【FAQ】What are the moisture requirements for dry granulation?

Optimal moisture range: Dry granulation requires the raw material moisture content to be controlled between 8% and 18%. For pure organic fertilizer powder that has been fully decomposed, fermented, and dehydrated, the moisture content should be ≤15% to 20%. Within this moisture range, the material has good compressibility and formability—it will not be too dry, resulting in loose granules and insufficient strength, nor too wet, causing "roller sticking" or sticking to the mold.

Consequences of excessively low moisture content: When the moisture content is below 8%, the material particles lack the necessary binding force, making them prone to loosening and breakage after extrusion, significantly reducing the granulation rate, and simultaneously accelerating roller wear. In this case, a suitable amount of water can be sprayed during the mixing stage, but the amount of water added at one time should not exceed 2% of the total weight of the material, and it must be thoroughly mixed in a mixer to ensure uniform moisture distribution before entering the granulator.

Consequences of excessively high moisture content: When the moisture content exceeds 18%, the material will squeeze out free water under high pressure, mixing with fine powder to form a paste that adheres to the roller surface, causing a "roller paste" phenomenon—the roller skin pits are filled, and the granules cannot be formed normally. At the same time, excessive moisture will cause the extruded granules to absorb moisture and clump during subsequent storage. Countermeasures: Pre-dry the excessively wet material, or add dry return material (moisture content <3%) to reduce the overall moisture content.

Process matching suggestions: The advantages of dry granulation are no drying process, room temperature granulation, one-time forming, low investment, and low energy consumption. However, this requires a reliable pre-drying system (such as a drum dryer or airflow dryer) to precisely control the moisture content of the fermented and decomposed material to the target range. It is recommended to install an online moisture meter at the granulator inlet to monitor and adjust drying parameters in real time, ensuring the incoming moisture content remains stable within the optimal range.