Common fertilizer extrusion granulators include double-roll extrusion granulators and flat (ring) die extrusion granulators. During the processing of compound fertilizers, these granulators may increase nitrogen elements according to needs, and some use urea as the source of nitrogen elements, which can easily absorb moisture in the air and cause compound fertilizer particles to stick together. Therefore, it is often said that the double-roll extrusion granulator is a dry powder granulator, which has a better effect on processing granules for raw materials with a moisture content of less than 10%. For wet materials, necessary anti-hardening technology must be carried out. For the storage of fertilizer granules containing moisture as raw materials of compound fertilizers, it is necessary to avoid hardening.
The principle and water requirement of compound fertilizer extrusion granulator processing granules
The working principle of the extrusion granulator is mostly dry powder as the main raw material. When the brittle material is squeezed, part of the particles are crushed, and the fine powder fills the gaps between the particles. In this case, if the free chemical bonds on the newly generated surface cannot Rapidly saturated with atoms or molecules from the surrounding atmosphere, the newly generated surfaces come into contact with each other and form strong recombination bonds. For the extrusion of the roller, the roller skin has a spherical opposite groove, which is extruded into a spherical shape, and the particles extruded by the flat (ring) die are columnar. Extrusion granulation requires relatively low moisture content. If the moisture is too high, it is necessary to add a drying system to the processing technology.
Solution to adverse effects of nitrogen source moisture absorption type in compound fertilizer granulation process
The crux of the compaction in the compound fertilizer granulation process is mostly the high water content caused by the nitrogen source urea absorbing water. Mechanistically speaking, the initiation and speed of “slow burning” of compound fertilizers do not increase with the increase of ammonium nitrate and potassium chloride content. For example, a mixture containing 80% ammonium nitrate and 20% potassium chloride does not burn, but contains A mixture of 30% diatomaceous earth, 55% ammonium nitrate, and 15% potassium chloride produces a stronger “slow burn”.
Compound fertilizer particles with urea as nitrogen source have high hygroscopicity and low softening point; biuret and adducts are easily formed when the temperature is high; urea will be hydrolyzed when the temperature is high, resulting in the loss of ammonia.
This is necessary to solve the high water content caused by the nitrogen source absorbing water. Reduce nitrogen source When calcium superphosphate exists, water-soluble phosphorus will be degraded; when producing urea-common calcium superphosphate compound fertilizers, common superphosphate must be pretreated, such as ammoniation, which can eliminate adducts Generate, or add calcium magnesium phosphorus to neutralize the free acid of superphosphate, and convert the free water into crystal water, improve product quality, or add ammonium sulfate, which can reduce the moisture of the finished product and strengthen the hardness of the finished product; when there is chlorine When ammonium is converted, urea and chlorine form an adduct, which increases the crystallization, which makes the rewarming fertilizer easy to cause agglomeration of the finished product during storage; therefore, the compound fertilizer with urea as the nitrogen source should pay special attention to the drying and cooling process. For example, the drying temperature should not be too high, the drying time should not be too long, the moisture content specified in the quality standard should be met, the melting phenomenon during the production process should be avoided, and no caking should be kept during the storage process.
The above are the reasons for the high moisture in the granulation process of the compound fertilizer granulator, which causes compaction. The main method to avoid compaction is the use of drying system. Pretreatment of materials, addition of elements and other methods, so as to realize the processing and non-destructive preservation of compound fertilizer particles.
Post time: Dec-10-2022
