High-tower granulation technology represents a major technological revolution in compound fertilizer production. Its core lies in “melt-to-granulation”—high-temperature molten fertilizer slurry is sprayed from the top of a tower, cooling and solidifying during its free fall to directly form rounded granules. This technology bypasses the multiple steps of traditional granulation, including crushing, mixing, granulation, and drying, achieving a shorter production process, higher efficiency, and higher quality in compound fertilizer production.
I. Pain Points of Traditional Compound Fertilizer Granulation
Traditional wet processes such as rotary drum granulation and disc granulation require crushing and mixing raw materials, followed by adding water or steam for granulation, and then drying, cooling, and sieving. This process is lengthy, energy-intensive, and the granule strength is greatly affected by moisture content and drying efficiency. The critical relative humidity decreases after urea and potassium salts are mixed, making them prone to moisture absorption and clumping. Even slight errors in the drying process can lead to granule pulverization. The emergence of high-tower granulation technology fundamentally bypasses these problems.
II. Principle of Melt Drop Granulation The core of high-tower granulation is a three-step process: melting, spraying, and cooling. First, raw materials such as urea, monoammonium phosphate, and potassium chloride are heated to 120℃–140℃ in a melter to form a low-viscosity melt with good flowability. Then, the melt is pumped by a high-pressure pump to a rotating or static nozzle at the top of the tower, where it is atomized into uniform droplets. These droplets fall freely within the 80–120 meter high tower, coming into counter-current contact with cold air flowing upwards, and solidify within tens of seconds, forming 2–4 mm spherical particles. The entire process requires no water addition or subsequent drying, resulting in particles with extremely low moisture content.
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III. Four Major Advantages of this Revolutionary Process
1. Superior Particle Quality: Under the influence of surface tension, the melt naturally shrinks into spheres, resulting in smooth, rounded particles with high strength, resistance to clumping, and good flowability, making them suitable for mechanized fertilization.
2. Extremely short process and low energy consumption: Eliminating drying and cooling processes reduces energy consumption per unit product by more than 30% compared to traditional processes, and produces no wastewater or exhaust gas emissions.
3. Uniform nutrients: The melt is mixed at the molecular level, ensuring that the nitrogen, phosphorus, and potassium ratios of each granule are completely consistent, resulting in stable fertilizer efficacy.
4. Significant advantages for high-nitrogen formulations: Particularly suitable for producing high-nitrogen compound fertilizers (such as 30-0-0, 28-6-6, etc.), which is difficult to achieve stably with traditional rotary drum granulation.
IV. Key Technical Control Points High-tower granulation requires extremely high process control. The melt temperature must be precisely controlled at 130℃±5℃. Excessive temperature will decompose urea, while insufficient temperature will result in insufficient fluidity and nozzle clogging. The nozzle rotation speed and orifice diameter determine the particle size and must be dynamically adjusted according to the formulation. The speed and temperature of the rising airflow within the tower must match the droplet falling speed to prevent particle adhesion or drift. Furthermore, impurities and moisture in the melt must be strictly limited; otherwise, they will clog the nozzles and affect the granulation rate.
V. Applications and Prospects High-tower granulation technology emerged in China in the 1990s and is now widely used in the production of urea-based compound fertilizers. Its disadvantages include high equipment investment, long tower construction period, and limitations on high-nitrogen systems. Excessive phosphorus and potassium content increases melt viscosity, making granulation difficult. In the future, with advancements in melt modifiers and intelligent nozzle technology, high-tower granulation is expected to expand into medium- and high-phosphorus formulations, further broadening its application scope.
High-tower granulation technology, with its simple logic of “melt falling directly to form granules,” has reshaped the process route of compound fertilizer production. It is not merely an upgrade in equipment but also a subversion of traditional granulation concepts. For compound fertilizer companies pursuing high quality and low energy consumption, high-tower granulation remains an advanced direction worthy of in-depth research.