NPK 18-18-18 is a high-concentration balanced compound fertilizer with a total nutrient content of 54%, with equal proportions of nitrogen, phosphorus, and potassium, suitable as a base fertilizer for various crops. The key to producing this formula lies in precise ingredient proportioning, efficient mixing, steam drum granulation, and strict drying, cooling, and coating processes. This article uses a standardized production line with an annual capacity of 50,000 tons as an example to break down the complete process from raw materials to finished product.
I. Raw Material Weighing: Accuracy Determines Nutrient Deviation
Common raw materials for producing 18-18-18 include: urea (N≥46%), monoammonium phosphate (11-44-0 or 10-50-0), potassium chloride (K₂O≥60%), and a small amount of fillers (such as clay or diatomaceous earth, used to adjust the total nutrient content).
Equipment Configuration: Multi-compartment static scales or loss-in-weight belt scales are used, with each compartment weighed independently, and the dynamic cumulative error ≤0.5%.
Example Formulation (per ton of product): Urea approximately 391 kg, Monoammonium Phosphate (11-44-0) approximately 409 kg, Potassium Chloride approximately 300 kg, Filler approximately 50 kg, plus 20-30 kg of Bentonite binder.
Key Controls: Calibrate the weighing sensor once per shift to ensure that the deviation of nitrogen, phosphorus, and potassium content is within ±0.5%.
II. Mixing: Uniformity ≥90% The weighed raw materials enter a twin-shaft paddle mixer or a horizontal ribbon mixer.
Parameter Requirements: Mixing time 2-3 minutes, uniformity coefficient of variation CV < 10%. For hygroscopic urea and potassium chloride, the mixing process should be sealed and supplemented with a small amount of anti-caking agent.
Discharge: The mixed powder is conveyed to the buffer silo before the granulator via an elevator.
III. Granulation: Steam drum granulation as the core method. Due to the high nitrogen content of the 18-18-18 formulation, urea is easily melted at high temperatures; therefore, a steam drum granulator is recommended.
Working Principle: Saturated steam at 0.3-0.5 MPa is introduced into the drum, raising the powder temperature to 55-65℃. The material agglomerates into granules during the rolling motion. The steam provides both heat and liquid phase, eliminating the need for additional water.
Equipment Parameters: Drum diameter 2.2-2.5 m, rotation speed 12-15 rpm, filling rate 15%-20%. The discharged granules after granulation have a particle size concentrated between 2-4.5 mm, with a granulation rate of 65%-75%.
Precautions: Strictly control the steam valve opening to prevent localized overheating that could cause urea to melt and stick to the walls. If the granules are too small, the rotation speed can be appropriately reduced or the residence time extended.
IV. Drying and Cooling: Locking in Strength and Moisture The wet granules after granulation have a moisture content of approximately 4%-5%, requiring drying and cooling.
Dryer: A counter-current rotary drum dryer is used. The inlet hot air temperature is 160-180℃, and the outlet temperature is ≤65℃. After drying, the moisture content is reduced to below 2%. The internal lifting plate structure must prevent high-nitrogen particles from sticking to the walls.
Cooler: The dried hot granules enter a rotary cooler, where they are forcibly cooled to below 40°C using ambient air or cold air. Insufficient cooling will lead to clumping after packaging.
Sieving: After cooling, the granules are separated into qualified particles (2-4.5mm) through a double-layer grading sieve (4.5mm upper layer, 2mm lower layer). Oversized particles are crushed and returned to the granulator along with the fine powder.
V. Coating and Packaging: Anti-caking and Commercialization
To prevent the product from absorbing moisture and clumping again during storage and transportation, a coating treatment is required.
Coating Machine: A small rotary cylinder with built-in high-pressure nozzles atomizes and sprays 0.2%-0.5% liquid anti-caking agent (vegetable oil-based or mineral oil-based) onto the granule surface.
Packaging: After coating, the granules enter an automatic quantitative packaging scale (25kg or 50kg per bag), are sealed in double-layer woven bags with an inner moisture-proof film lining, and the production date and nutrient content are printed on them. In summary, the NPK 18-18-18 production line requires high-precision equipment, strict temperature control during granulation, and anti-sticking drying. Following a standardized process of “weighing → mixing → steam drum granulation → drying and cooling → coating and packaging,” it can stably produce high-quality compound fertilizers with a particle strength ≥15N, moisture content ≤2%, and nutrient deviation compliance rate ≥98%. We specialize in the R&D and manufacturing of complete compound fertilizer production lines, and our mature solutions include high-concentration formulations such as NPK 18-18-18—providing one-stop supply of equipment for the entire process, from weighing and batching to coating and packaging.
The NPK 18‑18‑18 production line exemplifies the integration of advanced npk fertilizer manufacturing technology with rigorous process control, from raw material handling to finished product packaging. The entire npk blending fertilizer production line begins with precise npk fertilizer formula processing, where urea, monoammonium phosphate, and potassium chloride are accurately weighed and mixed in a high‑efficiency npk blending machine (or BB fertilizer blender) to ensure a uniformity coefficient CV < 10%. This homogeneous blend then feeds into the core npk fertilizer granulator machine (steam rotary drum granulator), which operates at 55‑65°C with controlled steam to achieve a granulation rate of 65‑75% and produce uniform 2‑4.5 mm granules. For producers requiring additional flexibility, the same base formulation can be processed through a npk fertilizer granule machine (such as a disc or roller press) to meet different market demands. After granulation, the material undergoes low‑temperature drying (≤180°C), gentle cooling, and double‑layer screening, followed by coating and automatic bagging. The final product, with nutrient deviation within ±0.5%, moisture ≤2%, and strength ≥15N, is also ideal for downstream npk bulk blending machine operations, where its uniform particle size prevents segregation during blending with other compatible materials. By mastering the entire spectrum – from formula design, blending, granulation, drying, to coating and packaging – manufacturers can consistently produce a balanced, high‑concentration fertilizer that meets the demands of modern agriculture, delivering both agronomic performance and excellent handling properties.