Coating is important for preserving the quality of fertilizer by protecting these against moisture uptake and physical damage under handling. Yara Technology Center has developed efficient coatings for the various grades to substantially:
- Reduce water absorption when exposed to humid air
- Reduce caking tendency
- Reduce dust formation
In addition, a pigmented coating is often used to give a certain colour to the product. Coating agents used to improve quality of fertilizers are harmless to plants, soil or human beings.
Fertilizers and salt products generally tend to agglomerate during transport and storage. In order to prevent caking, fertilizers are treated with various agents that normally include a surface active compound and a fine inert powder. The surface active compound controls crystal formation such that strong bridges are not formed, the powder reduces the surface contact area.
Preventing dust formation
The amount of dust released from fertilizer products depends on several physical properties like particle strength and shape, ways of handling and the coating system applied.
Under normal conditions all ammonium nitrate based fertilizers are stable materials. When stored in direct sunlight temperature fluctuations can occur. That will make the fertilizers swell and physically break down.
The break down is higher if the product is inadequately stabilised and/or has a high water content.
Ammonium nitrate occurs in different stable crystalline forms; changing from one to another is accompanied by volume changes. The transition at 32 °C results in density changes and can cause the product to break down into fines if the product is heated or cooled while passing this temperature.
AN 33.5 and some other products high in ammonium nitrate contain stabilizers that minimize thermocycling.
However, during long periods of storage these products may still degrade if the conditions for thermocycling are favorable.
Always monitor the climatic conditions, especially where products are stored in bulk.
The air can release approximately 10-15 grams of water/m3 per night in a hot and humid climate. This means approximately 90 litres/day or 1,260 litres in two weeks in a small warehouse of 1 000 Mt (30x20x10).
It is important to lead the water outside. In new projects roof insulation is used to reduce temperature variation. Always sheet the product.