Agitated Thin Film Dryer (ATFD)

An Agitated Thin Film Dryer (ATFD) is the final drying stage in most Zero Liquid Discharge (ZLD) plants. It takes the thick, concentrated slurry that leaves an evaporator or crystalliser and dries it to a solid. Inside a jacketed cylindrical shell, a rotor fitted with blades spreads the incoming feed into a thin, continuously wiped film against the hot wall. Because the film is thin and constantly renewed, heat transfers rapidly and the water flashes off quickly, even from materials that are viscous, sticky, or prone to fouling.

This thin-film, short-residence-time action is what makes the ATFD uniquely suited to difficult residues. Heat-sensitive materials spend very little time on the hot surface, so they dry without degrading — and the option to run under vacuum lowers the boiling temperature further. Viscous and fouling slurries that would bake onto a static surface are kept moving by the rotor, so the heat transfer surface stays effective and the dryer runs continuously.

In the ZLD chain, the ATFD is what makes zero liquid discharge truly zero. After Multiple Effect Evaporators and Mechanical Vapour Recompression concentrate the effluent and a crystalliser forms salt, the ATFD dries the final residue into a free-flowing powder or cake that can be sent for disposal or, where a single salt has been recovered, reused. The vapour driven off is condensed and recovered as distillate.

Spans engineers ATFD systems for reliable continuous operation on demanding residues, selecting rotor design, heating media, orientation, and metallurgy to suit the material so the plant achieves a genuinely dry output and true zero liquid discharge.