A processing vessel (1) provided with a material inlet (2, 3, 4, 5) and a processed material outlet (25) wherein the material flows continuously through the vessel which is split into a series of zones (6, 7, 8) through which the material passes wherein the zones are shielded from each other by controlling the rate at which the material flows and an increasing level of vacuum is applied inconsecutive zones and the system is provided with acoustic energy which imparts energy to the process material by virtue of the contact between the zone dividers and the process material and processing material in such a vessel.