organic fertilizer production line

Introduction: The Urgent Need to Address the Global Sulfur Nutrient Gap

In modern intensive agriculture, macronutrient fertilizers such as nitrogen, phosphorus, and potassium are widely used, but sulfur, a key secondary nutrient, is often overlooked. Sulfur is essential for synthesizing sulfur-containing amino acids, proteins, vitamins, and chlorophyll formation, directly impacting crop yield and quality. However, with the strengthening of global industrial emission reduction measures, atmospheric sulfur deposition from natural sources (e.g., volcanic activity) and anthropogenic sources (e.g., fossil fuel combustion) continues to decline, leading to increasing deficiencies of bioavailable sulfate in many farmland soils. Simultaneously, industrial processes like oil refining and natural gas processing generate millions of tons of elemental sulfur by-products annually, some of which are not utilized efficiently. This acute supply-demand contradiction highlights the extreme urgency of developing sustainable technologies to convert industrial sulfur by-products into efficient agricultural fertilizers. This study focuses on the design and preparation of high-nitrogen sulfur fertilizers, aiming to closely integrate industrial sulfur resources with crop nitrogen demand through innovative engineering solutions, providing new nutrient management strategies for the sustainable production of global food and energy crops.

I. Core Research Approach: From Liquid Formulation to Solid Formation

To overcome issues with traditional sulfur-containing fertilizers, such as low nitrogen content, poor physical properties, or uncoordinated nutrient release, this study followed a systematic material design and engineering pathway. The research consisted of two closely linked core stages: first, the development of a high N:S ratio liquid fertilizer matrix based on precise phase diagram analysis; second, the preparation of composite solid granular fertilizers with high physical strength and balanced nutrients by granulating this matrix with various functional additives. This “liquid-solid” combined strategy not only ensures precise ratio and high uniformity of nitrogen and sulfur nutrients in the product but also addresses practical problems during storage and application by optimizing granule structure.

1. Liquid Phase System Design and Formulation Determination

The foundation of the research was a detailed phase composition analysis of the ternary system composed of urea, urea sulfate (2CO(NH₂)₂·H₂SO₄, i.e., diurea sulfate), and water. By precisely determining the phase equilibrium relationships of this system at different temperatures and concentrations, the researchers were able to draw clear phase diagrams. Based on these diagrams, the physical state (e.g., solution, slurry, or crystals) of the system at different ratios can be accurately predicted and controlled, thereby avoiding issues like crystallization blockages during production. Ultimately, the research team successfully optimized a formulation for a diurea sulfate-based liquid fertilizer with a high nitrogen-to-sulfur ratio (N:S ≈ 15:1). This liquid product has high nitrogen content, sulfur in the plant-available sulfate form, and exhibits good low-temperature stability and fluidity. It can be used either as an end-product for foliar or fertigation application, or as a core raw material for producing high-grade compound granular fertilizers.

2. Composite Granulation and Performance Enhancement of Solid Granular Fertilizer

To make the product more suitable for the storage, transportation, and mechanized application of bulk fertilizers, the second stage of the research focused on converting the liquid matrix into high-strength composite granules. The researchers designed three different additive formulations for granulation experiments:
(i) Dolomite Formulation: Using the natural mineral dolomite (mainly calcium magnesium carbonate) as an additive and filler. Dolomite not only provides the secondary nutrients calcium and magnesium, improving soil pH, but its particulate structure also helps enhance the fertilizer’s friability and compressive strength.
(ii) Industrial By-product Formulation: Innovatively using a by-product of the phosphoric acid extraction process—hemihydrate calcium sulfate (CaSO₄·0.5H₂O)—as an additive. This approach achieves “treating waste with waste,” converting an industrial solid waste into an effective fertilizer component. It provides sulfur and calcium while reducing production costs, embodying the circular economy concept.
(iii) Complete Nutrient Composite Formulation: To prepare a more comprehensive fertilizer, a mixture of dolomite, diammonium phosphate, and potassium chloride was used as the additive. Through precise formulation, a compound granular fertilizer with a nutrient label of 16-16-16-5.5(S)-0.4(MgO)-0.6(CaO) was successfully produced. This means the fertilizer contains 16% nitrogen (N), 16% phosphorus (P₂O₅), 16% potassium (K₂O), 5.5% sulfur (S), and significant amounts of magnesium and calcium.

Granulation was not the end point. The research team used X-ray diffraction technology to monitor in real-time the dynamic changes in the crystalline phase composition of the granules during the curing (storage) process. They found that over time, slow crystallization and rearrangement reactions occur within the granules, forming more stable crystal structures, a process known as “post-curing.” Experimental data showed that after 30 days of curing, the compressive strength of the composite granular fertilizer increased significantly from an initial ~1.200 MPa to 3.800 MPa. This strength index exceeds that of many conventional compound fertilizers on the market, indicating that the product has excellent anti-caking and abrasion resistance, can withstand the physical impacts of long-distance transportation and mechanized spreading, and ensures stable quality from the factory to the field.

II. Technical Advantages and Application Prospects

The high-nitrogen sulfur compound fertilizer developed in this study possesses multiple significant advantages:

· Efficient Nutrient Synergy: The combination of high nitrogen with sulfur in the sulfate form promotes crop assimilation and utilization of nitrogen, improving protein synthesis efficiency. This is particularly effective for sulfur-loving crops such as rapeseed, onions, and garlic.

· Resource Recycling: The core technology converts sulfur from refining by-products and gypsum from the phosphoric acid industry into high-value agricultural inputs, perfectly aligning with the principles of green chemistry and the circular economy, thereby reducing environmental burdens.

· Superior Product Physical Properties: Through innovative formulation and process, historical challenges of sulfur-containing fertilizers, such as being prone to deliquescence and having poor strength, have been addressed. The product features uniform granules, high strength, and good flowability.

· Convenient and Flexible Application: The derived liquid formulation is suitable for precision agriculture and foliar supplementation, while the solid granular formulation is suitable for field basal or top-dressing applications, meeting the needs of different agricultural systems.

Looking ahead, this technology has broad application prospects. Globally, especially in temperate agricultural regions severely affected by reduced sulfur deposition and large-scale cash crop plantations, there is huge demand for such customized high-nitrogen sulfur fertilizers. Future research could focus on conducting long-term field trials in different soil-crop systems to quantify their yield-enhancing, quality-improving effects and environmental benefits, and further optimizing the process to reduce energy consumption and costs for large-scale production.

From Innovative Formulation to Industrial-Scale Granulation

The development of high-nitrogen sulfur fertilizers exemplifies the sophistication of modern npk fertilizer production technology. Transforming this specialized liquid or powder formulation into a market-ready solid product requires integration into a complete npk fertilizer production line. The process begins with precise batching using a npk blending machine or a bulk blending fertilizer machine to ensure the accurate combination of nitrogen sources (like diurea sulfate), sulfur components, and other additives such as dolomite or potassium chloride. This precise mixture is the foundation of the entire manufacturing of npk fertilizer process.

The uniformly mixed material then enters the core fertilizer granulation stage. Advanced npk granulation machine technology is employed, utilizing equipment such as a npk fertilizer granulator machine or a disc granulator machine to transform the blend into dense, uniform granules. This specialized npk fertilizer machine must be capable of handling the unique properties of the high-nitrogen sulfur matrix to achieve the desired compressive strength and physical stability. The entire npk fertilizer manufacturing process—from precision blending to controlled granulation and curing—demonstrates how industrial-scale engineering is essential to translate innovative nutrient formulations into practical, high-performance fertilizers that address specific global agricultural challenges, such as sulfur deficiency, while maintaining efficient and reliable production.

Conclusion

Faced with the global challenges of soil-available sulfur deficiency and the mismatch of industrial sulfur resources, this study has successfully developed a complete set of technologies for high-nitrogen sulfur fertilizers in forms ranging from liquid to granular through precise phase engineering and material design. This technology not only achieves the scientific combination of nitrogen and sulfur nutrients and the high-value utilization of industrial by-products but also endows the product with excellent physical properties through ingenious granulation processes. This marks a solid step forward in connecting industrial and agricultural ecosystems and building a sustainable nutrient management system, providing powerful scientific and technological support for ensuring global food security and promoting the green transformation of agriculture.

Introduction: The Union of Precision Nutrition and Efficient Production

In modern agricultural production, NPK compound fertilizers are highly favored because they can provide the three core elements—nitrogen (N), phosphorus (P), and potassium (K)—required by crops in a single application. However, transforming blended powdered raw materials into uniform, strong granules suitable for application and storage, and producing precise nutrient ratios for different crop needs, are two critical technical steps. These rely on selecting appropriate granulation equipment and scientific formulation design, respectively. Understanding the characteristics of mainstream granulators and the application scenarios of common NPK ratios provides important guidance for both fertilizer producers and agricultural practitioners.

I. Three Mainstream Granulators: Each with Its Strengths, Suiting Different Needs

The process of converting NPK compound fertilizer raw materials into granules is primarily achieved through physical or chemical agglomeration. Currently, there are three widely applied technological pathways in the market, corresponding to three core pieces of equipment.

1. Double Roller Extrusion Granulator: Representative of Energy-Efficient Dry Process

This equipment employs a “dry” granulation principle. It feeds uniformly mixed dry powder between two counter-rotating rollers. The roller surfaces are engraved with precise hemispherical molds (pockets). Under immense mechanical pressure (typically 20-50 MPa), the powder is forcibly compacted into dense sheets, which are then crushed and screened to obtain uniformly sized granules.

Core Advantages: The entire process requires no added water or binders and no subsequent drying, resulting in very low energy consumption and a simple process. The resulting granules are strong, dense, and resistant to caking, making them ideal for storage and long-distance transportation. The equipment investment is relatively low, and the compact structure makes it particularly suitable for small and medium-sized fertilizer plants with an annual output of 10,000 to 50,000 tons.

2. Rotary Drum Granulator: The Industrial Workhorse for Large-Scale Continuous Production

A rotary drum granulator is a large, slightly inclined rotating cylinder. Powdered raw materials continuously tumble inside the drum while an appropriate amount of water or steam is sprayed onto the material bed via nozzles as a binding medium. During the tumbling process, fine powder gradually agglomerates into balls, growing larger like “rolling a snowball.”

Core Advantages: Huge processing capacity, with single-machine output potentially reaching tens of tons per hour, making it ideal for achieving annual capacities of tens of thousands or even hundreds of thousands of tons. When using steam granulation, the heat and moisture provided by the steam promote the dissolution and recrystallization of salts in the material, forming stronger granules and reducing the subsequent drying load. The process is flexible, allowing control over granule size by adjusting liquid spray volume and drum parameters.

3. Disc Granulator: The Classic Choice for Flexible, Small-Batch Production

A disc granulator consists of an inclined, rotating shallow pan. Raw materials are fed from the top, and binder is sprayed from above. Under the combined effects of centrifugal force, gravity, and friction, the material moves along a spiral trajectory, continuously agglomerating into balls until qualified granules spill over the pan’s edge.

Core Advantages: The granulation rate is high, and the granules have good sphericity. The equipment is intuitive and easy to operate, allowing for easy observation and adjustment during the granulation process. It has low investment costs and a small footprint, making it ideal for small-scale fertilizer plants, pilot production lines, or the production of various types of specialty fertilizers in small batches.

II. Decoding NPK Formulations: The Agronomic Language Behind the Numbers

The numeric codes like “15-15-15” or “16-6-18” on the packaging are the “ID cards” of NPK compound fertilizers, representing the mass percentages of total nitrogen (N), available phosphorus (P₂O₅), and available potassium (K₂O), respectively.

1. Balanced Formulations: The Universal Foundation

Examples like “15-15-15” or “17-17-17” indicate equal content of the three nutrients. These fertilizers provide comprehensive and balanced “complete nutrition” for crops. They are suitable for the entire growth period of most field crops (e.g., wheat, corn, rice) or as a safe base fertilizer choice when soil nutrient status is unknown.

2. High Phosphorus-Potassium Formulations: Promoting Flowering and Fruit Setting

For example, formulas such as “15-10-20” or “11-6-23”. Phosphorus helps in flower bud differentiation and root development, while potassium promotes fruit enlargement, improves sweetness and color, and enhances stress resistance. Therefore, these formulas are particularly suitable for topdressing fruit trees, fruiting vegetables, and cucurbit crops during the flowering, fruiting, and fruit enlargement stages, effectively increasing yield and quality.

3. High Nitrogen Formulations: Promoting Vegetative Growth

Examples like “20-8-18” or “15-5-5.” Nitrogen is key for chlorophyll and protein synthesis and significantly promotes stem and leaf growth. These fertilizers are suitable for the rapid growth stages of leafy vegetables (e.g., spinach, lettuce) or for promoting seedling growth in grasses (e.g., turf, forage).

4. Customized Formulations: Precise Response

Many formulations are designed for specific regional soil conditions or special crop needs. For example, in potassium-deficient acidic red soils in southern regions, formulations with relatively high potassium content can be chosen. For chlorine-sensitive crops (e.g., tobacco, potatoes), sulfur-based compound fertilizers (using potassium sulfate as the potassium source) are needed instead of chlorine-based ones.

III. How to Match Equipment with Formulations?

Choosing a granulator and deciding which fertilizer formulations to produce require comprehensive consideration:

· Choose Equipment Based on Production Scale: Small factories or businesses producing a variety of products can choose disc granulators; medium-sized factories prioritizing cost-effectiveness and energy efficiency can opt for double-roller extrusion granulators; while large-scale industrial production requires the use of rotary drum granulators.

· Choose Equipment Based on Raw Material Characteristics: For heat-sensitive materials or when aiming to avoid adding a drying step, double roller extrusion is preferable; when utilizing chemical reactions (e.g., ammonium sulfate with phosphate rock), rotary drum steam granulation is often used.

· Determine Formulations Based on Target Market: Analyze the main crops, soil survey data, and farmers’ fertilization habits in the service area to determine 2-3 core formulations to promote, achieving precise product positioning.

Integrating Formulation Science with Production Efficiency

The efficient production of diverse NPK formulations relies on a sophisticated npk fertilizer manufacturing process. This process begins with precise formulation using a npk blending machine or npk bulk blending machine to ensure the exact nutrient ratio. The mixed powder then enters the granulation stage, the core of modern npk fertilizer production technology. Advanced npk granulation machine technology offers multiple pathways, including the use of a fertilizer roller press machine for dry compaction or other granulators for wet processes.

The choice of technology directly impacts both NPK compound fertilizer production capacity and the final NPK fertilizer production price. Efficient, high-capacity lines using specialized npk fertilizer granulator equipment can lower unit costs. The entire npk production process, from blending to shaping, must be optimized to balance product quality with economic viability. This integration of precise agronomic formulation with cost-effective, scalable manufacturing engineering is what enables the global supply of tailored, high-quality compound fertilizers that meet the specific needs of modern agriculture.

Conclusion

The production of NPK compound fertilizer is a perfect combination of mechanical engineering and agricultural science. From roller, drum to disc, each granulation technology provides an optimal solution for different production scenarios; from balanced, high-potassium to high-nitrogen, each formulation number carries a deep understanding of crop needs. For producers, wise choices mean higher efficiency, lower costs, and more competitive products; for growers, correct understanding means more scientific fertilization, higher yields, and more sustainable agriculture. In this era pursuing precision and efficiency, understanding these fundamental principles is the first step towards smart agriculture.

On farms, in small workshops, or on organic fertilizer production lines, you often see a compact and simple machine—the . It compresses various loose biomass raw materials, such as straw, sawdust, feed, and even animal manure, into dense, solid pellets. How does this machine actually work? And what are its unique advantages?

Working Principle: The Union of Pressure and Nature

The core working principle of the flat die pelleting machine is clever and efficient. After the operator feeds the raw material into the hopper, the press rollers inside the machine begin to rotate, forcing the material against a flat die plate with many small holes. Under the high pressure and the heat generated by friction, the lignin in the biomass raw material (especially plant-based material) softens, acting as a natural binder that tightly bonds the material together. Finally, it is extruded through the small holes, forming uniform cylindrical strands. A cutter then chops these “strands” into pellets of standard length.

The entire process essentially mimics nature’s compaction process but greatly accelerates and standardizes it through mechanical force.

Core Features: Simple, Flexible, User-Friendly

The design of the flat die pelleting machine fully considers the practical needs of small-scale production, boasting several standout features:

Simple and Compact Structure: It mainly consists of a flat die, press rollers, a transmission device, and a feeding system. Its mechanical structure is straightforward, and it has a small footprint, making it very suitable for locations with limited space.

Wide Raw Material Adaptability: It can handle everything from agricultural waste (straw, rice husk) and feed ingredients (corn, soybean meal) to organic fertilizer materials (livestock and poultry manure). It also offers good tolerance for variations in particle size and moisture content (typically between 10%-20%).

Adjustable Pellet Specifications: By replacing the flat die plate with different hole diameters (commonly 2-12 mm), pellets of various sizes can be produced to meet different needs for feed, fuel, or fertilizer.

Easy Operation and Maintenance: Most models use manual or semi-automatic feeding, making them easy to operate. Daily maintenance primarily involves lubrication and cleaning, and core components like the flat die and rollers are also easy to disassemble and replace.

Relatively Low Energy Consumption: Compared to ring die pellet mills of similar output, small and medium-sized flat die mills have lower power requirements, helping to reduce operating costs for small-scale production.

Unique Advantages: The Ideal Choice for Small-Scale Production

Based on these features, flat die pelleting machines demonstrate significant advantages in small-scale application scenarios:

Low Investment Cost: The equipment itself has a relatively low manufacturing cost and an affordable price. It often doesn’t require complex supporting pre-processing equipment (like fine grinders), leading to a short investment payback period. This makes it ideal for individuals or small businesses with limited budgets.

High Flexibility and Mobility: Many models are designed with wheels, allowing them to be easily moved to the location of the raw materials for on-site processing. This avoids the high cost and hassle of transporting large volumes of loose raw materials (like whole bales of straw), enabling an efficient “bring the machine to the material” model.

Versatility: The same machine, by changing the die and adjusting parameters, can produce livestock feed, biomass fuel pellets, and organic fertilizer, greatly enhancing equipment utilization and economic value.

Reliable Pellet Quality: The produced pellets have uniform density and moderate hardness. They offer good palatability as feed, high combustion efficiency as fuel, and are easy to store and transport.

Granulation Equipment Spectrum: From Small-Scale to Industrial Production

The flat die pelleting machine occupies a specific niche within the wide array of fertilizer granulation processes. It is an ideal solution for small-scale or on-site processing of organic materials, contrasting with the large-scale systems used for compound fertilizers. Industrial-scale npk fertilizer production line operations employ different core technologies, such as a disc granulator for shaping spherical pellets in a disc granulation production line, or a double roller press granulator in a roller press granulator production line for dry compaction.

For organic fertilizer, the production chain often begins with a windrow composting machine before the material enters a formal organic fertilizer production line or a bio organic fertilizer production line. These lines may use various fertilizer granulator types, including the disc granulator machine, depending on the product specification. The npk blending machine is a critical component in compound fertilizer lines for precise formulation before granulation. This diversity in equipment—from the simple flat die press to complex industrial systems—highlights how fertilizer granulation processes are tailored to scale, raw material, and final product requirements, ensuring efficient production across the entire spectrum of modern fertilizer manufacturing.

Conclusion

The flat die pelleting machine is like a “small but capable” workhorse. It may not have the staggering output of large ring die production lines, but with its low cost, high flexibility, ease of operation, and strong raw material adaptability, it plays an irreplaceable role in small-scale production, decentralized processing, and localized resource utilization. Whether it’s turning agricultural waste into valuable products or producing custom feed for one’s own farm, the flat die pelleting machine offers an efficient and practical solution.

 In modern agriculture, nitrogen fertilizer is crucial for ensuring food production. However, one efficient and inexpensive nitrogen source—ammonium chloride—has been hindered from reaching its full potential due to a “physical flaw”: it’s notoriously difficult to form into granules.

Why Granular Fertilizer Matters

Imagine two types of fertilizer: one is a light powder that can easily blow away in the wind; the other consists of uniform, sturdy pellets. Which one is preferable? The answer is clear. Granular fertilizer is easier to spread mechanically, allows for precise dosage control, releases nutrients more steadily, and suffers minimal loss during transport and storage. Therefore, “granulation” is a key step in fertilizer production.

Nitrogen fertilizers like urea and ammonium sulfate can be granulated relatively easily. But ammonium chloride is a stubborn exception. Due to the strong ionic bonds between its ammonium and chloride ions, traditional tumble-granulation methods are largely ineffective. In the past, factories had to resort to “extrusion granulation” technology—forcing the material through a die to form strands, which are then cut into pellets, much like making noodles. This method not only causes severe equipment corrosion but is also energy-intensive, low-yielding, and costly. Consequently, ammonium chloride has typically been sold as a powder or used as a minor component in compound fertilizers, limiting its widespread application.

The Search for a “Binder”: From Failure to Breakthrough

How can loose ammonium chloride powder be made to coalesce into solid, individual pellets? The key for researchers was to find an effective “binder.” It’s similar to baking, where you need the right ingredients to bind the flour together.

The research team tested a wide variety of potential binders, including fly ash, zeolite powder, kaolin, and even various sulfates and chlorides. Most results were unsatisfactory: either the binding effect was too weak, leading to excessively long granulation times; or the resulting pellets were too fragile, crumbling easily; or the pellet shape was too irregular for practical use.

A turning point came with a substance called polyaluminum chloride (PAC). PAC is commonly used as a coagulant in water treatment, causing impurities in water to clump together and settle. It was this very “agglomerating” property that gave researchers hope.

The Magic of “Binding” and “Assistance”

Experiments revealed that when powdered polyaluminum chloride was mixed with ammonium chloride, along with a small amount of urea as a “granulation aid,” something remarkable happened. In a disc granulator at room temperature, the mixture could quickly and efficiently form uniform, round pellets.

The scientific principles behind this are quite ingenious:

Overcoming Electrostatic Repulsion: Tiny ammonium chloride particles repel each other due to similar surface charges, making aggregation difficult. PAC releases a multitude of highly positive-charged ions in water. This “army of positive charges” can effectively neutralize the negative charges on the powder surfaces, weakening electrostatic repulsion and clearing the path for particle agglomeration.

Building “Molecular Bridges”: The PAC molecule structure features numerous active groups. These act like tiny “hands” that can grab onto multiple ammonium chloride particles simultaneously, forming strong “particle-polymer-particle” composite bridges between them, thereby helping small particles grow into larger ones.

Urea’s Crucial Assist: Using PAC alone showed improvement, but adding urea led to a leap in granulation speed and quality. Urea and ammonium chloride can interact at a microscopic level to form a stable inclusion compound. This structure further reinforces the internal molecular network of the pellet, making it denser and stronger.

Ultimately, the research team identified a “golden formula”: a mixture of ammonium chloride, urea, and PAC in a mass ratio of approximately 74:18:8. Pellets produced with this formula achieved an average hardness of about 20 Newtons, fully meeting the strength requirements for practical application.

New Hope for Greener Agriculture

The success of this research is more than just a technical breakthrough. Ammonium chloride itself is a high-quality nitrogen fertilizer with good nitrogen use efficiency and low cost. Enabling its efficient, low-cost granulation means farmers could have access to a more economical, user-friendly, and equally effective granular nitrogen fertilizer option in the future.

The deeper significance lies in environmental protection. Nitrogen fertilizer loss is a major contributor to issues like water eutrophication and soil acidification. Granulated ammonium chloride, due to its slower release and physical stability, can reduce losses from volatilization and leaching during application. This improves fertilizer use efficiency and helps mitigate agricultural non-point source pollution at its source.

From a difficult-to-handle powder to smooth, robust pellets, the “shaping” journey of ammonium chloride is a vivid example of how science and ingenuity can transform a challenge into an opportunity. It shows us that through a deep understanding and clever application of material properties, we can add a vital building block to the foundation of sustainable agriculture.

From Scientific Breakthrough to Industrial Production

The successful development of an effective binder for ammonium chloride granulation is a prime example of innovation within npk fertilizer production technology. This advancement must be integrated into the broader npk fertilizer manufacturing process to be commercially viable. The process would begin with precise raw material formulation, potentially using a npk blending machine or npk bulk blending machine to mix the ammonium chloride, urea, and binder in the correct ratio.

This uniformly mixed powder would then proceed to the granulation stage of a complete npk fertilizer production line. Specialized npk granulation machine technology would be employed, utilizing equipment such as a npk fertilizer granulator machine (like a disc granulator) designed to handle the specific properties of the formulated mix. The integration of such specialized formulations and binders into established production systems demonstrates how npk fertilizer production technology continuously evolves, enabling the efficient manufacturing of a wider range of high-quality, user-friendly, and environmentally considerate fertilizer products for global agriculture.