Fluidization at Vacuum Conditions

The development of a fluidized bed depends mainly on the kinetic energy, which is provided by the inlet gas (air or another gas respectively solvent vapour). It also depends on the equivalent differential pressure (Ap) above the fluidized bed [2]. 

Two factors define the development of a fluidized bed. The first factor is the density of the gas respectively of the solvent vapour. It depends on pressure and temperature. Vapours of common solvents have higher densities compared to air (or nitrogen). As a process gas for fluidized bed operations acetone vapours, for example, have similar properties at 500 mbar (abs) as air at atmospheric condi-tions. Different solvent vapours such as methanol (standard density 1.43 kg m ) or toluene (4.11 kg m ) have little influence on the fluidization. The solvent should not be arbitrary, which inasmuch makes it beneficial. 

The second factor is the gas velocity. It is easier to control on one hand it also has a larger influence on the other hand, because in the equation it is squared. The weight deficits at vacuum conditions can be compensated by higher velocities and with that higher volume flow rates. Duplication can be roughly estimated compared to machines operated at normal pressures. This can be accompUshed technologically by a specific blower. The rate of turbulence is equivalent to normal pressure processing. 

The fluidization behaviour is mainly influenced by the weight of the bed and the size of the particles. Solid particles with a density of up to about 1.5kgm and a maximum particle size of 3 mm can easily be fluidized. 

---