3. Techniques used

3.1 Batch process

The old method consisted of heating the loaded tar in a retort until it boiled, then collecting the oils in a condenser. The boiler was heated directly by the fuel flames. At the end of the distillation process, the pitch remaining in the retort was emptied into storage, and the next operation could be restarted.

Europe still has a few small units with 60 m ³ boilers, but this dying process has been replaced by continuous processes similar to the primary fractionation of crude in oil refineries.