Pyrolysis char with 6 mm lumps cannot be directly fed into an ACM classifier mill or fluidized bed jet mill, as oversized chunks cause rotor overload, unstable fluidization, accelerated wear and poor de‑agglomeration. Therefore, 6 mm rCB feed requires a dedicated pre‑crushing and screening circuit before the main ultra‑fine grinding stage.
Step 1: Pre‑Crushing & Magnetic Separation
The incoming 6 mm pyrolysis char first enters a secondary crusher, typically a small impact crusher or hammer pre‑crusher. The crusher reduces the maximum lump size down to ≤2–5 mm for ACM milling, or ≤1–2 mm if the target is fluidized bed jet milling.
Immediately after crushing, high‑intensity magnetic separation removes steel wire fragments and iron grit released from broken char lumps. This step is critical: crushing opens up char clumps and exposes embedded steel contaminants, which must be extracted before fine grinding to protect mill rotors, liners or jet nozzles.
Step 2: Vibrating Screening / Sieve Classification
After crushing and magnetic separation, the material passes through a vibrating screen.
- Particles smaller than the screen cutoff (2–5 mm or 1–2 mm) move forward to drying and main milling.
- Any oversize material that fails the screen is returned back to the pre‑crusher for re‑crushing. This closed-loop screening ensures the feed size into the main mill stays within the designed specification.
Step 3: Drying
The screened rCB is sent to a dryer to reduce moisture (usually below 1–2%). Moisture makes porous char agglomerate and stick inside the grinding chamber, disrupting air classification and causing blockages.
Step 4: Main Ultra‑Fine Grinding
Option A: ACM Air Classifier Mill (Most Common)
The pre‑treated, ≤2–5 mm feed is metered into the ACM mill. High-speed hammers strike the porous carbon agglomerates for de‑agglomeration. The built‑in dynamic classifier wheel separates fine qualified powder; coarse agglomerates fall back to the grinding zone for repeated impact. The finished fine rCB is captured by baghouse filters.
Option B: Fluidized Bed Opposed Jet Mill
If the final product is high‑spec ultra‑fine rCB, the 6 mm feed must be crushed and screened down to ≤1–2 mm before entering the jet mill. Inside the jet mill, supersonic opposed jets accelerate particles for particle‑on‑particle de‑agglomeration. The integrated top classifier controls particle size and recycles coarse clusters.
Step 5: Final Collection & Quality Control
Fine rCB powder is collected by bag filters. Optional online metal detection and PSD testing verify residual steel content and particle size before packaging.
Key Challenges of 6 mm Feed
- Higher pre‑crushing load: 6 mm lumps require extra crushing capacity compared to fine char feed.
- More embedded steel exposure: Larger char lumps often trap steel wire inside; crushing releases these metal contaminants, so magnetic separation must be installed after crushing.
- Risk of uneven feeding: Poor crushing control can leave occasional oversized chunks that disturb the main mill’s air flow and classification stability.
rCB feed at 6 mm is first reduced by secondary pre‑crushing, then screened to remove oversize, with magnetic separation to capture newly exposed steel impurities. After drying, the controlled-size feed enters the ACM or fluidized bed jet mill for closed‑circuit ultra‑fine de‑agglomeration and classification. This multi-stage pre-treatment chain converts 6 mm coarse pyrolysis char into consistent fine rCB powder.
