Fluidization in Packed Bed

Fluidization

• When a fluid passes upward through a packed bed, the manometric pressure gradient increases as the fluid velocity (U) increases.
• At a certain point, the pressure drop is just sufficient to support the immersed weight of the particles, and the particles become "fluidized" and free to move around in the fluid.
• At this point, the manometric pressure gradient (Dp) is related to the bed height (H) and the minimum fluidization porosity (εmf) by the equation: Dp=H ¼ ð1 εmfÞ rp r g (5.2)

Characteristics of Fluidized Beds

• Bubbles form in a fluidized bed, with gas and solid velocities shown in Figure 5.3.

Classification of Fluidized Bed Applications

• Table 5.1 provides a classification of fluidized bed applications according to predominating mechanisms, including:
  • Physical processes
  • Chemical processes
  • Heat and/or mass transfer between gas/particles
  • Heat and mass transfer between particle/particle or particle/surface
  • Heat transfer between bed/surface
  • Gas/gas reactions in which solid acts as catalyst or heat sink
  • Gas/solid reactions in which solids are transformed
• Examples of industrial processes that use fluidized beds include:
  • Solids drying
  • Absorption of solvents
  • Cooling of fertilizer prills
  • Food freezing
  • Plastic coating of surfaces
  • Coating of pharmaceutical tablets
  • Granulation
  • Mixing of solids
  • Dust filtration
  • Heat treatment of textile fibers, wire, rubber, glass, metal components
  • Constant temperature baths
  • Oil cracking, reforming
  • Manufacture of various chemicals and materials
  • Coal combustion
  • Coal gasification
  • Roasting of nickel and zinc sulphides
  • Incineration of liquid and solid waste
  • Production of various chemicals and materials
  • Catalyst regeneration
  • Decomposition of limestone
  • Production of UF6, AlF3
  • Production of UO2, UO3