Patent ID: 7147717

Claim:
In a Wurster-type fluidized bed apparatus for applying a coating liquid to a particulate feed material which comprises a distribution of particle sizes including larger particles, smaller particles and fines, said apparatus including a container, a distribution plate, at least one Wurster tube spaced above said distribution plate and defining a central up-bed region and a surrounding peripheral down-bed region, said distribution plate having a plurality of openings, a source of fluidizing gas directed through said distribution plate into said Wurster tube, a source of coating liquid, and a spray nozzle within said at least Wurster tube for directing a spray of coating liquid into said up-bed, whereby said particles are coated by being repeatedly circulated past said spray nozzle, the improvement comprising: a separator screen surrounding said spray nozzle, said separator screen excluding said larger particles while permitting at least a portion of said smaller particles and fines to preferentially pass through said separator screen and into said spray of coating liquid ahead the remaining larger particles, whereby said smaller particles and fines are preferentially agglomerated.