Dry granulation for organic fertilizer is often misunderstood as a simple process of “pressing powder into granules using a single machine.” In reality, an “organic fertilizer dry granulator”—most commonly represented by the roller-press (extrusion) granulator—is a category of equipment designed to form granules under low-moisture conditions through mechanical pressure. The ability to consistently produce high-quality granules depends not only on the granulator itself but also on whether the preceding processing stages have prepared the feedstock correctly. The double-screw compost turner and the semi-wet material crusher are two indispensable nodes in this production chain.
The first node occurs within the fermentation bay, handled by the double-screw compost turner. Fresh manure often has a moisture content exceeding 70%, making it impossible to process directly through any dry granulation system. The double-screw turner utilizes two counter-rotating auger shafts to lift and aerate the compacted material at the bottom of the pile. Capable of reaching depths of 1.8 to 2.5 meters, this design offers significantly higher oxygenation efficiency than single-screw models. Beyond supplying oxygen, the turning process facilitates the continuous release of moisture as water vapor, gradually bringing the material’s moisture content down to a level suitable for subsequent stages, while also ensuring a uniform degree of decomposition. If the turning process is inadequate—resulting in material that is dry on top but wet at the bottom—all downstream processes will suffer the consequences of this inconsistency.
The second node takes place in the crusher, performed by a semi-wet material crusher. Even after decomposition, the material typically retains a moisture content between 25% and 55%; it is highly adhesive and contains fibrous matter that can easily clog the screens of conventional crushers. Semi-wet material crushers generally eliminate the bottom screen and employ a dual-stage rotor configuration—performing coarse crushing followed by fine pulverization—to transform irregular clumps into a fine powder with a relatively uniform particle size. This step does not alter the chemical properties of the material; however, it determines whether the rollers of the dry granulator encounter a uniform, fine powder or a heterogeneous mixture of coarse and fine particles.
The third stage involves the organic fertilizer dry granulator. Equipment of this type—exemplified by roller-press granulators—compresses powdered material (typically with a moisture content below 5%) into dense sheets at ambient temperature, which are subsequently crushed and screened into granules. The entire process requires neither the addition of water nor an increase in temperature. The operational window for the input material is quite narrow: if the moisture content is too high, the material will slip between the rollers; if the particle size is too coarse, the rollers will fail to “bite” the material consistently, leading to poor uniformity in granule strength. Consequently, the reliability of dry granulation is not determined solely by the parameters of the granulator itself. Rather, successful granulation depends on the preceding steps: the compost turner must ensure proper moisture levels and maturity, and the crusher must achieve the correct particle size. Each of the three stages plays a distinct, essential role; if any one is neglected, the dry granulation process cannot function effectively.