A turbo classifier is a high-speed dynamic air classifier widely used in ACM classifier mills and standalone classification systems for recovered carbon black (rCB). It uses a rotating turbo wheel with multiple radial blades to generate centrifugal force, separating fully de‑agglomerated fine rCB from coarse incompletely broken char clusters. It precisely controls the coarse tail (D97) and narrows particle size distribution, which is critical for producing high-value tire-grade rCB.
Core Working Principle
The turbo classifier operates based on the balance between two competing forces acting on suspended rCB agglomerates:
- Air drag force: The process air carries rCB particles upward toward the turbo wheel, pulling particles through the gaps between the turbo blades.
- Centrifugal force: The fast-spinning turbo blades throw particles outward. Heavier, larger agglomerates experience stronger centrifugal force.
- Fine agglomerates: Air drag > centrifugal force. They pass through the blade gaps and flow to the baghouse collector.
- Coarse agglomerates: Centrifugal force > air drag. They are thrown outward, fall back to the grinding zone for re-deagglomeration.
Step-by-Step Separation Process for rCB
- Particle transport
After impact or jet milling, rCB agglomerates are suspended in the process air stream and delivered evenly to the inlet of the turbo classifier. - Turbo wheel creates strong centrifugal field
The turbo wheel rotates at adjustable high speed. The radial blades sweep the particle-laden air, creating a sharp separation zone. The blade geometry is designed to minimize turbulence and particle clustering, reducing misclassification. - Cut-point separation
The turbo wheel speed directly sets the cut size. Higher rotational speed increases centrifugal force, only allowing smaller agglomerates to pass, lowering D97. Reducing speed raises the cut point, increasing throughput but allowing larger particles into the finished powder. - Closed-circuit recirculation
Rejected coarse agglomerates drop back into the grinding chamber. They undergo repeated impact or jet milling until their size is below the classifier cut point. This closed loop prevents coarse material from escaping and tightens the PSD.
Key Operational Parameters
- Turbo rotational speed: Primary adjustment for D50 and D97.
- Airflow volume: Controls drag force; airflow must be matched to turbo speed to avoid particle bypass.
- Feed loading: Overloading causes particle crowding, agglomerate re-clumping and poor separation, which increases D97.
Advantages for rCB Processing
- Sharp cut point: Excellent coarse tail control, ideal for tire-grade rCB with strict D97 specifications.
- Wide adjustable range: Can switch between different rCB grades by changing turbo speed without major mechanical changes.
- Compact integration: Fits directly on top of ACM mills, forming a single grinding-classifier unit with small plant footprint.
- Stable continuous operation: Suitable for 24/7 large-scale rCB production.
Limitations
- Turbo blades are subject to wear. Residual steel grit or hard char particles will abrade the blades over time, distorting the blade gap and causing coarse leakage. Upstream magnetic separation is mandatory.
- High moisture makes rCB sticky, causing agglomerates to stick to turbo blades and reduce classification efficiency.
A turbo classifier separates rCB by using a rotating bladed turbo wheel to generate centrifugal force. Fine qualified agglomerates pass through the wheel with airflow, while coarse clusters are rejected and recycled back for regrinding. Operators adjust turbo speed to control the cut size, delivering tightly controlled D97 and narrow PSD for high-value recovered carbon black.
