Caking is a problem that fertilizer industry has long been committed to solve. It occurs during the processing, storage and transportation of compound fertilizer. Since fertilizer is hygroscopic, salt bridge forms in the process of evaporation and recrystallization, so that small particles become large particles and caking happens. Caked fertilizer is difficult to crush. It is unavailable for mechanical application and will block the nozzle. For cash crop like tobacco and tea, the powder that produced after crushing the cake will attach onto the crops, and affect their quality. To avoid caking, several measures could be taken.
1. Rational collocation of raw materials. The compound is easier to absorb the moisture than the basic fertilizer. When choosing raw materials, we should take both the hygroscopicity of basic fertilizer and the compound into consideration to get a high CRH value. Some inorganic salt can improve the crystal habit. Some can promote the formation of double salt to improve the hygroscopicity.
2. Strictly control the moisture content of the finished product, reduce the evaporation of moisture. Strictly control the moistening degree when granulating depending on different materials.
3. Strictly control the particle size of raw materials and improve the effect of screening, avoiding caking resulting from uneven particle size, matte surface and too much small particles. The rotary drum fertilizer granulator adopts wet method to roll the round fertilizer particles. The particles have high quality.
For the rotary screening machine, the fertilizer granules are screened by the rotating of the drum, and granules with large size move forward along the drums gradient, screened gradually through different screen.
4. Use fertilizer rotary cooling machine to decrease the packing temperature to lower than 40. The cooling machine is always used together with the drying machine to greatly increase the cooling speed, improve the cooling rate, and further remove the water and reduce the temperature.
5. Use fertilizer rotary coating machine to coat the granules with oil or powder anti-caking agents, When the screened fertilizer granules are rolling in the rotary drum, the compressed air and nozzle atomize the prepared oil agent and coat on the surface of the particles. The screw conveyer throws the talcum powder or other powder agent on the surface, forming a hydrophobic layer to avoid the moisture exchange between granules. The dosage of the powder is controlled by the variable-speed motor. Combined utilization of oil and powder anti-caking agents will have a lower cost and better effect. Some anti-caking agents also have the effect of slow release, prolonging the fertilizer efficiency and increasing the utilization rate.
6. For the storage of compound fertilizer, the following should be kept in mind:
* Store in cool and dry warehouse. Don’t put it in the places with direct sunshine, high temperature or moisture.
* Reduce the times of loading and unloading.
* Reduce stack height so that to reduce the stack pressure.
* Reduce storage time.