text: In its simplest configuration, a bubble column consists of a vertically-arranged cylindrical column filled with liquid. The gas flow rate is introduced at the bottom of the column through a gas distributor. The gas is supplied in the form of bubbles to either a liquid phase or a liquid-solid suspension. In this case, the solid particle size (typically a catalyst) ranges from 5 to 100 μm. These three-phase reactors are referred to us as slurry bubble columns.
  The liquid flow rate may be fed co-currently or counter-currently to the rising bubbles, or it may be zero. In the latter case, the column operates in batch condition. 
  Bubble columns offer a significant number of advantages: excellent heat and mass transfer between the phases, low operating and maintenance costs due to the absence of moving parts, solids can be handled without any erosion or plugging problems, slow reactions can be carried out due to the high liquid residence time (this is the case for gas-liquid reactions with a  Hatta number Ha <0.3), reasonable control of temperature when strongly exothermic reactions take place. However, the back-mixing of the liquid phase (the result of buoyancy-driven recirculation) is a limitation for bubble columns: excessive back-mixing can limit the conversion efficiency. The reactor may be equipped with internals, baffles, or sieve plates, to overcome the back-mixing problem with an inevitable modification in the fluid dynamics.
  Bubble columns are extensively used in many industrial applications. They are of considerable interest in chemical processes involving reactions like oxidation, chlorination, alkylation, polymerization, and hydrogenation, as well as in the production of synthetic fuels via a gas conversion process ( Fischer-Tropsch process) in biochemical processes such as fermentation and biological wastewater treatment.