Rolled Spheres vs. Pressed Granules: Two Technical Pathways for Organic Fertilizer Granulation

When the same batch of decomposed organic fertilizer powder is fed into different granulation systems, the resulting granules exhibit starkly contrasting characteristics. Granules from a disc granulation line are round, uniform, and smooth—a handful looks like black pearls. In contrast, granules from a double-roller press granulator feature fine surface indentations and feel dense and heavy, resembling compacted medicinal tablets. Underlying these visual differences are two completely distinct physical mechanisms: the formation of spheres through rolling versus the formation of granules through compression. The disc granulator operates on the principle of "agglomeration." Its core component is a rotating disc mounted at an incline, typically adjustable between 35° and 45°. Decomposed, pulverized organic powder is evenly fed onto the disc via a conveyor belt. Driven by friction at the disc's base, the material rises to a certain height before rolling back down, while simultaneously being pushed toward the rim by centrifugal force. As a fine water mist is sprayed from above, liquid bridge forces form on the surfaces of the particles; using recycled fines as nuclei, the particles agglomerate layer by layer—growing larger like a rolling snowball—until the balance between particle mass and centrifugal force causes them to spill over the disc's rim. Throughout this process, the urates and humic colloids naturally present in organic materials (such as chicken manure) are fully utilized. The pelletization rate typically reaches 85%–93%, and granule diameters can be flexibly controlled between 2 and 8 mm by adjusting the disc's tilt angle, rotation speed, and water spray volume. The rotation speed and tilt angle must be carefully matched; for a disc with a 2.2-meter diameter, the speed is usually maintained between 18 and 22 revolutions per minute. Excessive speed generates too much centrifugal force, preventing the material from agglomerating, while insufficient speed results in inadequate mixing intensity.

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