Mixing granulation of different NPK fertilizers is the core of compound fertilizer processing. Fertilizer production line generally uses the following methods to granulate:
1. Extrusion granulation is a method of making dry powder or wet powder containing binder into cylindrical, spherical or sheet shape by mechanical processing such as extrusion, roller extrusion or pressing. The technology of dry granulation is used in the flat die pellet mill, the ring die pelleting machine and the double roller granulator.
2. Agglomerating granulation, which is under the action of rotation, vibration, agitation and so on, makes the wet powder in motion agglomerate. Or use the fluidized bed to make the material obtain the cohesive force by supplying the spray liquid binder) so as to grow into the appropriate particles. This method is used in disc granulator and rotary drum granulator.
3. Crushing granulation, which is to crush the block material into particles of appropriate size.
4. Melt granulation, which is a method of cooling and hardening molten liquid for granulation.
5. Spray granulation. It is a method of directly forming granules after concentrating the solid in the liquid.
6. The method of crystallization and granulation in liquid phase is to make materials precipitate and crystallize in liquid phase, at the same time, agglomerate into spherical particles by the action of liquid bridging agent and agitation. This technology is widely used in pharmaceutical industry. Because the shape of the particles is spherical, it is also called spherulite granulation, which is called spherulite granulation for short. Spherulite is a kind of spherical particle formed by the crystallization and aggregation of pure materials. It has good fluidity, filling and compression formability. In recent years, the technology has been successfully applied to functional pellets.