(51b) Fluidization of Uniform Spherical Beads

Ion exchange technology is well suited for industries using low concentration separation processes. This includes the nuclear industry where treatment of effluent and waste streams requires selective removal of nuclides normally very low in concentration. At the Waste Treatment Plant Project (WTP) in Richland, WA, ion exchange technology is being used to remove Cs-137 from the radioactive liquid waste stream. A novel form of resorcinol formaldehyde (RF) was chosen. This resin demonstrates the same characteristics of RF (an organic, elutable resin), and also has the benefit of being a uniform-size spherical bead material.

Because the ion exchange resin loses its effectiveness over time, the system is designed for removal and replacement of spent resin with fresh resin. To remove the resin, it is first fluidized to ensure the bed will effectively flow and then slurried out of its vessel. Following removal, fresh resin is added by slurry transport into the vessel. In designing the ion exchange system, testing was performed to determine conditions for optimal fluidization of RF resin.

Fluidization of uniform size, spherical beads of resorcinol formaldehyde ion exchange resin was measured in a dilute aqueous solution (0.5 M NaOH) and a 5 M sodium salt solution. Bed height and evenness of flow distribution were measured. Fluidized bed height was predicted from incipient fluidization to terminal velocity using equations derived from basic bead and fluid properties and compared to measured values with one constant fit to all the data. Optimum fluidization was determined from flow jet or spout height. Measurements focused on superficial flow velocities of 2 to 20% of terminal velocity.

Analysis of test results indicate that the optimal fluidization velocity of the RF resin is ~12 cm per minute. The equations used are generic for uniform spherical particle fluidization. Therefore, fluidization of packed beds consisting of any kind of uniform spherical particles can follow the same procedure to determine bed heights and optimal velocities.

Key Words:

resorcinol formaldehyde, ion exchange, fluidization velocity, spherical bead resin.