Top-Spray Agglomeration

The fluid bed granulation process (also known as agglomeration) involves suspending particulates in an air stream and spraying a liquid from the top down onto the fluidized bed. Particles in the path of the spray get slightly wetted and become tacky. The tacky particles collide with other particles and adhere to them to form a granule.

Dry-Stage vs Wet-Stage Agglomeration

There are two different modes of fluid bed agglomerating: dry stage and wet stage. In dry-stage granulation, the particles only require a slight wetting to become tacky and stick to each other. The granulating solution is applied at a rate less than or equal to the evaporation rate. Thus the particles remain "dry" through the entire process. In wet-stage granulation, the particles require significant wetting before they become tacky enough to stick to each other. The granulating solution is applied at a rate higher than the evaporation rate until the particles build up enough moisture to granulate. The characteristics of the particles when wet and the type of granulating solution being used will determine which mode of granulating is most appropriate. While dry-stage is more common, wet-stage granulating allows for denser products. Fluid Air Dry Stage / Wet Stage graph with steady evaporation rate line of liquid addition

Fluid Air microscopic agglomerated particles from conventional spray dryer
Conventional Spray Dryer
10 lbs/hr - 190 °C

Fluid Air microscopic view of electrostatic agglomeration of particles 10lbs/hr at 90 deg C
Electrostatic Spray Dryer
10 lbs/hr - 90 °C

*Same feedstock formula used for both examples

Pulse Width Modulation

By controlling the electrostatic charge applied to the feed on an intermittent basis, agglomeration while drying becomes possible. This patent-pending technology - called - Pulse Width Modulation (PWM) precludes the need for expensive secondary agglomeration operations within the spray drying process.

By controlling the voltage applied to the spray droplet as it is being atomized, some particles form an outer shell readily, while others develop their shell gradually resulting in a wet or tacky particle. As these two types of particles colloid, they bond forming an agglomerated particle. This results in a finished product with larger particles and fewer fines which flows freely. Fluid Air electrostatic agglomeration time-lapse illustration with yellow-and-blue particles