Phosphate Rocks Chapter 37: NPK Granulation

You can granulate anything, even sand and water, given the right conditions of temperature, moisture, speed of rotation and residence time. 

The process for turning fine particles into larger granules with the right mix of nitrogen, phosphorus and potassium was developed by SAI with French company Grande Paroisse. Elegant and simple on paper, it took skill to operate. 

Solid flow was the cause of most problems. The chutes choked all the time. If the material was damp, it clung to the rubber lining and narrowed the throat. If a lump fell from the sparger through the grizzly it blocked the chute, and the rest of the material built up on top. 

The chutes were kept clear with a set of valiant boxers – the politest name for them. These sturdy shafts, with hemispherical tips, plunged into soft rubber diaphragms set into the chutes. The frequency of stroke could be adjusted, along with the speed of attack, the depth of thrust, and rate of withdrawal, creating a regular, rhythmic motion.