Impeller stabilizers

In the Agitair Rotation machine (Fig, 19-76), the impeller is a Rat rubber-covered disk with steel Fingers extending downward From the peripheiw, A rubber-covered stabilizer eliminates dead spots in the agitation zone and improves biibble-ore contact. The degree oF aeration is controlled bv regulating air volume on each cell with an individual air v alv e. Air is supplied at 10 x lO Pa (1,5 IbF/iir),... 

The proper method to remove the catalyst involves stabilization. The method for this is usually recommended by the catalyst manufacturer. With the reactor still closed, cold and flushed with nitrogen, admit nitrogen with less than 1 % oxygen in it, while the impeller is running. This oxidizes the organics and the metallic surface of the catalyst under well-controlled conditions after which the catalyst can be exposed to air without danger of overheating. 

An example of liquid/liquid mixing is emulsion polymerization, where droplet size can be the most important parameter influencing product quality. Particle size is determined by impeller tip speed. If coalescence is prevented and the system stability is satisfactory, this will determine the ultimate particle size. However, if the dispersion being produced in the mixer is used as an intermediate step to carry out a liquid/liquid extraction and the emulsion must be settled out again, a dynamic dispersion is produced. Maximum shear stress by the impeller then determines the average shear rate and the overall average particle size in the mixer. 

The impeller configuration has a major impact on stability and operating envelope. There are two impeller configurations in-line and back-to-back, or opposed. With the in-line design, all impellers face in the same direction. With the opposed design, impeller direction is reversed in adjacent stages. 

This research used mechanically agitated tank reactor system shown in Fig. 1. The reactor, 102 mm in diameter and 165 mm in height, was made of transparant pyrex glass and was equipped with four baffles, 120 mm in length and 8 mm in width, and six blades disc turbine impeller 45 mm in diameter and 12 mm in width. The impeller was rotated by electric motor with digital impeller rotation speed indicator. Waterbath thermostatic, equipped with temperature controller was used to stabilize reactor temperature. Gas-liquid mass transfer coefficient kia was determined using dynamic oxygenation method as has been used by Suprapto et al. [11]. 

Adding stabilizer fins to the impeller blades will help reduce some of these loads. Such fins also permit the agitator to operate closer to critical speed, perhaps at 80 percent rather than 65 percent. 

Suppose, for instance, that the 2.5-in shaft is used and stabilizer fins add 16 lb (7.3 kg) to the weight of the lower impeller. The equivalent weight increases accordingly ... 

Equation (18-39) displays the competing factors that stabilize secondary nucleation in an operating crystallizer when nucleation is due mostly to impeller-crystal contact. Any increase in particle size produces a fifth-power increase in nucleation rate, tending to counteract the direction of the change and thereby stabilizing the crystal-size distribution. From dimensional argument alone the size produced in a mixed crystallizer for a (fixed) nucleation rate varies as (B ). Thus, this fifth-order response of contact nucleation does not wildly upset the crystal size distribution but instead acts as a stabilizing feedback effect. 

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