-vapor interface in the vessel. 

Ace Glass Inc., catalog no. 8256-G, stirring rod 8258-A 2 -in., paddle-type Teflon agitator blade. 

Intimate mixing is accomplished in change-can mixers in two ways. One method is to have the mixing-unit assembly revolve in a planetary motion so that the rotating blades sweep the entire circumference of the can (Fig. 18-39). The other is to mount the can on a rotating turntable so that all parts of the can wall pass fixed scraper blades or the agitator blades at a point of minimum clearance. 

The mixing curve can be obtained for any reactor/agitator system. Equipment vendors usually have a curv e for a particular system, provided the agitator blades, baffling and other internals have not been altered. An alternative is to build a geometrically similar model in the laboratory and determine the mixing curve with a mixing kit [2,3 ... 

Notes For three sets of agitator blades, for a 350-gal reactor. 

Agitated batch driers consist of a jacketed cylindrical vessel with agitator blades designed to scrape the bottom and walls. They may operate at atmospheric pressure or under vacuum. Pasty materials that could not be handled in tumbling or fluidized-bed driers, may be successfully dried at rates higher than can be achieved in an oven. 

In a moving and stirred bed reactor, the most inqrortant parameters representing the feedstock flowing behavior are the residence time the velocity of feedstock movement and the feedstock bed thickness in the reactor The "Single Blade Volume Output" model proposed in this work is based on the assumption that at the outlet of the reactor, the amount of feedstock accumulating in front of each agitation blade is determined by the value of Abusing a power expression,... 

The batch scale rotative reactor was developed and used as a tool to validate the new heat transfer model [4, 6]. The batch reactor consists of a well insulated tank which contains molten salt and is equipped with heating elements in order to be able to heat the salt to the set point temperature. A second well insulated tank can be placed in the salt bath. The feedstock enters the reactor through the feedpipe. The same agitation blades as those found in the industrial reactor are used. The stirring mechanism transports and agitates the feedstock in a circular manner. The center of the reservoir is kept free of feedstock by a scraping mechanism. The diameter of the feedstock tank is 107 cm and the effective heat transfer area is 0.82 m [6]. 

The PDU vacuum pyrolysis reactor is a semi-continuous horizontal pilot plant reactor 3 m long with a diameter of 0.6 m and a throughput capacity of about 50 - 200 kg/h, depending on the feedstock treated. The configuration of the PDU reactor is almost the same as that of the industrial reactor, except t t the PDU has smaller agitation blades. Two types of tests have been conducted with this reactor, the cold and the hot runs. In the cold tests, the particle flow behaviour is studied by a stimulus-response technique, under different agitation speeds and feed rates. The hot tests enable the conversion to be determined as a function of the feed rate and the agitation speed. 

The main parameter influencing the value of y is the speed of the agitation blades [7]. Through cold tests in the rotative reactor, the experimental values of / can be determined. The results are shown in Table 3. 

Figure 6 Predicted Residence Time in the Industrial Reactor as a Function of the Velocity of the Agitation Blades.

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