Adding a certain proportion of accelerators during the granulation process of fertilizers can help the raw material powder and particles to agglomerate, improve granulation efficiency, increase the yield rate, and improve the physical properties of particles (strength, surface morphology, anti-disintegration, etc.). In wet granulation, such as drum granulation and stirring granulation, by adding granulation liquid such as water, to the raw material powder particles, the surface of the powder particles is moistened, and solid-liquid cross-linking is formed to agglomerate into particles. On the other hand, in dry granulation, such as briquetting granulation and extrusion granulation, since granulation is completed by the force between molecules, there is no need to add granulation accelerators.
Types of granulation accelerators
Granulation accelerators for fertilizers should have the following functions:
- A certain degree of adhesion
- High surface tension
- High solid cross-linking strength after drying.
- Low cost
- No harm to crops when mixed with fertilizers
- Biodegradability of synthetic organic materials
Selection of granulation accelerator
Most chemical fertilizers are water-soluble salts. During the granulation process, liquid bridges are formed between powder and particles through dissolution and precipitation in water or granulation liquid, which becomes the driving force for particle agglomeration. Phosphoric acid fertilizers such as monoammonium phosphate (MAP), superphosphate, and triple superphosphate have high solution viscosity. Especially when the pH value is close to neutral, their surface tension and viscosity are further increased, and the adhesion is increased. Granulation accelerators form liquid cross-links between powder particles during the granulation process. The crystal bridges formed after drying have high solid cross-linking strength, which plays a role in promoting granulation. If the proportion of ammonium phosphate (MAP), superphosphate, and triple superphosphate in the fertilizer formula is above 20%, high-strength particles can be granulated with water alone without adding granulation accelerators. In contrast, ammonium sulfate, urea and potassium raw materials such as potassium chloride and potassium sulfate in nitrogen raw materials have relatively small surface tension even in saturated solutions, low solution viscosity and low bonding particle strength. Therefore, in the fertilizer granulation using them as raw materials, adding granulation promoter is effective to improve granulation efficiency and particle physical properties. In particular, urea has low apparent density, large powder porosity and small repose angle, making it difficult to mix evenly with other raw materials. The viscosity and surface tension of saturated solutions are also low, making it difficult to form dense particles. When the proportion of urea in the raw materials exceeds 25%, it is recommended to use granulation promoter.
The appropriate granulation promoter is selected by comprehensive consideration of the type of raw materials, mixing ratio and granulation method.
Commonly used granulators:
Using rotary granulation, water or granulation promoter is sprayed in mist during the production process, and the material rotates and rolls along the inside of the granulation container. The particles collide with one another and combine to become larger, and finally grow to the required size.
During the extrusion granulation process, granulation accelerator and water are added to the raw materials and mixed for granulation. Bentonite and konjac flour are preferably used as granulation accelerators to reduce costs and ensure fertilizer nutrients. Gypsum, sodium humate, waste molasses or lignin sulfonate can also be used as needed.
It adopts the working mode of granulation while stirring. Add granulation liquid, mix and stir through the stirring teeth, and gradually form compact spherical particles.
As the demand for efficient and environmentally friendly fertilizers increases, the research and development of granulation accelerators will continue to develop in the direction of multifunctionality and efficiency. At the same time, we also produce a variety of products such as biological fermentation bacteria and rapid heating composting machines. These products not only improve the production efficiency of fertilizers, but also improve soil quality and promote plant growth.
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