Direct answer
How do you manage pyrolysis?
Treat it as a sealed thermochemical reactor with a defined atmosphere, a defined vapour fate, and a mass balance that closes. The kiln is 30% of the plant. The other 70% is feed prep, inerting, quench or oxidiser, scrubbers, char cooling, and instrumentation.
1. Feed
- Dry to the spec. Sludge to ~90% DS before PYREG-class units. Biomass moisture steals heat and inflates “oil”.
- Size to the reactor. Fluid beds need millimetres; kilns tolerate chunks; screws hate wire and tramp metal.
- Sort plastics. PVC and PET are contaminants in an oil plant. Tires need steel and textile removal either before or after.
- Batteries: discharge, then either inert shred or whole-cell thermal. Never open a live module on a conveyor.
2. Atmosphere
Purge to < a few percent O2 before heat. Run under N2 or recycled non-condensable gas slightly below atmospheric (Biogreen documents “below atmospheric”) so leaks go in, not out — unless you have a designed oxidiser draft. Measure O2, CO, and pressure. A positive-pressure hatch is how workers meet pyrolysis vapour.
3. Pick one fate for vapour
| If you want… | Vapour path | Setpoints |
|---|---|---|
| Oil | Hot out → quench condenser → oil tank → non-condensables to burner | Vapour seconds, not minutes. Avoid 600 °C freeboard. |
| Char + heat (sludge, PFAS) | All vapour to thermal oxidiser | Oxidiser ≥850–950 °C, then fast quench. Steam helps PFAS mineralisation. |
| Battery HF control | Closed duct → lime/caustic scrub → stack | Never a charcoal filter as the only HF barrier. |
4. Scrub what the chemistry will make
- HCl — PVC, chlorinated binders. Alkali scrub. Corrosion of the first cold surface.
- HF / POF3 — LiPF6, PVDF, some PFAS. Lime slurry to CaF2. Analyse F in wastewater.
- H2S / organosulfur — tires. Gas is often 50+ MJ/Nm3 N2-free and still needs sulphur management.
- NH3 / HCN — sludge, some plastics. SNCR on the oxidiser is used on battery crush-gas trains in Chinese process descriptions.
- Dioxins — if Cl + a 250–400 °C cool-down. Fast quench after the oxidiser is not optional.
- Particulate / rCB / fibres — baghouse. ACM and battery BM are respirable when dry.
5. Solids out
Char, rCB and black mass are hot and often still reducing. Cool under inert below the auto-ignition window before air. Water-jacketed screws are standard. A char fire in a skip is a common first-year incident. For sludge biochar, metals concentrate (the mass shrinks); check exceptional-quality ceilings, not just PFAS.
6. Oil, if you make it
Phase-separate water. Filter char fines. For plastic oil, plan hydrotreating or a steam-cracker spec (Plastic Energy / Shell / Technip-class upgraders exist because raw PPO is not diesel). Tire oil is a BTEX and sulphur problem as well as a fuel. Do not put raw PPO in a truck tank and call it circular.
7. Close the balance
Weigh feed, oil, char, and gas (or oxidiser duty as a proxy). Target 95%+ closure. The missing 5–15% in vendor trials is usually water, leaks, or “gas we did not meter”. For PFAS, close fluorine, not just C8 analytes.
8. Instrumentation that pays for itself
- Solids T in at least three zones (the Energy & Fuels tire plant used 450 / 550 / 775 °C on purpose).
- Vapour T at the outlet and at the quench.
- O2, CO, draft.
- Feed rate and screw rpm (dwell).
- HF/HCl in the scrubber bleed.
If those five are not on a historian, you do not have a process. You have a heated drum.