What are the common problems encountered during NPK fertilizer granulation?

NPK compound fertilizer granulation is the core process in the NPK fertilizer production line, directly determining the product's appearance, strength, nutrient uniformity, and application effect. Due to the significant differences in the physicochemical properties of nitrogen, phosphorus, and potassium raw materials, and the fact that the granulation process is affected by multiple factors such as temperature, humidity, and proportion, various problems are prone to occur during production. These problems not only affect production efficiency but may also reduce product quality and increase production costs. The following outlines the most common problems and basic solutions in NPK fertilizer granulation, based on practical production experience.

Insufficient granule strength and easy pulverization are the most common problems in the granulation process. This manifests as loose finished granules that are easily broken and produce dust during handling and storage, and are prone to caking or loss during application. The main causes are unreasonable raw material ratios, such as an excessively high proportion of rigid raw materials like phosphate rock powder and potash fertilizer, and insufficient binding materials; improper control of granulation moisture, where too much moisture leads to soft granules, and too little prevents the formation of a strong bond; and incomplete drying of the granules, resulting in excessive internal moisture and subsequent moisture absorption and pulverization. Solutions include optimizing the raw material ratio, adding appropriate amounts of binders such as bentonite and starch, strictly controlling the granulation moisture within a suitable range, and adjusting the drying temperature and time to ensure that the granule moisture content meets the standards.

Uneven granule size and oversized granules are also common, meaning the finished product contains a mixture of coarse and fine granules, failing to meet industry standards. This is mainly due to unreasonable granulator speed; too fast a speed results in excessively fine granules, while too slow a speed results in excessively large granules; worn or clogged sieve mesh, preventing effective classification; and insufficient fineness of raw material crushing, where large raw material particles are not fully mixed, affecting granulation uniformity. Solutions require timely adjustment of the granulator speed, regular inspection and replacement of sieves, ensuring that the raw material crushing fineness meets the requirements, and optimizing the mixing process to ensure uniform mixing of raw materials.

Granule caking and severe moisture absorption often occur during the storage stage after granulation, although some caking may also occur during the granulation process itself. The core reasons for these problems are the strong hygroscopicity of nitrogen fertilizers (such as urea and ammonium chloride) in NPK fertilizers, resulting in rough particle surfaces and high porosity after granulation, making them prone to absorbing moisture from the air; insufficient drying and cooling, leading to a large temperature difference between the inside and outside of the particles, causing condensation and moisture regain; and excessive humidity in the packaging and storage environment. Solutions require improving the granulation process, increasing the smoothness of the particle surface, optimizing the drying and cooling process to ensure the particle temperature drops to room temperature before packaging, and using moisture-proof packaging materials and storing the product in a dry and well-ventilated environment.

In addition, problems such as uneven nutrient distribution and NPK fertilizer granulator blockage may also occur. Uneven nutrient distribution is mainly due to insufficient mixing of raw materials, requiring strengthened control of the mixing process; granulator blockage is often caused by excessive moisture in the raw materials and excessive feeding speed, requiring control of the feed rate and moisture content, and regular cleaning of the granulator.

In summary, the key to NPK fertilizer granulation lies in controlling the three core factors: raw material ratio, moisture content, and temperature, and optimizing the parameters of each stage of mixing, granulation, drying, and cooling. Only by promptly identifying various problems in the NPK production line and precisely adjusting the process can high-quality, qualified NPK compound fertilizers be consistently produced, improving product competitiveness and production efficiency.