Fluid Bed Reactors

1
Fluid Bed Reactors

• Chapter (Not in book)
• CH EN 4393
• Terry A. Ring

2
Overlap of phenomenon

• Kinetics
• Depend upon solid content in bed
• Mass Transfer
• Depends upon particle Re number
• Heat Transfer
• Depends upon solid content in bed and gas Re
• Fluid Dynamics
• Fluidization function of particle Re
• Particle elution rate
• Distribution Plate Design to prevent channeling

3
Packed Bed

• Pressure Drop

Void Fraction, e0.2-0.4
4
Now if particle are free to move?

• Void Fraction

Void Fraction, e0.2-0.4 packed Becomes eMF0.19
to eF0.8.
MF Pressure drop equals the weight of Bed
5
Fluid Bed Pressure Drop

• Lower Pressure Drop _at_ higher gas velocity
• Highest Pressure Drop at onset of fluidization

6
Bed at Fluidization Conditions

• Void Fraction is High
• Solids Content is Low
• Surface Area for Reaction is Low
• Pressure Drop is Low
• Good Heat Transfer
• Good Mass Transfer

7
Distributor Plate Design

• Pressure Drop over the Distributor Plate should
  be 30 of Total Pressure Drop ( bed and
  distributor)
• Pressure drop at distributor is ½ bed pressure
  drop.
• Bubble Cap Design is often used

8
Elution of Particles from Bed

• Particle Terminal Setting Velocity
• When particles are small they leave bed

Gas Velocity
9
Cyclone

• Used to capture eluted particles and return to
  fluid bed
• Design to capture most of eluted particles

10
Cyclone Cut Size

• Diameter where 50 leave, 50 captured

11
Size Selectivity Curve
12
Mass Transfer

• Particle Mass Transfer
• Sh KMTD/DAB 2.0 0.6 Re1/2 Sc1/3
• Bed Mass Transfer
• Complicated function of
• Gas flow
• Particles influence turbulence
• Particles may shorten BL
• Particles may be inert to MT

13
Fluid Bed Reactor Conclusions

• The hard part is to get the fluid dynamics
  correct
• Kinetics, MT and HT are done within the context
  of the fluid dynamics

14
Heat Transfer

• Particle Heat Transfer
• Nu hD/k 2.0 0.6 Re1/2 Pr1/3
• Bed Heat Transfer
• Complicated function of
• Gas flow
• Particle contacts