The granular compound fertilizer has complete nutrients, uniform distribution and no segregation (stratification). It has the advantages of high nutrient utilization rate, good fertilizer efficiency, good mechanical strength, strong fluidity, less dust, less environmental pollution, easy mechanized fertilization and aviation fertilization. According to the chemical properties of the soil, the growth requirements of the crops, the use of different nutrient distribution ratios, or the use of a package, can improve the dissolution rate of nutrients in the soil, scientific fertilization, improve fertilizer efficiency, thereby improving the utilization rate of fertilizers, and obtaining better agricultural production.
At present, the granulation production process often used in the NPK fertilizer production line is mainly based on the pellet production process and the extrusion granulation process.
The granulation process of the pellet method is based on monomeric base fertilizers such as: urea, ammonium nitrate, ammonium chloride, ammonium sulfate, monoammonium phosphate, diammonium phosphate, heavy calcium, calcium, potassium chloride (potassium sulfate), etc. After the raw materials are pulverized to a certain fineness, the materials are agglomerated and granulated by humidification and heating in a rolling bed of a drum granulator (or a disc granulator), and in the granulation process, a small amount of phosphoric acid and ammonia were added to the drum granulator to improve the granulation conditions. The granulated materials are dried, sieved and cooled to obtain NPK compound fertilizer products, which is one of the widely used methods in the world. The early US and India, Japan, Thailand and other Southeast Asian countries have adopted this method.
The raw materials of the method are widely available, the processing process is simple, the investment is small, the production cost is low, the production speed is fast, the production flexibility is large, the product taste adjustment is simple and easy, the versatility is strong, the raw materials used are all solid, and the raw materials are The dependence is not strong. Because it is the secondary processing of basic fertilizer, there is almost no environmental pollution. Since most of the basic fertilizers in China are powdery and granular, most of the small and medium-sized compound fertilizer plants in China use this method. . At present, this kind of production technology has become increasingly mature in China.
The extrusion granulation process is a dry granulation process in which solid materials are agglomerated by external pressure. It has the following advantages:
1. The production process generally does not require a drying and cooling process, and is particularly suitable for heat sensitive materials, while saving investment and energy consumption.
2. The operation is simple; no three wastes are discharged during production.
3. It can produce high-concentration compound fertilizer with lower concentration than general compound fertilizer. Organic fertilizer and other nutrients can also be added in production.
But the extrusion granulation method also has some shortcomings:
1. As key equipment for extrusion granulation, due to problems such as equipment manufacturing and material of the pressure-receiving parts, the material consumption during production is high and the failure rate is high.
2. The production capacity of the roller press granulator is small and it is difficult to achieve scale production. Therefore, the method is generally used for production scales of 30,000 tons/year or less. The method is currently mainly used for compound fertilizers such as rare earth ammonium bicarbonate.