The vertical cuttings dryer drives OOC to roughly 3–5%. For many regulatory environments that is sufficient. For others — the North Sea under OSPAR 2000/3, certain onshore sites, operator-set limits — it is too high. That is where thermal treatment begins. A TDU removes hydrocarbons by applying heat — driving the oil off solids by vaporisation rather than centrifugal force — with OOC routinely below 1%.
The three types
| Type | Temperature | Typical OOC | Key feature |
|---|---|---|---|
| LTTD | 150–350 °C | <1% (0.1–0.5%) | Indirect heat; recovers base oil for reuse; mobile |
| HTTD / incineration | 500–1,200 °C | Near-zero | Destroys organics completely; no oil recovery |
| TCC (thermomechanical) | ~200–280 °C friction | <1% (0.3–0.8%) | Friction-generated heat; compact; the North Sea OSPAR solution |
LTTD oil recovery: unlike incineration, LTTD recovers base oil as a reusable product. On OBM wells where base oil costs $1,000+/tonne, this economic return offsets a significant part of the TDU operating cost.
When it's required
- North Sea / OSPAR 2000/3: >1% oil on dry cuttings cannot be discharged. VCD cannot consistently reach 1%; TCC and LTTD can.
- Onshore sensitive sites near groundwater or protected land.
- Operator zero-discharge commitments.
The chain: VCD feeds the TDU
Thermal treatment follows the VCD — it doesn't replace it. VCD removes the bulk of free base oil (15–20% → 3–5%), reducing the thermal unit load. Correct train: shaker → VCD → TDU, with centrifuge processing VCD effluent. The economics and throughput both improve when the VCD does the heavy lifting first.