Removing steel wire from waste tire pyrolysis char involves a systematic approach combining pretreatment (before pyrolysis) and post-pyrolysis separation techniques. The process leverages the magnetic properties of steel and physical differences between steel and carbon char to achieve efficient separation, with typical removal efficiencies exceeding 99%.
1. Pre-Pyrolysis Steel Wire Removal (Recommended for Continuous Plants)
Pre-separation is critical for protecting pyrolysis reactors from damage and improving product quality.
Key Steps:
- Tire Shredding: Use industrial shredders to reduce whole tires to 5–10 cm chips. For continuous systems, further crush to 20mm wire-free chips.
- Primary Magnetic Separation:
- Overband Magnet: Installed above conveyor belts to remove 90% of steel chunks (bead wires and large wire pieces).
- Drum Magnet: Processes shredded material to capture 9% of fine wire fragments.
- Secondary Screening: Use vibrating screens to separate remaining small steel particles before reactor feeding.
Benefits:
- Prevents reactor wear and tear from steel abrasion
- Reduces post-pyrolysis separation load
- Improves pyrolysis efficiency by ensuring uniform feedstock
2. Post-Pyrolysis Steel Wire Separation (Standard for Batch Plants)
After pyrolysis at 320–550°C in oxygen-deficient conditions, steel wires remain intact (melting point ~1538°C) while rubber converts to oil, gas, and carbon char.
Step 1: Safe Discharge & Cooling
- Discharge solid residues (char + steel) via water-cooled screw systems to below 50°C to prevent oxidation and facilitate handling.
- For batch reactors:
- After cooling, manually extract bundled steel wires using grapple loaders or steel wire pulling machines.
- Remove large wire masses first before processing carbon char.
Step 2: Primary Magnetic Separation (Main Technique)
| Equipment Type | Working Principle | Separation Efficiency | Application |
|---|---|---|---|
| Drum Magnetic Separator | Rotating magnetic drum attracts steel while char falls off | 95–98% | Large-scale operations |
| Overband Magnetic Separator | Suspended magnet above conveyor belt captures steel | 90–95% | Post-discharge processing |
| Plate Magnet | Stationary magnetic plate removes fine steel particles | 99%+ | Final purification stages |
Process: Feed cooled char-steel mixture onto magnetic separator conveyor. Steel adheres to magnetic surface while carbon char continues along the belt. Scrapers or belt reversal releases collected steel.
Step 3: Secondary Purification (For High-Purity Char)
For applications requiring 99.5%+ steel-free char (e.g., recovered carbon black – rCB production):
- Fine Grinding: Mill carbon char to 10–50 μm particle size.
- High-Intensity Magnetic Separation: Use alternating magnetic fields to remove micro-steel particles (down to 10 μm).
- Air Classification/Wind Separation: Utilize density differences (char: 1.8–2.1 g/cm³; steel: 7.87 g/cm³) to separate remaining steel dust.
- Screening: Use 100–200 mesh screens to remove oversized steel fragments.
3. Advanced Separation Technologies (For Specialized Applications)
3.1 Eddy Current Separation
- Effective for non-magnetic stainless steel (rare in tires but possible in some cases)
- Uses high-frequency alternating magnetic fields to create eddy currents in conductive materials, generating repulsive force that separates steel from char.
3.2 Wet Separation (For Ultra-High Purity)
- Density Separation: Mix char with water; steel sinks while char floats (adjust pH to prevent char agglomeration).
- Flotation: Add surfactants to enhance char buoyancy; steel settles at the bottom.
4. Best Practices for Optimal Separation
- Temperature Control: Ensure complete pyrolysis (450–550°C) to eliminate rubber binding steel wires.
- Sequential Processing: Combine multiple separation stages (primary → secondary → tertiary) to achieve 99.9% steel removal.
- Equipment Maintenance:
- Clean magnetic surfaces regularly to prevent buildup affecting separation efficiency
- Replace worn screens to maintain consistent particle size separation
- Steel Recovery:
- Bundle large steel wires for direct smelting
- Process fine steel particles into steel shot or rebar for additional revenue streams.
5. Typical Process Flowchart
Waste Tires → Steel Bead Removal → Shredding (5–10 cm) → Pre-Magnetic Separation → Pyrolysis Reactor (320–550°C) → Water-Cooled Discharge (≤50°C) → Post-Magnetic Separation → Fine Grinding → High-Intensity Magnetic Separation → Air Classification → Steel-Free Carbon Char (99.5%+ purity)
6. Key Considerations
- Batch vs. Continuous Plants: Batch plants typically remove steel manually after pyrolysis, while continuous systems use automated pre-separation.
- Char Quality Requirements: Higher purity applications (e.g., rCB for rubber compounds) demand more advanced separation techniques.
- Safety: Always cool residues before handling to prevent burns and fire risks.
By implementing this multi-stage approach, you can efficiently remove steel wire from waste tire pyrolysis char, producing high-quality carbon char suitable for various industrial applications while recovering valuable steel for recycling.