The sulfur-coated urea production line focuses on the slow-release modification needs of conventional urea. Through a closed-loop process of “urea pretreatment – melt sulfur coating – cooling and solidification – finished product grading,” it achieves large-scale production of 15 tons/hour of sulfur-coated urea. The finished granules use urea as the core and sulfur as the slow-release coating layer, combining the advantages of long-term nutrient release and environmental protection and energy saving. It is suitable for large-scale planting scenarios such as grain crops and cash crops, significantly improving fertilizer utilization.
Production Line Configuration and Core Details
I. Urea Pretreatment Unit: Laying the Foundation for Sulfur Coating
(I) Raw Material Storage and Quantitative Feeding
Urea Raw Material Silo: Equipped with two 50m³ conical raw material silos (total volume 100m³), made of carbon steel with an anti-corrosion coating. The silo cone angle is 65°, and a vibrator and star-shaped unloader are installed at the bottom to prevent urea granule bridging and blockage. The raw material silo is equipped with a pulse dust collector at the top to collect feed dust. The dust emission concentration is ≤10mg/m³, meeting environmental protection standards.
Precision Feeding System: Two frequency-controlled belt feeders (model DTⅡ-500) are used, each with a feeding capacity of 7.5-8 tons/hour. Combined operation meets the production capacity requirement of 15 tons/hour. The feeders are equipped with weight sensors to provide real-time feedback on the feed amount. The speed is adjusted via a PLC system, with a batching error ≤±0.5%.
(II) Urea Screening and Preheating
Grading and Screening Machine: One Φ1.8×6.0 meter drum screen is used, employing a single-layer screen (pore size 2.5-4.5mm) to screen out uniformly sized urea particles (removing <2.5mm fragments and >4.5mm large pieces), ensuring uniform sulfur coating. Non-conforming particles are conveyed to a crusher via a return conveyor belt for crushing and recirculation, achieving a material utilization rate of 99% and a screening efficiency of 18 tons/hour.
Low-temperature preheater: A Φ1.5×12 meter drum preheater is used, employing indirect steam heating to raise the temperature of urea particles from room temperature to 40-50℃. Preheating reduces the surface tension of the urea particles, facilitating the adhesion of the sulfur coating layer, while preventing rapid solidification of sulfur due to low-temperature urea, which would affect the continuity of the coating. The preheater is equipped with a temperature sensor, ensuring precise temperature control with an error ≤±2℃.
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II. Core Sulfur Coating Unit: Key to Slow-Release Layer Formation
(I) Sulfur Melting System
Melting Tanks: Three 10m³ stainless steel melting tanks are configured (2 in use, 1 as standby), using electric heating + circulating heat transfer oil to heat solid sulfur (particle size ≤5mm) to 125-135℃, melting it into liquid sulfur (viscosity ≤0.02Pa・s). The melting tank is equipped with a level sensor and an automatic replenishment device to maintain a stable liquid level. A single tank has a melting capacity of 6 tons/hour, meeting coating requirements.
Sulfur transfer pumps: Three gear-type insulated transfer pumps (temperature resistance ≥150℃) are used to pressurize and transfer liquid sulfur to the coating machine. The transfer pressure is controlled at 0.3-0.5MPa, and the flow rate is adjustable from 300-500kg/hour (sulfur addition accounts for 8%-12% of the total urea content, adapting to different slow-release cycle requirements). The transfer pipeline adopts a double-layer insulation design, with the outer layer wrapped in rock wool to prevent sulfur from cooling, solidifying, and clogging the pipeline.
(II) High-efficiency coating machine
Core equipment selection: Two Φ2.2×8.0 meter roller-type coating machines (7.5 tons/hour per machine) operate in parallel, with a total capacity of 15 tons/hour. The inner wall of the coating machine’s drum is lined with high-temperature and wear-resistant plates, and a spiral layout with lifting plates drives the material in a “tumbling-spraying-rolling” motion, ensuring that each urea granule is evenly contacted with liquid sulfur.
Coating process details: Liquid sulfur is evenly sprayed onto the surface of the urea granules inside the drum through atomizing nozzles (0.8mm orifice diameter), with an atomization pressure of 0.4MPa, forming a uniform sulfur film layer with a thickness of 0.1-0.3mm. The coating machine is equipped with a variable frequency speed control system, allowing the drum speed to be adjusted within the range of 8-15 r/min, controlling the material residence time to 3-5 minutes to ensure a dense, gap-free coating layer.
Auxiliary coating optimization: Depending on requirements, 0.5%-1% paraffin wax or asphalt can be added as a sealant, sprayed synchronously with the sulfur through an independent atomization system to fill the pores in the sulfur film layer, further enhancing the slow-release effect and extending the nutrient release period to 3-6 months.
III. Post-processing and Curing Unit: Ensuring Finished Product Quality
(I) Cooling and Curing
Counter-flow Cooler: Equipped with two Φ1.8×15 meter drum coolers (each with a processing capacity of 8 tons/hour), using counter-flow cooling with ambient temperature air to rapidly reduce the temperature of the coated particles from 100-110℃ to below 30℃. The cooler has a built-in air guide device to enhance heat exchange efficiency. The cooling time is controlled within 10 minutes to ensure complete curing of the sulfur coating layer, achieving a hardness of over 2.0MPa and preventing damage.
Cooling Air Treatment: A small amount of sulfur dust carried by the cooling air is collected by a pulse dust collector with a collection efficiency of 99.5%, avoiding environmental pollution. The collected sulfur dust can be recycled back to the melting tank for reuse.
(II) Grading and Anti-caking Treatment
Finished Product Screening: Two Φ1.5×4.0 meter vibrating screens are used, employing a double-layer screen design. The upper screen (5.0mm aperture) separates oversized agglomerated particles, while the lower screen (2.0mm aperture) screens qualified finished products, achieving a qualified particle pass rate of 98%. Unqualified particles are crushed and returned to the pretreatment stage, resulting in a material utilization rate of 99%.
Anti-caking Spraying: A small spraying device is added after screening to spray 0.1%-0.2% of an anti-caking agent (such as talc suspension) onto the surface of the finished particles. Through natural mixing during the belt conveyor process, the agent adheres evenly to the particle surface, preventing agglomeration during storage.
IV. Finished Product Storage and Packaging Unit: High-Efficiency Output
Finished Product Warehouse: Equipped with 3 x 100m³ finished product warehouses (total volume 300m³), featuring a sealed design and equipped with dehumidification and ventilation devices to maintain relative humidity ≤60% and prevent finished products from absorbing moisture. A quantitative unloading device is installed at the bottom of the warehouse for continuous and stable discharge.
Automated Packaging: Utilizes 4 dual-station automatic packaging scales (120 bags/hour per scale), supporting rapid switching between 25kg and 50kg specifications, with a measurement error ≤±0.2kg. The packaging machine is equipped with a dust cover and automatic sewing device to reduce dust emissions. Packaged finished products are transferred to the finished product stacking area via belt conveyor. The entire process is automated, minimizing manual intervention.
V. Environmental Protection and Intelligent Control Unit: Stable and Environmentally Friendly Operation
(I) Environmental Treatment System
Waste Gas Treatment: The small amount of sulfur vapor generated by the melting tank and coating machine is recovered by a condensation recovery device. Uncondensed waste gas is purified by an activated carbon adsorption tower before being discharged. The waste gas emission concentration complies with the “Integrated Emission Standard for Air Pollutants”. Wastewater Treatment: Wastewater from the production line cleaning process is treated in an oil separator and sedimentation tank before being recycled for equipment cleaning, achieving zero wastewater discharge.
(II) Intelligent Control System: An integrated PLC central control system with a touchscreen interface monitors the operating parameters of each piece of equipment in real time (sulfur melting temperature, coating machine speed, cooling temperature, feed rate, etc.), supporting automatic fault alarms and data recording (storage period ≥ 90 days). The system supports remote monitoring and operation, facilitating real-time monitoring of production status by management personnel.
Key equipment (melting tank, coating machine, cooler) is equipped with safety interlock devices, such as automatic power-off for overheating of the melting tank and automatic shutdown for overload of the coating machine, ensuring production safety.
Core Advantages and Application Value of the Production Line: High and Stable Production Capacity: The dual-machine parallel configuration achieves an hourly output of 15 tons and an annual capacity of 120,000 tons (calculated based on 300 days of operation per year and 8 hours per day), meeting the needs of large-scale production. Excellent slow-release effect: The dense and uniform sulfur coating allows for flexible adjustment of the nutrient release cycle (3-6 months), increasing fertilizer utilization by 30%-40% compared to conventional urea, while reducing nutrient loss and environmental pollution.
Environmentally friendly and energy-saving: A fully sealed design and dust recovery system result in low pollutant emissions; the preheater and melting tank utilize energy-saving heating technology, reducing energy consumption by 10% compared to conventional production lines.
Enabling Enhanced-Efficiency Fertilizers Through Specialized Production
This sulfur-coated urea production line represents a highly specialized segment within the broader fertilizer manufacturing industry. It focuses on creating a value-added, controlled-release product from a single nutrient source, demonstrating the sophistication possible with modern npk fertilizer production technology.
While this line produces a specialized single-nutrient product, it shares its industrial ecosystem with the equipment used for the manufacturing of npk fertilizer. The production of traditional compound fertilizers often relies on a complete npk fertilizer manufacturing process that begins with precise blending using an npk blending machine or a bulk blending fertilizer machine. The blended mixture is then shaped using an npk fertilizer granulator machine employing advanced npk granulation machine technology as part of a suite of npk fertilizer granulator machine equipment. The scale and efficiency of such integrated systems determine a plant’s overall NPK compound fertilizer production capacity. Therefore, a sulfur-coating line is a complementary technology, adding a specific functionality that works alongside, rather than replaces, conventional bulk blending and granulation systems.Ultimately, the ability to offer both conventional NPK blends and advanced coated products allows manufacturers to serve a wider market, from basic nutrient supplementation to precision, efficiency-focused agriculture.
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