What is the process of fertilizer spraying and granulation?

The spray granulation process is mainly based on the principle of liquid-solid two-phase flow. Spray a solution containing solutes (such as various fertilizer components) into small droplets through a nozzle, while fully contacting solid particles (seed crystals or return particles) in a fluidized state. The droplets adhere and spread on the surface of the solid particles, and gradually form a uniform coating on the surface of the solid particles as water evaporates and solutes crystallize, allowing the particles to continuously grow and ultimately form a particle product with certain particle size and properties.

technological process
 
1. Raw material preparation
Firstly, various required raw materials are pretreated, such as crushing and screening solid materials to achieve the appropriate particle size requirements for subsequent mixing and granulation. For liquid raw materials, filtration and impurity removal operations should be carried out to ensure their purity and fluidity.
In fertilizer production, urea, ammonium phosphate, potassium fertilizer, etc. are mixed in a certain proportion to make a mother liquor, and small particles are prepared as seeds or return materials.
2. Spray granulation
1. Transport the prepared mother liquor to the nozzle at the top of the granulator, and spray the mother liquor into the granulator in a mist form through the nozzle.
2. At the same time, add the seed crystals or return particles from the feeding port of the granulator, and use a stirring device or airflow inside the granulator to make them in a fluidized state, fully contacting the sprayed mother liquor droplets. The mother liquor droplets quickly adhere to the surface of the particles, and as the water evaporates and the solute crystallizes, the particles gradually grow.
3. Drying
1. The wet granules after granulation contain a certain amount of moisture and need to be dried in a drying equipment. Common drying equipment includes rotary dryers, fluidized bed dryers, etc.
During the drying process, hot air is introduced into the dryer to evaporate the moisture in the particles and discharge it with the airflow, thereby reducing the moisture content of the particles and meeting the quality requirements of the product. Generally, the moisture content of the dried particles is controlled to be below 2%.
4. Screening
1. The dried particles enter screening equipment such as vibrating screens, rotary screens, etc., and are classified according to different particle size ranges.
2. Generally, particles that meet the product particle size requirements are collected as finished products. Large particles that do not meet the requirements are crushed and re added to the granulation system as return materials, while small particles can be recycled as seed crystals.
5. Cooling and coating
The screened finished particles generally have a high temperature and need to be cooled by cooling equipment to reduce their temperature to room temperature or close to room temperature for storage and transportation.
In order to improve the stability, moisture resistance, and slow-release performance of the particles, sometimes the cooled particles are coated. The coating material can be paraffin, resin, polymer, etc. By dissolving the coating material and spraying it on the surface of the particles, a protective film is formed.

process characteristics
 
Advantages
Particle uniformity: capable of producing particle products with uniform particle size and regular shape, with good appearance quality, good flowability, and easy storage, transportation, and application.
High production efficiency: It can achieve continuous production, has a large production capacity, and can meet the needs of large-scale industrial production.
Good product performance: By adjusting process parameters and raw material formulas, the strength, solubility, nutrient content, and other properties of particles can be flexibly controlled to meet the needs of different users and application scenarios.
Disadvantages
High energy consumption: During the process of spray granulation, it is necessary to heat and dry the raw materials, which consumes a large amount of heat and electricity, resulting in relatively high production costs.
Large equipment investment: The spray granulation process requires specialized granulators, dryers, screening equipment, etc., and the purchase, installation, and maintenance costs of the equipment are relatively high.
High requirements for raw materials: The particle size, moisture content, flowability, and other properties of the raw materials have a significant impact on the granulation effect, requiring strict pretreatment and quality control of the raw materials.