【FAQ】From wet material to dry powder and finally granules—how does a single production line manage three state transitions?

First transition: High moisture to semi-dry—achieved via the twin-screw windrow turner. Fresh livestock and poultry manure typically has a moisture content exceeding 60%, making it viscous and oxygen-deprived. Direct crushing would clog screens, while direct granulation would cause sticking to the granulating pan. The first step requires allowing the material to "breathe." The twin-screw windrow turner uses symmetrical screw shafts to lift material from the bottom of the pile to the surface, introducing fresh air into the core; moisture evaporates continuously during the turning process, and the organic matter decomposes simultaneously. The turning depth reaches 1.2–2.5 meters, material mixing uniformity exceeds 92%, and the fermentation cycle can be controlled at approximately 15 days. After this step, the moisture content drops from over 60% to 35%–45%, transforming the material from "wet sludge" into "semi-dry material."

Second transition: Semi-dry to fine powder—achieved via the semi-wet material crusher. Although the moisture content of the fermented material has been reduced, turning and compression often create hard clumps and fibrous tangles. This stage requires a semi-wet material crusher. It employs a dual-stage rotor structure: the upper stage performs coarse breaking and loosening, while the lower stage handles fine crushing and homogenization. A screenless bottom design allows material with 30%–50% moisture content to discharge directly, preventing wet material from clogging the screen. The crushed material achieves greater uniformity and increased specific surface area, providing a stable input state for the subsequent drying and extrusion granulation processes. If this step is skipped, clumps and long fibers entering the granulator can cause roller slippage and inconsistent granule strength.

The third transformation—converting fine powder into granules—relies on double-roller extrusion granulation. Dry granulation requires the material's moisture content to be controlled between 8% and 15%, with a particle fineness typically below 0.6 mm. Twin-roller extrusion granulators use a pair of counter-rotating rollers to compress powder into dense sheets under high pressure; these sheets are subsequently crushed and screened to produce granules. The entire process requires neither water addition nor drying, resulting in significantly lower energy consumption compared to wet granulation methods. However, the roller shells are wear parts; they must be replaced if the pattern depth wears down by more than two-thirds, the effective thickness decreases by one-third, or if cracking or spalling occurs. The complete roller-compaction granulation line also requires a buffer bin and a closed-loop material recycling system to return undersized fines and oversized granules to the extruder for reprocessing; the recycle ratio is typically maintained between 30% and 50%.