2.1. Cavitation of charcoal
The study was carried out on charcoal obtained from an industrial installation located in the Bieszczady Mountains (southeastern Poland). The production process was performed using deciduous wood. Before starting dry distillation, feedstock was ground and treated with drying gases at 160-180 °C. Then, the material was placed in a retort. After closing the retort, the residual water evaporates, and the thermal decomposition of the wood begins. It is initiated by hot gases of 250-300 °C, moving from the central part of the retort (annealing zone). The process is exothermic. The organic mass of wood is charred. The partially charred wood mass has a reduced volume; hence, it moves down the retort and enters the annealing zone. Here, at 500-550 °C, the final form of charcoal is formed (Lewandowski and Milchert, 2011).
The cavitation process was carried out in 10% w/w aqueous charcoal mixture (particle size of 0-0.5 mm). The suspension was placed in a tank to which a 2.5 kW cavitation pump was connected. After passing through the pump, the suspension was returned to the tank (closed circuit). The micronisation time for 150 dm3 of the suspension was 2 hours, and the temperature increase during the cavitation process was from 40 °C (initial stage) to 60 °C (final stage).