What is Ammonium Sulfate Granulation?
Ammonium sulfate granulation refers to the process of processing powdered or crystalline ammonium sulfate (containing 20% to 21% nitrogen and 24% sulfur) into uniform granules through physical or chemical methods. Ammonium sulfate is highly hygroscopic and prone to caking. Powdered products absorb moisture from the air and harden into lumps during storage and transportation, making fertilization difficult. Granulation not only solves the caking problem but also allows for blending with phosphate and potassium fertilizers.
I. Roller Extrusion Granulation: The Preferred Dry Method
Roller extrusion granulation is the most economical dry method for ammonium sulfate granulation. The moisture content of the raw ammonium sulfate powder needs to be controlled below 3%, and the particle size requirement is 95% passing through an 80-mesh sieve. The material is fed between two counter-rotating rollers through a feeding system, compressed into a strip-shaped cake under a linear pressure of 150 to 250 MPa, then broken into irregular particles by a crusher and pelletizer. Finally, it is screened in two stages (3.5 mm upper screen and 1.5 mm lower screen) to obtain finished particles of 2 to 3 mm. The core advantage of this process is that drying is not required—ammonium sulfate does not generate additional moisture during extrusion, and it can be directly packaged after molding. However, it should be noted that ammonium sulfate crystals have high hardness, and it is recommended that the wear-resistant layer of the rollers in the roller extrusion granulator be treated with tungsten carbide welding. The lifespan of conventional alloy rollers when processing ammonium sulfate is only 60 to 70% of that when processing ordinary compound fertilizer.
II. Steam Roller Granulation: A Wet Process for Round Particles
For markets that require spherical particle appearance, steam roller granulation is a better choice. The process is as follows: Ammonium sulfate powder is premixed with a small amount of recycled material (ratio approximately 1:0.5 to 1:1) in a mixer, and then fed into the roller granulator. Saturated steam at a pressure of 0.2 to 0.4 MPa is introduced into the drum, raising the material temperature to 60 to 80 degrees Celsius. Under the rotation of the drum, the moist material rolls and agglomerates to form spherical particles. This method achieves a granulation rate of 75% to 85%, but the resulting particles have a high moisture content (approximately 8% to 12%), necessitating a drying process—using a rotary dryer to reduce the moisture content to below 1%, with the drying temperature controlled at 90 to 110 degrees Celsius. Excessive temperature will cause the ammonium sulfate to decompose and discolor.
III. Melt Granulation: A Special Path for High-Purity Products
Melt granulation is suitable for processing high-purity ammonium sulfate, such as industrial-grade or water-soluble products. Utilizing the characteristic that ammonium sulfate melts at 100 to 110 degrees Celsius and begins to decompose above 140 degrees Celsius, the powder is heated to 110 to 120 degrees Celsius to form a melt, which is then cooled and solidified into spherical particles using a granulation nozzle or steel belt granulator. This process produces granules with a smooth surface and the highest sphericity, requiring no binders. However, the energy consumption of the melting process is significantly higher than the previous two methods—approximately 300,000 to 400,000 kcal per ton of product. Furthermore, melt granulation requires stainless steel equipment to prevent corrosion, and the investment per line is 2 to 3 times that of extrusion granulation.
Three Criteria for Process Selection: When choosing an ammonium sulfate granulation process, it is recommended to consider the following three dimensions: Product Positioning: For ordinary agricultural-grade ammonium sulfate, roller extrusion granulation is sufficient to meet the requirements of blended fertilizer raw materials, with the lowest investment; high-end water-soluble fertilizers or export-grade products require consideration of melt granulation. Production Capacity: For production capacities below 5 tons per hour, extrusion granulation is recommended due to its compact equipment and lack of a drying process; for production capacities above 10 tons per hour, steam drum granulation offers a more advantageous unit cost. Raw Material State: Dry powder with a moisture content below 2% is suitable for extrusion granulation; wet materials with a moisture content of 4% to 6% are more suitable for steam drum granulation because the front-end drying step can be omitted.
Key Process Considerations for Recycled Material Ratio Control
Regardless of the chosen process, controlling the recycled material ratio is the core of optimizing ammonium sulfate granulation. Ammonium sulfate powder has low viscosity, and direct granulation of pure powder is ineffective. A well-designed process requires mixing the fine powder (less than 1 mm) sieved from the finished product with the new raw material at a ratio of 3:7 to 5:5. The fine powder acts as “seeds,” providing nucleation sites and significantly improving the granulation rate. For every 10 percentage point reduction in the recycled material ratio, the overall production line capacity increases by approximately 8% to 12%, while the drying load decreases simultaneously. It is recommended that new production lines initially set the recycled material ratio at 1:1, gradually reducing it to 3:7 after the process stabilizes to find the optimal balance between granulation rate and production capacity.
Aligning Granulation Technology with Product and Market Requirements
The granulation of ammonium sulfate exemplifies how a single raw material can follow multiple process paths depending on purity targets, particle aesthetics, and capacity constraints. For producers integrating ammonium sulfate into broader compound fertilizer portfolios, a double roller press granulator offers the most capital-efficient dry-process route, eliminating thermal drying while delivering dense, durable pellets suitable for downstream blending. When spherical morphology is non-negotiable—such as for premium retail or export markets—steam-assisted drum systems within a conventional inorganic fertilizer machine train provide the necessary agglomeration chemistry, albeit with added fertilizer drying and cooling machine stages to stabilize hygroscopic particles. Beyond standalone granulation, ammonium sulfate granules frequently serve as feedstock within an npk blending fertilizer production line, where an npk blending machine, npk bulk blending machine, or BB fertilizer blender combines them with urea and potash to create customized compound formulations without chemical reaction. Whether deployed as a primary npk fertilizer granulator machine or as a blending component, the upstream fertilizer crusher and mixer and downstream fertilizer screening equipment remain essential for size uniformity and nutrient consistency. Ultimately, the optimal ammonium sulfate process is not an absolute choice but a calibrated decision among extrusion, steam drum, and melt routes—each aligned with the producer’s energy budget, equipment infrastructure, and the specific agronomic value proposition demanded by the target market.
We offer a full range of ammonium sulfate processing equipment, including roller extrusion granulators and drum granulation lines. We can also customize the optimal process route and recycled material ratio control scheme free of charge based on your product positioning, production capacity, and raw material moisture content, helping you achieve a stable conversion from powder to high-quality granules with minimal investment.