2026/09/24
What Causes Excessive Powder in Finished Granules?
Excessive powder in finished granules (i.e., high powdering rate, exceeding powder content standards) is one of the most common quality problems in fertilizer production. Based on industry experience, the main causes can be attributed to two main areas: insufficient screening efficiency and uncontrolled drying process. These two factors often influence each other and require systematic investigation.
I. Insufficient Screening Efficiency
The screening process is a crucial step in granule grading. If screening efficiency is insufficient, a large amount of fine powder and broken particles will mix into the finished product, directly leading to excessive powder content in the packaged product. Specific reasons include:
Screen Clogging or Damage: Damp materials and fibrous impurities clog the screen, preventing effective separation of fine powder; damaged screens allow large particles to mix with fine powder.
Inappropriate Screen Mesh Size Selection: If the screen aperture is too large, fine powder passes through along with qualified granules; if the aperture is too small, qualified granules are mistakenly screened as recyclable material, reducing output.
Improperly set amplitude or frequency of the screening machine: Insufficient amplitude prevents sufficient material loosening and stratification; excessive frequency causes excessive material jumping, leading to secondary particle breakage.
Undersized equipment: Insufficient screening machine capacity results in an excessively thick material layer, significantly reducing screening efficiency.
II. Over-drying: Uncontrolled temperature and residence time during the drying process severely weaken particle strength, causing significant breakage into powder during subsequent conveying and screening. Specifically: Excessively high hot air temperature: Exceeding the safety limit (e.g., over 80℃ for organic fertilizer) causes rapid surface water loss and a sudden increase in internal steam pressure, leading to particle bursting or micro-cracks.
Excessively long drying time: Prolonged residence time in the drum causes repeated tumbling and friction, resulting in severe surface wear and the production of large amounts of powder.
Insufficient moisture content: Over-dehydration causes particles to lose necessary toughness, becoming brittle and easily broken by slight impact.
In addition, insufficient particle strength (e.g., excessive moisture or insufficient binder during granulation) and excessive impact during conveying (e.g., excessive drop height of elevators or belt conveyors) can also exacerbate powder generation.
III. Comprehensive Troubleshooting and Solutions When excessive powder is found in the finished product, troubleshooting can be carried out step by step in the following order:
Check the screen: First, stop the machine and check whether the screen is clogged or damaged. Clean or replace the screen.
Check drying parameters: Verify whether the hot air temperature is too high and whether the output moisture content is too low (organic fertilizer should be controlled at 10%–12%, compound fertilizer should be ≤2%). If necessary, reduce the hot air temperature or shorten the drying time.
Check particle strength: Test the particle hardness by hand or with a compressive strength tester. If the strength is insufficient, trace back to the granulation process and adjust the amount of moisture or binder added.
Check the conveying system: Reduce the drop height of elevators and belt conveyors, and install buffer chutes.
Through the above systematic troubleshooting and adjustments, the powder content of the finished product can be controlled below 5%, ensuring that the product quality meets standards.