Currently, there are four main granulation methods in the production of compound fertilizers. Please share your views on the advantages and disadvantages of each of these four granulation methods

1. Spraying granulation, which evolved from the traditional monoammonium slurry granulation method. 2. Disk granulation. 3. Ammoniation drum granulation. 4. The currently popular tower granulation method (which is further divided into single-tower (tall tower) and double-tower (low tower) types) is suitable for materials in a dissolved state. Disk and drum granulation works on a principle similar to that of snowballing, requiring the addition of auxiliary materials such as clay. In tower granulation, the material fed into the tower is granulated while it is in a molten state, similar to the formation of hailstones. Granulation by spraying and tower granulation result in particles with uniform size and high mechanical strength, which thus improves the quality of the fertilizer. Comparison between drum ammoniation granulation compound fertilizers and spraying granulation compound fertilizers: At present, there are mainly two production methods for S-NPK compound fertilizers manufactured in China, namely drum ammoniation granulation and spraying granulation. The compound fertilizers produced by these two methods differ significantly, mainly in the following aspects: 1. Product advantages: Drum ammoniation granulation compound fertilizers can produce 15–15–15 type products, with a more balanced nutrient ratio ； Spray granulation can only produce products with the composition 12-18-15 or 13-17-15. The nitrogen content in the compound fertilizers produced by drum ammoniation can be as high as over 14%, while the water-soluble phosphorus content can reach over 95%. In contrast, the nitrogen content in compound fertilizers produced by spray granulation is low, around 12%, and the water-soluble phosphorus content is around 80%; thus, their efficacy is far inferior to that of the products manufactured using drum ammoniation. 2. Production process: The drum ammoniation process utilizes a tubular reactor; the entire reaction takes place within this tubular reactor. The degree of neutralization achieved in this process is over 1.5, and the reaction residence time is short, at less than 10 seconds. As a result, the product contains a high level of nitrogen. Due to the short reaction time, there is not enough time for phosphate precipitates to form, so there is no degradation of phosphorus, leading to a high level of water-soluble phosphorus. The granulation process by spraying involves traditional tank neutralization; the reaction duration is long, exceeding 30 minutes, resulting in a low degree of neutralization, around 1.1 only. As a consequence, the nitrogen content in the resulting product is low. The long reaction time also leads to the precipitation of phosphates from phosphoric acid, which causes a reduction in phosphorus levels; hence, the water-soluble phosphorus content is low. 3. Technical level: The production process for spray granulation is relatively mature, with stable operation; currently, there are many enterprises engaged in this production ； Due to the narrow range of operational conditions and the difficulty in controlling the process, drum ammoniation granulation is not widely used; few manufacturers are able to operate it properly. In China, less than 10 companies currently use this process, with only 8 or 9 of them actually employing the full-slurry method. It is not possible to draw simple conclusions regarding several granulation processes; for manufacturers that produce granular ammonium phosphate, spray granulation is a better option. For manufacturers equipped with urea production facilities, tower granulation is a better option, as it allows for the production of both urea and compound fertilizers. Disk granulation is more suitable for the production of compound fertilizers alone. The source of raw materials used in different locations is also important; the drum ammoniation granulation process requires high-concentration phosphoric acid and a large amount of liquid ammonia. It is recommended to read articles on related topics. Dry material mixing and granulation: In the early processes of mixing solid powder materials to produce powdered fertilizers, additional steps such as granulation, drying, crushing of coarse particles, and returning fine particles for further granulation were added, resulting in dried granular products. Urea-dicalcium phosphate-potassium chloride granular compound fertilizer belongs to this category. Dry powder mixing and granulation with the addition of some liquid raw materials: When granulating solid powdered materials, sulfuric acid, phosphoric acid, or nitric acid is introduced into the granulator, along with a certain amount of water vapor; gaseous ammonia is also added to neutralize the acids introduced or to neutralize the acidic components in the solid materials. Relying on the heat of neutralization and the enthalpy brought in by saturation and vapor, the liquid phase (including the salt solution and water formed as a result of the reaction) is introduced to promote agglomeration into particles. The urea-ammonium phosphate-potassium chloride system, as well as the granulation of ammonium chloride-ammonium phosphate-potassium chloride materials, falls into this category. Slurry granulation process: The slurry formed from the reaction materials is applied to the surface of the core particles; through continuous application of this slurry, the particles grow in size. The particles are then dried to evaporate the moisture, resulting in hard, well-flowing granular products. Due to the wide range of particle size distribution in the returned material, coating and bonding always occur simultaneously; for certain materials and granulation types, one form of granulation always predominates. The granulation of ammonium phosphate fertilizers falls into this category. Melting granulation process: Cooling or condensing the molten slurry (a melt with very low moisture content) to form particles. *Granulation of AO acid and AN melts falls into this category.

It’s not right upstairs, is it? Are these the four granulation methods? I think they are extrusion, disk, drum, and tower – unless the classification methods are different. Could the original poster tell us which four methods are being compared? There’s too much hype around these concepts these days.