Mechanical agitator design

Rotation speeds to 40 r/min are possible with cakes typically 3 to 6 mm (0.12 to 0.24 in) thick. Filter sizes range from 930 cm to 19 m (1 to 207 ft") with 93 percent of the area active. The slurry is fed into a conical feed tank designed to prevent solids from settling without the use of mechanical agitators. The proper hquid level is maintained by overflow, and submergence ranges from 5 to 70 percent of the drum circumference. 

Often heat removal causes design problems for scale-up. Mechanical agitation coupled with a metabolic heat from the growing biomass... 

As mentioned above batch crystallizers are usually simple vessels provided with some means of mechanical agitation or particulate fluidization. These have the effect of reducing temperature and concentration gradients, and maintain crystals in suspension. Baffles may be added to improve mixing and heat exchange or vacuum systems may be added, as appropriate. Various design combinations are available and some are illustrated in Figure 7.1. 

Mass transfer across the liquid-solid interface in mechanically agitated liquids containing suspended solid particles has been the subject of much research, and the data obtained for these systems are probably to some extent applicable to systems containing, in addition, a dispersed gas phase. Liquid-solid mass transfer in such systems has apparently not been studied separately. Recently published studies include papers by Calderbank and Jones (C3), Barker and Treybal (B5), Harriott (H4), and Marangozis and Johnson (M3, M4). Satterfield and Sherwood (S2) have reviewed this subject with specific reference to applications in slurry-reactor analysis and design. 

Y. T, Shah, Design Parameters for Mechanically Agitated Reactors Mooson Kwauk, Particulate Fluidization An Overview... 

Reviews on mechanically agitated reactors have been presented recently by Shah (1991) and Carpenter (1997). The latter discussed the construction of such reactors and the influence of design and operational parameters on the behaviour of the phases and possible interaction between them in detail. 

In a bubble-column reactor for a gas-liquid reaction, Figure 24.1(e), gas enters the bottom of the vessel, is dispersed as bubbles, and flows upward, countercurrent to the flow of liquid. We assume the gas bubbles are in PF and the liquid is in BMF, although nonideal flow models (Chapter 19) may be used as required. The fluids are not mechanically agitated. The design of the reactor for a specified performance requires, among other things, determination of the height and diameter. 

The second device shown is a cyclone inlet that uses centrifugal force, rather than mechanical agitation, to disengage oil and gas. This inlet can have a cyclonic chimney, as shown, or may use a tangential fluid race around walls. Designs arc proprietary, but most use an inlet nozzle sized to create a fluid velocity of about 20 fps around a chimney whose diameter is two-thirds the vessel diameter. 

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