Compound fertilizer granulation

In agriculture, nitrogen (N), phosphorus (P2O5), and potassium (K2O) in the soil are lost due to harvest. Therefore, in order to supplement the soil with these nutrients, fertilization is required. In the past, only organic fertilizer was used. In addition to minerals, nitrogen, there are humus, bacteria and carbon dioxide. Now, due to intensive farming, more natural or synthetic mineral fertilizers are applied.

In addition to the application of a single fertilizer, it is also necessary to apply compound fertilizers containing nitrogen, phosphorus and potassium, that is, fertilizers containing two or more nutrients, such as nitrogen and phosphorus, nitrogen and potassium, phosphorus and potassium, and nitrogen and phosphorus and potassium. Some compound fertilizers also contain calcium oxide, magnesium oxide and some trace elements (that is, substances that help plant growth and act like vitamins).

In order to ensure that various nutrients are fully absorbed and utilized, different compound fertilizer formulas are required according to the soil quality and crops. In fact, due to the rapid consolidation of the world's population and the continuous reduction of soil due to blind farming, the demand for multi-element fertilizers is rising, because for modern mechanical farming, the use of compound fertilizers can achieve greater yields.

The key factors affecting the use of chemical fertilizers are storage, transportation and handling performance. Before the 1920 s, chemical fertilizers were applied in powder form. Although powdered fertilizer is relatively easy to mix, it has many shortcomings: such as segregation, uncontrollable agglomeration, poor fluidity, and easy to form dust and lose during use. However, with the development of granulation technology, these unfavorable factors are gradually decreasing.

The fertilizer granulation technology that has been developed generally has two kinds of wet and dry methods, in which the dry method is to press into a group without the addition of a binder, and then crush and screen into granular products. In addition, some fertilizers can be granulated by melting, spraying and cooling in a tower.

In wet granulation, the wet strength produced by the capillary effect of the liquid binder plays a vital role in the granulation process. In the subsequent drying stage, the chemical reaction between the components and the crystallization of the dissolved matter The solid bridge produces the particles. The representative equipment of this technology is a drum, a rotating disc, a mixer, a dryer, a cooler and a fluidizing device.

Binder-free pressure granulation technology is a competitive technology. In general, the particles are not formed by the solid bridge between the particles, but by the force between the molecules to form the particle strength. Due to the short distance of this attractive force, the size of the particles is required to be similar, and external pressure is required.

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