Air Lift or Bubble Column Reactors
In these reactors mixing circulation and aeration is performed by gas injection and if needed by additional external liquid circulation to obtain the required mixing pattern. Figure 5, gives an example of a possible configuration. This usually results in less shear for a given quality of mixing than in stirred tanks. Air lifts give more vigorous recirculation for the same air flow, but often lower oxygen transfer rates than bubble columns. To limit shear, small bubbles can be used in aeration, but depending on conditions this may cause excessive foaming and requires more energy for their generation at porous distributors.
Figure 5. The concept of an air lift reactor.
Special designs for immobilized cells have been proposed (Figure 6), that avoid the problems associated with separation of particles at the reactor outlet.
Figure 6. Bubble column and air lift reactors: (a) bubble column; (b) air lift reactor; (c) air lift with particle separator; (d) packed bed air lift, , (adopted by ref. 5).