Bubble and Elutriation Control in Fluidized Beds with Electric Fields

Publication Reference: 
24-04
Author Last Name: 
Colver
Authors: 
G M Colver
Report Type: 
ARR
Research Area: 
Powder Flow
Publication Year: 
1995
Publication Month: 
01
Country: 
United States

To classify the characteristics of Geldart-A powders in bubbling fluidized beds utilizing electric fields, we have developed the electric field operation map for bubble control relating three variables: electric field strength, frequency and superficial velocity. The map includes regions of expanded bubble control, bed freezing, and elutriation control. These deliniations define our goals for the development of a uniBed theory of bubble control for ac and dc fields.

Perturbation theory and interparticle force theory have led to the evaluation of a powder modulus of elasticity. Results for 3 types of FCC and glass powders are reported. Early discrepancies in utilizing perturbation theory appear to have been resolved. Future studies will include the effects of particle diameter, relative humidity, and high temperatures.

In this reprt we continue our development of a unified theory of bubble control utilizing continuum and particle theories. Studies are reported at the frozen bed limits for ac and dc field and for bubble stabilization based on our extension of the Davidson bubble model. Van der Waals forces are now being incorporated in our ac and dc models. Scaling parameters are being developed and reported for our future work with large beds.

Our new high temperature facility is now operational and continues to be developed. A problem remains with the quartz sinter used for gas distribution in the bed. Our preliminary data from this facility indicate that:

- Bubble control remains effective at elevated temperatures depending on the increase in electrical conductivity of the material; for example, fresh Zeolitic FCC was successfully tested up to 465 “C for bubble control.

- The bed modulus of elasticity decreases with increasing temperature for fresh Zcolitic F C C .

- The bed modulus of elasticity increases approximately linearly with electric field strength for 3 kinds of FCC’s tested and for glass.

The strong influence of electric fields in controlling elutriation is now established for both ac and dc fields. This year a specially designed electrode-from-below fluidized bed was developed for these studies that is capable of measuring both particle charge and elutriation constants. Some first results on naturally occurring and induced particle charging within the bed are presented indicating significant particle charging -lOa C/kg for 8.66 pm sand fines. Particle charge remains an important variable for our interparticle force theory relating to elutriation control.