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1. Granulation process: The basic principle of the granulation process is that the base fertilizer with a certain fineness has its particle surface wetted by the liquid phase generated from the dissolution of salts, as well as by water or steam. Under appropriate liquid-phase conditions, mechanical stirring causes the particles to move continuously, leading to collisions, compression, and rolling between them, which in turn enables them to stick together and form granules. Depending on the granulation equipment, it can be divided into processes such as disk granulation and drum granulation. This process is simple and mature ； Easy to operate and control ； It has relatively strong adaptability to raw materials, and the product specifications can be easily adjusted; various basic fertilizers can be used for granulation to produce compound fertilizers with different nutrient concentrations ； The device has strong versatility ； The requirements for setting up a factory are low, and there are no restrictions on raw materials. However, the disadvantages of this process are low granulation efficiency, high energy consumption, poor appearance of the particles, and limited flexibility in the production of urea-based fertilizers with high nitrogen ratios. 2. Process flow of the slurry method: The principle of the granulation process using the slurry method is that a portion of the base fertilizer used for granulation is fed into the granulator in slurry form; this slurry, acting as a liquid phase, combines with other powdered and granular materials as well as recycled material within the granulator to form particles. Depending on the different types of granulators, this process can be further divided into: (1) drum granulation process, (2) disk granulation process, (3) slurry granulation process, (4) twin-screw granulation process, (5) fluidized bed granulation process, and (6) drum curtain granulation process. Based on the raw materials of the slurry, they can be classified into urea-based, **-based, and ammonium phosphate. Domestic phosphorus compound fertilizer production relies primarily on spray granulation, including the imported DAP/NPK production facilities, the numerous slurry method phosphate ammonium plants, and the sulfur-based compound fertilizer plants that use phosphoric acid as a key component. This method combines granulation and drying, forming particles through coating, bonding, and self-granulation; the resulting particle products possess good physical, chemical, and mechanical properties. China’s largest single set of compound fertilizer production facility – Tianji Coal Chemical Industry’s 900,000-ton per year nitrate phosphate fertilizer plant – is the only one in the country to use a twin-axis granulation process. Some of the slurry-based urea-based (**-based) compound fertilizer production technologies are patented technologies that have been researched and promoted by the Shanghai Institute in recent years (patent number 00116235.7). This process makes use of urea’s properties of high solubility and low melting point, as well as the heat from its slurry, to directly spray ≥95% concentrated solutions or molten salts into a granulator where they combine with other powdered and granular materials to form particles. The process flow diagram is shown in Figure 2. This process utilizes a urea (or **) solution with a low water content, which not only facilitates the water balance of the entire production facility; moreover, during the granulation process, the urea (or **) solution releases crystallization heat, enabling an increase in the granulation temperature and a reduction in the moisture content of the product at the outlet of the granulator, thereby increasing the drying load. Solution granulation enables the granulation process to exhibit both agglomeration characteristics and coating effects, resulting in a smoother appearance of the product, increased particle strength, and **improved automation levels in process control. Some slurry-based processes can use the semi-finished products from urea (or **) production plants as raw materials, thereby eliminating the costs associated with urea granulation as well as the expenses for packaging and transporting the product. Additionally, these processes make full use of the thermal energy contained in urine, reducing energy consumption during production and the cost of the final product. They represent a viable option for urea (or **) production plants seeking to improve their product portfolio by adopting this type of compound fertilizer production method. The process for 3-granule nitrogen-potassium compound fertilizer (NPK blended fertilizer) – the slurry method without drying and granulation – is a blended fertilizer production process recently developed by the Shanghai Research Institute. It is possible to produce nitrogen-potassium fertilizers (which can be used as raw materials for blended fertilizers; the process flow is shown in Figure 3), as well as nitrogen-phosphorus-potassium compound fertilizers (the general process flow is shown in Figure 4). The slurry can be a urea solution or melt ； It can also be a eutectic compound formed from urea solution and potassium chloride (or potassium sulfate) ； The slurry, along with the liquid phase and phosphorus sources such as heavy calcium carbonate and ammonium phosphate, as well as potassium salts (potassium chloride or potassium sulfate), is applied or bonded into balls within a granulator. The granulator can be a drum, a disk, or a drum-type curtain. 4. Melt granulation process: The characteristic of the melt granulation process is that the material is in a high-temperature molten state; it is a low-water-content, flowable melt that is directly sprayed into a cooling medium (which is usually air or a liquid in which the molten material does not dissolve, such as mineral oil). As the material cools, it solidifies into spherical particles ； Alternatively, the fluidized melt can be sprayed onto the return particles in the mechanical granulator, thereby coating or bonding them on the surface of the fine particles to form particles that meet the required specifications. Evaporating or concentrating a solution does require energy, but it is much more efficient in terms of energy utilization compared to dry granular products; moreover, in certain production processes, the heat of reaction can be fully utilized to evaporate some or even all of the water ； In conventional granulation processes, the dryer is usually the largest and most expensive piece of equipment in the granulation system; however, melt granulation does not require drying, which saves on investment and energy consumption.