Air-lifts

Other than the biofilter and culture chambers, recirculating systems typically also employ one or more settling chambers or mechanical filters to remove soHds such as unconsumed feed, feces, and mats of bacteria that slough from the bio filter into the water. Each recirculating system requires a mechanical means of moving water from component to component. That usually means mechanical pumping, though air-lifts can also be used. 

For large-scale bioreactors (21), especially those of the air lift type (22), the gas phase is best considered as being in plug dow, so that a log mean value of driving force is obtained ... 

External and internal loop air-lifts and bubble column reactors containing a range of coalescing and non-Newtonian fluids, have been studied (52,53). It was shown that there are distinct differences in the characteristics of external and internal loop reactors (54). Overall, in this type of equipment... 

Plant Cell Culture. Air-lift bioreactors have been favored for plant cell systems since these cultures were first studied (4). However, they can give rise to problems resulting from flotation of the cells to form a meringue on the top. It is interesting to note that some reports indicate that stirred bioreactors do not damage such cells (4). 

Single-Cell Protein. Systems involving single-cell proteins are often very large throughput, continuous processing operations such as the Pmteen process developed by ICI. These are ideal for air-lift bioreactors of which the pressure cycle fermenter is a special case (50). 

A mathematical model of the operating characteristics of a modem HLW storage tank has been developed (60). This model correlates experimental data for the rate of radiolytic destmction of nitric acid, the rate of hydrogen generation owing to radiolysis of water, and cooling coil heat transfer. These are all functions of nitric acid concentration and air-lift circulator operation. 

Fig. 7. Plant for spray-drying of detergents and soaps. 1, Burner 2, air combustion 3, cold air fan 4, hot air generator 5, spray-drying tower 6, cleaning ring 7, no22les circuit 8, tower suction cyclones group 9, tower suction fan 10, double-flap dischargers 11, recovery powder cyclone 12, recovery powder fan 13, belt conveyor 14, air lift 15, air lift suction cyclones 16, air lift suction fan 17, double-flip dischargers 18, vibrating sieve.

Fluid-Displacement Pumps In addition to pumps that depend on the mechanical ac tion of pistons, plungers, or impellers to move the liquid, other devices for this purpose employ displacement by a secondary fluid. This group includes air lifts and acid eggs. 

A simplified sketch of an air lift for this purpose is shown in Fig. 10-57. Ingersoll-Rand has developed empirical information on air-hit performance which is available upon request. 

FIG. 10-57 Simplified sketch of an air lift, showing submergence and total head. 

FIG. 12-95a Air-lift pneumatic-conveyor dryer includes partial recycle of dry product and expanding tube and cone sections to provide longer holdup for coarse particles. (Bepex Coip. )... 

Dyna Sand Filter. A filter that avoids batch backwashing for cleaning, the Dyna Sand Filter is available from Parkson Corporation. The bed is continuously cleaned and regenerated by recycling solids internally through an air-lift pipe and a sand washer. Thus a constant pressure drop is maintained across the bed, and the need for parallel fdters to low continued on-stream operation, as with conventional designs, is avoided. 

FIG. 24-4 Air-lift fermenters (a) Concentric cylinder (h) external recycle. 

Deep anodes consist of parallel-connected single anodes which are set in boreholes 50 to 100 m deep with a diameter of 0.3 m. The boreholes can be produced by a variety of boring methods, but the air lift method has proved particularly suitable (see Fig. 9-10). The borehole is filled with water to ground level according to the principle of a mammoth pump. Compressed air is fed via a pipe to... 

Fig. 9-10 Drilling for a deep anode bed with the air lift method.

An improved design undertaken by Sacony used high-velocity gases to replace the mechanical elevator systems as catalyst carriers. These so-called air-lift units improved upon the Thermofor process both in terms of economies and octane numbers. It was, however, only with the fluid cracking process that catalytic technology realized fully continuous production. 

Fluid cracking retained the moving bed concept of the catalyst transported regularly between the reactor and regenerator. And as with the air-lift systems, the fluid plant rejected mechanical carrying devices (elevators) in favor of standpipes through which the catalyst fluid traveled. 

Two types of bioreactors have been used to produce SCP from sugar sources, namely stirred/baffled type and the air-lift with draught tube type (figure 4-5), with various capacities up to 400 m. 

Figure 4.5 Fermentor types used in the production of SCP from sugar sources, (a) Stirred baffled system, (b) and (c) air lift systems...

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