In organic fertilizer production, cow manure has always been an important raw material source due to its wide availability and balanced nutrients. However, the unique rumination characteristics of the cow’s digestive system result in a large amount of residual crude fiber in its manure, reaching 30%-40%. If these undigested straw fragments and grass fibers are used directly for granulation, they often lead to loose, easily cracked pellets, severely affecting product quality. The key to solving this problem lies in the refined processing of crude fiber and the selection of a suitable granulation process.
The Impact of Crude Fiber on Granulation
The crude fiber in cow manure mainly comes from undigested cellulose, hemicellulose, and lignin in the feed. These fibers are tough and highly elastic, making them difficult to compress during granulation and easily forming a “skeleton” within the pellets, resulting in insufficient bonding between pellets. If the fibers are too long (over 10mm), burrs easily appear on the surface of the pellets after granulation. During drying, moisture evaporates rapidly, causing the pellets to crack along the fiber direction, significantly reducing the product qualification rate.
Pretreatment: Fiber Refinement is Fundamental
The core of cow dung granulation lies in the pretreatment stage. After fermentation and composting, the cow dung first needs to be processed by a high-moisture material crusher. This type of crusher uses a dual-shaft shearing structure, which can cut coarse fibers into short filaments less than 5mm, while simultaneously breaking up clumps. If the fiber content of the raw material is particularly high (e.g., pure cow dung exceeding 80%), a chain crusher can be added for secondary fine crushing, further controlling the fiber length to within 3mm. The pretreated material feels loose to the touch, with no long fibers visible to the naked eye, creating favorable conditions for subsequent granulation.
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Pelletizing Equipment Selection: High-Pressure Compression is Key
Given the characteristics of coarse cow dung fibers, a roller extrusion granulator is the ideal choice for the granulation process. Unlike disc granulators that rely on rolling agglomeration, roller extrusion forces the material into shape under high pressure. After the material enters the gap between two opposing rotating rollers, under a high pressure of 15-25MPa, the fibers and fine powder are tightly compressed, forming a dense structure inside the granules. This process does not rely on moisture or binders, making it particularly suitable for molding fibrous materials. The granules produced by high-pressure extrusion have a compressive strength of 15-20N and are not easily pulverized even during long-distance transportation.
For scenarios requiring the production of round granules to meet specific market demands, a rotary polishing machine can be added after extrusion. The polishing machine, through low-speed rotation, rubs the flattened spherical or irregular granules together, removing sharp edges and creating a smooth, rounded surface, while further increasing granule density.
The success of cow dung granulation depends on the coordinated efforts of the preceding and following processes. During the fermentation stage, the material should be fully decomposed, with the C/N ratio controlled at 25-30:1. After decomposition, the fibers are partially softened, making them easier to crush. During batching, 10%-20% of powdered auxiliary materials (such as humus or weathered coal) can be appropriately added to fill the fiber gaps and enhance granule bonding. The drying process uses low-temperature, high-volume airflow (≤60℃) to prevent the fibers from becoming brittle and cracking due to high temperatures.
From coarse, long fibers to dense granules, the technical path of cow dung granulation is clearly traceable. By combining refined pretreatment with high-pressure molding technology, coarse fiber raw materials that were originally difficult to process can be transformed into high-quality organic fertilizer granules, truly realizing the circular value of “turning waste into treasure”.
The challenge of granulating cow manure, with its high crude fiber content, highlights the need for a tailored approach within the organic fertilizer granulator series. While a rotary drum granulator is a common choice for many materials, its wet agglomeration process may not provide the compressive force needed to bind tough fibers. For this application, a dry compaction method is far more effective. A fertilizer compactor, such as a double roller press granulator, applies high mechanical pressure to force the fibers and fine powder into dense, strong granules. This represents a strategic application of fertilizer production machine technology. For very small-scale or specialty applications, a flat die pelleting machine could also be considered, though its capacity may be lower. The success of this approach, however, is not solely dependent on the granulator. It begins upstream with effective composting, managed by a double screws compost turning machine or a large wheel compost turning machine for windrow operations. A windrow composting machine provides the initial aeration. The key is that the same principles of fiber refinement and high-pressure compaction apply, regardless of the specific turning technology used for fermentation. By integrating robust composting with a high-pressure fertilizer compactor, the challenge of cow manure granulation is transformed into an opportunity to produce a high-value, dense organic fertilizer.