The production process of controlled-release fertilizers mainly includes the following steps:
Raw Material Preparation
Firstly, various fertilizer raw materials need to be prepared. For example, urea, ammonium phosphate, potash fertilizer, etc. are used as the basic sources of nutrients. Meanwhile, coating materials for wrapping fertilizer granules also need to be prepared. Commonly used coating materials include thermoplastic resins (such as polyolefins), sulfur, etc. The quality and performance of these raw materials have a crucial impact on the final effect of controlled-release fertilizers.
Granulation
After mixing the basic fertilizer raw materials according to a certain formula ratio, fertilizer granules are made through granulation equipment such as rotary drum granulators, disc granulators, extrusion granulators, etc. During this process, parameters such as the size, shape, and strength of the granules need to be well controlled to meet the requirements of subsequent coating and use. For example, the size of the granules should be uniform to avoid the influence of overly large or small granules on the coating effect and fertilizer release performance.
Preparation of Coating Materials
If it is resin coating, the resin and other coating materials need to be heated and melted or dissolved in an organic solvent to make them in a state where they can evenly wrap the fertilizer granules. If it is sulfur coating, the sulfur needs to be heated to an appropriate temperature to turn it into a liquid state for subsequent wrapping operations.
Coating
The fertilizer granules after granulation are conveyed to the coating equipment. In the coating equipment, the fertilizer granules are evenly wrapped with a layer of coating material. The thickness of the coating is a key factor, which directly determines the controlled-release performance of the fertilizer. If the coating is too thick, it may lead to too slow nutrient release and fail to meet the growth requirements of crops; if the coating is too thin, it may not be able to effectively control the nutrient release rate and fail to achieve the purpose of controlled release. For example, by precisely controlling the parameters of the coating equipment, the thickness of the resin coating can be within a certain range, such as from several tens of micrometers to several hundreds of micrometers.
Drying (If Necessary)
During the coating process, if a solvent is used to dissolve the coating material, or the coating material itself contains a certain amount of moisture, then after the coating is completed, the fertilizer needs to be dried. Drying equipment such as hot air dryers can be used to remove the solvent or moisture on the surface of the fertilizer granules to ensure the integrity and stability of the coating.
Post-treatment
Post-treatment is carried out on the coated fertilizer, including screening, grading, etc. Unqualified granules (such as those with broken coatings or adhered granules) are screened out, and the qualified products are graded according to standards such as granule size. This can ensure the consistency of the quality of controlled-release fertilizer products and improve their market competitiveness.
Packaging
Finally, the qualified controlled-release fertilizer products after post-treatment are packaged. The packaging material should be able to protect the fertilizer from moisture and external force damage. At the same time, the information such as the composition, nutrient content, usage method, and controlled-release period of the product should be clearly labeled to facilitate users’ use.