A fluidized bed jet mill achieves ultra‑fine grinding of recovered carbon black (rCB) mainly through fluidized particle suspension, opposed supersonic jet collision, integrated dynamic classification, and optimized closed‑circuit recirculation. Unlike mechanical impact mills that rely on rotating hammers, it de‑agglomerates porous pyrolysis char clusters by particle‑to‑particle collision, minimizing metal contamination while delivering tightly controlled ultra‑fine powder.
1. Fluidized Bed Formation to Disperse rCB Agglomerates
Pre‑treated, dry, metal‑free rCB feed enters the grinding chamber. Compressed air or nitrogen is injected through multiple opposed nozzles at the chamber bottom. The high‑velocity gas lifts and suspends the rCB powder, forming a turbulent fluidized bed.
In this boiling state, the porous rCB agglomerates are fully separated from one another. This eliminates particle stacking and dead zones, so every carbon cluster can enter the central collision zone. Uniform dispersion is the foundation for consistent ultra‑fine de‑agglomeration.
2. Opposed Supersonic Jets for Particle‑On‑Particle Comminution
The gas accelerates suspended rCB agglomerates to supersonic speed. Multiple jets point toward the same central collision point. When high‑speed carbon clusters crash head‑on, the impact force breaks weak bonding between aggregated carbon black primary particles.
This process is de‑agglomeration rather than crushing primary carbon spheres. It splits loose pyrolysis char clusters without damaging the intrinsic carbon black microstructure, preserving the reinforcing properties required for rubber and polymer applications. Since comminution occurs between particles, contact with metal chamber walls is greatly reduced, limiting iron pickup.
3. Top‑Mounted Dynamic Classifier for Ultra‑Fine Size Control
Ground particles rise upward with the gas stream to the high‑speed dynamic classifier wheel installed at the top of the mill. The rotating wheel creates a strong centrifugal force field.
- Ultra‑fine particles that meet the target PSD (such as D97 < 5 μm) have low mass; drag force from the gas overcomes centrifugal force, so they pass through the classifier wheel and flow to the baghouse collector.
- Coarse, incompletely de‑agglomerated agglomerates experience stronger centrifugal force. They are rejected by the classifier, fall back to the fluidized bed, and re‑enter the jet collision zone for repeated processing.
By adjusting the classifier rotation speed and jet gas pressure, operators precisely tune the cut point to achieve ultra‑fine rCB grades. Higher classifier speed produces finer finished powder.
4. Closed‑Circuit Recirculation Guarantees Fineness Uniformity
The continuous recirculation of coarse agglomerates is critical for ultra‑fine results. Particles cannot exit the system until they reach the required particle size. This prevents oversized grit from leaking into final product and delivers a narrow particle size distribution.
The gas expansion from the nozzles also produces an adiabatic cooling effect. Grinding stays at low temperature, avoiding thermal degradation of rCB surface activity during ultra‑fine processing.
5. Pre‑Treatment Enables Stable Ultra‑Fine Operation
To sustain ultra‑fine grinding performance, upstream pre‑treatment is mandatory:
- High‑intensity magnetic separation removes steel wire and iron fines to protect nozzles and chamber from abrasion;
- Drying reduces moisture to prevent sticky rCB agglomerates that block jets and distort particle classification;
- Sieving removes large lumps to maintain stable fluidization.
The fluidized bed jet mill achieves ultra‑fine rCB grinding by fluidizing pyrolysis char, accelerating agglomerates via opposed supersonic jets for particle‑on‑particle de‑agglomeration, and using an integrated dynamic classifier to separate fine powder and recycle coarse clusters. This combination delivers ultra‑fine, low‑contamination rCB with narrow PSD, while retaining the original reinforcing structure of recovered carbon black.
